Altered Glenohumeral Biomechanics in Proximal Humeral Fractu
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There is little biomechanical evidence to support the traditional guideline that 45° represents acceptable proximal humerus deformity. Evaluation was done on glenohumeral contact pressure (GP) and area, subacromial contact pressure, and joint abduction to assess biomechanical changes with different proximal humerus deformities.

15 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 15°, 30°, and 45° 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 45° led to notable increases in GP compared with the intact state. -Varus deformities of 30° and 45° caused significant increases in subacromial pressures and limited abduction markedly from 60° to 54.2° and 44.6°.

It was observed that varus and antecurvatum proximal humerus deformities as small as 15° were associated with notable alterations in glenohumeral joint mechanics. With valgus and retrocurvatum deformity, statistically significant joint alterations occurred only at higher deformity levels.

Source: https://journals.lww.com/jaaos/Abstract/9900/Altered_Glenohumeral_Biomechanics_in_Proximal.71.aspx
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