Risk Factors for Revision After Early and Delayed Total Hip Arthroplasty Dislocation. An Analysis of Lithuanian Arthroplasty Register.

Introduction: Despite relatively low incidence, dislocation remains one of the main reasons for total hip arthroplasty (THA) revision. It is a devastating complication for a patient and a surgeon, and has high burden on the healthcare system. The aim of the present study was to assess and compare the risk factors for revision after early and delayed THA dislocations.

Methods: Some 3403 THA through posterior approach for primary osteoarthritis were retrospectively studied in the Lithuanian Arthroplasty Register from 2011 to 2018. Three months after THA was the splitting time between the first event of early and delayed dislocations. Revision was set as outcome measure. Gender, affected side, number of dislocations, femoral head and neck size, and prosthesis fixation type were tested as risk factors for revision after early and delayed THA dislocations.

Results: Dislocation occurred in 108 patients (3.2%), and 26 cases (0.8%) required revision. Men had statistically significant higher risk for revision due to early dislocation [hazard ratio (HR) 4.7; 1.3-17.7 confidence interval (CI)] and considerably lower risk for revision due to delayed dislocation (HR 0.5; 0.1-1.7 CI). The left side THA had twice the risk as compared to the right in the early settings (HR 2.1; 0.6-6.9 CI) which equalized after three months (HR 1.1; 0.4-3.1 CI). Some 32 mm femoral head had significantly lower risk in the early group as compared to 28 mm head (HR 0.3; 0.1-0.5 CI). Short head was associated with increased risk for revision after early dislocation, although, not statistically significant. Prosthesis fixation type was not a risk factor for revision surgery neither after early nor after delayed dislocation.

Conclusion: The unique finding of gender separation was found -- men tend for revision after early dislocation and women after delayed dislocation. In early stage, additional precautions should be considered when 28 mm short metal heads are used.