Background:
Bicipital groove location has been used as a reference for humeral stem orientation in total shoulder arthroplasty to recreate humeral head retroversion. However, anatomic variability has rendered its use for prosthetic orientation problematic in cases of comminuted proximal fractures. We hypothesized that variability in groove rotation is directly related to variability in humeral head retroversion and that by defining the degree of groove rotation, humeral head retroversion can be predicted.
Methods:
Computed tomographic scans (1-mm sections) were obtained along the entire lengths of thirty-four cadaveric humeri, and three-dimensional models were created by using computer-assisted design software. Humeral head retroversion was determined in reference to the transepicondylar axis. The bicipital groove was mapped from proximal to distal, and the rotation of the groove in relationship to the transepicondylar axis was tracked over the entire length of the groove. The overall groove rotation and the rotation of its proximal, intermediate, and distal 15-mm segments were determined.
Results:
The average humeral head retroversion was 21°, and the average angles of groove rotation in relation to the transepicondylar axis for the overall groove and the proximal, intermediate, and distal segments were 65°, 60°, 63°, and 71° of internal rotation relative to the transepicondylar axis, respectively. Pearson correlation coefficients between bicipital groove rotation and humeral head retroversion were ≥0.78 for all segments.
Conclusions:
A previously unknown direct correlation between bicipital groove rotation and humeral head retroversion was found to exist. The ability to predict humeral head retroversion when mapping only the distal third of the groove has potentially important clinical implications because the distal third is often the only portion of the groove remaining in patients with a comminuted proximal humeral fracture. This is particularly relevant with computer-navigated surgery.
Clinical Relevance:
Improved understanding of the anatomic variability of the proximal part of the humerus may ultimately allow improved patient-specific reconstruction after shoulder arthroplasty for fracture.
