At the time of revision arthroplasty, the metallic femoral head was found to be articulating directly with the metallic dual-mobility liner. On exploration of the left hip, the polyethylene component could not be located anywhere in the hip. We surmised the polyethylene component was located in an intrapelvic position, but by reaching around the pelvic brim, we could not palpate or reach it definitively, and we did not feel it could be safely retrieved without a separate incision and exploratory surgery. A decision was made to complete the revision arthroplasty without attempted retrieval of the polyethylene component.
The acetabular component was revised to a less abducted and slightly less anteverted position to improve stability (Fig. 3). The components placed at revision were a 60-mm press-fit Tritanium® acetabular component, a 60- × 46-mm metallic liner, a 46- × 28-mm highly crosslinked polyethylene component (Modular Dual Mobility X3®; Stryker®), and a 28 mm+8.5-mm femoral head (DePuy). The femoral stem was found to be stable and was retained.
Postoperatively, CT of the pelvis confirmed intrapelvic location of the polyethylene component medial and superior to the anterior wall of the acetabulum (Fig. 4). No compression of any intrapelvic vital structures was observed. A discussion was held with the patient concerning risks and potential benefits of a separate procedure with a retroperitoneal approach to retrieve the polyethylene insert. A joint decision was made not to retrieve the component, with the understanding that retrieval could be performed in the future should the intrapelvic component cause symptoms. At 3 months followup, the patient is doing well clinically. At this time, we do not plan to perform serial CT scans unless symptoms should arise.
Enthusiasm for dual-mobility constructs in primary and revision THAs has increased in recent years owing to the potential for increased hip stability. A known complication of this category of implants is intraprosthetic dislocation (with disassociation of the larger polyethylene head from the smaller femoral head) with a long-term incidence reported at 2% to 4% . In THAs using conventional components and modular trial implants, intrapelvic migration along the path of the psoas sheath of trial and final modular prosthetic femoral heads has been reported [3-5, 8, 13, 16, 17]. Several case reports have described intraprosthetic dislocations in which, at the time of revision, the polyethylene component was in the gluteal musculature or the hip capsule [1, 12, 15]. To our knowledge, this is the first report of intrapelvic migration and entrapment of a dual-mobility polyethylene component associated with dislocation of a dual-mobility bearing.
Surgeons should be aware of three main learning points associated with this complication: (1) The diagnosis of an intraprosthetic dislocation may be missed if radiographs are not high-quality AP and lateral views of the hip. The key to diagnosis is eccentricity of the femoral head in the acetabulum. (2) Once intraprosthetic dislocation has occurred, the free polyethylene bearing may migrate. (3) If intrapelvic migration of the component occurs, it makes for difficult decisions between the surgeon and patient regarding whether retrieval or retention is the best management. This diagnosis can be difficult because of radiolucency of the polyethylene component which may be difficult or impossible to identify on a standard radiograph. Even retrospectively, we were unable to see the shadow of the polyethylene component to identify its location on postreduction radiographs.
Surgeons should be aware of the potential for migration of the polyethylene bearing when performing revision surgery on a patient with apparent intraprosthetic dislocation of a dual-mobility construct. When intrapelvic migration of this component has occurred, a clinical dilemma exists regarding retrieval versus retention of the component. Patients understandably will be concerned by the idea of leaving the component in place, however education regarding the potential complications of retrieval including hernia, neurovascular injury, or urologic injury should be discussed. Retrieval of trial femoral heads entrapped in the pelvis may be performed through a separate surgical approach at the time of surgery [3, 5, 13]. One study regarding leaving trial femoral heads that have become entrapped intrapelvically did not identify adverse effects, and patients have remained asymptomatic when such implants have been left in an intrapelvic position . Whether the morbidity of proceeding with a separate incision to retrieve an entrapped intrapelvic component is justified remains debatable. With our patient, because the retained component is a sterile, rounded, smooth polyethylene that does not appear to be compressing vital structures, a decision was made in consultation with the patient not to remove the implant.
