Heikkinen E, Lanning P, Suramo I, Puranen J
Acta Orthop Scand. 1980 Jun;51(3):501-3. doi: 10.3109/17453678008990831.
The correlation between delayed venous drainage from the femoral neck and "head at risk" factors were studied in 47 patients (50 hips) with Perthes' disease. A good correlation was found between markedly disturbed venous drainage and "head at risk" factors. Lateral subluxation of the femoral head and Gage's sign correlated best with pathological venography. Thus a severely disturbed venous return from a hip with Perthes' disease seems to be a poor prognostic sign.