Computer Navigation in Total Knee Replacement Surgery. Effect on Outcome
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Background: In total knee replacement surgery (TKR), the surgeon aims to align the implant according to the mechanical axis of the limb. Among knee surgeons the dominating belief is that good alignment reduces wear and loosening of the implant, and optimizes patellar tracking, range of motion and function of the knee, although the evidence is limited. Computer navigation has been used in total knee replacement surgery for more than a decade to improve the alignment (abbr. CAS – computer assisted surgery). The term “navigation” in this setting refers to positioning of the implant relative to the anatomy of the knee. Conventional (traditional) navigation, or positioning, is performed by the use of intramedullary or extramedullary rods to align the implant according to the mechanical axis of the limb (abbr. CONV – conventional TKR). In contrast, with the classical image-less computer navigation there is no need of intramedullary rods, and image-less computer navigation utilizing infrared cameras and advanced software, is shown to be more accurate than conventional navigation. However, it is costly and time consuming. The purpose of this thesis was to investigate the relationship between use of computer navigation and outcome.
Methods: To what extent this new technology must improve the outcome to become cost-effective, was evaluated in an economic model. One register study analyzes the outcome of computer navigated TKR, another register study investigates the survivorship and revision causes of the most common implant brands, and a randomized clinical trial (RCT) evaluates the functional and radiological outcome of CAS.
Results/discussion: Paper I shows that CAS might be cost-effective in TKR if the hospital volume is high and the cost of the equipment does not increase relative to the prices of today. Age of the patient is not likely to have any influence on costeffectiveness. However, the cost-effectiveness depends on a marginal improvement of implant survivorship. Based on the findings in paper IV with improved alignment and marginally improved functional scores, there is some reason to be optimistic in regard to impact on survivorship. On the contrary, the findings in paper II, with increased risk of revision in the short term, suggest that there might not be an improved survivorship with CAS in the long term, at least not the way it has been used in Norway. Results in Norway may differ from the results in other countries and is probably dependent on education of the surgeons in the use of this new technology, and also of the patient volume and thereby the surgeon’s experience with CAS. Additionally, the design of the implant and its compatibility with the computer navigation software and hardware, might affect the results as suggested in paper II. To further elucidate this aspect, a register study was performed analyzing revision causes and survivorship of the most used TKR implants in Norway. The mobilebearing LCS Complete seemed to perform inferiorly when computer navigated, and we suspected that the mobile-bearing design was difficult to navigate properly. To separate the negative effect of computer navigation from other causes of inferior survivorship, we decided to conduct a register study excluding the computer navigated knees, investigating revision causes and survivorship (paper III). Paper III showed that the LCS Complete and the LCS Classic both had a 7-fold increased risk of revision due to aseptic loosening of the tibial components, compared to the most used knee implant in Norway - the Profix knee. Even the femoral component had an increased risk of revision due to aseptic loosening. However, the 5 years Kaplan- Meier survival rates were 94.9 and 95.6 for the LCS Complete and LCS Classic, respectively, compared to 96.3 for the Profix. This difference is by many, not considered clinically significant, but the risk of aseptic loosening is more alarming and proven to be independent of CAS.
The project will continue to evaluate the reasons for aseptic loosening in the LCS knees by collaboration with other national registers and by studying revised and unused implants in the laboratory. The positive results of CAS, in paper IV, urge us to continue the evaluation of this technology as it develops, through repeated register analyses and clinical trials investigating improved types of navigation. The thesis is part of a larger project investigating long term survivorship with radiostereometric analysis and long term follow-ups.
Conclusion: Computer navigation in total knee replacement surgery has increased the operation time and resulted in inferior short term survivorship in Norway. However, the technology is more accurate than conventional technique, and the functional results are marginally improved by CAS. If these positive effects result in a better long term survivorship of the implant, the technology is getting more userfriendly and the operation time is reduced, the technology is likely to be costeffective and beneficial for the patients.