Table 3. Tonnis and Kuhlmann Classification of AVN of the proximal end of the femur.

Grade	Description
I	Capital ossific nucleus is slightly granular and irregular, self-limiting and without sequelae.
II	The margins of the ossific nucleus are more irregular, greater mottling and granularity than in grade 1 cases; cystic changes may be present within the ossific nucleus. regress with time, sometimes leaving a mild flattening of the head.
III	The ossific nucleus as a whole is fragmented or appears as a flat strip. This grade may develop even before the ossific nucleus has appeared. Deformity resolves if the physis is undamaged.
IV	There is involvement of the physis, leading to serious growth. Irregulaties may be seen along both edges of the physis, though in some cases metaphyseal involvement is not apparent until valgus or varus-type growth disturbances and shortening of the femoral neck have occurred.