LARGER ARTICULATIONS REDUCE DISLOCATION AND REVISION FOR DISLOCATION WITHOUT INCREASED LINEAR WEAR AT TEN-YEAR FOLLOW-UP IN A RANDOMIZED TRIAL

Abstract

The primary aim of this study was to determine dislocation and revision total hip replacement (THR) up to ten years following primary THR, as well as rates of polyethylene wear, in patients previously enrolled in a randomised controlled trial (RCT) which compared 28 mm and 36 mm metal on highly cross-linked polyethylene (XLPE) articulations.

328 primary THR patients were enrolled in the RCT in Australia. Dislocation was identified from hip instability and hospital visit questionnaires completed by patients or, if they were unable to do so, by their next of kin or primary carer, or General Practitioner. All reported dislocations were confirmed radiographically. Patients' names were cross-matched with the Australian National Joint Replacement Registry to determine whether the index hip had undergone revision THR. Linear wear was measured on plain radiographs using PolyWare (Rev 5, Draftware Developers, Vevay IN, USA). A separate RCT examined the mean proximal wear rate of 28 and 36 mm articulations using radiostereometric analysis (RSA).

At 10 years, 110 patients were deceased and 3 patients were lost to follow-up. Overall, dislocation was identified in 8 of 167 (5%) patients with a 28 mm articulation and 2 of 158 (1%) patients with a 36 mm articulation. Three patients experienced recurrent dislocation; all had a 28 mm articulation. 320 (163 28 mm; 157 36 mm) patients were successfully cross-matched with Registry data to identify revision THR. Three patients, all with a 28 mm articulation, underwent revision because of dislocation. Other reasons for revision were infection (1:2), periprosthetic fracture (0:3), loosening/lysis (1:2) and liner fracture (0:1). Adequate radiographs were available to measure wear in 122 hips (67:55) using PolyWare. Excluding bedding in, the mean annual linear wear rate from 1–10 years was 0.04 mm/yr for both 28 and 36 mm articulations (p=0.48). The more sensitive RSA data indicated that at 7 years following primary THR, the mean annual wear rate did not exceed 0.02 mm/yr with either articulation.

Up to 10 years following primary THR, 36 mmm articulations were associated with fewer dislocations and revisions for dislocation and did not increase the mean annual linear wear rate.