Letter to the Editor: Polyethylene Liner Dissociation is a Complication of the DePuy Pinnacle Cup: A Report of 23 Cases.

BACKGROUND Polyethylene liner dissociation is a rare but catastrophic event in total hip arthroplasty (THA), and certain implant designs are known to be at greater risk. Although the DePuy Pinnacle (Warsaw, IN, USA) modular acetabular construct has an excellent record of fixation and wear, an unexpectedly high number of liner dissociations has been noted. QUESTIONS/PURPOSES The purposes of this study were (1) to characterize the clinical parameters observed in a large group of patients who have experienced liner dissociations with the DePuy Pinnacle acetabular component; (2) to describe the radiographic findings in this group of patients; and (3) to calculate a minimum frequency of this complication. METHODS Since 2001, 23 patients with previously well-functioning THAs presented with sudden atraumatic polyethylene liner dissociation at four separate institutions. These THAs were performed between 2001 and 2013. Eight different arthroplasty specialists had performed the index hip arthroplasties using the DePuy Pinnacle acetabular component with a polyethylene liner. Polyethylene failures were evaluated for liner type and radiographic cup position. For three of the surgeons who contributed cases, institutional registries allowed the calculation of the number of components of this type that they used during the period in question, which provided a conservative estimate of the frequency of this type of failure. RESULTS All 23 liner failures occurred atraumatically in previously asymptomatic THAs at a mean of 48 months (range, 3-138 months). Patients characteristically reported a new and sudden onset of discomfort with audible, reproducible squeaking. Surgical inspection of dissociated liners demonstrated displacement of polyethylene with shearing of the peripheral locking tabs. Radiographic evaluation demonstrated that 14 cups were well positioned and nine cups were malpositioned outside the so-called safe zone. Conservative estimates of the frequency of this complication from the three surgeons' practices whose institutional registries allowed calculation of the lowest possible frequency were 0.32% (six of 1888), 0.77% (three of 391), and 0.82% (three of 367). CONCLUSIONS With this report of 23 additional liner dissociations, we suggest that surgeons should be aware of the problem and take extra precautions when using this implant to ensure locking mechanism integrity at the time of surgery. We caution that the frequency of liner dissociation may be higher than previously reported. LEVEL OF EVIDENCE Level IV, therapeutic study.