A New Classification System for Forearm Deformities Caused by Hereditary Multiple Osteochondromas.

Purpose: The objective of this study was to evaluate the Masada and Jo classifications for clinical use in patients with forearm deformity caused by hereditary multiple osteochondroma and propose a new classification system that is all-inclusive and can guide clinical management.

Methods: A retrospective review of 275 forearms was performed. A split-sample approach was used, where 138 forearms were analyzed to create a new classification, which was then validated on the remaining 137 forearms. Radiographs were reviewed to determine the number and location of osteochondromas and the presence of radial head dislocation (RHD) and to measure radiographic parameters. Multivariable logistic regression analysis was performed to identify radiological parameters associated with RHD.

Results: According to the Masada and Jo classifications, 95 of 275 forearms (34.5%) were unclassifiable. Analyses of the split group (n = 138) revealed 42 forearms with RHD. All these had distal ulna lesions, qualifying as the greatest associated factor for RHD. Further subgroup multivariable logistic regression analysis of forearms with distal ulna lesions identified radiological parameter proportional ulna length as a statistically significant association of RHD, qualifying as "at-risk" criteria. The area under the receiver operating characteristic curve for proportional ulna length was 0.89, with a receiver operating characteristic-derived ideal value of ≤ 0.95 (sensitivity 0.86 and specificity 0.86).

Conclusions: We proposed a new classification system stratified into three groups-high, moderate, and low-risk of RHD-based on the identified factors associated with RHD. Type 1 comprises forearms with distal ulna osteochondromas-subdivided into type 1A (high-risk), where forearms meet the at-risk criteria for RHD and type 1B (moderate-risk), where forearms do not meet the at-risk criteria. Type 2 (low-risk) comprises forearms without distal ulna osteochondromas.

Clinical Relevance: Our classification system addresses the limitations of existing classifications by risk stratifying forearms into three groups-high, moderate, and low-risk of RHD.