Een Kritische Evaluatie Van De Outcome Evaluaties Na Totale Heup Arthroplastiek: Ontwikkeling Van Een Allesomvattend Outcome Platform

OVERVIEW OF THE GOALS OF THE THESISTotal hip arthroplasty (THA) has recently even been termed “the operation of the century”. The reported outcomes are excellent and therefore it seems difficult to improve the performance of hip replacement patients. This performance is however most often investigated by means of 1 single outcome parameter such as functional outcomes or complications. Nevertheless, the performance of a surgical procedure is not restricted to 1 outcome parameter but is the result of a complex interplay of various parameters. Narrowing the performance of a surgical procedure to 1 outcome parameter bears the risk that we remain blinded for other potential flaws or shortcomings. This is one of the lessons we learned from the introduction of new technologies such as hip resurfacing. This thesis critically appraises our contemporary outcome assessments and aims to design a more comprehensive outcome platform to fully picture the outcomes of patient cohorts following a THA. The thesis aims to provide evidence that our contemporary outcome assessments are either insufficient or have reached their limits of discriminative capacities to differentiate between 2 well performing surgical techniques (Goal 1). The optimization of outcome assessments is required to detect differences between 2 well performing surgical techniques: the direct anterior and postero-lateral surgical approach (Goal 2). These optimized outcomes should be integrated into a comprehensive outcome platform that aims picturing patient cohorts by means of 5 different outcome parameters: complications, functional outcomes, clinical outcome, biomechanical reconstruction and gait characteristics. The results from this thesis are used to design a multi-centre randomized controlled trial (RCT) that compares both approaches (Goal 3). The data of this RCT, together with a database of outcomes from healthy subjects, will be used to construct an evidence-based hip replacement risk index that allows detecting deviations from the ‘normal’ or ‘the gold standard’ already at an early stage (On-going research). The ultimate goal is to provide an evidence-based comprehensive screening tool that can be used to screen new technologies and surgical techniques for early flaws or deviations from the gold standard (Future research). This comprehensive research project combines the expertise of 5 scientific departments into 1 consortium. A research grant for this project was obtained by means of the IWT-TBM research project nr 100786. The thesis should be considered as the first part of this extensive research project.RESEARCH PROJECTS(1) The first chapter presents an extensive literature overview of outcome assessment in RCTs. This review showed that there is room for improvement because the performance of surgical techniques is often narrowed to 1 particular outcome parameter. As a result, we tend to neglect the ‘overall’ outcome. The literature review on the experiences with hip resurfacing learned that failures of hip procedures are a multi-factorial problem that can only be identified when comprehensive analyses are conducted. It appeared from this review that there could have been an index of suspicion when the results from some reports would have been considered together. Specific failure modes of hip resurfacing were introduced and it was the merit of the national joint replacement registries (NJRR) that large cohorts could allow identifying prognosticators for implant failure. However, the registries have a number of limitations and can therefore not replace well-conducted clinical trials. The registries flagged problems only after capturing 5- to 7-year data. It is in this gap of 5 to 7 years that clinical trials can play a crucial role as a screening tool for potential problems. It is by means of the comparison between the direct anterior (DAA) and postero-lateral approach (PLA) that we aim to optimize our outcomes. The current literature failed to detect any significant difference in the outcomes between the both approaches. The poster-lateral approach is considered the ‘gold standard’ to which an evidence-based DAA technique will be compared. In other words, comparing both approaches can be considered as a test case and validation of optimized outcome parameters that will be implemented in the comprehensive outcome platform.(2) In the second chapter an overview of the objectives and methodology of the thesis is provided. The goal of this thesis is to evaluate whether a comprehensive outcome platform can be created based upon a more global approach towards outcome assessments of surgical approaches in THA.