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PERSONALISED KNEE REPLACEMENT


Like many features of an individual person, each person’s knees are also to some extent different. Studies have shown that good alignment of a knee replacement is important for optimal outcome. In addition, the component sizing is also important. During conventional knee replacements, manual guides are used and a certain amount of “eye balling” is involved. Many studies have shown that this can result in a proportion of “outliers” who can have less than optimal function. Computer guided surgery has been shown to reduce the “outliers” but the surgery takes longer and special equipments are needed.

A very recent technological development is “patient specific instrumentation” or a “custom fit knee”. In this technique, MRI scan of the person’s hip, knee and ankle is done few weeks before the operation. A special computer software creates the three dimensional model of the patient’s knee and allows the surgeon to plan the bone cuts and component placement  on a personal computer. The model also allows the best sizing option and shape). These images are then used to create precise 3 dimensional plastic moulds which when placed on that particular patient’s knee during surgery allows customised bone preparation as planned previously in the computer. Essentially a the surgeon does a “virtual knee replacement” in the computer and then “executes” this plan during the actual surgery. Different companies call this technique by different names (PSI knee – Zimmer; Signature knee replacement – Biomet). Please see videos below for more detailed information.

Potential advantages compared to conventional knee replacements

1. Accuracy in alignment – already there are some studies showing better alignment (please see below) although there are other studies found no difference in the alignment. To some extent this is understandable as in addition to accuracy of the moulds, there are a number of surgeon dependent factors which will also affect the accuracy including accurate positioning of the moulds, precision of the saw cut and soft tissue balancing.  Most of the studies have concentrated mainly on the frontal plane alignment and it is now generally accepted a small variation in the frontal plane alignment is not of major significance. However, there are many other 3-dimensional factors including rotational alignment, fine tuning of the 3 dimensional positioning, fine tuning of the sizing to avoid overloading the patellofemoral compartment and maintaining of joint line including posterior femoral offset etc., which are probably more important than minimal variation in the frontal plane alignment and could be controlled in a better manner by planning in a 3 dimensional bone model. It goes without saying that careful planning by the surgeon is important to get the full benefit of this technology.

2. Reduced instrumentation – instead of the usual 7 or 8 trays of instruments required for conventional knee replacements, by making the trays size specific Mr.Ganapathi has been able to reduce the number of instrument trays to 2 or 3 which reduces the sterilization cost and also helps faster turnover of patients.

3. Faster Surgery – While intuitively it would be expected that the surgical time would be less with the pre-planning in a 3-D model in a computer, many studies have reported no difference or very little difference in the surgical time! In Mr.Ganapathi’s own practice, the surgical time during the initial few cases was not reduced. However, careful pre-operative planning, reduced instruments, faster turnover, streamlining the surgical steps and optimising intra-operative processes using the analogy of a Formula 1 pit stop has allowed Mr.Ganapathi to take full advantage of the PSI technology and reduced the surgical time significantly without compromising on outcome (see below for functional outcome).

 

4. Minimal blood loss and transfusion requirement In Mr.Ganapathi’s personal series, the blood transfusion requirement is significantly lower (less than 1% transfusion requirement for unilateral cases in a series of 150 PSI knees) compared to published studies on knee replacements using conventional instrumentation. This probably is related to the lesser soft tissue dissection and not invading the medullary canal of the thigh bone.

5. Functional outcome: While complications can still occur like in any other knee replacement and not every patient will have an entirely satisfactory outcome, in Mr.Ganapathi’s own series, the one year average patient reported functional outcome (PROMS score – Oxford hip score – 0 to 48 with 48 being the maximum score) seems to be favourable compared to that published from the UK National Joint Registry data.

NJR Data

6. Even in some difficult cases, the results have been good.

Example1: Bilateral severe arthritis with valgus deformities (pre-op and post-op x-rays)
Example 2: Bilateral severe arthritis with stiffness, valgus deformity and high BMI (pre-op and post-op x-rays)
Example 3: Bilateral severe arthritis with varus deformity and stiffness with preoperative flexion deformity > 20 degrees (pre-op and post-op x-rays, post-op clinical picture and post-op range of movement at one year)
Example 4: Previous femoral malunion with arthritis (pre-op and post-op x-rays)

Not all patients would be suitable for this technique. If there is a contra-indication to have an MRI scan (for example claustrophobia, pacemaker etc.,) this technique cannot be used. Similarly if there is a metal implant around the knee from previous surgery, this technique will not be suitable. However, more recently CT scan based technique is also now available.

