Humeral bone density losses after shoulder surgery and immobilization.

This study evaluates disuse osteoporosis of the proximal humerus after shoulder surgery and immobilization. This was accomplished by quantifying bone mineral density changes in 22 patients' proximal humeri after 6 weeks of immobilization for soft-tissue shoulder surgery. The bone mineral density of the humeral head, neck, and proximal diaphyseal subregions was determined 1 to 2 weeks before surgery and at 3, 6, and 12 weeks after surgery with dual-energy x-ray absorptiometry. By the sixth postoperative week statistically significant bone mineral density decreases of 6% to 14% were observed in the humeral neck and head subregions, respectively. The changes in these three regions diminished slightly after 6 weeks of remobilization, but the differences were still statistically significant. No significant bone mineral density changes occurred in any subregion or during any time interval in the nonoperated humerus. Our study represents the first report with dual-energy x-ray absorptiometry to quantify bone loss of the proximal humerus of patients after shoulder immobilization. Further long-term study is warranted to determine the clinical significance of this bone loss and to determine whether these losses are partially or fully recoverable.

Correlation of bone mineral density and femoral neck hardness in bovine and human samples.

Bone mineral density (BMD) is a predictor of fracture risk. The purpose of this study was to determine whether a correlation exists between femoral neck BMD and an indicator of mechanical bone strength in human and bovine samples. Human proximal femurs were obtained from seven men and two women undergoing total hip arthroplasty (THA), mean age 60.3 years. Preoperative BMD measurements of the femoral neck were obtained (Lunar DPX). A 3 cm2 area of interest on each excised femoral neck corresponding to the preoperative BMD measurement site was carefully marked and BMD was remeasured postoperatively. Ten excised bovine femoral necks were also measured for BMD. A bicortical core, each cortex 2.8 cm2 in area, containing the center of the area of interest was removed from the human and bovine femoral necks, cut into multiple 7-mm thick, multiple cross-sectional discs, and measured for hardness by indent depth (Rockwell International Hardness Tester, Wilson Mechanical Instruments, New York, NY). In vivo human femoral neck BMD measurements correlated with in vitro BMD measurements (r = 0.99). BMD measurements of human femoral necks were significantly lower than BMD measurements of bovine femoral necks (P < 0.05). Inverse relationships were found between in vivo and in vitro human BMD measurements and indent depth (r = -0.58 and -0.59, respectively). Bovine BMD measurements and indent depth were also inversely related (r = -0.64).(ABSTRACT TRUNCATED AT 250 WORDS)

Bone mineral density changes in the forearm after immobilization.

This study determined the early natural history of disuse osteoporosis in the ulna and radius. Six women and 2 men (mean age, 48.5 years; range, 35-60 years) having surgery on their wrists or hands had bone mineral density determined by single energy xray absorptiometry at 4 sites of the distal radius and ulna before operation, at cast removal (mean, 4.9 weeks after surgery), and after an average of 4.7 weeks of remobilization and hand therapy. A control group of 4 men and 4 women (mean age, 35.6 years; range, 24-46 years) had bone mineral density measurements of both forearms taken initially and again 5 weeks later. The patients had significant loss in bone mineral density at the ulna and distal sites of the forearm after 4.9 weeks of immobilization. Loss of bone mineral density continued at all 4 sites even after 4.7 weeks of remobilization and hand therapy. Bone mineral density increased significantly at the ultradistal radius of the contralateral forearm (which was not operated on) after 4.9 weeks, but this gain was no longer significant after 4.7 weeks of remobilization of the surgically treated forearm, suggesting that increased activity of the nonimmobilized forearm increased bone mineral density at certain sites. No changes in bone mineral density were seen in the control group. Immobilization of the forearm after hand or wrist surgery significantly decreases bone mass in the distal radius and ulna.

Thyrotropin-releasing hormone (TRH) effects on spinal cord neuronal excitability.

TRH is found in terminals in the dorsal, lateral, and ventral horns of the spinal cord and apparently has at least a weak facilitatory effect on excitability of neurons in all these locations. These findings suggest that TRH may facilitate transmission in somatosensory pathways, enhance sympathetic outflow from the spinal cord, and facilitate somatic motoneuron excitability, at least transiently. All studies that have examined TRH effects on spinal neuronal excitability have used exogenously administered TRH. Virtually nothing is known about how spinal neuronal functioning might be affected by TRH released from terminals after activation of TRH-containing cell bodies. The acquisition of this knowledge awaits the development of specific TRH antagonists. Preliminary experiments suggest that TRH may have prolonged facilitatory effects on the excitability of developing or damaged spinal cord neurons. Further studies are necessary to determine how TRH interacts with other neuroactive peptides and monoamines to affect excitability of neurons in the developing, damaged, and normal adult spinal cord.