Dissociation of Bipolar Hemiarthroplasty of the Hip: a case report of uncommon complication

Component dissociation after a bipolar hemiarthroplasty is an uncommon complication that usually necessitates reoperation due to difficulties in closed reduction. Only a few cases have been published in the recent literature.

A. Vasileios & P. Spyridon presents a case of disassembly location of in a 68-year-old woman who underwent bipolar hemiarthroplasty 10 years ago due to a left hip femoral neck fracture. She began complaining about pain and difficulty to bear weight after an unintentional internal rotation movement of her left hip. The initial radiographs showed the disassembly of the bipolar hip prosthesis, and it was a type II dissociation. The patient underwent conversion to total hip arthroplasty.

Types of dissociation based on the location of the locking ring in a series of seven cases of bipolar prosthesis dissociation due to marked polyethylene wear: type I, where the locking ring is loosened but the femoral ball is not dislocated;

type II, where the locking ring is loosened and the inner femoral head is dislocated; and

type III, where the inner femoral head is dislocated but locking ring remains attached to the outer cup. Also known as spontaneous type, it is extremely unusual and is caused by interacetabular dislocation due to a breakdown of the locking mechanism. The inner head dislocates posteriorly, while the outer head remains in place.

A case report

A 68-year-old woman came to the accident and emergency department to the hospital complaining about left hip pain and inability to bear weight after a spontaneous internal rotation movement of her left hip during mobilization out of bed, with no history of falling.

She was a nonsmoker, with a history of hypertension, who underwent a bipolar hip hemiarthroplasty for a left hip femoral neck fracture in another hospital 10 years ago. A bipolar self-centering head was combined with a cementless stem. The patient was entirely self-sufficient in daily activities and could walk without assistance. The left lower limb was shortened and externally rotated with a restricted range of motion on clinical examination, raising concerns for dislocation. The neurovascular system was intact.

On the initial x-rays dissociation between the polyethylene ring and the inner femoral head was observed, while the outer head was still in the acetabulum. Varus position of the outer head and osteoarthritic changes of the acetabulum were identified. No closed reduction maneuver was attempted and the patient was admitted to the orthopaedic ward. The erythrocyte sedimentation rate and C-reactive protein levels were normal.

Four days later, the patient underwent a conversion of the bipolar hemiarthroplasty to total hip arthroplasty under spinal anesthesia. The patient was placed in the lateral decubitus position, the skin was incised over the previous scar, and a posterior approach to the left hip was used. Dislocation between the inner head and the polyethylene was observed, while the locking ring was dislodged but still attached to the inner head, with an excessive amount of wear. The prosthetic acetabular component was found to be intact, with no signs of wear, and still located inside the native acetabulum. No findings of trunnionosis were observed at the time of revision. The stem was well fixed and left in place, while the inner head, the polyethylene ring, and the outer head were removed.

An uncemented, hemispherical, multiple-hole, acetabular component with 52 mm diameter was placed along with a polyethylene-bearing surface and a skirted metallic femoral head (12/14, 32 mm, XXL). Intraoperative cultures were negative.

Weight-bearing was limited for 6 weeks until cup ingrowth could be achieved. There were no postoperative complications, and the patient was discharged 4 days after the operation.

At 1-month follow-up, no complications were observed, partial weight-bearing was obtained using crutches, and the radiograph showed ongoing integration of the acetabular component. The patient was encouraged to gradually return to full weight bearing after 6 weeks. She was able to walk without any restrictions after 3 months. Finally, at 12-month follow-up, the patient was able to return to her everyday activities, with a Harris Hip Score of 87.2 at that time.

Further reading:

Dissociation of Bipolar Hemiarthroplasty of the Hip

Athanasiou Vasileios, Papagiannis Spyridon

Arthroplasty Today 16 (2022) 119 -123

https://doi.org/10.1016/j.artd.2022.05.003