OTA 2005 Posters

Scientific Poster #54 Basic Science

:Biomechanical Comparison of a Unique Locking Plate versus a Standard Plate for Internal Fixation of Proximal Humerus Fractures in a Cadaveric Model

Stephen M. Walsh, MD (n); Rudy Reindl, MD (n); Lorne Beckman (n); Gregory K. Berry, MD (n); Edward J. Harvey, MD (a-Synthes);

Thomas Steffen, MD, PhD (n);

McGill University Health Centre, Montreal, Quebec, Canada

Purpose: This study was undertaken to compare the biomechanical properties and efficacy of plate fixation with or without locking screws for surgery of two-part proximal humerus fractures. Multiple-plane locking plate and cloverleaf plate designs were tested to determine their ability to maintain fixation on the humeral head.

Methods: Eight matched pairs of cadaver proximal humeri were dissected with 7-mm osteotomy defects created at the surgical neck (OTA classification 11-A3.3), one side repaired with a proximal humerus locking plate and the other with a cloverleaf plate. The rotator cuff musculature was loaded to plate/head construct failure via a servohydraulic testing machine under displacement control to simulate the deforming forces present in vivo.

Results: The average maximum load to failure was greater in proximal humerus locking plates (876 N±204) than in cloverleaf plates (712 N±344); P=0.007.

Conclusion/Significance: Previous biomechanical studies have not taken into account the clinical mode of failure when testing internal fixation modalities for proximal humerus fractures. The current study has reproduced failure into varus by relying on the rotator cuff musculature as the primary deforming force. The locking plate displayed greater holding power on the humeral head in the model tested. Many two-part fractures of the proximal humerus are treated conservatively due to the frequent failure of common internal fixation modalities. This is done with the acceptance of possible malunion or nonunion and potential loss of function. A more reliable method for stable internal fixation is therefore desirable. In the cadaveric, two-part proximal humerus fracture model that was created, the locking plate displayed significantly greater holding power of the humeral head. Clinical relevance is unproven but may be manifested in vivo as improved early range of motion exercises and functional outcome.