|Abstract / Summary|
Total hip arthroplasties (THA) have, without doubt, made life better for millions of people worldwide who have struggled with pain, restrictions in everyday activities, and reduced quality of life (QoL) due to debilitating primary hip osteoarthritis (OA) or as a consequence of previous hip injuries. The vast majority of patients experience a satisfactory level of recovery of their daily living capacity and report excellent results. A primary THA will survive for 15 years for approximately 90% of patients and much longer still in most cases. However, serious complications may still occur. Dislocation is one of the most commonly reported complications, with a risk ranging from 0.2% to 10% after a primary THA and even higher after revision surgery. Most dislocations are managed by closed reduction of the prosthesis. Up to 50% of patients will experience recurrent dislocations, though, and many will require new surgery to restore stability. The great variation in the reported incidence rates of dislocation is partly due to significant differences in study designs, indications for surgery, surgical approaches, and follow-up periods. To date, we do not have an adequate overview of THA dislocations in Denmark and, maybe more importantly, we are simply not aware of the impact of dislocations on QoL and self-reported hip function in the years after this complication occurs. We therefore designed the following five studies in an attempt to mitigate the gaps in our current knowledge:
Study I: Our aim was to systematically review the literature for studies reporting patient-reported outcome measures (PROMs) after hip dislocation in patients with primary THA in comparison with in patients without any dislocation. We identified 3,460 unique studies using a simple and broad search query yet, of these, only two studies met the inclusion criteria.
Study II: Our aim was to report the “true” cumulative incidence of hip dislocations within two years of index surgery for all primary THAs conducted in Denmark from 2010 to 2014 due to hip OA. Secondary, we sought to analyze available patient- and surgery-related risk factors for validated dislocations. We included 31,105 primary THAs and validated 1,861 dislocations among 1,079 THAs after reviewing more than 5,000 patient files. The “true” two-year cumulative incidence of hip dislocation was 3.5% (95% confidence interval (CI): 3.3-3.7). Age, sex, American Society of Anesthesiologists (ASA)-score, head size and type, fixation method, and surgical approach were identified as independent significant risk factors for dislocation.
Study III: Our aim was to develop an algorithm designed to identify patients with dislocation in the Danish National Patient Register (DNPR) with high sensitivity, specificity, and predictive values. The algorithm consisted of five steps, including both correct codes for dislocation and, alternatively, frequently used codes for dislocation that we validated in Study II. The combination of the correct diagnosis and procedure code produced a sensitivity of 63% and a positive predictive value (PPV) of 98%. After adding in alternative codes, we succeeded with increasing the sensitivity to 91%, while maintaining the PPV at 93%. The specificity was, in all steps, greater than 99%.
Study IV: Our aim was to compare QoL and hip-specific outcome measures in patients with a single or recurrent episode of THA dislocation and patients without any complications. We identified 1,010 living patients with one or more dislocations. We then matched patients with dislocation 1:2 based on age, sex, and date and hospital of primary surgery to patients without dislocation. We found that both health- and hip-related QoL were markedly and persistently reduced after THA dislocation as compared with in the control group even two to five years after the latest dislocation.
Study V: Our aim was to analyze surgery- and patient-related risk factors for both dislocation and re-revision of any cause after first-time hip revision due to dislocation. We identified 1,678 patients with a primary THA due to OA and a first-time revision due to dislocation between 1996 to 2016. After the first-time revision due to dislocation, 22.4% of these patients experienced a new dislocation and 19.8% were re-revised for any reason. We found that those patients revised with a dual mobility cup and a constrained liner exhibited a lower risk of dislocation but not so for a re-revision. The performance of a head/liner exchange was associated with a higher risk of both dislocation and subsequent re-revision as compared with a full cup revision.
In conclusion, we identified the true two-year cumulative incidence of hip dislocation after primary THA in Denmark to be 3.5%. This level is well in line with data from other countries that use the posterior approach during surgery but may be higher than outcomes of alternative approaches. We also succeeded with the creation of an acceptable algorithm that could be suitable for monitoring dislocations in a Danish quality register in the future. As we stated that the knowledge of patient-reported QoL and subjective hip function post-dislocation was merely non-existent, we have conducted the largest study to date regarding this matter. Despite the limitations inherent in the cross-sectional study design, we found that many patients suffer from the consequences of a dislocation for several years. At last, we sought to find risk factors for dislocation after both primary THA and revision procedures due to dislocation in order to increase the understanding of which patients and surgical techniques are associated with higher risks.