Bone loss of spaceflight

Background

Physiology

• Bone remodeling a continuous process where osteoclasts resorb old bone and osteoblasts form new bone. In microgravity, this balance is disrupted, leading to increased resorption and decreased formation. Weight-bearing bones, such as the hips and spine, are most affected due to the lack of gravitational stress.
• Calcium balance can be calculated as the difference between dietary intake and fecal and urinary excretion

Clinical Features

• In a six month’s duration, total body mineral density loss averages:
  • Pelvis - 12%
  • Lumbar spine - 6%
  • Femoral neck -8%
• There is significant variability with bone loss and most astronauts do no fully preflight density

Differential Diagnosis

Space medicine

• Anemia of spaceflight
• Bone loss of spaceflight
• Contact dermatitis of spaceflight
• Ocular foreign body (microgravity)
• Ebullism syndrome
• Interpersonal conflicts in spaceflight
• Nitrogen tetroxide toxicity
• Hydrazine toxicity
• Pulmonary disorders of spaceflight
• Sleep disorders of spaceflight
• Space adaptation syndrome
• Space dentistry
• Space motion sickness
• Spaceflight headache
• Spaceflight testicular torsion
• Spaceflight urinary retention
• Spaceflight urinary tract infection

Management

Mission countermeasures

• Weighted exercise although often peformed do not inhibit spaceflight associated bone loss
• Pharmaceuticals:
  • Bisphosphonates - inhibit osteoclastic resorption but do not prevent muscle function declines

Postflight bone mineral density rehab

• Depending on mineral loss percentages and affected regions, astronauts undergo progressive weight exercises
  • Spine: deadlifts and squats
  • Calcaneal: Heel raises
  • Femoral trochanter: Foot centered shallow single-leg press
  • Femoral neck: squats
  • Hips: Jump exercises

See Also

• Space medicine