Three-dimensional measurement of humeral retroversion on a large academic cadaveric database

Background

The 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° to 35° in healthy adults. However, a wide range of individual variability has been reported in literature, with reported values ranging from −6° to 74°. Various imaging modalities including X-rays, computed tomography scans, and magnetic resonance imaging have historically been used to measure this angle, but conventional 2-dimensional technologies may result in inaccuracy and variability in angular measurements. Therefore, recent studies have focused on using 3-dimensional (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.

Methods

We examined the right and left cadaveric humerus from 559 individuals (146 females and 413 males). All of the humeri underwent computed tomography 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 and (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.

Results

The HPNA was found to be 137.7° ± 1.04° for males and 136.34° ± 1.4° for females with a 95% confidence interval. HRA was found to be 39.89° ± 12.77° for males and 38.89° ± 3.15° for females with a 95% confidence interval. Results of analysis of variance revealed that males had a statistically significant larger HRA than females (P < .001).

Conclusion

Our 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.