An anatomic classification for heterotopic ossification about the hip

Abstract

Study design: Retrospective cohort.

Summary of background data: Heterotopic ossification (HO) about the hip is a debilitating condition that can occur after fixation for acetabular fractures, total hip replacement, or polytrauma with closed head injuries. No classification exists that informs surgical treatment.

Purpose: To establish a classification system for HO about the hip by reviewing a consecutive series of HO at a single institution. It was hypothesized that HO about the hip could be grouped into a novel classification scheme based upon the location and involved structures of the hip.

Methods: Retrospective chart review of single center's case log for HO excision from 2004 to 2018 was performed. Inclusion criteria included all patients undergoing excision of heterotopic bone excision about the hip. Demographic data, pre and post hip range of motion, surgical approach for each surgery, index surgery date and interval to excision are reported as well as presence and location of HO and Brooker classification.

Results: A total of 36 patients (21 men and 15 women) and 40 hips were identified meeting inclusion criteria. The mean age at the time of the index surgery was 47 (range, 16-77 years). Traumatic injury with fracture (35%) included 9 acetabular fractures (22%), 2 long bone fractures (5%) treated with intramedullary devices, one displaced femoral neck fracture (2%), and one pelvic ring injury (2%). Total hip arthroplasty accounted for 32% of patients. Brooker classification was type 4 (35%), 3 (25%), 2 (23%), 1(17%) which translated to 55% anterior, 48% posterior, 3% medial with respect to location. Average improvement in hip flexion and abduction was 22 and 8°, respectively.

Conclusion: This study identified discrete locations for heterotopic ossification following hip or acetabulum surgery. Both posterior and anterior structures are implicated in the formation of HO, and this investigation presents a novel classification to guide surgical approach for HO excision based upon location.

Keywords: Acetabulum; Heterotopic ossification; Hip; Hip replacement; Trauma.

Fig. 1

Pelvis radiograph demonstrating Brooker 4 ectopic bone formation about the left hip following open reduction internal fixation of an acetabulum fracture in a 58-year-old male one year after his index procedure. At time of presentation and 1 year from surgery, passive left hip range of motion was 0° of flexion and 0° of abduction.

Fig. 2

Volume rendering reconstruction computed tomography scans of pelvis demonstrating ectopic bone formation about posterior hip involving abductors and short external rotators.

Fig. 3

Volume rendering reconstruction computed tomography scans of pelvis demonstrating ectopic bone formation about posterior hip involving abductors and short external rotators.

Fig. 4

Pelvis radiograph demonstrating resection of left hip heterotopic ossification from patient in Figure 1. At final follow up, passive hip range of motion was 85° of flexion and 30° of abduction.