Although rare, endocrine disorders must be considered in every patient with SUFE. Loder [1] identified two types of SUFE; idiopathic type and atypical type where there is an underlying endocrine disorders or other aetiology. He studied the demographics of 433 patients with 612 SUFEs (285 idiopathic, 148 atypical) and found that weight and age were predictors for atypical SUFE and he recommended the age-weight test: the test was defined as negative when age younger than 16 years and weight ≥50th percentile and positive when beyond these boundaries. The probability of a child with a negative test result having an idiopathic SUFE was 93 %, and the probability of a child with a positive test result having an atypical SCFE was 52 %.

Slipped upper femoral epiphysis was traditionally classified as (1) pre-slip: patient has symptoms with no anatomical displacement of the femoral head, (2) acute: there is an abrupt displacement through the proximal physis with symptoms and signs developing over a short period of time (<3 weeks), (3) Chronic: present with pain in the groin, thigh, and knee of more than 3 weeks, often ranging from months to years and (4) acute on chronic: initially, patient has chronic symptoms, but develops acute symptoms as well following a sudden increase in the degree of slip [2, 3].

However, in a classic paper by Loder [4, 5] a new, clinically more relevant classification was introduced. SUFE was classified based on the patient weight-bearing status into stable when patient is able to ambulate and bear their weight and unstable when patient is unable to ambulate with or without crutches. In his series of 55 SUFEs, Loder showed that avascular necrosis (AVN) developed in 47 % of unstable slips but none of stable hips. However, unintentional reduction of the slip occurred in 26 unstable slips (out of 30) and in only 2 of the stable slips (out of 25). [4]. Several other papers confirmed Loder’s findings [6, 7–9].

Grading the severity of the slip is usually based on the radiographic findings. The Southwick angle is the most commonly used [10]. The angle is measured on the lateral view of the both hips by drawing a line perpendicular to a line connecting the posterior and anterior tips of the epiphysis at the physis. The angle between the perpendicular line and the femoral shaft line is called the lateral epiphyseal shaft angle. The Southwick angle is the difference between the lateral epiphyseal shaft angle of the slipped and the non slipped sides (Fig. 6.3). In patients with bilateral involvement, 12° is subtracted from each of the measured lateral epiphyseal angles. Mild slip (grade I) has an angle difference of less than 30°, moderate slip (grade II) has an angle difference of between 30 and 50 degrees and severe slip has a difference of over 50 degrees.

Treatment aim is to prevent progression of the slip without complications. Reduction of the slip to near anatomical position is desirable but this is tempered by the higher risk of AVN and chondrolysis (CL) which are surrogates for bad outcomes. The choice of treatment depends on the type of slip, its severity, and surgical expertise.