Three-Dimensional Measurement of Humeral Retroversion on a Large Academic Cadaveric Database

Abstract

BackgroundThe Humeral Retroversion Angle (HRA) has been described in the literature as the orientation of the humeral head compared with the epicondylar axis of the distal humerus. HRA is a crucial measurement for designing shoulder prostheses and surgical technique, and is often noted to range from 25-35 degrees in healthy adults. However, a wide range of individual variability has been reported in literature, with reported values ranging from -6 and 74 degrees. Various imaging modalities including, X-rays, CT scans and MRI have historically been used to measure this angle, but conventional 2D technologies may result in inaccuracy and variability in angular measurements. Therefore, recent studies have focused on using 3D modalities to measure HRA. These studies have shown promising results regarding accuracy and clinical significance, although most have only included a small number of subjects and have not procured conclusive findings. This study aims to measure the HRA in a large sample of subjects using 3D imaging to establish measurements for the general population. MethodsWe examined the right and left cadaveric humerus from 559 individuals (146 females, 413 males). All of the humeri underwent CT scan and surface models generated. 3D landmarks were automatically calculated on each 3D bone using custom written software in C++. Those landmarks were used to calculate 1) HRA as the angle between the epicondylar axis and the humeral neck axis. 2) Humeral Proximal Neck Angle (HPNA) as the angle between the humeral neck axis and the anatomical axis. Descriptive statistics of both HRA and HPNA was analyzed using JMP Pro statistical software version 15.2.0. ResultsThe HPNA was found to be 137.7⁰ ± 1.04⁰ for males and 136.34⁰ ± 1.4⁰ for females with a 95% confidence interval. HRA was found to be 39.89 ⁰ ± 12.77⁰ for males and 38.89 ⁰ ± 3.15⁰ for females with a 95% confidence interval. Results of ANOVA revealed that males had a statistically significant larger HRA than females (p<0.001). ConclusionOur study suggests using a standardized measurement for the HRA, which we believe may improve operative outcomes. However, future prospective trials are required to validate our results in a clinical setting.