Significance of synovitis in Legg-Calvé-Perthes disease.

Synovitis is an important feature in Legg-Calvé-Perthes disease (LCPD) with a significant prognostically negative impact on clinical symptoms, cartilage biochemistry, mechanical properties of the cartilage, joint biomechanics, and prognosis toward healing with a congruent, spherical head of femur. Synovitis causes cartilage edema, deterioration of the cartilage's mechanical properties, cartilage hypermetabolism, and, subsequently, cartilage hypertrophy. This sequence of events could explain the clinical course, which consists of cartilage hypertrophy, lateral subluxation, anterolateral deformation of the head, and, subsequently, joint incongruence in prognostically poor cases of LCPD. A factor in the deformation of the hypertrophic cartilage of the epiphysis is decreased range of motion of the hip, because of pain caused by the increase in intracapsular pressure and the subsequent decrease in the "molding" ability of the acetabulum. Synovitis in LCPD causes an increased intracapsular pressure, the magnitude of which may, in some patients, intermittently compromise the blood supply to the proximal femoral epiphysis. Whether synovitis is the consequence of, or precedes, the loss of blood supply and epiphyseal necrosis is not yet established. Significant and persistent synovitis during the entire course of the disease emphasizes the importance of magnetic resonance imaging as the method of choice for the diagnosis and the prognosis, as well as the monitoring of therapy. The prognostically negative effects of synovitis suggest that more therapeutic efforts should be focused on the treatment of synovitis, from a palliative and prognostic point of view.