Perthes disease is a disease of childhood with a peak incidence from ages 4 to 8 years. Children affected limp and complain about pain in the groin, thigh, or knee. Contractions may develop. In about 15% of cases, metachronous bilateral affection can be seen. Although ischemia may well be the cause of Perthes disease, the etiology to date is not clear. Without timely treatment the disease will follow several distinct stages, potentially leading to deformity, broadening and flattening of the femoral head and of the proximal femur, functional impairment, and premature osteoarthritis. Therefore, early diagnosis and treatment is mandatory. In the healthy child, the femoral epiphysis exhibits the high signal intensity of fatty marrow in T1-weighted sequences.
In the early stages of Perthes disease, there are signal inhomogeneities in the periphery of the femoral head with foci of globular or linear signal loss in the T1-weighted sequences. In T2-weighted sequences, these alterations usually are less conspicuous. Often there is joint effusion and a lateral position of the femoral head (Dillon et al. 1990; Heuck et al. 1988) with reduced size of the ossification centers compared to the contralateral side. Normal bone marrow extending from the metaphysis into the epiphysis is called a metaphyseal spur and considered to indicate regeneration.
Depending on the outcome, there is reconversion to fatty marrow in the epiphysis presumably due to revitalization (Fig. 8.6.7). Already early in the course of the disease a thickening of the cartilage can be found (Jamamillo et al. 1995). Since this occurs predominantly on the medial aspect of the femoral head (and since there may be additional synovitis), it results in loss of containment of the femoral head (Rush et al. 1988).
Joint effusion is evident in T2-weighted sequences and usually is most prominent in the inferomedial aspect of the joint. Band-like low signal intensity abnormalities, i.e., filling defects inferomedially correspond to edematous and fibrous swelling of the joint capsule. The articular cartilage may show increased signal intensity on the T2-weighted sequences.
As MRI has been described to be more sensitive for the diagnosis of Perthes disease than are radiography and scintigraphy, it is recommended when there are clinical complaints but unrevealing radiographs. In this connection, exclusion of Perthes disease is valuable also since it helps to avoid unnecessary followup examinations.