• Stephen Walsh, Rudy Reindl, Edward Harvey, Gregory Berry, Lorne Beckman, and Thomas Steffen.
• McGill University Health Centre, Department of Orthopaedic Surgery, Montreal General Hospital, Room B5.159.5, 1650 Cedar Ave, Montreal, Quebec, Canada H3G 1A4.
• Clin Biomech (Bristol, Avon). 2006 Dec 1;21(10):1027-31.

BackgroundNewer internal fixation devices with a locking mechanism between the plate and the screw have recently been released. The efficacy of these plates in the proximal humerus has yet to be fully described. There is a need to compare the biomechanical properties of 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.MethodsEight matched pairs of cadaveric shoulders with 7-millimeter osteotomy defects at the surgical neck simulating two-part fractures of the proximal humerus were loaded to failure in thirty degrees of glenohumeral abduction. One side was repaired with a proximal humerus locking plate and the other with a cloverleaf plate. The rotator cuff musculature was then loaded via a servo-hydraulic testing machine under displacement control to simulate the deforming forces present in vivo.FindingsThe average maximum load to failure was greater in proximal humerus locking plates than in cloverleaf plates (876 versus 712; P=0.04).InterpretationIn 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.

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