Bone remodelling in humans is load-driven but not lazy.

Area of Science:

• Orthopedics and Bone Biology
• Biomechanics and Mechanobiology

Background:

• Bone remodelling, the process of bone formation and resorption, is traditionally thought to be influenced by mechanical loading.
• Previous models proposed thresholds and a 'lazy zone' for bone adaptation, primarily based on animal studies, leaving human micro-scale evidence limited.
• Understanding load-adaptive bone remodelling in humans is crucial for developing effective osteoporosis treatments and fracture prevention strategies.

Purpose of the Study:

• To investigate the relationship between physiological tissue loading and microstructural bone remodelling in healthy postmenopausal women.
• To determine if a 'lazy zone' exists in human bone remodelling in response to mechanical loading.
• To provide direct evidence for load-driven bone remodelling at the micro-scale in humans.

Main Methods:

• Utilized novel high-resolution computed tomography (CT) imaging to capture bone microstructural changes.
• Employed advanced computational methods to quantify physiological tissue loading within the bone.
• Correlated identified sites of bone remodelling with calculated tissue loading levels in participants.

Main Results:

• Demonstrated a strong, direct linear correlation between bone remodelling sites and tissue loading in healthy postmenopausal women.
• Found no evidence of a 'lazy zone,' indicating that bone remodelling occurs across a continuous range of loading.
• Provided unbiased, quantitative evidence supporting load-driven bone remodelling in the human skeleton.

Conclusions:

• Human bone remodelling is directly and linearly influenced by mechanical tissue loading, challenging previous threshold-based models.
• The absence of a 'lazy zone' suggests a continuous adaptive response to mechanical stimuli in human bone.
• Findings indicate that bone remodelling mechanisms in humans are similar to those observed in animal models.