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COMPUTER GUIDED SURGERY


Many aspects of our modern lifestyle depend on computers and it is no surprise that this technology is also now being used to aid surgeons in performing surgeries like joint replacements where precision is required.

How does it work?

In simple terms, computer guided surgery is similar to that of satellite navigation (GPS) used in cars. In GPS technology, the location of the car is identified by the signal received from the different GPS satellites by the GPS receiver in the car. Once the car location is identified, the route can be planned. Similarly, in computer guided joint replacements, special trackers which emit infrared signals are fixed to the bones and they act like satellites. During the operation, the surgeon maps the hip or knee joint by special instruments which also emit infrared rays. These signals are picked up by an infrared receiver camera which relays the message to a computer. The computer creates a three dimensional model of the joint and gives a plan for the surgeon how much bone to take off and how to position the implants (like the route map). After every cut he makes in the bone, he can also verify it in real time through the computer to make sure the cuts are accurate.

What is the recent evidence from Australian joint registry?

Recent data from Australian Joint Registry has shown that there is better survival rate for knee replacements done by computer guided surgery compared to conventional knee replacements in patients under 55 years and for all age groups when failure due to aseptic loosening alone was considered.

Does the computer replace the surgeon?

No. The surgeon still does the operation (like you have to still drive the car). Thus this technology aids the surgeon rather than replace him!

Is it new?

This technology has been used for over a decade. However, the equipments were bulky and not user friendly. With improvements in computer technology, they have become much more user friendly.

What is the main advantage?

The main advantage is that it helps to decrease the margin of human error. Most of the hip and knee replacements are done with the aid of manual instruments, the accuracy of which depends on the many factors including the “feel” and “experience of the surgeon”. Many studies have shown that when joint replacements are done with traditional manual methods, there are groups of patients called the “outliers” where the implants are placed in less than the ideal position. This can lead to early wear of the joint (like the car tyres wear early if they are not aligned properly) leading to further complex revision surgery.

How accurate is it?

While most of the hand held GPS receivers in the cars have an accuracy of 10-20 metres, the accuracy of the computer technology used in orthopaedic surgery is within 1-2 mm/degrees. This amount of accuracy is important as studies on knee replacements have shown that if they are placed out of alignment by even 3 degrees, the can fail early. Similarly, higher failure rate can occur following hip resurfacing if the implants are not placed in a narrow zone of safety.

What are the other advantages?

Apart from the accuracy in bone cuts, this technology also allows the surgeon to see in real time how well the leg is aligned during surgery as well as soft tissue balancing during knee replacements. Studies have also shown that if the alignment following knee replacements is accurate, the patients have shorter length of stay and improved early function. Some of the studies on knee replacements have also shown that there is less blood loss and fat embolism.

 

How widely is computer guided surgery done in UK?

In some of the European countries like Germany, many of the joint replacements are done with computer guidance. In the UK, the proportion of joint replacements done with computer guidance is still less.

Essentially the computer guided technology works on the basis of triangulation of points. There are three main components: the sensor or the capturing device, the pointer and the trackers.

Sensor

Pointer

Tracker

In the Stryker Navigation system (which Mr.Ganapathi uses), the pointer and the trackers actively send infrared signals which are received by the sensors. During the operation, the surgeon places the two trackers on to pins attached to the bone. These act as fixed reference points. The triangulation is done by a combination of the pointer and the two trackers. This allows the surgeon to map the patient’s knee joint, check the knee alignment and tracking before doing the bone cuts. At each stage of the bone cut the surgeon can verify the accuracy of the bone cut in the navigation computer screen before proceeding to the next step.

Before placing the final implants, the surgeon can check the alignment, tracking and range of movement with trial implants.

Diagrammatic representation of the Theatre setup for computer guided knee replacement

Diagrammatic representation of the tracker positioning in the thigh bone (femur) and the leg bone (tibia)

The following is a video demonstration of a computer guided knee replacement performed by Mr.Ganapathi using Stryker Navigation System (the video is a screen shot of the computer screen during the procedure)

So what does the surgeon see in the computer screen?

1. The surgeon can see the preoperative alignment and maltracking

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Preoperative alignment showing the deformity

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Preoperative tracking (showing maltracking)

2. The computer also guides the surgeon about the amount of bone to be cut

3. In addition, at each step the surgeon can check the accuracy of the bone cut

The green (planned) and yellow  lines (actual cuts) in the following pictures are superimposed showing the accuracy of the bone cut

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Distal femur cut

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Rotational alignment

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Proximal tibial cut

4. The surgeon can also verify  whether correct alignment and tracking has been achieved using trial implants before implanting the definitive implants

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Restoration of good alignment after surgery

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Restoration of satisfactory tracking after surgery

Hip resurfacing is a bone conserving surgical option used in managing hip arthritis (instead of a total hip replacement) in young and active patients with good bone stock. In a conventional total hip replacement the ball of the hip joint is cut along with the neck of the femur and is replaced by a metal implant. In hip resurfacing the ball of the hip joint is preserved to a large extent and is only reshaped to fit a metal cap. The femoral neck is not cut. The rationale behind hip resurfacing is that there is preservation of bone stock for future revision surgery. Another potential advantage is that once the soft tissues have healed there is very less chance of hip dislocation (compared to conventional total hip replacement) and they can lead an active lifestyle with very little restriction.

Conventional Total Hip Replacement

Hip Resurfacing

However, it is technically difficult procedure as the surgeon has to work his way around with the ball of the hip joint in place unlike a conventional hip replacement where the space created by removing the ball of the hip joint makes the procedure easier. In addition, the ball of the hip joint is also often misshapen.

Femoral neck is not cylindrical

Abnormal shape of the femoral head makes it difficult to judge the guide wire position correctly

Computer screen picture showing the position of the guide wire
Computer screen picture showing the
position of the guide wire

Many studies have shown that there is a narrow margin of error in placement of the components during surgery to avoid sub-optimal results. For example, it the angle of placement of the femoral component is not correct, this can lead to fracture of the femoral neck near the junction between the cap and the bone. It is difficult with conventional manual jigs to accurately place the femoral component in place and there can be “outliers” where the component is not placed in the optimal position.

The accuracy of the femoral component placement is improved with computer guidance. In this method, the surgeon maps the top of the thigh bone of that particular patient with special pointer. The computer creates a three dimensional map from that information. The surgeon can then visually see where to place the preliminary guide wire for optimal placement and can do finer adjustments in real time feedback from the computer screen.

Mr.Ganapathi has recently published his research work (see below) on the difference in the accuracy between computer guided surgery and conventional manual jig. The study showed that there was a significant difference between the planned position of the femoral component and the final placement when using conventional manual jigs when compared with computer guided surgery.

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Comparison of error between the planned position and final placement

Femoral component positioning in hip resurfacing with and without navigation.

Clin Orthop Relat Res. 2009 May;467(5):1341-7.

Ganapathi M, Vendittoli PA, Lavigne M, Günther KP.

Early failures after hip resurfacing often are the result of technical errors in placing the femoral component. We asked whether image-free computer navigation decreased the number of outliers compared with the conventional non-navigated technique. We retrospectively compared 51 consecutive hip resurfacings performed using image-free computer navigation with 88 consecutive hip resurfacings performed without navigation. Patient demographics were similar. There were no differences in the average native femoral neck-shaft angles, planned stem-shaft angles, or postoperative stem-shaft angles. However, when the postoperative stem-shaft angle was compared with the planned stem-shaft angle, there were 33 patients (38%) in the non-navigated group with a deviation greater than 5 degrees in contrast to none in the navigated group. Notching was present in four patients in the non-navigated group and none in the navigated group. The average operative time was 111 minutes for the navigated group and 105 minutes for the non-navigated group. Image-free navigation decreased the number of patients with potentially undesirable implant placements).