If you are interested in having this surgery done privately, Mr.Ganapathi would be able to offer this type of knee replacement at Spire Yale Hospital, Wrexham. For further enquiries please click here.

Preoperative deformity
Preoperative x-rays
3-D model of the knee
Planned bone resection
Planned knee replacement
How the 3-D moulds will look on the patient’s knee
Before & After Knee Replacements
Preop and post operative x-rays (cruciate retaining knee replacements)
Excellent function at 3 months after both knee replacements

PSI knee replacement on S4C

PSI knee Signature knee Mr.Ganapathi

PSI Knee Replacement computer workflow

Personalised Knee Replacement

Case Study 1 – Complex Varus with Valgus on the Other Side – Windswiped Knees





Case Study 2 – Complex Valgus







 




Case Study 3 – Severe Patello-femoral Arthritus




Case Study 4 – Severe Stiffness





 

Case Study 5 – Previous High Tibial Osteotomy



AWARDS

1. The improvement which Mr.Ganapathi (in conjunction with theatre staff) has brought to theatre efficiency and faster rehabilitation by using this novel technique has been acknowledged by Betsi Cadwaladr University Health Board by awarding runner up prize at the “Improvement Award 2012” function.

2. ‘Best Podium presentation award’ in the CAOS UK Annual Meeting Nov 2013  (Computer Assisted Orthopaedic Surgery) for ‘Importance of Surgeon’s planning during PSI knee replacement’.

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PRESENTATIONS

1.’ My PSI Journey ‘

Invited speaker at the PSI user group meeting, Warrington – May 2012.

2. Comparison of peri-opertative outcomes of TKRs done using Computer Navigation and PSI

Invited speaker at the 6th International Arthroplasty Conference, Sharm El Sheik, Egypt – Jan 2013.

3. Single surgeon experience of 100 consecutive TKA using Zimmer PSI technique

Invited speaker at the 6th International Arthroplasty Conference, Sharm El Sheik, Egypt – Jan 2013.

4. Importance of planning and how PSI works in a public hospital setting

Invited speaker at the PSI user group meeting, Florence, Italy – April 2013.

5. Comparison of peri-operative outcomes of TKRs done using Computer Navigation and Patient Specific  Instrumentation

S.Aranganathan, S.Thati, M Ganapathi – Poster presentation at the 14th Annual Oswestry Registrars’ Research Day, Oswestry – April 2013.

6. Comparison of peri-operative outcomes of TKRs done using Computer Navigation and Patient Specific  Instrumentation

S.Aranganathan, S.Thati, M Ganapathi – Poster presentation at the Welsh Orthopaedic Society meeting, Llandudno – May 2013.

7. Preoperative planning in Patient Specific Instrumentation Total Knee Replacement

S.Aranganathan, S.Thati, M Ganapathi – Podium presentation at the IOS UK Annual Meeting, Huddersfield – June 2013.

8. Patient Specific Instrumentation Total Knee Arthroplasty improves theatre efficiency

S.Aranganathan, S.Thati, M Ganapathi Poster presentation at the IOS UK Annual Meeting, Huddersfield – June 2013.

9. Comparison of peri-operative outcomes of TKRs done using Computer Navigation and Patient Specific  Instrumentation

S.Aranganathan, S.Thati, M Ganapathi – Poster presentation at the All Wales Registrars’ Meeting, Cardiff – July 2013.

10. A single surgeon experience in using Patient Specific Instrumentation technique for knee replacement 

S.Aranganathan, S.Thati, M Ganapathi – Podium presentation at the BOA Annual Congress, Birmingham – October 2013.

11. Patient Specific Instrumentation – preoperative planning

S.Aranganathan, S.Thati, M Ganapathi – Poster presentation at the 34th SICOT Orthopaedic World Congress, Hyderabad, India – October 2013.

12. Patient Specific Instrumentation Total Knee Arthroplasty improves theatre efficiency

S.Aranganathan, S.Thati, M Ganapathi – Poster presentation at the 34th SICOT Orthopaedic World Congress, Hyderabad, India – October 2013.

13. Comparison of perioperative outcomes of TKRs done using Computer Navigation and Patient Specific Instrumentation

S.Aranganathan, S.Thati, M Ganapathi – Podium presentation at the 34th SICOT Orthopaedic World Congress, Hyderabad, India – October 2013.

14. ‘PSI Effect’

Invited speaker at the 34th SICOT Orthopaedic World Congress, Hyderabad, India – October 2013.

