Abstract
BackgroundShort-stem humeral replacements achieve fixation by anchoring to the metaphyseal trabecular bone. Fixing the implant in high-density bone can provide strong fixation and reduce the risk of loosening. However, there is a lack of data mapping the bone density distribution in the proximal humerus. The aim of the study was to investigate the bone density in proximal humerus.MethodsEight computed tomography scans of healthy cadaveric humeri were used to map bone density distribution in the humeral head. The proximal humeral head was divided into 12 slices parallel to the humeral anatomic neck. Each slice was then divided into 4 concentric circles. The slices below the anatomic neck, where short-stem implants have their fixation features, were further divided into radial sectors. The average bone density for each of these regions was calculated, and regions of interest were compared using a repeated-measures analysis of variance with significance set at P < .05.ResultsAverage apparent bone density was found to decrease from proximal to distal regions, with the majority of higher bone density proximal to the anatomic neck of the humerus (P < .05). Below the anatomic neck, bone density increases from central to peripheral regions, where cortical bone eventually occupies the space (P < .05). In distal slices below the anatomic neck, a higher bone density distribution in the medial calcar region was also observed.ConclusionThis study indicates that it is advantageous with respect to implant fixation to preserve some bone above the anatomic neck and epiphyseal plate and to use the denser bone at the periphery.
Highlights
Short-stem humeral replacements achieve fixation by anchoring to the metaphyseal trabecular bone
Considering each proximal to distal slice as a whole, it was found that apparent bone density was at its maximum at slice 1 (0.45 g∙cm−3), was at its minimum at slice 8 (0.20 g∙cm−3), just below the anatomic neck, and increased to 0.24 g∙cm−3 by the most distal slice (Fig. 2)
The peripheral zone, which contains the cortex, had the highest density value in all slices, but a trend for increasing density from zone 1 to 3 was observed. This effect is a result of the continual decrease in bone density in the central zones from proximal to distal in contrast to that of the peripheral zones, where, after decreasing, density starts increasing in regions below the anatomic neck, from slice 8 to 12 (Fig. 3)
Summary
Short-stem humeral replacements achieve fixation by anchoring to the metaphyseal trabecular bone. The proximal humeral head was divided into 12 slices parallel to the humeral anatomic neck. The slices below the anatomic neck, where short-stem implants have their fixation features, were further divided into radial sectors. Results: Average apparent bone density was found to decrease from proximal to distal regions, with the majority of higher bone density proximal to the anatomic neck of the humerus (P < .05). In distal slices below the anatomic neck, a higher bone density distribution in the medial calcar region was observed. Conclusion: This study indicates that it is advantageous with respect to implant fixation to preserve some bone above the anatomic neck and epiphyseal plate and to use the denser bone at the periphery.
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