A very recently published study has also shown the superiority of computer navigation in precise positioning of the femoral component compared to conventional jigs (up to eight times less error than conventional jigs).

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A comparison of conventional guidewire alignment jigs with imageless computer navigation in hip resurfacing arthroplasty. J Bone Joint Surg Am. 2010 Aug 4;92(9):1834-41. Olsen M, Chiu M, Gamble P, Boyle RA, Tumia N, Schemitsch EH.

In addition to the femoral component positioning, it is recently being recognised that the cup positioning is also important in hip resurfacing to decrease the incidence of adverse reaction due to metal ion problems. Computer navigation has also been shown to be much more precise than conventional jigs and “eye balling” (please see the section on Computer Guided Total Hip Replacement for further details).

 Mr.Ganapathi  routinely uses computer guided surgery when performing hip resurfacing and the following video demonstrates one such case (the video is the screen shot of the computer screen during the procedure).

The following are some relevant selected scientific references:

1. A comparison of conventional guidewire alignment jigs with imageless computer navigation in hip resurfacing arthroplasty.

J Bone Joint Surg Am. 2010 Sep;92(9):1834-41.

Olsen M, Chiu M, Gamble P, Boyle RA, Tumia N, Schemitsch EH.

Martin Orthopaedic Biomechanics Laboratory, Institute of Biomaterials and Biomedical Engineering, St. Michael’s Hospital, University of Toronto, 5-066 Shuter Wing, 30 Bond Street, Toronto, ON M5B 1W8, Canada.

Abstract: BACKGROUND: Correct positioning of the initial femoral guidewire is vital in order to prepare the femoral head properly for hip resurfacing. The purpose of the present investigation was to determine the accuracy and precision of the placement of the initial femoral guidewire with use of conventional alignment jigs and to compare the results with those of imageless computer navigation. METHODS: Five commercially available jigs (two lateral pin jigs, two neck centering jigs, and one head planing jig) were obtained. Four surgeons used each jig and navigation three times to insert a guidewire in 10 degrees of relative valgus and neutral version into individual synthetic femora. A single surgeon then used each jig three times to align the initial guidewire in 10 degrees of relative valgus and neutral version in each of ten human cadaver femora. Radiographs of the synthetic and human femora were made to assess and compare guidewire inclination and version between conventional instrumentation and navigation. RESULTS: Navigation provided ranges of error in the coronal guidewire alignment of up to eight times less than the conventional jigs, but both methods provided similar ranges of error for version. In both arms of the study, there were significant differences in coronal alignment accuracy between the two neck centering jigs. Next to navigation, one lateral pin jig provided the most accurate coronal placement of the initial guidewire whereas one neck centering jig provided the most precise coronal placement of the guidewire. Navigation was similar to conventional jigs in terms of the accuracy and precision of guidewire version. CONCLUSIONS: In hip resurfacing arthroplasty, the choice of a femoral alignment device may influence the accuracy and precision of guidewire insertion, ultimately impacting femoral component placement. Imageless computer navigation can facilitate accurate and precise coronal alignment of the initial femoral guidewire, superior to that of conventional instrumentation. CLINICAL RELEVANCE: The results of this study may aid surgeons in the selection of alignment instruments for placement of the initial femoral guidewire during hip resurfacing.

2. Imageless computer navigation of hip resurfacing arthroplasty.

Oper Orthop Traumatol. 2010 Jul;22(3):307-16.

Schnurr C, Nessler J, Koebke J, Michael JW, Eysel P, König DP.

LVR Klinik für Orthopädie, Viersen, Germany.

Abstract: OBJECTIVE : Precise implantation of hip resurfacing arthroplasty by imageless computer navigation. Hence a malalignment of the femoral component, leading to early loss of the implant, can safely be avoided. INDICATIONS : Coxarthrosis in patients with normal bone mineral density; only minor deformity of the femoral head that enables milling around the femoral neck without notching. CONTRAINDICATIONS : Osteoporosis; large necrosis of the femoral head; metal allergy; small acetabular seat and corresponding wide femoral neck, leading to needless acetabular bone loss; pregnancy, lactation. SURGICAL TECHNIQUE : Hip joint exposure by a standard surgical approach, bicortical placement of a Schanz screw for the navigation array in the lesser trochanter. Referencing of the epicondyles, the four planes around the femoral neck and head by use of the navigation pointer. Planning of the desired implant position on the touchscreen of the navigation device; a guide wire is inserted into the femoral head and neck using the navigated drill guide; navigated depth drilling is performed. The femoral head is milled using the standard instruments. The acetabular bone stock is prepared with the conventional instrumentation; high-viscosity cement is finger-packed on the reamed head and the femoral component is inserted. Hammer blows should be avoided to prevent microfractures. Verification of the implant position by the navigation device; displacement of the Schanz screw; joint reposition and closure of the wound. POSTOPERATIVE MANAGEMENT : Standard postoperative management after hip arthroplasty. RESULTS : The comparison of 40 navigated and 32 conventionally implanted ASR((R)) prostheses resulted in a significant reduction of outliers by use of computer navigation (navigated procedures: one outlier, conventional procedure: nine outliers; p < 0.001). Accuracy of the navigation device was tested by analysis of planned and verified implant position: CCD angle accuracy was 1 degrees , antetorsion accuracy was 1 degrees , and offset accuracy was 1.5 mm. An ongoing computed tomography- based anatomic study proved a varus-valgus accuracy of the navigation device of 1 degrees .

3. How accurate is image-free computer navigation for hip resurfacing arthroplasty? An anatomical investigation.

J Orthop Sci. 2009 Sep;14(5):497-504.

Schnurr C, Nessler J, Meyer C, Schild HH, Koebke J, König DP.

Rheinische Klinik für Orthopädie Viersen, Viersen, Germany.

Abstract: BACKGROUND: The existing studies concerning image-free navigated implantation of hip resurfacing arthroplasty are based on analysis of the accuracy of conventional biplane radiography. Studies have shown that these measurements in biplane radiography are imprecise and that precision is improved by use of three-dimensional (3D) computer tomography (CT) scans. To date, the accuracy of image-free navigation devices for hip resurfacing has not been investigated using CT scans, and anteversion accuracy has not been assessed at all. Furthermore, no study has tested the reliability of the navigation software concerning the automatically calculated implant position. The purpose of our study was to analyze the accuracy of varus-valgus and anteversion using an image-free hip resurfacing navigation device. The reliability of the software-calculated implant position was also determined. METHODS: A total of 32 femoral hip resurfacing components were implanted on embalmed human femors using an image-free navigation device. In all, 16 prostheses were implanted with the proposed position generated by the navigation software; the 16 prostheses were inserted in an optimized valgus position. A 3D CT scan was undertaken before and after operation. RESULTS: The difference between the measured and planned varus-valgus angle averaged 1 degrees (mean +/- SD: group I, 1 degrees +/- 2 degrees ; group II, 1 degrees +/- 1 degrees ). The mean +/- SD difference between femoral neck anteversion and anteversion of the implant was 4 degrees (group I, 4 degrees +/- 4 degrees ; group II, 4 degrees +/- 3 degrees ). The software-calculated implant position differed 7 degrees +/- 8 degrees from the measured neck-shaft angle. These measured accuracies did not differ significantly between the two groups. CONCLUSIONS: Our study proved the high accuracy of the navigation device concerning the most important biomechanical factor: the varus-valgus angle. The software calculation of the proposed implant position has been shown to be inaccurate and needs improvement. Hence, manual adjustment of the implant position in the software-planning step is frequently required.

