International Outcomes of Total Hip Arthroplasty: Influence of Patient, Implant, and Surgical factors on Total Hip Arthroplasty Survivorship in Sweden, the US, and Australia

Abstract Background Hip osteoarthritis (OA) is debilitating disease resulting in pain, stiffness, and reduced physical function. Although total hip arthroplasty (THA) is a successful treatment for OA, some THAs require revision surgery due to infection, dislocation, aseptic loosening, fracture and other reasons. Numerous factors influence the success of THA including patient, surgical, hospital and implant factors. Understanding the influence of these factors on THA risk of revision is critical for prevention of revision surgery. Internationally, arthroplasty registries play a critical role in identifying patient and clinical practices at higher risk for THA revision surgery. Several national and regional arthroplasty registries exist worldwide. Collaborations of these registries provide an opportunity to evaluate differences in patients, clinical practices, risk factors, and outcomes between countries. Objective The purpose of this thesis was to examine variation in patient, surgical, implant characteristics, and THA outcomes in Sweden, US and Australia to identify THA risk factors and clinical best practices. The five studies in this thesis investigated: 1. Meta-analysis as an alternative to individual patient data analysis by comparing the risk of revision of porous tantalum cups versus other uncemented cups in primary total hip arthroplasties from Sweden, Australia, and a US cohort. 2. Variation in patient characteristics and co-morbidities, surgical approach, implant characteristics, hospital settings and THA revision rates between Sweden, Australia, and the US to identify differences in practices and opportunities for improving THA outcomes internationally. 3. Implant-specific sources of variation in THA implant survival across the US, Sweden, and Australia by examining implant survival of Exeter and Summit THAs. 4. Patient, implant, clinical practices and hospital predictors of THA revision in Sweden, Australia, and the US. 5. The influence of more granular patient-related factors (i.e., age, gender, body mass Index, and comorbidities) on THA risk of revision in a US healthcare setting Patient and methods Primary THAs with an OA diagnosis were identified using the Swedish, Australian, and Kaiser Permanente registries. The study time period was 2003-2015 for studies I, II, and III. Study IV’s timeframe was 2001-2016 and study V’s time period was 2008-2016. Kaplan Meier statistics were used to assess time to revision with censoring for death and loss to follow-up. Multivariable cox regression models were used to identify patient, implant, surgical, and hospital factors associated with revision surgery. Results Patient-level data analysis and meta-analytic approaches yielded the same results with the porous tantalum cups having a higher risk of revision than other uncemented cups. Patients, implants and surgical practices differed between the countries. Sweden’s 5- and 7-year THA survival was higher than Australia and the US. However, when patient characteristics, fixation and implants were controlled for THA survival was similar between countries. Predictors of THA revision also differed by country. In the US cohort, increased number of comorbidities and certain comorbidities had higher risk of all cause, revision due to dislocation, and septic revision. Conclusions Meta-analysis is a viable method for enhancing international registry collaboration. In comparing THA survival across countries, implant selection plays a critical role. Predictors of THA revision differ between countries most likely due to variation in clinical practices and implant selection. The number of patient co-morbidities and higher risk comorbidities should be considered by surgeons and patients prior to THA surgery