Bone loss in the lower leg during 35 days of bed rest is
predominantly from the cortical compartment
Rittweger J., Šimunič B., Bilancio G., De Santo N., Cirillo M., Biolo G., Pišot R., Eiken O., Mekjavić I., Narici M., Narici M., Bone loss in the lower leg during 35 days of bed rest is
predominantly from the cortical compartment, Bone, 2009, 44, 4, str. 612-618.
Abstract (English) Immobilization-induced bone loss is usually
greater in the epiphyses than in the diaphyses. The larger fraction of
trabecular bone in the epiphyses than in the diaphyses offers an intuitive
explanation to account for this phenomenon. However, recent evidence
contradicts this notion and suggests that immobilization-induced bone loss
from the distal tibia epiphysis is mainly from the cortical compartment.
The aim of this study was to establish whether this pattern of bone loss
was a general rule during immobilization. Wemonitored various skeletal
sites with different tissue composition during 5 weeks of immobilization.
Ten healthy male volunteers with mean age of 24.3 years (SD 2.6 years)
underwent strict horizontal bed rest. Bone scans were obtained during
baseline data collection, at the end of bed rest and after 14 days of
recovery by peripheral Quantitative Computed Tomography (pQCT). Sectional
images were obtained from the distal tibia epiphysis (at 4% of the tibia's
length), from the diaphysis (at 38%), from the proximal metaphysis (at 93%)
and from the proximal epiphysis (at 98%), as well as from the distal femur
epiphysis (at 4% of the femur's length) and from the patella. Relative bone
losses were largest at the patella, where they amounted to - 3.2% (SD 1.8%,
p < 0.001) of the baseline values, and smallest at the tibia diaphysis,
where they amounted to - 0.7% (SD 1.0%, p = 0.019). The relative losses
were generally larger from cortical than from trabecular compartments (p =
0.004), and whilst all skeletal sites depicted such cortical losses,
substantial trabecular losses were found only from the proximal tibia
epiphysis. Results confirm that the differential losses from the various
skeletal sites cannot be explained on the basis of trabecular vs. cortical
tissue composition differences, but that endocortical circumference can
account for the different amounts of bone loss in the tibia. The present
study therefore supports the suggestion of the subendocortical layer as a
transitional zone, which can readily be transformed into trabecular bone in
response to immobilization. The latter will lead to cortical thinning, a
factor that has been associated with the risk of fracture and with
osteoarthritis.