4. Imageless computer navigation for placement of the femoral component in resurfacing arthroplasty of the hip.

J Bone Joint Surg Br. 2009 Mar;91(3):310-5.

Olsen M, Davis ET, Waddell JP, Schemitsch EH.

Division of Orthopaedic Surgery, Department of Surgery, St Michael’s Hospital, University of Toronto, 30 Bond Street, Toronto, Ontario, Canada M5B 1W8.

Abstract: We have investigated the accuracy of placement of the femoral component using imageless navigation in 100 consecutive Birmingham Hip Resurfacings. Pre-operative templating determined the native neck-shaft angle and planned stem-shaft angle of the implant. The latter were verified post-operatively using digital anteroposterior unilateral radiographs of the hip. The mean neck-shaft angle determined before operation was 132.7 degrees (118 degrees to 160 degrees ). The mean planned stem-shaft angle was a relative valgus alignment of 9.7 degrees (SD 2.6). The stem-shaft angle after operation differed from that planned by a mean of 2.8 degrees (SD 2.0) and in 86% of cases the final angle measured within +/- 5 degrees of that planned. We had no instances of notching of the neck or varus alignment of the implant in our series. A learning curve was observed in the time taken for navigation, but not for accurate placement of the implant. Navigation in hip resurfacing may afford the surgeon a reliable and accurate method of placement of the femoral component.

5. Component alignment in hip resurfacing using computer navigation.

Clin Orthop Relat Res. 2009 Apr;467(4):917-22

Bailey C, Gul R, Falworth M, Zadow S, Oakeshott R.

Sportsmed SA, 32 Payneham Road, Stepney, Adelaide, SA 5069, Australia.

Abstract: The use of computer navigation during hip resurfacing has been proposed to reduce the risk of a malaligned component and notching with subsequent postoperative femoral neck fracture. Femoral component malalignment and notching have been identified as the major factors associated with femoral neck fracture after hip resurfacing. We performed 37 hip resurfacing procedures using an imageless computer navigation system. Preoperatively, we generated a patient-specific computer model of the proximal femur and planned a target angle for placement of the femoral component in the coronal plane. The mean navigation angle after implantation (135.5 degrees) correlated with the target stem-shaft angle (135.4 degrees). After implantation, the mean stem-shaft angle of the femoral component measured by three-dimensional computed tomography (135.1 degrees) correlated with the navigation target stem-shaft angle (135.4 degrees). The computer navigation system generates a reliable model of the proximal femur. It allows accurate placement of the femoral component and provides precise measurement of implant alignment during hip resurfacing, thereby reducing the risk of component malpositioning and femoral neck notching.

6. Femoral component positioning in hip resurfacing with and without navigation.

Clin Orthop Relat Res. 2009 May;467(5):1341-7.

Ganapathi M, Vendittoli PA, Lavigne M, Günther KP.

Maisonneuve-Rosemont Hospital, Montreal, QC, Canada.

Abstract: Early failures after hip resurfacing often are the result of technical errors in placing the femoral component. We asked whether image-free computer navigation decreased the number of outliers compared with the conventional nonnavigated technique. We retrospectively compared 51 consecutive hip resurfacings performed using image-free computer navigation with 88 consecutive hip resurfacings performed without navigation. Patient demographics were similar. There were no differences in the average native femoral neck-shaft angles, planned stem-shaft angles, or postoperative stem-shaft angles. However, when the postoperative stem-shaft angle was compared with the planned stem-shaft angle, there were 33 patients (38%) in the nonnavigated group with a deviation greater than 5 degrees in contrast to none in the navigated group. Notching was present in four patients in the nonnavigated group and none in the navigated group. The average operative time was 111 minutes for the navigated group and 105 minutes for the nonnavigated group. Image-free navigation decreased the number of patients with potentially undesirable implant placements.

7. Navigation reduces the learning curve in resurfacing total hip arthroplasty.

Clin Orthop Relat Res. 2007 Oct;463:90-7.

Cobb JP, Kannan V, Brust K, Thevendran G.

Imperial College London, Charing Cross Hospital, London, UK.

Abstract: Hip resurfacing is a novel technique with a substantial learning curve resulting in poor outcomes for many patients. We asked whether navigation would influence this learning curve and accuracy of implantation. Twenty medical students earning their degree in surgical technology participated in a randomized trial. We provided instruction about the surgical technique, including the use of conventional instrumentation, the use of a computed tomography-based planner for hip resurfacing, and a navigation system. The 20 students were then split into three groups undertaking these tasks in three different orders. Synthetic femurs replicated normal, osteoarthritis, slipped capital femoral epiphysis, and coxa valga. The mean error using the conventional method to insert a guidewire was 23 degrees; using the computed tomography plan method it was 22 degrees; and using navigation was 7 degrees. Students produced similar accuracy, even in their first attempt, on difficult anatomy when provided navigation. Motivated students rapidly achieved an expert level of accuracy when provided with navigation. Learning a conventional method first did not improve performance, even in difficult cases. Our data suggest navigation may play an important role in reducing the learning curve in hip resurfacing arthroplasty and other tasks in arthroplasty in which a high degree of accuracy is clinically important.

8. The accuracy of image-free computer navigation in the placement of the femoral component of the Birmingham Hip Resurfacing: a cadaver study.

J Bone Joint Surg Br. 2007 Apr;89(4):557-60.

Davis ET, Gallie P, Macgroarty K, Waddell JP, Schemitsch E.

St Michael’s Orthopaedic Associates, 800-55 Queen Street East, Suite 800, Toronto, Ontario M5C 1R6, Canada.

Abstract: A cadaver study using six pairs of lower limbs was conducted to investigate the accuracy of computer navigation and standard instrumentation for the placement of the Birmingham Hip Resurfacing femoral component. The aim was to place all the femoral components with a stem-shaft angle of 135 degrees . The mean stem-shaft angle obtained in the standard instrumentation group was 127.7 degrees (120 degrees to 132 degrees ), compared with 133.3 degrees (131 degrees to 139 degrees ) in the computer navigation group (p = 0.03). The scatter obtained with computer-assisted navigation was approximately half that found using the conventional jig. Computer navigation was more accurate and more consistent in its placement of the femoral component than standard instrumentation. We suggest that image-free computer-assisted navigation may have an application in aligning the femoral component during hip resurfacing.

9. A comparison of conventional guidewire alignment jigs with imageless computer navigation in hip resurfacing arthroplasty.

J Bone Joint Surg Am. 2010 Aug 4;92(9):1834-41.

Olsen M, Chiu M, Gamble P, Boyle RA, Tumia N, Schemitsch EH.

Martin Orthopaedic Biomechanics Laboratory, Institute of Biomaterials and Biomedical Engineering, St. Michael’s Hospital, University of Toronto, 5-066 Shuter Wing, 30 Bond Street, Toronto, ON M5B 1W8, Canada.

Abstract: BACKGROUND: Correct positioning of the initial femoral guidewire is vital in order to prepare the femoral head properly for hip resurfacing. The purpose of the present investigation was to determine the accuracy and precision of the placement of the initial femoral guidewire with use of conventional alignment jigs and to compare the results with those of imageless computer navigation.

