Contribution of the olecranon to elbow stability: an in vitro biomechanical study.

Background: The amount of the olecranon that can be removed without substantially affecting the kinematics and stability of the elbow is controversial. The purpose of this study was to determine the effect of serial resections of the olecranon on elbow kinematics and stability.

Methods: Eight fresh, previously frozen cadaver arms were mounted in an in vitro motion simulator, and kinematic data were obtained with use of an electromagnetic tracking system for active and passive motion. Flexion was studied in the varus, valgus, horizontal, and dependent positions. Custom-written three-dimensional computer navigation software was utilized to guide serial resection of the olecranon in 12.5% increments from 0% to 100%. A traditional triceps advancement repair was performed following each resection. Flexion angle, amount of olecranon resection, and active and passive motion measurements were compared.

Results: Serial resection of the olecranon resulted in a significant increase in varus-valgus angulation with the arm in the varus (p < 0.04) and valgus (p = 0.01) orientations. Ulnohumeral rotation significantly increased in the varus (p < 0.001) and valgus (p < 0.007) orientations. Angular (p = 0.02) and rotational (p < 0.001) kinematics were greater with passive compared with active motion. There was no difference in elbow kinematics following olecranon resection with the arm positioned in the horizontal and dependent positions.

Conclusions: Valgus-varus angulation and ulnohumeral rotation progressively increase with sequential excision of up to 75% of the olecranon. Elbow stability is progressively lost with sequential excision, with gross instability noted at resection of > or = 87.5% of the olecranon.