This in vitro study, conducted with an experimental protocol previously validated in the literature, helps quantify the actions of the MPFL, the VMO, and the MPML/MPTL respectively, and identify areas of joint motion where these structures have the most significant influence. This confirms the importance of reconstruction in the treatment of chronic patellar instability. During its reconstruction, care should be taken to adjust the MPFL balance during the initial 20°-30° of flexion.

The concept of a dual articulation acetabular cup was developed by Prof. Bousquet in 1974. This concept has been shown to provide high stability after revision and primary total hip arthroplasty. The aim of our study was to evaluate the incidence of prosthetic instability in a consecutive homogeneous series of 384 primary dual mobility cups. Incidence of instability and implant survival were evaluated. Mean follow-up was 15.3 years (range, 12-20). There was no early or late instability. On the acetabular side there were 13 aseptic loosenings, 14 intraprosthetic dislocations, and seven polyethylene wear cases that required replacement of the liner. The cumulative survival rate of the dual-articulation acetabular cup using surgical revision for aseptic loosening as the endpoint was 95.9%±4.1% at 18 years postoperatively. Our series proves the good long term behaviour of dual-articulation acetabular components in primary arthroplasty. Their excellent survivorship rate and the absence of episodes of prosthetic instability increase our confidence in this concept. Résumé Le concept de cupule à double mobilité a été inventé par le Professeur Gilles BOUSQUET en 1974. Ce concept a permis de mettre en évidence une importante stabilité des hanches, notamment après révision mais également dans les prothèses totales de hanches de première intention. Le but de cette étude est d'évaluer l'incidence et l'instabilité sur une série homogène consécutive de 384 hanches traitées avec cupule à double mobilité. Le taux d'instabilité des implants sur les patients survivants a été évalué. Le suivi moyen a été de 15,3 ans (de 12 à 20 ans) au plus long recul, il n'y a aucune instabilité ni primaire, ni tardive. Par contre, il existe 13 descellements aseptiques acétabulaires, 14 luxations intra prothétiques, 7 usures du polyéthylène qui ont nécessité un remplacement du PE. Le taux de survie cumulé de cette cupule à double mobilité est de 95,9%±à 18 ans si l'on prend comme critère la révision pour descellement aseptique. Cette série prouve le bon devenir à long terme de cette articulation dans les prothèses totales primaires, avec un excellent taux de survie et l'absence de phénomènes de luxation inhérentes à ce concept.

Background The dual-mobility concept was proposed as an alternative to prevent postoperative dislocation events. However, intraprosthetic dislocation (IPD) is a troublesome and specific complication induced by the loss of the polyethylene retentive rim and escape of the femoral head from the polyethylene liner. The factors associated with IPD are unknown as only isolated cases have been reported and do not provide a clear understanding of the mechanisms of failure.Questions/purposes We therefore (1) identified features related to different types of IPD and (2) determined factors related to the timing of IPD. Methods We identified 81 cases (80 patients) with IPD from among 1960 primary THAs performed between January 1985 and December 1998. To classify the types of IPD we considered perioperative (presence of arthrofibrosis, cup loosening, and type of liner wear) and radiographic (radiographic cup loosening or migration, and ossification) features. Results We identified three types of IPD with the following causal mechanisms: Type 1 was pure IPD without arthrofibrosis and without cup loosening (n = 26), Type 2 was IPD secondary to blocking of the liner (n = 41), and Type 3 was IPD associated with a cup loosening (n = 14). The mean times of onset were, 11, 8, and 9 years after THA, respectively. We found no difference according to the stem design regarding timing of the IPD. Conclusions This new IPD classification allows clinicians to anticipate the possible conditions they will encounter with revision surgery and plan surgery (cup removal, liner exchange, synovectomy). The implant characteristics and this new classification accounted for the differences in the timing of occurrence.

Purpose The longest follow-up dual mobility series from inventor Gilles Bousquet focussing on implant survival and the incidence of dislocation. Methods This was a retrospective study from 1985 to 1990, on 240 hips using a PF® modular femoral stem and a dual mobility Novae® tripodal socket (SERF). Results The 22-year follow-up global survival rate was 74%. No dislocation occurred, 41 hips were revised, including ten retentive failures (RF), 12 hips were lost to follow-up, 87 patients (99 hips) died without revision, and 90 hips were still in situ. Conclusion The dual mobility socket global survival rate is comparable to similar series. The 0% dislocation rate demonstrates the success of dual mobility with regard to implant stability. The main issues were cup fixation, which might be improved by the use of macrostructures and HA coating, and osteolytic lesions, caused by polyethylene wear. Traditionally suitable for patients older than 60 years, dual mobility might be extended for use in patients over 50.

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