METHODS:

Five commercially available jigs (two lateral pin jigs, two neck centering jigs, and one head planing jig) were obtained. Four surgeons used each jig and navigation three times to insert a guidewire in 10 degrees of relative valgus and neutral version into individual synthetic femora. A single surgeon then used each jig three times to align the initial guidewire in 10 degrees of relative valgus and neutral version in each of ten human cadaver femora. Radiographs of the synthetic and human femora were made to assess and compare guidewire inclination and version between conventional instrumentation and navigation.

RESULTS:

Navigation provided ranges of error in the coronal guidewire alignment of up to eight times less than the conventional jigs, but both methods provided similar ranges of error for version. In both arms of the study, there were significant differences in coronal alignment accuracy between the two neck centering jigs. Next to navigation, one lateral pin jig provided the most accurate coronal placement of the initial guidewire whereas one neck centering jig provided the most precise coronal placement of the guidewire. Navigation was similar to conventional jigs in terms of the accuracy and precision of guidewire version.

CONCLUSIONS:

In hip resurfacing arthroplasty, the choice of a femoral alignment device may influence the accuracy and precision of guidewire insertion, ultimately impacting femoral component placement. Imageless computer navigation can facilitate accurate and precise coronal alignment of the initial femoral guidewire, superior to that of conventional instrumentation.

CLINICAL RELEVANCE:

The results of this study may aid surgeons in the selection of alignment instruments for placement of the initial femoral guidewire during hip resurfacing.

 

While performing a conventional total hip replacement, the surgeon decides on the placement of the components taking into account various factors including the position of the patient, local anatomy of the pelvis and the hip, x-ray appearance etc., However, it is difficult to place the component s in the correct position each time as there is so much variability and in addition, the position of the patients hip changes during surgery when the soft tissues are retracted to allow exposure of the hip joint. Thus even in the most experienced surgeon’s series, there will be a group of “outliers” in whom the components are placed in less than optimal position. This may lead to complications like hip dislocation and excessive limb length discrepancy. While these complications are multifactorial  and not entirely avoidable, it may be decreased to some extent if the components are placed accurately.

Similar to computer guided knee replacements, computer guidance can be used to during hip replacements as well. However, the technology is somewhat  more cumbersome and often requires the position of the patient to be changed during surgery. There is still some variability in the component placements (although the “outliers” are decreased as demonstrated in many studies).

In a study in which Mr.Ganapathi was involved and presented in the CAOS (Computer Aided Orthopaedic Surgery) UK meeting 2008, the leg length discrepancy and offset restoration were restored to a fairly accurate degree when using computer guided hip replacement. (LIMB LENGTH AND FEMORAL OFFSET RECONSTRUCTION DURING THA USING CT-FREE COMPUTER NAVIGATION. M. Ganapathi; P.A. Vendittoli; and M. Lavigne. Journal of Bone and Joint Surgery – British Volume, Vol 91-B, Issue SUPP_III, 399).

In addition to avoiding complications like hip dislocation, it is becoming increasingly clear that the position of the acetabular component (cup position) is also important to decrease adverse reactions when using modern bearing surfaces like metal on metal bearings (for both hip resurfacing and large diameter head total hip replacements). If the cup position is not optimal, there may be edge loading of the cup land this can lead to excessive wear debris and related adverse effects.

While cup positioning is not the only factor which has been associated with metal ion/debris related problems, it is a variable which could be improved. Multiple studies have shown that large variation in the cup positioning is present even among senior surgeons when using “conventional jigs” and “eye balling”.  While computer guided acetabular cup positioning is somewhat cumbersome, it has also been shown in multiple studies that is is much more precise (see literature references below).

With increasing evidence becoming available that position of cup placement is important, Mr.Ganapathi  is in the process of evaluating the use of computer guidance while placing the acetabular cup during hip resurfacing and large diameter head total hip replacements as well as in some selected cases of complex hip replacements.

The following is a video demonstration of Mr. Ganapathi performing a computer guided acetabular cup positioning ( the video is a screen shot of the computer screen during the procedure).

The following examples show that precise placement of the acetabular cup position could be achieved with the help of computer guided surgery

Case 1


X-ray showing severe arthritis left hip

Pre-operative planning for left hip resurfacing

Computer guided acetabular cup placement

Post-op x-ray shows acetabular cup position closely matches the computer image position

Case 2


X-ray showing severe arthritis in both hips

Pre-operative planning for left hip resurfacing

Computer guided acetabular cup placement

Post-op x-ray shows acetabular cup position closely matches the computer image position

Case 3


X-ray showing severe arthritis right hip

Pre-operative planning for right hip replacement

Computer guided acetabular cup placement

Post-op x-ray shows acetabular cup position closely matches the computer image position

The following are some relevant selected scientific references:

1. Accuracy of acetabular cup placement in computer-assisted, minimally-invasive THR in a lateral decubitus position.

Int Orthop. 2010 May 21. [Epub ahead of print]

Sendtner E, Schuster T, Wörner M, Kalteis T, Grifka J, Renkawitz T.

Orthopedic Department, Asklepios Klinik Bad Abbach, Bad Abbach, Germany.

Abstract: In a prospective and randomised clinical study, we implanted acetabular cups either by means of an image-free computer-navigation system (navigated group, n = 32) or by free-hand technique (freehand group n = 32, two drop-outs). Total hip replacement was conducted in the lateral position and through a minimally invasive anterior approach (MicroHip). The position of the component was determined postoperatively on CT scans of the pelvis using CT-planning software. We found an average inclination of 42.3 degrees (range 32.7-50.6 degrees ; SD+/-3.8 degrees ) and an average anteversion of 24.5 degrees (range 12.0-33.3 degrees ; SD+/-6.0 degrees ) in the computer-assisted study group and an average inclination of 37.9 degrees (range 25.6-50.2 degrees ; SD+/-6.3 degrees ) and an average anteversion of 23.8 degrees (range 5.6-46.9 degrees ; SD+/-10.1 degrees ) in the freehand group. The higher precision of computer navigation was indicated by the lower standard deviations. For both measurements we found a significant heterogeneity of variances (p < 0.05, Levene’s test). The mean difference between the cup inclination/anteversion values displayed by computer navigation and the true cup position (CT control) was 0.37 degrees (SD 3.26) and –5.61 degrees (SD 6.48), respectively. We found a bias (underestimation) with regard to anteversion determined by the imageless computer navigation system. A bias for inclination was not found. Registration of the landmarks of the anterior pelvic plane in lateral position with undraped percutaneous methods leads to an error in cup anteversion, but not to an error in cup inclination. The bias we found is consistent with a correct registration of the anterosuperior iliac spine (ASIS) and with a registration of the symphysis 1 cm above the bone, corresponding to the less compressible overlying soft tissue in this region. There was no significant correlation between the bias and the thickness of soft tissue above the pubic tubercles. We suggest use of a percutaneous registration of ASIS and an invasive registration above the pubic tubercles when computer-assisted navigation is performed in minimally invasive THR in a lateral position.

2. Navigated and nonnavigated total hip arthroplasty: results of two consecutive series using a cementless straight hip stem.

Orthopedics. 2008 Oct;31(10 Suppl 1).

Mainard D.

Centre Hospitalier Universitaire Nancy, France. Nancy, France.

