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. 2013 Mar;471(3):965-70.
doi: 10.1007/s11999-012-2639-2. Epub 2012 Oct 10.

Intraprosthetic dislocation: a specific complication of the dual-mobility system

Remi Philippot  1 , Bertrand Boyer, Frederic Farizon
Affiliations

Intraprosthetic dislocation: a specific complication of the dual-mobility system

Remi Philippot et al. Clin Orthop Relat Res. 2013 Mar.

Abstract

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.

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

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Figures

Fig. 1
Fig. 1
The AP postoperative radiograph shows a PF® (Serf) stem combined with a Novae® (Serf) dual-mobility cup on the right side. On the left side there is a Pro® stem combined with a Novae® dual-mobility cup. Type I IPD is evident on the left side.
Fig. 2
Fig. 2
Both stems differed in the femoral neck diameter and material, which was 16 mm and stainless steel, respectively, for the PF® (Serf) femoral stems on the left and 13 mm and titanium, respectively, for the PRO® (Serf) femoral stems on the right.
Fig. 3
Fig. 3
The press-fit NOVAE-1® Serf components are shown. These tripod cups feature two impacted anchorage studs and one superior fixation screw. (Reproduced with permission from Serf Dedienne Santé Implants Orthopédiques & Dentaires, Décines, France.)
Fig. 4
Fig. 4
This postoperative radiograph shows a Type I IPD in a patient with 15 years followup. No acetabular loosening is seen.
Fig. 5
Fig. 5
The perioperative photograph shows a Type II IPD. There is blockage of the large articulation of the dual-mobility system with extensive fibrosis.
See this image and copyright information in PMC

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