Effect of femur position on the angular measurement of slipped capital femoral epiphysis

A femur model was used to simulate a slipped capital femoral epiphysis (SCF E). Wedges were inserted into a cut in the femoral neck to create SCFEs of 25, 50, and 75 degrees. The effects of femur position on the angular measur ement of SCFE were studied by taking radiographs of the SCFE at preselected positions of rotation and abduction, which were ensured by a holding devic e. The views selected were the cross table lateral (CTL), Billing lateral, and frog lateral (FL) projections. FL views were obtained at 22.5, 45, and 67.5 degrees of abduction. The rotational positions were 20 degrees interna l, neutral, and 15, 30, 45, and 60 degrees external. Slip angles were measu red from these radiographs. The CTL and FL projections accurately portrayed any severity of an SCFE at all positions except for 35 and 60 degrees of e xternal rotation. The Billing view falsely portrayed a severe SCFE at all p ositions of rotation. The most accurate representation of an SCFE is seen o n either the CTL or FL view when the external rotation of the femur does no t exceed 30 degrees.