15. Comparison of peri-operative outcomes of TKRs done using Computer Navigation and Patient Specific  Instrumentation

S.Aranganathan, S.Thati, M Ganapathi – Podium presentation at the 7th Annual CAOS UK Conference, London – November 2013.

16. Careful planning during virtual knee replacement improves component prediction and reduced intraoperative changes

S.Aranganathan, S.Thati, M Ganapathi – Podium presentation at the 7th Annual CAOS UK Conference, London – November 2013 (Won the Best Podium Presentation Award).

17. MRI study of distal femoral rotational axes and their effect on flexion gap

A.Kaminskas, S.Thati, M Ganapathi – Podium presentation at the 7th Annual CAOS UK Conference, London – November 2013.

18. PSI knee replacement – a single surgeon experience in a DGH

S.Thati, M Ganapathi – Podium presentation at the BAPIO Annual Congress, Cardiff – November 2013.

19. The Importance Of Surgeon’S Input In Preoperative Planning Of Patient Specific Knee Replacement

S.Thati, S. Aranganathan, M Ganapathi – Has been accepted for poster presentation at the 15th EFORT Congress,  London – June 2014.

20. Anatomical Variation In Distal Femoral Rotational Axes And Its Effect On Flexion Gap: MRI Analysis 

 A.Kaminskas, S.Thati, M Ganapathi – Has been accepted for poster presentation at the 15th EFORT Congress,  London – June 2014.

The following are some relevant selected scientific references:

1. Frontal plane alignment after total knee arthroplasty using patient-specific instruments.

Int Orthop. 2013 Jan;37(1):45-50. doi: 10.1007/s00264-012-1732-1.

Daniilidis K, Tibesku CO.

Department of Orthopaedic Surgery, Annastift Hannover Medical School, Hannover, Germany.

PURPOSE: Although total knee arthroplasty (TKA) is regularly associated with favorable outcomes, considerable research efforts are still underway to improve its ability to achieve a neutral postoperative mechanical axis. Patient-specific instrumentation (PSI) was introduced with this and other goals in mind. The current retrospective study was designed to determine whether PSI would lead to a hip-knee-ankle angle (HKA) within ±3° of the ideal alignment of 180°.

METHODS: A long-leg x-ray of the knee was performed after an average of 3.5 months (SD, three to four months), following 124 TKAs performed by a single surgeon using PSI technology (VISIONAIRE; Smith & Nephew). In addition to HKA, the zone of the mechanical axis (ZMA; zone of the tibial base plate where the mechanical axis of the limb intersects with the tibial base plate) was analysed, with the ideal intersection occurring centrally.

RESULTS: There were 100 knees (average age, 66.8 years) with follow-up data available. The average HKA changed from 175.5±5.6° preoperatively to 178.5±1.7° postoperatively. The rate of ±3° and ±5° HKA outliers was 11 % and 3 %, respectively. In terms of ZMA, the mechanical axis passed through the central third of the knee in the majority of cases (93 knees, 93 %). There were no intra-operative complications with the use of PSI.

CONCLUSIONS: The use of PSI technology was able to achieve a neutral mechanical axis on average in patients undergoing TKA. Further follow-up will be needed to ascertain the long-term impact of these findings.

2. Improved femoral component rotation in TKA using patient-specific instrumentation.

Knee. 2012 Nov 7. pii: S0968-0160(12)00198-6. doi: 10.1016/j.knee.2012.10.009.

Heyse TJ, Tibesku CO.

Department of Orthopedics and Rheumatology, University Hospital Marburg, Germany.

BACKGROUND: Patient-specific instrumentation (PSI) was introduced in an attempt to reduce positional outliers of components in total knee arthroplasty (TKA). It was hypothesized that PSI could help with the positioning of femoral components in optimal rotational alignment.

METHODS: A magnetic resonance imaging (MRI) analysis of 94 patients following TKA was conducted. Of these, 46 operations were performed using PSI and 48 using conventional instrumentation. The rotation of the femoral components was determined in the MRI and deviations >3° were considered outliers. Data were analyzed for positional outliers, observer reliability, and a variance comparison between implant groups.

RESULTS: There was excellent inter- and intraobserver reliability with low standard deviations for the determination of femoral component rotation. There were significantly more outliers in the conventional (22.9%) group than in the PSI group (2.2%, p=0.003).

