COMPUTER ASSISTED KNEE ARTHROPLASTY DOES NOT RESULT IN IMPROVED FUNCTIONAL OUTCOME AT ONE YEAR COMPARED WITH CONVENTIONAL INSTRUMENTATION

Abstract

Introduction: Computer assisted knee arthroplasty (CAKA) has been shown in a number of studies to result in better post-operative alignment of prostheses. However good prosthetic alignment is only one part of total knee arthroplasty surgery and outcome is likely to depend on other factors such as soft tissue balancing. Our study aimed to compare the functional outcome following knee arthroplasty using CAKA or conventional instrumentation, and to determine whether the theoretical advantage of improved prosthesis alignment with CAKA resulted in improved functional outcome.

Materials and Methods: Data on 299 patients have been recorded to date. 139 patients have a minimum one year follow up. No patients were lost to follow up All patients were operated on by a single surgeon at a dedicated arthroplasty centre and were allocated to one of two groups: Computer assisted navigation using a robot assisted technique (PiGalilieo, Plus Orthopaedics, Rotkreuz, Switzerland), or using conventional instrumentation. In both groups the prosthesis used was the TC-Plus Self-aligning bearing (Plus Orthopaedics). Functional outcome was measured using the Oxford Knee Score (OKS). There was no statistical difference in pre-operative OKS and demographic data between the two groups

A power analysis was performed with alpha of 0.05 and power of 80%. In order to detect a difference of 4 points in the OKS, 126 patients were required. This number was exceeded in our study at one year.

Results: The mean OKS at one year follow up was 24.9 (range 12–54, standard deviation (s.d) 9.8) for the CAKA group and 25.3 (range 12– 49, s.d. 9.7) for the control group. There was no significant difference in functional outcome at one year between the two groups (p = 0.41). At two years follow up the mean OKS was 25.39 (range 13–53, s.d. 10.3) for the CAKA group and 24.14 (range 12– 43, s.d. 9.1) for the control group (p = 0.33). The results for the two year follow up group should be treated with caution as further patient numbers are awaited to obtain adequate power.

Conclusion: Although several studies show that use of CAKA results in improved prosthesis alignment, our study indicates that CAKA does not result in improved functional outcome as assessed by the patient at short term follow up. Improved prosthesis alignment is thought to result in improved long term outcome, however long-term studies are necessary to show whether the known advantages of CAKA in improved prosthesis alignment results in improved patient satisfaction and increased implant survival in order to justify the increased costs associated with CAKA.