Long Bone Measurements

Various radiological measurements have been described in the long bones of the upper and lower limbs. These help in the diagnosis of diseased states but are also important as a useful tool in planning surgical treatment and subsequent follow-up of such conditions. In certain conditions, radiological measurements are used to assess disease progression (e.g. infantile tibia vara vs. physiological bowing). These measurements may be related to an individual long bone or the alignment of the bones and joints in the entire limb. Within individual bones, there may be an abnormality in the length of the bone (e.g. ulnar variance), angular deformity in a sagittal or coronal plane at various levels (e.g. post-traumatic deformity) or an abnormality in the anatomical twist around the longitudinal axis (e.g. femoral and tibial torsion). Deformity in individual bones or the joint surfaces associated with soft tissue laxity may result in abnormal alignment of the entire limb. This results in abnormal biomechanics and disproportionate transmission of load within the weight bearing joints. It is widely accepted that a malaligned state may lead to degenerative changes in the adjacent joints. Indeed the most important long-term consequence of a deformity in a long bone or malalignment in the entire limb is the early development of degenerative arthritis. Within the paediatric population, there is an increased potential of remodelling with growth, and this factor should be kept in mind whilst planning treatment. There may be spontaneous correction of angulation with growth and a larger angular deformity may be tolerated as compared to adults. In terms of length discrepancies, one should also keep in mind the predicted length at skeletal maturity. It is therefore important to be aware of the technique of performing these measurements and to have knowledge of the normal reference values.