Altered Glenohumeral Biomechanics in Proximal Humeral Fracture Malunion.
- 2021
Available online from MWHC library: Oct 1993 - present, Available in print through MWHC library: 1999 - present
DISCUSSION: Varus and antecurvatum proximal humerus deformities as small as 15degree were associated with notable alterations in glenohumeral joint mechanics. With valgus and retrocurvatum deformity, statistically significant joint alterations occurred only at higher deformity levels. Copyright (c) 2020 by the American Academy of Orthopaedic Surgeons. INTRODUCTION: There is little biomechanical evidence to support the traditional guideline that 45degree represents acceptable proximal humerus deformity. We evaluated glenohumeral contact pressure (GP) and area, subacromial contact pressure, and joint abduction to assess biomechanical changes with different proximal humerus deformities. METHODS: Fifteen fresh-frozen cadaver shoulders were used. Intact specimens were tested on a custom dynamic shoulder frame. Subsequently, a surgical neck fracture was made in each specimen and fixed using a custom dual hinge plate for fixation of 15degree, 30degree, and 45degree deformities in varus, valgus, antecurvatum, retrocurvatum, and combined varus-antecurvatum and valgus-retrocurvatum. Specimens were then retested. RESULTS: Compared with the intact state, GP was markedly lower with all levels of varus and varus-antecurvatum deformity. Valgus and combined valgus-retrocurvatum deformity of 45degree led to notable increases in GP compared with the intact state. Varus deformities of 30degree and 45degree caused significant increases in subacromial pressures and limited abduction markedly from 60degree to 54.2degree and 44.6degree (P < 0.001).