Abstract
Treatment of recurrent dislocation: approximately: 1/3 of failures (probably higher in the absence of a clear curable cause).
In the US: most popular treatment option: constrained liners with high redislocation and loosening rates in most reports. Several interfaces leading to various modes of failures.
In Europe: dual mobility cups (or tripolar unconstrained): first design Gilles Bousquet 1976 (Saint Etienne, France), consisting of a metal shell with a highly polished inner surface articulating with a mobile polyethylene insert (large articulation). The femoral head is captured into the polyethylene (small articulation) using a snap fit type mechanism leading to a large effective unconstrained head inside the metal cup. With dual mobility, most of the movements occur in the small articulation therefore limiting wear from the large polyethylene on metal articulation.
Contemporary designs include: CoCr metal cup for improved friction, outer shell coated with titanium and hydroxyapatite, possible use of screws to enhance primary stability (revision), cemented version in case of major bone defect requiring bone reconstruction.
Increased stability obtained through an ultra-large diameter effective femoral head increasing the jumping distance.
Dual mobility in revision for recurrent dislocation provided hip stability in more than 94% of the cases with less than 3% presenting redislocation up to 13-year follow-up. A series from the UK concerning 115 revisions including 29 revisions for recurrent dislocation reported 2% dislocation in the global series and 7% re-dislocation in patients revised for instability. A recent report of the Swedish hip arthroplasty register including 228 patients revised for recurrent dislocation showed 99% survival with revision for dislocation as the endpoint and 93% with revision for any reason as the endpoint.
One specific complication of dual mobility sockets: intra-prosthetic dislocation (ie: dislocation at the small articulation): often asymptomatic or slight discomfort, eccentration of the neck on AP radiograph, related to wear and fatigue of the polyethylene rim at the capturing are through aggressive stem neck to mobile polyethylene insert contact (3rd articulation). Risk factors include: large and aggressive femoral neck design implants, small head/neck ratio, skirted heads, major fibrosis and periprosthetic ossifications.
Current (over ?) use in France: 30% of primary THA, 60% in revision THA.
Proposed (reasonable) indications: primary THA at high risk for dislocation, revision THA for instability and/or in case of abductors deficiency, Undisputed indication: recurrent dislocation.
