Case 2: A 92-year-old woman underwent bipolar hemiarthroplasty under spinal anesthesia for a subcapital fracture of her right femur a month ago. Nine days after the surgery the patient fell off from her bed and sustained a posterior dislocation of the prosthesis. X-ray showed a displaced femoral head. The patient was sent to the OR for close reduction under general anesthesia. During the maneuvres, disassembly accidently occurred. The cup was dislodged and lying above while the small head fell into the acetabulum. Open reduction was performed as a result. Intraoperatively, the prosthesis was found intact and the locking mechanism functioned well. The head components were put back into place. After the reduction operation, the patient was given an orthopedic cast for immobilization of the lower limb for 4 weeks.
Case 3: An 85-year-old woman presented to our emergency department with right-sided hip pain after a fall. X-ray identified a transcervical fracture of the femur. Bipolar hemiarthroplasty was performed under general anesthesia. Six days later, she suffered a sudden pain and could not move the lower limb while changing the position in bed. Plain film radiographs showed a posterior dislocation. Close reduction was performed under general anesthesia and the patient was discharged after a week. Four weeks after discharge, she had hip dislocation again while in an attempt to sit up from a chair. When close reduction was performed, the polyethylene cup and the prosthetic head dissociated. The patient was taken to the OR where she underwent revision hemiarthroplasty. Intra-operatively we found that the external rotators were torn, and the femoral head components were disassembled and extruding through the repaired capsule and the abductor. No evidence of fractures of the acetabulum was observed, and the femoral components remained well fixed. The femoral head was substituted by the one with a longer neck (from 0 mm–8 mm) in order to obtain stronger soft tissue tension. The hip was reduced and its stability confirmed.
Case 4: A 76-year-old man underwent bipolar hemiarthroplasty after a subcapital fracture of his left femur. Four weeks later, he suffered sustained pain and could not move his left leg after falling down on the floor. X-ray showed dislocation of the femoral head [Figure 1C]. Patient was taken to the OR for close reduction under general anesthesia. Before routine maneuvres of reduction, we found that the outer bipolar shell was locked behind the acetabular rim [Figure 1D]. We therefore push the affected limb proximally and to turn the outer cup over on the acetabulum by internally rotated and adducted the leg, then routine close reduction of the dislocation [Figure 1E].
Hemiarthroplasty of the hip is a common treatment option in the elderly with femoral neck fractures. It gains advantages over total hip arthroplasty for its simpler procedures, less surgical trauma, and quicker postoperative recovery. Bipolar prosthesis brings satisfactory early and long-term outcomes and is recognized as having comparative, if not better, designs than that of unipolar ones.[2–4] Incidence of dislocation after hemiarthroplasty is low[5,6] and is not significantly different between unipolar and bipolar hip hemiarthroplasty.[7,8] But dissociation of femoral head components is a rare complication with bipolar prosthesis, in which case disassembly occurs between the polyethylene cup and the prosthetic head.[9,10]
Disassembly after bipolar hemiarthroplasty can occur for many reasons. In most of the cases, disassembly of the polyethylene cup and the inner femoral head occurs after manipulation for closed reduction under general anesthesia. When this happens, the outer bipolar shell can be locked along the acetabular rim, which requires the surgeon to apply traction force to reduce the dislocated hip, dissociation would occur while the inner head continued to be pulled. The mechanism was called “bottle-opener mechanism” [Figure 1F]. In the present cases, dissociation all happened during manipulation under general anesthesia, with polyethylene cup falling out of the acetabulum while the small head falling inside.
To approach such situations, proximal translation of the affected limb and adduction under fluoroscopic supervision is recommended [Figure 1G], in order to turn the outer cup over on the acetabulum by the effect of leverage [Figure 1H]. That makes the convex of the femoral head rather than the edge in contact with the acetabular bone. Then routine close reduction of the dislocation could follow [Figure 1I].
