925 - Overlooked and Underdiagnosed: A Case of Proximal Radioulnar Joint Osteoarthritis

Proximal radioulnar joint (PRUJ) osteoarthritis (OA)

Case Description:

43-year-old right-handed male presented with insidious onset of right elbow pain localized to the radial forearm. He described constant aching with mechanical symptoms, including crepitus during forearm rotation. Physical examination revealed point tenderness over the radial head and pain with both active and passive pronation/supination. Radiographs showed preserved joint spaces with subtle deformity of the radial head. Computed tomography (CT) revealed mild hypertrophic changes of the PRUJ consistent with chronic joint remodeling and degenerative OA. He previously trialed steroid injections to the elbow joint with suboptimal relief. We instead trialed a steroid injection with ultrasound (US) guidance to the PRUJ which provided marked symptom improvement, particularly with rotation-based activities. Surgical referral was deferred.

Discussions:

Chronic elbow pain is a frequent concern in outpatient settings, commonly attributed to tendinopathies or peripheral nerve entrapments. However, the PRUJ, a key articulation for forearm rotation and load transmission, is often overlooked. This synovial pivot joint stabilized primarily by the annular ligament is essential for pronation and supination. While OA typically affects the ulnohumeral and radiocapitellar joints, CT-based studies show PRUJ OA frequently coexists in patients with elbow OA and contributes to range-of-motion limitations. Radial notch osteophytes correlate with reduced flexion-extension and rotational arcs. Etiologies of PRUJ OA include primary degeneration, posttraumatic changes, inflammatory arthropathies, and crystalline disease. Imaging modalities such as US, CT, and MRI enhance diagnostic accuracy by visualizing osteophytes, subchondral cysts, ligament pathology, and bone marrow changes. CT remains the preferred tool for detailed bony assessment.

Conclusions:

This case emphasizes the need to consider PRUJ OA in patients with persistent lateral elbow pain and mechanical symptoms. Proper identification via advanced imaging can guide effective conservative management and prevent unnecessary interventions focused solely on more commonly implicated elbow structures.