Disassociation at the head–trunnion interface: an unseen complication of modular hip hemiarthroplasty

Abstract

A woman in her mid-90s underwent a left uncemented bipolar hemiarthroplasty for an intracapsular femoral neck fracture. Postoperative radiographs at 48h showed a disassociation of the left femoral prosthesis at the head–trunnion interface, with the bipolar head remaining in the acetabulum. There was no preceding trauma and the patient had mobilised postoperatively. The hip was revised to a monopolar head, and the patient's hip was protected postoperatively in a brace limiting flexion and external rotation. At 30 days following revision she was mobilising pain-free with a stable hip. Disassociation at the head–trunnion interface has never been reported in hip hemiarthroplasty, and is only described in relation to primary or revision total hip replacements (THR) following dislocation or trauma to the THR. This demonstrates a potential complication of modular prostheses for trauma.

What Are the Risk Factors for Dislocation of Hip Bipolar Hemiarthroplasty Through the Anterolateral Approach? A Nested Case-control Study

“…Dissociation is rare and has been reported in only a few case reports [4,7,8,13,16]. The reasons for disassociation after hemiarthroplasty have been reported as component selection and alignment, surgical technique, and patient factors [4,7,8,11,13,15,16]. Varley and Parker [25] reported that dissociations accounted for 12% of all dislocations in bipolar prostheses.…”

Gross trunnion failure after a metal-on-polyethylene total hip arthroplasty leading to dissociation at the femoral head-trunnion interface

“…GTF as a cause of dissociation at the femoral head-trunnion interface has just recently been studied, and over the past decade, there appears to be an increase in reported cases [3] . Dissociation at the femoral head-trunnion interface is more commonly seen following a traumatic event, such as reduction of a hip dislocation in which the inferior edge of the head is distracted against the acetabular component causing dissociation of the 2 components, or after direct trauma to the hip [10] . This case report demonstrates GTF with malformation of the trunnion leading to dissociation at the head-trunnion interface.…”

Five cases of early dissociation between the bipolar hip endoprosthesis cup components; either spontaneously or during reduction maneuvers

“… 26 There are very few case reports available in the literature about the dissociation of bipolar cups. 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 19 , 20 , 21 The dissociation between the components may occur during the hip dislocation, the reduction maneuvers, or spontaneously without any dislocation. 8 , 10 Three types of dissociation are described.…”