Radiology of postnatal skeletal development. IX. Proximal tibia and fibula.

Ossification usually begins in the proximal tibia within the first three months following birth. The initial secondary ossification is centrally located and spherical. Expansion and maturation then changes the ossification center to a more elliptical shape. Variability in this expansion medially and laterally may create marginal irregularity in the first few years, followed by a smooth border by five to six years. Subsequently ossification extends into the tibial spines as a single conical mass which eventually divides into two separate extensions. The physis remains relatively transverse throughout development although contouring occurs under each tibial weight-bearing compartment. Peripheral lappet formation appears within a few months. Anteriorly there is an undulation at the site of the cartilaginous tibial tuberosity. The proximal fibular physis begins as a transverse contour, but changes to one with peripheral lappet formation and multiple undulations. Secondary ossification begins just above the physis and extends proximally into the rest of the physis. However, the fibular styloid, similar to the ulnar styloid, does not ossify until late in skeletal maturation. The proximal fibular physis usually is situated 5 to 10 mm distal to the tibial physis. The tibiofibular joint morphology has considerable morphologic variation, and the joint may communicate with the knee joint.