Use of a dual mobility socket to manage total hip arthroplasty instability

Abstract

Unconstrained tripolar hip implants provide an additional bearing using a mobile polyethylene component between the prosthetic head and the outer metal shell. Such a design increases the effective head diameter and therefore is an attractive option in challenging situations of unstable total hip arthroplasties. We report our experience with 54 patients treated using this dual mobility implant in such situations. We ascertained its ability to restore and maintain stability, and examined component loosening and component failure. At a minimum followup of 2.2 years (mean, 4 years; range, 2.2-6.8 years), one hip had redislocated 2 months postoperatively and was managed successfully without reoperation by closed reduction with no additional dislocation. Two patients required revision of the implant because of dislocation at the inner bearing. Technical errors were responsible for these failures. Three patients had reoperations for deep infections. The postoperative radiographs at latest followup showed very satisfactory osseointegration of the acetabular component because no radiolucent line or osteolysis was reported. Use of this unconstrained tripolar design was successful in restoring and maintaining hip stability. We observed encouraging results at short-term followup regarding potential for loosening or mechanical failures.

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

Fig. 1A–B

The photographs show (A) the various components of the unconstrained tripolar device and (B) the implant assembled.

Fig. 2

The unconstrained tripolar device with additional superior flanges and a hook beneath the teardrop in case of compromised fixation is shown.

Fig. 3

The dual mobility socket had been cemented into a cage secured with screws at the time of the revision for instability. At latest followup, no evidence of cup loosening was reported although the screws had broken.

Fig. 4A–B

(A) The photographs show a failed attempt at stabilization with the addition of a socket wall. (B) This challenging situation was managed successfully using an unconstrained tripolar acetabular component.

Fig. 5

The photograph shows a dislocation at the inner bearing of the unconstrained tripolar device.