Abstract: The purpose of this study was to compare conventional and navigated technique and a recently developed straight hip stem for uncemented primary total hip arthroplasty. The results of two consecutive implantation series of 42 patients (nonnavigated) and 42 patients (navigated) were analysed for implant positioning and complications. All surgeries were performed by the investigator. Radiographic analysis of cup position showed a significant improvement with reduced radiologic inclination (53 degrees nonnavigated /44 degrees navigated; P < .001) and higher anteversion (7 degrees nonnavigated /12 degrees navigated; P <.001). The mean postoperative limb length difference was 6.2 mm (SD, 9.0 for nonnavigated) and 4.4 mm (SD, 6.4 for navigated). Intraoperative and early postoperative complications were not different. No dislocation occurred in either group. There was one intraoperative trochanter fracture that was not revised (nonnavigated) and one revision because of a periprosthetic fracture caused by fall down during rehabilitation (navigated). We conclude that acetabular implant positioning can be significantly improved by the use of navigated surgery technique. The data for postoperative limb length difference were still similar but within the expected range in both groups. The effect of improved cup positioning on mid and longterm results for both groups has to be investigated further.

3. Assessment of accuracy of acetabular cup orientation in CT-free navigated total hip arthroplasty.

Orthopedics. 2008 Oct;31(10).

Fukunishi S, Fukui T, Imamura F, Nishio S.

Department of Orthopedic Surgery, Hyogo College of Medicine, Nishinomiya, Japan.

Abstract: We have used the Orthopilot (Aesculap AG, Tuttlingen, Germany) computed tomography (CT)-free navigation system to ensure accurate and reproducible acetabular cup orientation. In this system, cup orientation is assessed with respect to bony configuration as determined by palpation of the anatomical landmarks (the bilateral anterosuperior iliac spines and the upper margin of the pubic symphysis). In this study, intraoperative cup orientation as presented by the OrthoPilot navigation system was compared with the value obtained through postoperative radiological assessment using CT Digital Imaging and Communications in Medicine (DICOM) data and Medical Image Processing, Analysis, and Visualization (MIPAV; National Institutes of Health, US Department of Health and Human Services, Bethesda, Maryland). Intra- and postoperative results obtained from 27 consecutive navigated total hip arthroplasties (THAs) were analyzed. For cup positioning, the desired inclination and anteversion angles were set within the “safe zone” proposed by Lewinnek. In the intraoperative evaluation, the mean inclination angle as determined by the navigation system was 43.5 degrees +/- 2.17 degrees (range, 39.9 degrees to 46.6 degrees ) after the final implantation. In contrast, the mean inclination angle determined by postoperative calculation using MIPAV was 44.9 +/- 3.3 degrees (range, 38.1 degrees to 55.0 degrees ). A discrepancy of >5 degrees was observed in only 1 hip. For the anteversion, the mean intra- and postoperative values were 11.1 degrees +/- 5.6 degrees (range, 0 degrees to 17.8 degrees ) and 13.5 degrees +/- 5.9 degrees (range, 5.1 degrees to 21.6 degrees ), respectively. Again, a discrepancy of >5 degrees was observed in 1 case. Mean differences between the intra- and postoperative values were 1.9 degrees +/- 1.9 degrees and 2.6 degrees +/- 1.6 degrees for inclination and anteversion, respectively. A good agreement between the intraoperative values presented by the navigation system and those in the postoperative CT evaluation was observed, and the validity of this navigation system was confirmed.

4. Reduced variability in cup positioning: the direct anterior surgical approach using navigation.

Acta Orthop. 2008 Dec;79(6):789-93.

Nogler M, Mayr E, Krismer M, Thaler M.

Department of Orthopedics, Medical University of Innsbruck, Innsbruck, Austria.

Abstract: BACKGROUND AND PURPOSE: Correct positioning of the acetabular component is important in total hip arthroplasty (THA). We evaluated the effect of an imageless navigation system on the accuracy of cup positioning using a minimally invasive direct anterior approach. METHODS: Hip replacements were performed in 44 cadaveric hips (22 cadavers) that were divided randomly into 2 groups. In the study group, THA was performed using an imageless navigation system. In the control group, no navigation system was used. CT scans were taken postoperatively. Using 3D reconstructions, the cup position was determined in relation to the frontal pelvic plane. The goal was to place each cup at 45 degrees of inclination and 20 degrees of anteversion, as recommended by the manufacturer. RESULTS: In the navigated group, there was a statistically significantly smaller range of deviation from the target angles of inclination and anteversion relative to the control group. INTERPRETATION: We conclude that imageless navigation improves the accuracy of cup placement in minimally invasive THA using the direct anterior approach.

5. Combined anteversion technique for total hip arthroplasty.

Clin Orthop Relat Res. 2009 Jan;467(1):119-27.

Dorr LD, Malik A, Dastane M, Wan Z.

The Arthritis Institute at Good Samaritan Hospital, Los Angeles, CA 90017, USA.

Abstract: Combined cup and stem anteversion in THA based on femoral anteversion has been suggested as a method to compensate for abnormal femoral anteversion. We investigated the combined anteversion technique using computer navigation. In 47 THAs, the surgeon first estimated the femoral broach anteversion and validated the position by computer navigation. The broach was then measured with navigation. The navigation screen was blocked while the surgeon estimated the anteversion of the broach. This provided two estimates of stem anteversion. The navigated stem anteversion was validated by postoperative CT scans. All cups were implanted using navigation alone. We determined precision (the reproducibility) and bias (how close the average test number is to the true value) of the stem position. Comparing the surgeon estimate to navigation anteversion, the precision of the surgeon was 16.8 degrees and bias was 0.2 degrees ; comparing the navigation of the stem to postoperative CT anteversion, the precision was 4.8 degrees and bias was 0.2 degrees , meaning navigation is accurate. Combined anteversion by postoperative CT scan was 37.6 degrees +/- 7 degrees (standard deviation) (range, 19 degrees –50 degrees ). The combined anteversion with computer navigation was within the safe zone of 25 degrees to 50 degrees for 45 of 47 (96%) hips. Femoral stem anteversion had a wide variability

6. Computer navigation in total hip replacement: a meta-analysis.

Int Orthop. 2009 Jun;33(3):593-7.

Gandhi R, Marchie A, Farrokhyar F, Mahomed N.

Surgery, University of Toronto, Toronto, Canada.

Abstract: Proponents of navigated hip arthroplasty have suggested that it may increase the precision of acetabular component placement. We conducted a systematic review and meta-analysis to evaluate the validity of this theory. We searched, in duplicate, MEDLINE, EMBASE and the Cochrane Central Register of Controlled Trials for randomised trials comparing the use of computer navigation with the freehand technique for acetabular cup placement within the desired alignment. We assessed the methodological quality of the studies and abstracted the relevant data. Tests of heterogeneity and publication bias were performed. From the three studies included, there was no evidence of heterogeneity between studies. A total of 250 patients were entered into the analysis. The beneficial odds ratio for the number of outliers was 0.285 (95% confidence interval [CI]: 0.143 to 0.569; p < 0.001). We conclude that navigation in hip arthroplasty improves the precision of acetabular cup placement by decreasing the number of outliers from the desired alignment.

7. Navigated non-image-based positioning of the acetabulum during total hip replacement.

Int Orthop. 2009 Feb;33(1):83-7

Jenny JY, Boeri C, Dosch JC, Uscatu M, Ciobanu E.

Centre de Chirurgie Orthopédique et de la Main, Hôpitaux Universitaires de Strasbourg, 10 Avenue Baumann, 67400, Illkirch-Graffenstaden, France.