(3) The third chapter provides a proof of concept of an evidence based direct anterior approach. The DAA is not new but is associated with a high complication rate. A novel and stepwise technique was developed to overcome this problem. The anatomic findings of 3 published studies were emerged into 1 femoral elevation strategy. The procedure is conducted on a regular OR table with the help of 1 ipsilateral assistant. The safety and reproducibility of this stepwise technique is investigated and validated by means of (1) a learning curve study of the first author compared to a PLA cohort, (2) a cadaver study of surgeons with different levels of experience and (3) a multi-centre initiation study with 3 surgeons of different surgical volume. The prospectively collected data of the first study will be used to investigate the optimization of other outcome parameters. (4) The fourth chapter investigates the variables that influence functional outcomes in addition to the optimization of the discriminative capacities of functional outcome scores. First, normative age-gender matched reference outcomes were collected from 1.000 healthy volunteers. This investigation also showed that multiple scores should be used to fully picture patient cohorts. Patient stratification should be evaluated based upon the presence of contra-lateral groin pain and age rather than on gender and BMI. Conventional statistical tests failed to detect significant differences between both cohorts because of the ceiling effect of most outcome scores. However, it was shown that the distribution of the data was different with DAA patients showing a more ‘normative functionality’. Alternative methods were used to fully understand the functionality of both procedures. This showed significant differences between both cohorts. We also investigated the incidence of subjective groin pain and clinical peri-articular pain. The ‘forgotten hip concept’ was introduced and validated. Significantly more DAA patients had a forgotten hip. It was shown that this clinical outcome parameter adds new information to the overall outcome of a hip replacement procedure. In the final section the arguments for designing a multicentre RCT with regards to functional and clinical outcomes are summarized.(5) The fifth chapter aims to investigate by means of a hip resurfacing model, how smaller cumulative changes in component positioning can lead to increased contact stresses of the articulating surface. Cumulative errors of both component displacements could lead to detrimental increases in contact stresses of up to 35%. Therefore, the hip joint centre of rotation (COR) should be reconstructed within a 5mm range from the native COR and the socket position should remain as closely as possible to the ‘neutral’ position. Reconstruction of the soft tissue biomechanics is represented by the reconstruction of the abductor moment arm. Radiographic measurement of the abductor moment arm is validated. The biomechanical profile of the DAA and PLA cohort was compared. The socket anteversion and leg length discrepancy were significantly higher in the PLA cohort, whereas socket inclination was significantly lower in the DAA cohort. No differences in abductor moment arm changes were found. In conclusion, component positioning was not jeopardized during the learning curve of the DAA without the use of fluoroscopy. In depth biomechanical analysis is required to fully understand the clinical relevance of the found differences.(6) The gait characteristics of DAA THA patients were significantly improved compared to matched hip resurfacing (SRA) patients in the sixth chapter. SRA has been promoted to be the hip replacement that allowed for the best recovery towards normal gait. This was not supported in our study. Direct lateral approach SRA showed the most distinct aberrations followed by posterolateral approach SRA. Although DAA patients did not reach the normal level at more than 12 months follow-up, the differences were markedly less pronounced than with hip resurfacing. Gait analysis provided additional information of the functionality following hip replacements. (7) The seventh chapter provides evidence for the design of a long-term follow-up RCT. The lessons learned from a RCT that was initiated 20 years ago showed that the number of patients that should be included to detect a difference in survivorship between 2 THA designs depends on the expected follow-up period and the age of the patient at time of inclusion.Including only patients <65 years in a RCT that is planned for at least 10 or 15 years of follow-up would require 60 and 40 patients, respectively in each treatment group. However, the numbers would have to be 110 and 100 patients if also patients >65 years would be included. The findings of prospective case series were used in the second section to support the choice for implants with a modular porous coated socket with a 32mm polyethylene liner. A well performing cemented and cementless stem design will be compared for long-term survivorship. The most important purpose is to design a database of implants that have been shown to be associated with excellent clinical outcome. These databases can then be considered as the ‘gold standard’ to create the hip replacement risk index that will allow comparing the outcomes of new technologies.(8) In the final chapter the integrated assessment platform is proposed and a summary of future research is provided. GENERAL CONCLUSIONOur continuous search for improved technologies needs to be supported by improved screening tools that allow picturing the overall outcome of a hip replacement procedure. The evidence-based direct anterior procedure and the postero-lateral approach seemed to perform equally well at first glance. However, it was only by means of optimized and multiple outcome assessments that differences between both approaches surfaced. These outcomes will be weighed and integrated into 1 hip replacement index. This index could allow better understanding the position of new technologies or other procedures relative to the ‘gold standard’ or the ‘normal population’.status: publishe