UCSF

BACKGROUND: Trapezial pommel, or ulnar osteophyte positioned at the vertex of the saddle-shaped facet, is a consistent structural appearance in osteoarthritis (OA) of the first carpometacarpal. This study investigates its relation to radiographic measures (modified Eaton staging and thumb OA [ThOA] index) and wear patterns (trapezial surface morphology and cartilaginous eburnation). METHODS: In all, 137 whole trapezia were explanted from 116 patients and evaluated for Eaton staging, morphology (saddle, cirque, or dish), and eburnation (degree of cartilaginous effacement) of the articular surface of the trapezium. In total, 131 Roberts views and 126 stress views were reviewed by 2 blinded senior surgeons for ThOA index and pommel size. Statistical analyses included Spearman correlation and linear regression. RESULTS: Standardized pommel size achieved good intrarater reliability (correlation coefficient: 0.80-0.98) and moderate interrater reliability (correlation coefficient: 0.60-0.67). The ThOA index and pommel size were significantly correlated across Roberts (rs = 0.51) and stress views (rs = 0.64). The ThOA index better distinguished between stages compared with pommel size. All the radiographic measures inversely correlated with preserved cartilage and varied across morphologies. Pommel size differed significantly between dish and saddle, and the ThOA index was significantly different between all morphologies when using stress views. CONCLUSIONS: We reliably quantified the pommel feature and demonstrated significant correlations with other radiographic and topologic measures of arthritic disease. If future studies can demonstrate that the pommel is a pathogenic process in ThOA and its correction can curb disease progression, the identification of the pommel feature may help guide targeted intervention.