Late polyethylene wear has been postulated as a potential mechanism of intraprosthetic dislocation in dual-mobility designs . Our patient sustained a dislocation early during her postoperative course making wear an unlikely cause of the disassociation of the smaller head from the polyethylene component. Retrospective review of serial radiographs in this case from outside institutions does not suggest any of the anterior hip dislocations were intrapelvic. Because the polyethylene component cannot be seen on radiographs, we are uncertain whether the polyethylene component was still attached to the femoral head at the time of the first anterior dislocation. One could postulate there was disengagement of the polyethylene component from the femoral head by disruption of the constrained polyethylene interface either at the time of hip dislocation or during reduction of the hip. We theorize that the disassociated polyethylene component was pushed intrapelvically along the psoas sheath, either during one of the patient's closed hip reductions or during the course of normal hip motion. In our patient, the Stryker dual-mobility acetabular system was used with a DePuy femoral head, which is considered an off-label use. However, to our knowledge, there are no major differences between Stryker® and DePuy cobalt-chrome 28-mm femoral heads.
Surgeons should be aware of intraprosthetic dislocation with dual-mobility articulations and the possibility that the polyethylene component could be entrapped in the pelvis after dislocation. Identification of eccentricity of the femoral head in the acetabular component after dislocation is essential to avoid missing the diagnosis of intraprosthetic dislocation in this setting. The possibility that the polyethylene component may not be retrievable may be discussed with the patient before surgery or preoperative cross-sectional imaging may be performed to definitively identify the location of the component before revision surgery.
1. Banzhof JA, Robbins CE, Ven A, Talmo CT, Bono JV. Femoral head dislodgement complicating use of a dual mobility prosthesis for recurrent instability. J Arthroplasty.
2. Batouk O, Gilbart M, Jain R. Intraoperative dislocation of the trial femoral head into the pelvis during total hip arthroplasty: a case report. J Bone Joint Surg Am.
3. Callaghan JJ, McAndrew C, Boese CK, Forest E. Intrapelvic migration of the trial femoral head during total hip arthroplasty: is retrieval necessary? A report of four cases. Iowa Orthop J.
4. Chu CM, Wang SJ, Lin LC. Dissociation of modular total hip arthroplasty at the femoral head-neck interface after loosening of the acetabular shell following hip dislocation. J Arthroplasty.
5. Citak M, Klatte TO, Zahar A, Day K, Kendoff D, Gehrke T, Dörner A, Gebauer M. Intrapelvic dislocation of a femoral trial head during primary total hip arthroplasty requiring laparotomy for retrieval. Open Orthop J.
6. Martino I, Triantafyllopoulos GK, Sculco PK, Sculco TP. Dual mobility cups in total hip arthroplasty. World J Orthop.
7. Farizon F, Lavison R, Azoulai JJ, Bousquet G. Results with a cementless alumina-coated cup with dual mobility: a twelve-year follow-up study. Int Orthop.
8. Kouzelis A, Georgiou CS, Megas P. Dissociation of modular total hip arthroplasty at the neck-stem interface without dislocation. J Orthop Traumatol.
9. Lachiewicz PF, Watters TS. The use of dual-mobility components in total hip arthroplasty. J Am Acad Orthop Surg.
10. McArthur BA, Nam D, Cross MB, Westrich GH, Sculco TP. Dual-mobility acetabular components in total hip arthroplasty. Am J Orthop (Belle Mead NJ).
11. Mohammed R, Cnudde P. Severe metallosis owing to intraprosthetic dislocation in a failed dual-mobility cup primary total hip arthroplasty. J Arthroplasty.
12. Odland AN, Sierra RJ. Intraprosthetic dislocation of a contemporary dual-mobility design used during conversion THA. Orthopedics.
13. Ozkan K, Ugutmen E, Altintas F, Eren A, Mahirogullari M. Intraoperative dislocation of the prosthetic femoral head into the pelvis during total hip arthroplasty. Acta Orthop Belg.
14. Philippot R, Adam P, Farizon F, Fessy MH. Bousquet G [Survival of cementless dual mobility sockets: ten-year follow-up][in French]. Rev Chir Orthop Reparatrice Appar Mot.
15. Philippot R, Boyer B, Farizon F. Intraprosthetic dislocation: a specific complication of the dual-mobility system. Clin Orthop Relat Res.
16. Talmo CT, Sharp KG, Malinowska M, Bono JV, Ward DM, LaReau J. Spontaneous modular femoral head dissociation complicating total hip arthroplasty. Orthopedics.
17. Ziv YB, Backstein D, Safir O, Kosashvili Y. Intraoperative dislocation of a trial femoral head into the pelvis during total hip arthroplasty. Can J Surg.