Extra-articular hip impingement due to heterotopic ossification formation at the anterior inferior iliac spine following previous pelvic external fixation

Abstract

Femoroacetabular impingements (FAIs), specifically cam type and pincer type, continue to be accepted as causes of intra-articular hip pathology and sources of hip pain. Reports of other causes of hip impingement including extra-articular causes have surfaced recently. One structure of importance is the anterior inferior iliac spine (AIIS) due to its inconsistent bony morphology and the pull of the rectus femoris muscle putting it at risk for an avulsion fracture. Under certain circumstances, open surgical excision of exostosis formation after an avulsion fracture of the AIIS has been used. The case below represents a clinical scenario in which a medically unstable and multiply injured trauma patient had an external pelvic fixator placed as part of the treatment plan for an unstable pelvic injury. Following this pelvic external fixation treatment, the patient went on to develop clinically significant heterotopic bone formation at the AIIS pin site with extra-articular hip impingement syndrome.

Heterotopic Ossification Secondary to Motor Vehicle Collision Trauma Leading to Femoroacetabular Impingement Syndrome: A Case Report

“…While the link between prior trauma and HO has been well-established in the literature, considerations of the clinical impact of periarticular hip HO have largely only been significantly investigated in impingement cases secondary to hip arthroplasty and arthroscopy. Moreover, only a small body of case reports describe impingement symptoms in the setting of other hip operations (e.g., pelvic external fixator placement) or atraumatic injury involving the AIIS (e.g., AIIS avulsion fracture) [ 15 , 16 ]. None have investigated the relationship between blunt trauma and the etiology of hip HO resulting in impingement symptoms.…”