A scintigraphic classification of Legg-Calvé-Perthes disease

Abstract

The onset of Legg-Calvé-Perthes (LCP) disease, avascular necrosis of the proximal femoral epiphysis, frequently is clinically undetectable for months before presentation. This traditional X-ray methods of diagnosis are insensitive for the diagnosis of early LCP as well as nonspecific for the diagnosis of advanced LCP. The X-ray may remain normal for weeks to months after the onset of LCP, and other disorders (steroid osteopathy, epiphyseal dysplasia) simulate the X-ray appearance of LCP during its later stages. Localization of bone-avid radiopharmaceuticals depends principally on bone perfusion and metabolism. Bone scintigraphy is a highly sensitive and specific means of detecting changes in bone perfusion. An understanding of the vascular anatomy of the pediatric hip and its revascularization mechanisms is essential for correlating the scintigraphic findings with the stages of healing in this disorder. Revascularization of bone can occur by recanalization of existing vessels or by neovascularization through the development of new vessels. Recanalization is a rapidly occurring process (minutes to weeks), whereas neovascularization is a prolonged process (months to years). The recanalization process has a characteristic scintigraphic pattern beginning with the visualization of a "lateral column" and is associated with a good prognosis for eventual outcome in LCP. Neovascularization also has a characteristic scintigraphic appearance ("base filling" and "mushrooming"), which is associated with a poorer prognosis because of the prolonged interval required for healing, which places the femoral head at risk for complications such as fracture, collapse, and extrusion. The scintigraphic staging classification presented here, when correlated with a modified Waldenstrom X-ray staging, readily differentiates three mechanisms of revascularization. The A (allright) track scintigraphic pattern represents the recanalization process, a process of short duration and good prognosis. The B (bad) track scintigraphic pattern represents the process of neovascularization, a process of long duration and poorer prognosis. A third process also is described in which complications of the healing process (collapse, extrusion), particularly during the reabsorptive phases of bone reconstitution when the bone is weakened, can cause conversion from track A to track B. Bone scintigraphy is useful in LCP for its ability to detect the disorder in its initial stages, thus allowing earlier treatment, and to provide prognostic information that may affect therapy.