Risk factors for dislocation after primary total hip replacement: meta-analysis of 125 studies involving approximately five million hip replacements.

BACKGROUND: Dislocation following total hip replacement (THR) is associated with repeated hospitalisations and substantial costs to the health system. Factors influencing dislocation following primary THR are not well understood. We aimed to assess the associations of patient-, surgery-, implant- and hospital-related factors with dislocation risk following primary THR.
METHODS: We did a systematic review and meta-analysis of all longitudinal studies reporting these associations. We searched MEDLINE, Embase, Web of Science, and Cochrane Library to March 8, 2019. Summary measures of association were calculated using relative risks (RRs) (with 95% confidence intervals, CIs). The review is registered on PROSPERO, number CRD42019121378.
FINDINGS: We identified 149 articles based on 125 unique studies with data on 4 633 935 primary THRs and 35 264 dislocations. The incidence rates of dislocation ranged from 0·12% to 16·13%, with an overall pooled rate of 2·10% (1·83-2·38) over a weighted mean follow-up duration of 6 years. Using median year of data collection, there was a significant decline in dislocation rates from 1971 to 2015. Comparing males vs females, age ≥70 vs <70 years, and high vs low income, RRs (95% CIs) for dislocation were 0·97 (0·88-1·08), 1·27 (1·02-1·57), and 0·79 (0·74-0·85) respectively. White ethnicity, drug use disorder, and social deprivation were each associated with an increased dislocation risk. Comparing body mass index (BMI) ≥30 vs. <30 kg/m2, the RR (95% CI) for dislocation was 1·38 (1·03-1·85). Medical and surgical history-related factors associated with dislocation risk included neurological disorder, psychiatric disease, comorbidity indices, previous surgery including spinal fusion, and surgical indications including avascular necrosis, rheumatoid arthritis, inflammatory arthritis, and osteonecrosis. Surgical factors such as the anterolateral, direct anterior, or lateral approach and posterior with short external rotator and capsule repair were each associated with reduced dislocation risk. At the implant level, larger femoral head diameters, elevated acetabular liners, dual mobility cups, cemented fixations and standard femoral neck lengths reduced the risk of dislocation. Hospital-related factors such as experienced surgeons and high surgeon procedure volume each reduced the risk of dislocation.
INTERPRETATION: Dislocation following primary THR is on a temporal decline. Surgical approaches that reduce dislocation risk can be used by clinicians when performing primary THR. Alternative bearings such as dual mobility can be used in individuals at high risk of dislocation. Modifiable risk factors such as high BMI and comorbidities may be amenable to optimisation prior to surgery. FUNDING: National Institute for Health Research.