An assessment of proximal humerus density with reference to stemless implants.

BACKGROUND

Shoulder arthroplasty humeral components have undergone several generational changes, with systems now offering shorter stems and stemless options. The stemless humeral implants obtain fixation in the trabecular bone of the proximal humerus through elaborate fixation features. To optimize implant design, the regional variations in bone density within the proximal humerus should be determined. As such, the purpose of this computed tomography-based study was to map the regional variations in bone density of the proximal humerus.

METHODS

The trabecular-canal of the proximal humerus was extracted from computed tomography scans of 98 subjects and divided into 13 slices and 5 subsections (central, anterior, posterior, medial, and lateral). The average apparent density (ρ) was then quantified in each subsection of the trabecular-canal.

RESULTS

Slice depth, subsection, and gender were all significant main effects, with additional significant interactions between slice depth, subsection, and osteoarthritic condition. The slices above the resection plane had the greatest ρ, with densities decreasing down the canal. The central subsection had significantly lower ρ than the peripheral sections, and the medial subsection tended to have the highest ρ (P < .001). Furthermore, the ρ of male subjects was significantly greater than that of female subjects (P < .001).

CONCLUSIONS

The apparent density of the proximal humerus' trabecular-canal is nonuniform. This has implications for the design of stemless implants, indicating that implants seeking purchase in higher density bone should take advantage of the peripheral regions of the trabecular-canal within the first 15-20 mm beneath the humeral head resection plane.