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

BACKGROUND: Dislocation following total hip replacement is associated with repeated admissions to hospital and substantial costs to the health system. Factors influencing dislocation following primary total hip replacement are not well understood. We aimed to assess the association of various factors with dislocation risk following primary total hip replacement. METHODS: We did a systematic review and meta-analysis of longitudinal studies reporting associations of patient-related, surgery-related, implant-related, and hospital-related factors with dislocation risk after primary total hip replacement. We searched MEDLINE, Embase, Web of Science, and the Cochrane Library for all relevant articles published up to March 8, 2019. Summary measures of association were calculated with relative risks (RRs) and 95% CIs. This study is registered on PROSPERO, number CRD42019121378. FINDINGS: We identified 149 articles based on 125 unique studies with data on 4 633 935 primary total hip replacements and 35 264 dislocations. The incidence of dislocation ranged from 0·12% to 16·13%, with an overall pooled incidence of 2·10% (95% CI 1·83-2·38) over a weighted mean follow-up duration of 6 years. Based on the median year of data collection, a significant decline in dislocation rates was observed from 1971 to 2015. The risk of dislocation did not differ significantly between male versus female patients (RR 0·97; 95% CI 0·88-1·08), was higher in those aged 70 years and older than in those younger than 70 years (1·27; 1·02-1·57), and was lower in those from high versus low income groups (0·79; 0·74-0·85). White ethnicity (only when compared with Asian ethnicity), drug use disorder, and social deprivation were significantly associated with increased dislocation risk. The risk of dislocation was higher in patients with body-mass index (BMI) of 30 kg/m2 or higher than in those with BMI lower than 30 kg/m2 (RR 1·38; 95% CI 1·03-1·85). Medical factors and those related to surgical history that were significantly associated with increased 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 approach with short external rotator and capsule repair were significantly 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 significantly reduced the risk of dislocation. Hospital-related factors such as experienced surgeons and high surgeon procedure volume significantly reduced the risk of dislocation. INTERPRETATION: Dislocation following primary total hip replacement has declined over time. Surgical approaches that reduce dislocation risk can be used by clinicians during primary total hip replacement, and 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 might also be amenable to optimisation before surgery. FUNDING: National Institute for Health Research.