Evora® chromium-cobalt dual mobility socket: results at a minimum 10 years' follow-up.

INTRODUCTION: The Evora chromium-cobalt alloy dual mobility socket claims to display a large articulation tribology different from that of stainless steel models, limiting the risk of intraprosthetic dislocation and wear. The present study reports a minimum of 10years' follow-up in a multicenter prospective series of 200 sockets previously reported on at 5years. HYPOTHESIS: The use of chromium-cobalt in dual mobility sockets provides a low rate of failure at 10years, especially as regards to osteolysis and intraprosthetic dislocation. MATERIALS AND METHODS: Two hundred hydroxyapatite-coated molded chromium-cobalt sockets without titanium interface were implanted without cement in 194 patients with a mean age of 70 years (range, 32-91 years). Clinical results were assessed on Postel Merle d'Aubigné and Harris scores, plain radiographs and survival analysis. RESULTS: At a mean 11 years' follow-up (10-13 years), 56 patients had died and 31 were lost to follow-up. Four underwent surgical revision (3 femoral components, and 1 socket for migration at 9 years with complete disappearance of the hydroxyapatite). A total of 109 implants were analyzable in 107 patients with a mean age of 81 years (55-93 years). At follow-up, the mean Harris score was 90 (75-96) and the PMA score 16.3 (14-18). There were no cases of loosening (except for the case reoperated on at 9 years) and no acetabular radiolucency or cysts. There were 2 cases of non-evolutive femoral radiolucency and 10 of femoral granuloma, involving head size > 22 mm (P<0.0001) and a cemented titanium stem (P=0.004) as risk factors. There were no dislocations in the large or small articulation. Ten-year survival was 99% (95% CI: 97.3%-100%) with socket revision as censorship criterion. DISCUSSION: The absence of dislocation in both small and large articulations confirmed the efficacy of the dual mobility concept and suggested an advantage for chromium-cobalt sockets in reducing the rate of intraprosthetic dislocation and preventing blockage of the large articulation by a better performance in the friction couple. Granulomas were associated with wear in cemented titanium stems and with heads greater than 22 mm in diameter. Ten-year survival was 99% (censorship criterion: revision for socket failure); there was, however, one case of socket loosening with disappearance of the hydroxyapatite, indicating that surveillance should be continued in this cohort.

Results of the Evora dual-mobility socket after a minimum follow-up of five years.

PURPOSE OF THE STUDY: Dislocation is a well-known complication of total hip arthroplasty. The risk can be reduced to one or two cases per thousand using a dual-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 study was to check the validity of these design changes. PATIENTS AND METHODS: The chromium-cobalt moulded cementless 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 180 degrees half sphere 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 cementless 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 femoral fixation in 193 implantations. The series included 97 women and 103 men with osteoarthritis (n=180), necrosis (n=16) and 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. RESULTS: The mean follow-up was six years and the minimum was five years. The mean age at surgery was 70 years (range, 32 to 91). 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, five to seven 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 to 6/5 to 6/1 to 6). None of the patients complained of anterior pain during active hip flexion in supine position (related to ilio-psoas irritation). Cup inclination was 46 degrees on average (range, 62 to 22 degrees ). Medialization, lateralization or ascension greater than 10mm from the center of rotation was not observed on the postoperative films. At the last follow-up, no measurable mobilization or migration could be identified on plain X-rays. Radiolucent 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 that developed a radiolucent 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. DISCUSSION: 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 and head skirts.

[Results of the Evora dual mobility socket: five years follow-up]. / Résultat à cinq ans de la cupule à double mobilité Evora.

PURPOSE OF THE STUDY: 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. PATIENTS AND METHODS: 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. RESULTS: 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. DISCUSSION: 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.