Slipped capital femoral epiphysis is divided into three types. Acute type is a fracture in proximal femoral growth plate. This type is generally caused by significant trauma. In chronic type, the femoral head slips gradually because of the brittleness of the growth plate. Chronic type is the most common. Slip progresses acutely during the chronic course in acute on chronic type. The most direction of the slip is posteroinferior. The direction has close relation to neck-shaft angle. Wilson [31] reported that 85 % of posteroinferior slip had 140°\\ of neck-shaft angle, According to Inhäuser [32], the head slips posterolateralinferiorly when severe coxa valga such as 160° of neck-shaft angle exists. In such coxa valga, growth plate in the standing position is almost parallel to the floor. Ordinal anteroposterior radiograph of the hip shows as if the head slips posteromedialinferiorly because of the externally rotated femur. Posteroinferior slip is obvious on the radiograph taken without rotation of the femur. Three-dimensional CT scan study supports this fact. Lateral view radiograph is thus essential to measure the slip-angle. Imhäuser’s method is quite useful to measure the angle [32]. The anatomical angle in his method is 10 or less degrees. In his criteria, 30 or less degrees is slight slip, 30–70 is moderate, and 70 or more is severe.

According to Harris [33], growth hormone accelerates the mitosis of the proliferating layer and causes the hypertrophy of the hypertrophied cartilage layer. Growth hormone decreases the yield strength of the growth plate while sexual hormone increases the strength. His report suggests that insufficient sexual hormone or excessive growth hormone may cause the slip. Relative excessive growth hormone can occur when secretion of the growth hormone continues after the growth period.

The growth-plate has three-dimensional unevenness, which has been confirmed by scanning electron microscopic studies. This unevenness gives the growth-plate a multi-directional endurance against compression, strain, and shear stress. The yield strength of a growth-plate depends on the degree of this three-dimensional unevenness [34, 35]. Acute slip is a kind of fracture and thus complete rupture occurs in the growth plate, or Salter-Harris Type II injury occurs. In chronic slip, repetition of stress causes gradual disruption and after that slip occurs when the stress exceeds the yielding strength. External rotation contracture occurs when the slip angle is 30 or more. Gait in externally rotated position due to the pain and bearing weight accelerates the disruption. According to Morscher [36], analyzed the posterior tilting angle and concluded that posterior stress force in internally rotated position is the main cause of slip. In slipped capital femoral epiphysis, motion range of the hip increases in external rotation and decreases in internal rotation. Flexion range is also limited. Drehmann’s phenomenon is obvious in slipped capital femoral epiphysis; as the thigh is flexed, it tends to roll into external rotation and abduction. After progress of the slip, varus deformity of the hip occurs and both Trendelenburg’s phenomenon and gait become obvious.