An Anatomic Study of Normal Humeral Shaft Bowing

Abstract

Introduction: Although humeral bowing is well known, the character and magnitude of this bow have not been studied. Through the use of paired osteological specimens, we examined the full length of the humerus with the use of a digitizer to analyze the diaphyseal humeral anatomy. Methods: Eight hundred forty-nine cadaveric humeri from an osteological collection were assessed with a digitizer to determine humeral morphology and bowing. Each bow was evaluated for the magnitude, angulation, and location. Multiple regression analysis was done to determine the relationship between sex and race and the measured parameters. Results: The average overall humeral length was 310 ± 20 mm. Six hundred fifty-two humeri (77%) had one bow, and 197 (23%) had two bows. The single-bow apex was located at 71% ± 4% of the full humeral length with a magnitude of 2.0 ± 1.4-mm displacement from the central shaft axis. Double-bow apices were located at 32% ± 4% and 72% ± 3% of the full humeral length with magnitudes of 4.6 ± 2.6 and 2.0 ± 1.8 mm. Single-bowed humeri demonstrated shaft angulation of 2.9° ± 1.7° at the bow apex, whereas double-bowed humeri demonstrated shaft angulations of 4.7° ± 2.2° proximally and 3.3° ± 1.8° distally. Female sex correlated with shorter length and single-bowed humeri. Black specimens correlated with longer length, more proximally located bows and single-bowed humeri. Conclusion: The humeral diaphyseal morphology in a large osteological collection demonstrate that almost one fourth of the specimens had a double bow with notable correlations with sex and race. As the indications for intramedullary fixation of humerus fractures grow, the bow characteristics should be considered in humeral nail placement and future designs. Level of Evidence: V