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
Preoperative alignment showing the deformity
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
Distal femur cut
Rotational alignment
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
Restoration of good alignment after surgery
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


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-
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.
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-
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).
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-
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-
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-
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-
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-
3. How accurate is image- free computer navigation for hip resurfacing arthroplasty? An anatomical investigation.
J Orthop Sci. 2009 Sep;14(5):497-
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-
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-
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-
5. Component alignment in hip resurfacing using computer navigation.
Clin Orthop Relat Res. 2009 Apr;467(4):917-
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-
6. Femoral component positioning in hip resurfacing with and without navigation.
Clin Orthop Relat Res. 2009 May;467(5):1341-
Ganapathi M, Vendittoli PA, Lavigne M, Günther KP.
Maisonneuve-
Abstract: Early failures after hip resurfacing often are the result of technical errors in placing the femoral component. We asked whether image-
7. Navigation reduces the learning curve in resurfacing total hip arthroplasty.
Clin Orthop Relat Res. 2007 Oct;463:90-
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-
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-
Davis ET, Gallie P, Macgroarty K, Waddell JP, Schemitsch E.
St Michael’s Orthopaedic Associates, 800-
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-
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-
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-
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-
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-
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-
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)-
4. Reduced variability in cup positioning: the direct anterior surgical approach using navigation.
Acta Orthop. 2008 Dec;79(6):789-
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-
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 +/-
6. Computer navigation in total hip replacement: a meta- analysis.
Int Orthop. 2009 Jun;33(3):593-
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-
7. Navigated non- image- based positioning of the acetabulum during total hip replacement.
Int Orthop. 2009 Feb;33(1):83-
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-
Abstract: We tested the hypothesis that the non-
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-
Honl M, Schwieger K, Salineros M, Jacobs J, Morlock M, Wimmer M.
Department of Orthopaedic Surgery, LKH Klagenfurt, A-
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-
9. Reduced variability of acetabular cup positioning with use of an imageless navigation system.
Clin Orthop Relat Res. 2004 Sep;(426):159-
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-




















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-
Rand JA, Coventry MB.
Department of Orthopedics, Mayo Clinic, Rochester, Minnesota 55905.
Abstract: One hundred ninety-
2. Insall Award paper. Why are total knee arthroplasties failing today?
Clin Orthop Relat Res. 2002 Nov;(404):7-
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-
3. Tibial component failure mechanisms in total knee arthroplasty.
Clin Orthop Relat Res. 2004 Nov;(428):26-
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-
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-
5. Patient- reported outcomes after total hip and knee arthroplasty: comparison of midterm results.
J Arthroplasty. 2009 Feb;24(2):210-
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-
6. Good alignment after total knee arthroplasty leads to faster rehabilitation and better function.
J Arthroplasty. 2009 Jun;24(4):570-
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-
7. Computer assistance increases precision of component placement in total knee arthroplasty with articular deformity.
Hernández-
Clin Orthop Relat Res. 2010 May;468(5):1237-
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-
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-
9. Does computer navigation in total knee arthroplasty improve patient outcome at midterm follow- up?
Int Orthop. 2009 Dec;33(6):1567-
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-
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-
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-
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-
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-
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-
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