A BIOMECHANICAL COMPARISON OF INTRAMEDULLARY NAILING SYSTEMS FOR THE HUMERUS

This study evaluated the rotational and bending stability of three int erlocking nail systems in paired cadaveric humeri. The Russell-Taylor Humeral Interlocking Nail, the Seidel Humeral Locking Nail, and the Tr ue-Flex Humeral Nail were mechanically tested in torsion and four-poin t bending. The Russell-Taylor and the Seidel interlocking nails are re amed systems that rely on proximal interlocking screws and distal scre ws or phalanges respectively for rotational stability. However, axilla ry nerve damage may result during proximal screw placement, and these systems exhibit low resistance to rotation. The True-Flex intramedulla ry nail is an unreamed system that relies on cross-sectional geometry to achieve rotational stability. By not relying on interlocking screws for stability, nerve damage associated with the screw placement may b e eliminated. However, the results indicate the cross-sectional geomet ry of the True-Flex nail is not able to provide the same degree of sta tic locking as the Russell-Taylor or Seidel interlocking nails. Humeri implanted with the Russell-Taylor and Seidel nails also had a signifi cantly greater torsional stiffness than the True-Flex nail. As expecte d, humeri implanted with the Russell-Taylor and Seidel nails also had a significantly greater bending stiffness than the True-Flex nail in b oth anterior-posterior and medial-lateral bending.