Muscle-Guided Mapping of the Post-Traumatic Heterotopic Ossification of the Elbow: A Novel CT-Based Study

Background: Heterotopic ossification (HO) involves abnormal bone formation in soft tissues near joints, commonly occurring after elbow trauma or surgery, leading to pain and functional limitations. Previous studies have primarily characterized HO distribution based on bony landmarks, lacking a detailed investigation into the characteristics of its distribution in periarticular soft tissue in post-traumatic elbows. This study aimed to (1) develop a muscle-guided classification system using computed tomography (CT) to map HO relative to elbow muscle-tendon units and (2) investigate correlations between HO location and severity.

Methods: In a retrospective study, 56 patients with HO and elbow stiffness following trauma were analyzed. CT imaging was used to classify HO into seven categories: Posterior - olecranon tip - triceps brachii (P-O-T); Posteromedial - medial gutter - flexor carpi ulnaris (PM-MG-FCU); Posterolateral - lateral gutter - anconeus (PL-LG-AN); Medial - medial epicondylar - flexor muscles (M-ME-FLEX); Lateral - lateral epicondylar - extensor muscles (L-LE-EXT); Anterior - humeroulnar joint - brachialis (A-HU-B); and Anterior - humeroradial - supinator (A-HR-SP). HO severity was graded (1-3) based on CT morphology, and correlations between HO location and severity were assessed.

Results: PM-MG-FCU was the most common HO location (67.9%). Significant correlations were found between HO severity and location, with higher rates of HO in grades 2 and 3, characterized by extensive mature bone formation and bone bridge development occurring in the PL-LG-AN, P-O-T, and PM-MG-FCU.

Conclusion: The muscle-guided classification system effectively delineated HO distribution near elbow muscle-tendon units. HO locations surrounding the anconeus, triceps brachii, and FCU (flexor carpi ulnaris) correlate with higher radiographic severity, providing valuable insights for treatment strategies.