A comparative mechanical analysis of plate fixation in a proximal phalangeal fracture model.

A biomechanical study compared the mechanical properties of hand and craniofacial plating systems commonly used in proximal phalangeal fractures. Two plates of each of the various systems were mounted dorsally on a yellow-birch-dowel model of a proximal phalanx after a transverse cut was made in the middle of the section of the dowel, modeling a midshaft transverse osteotomy or fracture. Torsional rigidity, as well as four-point bending rigidity in apex dorsal, lateral and volar directions, was achieved. Failure testing in apex palmar four-point bending was then examined. Between plating systems, torsion varied 1,600% and results of apex palmar testing varied 1,500%. Apex palmar moment-to-failure testing varied 1,000% and represented a 3.5%-38% range of intact proximal phalangeal strength. This also represented 12%-128% of the maximum calculated in vivo bending moments of the proximal phalanx. The wide variation in plate strengths and stiffness raises questions as to the suitability of certain plating systems with regard to early mobilization. Moreover, some plating systems tested were mechanically weaker than the reported strengths of certain Kirschner wire fixation techniques.