Abstract: We tested the hypothesis that the non-image-based navigation system used in our department was able to measure accurately the 3D positioning of the acetabular cup of a total hip replacement (THR) and to increase the accuracy of its implantation during THR. We studied 50 consecutive navigated implantations of a THR and compared the intra-operative measurement of the cup by the navigation system to the post-operative measurement by computed tomography (CT) scan. The mean difference between the navigated and CT scan measurements for cup inclination was 2 degrees . The mean difference between the navigated and CT-scan measurements for cup flexion was 4 degrees . These differences were significant but considered to be clinically irrelevant in most cases. A total of 73% of the cases were within the safe zone defined prior to the study. The non-image-based system used allows a precise orientation of the cup during THR.

8. Orientation of the acetabular component. A comparison of five navigation systems with conventional surgical technique.

J Bone Joint Surg Br. 2006 Oct;88(10):1401-5.

Honl M, Schwieger K, Salineros M, Jacobs J, Morlock M, Wimmer M.

Department of Orthopaedic Surgery, LKH Klagenfurt, A-9020 Klagenfurt, St. Veiter Strasse 47, Carinthia, Austria.

Abstract: We compared the orientation of the acetabular component obtained by a conventional manual technique with that using five different navigation systems. Three surgeons carried out five implantations of an acetabular component with each navigation system, as well as manually, using an anatomical model. The orientation of the acetabular component, including inclination and anteversion, and its position was determined using a co-ordinate measuring machine. The variation of the orientation of the acetabular component was higher in the conventional group compared with the navigated group. One experienced surgeon took significantly less time for the procedure. However, his placement of the component was no better than that of the less experienced surgeons. Significantly better inclination and anteversion (p < 0.001 for both) were obtained using navigation. These parameters were not significantly different between the surgeons when using the conventional technique (p = 0.966). The use of computer navigation helps a surgeon to orientate the acetabular component with less variation regarding inclination and anteversion.

9. Reduced variability of acetabular cup positioning with use of an imageless navigation system.

Clin Orthop Relat Res. 2004 Sep;(426):159-63.

Nogler M, Kessler O, Prassl A, Donnelly B, Streicher R, Sledge JB, Krismer M.

Department of Orthopaedic Surgery, Medical University of Innsbruck, Austria.

Abstract: Positioning the acetabular component is one of the most important steps in total hip arthroplasty; malpositioned components can result in dislocations, impingement, limited range of motion, and increased polyethylene wear. Conventional surgery makes use of specialized alignment guides provided by the manufacturers of the implants. The use of mechanical guides has been shown to result in large variations of cup inclination and version. We investigated acetabular cup alignment with the nonimage-based hip navigation system compared with a conventional mechanically guided procedure in 12 human cadavers. Postoperative cup position relative to the pelvic reference plane was assessed in both groups with the use of a three-dimensional digitizing arm. In the navigated group, a median inclination of 45.5 degrees and a median anteversion of 21.9 degrees (goals, 45 degrees and 20 degrees) were reached. In the control group, the median inclination was 41.8 degrees and the median anteversion was 24.6 degrees. The ninetieth percentile showed a much wider range for the control group (36.1 degrees-51.8 degrees inclination, 15 degrees-33.5 degrees anteversion) than for the navigated group (43.9 degrees-48.2 degrees inclination, 18.3 degrees-25.4 degrees anteversion). This cadaver study shows that computer-assisted cup positioning using a nonimage-based hip navigation system allowed for more consistent placement of the acetabular component.

Summary

  • Patient satisfaction following knee replacements is still not as good as hip replacements and over a quarter of the patients still have discomfort at 5 to 8 years following knee replacement.5
  • It is evident that further improvements need to be made to improve outcome following knee replacements.
  • A successful outcome following a knee replacement depends on many factors including patient expectation, activity level, preoperative function, severity of the arthritis, preoperative education, postoperative rehabilitation, design of the implant, surgical technique including soft tissue balance and alignment.
  • While computer guidance does not have an effect on many of the above factors, studies have shown that it is more precise and outliers are reduced.
  • Thus it allows control of an important variable which can be positively influenced at the time of surgery (better alignment) and hopefully it would lead to improved outcome following knee replacement.

Computer Guided Surgery can also help in special cases avoiding more complex surgery.

The following are some examples.

Case 1

X-ray showing severe arthritis in the knee with valgus deformity. The patient in addition has a femoral nailing done previously for a fracture of the femur (thigh bone).
Long Leg view showing that the fracture has also mal-united increasing the deformity. With conventional technique, the nail would have to be removed and it would have been difficult to correct the deformity due to the fracture.
With the help of computer guidance it was possible to do the knee replacement without removing the femoral nail . In addition it was also possible to correct the deformity due to the ma-union of the previous fracture by with a compensatory cut while doing the knee replacement
Computer navigation record showing the mal-tracking of the knee before the knee replacement
Computer navigation record showing that the mal-tracking  has been corrected after knee replacement
Clinical photographs at six weeks post surgery showing good alignment and function

Case 2


X-ray of the knee showing an unusual case of bone infarct, with sclerotic (hard) bone inside the medullary canal of the bones. With conventional technique, a rod would have to be passed in the thigh bone as a reference point. This would have been difficult in this case.
Computer guided surgery allowed the knee replacement to be done without the need to go through the hard bone

Case 3


X-rays of a patient with gross arthritis of the knee (severe varus and flexion deformity with bone loss)
Computer navigation record illustrating the severe varus and flexion deformity before surgery
Computer navigation record illustrating the severe varus and flexion deformity before surgery
Computer navigation record illustrating the ability to plan precisely the bone resection including the plan for 5 mm augment for the medial defect
Post-op x-rays showing good alignment
Computer navigation record showing good alignment following knee replacement
Computer navigation record showing the comparison between pre-op tracking (maltracking) and the correct tracking achieved following knee replacement

Scientific Literature

The following are some relevant selected scientific references:

1. Ten-year evaluation of geometric total knee arthroplasty.

Clin Orthop Relat Res. 1988 Jul;(232):168-73.

Rand JA, Coventry MB.

Department of Orthopedics, Mayo Clinic, Rochester, Minnesota 55905.

Abstract: One hundred ninety-three geometric total knee arthroplasties (TKA) were performed between 1972 and 1975 in 129 patients (66 women, 63 men; mean age, 69 years) with osteoarthritis. Of these, 102 knees were followed for a mean of 11 years. Eighty-three percent of the patients had mild or no pain. The revision rate was 20%, and the surgical complication rate was 12%. By actuarial analysis, the probability of retaining a geometric prosthesis at 10 years was 78%. With revision or moderate to severe pain as the end point, the predicted implant survival was 69% at 10 years. Lucent lines greater than 1 mm were present in 38% of the knees and progressed in 34%; they were more frequent in knees with greater than or equal to 3 degrees of varus axial alignment (p less than 0.05) or greater than or equal to 4 degrees of varus placement of the tibial component (p less than 0.05). The geometric prosthesis has provided a functional result in 69% of knees at 10 years, despite being the first two-part component knee replacement retaining the cruciate ligaments and using early surgical instrumentation and implant design.

2. Insall Award paper. Why are total knee arthroplasties failing today?

Clin Orthop Relat Res. 2002 Nov;(404):7-13.

Sharkey PF, Hozack WJ, Rothman RH, Shastri S, Jacoby SM.

The Rothman Institute, Philadelphia, PA 19107, USA.

