[Results of the Evora dual mobility socket: five years follow-up]

Dislocation is a well-known complication of total hip arthroplasty. The risk can be reduced to one or two cases per thousand using a double mobility cup. The survival rate achieved with the Bousquet implant is 95% at 10 years. The complications with this implant are early mobilization and inguinal pain. An overly large cup and insufficient primary and secondary fixation can be implicated. The design of the original implant was later modified to limit these early complications. The purpose of this work was to check the validity of the changes made.

The chromium-cobalt moulded cup was used. The outer surface of this cup presents large geometric striations and is coated with hydroxyapatite. The cup has the shape of a half sphere of 180 degrees and a posterior wall prolongation measuring 6.5mm. Three mechanisms were used for the primary fixation: an asymmetrical growth ring, four anchorage stems, and a superior screw. Two hundred cups were implanted in 194 patients. The femoral piece was a Charnley stainless steel implant (n=139), a titanium SEM implant (n=59) or another implant (n=12). Cement was used for 193 implantations. The series included 97 women and 103 men with osteoarthritis (n=180), necrosis (n=16), surgery for fracture and primary arthroplasty (n=9). The Harris and Postel-Merle-d'Aubigné scores were noted. Eight radiographic criteria were analyzed to assess the position of the cup and the radiological course of the interface.

Mean time to surgery was six years. Mean age at surgery was 70 years (range: 32-91) and varied depending on the operators from 67 to 73 years. At last follow-up: 17 patients had died, eight were lost to follow-up and five were bedridden. Three patients underwent revision surgery. Thus, this analysis included 170 prostheses followed for more than five years (mean: six years, range: 5-7 years). The Harris score improved from 48 to 92 and the Postel-Merle-d'Aubigné score from 2/5/4 to 5.8/5.9/5.5 (range: 4-6/5-6/1-6). None of the patients complained of anterior pain during hip flexion against resistance. Cup inclination was 46 degrees on average (range: 62-22 degrees ). Medialization, lateralization or ascension greater than 10mm of the centre of rotation was not observed on the postoperative films. At last follow-up, no measurable mobilization or migration could be identified on plain X-rays. Lucent lines, condensations and bony defects around the cup, when visible postoperatively, were not found on the last follow-up X-rays. There were two cemented femoral pieces, which developed a lucent line in the nonspecific metaphyseal area. There were no cases of granuloma and no cam effect. Three patients underwent revision for femoral loosening, fracture of the femur below the prosthesis, and hematogenous infection. There were no cases of dislocation.

Changing the design of the implant to modify its volume, material and primary fixation has eliminated the early mobilizations and inguinal pain described for the original Bousquet cup. These options have not had any deleterious effect on prosthesis stability. The question of long-term wear remains an important problem and requires optimization: a neck as thin as possible, optimized surfacing, elimination of laser marks, extraction leads, head skirts.