In an effort to determine if severe degrees of SCFE can be successfully treated with in situ pinning an anatomical study was undertaken to determine the relationship between severity of SCFE, the level of the metaphysis in relation to epiphysis on AP x-ray of the hip, the position of entry on the femoral neck and impaction/inclusion.

A dry bone specimen of a young adult without bony pathology was used to create a severe SCFE of varying degrees between 30 and 90 degrees. Standard x-rays AP pelvis and frog lateral were taken to determine the degree of SCFE. A titanium pin marker was inserted in the femoral neck to be centrally directed and placed in the femoral head for each degree of SCFE studied. The position of the pin was inspected as well as assessed with x-rays and CT. Computer model was then used to determine values for younger patients as well as the role that screw diameter will play.

Twelve degrees of SCFE were studied namely from 30 to 90 degrees. Varus and external rotation were simulated as well according to the tables of Rab. The results show that severe SCFE of more than 60 degrees pinning in situ as a method of management is associated with risk. SCFE of 70 degrees is pinned midway up the femoral neck. The screw penetrates the posterior neck and in younger children will penetrate in lesser degrees. Impaction is present in mild degrees of SCFE and demonstrated to contribute to failure of fixation.

The study illustrates that severe SCFE is difficult to pin in situ, associated with inclusion and impaction that will result in coxarthrosis and biomechanically not secure. If the level of the femoral neck metaphysis is proximal or at the same level as the epiphysis, the SCFE is of such a degree that the neck may be reconstructed given the limits of subtrochanteric and intertrochanteric osteotomies.