A biomechanical comparison of intramedullary nailing systems for the humerus

This study evaluated the rotational and bending stability of three interlocking nail systems in paired cadaveric humeri. The Russell-Taylor Humeral Interlocking Nail, the Seidel Humeral Locking Nail, and the True-Flex Humeral Nail were mechanically tested in torsion and four-point bending. The Russell-Taylor and the Seidel interlocking nails are reamed systems that rely on proximal interlocking screws and distal screws or phalanges respectively for rotational stability. However, axillary nerve damage may result during proximal screw placement, and these systems exhibit low resistance to rotation. The True-Flex intramedullary 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 be eliminated. However, the results indicate the cross-sectional geometry of the True-Flex nail is not able to provide the same degree of static locking as the Russell-Taylor or Seidel interlocking nails. Humeri implanted with the Russell-Taylor and Seidel nails also had a significantly greater torsional stiffness than the True-Flex nail. As expected, humeri implanted with the Russell-Taylor and Seidel nails also had a significantly greater bending stiffness than the True-Flex nail in both anterior-posterior and medial-lateral bending.