Spine (Vertebral Column): Surgical Anatomy
The spine has four natural curves: cervical lordosis, thoracic kyphosis, lumbar lordosis, and sacral kyphosis. Intervertebral discs sit between vertebral bodies, acting as shock absorbers and allowing movement. Facet joints permit controlled segmental movement. The spinal cord runs through the vertebral canal from C1 to L1-L2.
Normal Function
Surgical Anatomy perspective: Supports body weight, protects the spinal cord, provides attachment for muscles and ribs, and allows movement. Composed of 33 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4 fused coccygeal.
Lunar Adaptations
On Arrival (First Weeks)
Immediate height increase of 2-5 cm from disc expansion as compressive loading reduces. This can cause back pain from facet joint changes and paraspinal muscle stretching. Postural muscles experience altered loading demands.
6-Month Resident
Height increase stabilizes. Some disc rehydration may cause persistent mild back pain. Paraspinal muscles begin to atrophy from reduced postural demands. Bone resorption in vertebral bodies begins — particularly concerning for trabecular bone in lumbar spine.
Long-Term Resident (2+ Years)
Vertebral BMD loss: significant, particularly in lumbar spine. Disc volume changes partially stabilize. Long-term residents show measurably altered spinal curvature compared to pre-mission imaging. Vertebral compression fractures become a risk at this stage without prophylaxis. Height on Earth return decreases back toward baseline as discs recompress.