Excessive wear of polyethylene liner and failure of the locking ring mechanism can also contribute to dissociation. Under this circumstance, the bipolar shell usually still lies in the acetabulum with the inner head falling out of the acetabulum.
Dissociation as an iatrogenic complication warrants caution. Once closed reduction fails, open reduction has to be performed. Locking mechanism must be inspected and the short external rotator muscle should be repaired. Proper soft tissue tension should be maintained, and if necessary, by increasing the length of the neck (offset) to help maintain stability.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patients have given their consent for their images and other clinical information to be reported in the journal. The patients understand that their name and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Conflicts of interest
Bian YY: Preparation of case report, literature review, and writing the paper; Xiao K: Collecting the data; Weng XS: Providing ideas, giving recommendations, and reviewing the paper; Jin J and Wang LC: Providing clinical data; Zhang BZ: Providing clinical data and reviewing the paper.
1. Ye CY, Liu A, Xu MY, Nonso NS, He RX. Arthroplasty versus internal fixation for displaced intracapsular femoral neck fracture in the elderly: systematic review and meta-analysis of short- and long-term effectiveness. Chin Med J
2016; 129:2630–2638. doi: 10.4103/0366-6999.192788.
2. Inngul C, Hedbeck CJ, Blomfeldt R, Lapidus G, Ponzer S, Enocson A. Unipolar hemiarthroplasty versus bipolar hemiarthroplasty in patients with displaced femoral neck fractures: a four-year follow-up of a randomised controlled trial. Int Orthop
2013; 37 12:2457–2464. doi: 10.1007/s00264-013-2117-9.
3. Somashekar, Krishna SV, Sridhara Murthy J. Treatment of femoral neck fractures: unipolar versus bipolar hemiarthroplasty. Malays Orthop J
2013; 7:6–11. doi: 10.5704/MOJ.1307.007.
4. Hedbeck CJ, Blomfeldt R, Lapidus G, Tornkvist H, Ponzer S, Tidermark J, et al. Unipolar hemiarthroplasty versus bipolar hemiarthroplasty in the most elderly patients with displaced femoral neck fractures: a randomised, controlled trial. Int Orthop
2011; 35:1703–1711. doi: 10.1007/s00264-011-1213-y.
5. Kim Y, Kim JK, Joo IH, Hwang KT, Kim YH. Risk factors associated with dislocation after bipolar hemiarthroplasty in elderly patients with femoral neck fracture. Hip Pelvis
2016; 28:104–111. doi: 10.5371/hp.2016.28.2.104.
6. Mukka S, Lindqvist J, Peyda S, Broden C, Mahmood S, Hassany H, et al. Dislocation of bipolar hip hemiarthroplasty through a postero-lateral approach for femoral neck fractures: a cohort study. Int Orthop
2015; 39:1277–1282. doi: 10.1007/s00264-014-2642-1.
7. Madanat R, Makinen TJ, Ovaska MT, Soiva M, Vahlberg T, Haapala J. Dislocation of hip hemiarthroplasty following posterolateral surgical approach: a nested case-control study. Int Orthop
2012; 36:935–940. doi: 10.1007/s00264-011-1353-0.
8. Ninh CC, Sethi A, Hatahet M, Les C, Morandi M, Vaidya R. Hip dislocation after modular unipolar hemiarthroplasty. J Arthroplasty
2009; 24:768–774. doi: 10.1016/j.arth.2008.02.019.
9. Li L, Ren J, Liu J, Wang H, Sang Q, Liu Z, et al. What are the risk factors for dislocation of hip bipolar hemiarthroplasty through the anterolateral approach? A nested case-control study. Clin Orthop Relat Res
2016; 474:2622–2629. doi: 10.1007/s11999-016-5053-3.
© 2019 Chinese Medical Association
10. Georgiou G, Siapkara A, Dimitrakopoulou A, Provelengios S, Dounis E. Dissociation of bipolar hemiarthroplasty of the hip after dislocation. A report of five different cases and review of literature. Injury
2006; 37:162–168. doi: 10.1016/j.injury.2005.09.014.