Abstract: The incidence of failure after knee replacement is low, yet it has been reported that more than 22,000 knee replacements are revised yearly. The purpose of the current study was to determine current mechanisms of failure of total knee arthroplasties. A retrospective review was done on all patients who had revision total knee arthroplasty during a 3-year period (September 1997-October 2000) at one institution. The preoperative evaluation in conjunction with radiographs, laboratory data, and intraoperative findings were used to determine causes of failure. Two hundred twelve surgeries were done on 203 patients (nine patients had bilateral surgeries). The reasons for failure listed in order of prevalence among the patients in this study include polyethylene wear, aseptic loosening, instability, infection, arthrofibrosis, malalignment or malposition, deficient extensor mechanism, avascular necrosis in the patella, periprosthetic fracture, and isolated patellar resurfacing. The cases reviewed included patients who had revision surgery within 9 days to 28 years (average, 3.7 years) after the previous surgery. More than half of the revisions in this group of patients were done less than 2 years after the index operation. Fifty percent of early revision total knee arthroplasties in this series were related to instability, malalignment or malposition, and failure of fixation.

3. Tibial component failure mechanisms in total knee arthroplasty.

Clin Orthop Relat Res. 2004 Nov;(428):26-34.

Berend ME, Ritter MA, Meding JB, Faris PM, Keating EM, Redelman R, Faris GW, Davis KE.

Center for Hip and Knee Surgery, St. Francis Hospital, Mooresville, Mooresville, IN 46158, USA.

Abstract: The purpose of this study was to examine the failure mechanisms and factors associated with failure of a nonmodular metal backed cemented tibial component. Out of 3152 total knee replacements done for osteoarthritis, 41 tibial components had been revised (1.3%). Four distinct failure mechanisms were identified: 20 knees were revised for medial bone collapse, 13 for ligamentous imbalance, 6 for progressive radiolucencies, and 2 for pain. Factors associated with medial bone collapse were varus tibial component alignment more than 3.0 degrees , Body Mass Index higher than 33.7, and overall postoperative varus limb alignment. Ligamentous imbalance was more prevalent in knees with preoperative valgus deformity. There were no knees revised for tibial component polyethylene wear or osteolysis. We conclude that the dominant failure mechanisms for this component design are related to preoperative deformity, technical factors of component alignment, overall limb alignment, and ligamentous imbalance.

4. Malalignment: forewarned is forearmed.

Orthopedics. 2009 Sep;32(9). pii: orthosupersite.com/view.asp?rID=42850. doi: 10.3928/01477447-20090728-29.

Fang D, Ritter MA.

Department of Orthopedics, Indiana University School of Medicine, Indianapolis, Indiana, USA.

Abstract: Malalignment in total knee arthroplasty (TKA) is a major source of failure. Concern exists as to the acceptable window for overall coronal alignment in TKA. We evaluated the anatomical coronal alignment of 6070 primary TKAs using standard-length knee radiographs. The mean postoperative alignment was 4.8 degrees of valgus, with 1 standard deviation within the mean defining a range of 2.4 degrees to 7.2 degrees of valgus. The revision rate not related to infection for this well-aligned group was 0.5% (3 degrees =0.47%; 4 degrees =0.54%; 5 degrees =0.47%; 6 degrees =0.39%; 7 degrees =0.62%). In comparison, the failure rate for TKAs aligned in relative varus (<2.4 degrees of valgus) was 1.8% (P=.0004) and for those in valgus (>7.2 degrees of valgus) was 1.5% (P=.0027). Kaplan-Meier survival analysis confirmed these findings. The failure rates were statistically higher for the valgus and varus groups, compared to the well-aligned group within 1 standard deviation of the mean. Moreover, varus-aligned knees failed primarily by medial tibial collapse, whereas valgus-aligned knees failed because of ligamentous laxity. Restoring coronal alignment to between 2.4 degrees and 7.2 degrees of anatomical valgus is the most important surgeon-controlled factor in TKA.

5. Patient-reported outcomes after total hip and knee arthroplasty: comparison of midterm results.

J Arthroplasty. 2009 Feb;24(2):210-6.

Wylde V, Blom AW, Whitehouse SL, Taylor AH, Pattison GT, Bannister GC.

Bristol Implant Research Centre, Avon Orthopaedic Centre, Southmead Hospital, Bristol, UK.

Abstract: The aim of this study was to compare the midterm functional outcomes of total knee arthroplasty (TKA) and total hip arthroplasty (THA). A cross-sectional postal audit survey of all consecutive patients who had a primary joint replacement at one orthopedic center 5 to 8 years ago was conducted. Participants completed an Oxford hip score or Oxford knee score, which are self-report measures of functional ability. Completed questionnaires were returned from 1112 THA patients and 613 TKA patients, giving a response rate of 72%. The median Oxford knee score of 26 was significantly worse than the median Oxford hip score of 19 (P < .001). In conclusion, TKA patients experience a significantly poorer functional outcome than THA patients 5 to 8 years postoperatively.

6. Good alignment after total knee arthroplasty leads to faster rehabilitation and better function.

J Arthroplasty. 2009 Jun;24(4):570-8.

Longstaff LM, Sloan K, Stamp N, Scaddan M, Beaver R.

Department of Elective Orthopaedics, Royal Perth Hospital, Perth, Australia.

Abstract: The aim of this study was to identify what aspects of implant alignment and rotation affect functional outcome after total knee arthroplasty (TKA). One hundred and fifty-nine total knee arthroplasties were performed at the authors’ institution between May 2003 and July 2004. All patients underwent an objective and independent clinical and radiological assessment before and after surgery. A computed tomography scan was performed at 6 months. The alignment parameters that were measured included sagittal femoral, coronal femoral, rotational femoral, sagittal tibial, coronal tibial, and femorotibial mismatch. The cumulative error score, which represents the sum of the individual errors, was calculated. Functional outcome was measured using the Knee Society Score. Good coronal femoral alignment was associated with better function at 1 year (P = .013). Trends were identified for better function with good sagittal and rotational femoral alignment and good sagittal and coronal tibial alignment. Patients with a low cumulative error score had a better functional outcome (P = .015). These patients rehabilitated more quickly and their length of stay in hospital was 2 days shorter.

7. Computer assistance increases precision of component placement in total knee arthroplasty with articular deformity.

Hernández-Vaquero D, Suarez-Vazquez A, Sandoval-Garcia MA, Noriega-Fernandez A.

Clin Orthop Relat Res. 2010 May;468(5):1237-41.

Department of Orthopaedic Surgery, School of Medicine, University of Oviedo, Oviedo, Spain.

Abstract: BACKGROUND: The accuracy of computer navigation applied to total knee arthroplasty (TKA) in knees with severe deformity has not been studied. QUESTIONS/PURPOSES: The purpose of this study was to compare the radiographic alignment achieved in total knee replacements performed with and without navigation and to search for differences in the final alignment of two groups of patients (with and without previous joint deformities) using the same system of surgical navigation. METHODS: The first series comprised 40 arthroplasties with minimal preoperative deformity. In 20 of them, surgical navigation was used, whereas the other 20 were performed with conventional jig-based technique. We compared the femoral angle, tibial angle, and femorotibial angle (FTA) by performing a post-TKA CT of the entire limb. In the second series, 40 additional TKAs were studied; in this case, however, they presented preoperative deformities greater than 10 masculine in the frontal plane. RESULTS: The positioning of the femoral and tibial component was more accurate in the group treated with surgical navigation and FTA improvement was statistically significant. When comparing the results of both series, FTA precision was always higher when using computer-assisted surgery. As for optimal FTA, data showed the use of surgical navigation improved the results both in the group with preoperative deformity greater than 10 degrees in the frontal plane and in the group with minimal preoperative knee deformity. CONCLUSIONS: Surgical navigation obtains better radiographic results in the positioning of the femoral and tibial components and in the final axis of the limb in arthroplasties performed on both deformed and more normally aligned knees. LEVEL OF EVIDENCE: Level II, therapeutic study. 

