Endocrine Abstracts

What do we mean by ‘osteoporosis’? Essentially, bone of reduced mass that is abnormal at a micro-architectural level, with an increased propensity to fracture. The detection of such abnormality is not straight-forward. Any bone will fracture given sufficient force, and it might be thought that restricting further investigation to those who fracture following mild or trivial trauma would be the way forward. Defining what level of trauma should be regarded as ‘mild’ or ‘trivial’ is difficult, however, given the anisotropic nature of bone and the problems of accurate recall in trauma settings.

Clear clinical signs of osteoporosis are vertebral crush fractures and buckle fractures of the distal femur or proximal tibia. These can have particular value in the differentiation of normal from fragile bone in the pre-mobile infant.

Bone densitometry by DXA can measure bone mass, but does not distinguish between bone compartments – cortical vs trabecular bone – and the measurements are strongly influenced by size. In children with chronic disorders who are small, account needs to be taken of this confounding element.

New imaging techniques – volumetric and peripheral high resolution QCT, and MRI are still research approaches that have not entered mainstream clinical practice. Bone biopsy can provide both static and dynamic information on bone, but is site-specific. Microindentation is still a laboratory technique currently; a handheld device used in adults might damage the thinner, less mineralised cortical bone of a child’s tibia. Genetic panels for inherited bone fragility genes are improving diagnostic accuracy.

Current therapeutic interventions focus on anti-resorptive therapies, primarily bisphosphonates, as part of a multidisciplinary approach. Recent advances in the genetics of inherited bone fragility syndromes indicate alternative therapeutic targets in the canonical wnt-signalling pathway. There is still a need to provide clear advice regarding nutrition and exercise in all cases.