Synovitis is an important feature in Legg-Calve-Perthes disease (LCPD) with
a significant prognostically negative impact on clinical symptoms, cartila
ge biochemistry, mechanical properties of the cartilage, joint biomechanics
, and prognosis toward healing with a congruent, spherical head of femur. S
ynovitis causes cartilage edema, deterioration of the cartilage's mechanica
l properties, cartilage hypermetabolism, and, subsequently, cartilage hyper
trophy. This sequence of events could explain the clinical course, which co
nsists of cartilage hypertrophy, lateral subluxation, anterolateral deforma
tion of the head, and, subsequently, joint incongruence in prognostically p
oor cases of LCPD. A factor in the deformation of the hypertrophic cartilag
e of the epiphysis is decreased range of motion of the hip, because of pain
caused by the increase in intracapsular pressure and the subsequent decrea
se in the "molding" ability of the acetabulum. Synovitis in LCPD causes an
increased intracapsular pressure, the magnitude of which may, in some patie
nts, intermittently compromise the blood supply to the proximal femoral epi
physis. Whether synovitis is the consequence of, or precedes, the loss of b
lood supply and epiphyseal necrosis is not yet established. Significant and
persistent synovitis during the entire course of the disease emphasizes th
e importance of magnetic resonance imaging as the method of choice for the
diagnosis and the prognosis, as well as the monitoring of therapy. The prog
nostically negative effects of synovitis suggest that more therapeutic effo
rts should be focused on the treatment of synovitis, from a palliative and
prognostic point of view.