The straight head of rectus femoris: An underdiagnosed cause of chronic pain post hip replacement

Abstract

Groin pain following hip arthroplasty has a spectrum of aetiologies. Although mild post-operative pain at six months to a year is common, other causative factors should be considered where pain is severe or persistent. The rectus femoris (RF) muscle is the most common of the quadriceps tendons to be injured or strained. Pathologies are known to occur in athletic adults and children and include tendinopathy, tear, and avulsion, but the RF is rarely attributed to hip pain post-arthroplasty. However, tendinopathy may occur as a result of altered biomechanics and muscle loading. We performed a retrospective analysis of 100 patients, at our tertiary orthopedic hospital, who presented with chronic pain post hip arthroplasty. We identified three patients with RF straight (direct) head tendinopathy and one patient with RF straight (direct) head calcific tendinopathy. Established causes of chronic post-operative pain include septic/aseptic loosening, pseudotumor, iliopsoas bursitis/impingement, and bursitis. In this report, we describe the scanning technique, sonographic appearances, and our institutional experience of post-arthroplasty pathologies of the RF straight (direct) head which is an underreported cause of chronic pain following hip replacement. We also recommend including the RF straight (direct) head in routine US protocols of the post-operative hip.