Bone Loss in Astronauts, Cast-wearers, et alPosted by Dorothy on 2/14/05 at 13:58 (169050)
Thinking about astronauts/spines/decompression/bone loss, etc. (on another thread - sorry, Julie - I'm a weaver and a knitter; I guess I like threads....) - I've long known about astronauts' bone loss after being in space (see another post re this). This little section from a longer article also mentions people who've been in a cast and people who've been in bedrest for a time, so I thought people here might want to be reminded of this:
When a limb is immobilized in a cast, when an astronaut experiences zero gravity, or whenever a person lies down, the weight-bearing bones of the body such as those in the spine and leg, are relieved of their burden, a condition known as skeletal unloading.
When skeletal unloading persists for several weeks, bones start to deteriorate: the number of bone cells decreases, movement into the bone of such minerals as calcium and phosphorous slows, and production of bone-cell precursors called osteoprogenitor cells diminishes.
All these changes result in weakened, brittle bones prone to fracture.
While the bones of children may be able to eventually recover from such changes, adult bones have a harder time of it. Studies of Skylab and Salyut-6 long-term space missions (28-184 days) have found that, not only did astronauts on board the craft lose bone density during their missions, but five years later they had failed to recover to pre-launch bone density levels.