An 8- to 10-Year Follow-up of 26 Computer-assisted Total Knee Arthroplasties

Abstract

The objective of this article was to assess the long-term follow-up of the first 26 computer-assisted total knee arthroplasties (TKAs) performed between January, 1997, and December, 1998, using the prototype of the OrthoPilot (B. Braun Aesculap, Tuttlingen, Germany).

Three patients died of unrelated causes at 3, 8, and 9 years after surgery and one was lost to follow-up. One prosthesis was partially revised after 5 years of follow up, because of untimely wear of the polyethylene. Another will be revised because of femoral implant loosening. Therefore, results are based on 20 prostheses after a mean follow up of 98.25±10.28 months (range, 80-119), with a survival rate of 90%.

The majority of patients reported being satisfied or very satisfied with their prosthesis (17 patients; 85%), and three (15%) could not benefit fully from the prosthesis because of other issues, including spinal handicap, non operated homolateral coxarthrosis, and Parkinson’s disease.

Computer-assisted total knee arthroplasty (TKA) is becoming more widespread. Most reports published since 2001 note the accuracy and reliability of the various navigation systems.^1-11 We first implanted a computer-assisted TKA in January 1997 and thus are able to report long-term follow-up of the first 26 computer-assisted TKA procedures performed by a single surgeon between January 1997 and December 1998.

Materials and Methods

The series included 16 women and 10 men. The mean age of patients at surgery was 69.55±8.49 years (range, 48-80). Of the patients, 21 presented with genu varum and 5 with genu valgum. The right knee was involved in 11 cases and the left knee in 15. The mean preoperative hip-knee-ankle (HKA) angle was 174.15°±7.97° (range, 162°-190°). The mean preoperative International Knee Society (IKS) score was 30.37±16 points (range, 0-80) for the knee score, 40.14±17 points (range, 0-85) for the function score, and 70.44±26.75 points (range, 5-135) for the overall score. The mean preoperative flexion was 118.7°±12.4° (range, 75°-140°).

Twenty-six Search knee prostheses (B. Braun Aesculap, Tuttlingen, Germany) were used, 25 posterior cruciate ligament retaining prostheses, and one posterior cruciate ligament sacrificing prosthesis. The Search prosthesis is a flat-on-flat type, with a tibial titanium metal back used in the 15 first cases and cobalt-chromium back used in the remaining 11 cases.

The navigation device was a prototype of the OrthoPilot system (B. Braun Aesculap); that is, a kinematic model with no preoperative imaging.^12-15 At that time, we navigated only the mechanical axis of the lower leg, which was our initial goal for computer-assisted TKA, and we used a rigid body inserted on the iliac crest. Soft tissue release and rotation of the femoral implant were not navigated. Also, the intraarticular palpation did not include palpation of the middle of the femoral notch or of the middle of the tibial spines.

The postoperative lower leg alignment was assessed with long-standing leg radiograph, 2 to 4 months after surgery. Considering the mean age of patients at revision (78.2±8.7 years; range, 56-89 years), eleven patients reported by telephone questionnaire because they were unable to come back for examination and nine were reviewed clinically and radiologically.

Results

There were no immediate postoperative complications. Three patients died from unrelated causes (3, 8, and 9 years) and one was lost to follow-up. One prosthesis was partially revised after 5 years of follow-up, due to polyethylene wear (Figure 1), and another is scheduled for revision because of femoral implant loosening (Figure 2), which occurred after 8 years of follow up. These two prostheses had a postoperative HKA angle of 177°, one for a genu varum and one for a genu valgum. Therefore, the results are based on 20 prostheses still in place after a mean follow-up period of 98.25±10.28 months (range, 80-119), with a survival rate of 90%. Considering our method of revision, it was not possible to determine an accurate IKS score at review.

Concerning the postoperative radiological alignment, the mean HKA angle was 179.2°±1.67° (range, 176°-185°), with 92.3% of the knees aligned between 177° and 183°. We did not find any loosening of the implants in the nine patients who underwent radiographic examination at follow-up. Two tibial plateaus showed an obvious wear (2-3 mm). Seventeen (85%) patients reported being satisfied or very satisfied with their prosthesis and three (15%) could not benefit from the prosthesis because of other issues, including spinal handicap, non operated homolateral coxarthrosis, and Parkinson’s disease.


Figure 1: Wear of the medial side of the tibial plateau at 5-year follow-up. Figure 2: Loosening of the femoral implant at 9-year follow-up.

Discussion

Regarding mechanical axis, the 26 first cases presented a better result than that with another study we carried out from January 1998 to April 1999,¹⁴ (92.3% vs 84% of proper alignment (180°±-3°). We cannot explain this difference because the technique and device were identical. Was the greater confidence in the navigation system responsible for reduced surgical accuracy? We also note that the HKA angle was very accurate and close to that achieved with updated OrthoPilot software, including intraarticular palpation of the femoral notch and tibial spines.^6,7,9

The two cases we had to revise had an HKA angle of 177° (one genu varum and one genu valgum), a mechanical axis usually considered as acceptable for good survival of the prosthesis. Several causes other than the mechanical axis could explain these failures including design of the PCL-retaining prosthesis with a flat-on-flat gliding surface, poor ligament balancing, or poor polyethylene quality.

The overall survival rate for this study was 90%, similar to that for conventional series reported in the literature that indicate rates from 90% to 98%.^16-22 Nevertheless, our series is too short to be compared with historical conventional series, and it is easy to understand the difficulty of obtaining a better rate than 95% or 98% with 10 years of follow-up.

Since our study, many factors have changed such as the prosthesis, which is now a full congruent prosthesis with a floating plateau (e.motion FP, B. Braun Aesculap) as well as the OrthoPilot system. The rigid body of the iliac crest was removed in 2001, a time when we included palpation of the middle of the femoral notch as well as of the middle of the tibial spines. In 2003, we integrated navigation of soft tissue balancing and femoral rotation in correlation with HKA angle.

Conclusion

The results of this series are quite similar to those of other published series on procedures not using computer navigation.^16-22 Nevertheless, we used a non-congruent old prosthetic design which can explain why we could not prevent some polyethylene wear despite good alignment in 92.3% of the cases. Moreover the two revisions were performed for prostheses with an HKA angle of 177°.

Thus, considering the evolution of this technology, we need more studies and more follow-up to establish the superiority of computer-assisted TKA to conventional techniques.

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Authors

Dr Saragaglia is from the Department of Orthopaedic Surgery and Sport Traumatology, University of Grenoble, South Teaching Hospital; Dr Picard is from the Golden Jubilee National Hospital, Beardmore Street, Clydebank Glasgow; Dr Leitner is from B. Braun Aesculap, France.

Correspondence should be addressed to D. Saragaglia, University of Grenoble, South Teaching Hospital. 38130, Échirolles, France.

Dr Picard holds a patent from B. Braun Aesculap. Dr Leitner is an employee of B. Braun Aesculap. Dr Saragaglia has no financial relationships to disclose.