Is a cementless dual mobility socket in primary THA a reasonable option?

Abstract

Background: Dislocation after THA continues to be relatively common. Dual mobility sockets have been associated with low dislocation rates, but it remains unclear whether their use in primary THA would not introduce additional complications.

Questions/purposes: We therefore asked whether a current cementless dual mobility socket (1) reduced the dislocation rate after primary THA, (2) provided a pain-free and mobile hip, and (3) provided durable radiographic fixation of the acetabular component without any unique modes of failure.

Methods: We retrospectively reviewed 168 patients who underwent primary THA using a dual mobility socket between January 2000 and June 2002. The average age at surgery was 67 years. We assessed the rate of dislocation, hip function, and acetabular fixation on serial radiographs. Of the 168 patients, 119 (71%) had clinical and radiographic evaluation at a minimum of 5 years (mean, 6 years; range, 5-8 years).

Results: A long-neck option left the base of the Morse taper uncovered in 53 hips. Four patients underwent revision for dislocation between the femoral head and the mobile insert (intraprosthetic dislocation) at a mean 6 years; all four revisions occurred among the 53 hips with an incompletely covered Morse taper.

Conclusions: A current cementless dual mobility socket was associated with a pain-free and mobile hip and durable acetabular fixation without dislocations if the long-neck option was not used. However, intraprosthetic dislocation related to contact at the femoral neck to mobile insert articulation required revision in four hips. Surgeons should be aware of this specific complication.

Level of evidence: Level IV, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.

Fig. 1

The photograph shows the Tregor^® tripolar unconstrained acetabular component (Aston^® Medical, Saint Étienne, France) consisting of, from inside out, a spherical mobile polyethylene insert that accepts a 22.2- or 28-mm femoral head and is not constrained into a spherocylindrical metal shell made of CoCr. Photograph courtesy of Aston^® Medical.

Fig. 2A–B

(A) An AP radiograph shows the left hip a 50-year-old man with primary osteoarthritis treated with uncemented THA using a cementless dual mobility socket. (B) At 6.9-year followup, he experienced discomfort in the groin. The AP view of the hip shows a typical aspect of intraprosthetic dislocation with an eccentric femoral neck when compared to the center of the metal shell.

Fig. 3

The diagram shows the contact between the rough Morse taper and the mobile polyethylene insert with a long-neck option that leaves the base of the Morse taper uncovered.

Fig. 4

The photograph shows a revised mobile polyethylene insert for intraprosthetic dislocation. Gross wear and deformation at the capturing area are visible.