Femur (Thigh Bone)
The femur consists of a proximal head, neck, two trochanters (greater and lesser), shaft, and distal condyles. The femoral neck is a critical fracture site in osteoporosis. The proximal femur receives stress from weightbearing and muscle attachments; the femoral neck is subjected to bending forces.
Normal Function
The longest and strongest bone in the body. Supports body weight, provides attachment for major muscle groups of the thigh and hip, and forms the knee joint distally and hip joint proximally.
Lunar Adaptations
On Arrival (First Weeks)
Immediate reduction in mechanical loading from 1/6g reduces bone formation signals. Bone resorption begins to exceed formation. Osteoclast activity increases relative to osteoblast activity.
6-Month Resident
Bone mineral density (BMD) measurably reduced, particularly in the femoral neck and trochanteric region — the weight-bearing zones that receive the greatest mechanical stimulus on Earth. DXA shows progressive trabecular loss.
Long-Term Resident (2+ Years)
Without bisphosphonate therapy, BMD loss of 10-20% from baseline. Microarchitectural changes: cortical thinning, trabecular dropout. Femoral neck T-score may reach osteoporotic range (<-2.5). Fracture risk substantially elevated. Partial recovery occurs on Earth return but architectural changes may persist.