Introduction
Avascular necrosis of the hip (AVN) is a disease which causes a lack of blood supply in the femoral head, resulting in the bone death, and a subsequent biomechanical failure of the hip joint. Current treatment is mainly to seek for total hip replacement. However, the majority of these affected patients < 60 years of age, having total hip replacement will lose the ability to engage in massive physical work, or lower their life qualities. On the contrary, hip resurfacing arthroplasty (HRA), which is a femoral head preserving surgery, seems to be an ideal intervention for AVN patients because HRA does not change native hip anatomy and helps restoring hip joint. The present question when performing HRA on AVN patients is, surgeons do not know to what lesion extent can they perform such surgery. This thesis aims to review all aspects of AVN, to find out whether the HRA is more cost-effective than THA, to determine the maximum lesion extent to perform HRA, and to plan the surgery better.
Method
First, we did a comprehensive review on AVN’s mechanism, treatments and staging systems. Second, we use a health economic model to simulate the benefits of performing HRA over THA. Third, we simulate a series of lesions with bone graft HRA in composite bone mechanical tests under healthy human walking load in the hip joint, and compare these lesions data to non-lesion data. From these data, we are able to summarise an indication table for AVN-HRA classification. Last, we develop a pre-operative planner to optimse HRA on AVN, and validate the planner’s reliability and reproducibility. All these steps have never been fully studied before.
Results
First, the AVN prevalence rates in easter Asian countries were quite high, and the non-surgical treatment cannot cure AVN, as well as the lack of hip resurfacing AVN staging system. Second, the health economic model (Markov model), specifically its Monte Carlo simulation showed a 60% probability that HRA was more cost-effective than THA during 10 years post-operatively. Third, the simulated lesions on HRA mechanical tests demonstrated that 10mm depth of lesion down from the tip of the prepared femoral head with autograft, were able to achieve initial stability. Any lesion depth deeper than 10mm is not recommended for hip resurfacing. Four, the inter-observer and intra-observer reliability and repeatability were all higher than 80% using our pre-operative planner, meaning that this planner is reliable enough to be a workhorse for AVN hip resurfacing pre-operative planning.
Conclusion
Overall, our results showed that HRA is more cost-effective than THA, and we found out that 10mm of lesion depth was on the margin of the safe HRA, with autograft to fill the defect cause by lesion. Finally, we created a reliable planner that helps planning AVN HRA preoperatively. Our results well matched the hypothesis mentioned above.