Objective: To investigate the impact of posttraumatic humeral shaft malalignment on the ability to position the hand in space.
Methods: Two unique models were created: a cadaveric model and a computerized 3-dimensional (3D) model. In the cadaveric model, a midshaft transverse osteotomy of the humerus was created to simulate fracture. The osteotomy was fixed in varying degrees of coronal and sagittal malalignment. The hand's ability to reach 6 different bony landmarks was assessed as a surrogate measure of function. Subsequently, a healthy male volunteer underwent full-body magnetic resonance imaging with subsequent 3D skeletal recreation. A "virtual" midshaft transverse osteotomy was created. The osteotomy was angulated in various degrees of coronal and sagittal malalignment, and the hand's ability to reach the same 6 bony landmarks was measured.
Results: In the cadaveric model, varus angulation was better tolerated than valgus and sagittal deformity. Varus deformity less than 25 degree did not have a negative influence. Valgus angulation of 20 degree resulted in a more severe deficit. Estimated function of the upper extremity was most sensitive to sagittal deformity. These trends were confirmed in the 3D model.
Conclusions: The direction and magnitude of posttraumatic humeral shaft malalignment independently affect the ability to position the hand in space, a surrogate measure of function. Upper extremity function may be more sensitive to posttraumatic humeral shaft malalignment than previously reported. Clinical studies investigating the impact of humeral shaft malalignment on the functional use of the upper extremity are warranted to clinically confirm these findings.
Level of evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.