Year: 2000
Type: article
Abstract: To the Editor: Although it is widely recognized that bones respond to the mechanical stimulus of muscle contraction by modifying their mass and architecture, a role for sarcopenia in age-related osteoporosis, has recently been hypothesized.1,2 If the reduction in muscle mass, a major landmark of the frailty syndrome in older persons, is the primary cause of a proportional reduction in bone mass, the ratio between bone and muscle should remain constant because both the nominator and the denominator of the fraction decrease. However, it can be hypothesized that when the bone mass is reduced primarily because of an endocrine-metabolic disorder, the muscle mass remains unaffected and, therefore, the bone/muscle ratio is reduced. Indeed, a distinction between frailty-related osteopenia, in which low bone mass is a physiologic adaptation to sarcopenia from true osteoporosis, a primary bone disorder associated with low bone mass structural fragility and high risk of spontaneous fractures has been proposed but never fully demonstrated.3 Distinguishing between these two syndromes may be important because these two clinical entities may respond to treatments differently. We tested the hypothesis that women affected by true osteoporosis develop a reduction of bone mass that is not paralleled by a comparable reduction in muscle mass. This characteristic could be used to differentiate true osteoporosis from frailty-related osteopenia. Cortical bone and muscle cross-sectional areas at the lower leg were measured by quantitative CT in 23 postmenopausal women with clinically manifest osteoporosis indicated by radiological evidence of multiple osteoporotic fractures (21 with at least one vertebral fracture) and in 23 age-matched postmenopausal controls. Both cortical bone and muscle areas were measured at the junction of the proximal third with the distal two-thirds of the right tibia by means of a latest generation peripheral quantitative computed tomography (XCT 2000, Stratec, Pforzheim, Germany).4 Cortical and muscle areas were assessed using a threshold procedure: cortical area was measured first, and then fat tissue and the total bone area were subtracted sequentially from the whole limb cross-section to yield the muscle area. Although women with osteoporotic fractures had, on average, significantly less bone area than age-matched controls, we found a wide overlap between the two distributions and no significant difference in muscle area (Table 1). We found a strong linear correlation between bone and muscle area in both groups of women (Figure 1). Women with osteoporotic fractures had bone areas lower than expected given their muscle areas. In linear regression analyses fitted separately for the two groups (Figure 1), we found similar slopes (2.98 vs 2.73) but significantly different intercepts (32.29 vs 113.84; P <. 0001). These findings suggest that the reduction in bone mass often observed in women with osteoporotic fractures is attributable to a primary bone-related pathophysiologic process. The bone/muscle ratio may help to identify women with true osteoporosis from those in whom reduction in bone mass is merely the consequence of severe sarcopenia in the context of age- associated frailty and not a primary disturbance of bone metabolism.
Language: English
Subfield: Orthopedics and Sports Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W2054754721