The incidence of dissociated liners in 4,751 consecutive total hip arthroplasties using Pinnacle polyethylene acetabular liners.

INTRODUCTION

Acetabular liner dissociation is a complication exclusive to modular designs. We present a single surgeon series of 8 polyethylene liner dissociations with the Pinnacle Acetabular System (DePuy Orthopaedics) from over 4,750 cases. We also present a review of the literature and data from the UK National Joint Registry (NJR) on dissociation in total hip arthroplasty (THA).

METHODS

The Pinnacle Acetabular System has been used exclusively by the senior author since April 2003, and to date 5,882 have been implanted (837 ceramic liners, 4,751 polyethylene liners (1,606 Enduron/3,145 Marathon) and 294 metal liners). We reviewed all cases of liner dissociation from this cohort to determine an overall incidence with polyethylene liners, identify associated risk factors, and report the outcome following revision surgery.

RESULTS

Our incidence of this complication is 8 out of 4,751 cases (0.17%). Review of these cases and the literature suggests that femoral neck impingement against the polyethylene liner and/or edge loading may produce fatigue failure of the locking mechanism and subsequent dissociation.

CONCLUSIONS

Ensuring correct liner seating/locking, minimising impingement, achieving appropriate component version and avoiding radiographic cup inclinations >50° should minimise the risk of liner dissociation. Any new noise or squeaking from a polyethylene liner should undergo radiographic investigation to exclude dissociation. We recommend managing late cases of liner dissociation with revision of the acetabular shell if the cup orientation could be improved or if there is any damage to the liner-locking groove, to reduce the risk of recurrence.