CONCLUSION: In this setup, PSI was effective in significantly reducing outliers of optimal rotational femoral component alignment during TKA.

3. Improved accuracy of alignment with patient-specific positioning guides compared with manual instrumentation in TKA.

Clin Orthop Relat Res. 2012 Jan;470(1):99-107. doi: 10.1007/s11999-011-1996-6.

Ng VY, DeClaire JH, Berend KR, Gulick BC, Lombardi AV Jr.

Department of Orthopaedics, The Ohio State University Medical Center, Columbus, OH, USA.

BACKGROUND: Coronal malalignment occurs frequently in TKA and may affect implant durability and knee function. Designed to improve alignment accuracy and precision, the patient-specific positioning guide is predicated on restoration of the overall mechanical axis and is a multifaceted new tool in achieving traditional goals of TKA.

QUESTIONS/PURPOSES: We compared the effectiveness of patient-specific positioning guides to manual instrumentation with intramedullary femoral and extramedullary tibial guides in restoring the mechanical axis of the extremity and achieving neutral coronal alignment of the femoral and tibial components.

METHODS: We retrospectively reviewed 569 TKAs performed with patient-specific positioning guides and 155 with manual instrumentation by two surgeons using postoperative long-leg radiographs. For all patients, we assessed the zone in which the overall mechanical axis passed through the knee, and for one surgeon’s cases (105 patient-specific positioning guide, 55 manual instrumentation), we also measured the hip-knee-ankle angle and the individual component angles with respect to their mechanical axes.

RESULTS: The overall mechanical axis passed through the central third of the knee more often with patient-specific positioning guides (88%) than with manual instrumentation (78%). The overall mean hip-knee-ankle angle for patient-specific positioning guides (180.6°) was similar to manual instrumentation (181.1°), but there were fewer ± 3° hip-knee-ankle angle outliers with patient-specific positioning guides (9%) than with manual instrumentation (22%). The overall mean tibial (89.9° versus 90.4°) and femoral (90.7° versus 91.3°) component angles were closer to neutral with patient-specific positioning guides than with manual instrumentation, but the rate of ± 2° outliers was similar for both the tibia (10% versus 7%) and femur (22% versus 18%).

CONCLUSIONS: Patient-specific positioning guides can assist in achieving a neutral mechanical axis with reduction in outliers.

4. Comparison of custom to standard TKA instrumentation with computed tomography.  

Knee Surg Sports Traumatol Arthrosc. 2013 Aug 25.

Ng VY, Arnott L, Li J, Hopkins R, Lewis J, Sutphen S, Nicholson L, Reader D, McShane MA.

Author information Department of Orthopaedics, The Wexner Medical Center, The Ohio State University

Abstract

PURPOSE: There is conflicting evidence whether custom instrumentation for total knee arthroplasty (TKA) improves component position compared to standard instrumentation. Studies have relied on long-limb radiographs limited to two-dimensional (2D) analysis and subjected to rotational inaccuracy. We used postoperative computed tomography (CT) to evaluate preoperative three-dimensional templating and CI to facilitate accurate and efficient implantation of TKA femoral and tibial components.

METHODS: We prospectively evaluated a single-surgeon cohort of 78 TKA patients (51 custom, 27 standard) with postoperative CT scans using 3D reconstruction and contour-matching technology to preoperative imaging. Component alignment was measured in coronal, sagittal and axial planes.

RESULTS: Preoperative templating for custom instrumentation was 87 and 79 % accurate for femoral and tibial component size. All custom components were within 1 size except for the tibial component in one patient (2 sizes). Tourniquet time was 5 min longer for custom (30 min) than standard (25 min). In no case was custom instrumentation aborted in favour of standard instrumentation nor was original alignment of custom instrumentation required to be adjusted intraoperatively. There were more outliers greater than 2° from intended alignment with standard instrumentation than custom for both components in all three planes. Custom instrumentation was more accurate in component position for tibial coronal alignment (custom: 1.5° ± 1.2°; standard: 3° ± 1.9°; p = 0.0001) and both tibial (custom: 1.4° ± 1.1°; standard: 16.9° ± 6.8°; p < 0.0001) and femoral (custom: 1.2° ± 0.9°; standard: 3.1° ± 2.1°; p < 0.0001) rotational alignment, and was similar to standard instrumentation in other measurements.

CONCLUSIONS: When evaluated with CT, custom instrumentation performs similar or better to standard instrumentation in component alignment and accurately templates component size. Tourniquet time was mildly increased for custom compared to standard.

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