8. Imageless computer assisted versus conventional total knee replacement. A Bayesian meta-analysis of 23 comparative studies.

Int Orthop. 2010 Apr 8. [Epub ahead of print]

Brin YS, Nikolaou VS, Joseph L, Zukor DJ, Antoniou J.

Department of Orthopaedic Surgery, Jewish General Hospital, McGill University, Montreal, Quebec, Canada.

Abstract: We have undertaken a meta-analysis of the English literature, to assess the component alignment outcomes after imageless computer assisted (CAOS) total knee arthroplasty (TKA) versus conventional TKA. We reviewed 23 publications that met the inclusion criteria. Results were summarised via a Bayesian hierarchical random effects meta-analysis model. Separate analyses were conducted for prospective randomised trials alone, as well as for all randomised and observational studies. In 20 papers (4,199 TKAs) we found a reduction in outliers rate of approximately 80% in limb mechanical axis when operated with the CAOS. For the coronal femoral and tibial implants positions, the analysis included 3,058 TKAs. The analysis for the femoral implant showed a reduction in outliers rate of approximately 87% and for the tibial implant a reduction in outliers rate of approximately 80%. Imageless navigation when performing TKA improves component orientation and postoperative limb alignment. The clinical significance of these findings though has to be proven in the future. 

9. Does computer navigation in total knee arthroplasty improve patient outcome at midterm follow-up?

Int Orthop. 2009 Dec;33(6):1567-70. Epub 2008 Nov 26.

Kamat YD, Aurakzai KM, Adhikari AR, Matthews D, Kalairajah Y, Field RE.

The South West London Elective Orthopaedic Centre, Epsom and St. Helier University Hospitals NHS Trust, Epsom, Surrey, KT18 7EG, UK. yogeesh.kamat@gmail.com

Abstract: Computer navigation assistance in total knee arthroplasty (TKA) results in consistently accurate alignment of prostheses. We aimed to compare the outcome of computer-navigated and conventional TKA and to analyse the radiologically malaligned knees. We analysed 637 primary TKA, carried out by a single surgeon, over five consecutive years and divided them into two cohorts: group 1 = STA (standard instrumentation) and group 2 = CAS (computer-assisted surgery). There was no significant difference between the average Oxford Knee Scores (OKS) of the two groups at any time from one to five years. However, the malaligned TKA at three years had a worse OKS. At medium term there is no difference in clinical outcome measures that can be attributed to the surgeon having used computer-assisted navigation for TKA. But group 1, having a higher proportion of malaligned TKA, might show worsening of OKS at long term.

10. Comparison of functional and radiological outcomes after computer-assisted versus conventional total knee arthroplasty: a matched-control retrospective study.

J Orthop Surg (Hong Kong). 2008 Aug;16(2):192-6.

Ek ET, Dowsey MM, Tse LF, Riazi A, Love BR, Stoney JD, Choong PF.

Department of Orthopaedics, University of Melbourne, St Vincent’s Hospital, Melbourne, Australia.

Abstract: PURPOSE: To compare the radiological and functional outcomes of patients who underwent either computer-assisted or conventional total knee arthroplasty (TKA). METHODS: Two groups of 50 patients each underwent either computer-assisted or conventional TKA were retrospectively studied. Patients were matched according to body mass index (BMI), gender, and age. Three senior orthopaedic surgeons with comparable experience performed all surgeries, using 3 different prostheses. The surgical approach and peri- and postoperative regimens were the same. The mechanical axis and the tibial and femoral angles were measured using standardised long-leg weight-bearing radiographs. Overall function was assessed using the Short Form-12 (SF-12) and International Knee Society (IKS) scores. RESULTS: No intra-operative technical difficulties were encountered in either group. The computer-assisted group resulted in more consistent and accurate alignments in both the coronal and sagittal planes and better SF-12 and IKS scores. In obese patients (BMI=30 kg/m2 or more), computer-assisted TKA provided better alignment than the conventional technique. CONCLUSION: Computer-assisted TKA improves implant positioning, limb alignment, and overall functional outcome. It may be particularly advantageous for obese patients.

11. Does accurate anatomical alignment result in better function and quality of life? Comparing conventional and computer-assisted total knee arthroplasty.

J Arthroplasty. 2009 Jun;24(4):560-9.

Choong PF, Dowsey MM, Stoney JD.

Department of Orthopaedics, St Vincent’s Hospital, University of Melbourne, Melbourne, Victoria, Australia.

Abstract: This is a randomized prospective controlled trial comparing the alignment, function, and patient quality-of-life outcomes between patients undergoing conventional (CONV) and computer-assisted (CAS) knee arthroplasty. One hundred and fifteen patients (60 CAS, 55 CONV) underwent cemented total knee arthroplasty. Three patients were lost to follow-up. Eighty-eight percent (CAS) vs 61% (CONV) of knees achieved a mechanical axis within 3 degrees of neutral (P = .003). Aligning femoral rotation with the epicondylar axis was accurately achieved in CAS and CONV with no significant difference. Patients with coronal alignment within 3 degrees of neutral had superior International Knee Society and Short-Form 12 physical scores at 6 weeks, 3 months, 6 months, and 12 months after surgery. Computer-assisted total knee arthroplasty achieves greater accuracy in implant alignment and this correlates with better knee function and improved quality of life.

12. Comparison Between Computer-Assisted-Navigation and Conventional Total Knee Arthroplasties in Patients Undergoing Simultaneous Bilateral Procedures: A Randomized Clinical Trial

J Bone Joint Surg Am.  2011; 93:1190

Guo-qiang Zhang,  Ji-ying Chen,  Wei Chai,  Ming Liu, Yan Wang

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Abstract-Background:  Total knee arthroplasty has been increasingly used for young and active patients, and prosthesis durability is important in these patients. The accuracy of implant placement has been one of the major factors that determine the long-term survival of the prosthesis. The purpose of this study was to compare the accuracy of prosthetic alignment between computer-assisted-navigation and conventional total knee arthroplasties. Methods:  From March 2007 to June 2008, thirty-two patients with bilateral knee osteoarthritis underwent simultaneous bilateral total knee arthroplasty with the same type of implant in each knee. The subjects included seven men and twenty-five women, with an average age of sixty-three years. For each patient, the bilateral total knee arthroplasty was performed with computer-assisted navigation in one knee and a conventional technique in the other. The operative technique and the order of the surgical procedures were randomized. The patients and surgeons conducting the follow-up study and performing the imaging measurements were blinded to the type of surgical procedure. Results:  There was a significant difference between the two groups with regard to the alignment of the knee prosthesis in the coronal and sagittal planes. Nine knee implants (28%) in the conventional group, compared with no knee implants in the computer-navigation group, deviated >3° from the mechanical axis in the coronal plane. The coefficient variation of data in the conventional group was three times greater than that in the computer-navigation group. There was no significant difference in the rotational angle of the femoral component between the two groups. The Hospital for Special Surgery (HSS) scores at six months postoperatively were substantially increased compared with the preoperative scores in both groups. Conclusions:  Computer-assisted navigation consistently provided coronal plane alignment within 3° of the mechanical axis, which was significantly better than the alignment obtained with conventional total knee arthroplasty.

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