Bone mineral loss and recovery after 17 weeks of bed rest

Abstract

The purpose of this work was to determine the rate and extent of bone loss and recovery from long-term disuse and in particular from disuse after exposure to weightlessness. For this purpose, bed rest is used to simulate the reduced stress and strain on the skeleton. This study reports on the bone loss and recovery after 17 weeks of continuous bed rest and 6 months of reambulation in six normal male volunteers. Bone regions measured were the lumbar spine, hip, tibia, forearm, calcaneus, total body, and segmental regions from the total-body scan. The total body, lumbar spine, femoral neck, trochanter, tibia, and calcaneus demonstrated significant loss, p less than 0.05. Expressed as the percentage change from baseline, these were 1.4, 3.9, 3.6, 4.6, 2.2, and 10.4, respectively. Although several areas showed positive slopes during reambulation, only the calcaneus was significant (p less than 0.05), with nearly 100% recovery. Segmental analysis of the total-body scans showed significant loss (p less than 0.05) in the lumbar spine, total spine, pelvis, trunk, and legs. During reambulation, the majority of the regions demonstrated positive slopes, although only the pelvis and trunk were significant (p less than 0.05). Potential redistribution of bone mineral was observed: during bed rest the bone mineral increased in the skull of all subjects. The change in total BMD and calcium from calcium balance were significantly (p less than 0.05) correlated, R = 0.88.

High sodium chloride intake exacerbates immobilization-induced bone resorption and protein losses

“…Calcium excretion was 74% higher. Disregarding a potential additional positive effect of the low-salt diet on bone, immobilization itself led to an increase in bone resorption of 24% (preambulatory phase to intervention with low NaCl) during low salt intake and HDBR, as stated by other authors previously (4,21,37,42,60). Most notably, the effect of the high salt intake in HDBR-an increase in one bone resorption marker (CTX) of 76% (preambulatory to intervention with high NaCl)-seems to have been much more pronounced than the effect of immobilization itself and highlights the importance of diet for immobilized persons, space travelers, and people with a sedentary lifestyle.…”

Evaluation and Management of Vertebral Compression Fractures

“…It has been hypothesized that fractures in vertebral bodies occur because of an increased load on the spine cause by contraction of paraspinal muscles. 16,22,23 It has been suggested that approximately 30% of compression fractures in patients with severe osteoporosis occur while the patient is in bed. 24 27 Patients with multiple compression fractures and progressive loss of vertebral body height may develop excessive thoracic kyphosis and lumbar lordosis.…”

“…In addition, it has been reported that bone mineral density decreases 0.25% to 1.00% per week in patients who are on bed rest. 23,40 To reduce pain and thus promote early mobilization with conservative management, appropriate analgesics should be prescribed. Narcotics should be reserved for patients who receive inadequate relief from regular analgesics.…”

“…These procedures, however, are challenging because it is difficult to achieve adequate fixation in osteoporotic bone. 23,25 Percutaneous vertebroplasty is one of the favored methods of treating painful VCFs. 25 It encompasses augmentation of the vertebral body by injection of polymethylmethacrylate (PMMA).…”

Decreased bone turnover with balanced resorption and formation prevent cortical bone loss during disuse (hibernation) in grizzly bears (Ursus arctos horribilis)

“…When lost bone can be completely recovered following disuse, the required remobilization time is 2-3 times longer than the length of the disuse period because the rate of bone loss during inactivity is 2-3 times greater than the rate of bone recovery during remobilization [14,17,18]. However, bears in northern climates experience annual periods of disuse (hibernation) and activity that are approximately equal in length (6 months), yet black bear (Ursus americanus) cortical bone does not suffer any detrimental mechanical or structural consequences with age despite these relatively short recovery periods [19][20][21][22].…”