Abstract
Introduction
Alumina-on-alumina bearings exhibit low wear rates in vitro and one commonly used ceramic implant is the Trident system (Stryker, Mahwah, NJ). There are some reports of incomplete seating of the ceramic liner in the Trident acetabular shell. However, it is often difficult to detect incomplete seating intraoperatively. We sought to prevent incomplete seating using intraoperative radiography.
Materials and Methods
We retrospectively reviewed 19 hips in 17 patients who had undergone primary total hip arthroplasty using a Trident shell with a metal-backed alumina liner between 2007 and 2010. There were 16 women and 1 man, with an average age of 45.7 years. Preoperative diagnosis revealed 14 cases of osteoarthritis and 5 cases of osteonecrosis. All procedures were performed using a posterolateral approach with PSL cups. The minimum follow-up time was 12 months (average 28 months). All procedures included an intraoperative anteroposterior view radiograph to evaluate cup seating. If incomplete seating was recognized we reinserted the liner. Postoperatively, radiographs (supine anteroposterior and cross table lateral views) and computed tomography were performed in all cases in order to assess any residual incomplete seating. We investigated whether it was possible to avoid incomplete seating using intraoperative radiography.
Results
Six (32%)of 19 hips had evidence of incomplete seating. Of these, 3 revealed incomplete seating on intraoperative radiography, 2 were reinserted adequately, and the liner was replaced with a polyethylene liner in one case. Postoperative radiography revealed incomplete seating in 3 cases. One hip had become correctly seated as shown by follow-up radiography at 3 months and the other hips remained incompletely seated for the follow up period. The location of the gap between the socket and liner caused by incomplete seating was inferomedial in all cases, as seen on the intraoperative anteroposterior view radiographs. We were able to avoid incomplete seating in all of these cases except for one, which was missing the gap. Cases in which the location of the gap was anterior could not be diagnosed by intraoperative radiographs, and were diagnosed postoperatively. Incomplete seating was seen in 3 of 9 cases that used a 2.8 mm shell thickness, and in 3 of 10 cases that used a 3.8 mm thickness. No case had complete dislocation or failure of the ceramic liner. There were no revision surgeries.
Discussions
Although there have been no published case reports regarding complete dislocation or failure of the ceramic liner caused by incomplete seating, adverse influences that are caused by incomplete seating remain uncertain. Some reports describe that incomplete seating was potentially attributed to poor exposure, bony and soft tissue impingement, and cup deformity. The attempt to avoid incomplete seating using intraoperative radiography was effective in cases where medial or lateral gaps were seen. However, it was ineffective in cases where gaps were anterior or posterior. Trident system ceramic liners need to be used with care to avoid incomplete seating.
