Displaced femoral neck fractures represent approximately 40% of hip fractures, which rank in the top 10 of all impairments worldwide.1-2 Hemiarthroplasty is a treatment of choice for older and less active patients who have sustained a displaced femoral neck fracture.2 Hemiarthroplasty complications include stem loosening, prosthetic head dislocation, and acetabular protrusion. This article presents a rare complication of bipolar modular component disassembly.
| || || |
| Figure 1: Subcapital fracture of the left femur. Figure 2: Radiograph 1 week after bipolar hemiarthroplasty of the left hip. |
An 85-year-old woman was treated with a cemented bipolar hemiarthroplasty through a posterior approach (Gibson approach) after a subcapital fracture of her left femur on April 5, 2003 (Figures 1, 2). Two years later, she sustained disassembly between the polyethylene cup and the prosthetic head with both items still in the acetabulum (Figure 3). A decision was made to perform open reduction. Intraoperatively, there was no sign of erosion of the polyethylene cup, and the prosthesis was found in neutral position. The femoral stem was well fixed, and the prosthetic femoral head was undamaged. The original outer shell with an inner liner of ultra high molecular weight polyethylene were assembled and placed securely on the metal femoral head. A definite click was felt when the femoral head was fully seated. The linear rotated freely on the femoral head.
The postoperative period was uneventful, and the patient was discharged 6 days after surgery. At the time of the final follow-up (36 months), radiographs showed no acetabular erosion, polyethylene wear, femoral subsidence, or component migration (Figure 4).
Bipolar hemiarthroplasty has been advocated for the treatment of fractures of the femoral neck since the 1970s.3 But there are still considerable differences of opinion regarding the choice of unipolar prosthesis, bipolar prosthesis, or total hip arthroplasty (THA). Advocates cited the ease of implantation, reduced blood loss, lower dislocation rate, as well as the ease of acetabular revision when compared with conventional THA. Some authors prefer bipolar to unipolar components because of increased range of movement, variable choice of head size, adjustment of neck length, and decreased wear of the acetabulum.4,5
| || || |
| Figure 3: Two years after bipolar hemiarthroplasty, radiographs showing disassembly between the polyethylene liner and ball head. Figure 4: Radiograph 2 years after the second operation showing prothesis with good orientation and acetabulum coverage. |
An English literature search was conducted on Ovid MEDLINE covering the span from 1970 to 2007 to identify reports of disassembly of bipolar components. The search was performed with limiting factors of human and English language. The key words for the search included disassembly,dissociation, and bipolar hemiarthroplasty. Some papers were found by manual methods. Additional articles identified from these references that contained relevant supporting information were then included. Only 6 cases of disassembly of bipolar components were found to have been reported in the English literature. In almost all the cases, the injury was caused without any significant force, as only 2 patients reported a fall. Most of them were elderly women. We classified them into 3 types according to the etiology. First is iatrogenic disassembly. Three cases of bipolar disassembly occurred as a complication of the reduction of dislocation.6,7 The reason for separation appeared to be a bottle-opener effect by locking the cup on the posterior acetabular rim, while limp traction was applied during reduction maneuvers.6,7 Second is the erosion of the polyethylene liner. Georgiou et al6 reported a case of dissociation of bipolar hemiarthroplasty due to severe erosion of polyethylene 10 years postoperatively. Any stain between the surfaces of head components could increase the friction of motion, accelerating wear of the polyethylene liner. In this case, spontaneous disassembly was associated with a dislocation of the hip. Spontaneous disassembly is uncommon and seemed to have been caused by a failure of the locking mechanism between the head components, resulting in an intra-acetabular dislocation. The patient was in a flexed position cleaning a bathtub without major accident or acute activity, and the hip probably tried to dislocate posteriorly, but, instead of dislocation occurring, disassembly occurred with the head still staying within the acetabulum. We suspected that the modular systems may have dissociated at a certain critical point due to internal characteristics. We reassembled the original devices and the patient was well at follow-up. Another reason for the spontaneous disassembly is erosion of the acetabular, which could lead to the disassembly of the components due to reduction of acetabulum coverage and alignment of the prosthesis, as well as the mechanical failure of the polyethylene liner.6 However, the current case showed no signs of acetabular erosion.
There is a general trend in favor of bipolar prostheses over unipolar prostheses. In some areas of China, unipolar hemiarthroplasty is no longer performed. Although the potential disadvantages of bipolar systems shown here do not outweigh the advantages, we should rethink the status of bipolar hemiarthroplasty. Can bipolar hemiarthroplasty replace unipolar hemiarthroplasty, or, on the contrary, should bipolar hemiarthroplasty be replaced by total hip arthroplasty or unipolar hemiarthroplasty? One study from the United States suggested that there is no advantage to using bipolar prostheses in treating femoral neck fractures compared with unipolar in the elderly patient.5 Calder et al8 suggested that a unipolar prothesis may give better short-term results in octogenarians. They saw no justification for the use of the expensive bipolar hip prothesis in patients >80 years of age, regardless of their mental state or mobility.
Although extremely rare, spontaneous disassembly of a bipolar prothesis due to a dislocation of the hip should be considered as a mechanical cause of failure following hemiarthroplasty. Open reduction is required and revision surgery is judged by the locking mechanism between components. When there is no acetabular and polyethylene linear erosion, we believe that the original components can be used again.
- Johnell O, Kanis JA. An estimate of the worldwide prevalence, mortality and disability associated with hip fracture. Osteoporos Int. 2004;15(11):897-902.
- Heetveld MJ, Raaymakers EL, Luitse JS, Nijhof M, Gouma DJ. Femoral neck fractures: can physiologic status determine treatment choice? Clin Orthop Rel Res. 2007; (461):203-212.
- Bochner RM, Pellicci PM, Lyden JP. Bipolar hemiarthroplasty for fracture of the femoral neck. Clinical review with special emphasis on prosthetic motion. J Bone Joint Surg Am. 1988; 70(7):1001-1010.
- Floren M, Lester DK. Outcome of total hip arthroplasty and contralateral bipolar hemiarthroplasty: a case series. J Bone Joint Surg Am. 2003; 85(3):523-526.
- Ong BC, Maurer SG, Aharonoff GB, Zuckerman JD, Koval KJ. Unipolar versus bipolar hemiarthroplasty: functional outcome after femoral neck fracture at a minimum of thirty-six months of follow-up. J Orthop Trauma. 2002; 16(5):317-322.
- 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 the literature. Injury. 2006; 37(2):162-168.
- Star MJ, Colwell CW Jr, Donaldson WF III, Walker RH. Dissociation of modular hip arthroplasty components after dislocation. A report of three cases at different dissociation levels. Clin Orthop Rel Res. 1992; (278):111-115.
- Calder SJ, Andeson GH, Jagger C, Harper WM, Gregg PJ. Unipolar or bipolar prosthesis for displaced intracapsular hip fracture in octogenarians: a randomised prospective study. J Bone Joint Surg Br. 1996; 78(3):391-394.
Drs Guo, Yang (Huilin), Yang (Tongqi), and Tang are from the Department of Orthopedics, The First Affiliated Hospital of Soochow University, Suzhou, China.
Drs Guo, Yang (Huilin), Yang (Tongqi), and Tang have no relevant financial relationships to disclose.
Correspondence should be addressed to: Jiong Jiong Guo, MD, Department of Orthopedics, The First Affiliated Hospital of Soochow University, Suzhou 215006, China.