Radiologic anatomic study of the humeral medullary canal.

Hypothesis/background: Patient-specific implants have become an increasingly researched area to improve surgical outcomes. Patient-specific implants have been suggested to provide advantages for better implant alignment and thus improve surgical outcomes. One such area for application is in the use of intramedullary nails for humeral fracture stabilization. However, the anatomy of the canal is not well defined, especially in a larger scale demographic study.

Methods: In this observational cross-sectional study, axial computed tomography scans of 150 humeri were used to measure the cortical thickness and canal width in both coronal and sagittal orientations. Measurements were made at 7 evenly spaced levels along the humerus from the surgical neck to the point immediately superior to the supracondylar ridge. X-rays were used to measure the valgus, recurvatum, and procurvatum angles, along with their associated locations. Demographic data recorded included age, gender, body mass index (BMI), race, and ethnicity.

Results: The mean coronal canal widths decreased inferiorly from the surgical neck to midshaft before increasing to the supracondylar fossa. Mean sagittal widths decreased along the complete course of the canal. The ratio of coronal to sagittal canal widths decreased from 1.09 at level 1 to 0.83 at level 5 before increasing to 1.30 at level 7. Females had significantly smaller canal widths and cortex thicknesses in both the sagittal and coronal planes throughout the course of the canal. There were no significant differences in canal widths among ethnicities. Age was positively correlated with the canal width in the coronal and sagittal orientations but was negatively correlated with cortical thickness in all 7 levels. BMI was not significantly correlated with canal width.

Conclusion/discussion: The data included in this study may be used to determine standard widths and measurements of the humerus. However, there are notable patterns or differences in the shape of the medullary canal of the humerus between subgroups. This study is the first to conduct a larger scale demographic investigation comparing the humeral canal characteristics among sex, ethnicity, age, and BMI. These data may serve as a platform to further investigate the course of the medullary canal.