Bone mineral density around cementless short stems after reverse shoulder arthroplasty: changes over time and its relationship to stem positioning.

BACKGROUND

There are numerous reports of bone adaptation observed on plain radiography studies after the use of cementless short stems in reverse shoulder arthroplasty. However, reports on changes in bone mineral density (BMD) around the stem using dual-energy X-ray absorptiometry (DEXA) are prominently absent. In the present study, we measured BMD around the stem using DEXA and investigated changes over time from postoperative year 1 to year 2. Additionally, the relationship between BMD changes, filling ratio, and stem alignment was examined.

METHODS

Forty-seven patients with short cementless stems who could be assessed via DEXA at 1-2 years postoperatively were included. After dividing the zones around the stem into 5, the BMD in each zone was measured, in addition to BMD changes and amount of change from postoperative year 1 to year 2. The relationship between filling ratio and stem alignment on postoperative plain radiography was assessed.

RESULTS

A significant decrease in BMD in zone 3 was observed between postoperative year 1 and year 2 ( = .02). Regarding filling ratio and stem alignment, a negative correlation between valgus stem alignment and BMD change observed in zone 1 (r = -0.470,  < .01). In addition, stem valgus greater than 6° correlated with a significant decrease in BMD in zone 1. ( = .01). No significant differences were found in the other zones. Furthermore, there was no correlation between filling ratio and BMD change.

CONCLUSION

In reverse shoulder arthroplasty cementless short stems, changes that that occurred between postoperative year 1 to year 2 demonstrated a decrease in BMD in zone 3. In addition, a decrease in BMD in zone 1 was observed with a stem alignment of valgus 6° or higher, suggesting that stem alignment within valgus 6° is required to prevent a decrease in BMD.