Measurement of all or part of the cross-sectional area of the tibia-fibula, the portion of the two bones of the lower leg of bipeds or hindlimb of quadrupeds (tibia, the medial and larger bone, and fibula, the lateral and smaller bone) which are fused to form a single bone, e.g. the distal third of the rodent tibia and fibula. The tibia-fibula cross-sectional area is a measurement of the extent of a plane through, that is, perpendicular to the longest axis of the bone.