Recurrence of dislocation following total hip arthroplasty revision using dual mobility cups was rare in 180 hips followed over 7 years

Abstract

Background: Dual mobility (DM) cups of mobile polyethylene were introduced to prevent total hip arthroplasty (THA) dislocation, but no large series with this design to treat recurrent instability have been reported.

Purpose: Our retrospective investigation ascertained the efficiency of DM cups in correction of recurrent dislocation and assessed any adverse effects.

Methods: One hundred eighty THAs with recurrent instability were revised to DM cups in 180 patients (mean age, 67.4 ± 11.7 years; range, 19 to 92 years). Thirty-one patients (17.2%) underwent at least one earlier THA revision, and 15 (10.3%) incurred non-union of the greater trochanter. Of the initial group in 2009, 145 patients had completed evaluations which included assessment of the Harris Hip Score and a radiographic assessment at a mean follow-up of 7.7 ± 2.2 years (range, 4 to 14 years). The rate of survival was calculated considering any reason for revision as failure.

Results: At follow-up, Harris hip score was 83.9 ± 16.1 (range, 21 to 100). Dislocation of the large articulation occurred in seven hips (4.8%), and only two recurred (1.4%) (one requiring additional revision). In addition, two intra-prosthetic dislocations of the small articulation (1.4%) were observed and needed revision surgery. The large number of earlier surgeries and non-union of the greater trochanter were related to recurrent instability. Two cups (1.4%) showed signs of definite loosening; six (4.1%) presented signs of possible loosening. Twenty-nine hips manifested femoral or acetabular osteolysis (20%), but only three were severe. Eight-year survival rate considering revision for any reason was 92.6% (95% CI, 85.5-96.4%).

Conclusions: This series indicates that DM cups are a viable option to treat recurrent THA instability. Their design provides a low risk of recurrent instability without increasing mechanical complications.

Keywords: bearing; dual mobility; hip arthroplasty; instability; polyethylene; revision; wear.

Fig. 1

DM cup: The mobile polyethylene insert is not constrained in the metal back constituting the large articulation. It is clipped over the femoral head (22- or 28-mm diameter) constituting the small articulation. Note the smooth aspect of the head–neck junction as well as the absence of an extraction hole

Fig. 2

Cementless DM cup with additional screw and pegs for treating recurrent dislocation

Fig. 3

Intra-prosthetic dislocation 5 years after revision of recurrent instability. The stem neck is not fully polished, which could favor polyethylene rim wear and dislocation of the small articulation. Cup exchange was needed as long as patient was referred 2 weeks after dislocation with lesions on the articulating inner wall of the metal back