Use of a Constrained Acetabular Liner to Prevent and Treat Recurrent Dislocation after Total Hip Replacement Arthroplasty.

The aim of the present study was to evaluate the dislocation rate and the risk factors leading to instability after primary and revision total hip replacement arthroplasty (THRA) with constrained acetabular liners (CAL), as well as treatment strategies for prevention of dislocation. From 1999 to 2017, drawing on two institutions' THRA registries, we retrospectively identified 46 THRA cases using a CAL that had been followed up for a minimum of 4 years. The patients comprised 39 women and 7 men, with an average age of 69.1 years (age range, 41-98). Of the 46 patients, CAL were used in 12 patients for prevention of dislocation in primary THRA and in 34 patients for treatment of recurrent dislocation after primary THRA. Clinical and radiological evaluation were performed. We evaluated the failure rate of CAL as well as the risk factors. The 12 patients who used CAL for prevention of dislocation in primary THRA had no dislocation. However, 12 (35%) of the 34 hips had a dislocation after use of CAL in revision THRA. Patients with an abductor muscle weakness grade of ≤3 had a higher rate of dislocation than those with a grade of ≥4 (grade 1; likelihood ratio = ∞, grade 2; likelihood ratio = 1.83, grade 3; likelihood ratio = 1.05, grade 4; likelihood ratio = 0.46, and grade 5; likelihood ratio = 0). The group of primary THRA with CAL had no dislocations, and this is a proper way for prevention of dislocation in high-risk patients. The group of revision THRA with CAL had a high dislocation rate (35%). Abductor muscle weakness below grade 3 was a risk factor for failure of CAL for hip dislocation. We recommend treating patients with recurrent dislocations with the presence of abductor muscle weakness below grade 3 with not only THRA using CAL but also applying additional abductor muscle reconstruction to reduce the risk of dislocation.