Bone Density versus Bone Quality

Bone quantity refers to the amount of bone tissue, typically measured by bone mineral density (BMD) using techniques like dual-energy X-ray absorptiometry (DXA). While lower BMD is associated with a higher risk of fractures, BMD alone does not fully capture bone strength, which is influenced by both bone quantity and quality.

Bone strength depends on both bone quantity and quality. Assessing bone quality offers a more complete understanding of fracture risk.

Bone quality encompasses several factors, including bone geometry, microarchitectural integrity, remodelling activity, and mineralisation:

• Bone geometry: Larger bone diameter improves resistance to compressive or bending forces, which partly explains why men are less prone to certain fractures, such as forearm fractures, compared to women.
• Microarchitectural integrity: Healthy trabecular bone resembles a well-connected honeycomb structure. In osteoporosis, excessive resorption creates larger, irregular spaces, weakening the bone and increasing fracture risk.
• Bone remodelling: High remodelling activity leaves numerous resorption lacunae on bone surfaces, acting as stress concentrators that weaken the bone structure, making it more prone to fracture.
• Mineralisation: Bone strength also depends on the degree of mineralisation. Bone that is older with lower remodelling rates tends to be more mineralised and stronger.

Quantitative Computed Tomography (QCT), peripheral QCT (pQCT), and high-resolution peripheral QCT (HR-pQCT) are advanced imaging techniques that can provide detailed measurements of bone quality. These techniques allow for the assessment of both cortical and trabecular bone by calculating parameters like bone cross-sectional area (CSA), cortical thickness, and volume. HR-pQCT offers detailed insights into the bone’s macro- and microarchitecture, particularly at the distal radius and tibia.