Page 34 - Slipped Capital Femoral Epiphysis Pathogenetic and Clinical aspects

Chapter 2
metaphyseal bump on the proximal femur. Usually, FAI is diagnosed on a radiograph. MRI can also be useful in measuring the aspherity of the head and the cam-type deformity by the alpha angle by Nötzli [81, 93]. Also on MRI, cartilage quality appears different in SCFE compared to the controls and, in addition, there is no relationship among clinical symptoms such as pain or hip function impairment [56, 82]. Delayed enhanced magnetic resonance imaging (dGEMRIC) in the mid-term follow-up of SCFE is also sufficiently sensitive to reveal degenerative changes, even in the absence of joint space narrowing that seems to be related to the degree of offset pathology [167].
Intraoperative cartilage damage of the acetabulum in SCFE produced by anterior cam impingement has been observed in 89-100% of cases, even in mild SCFE [62, 127, 165]. In a long-term study, Murgier et al. [89] found a direct relationship with the severity of slip and the existence of FAI. However, in a gait analysis study there was no relationship between the degree of radiographic deformity (Southwick angle, Klein’s line and Nötzi angle) and the severity of kinematic deviations [116]. Castaneda et al. [22] describes an 80% occurrence of FAI after 20 years of follow ups on 122 patients with stable SCFE hips treated with in situ fixation. Although not every radiological FAI will progress to osteoarthritis [45], the questions are which ones will progress, which hip will become symptomatic and which hip may need treatment? There seems to be no linear correlation between offset pathology and joint degeneration in patients with SCFE after intermediate FU (11.1 ± 3.8 years) [166]. The alpha angle correlates most strongly with FAI. Of 49 hips in 36 patients with SCFE (follow up mean 6.1 years) 32% had clinical signs of impingement at skeletal maturity. No correlation with the Southwick angle or Loder´s classification was found [27]. Wall et al. [146] confirmed this, finding no correlation between the Southwick angle and long-term hip function in 32 patients with 38 affected hips. In addition to the above some concluded that timely remodelling after screw fixation of SCFE showed significant improvement of the femoral head neck relationship [5, 26].
In conclusion, FAI is caused by the metapyseal prominence (cam-type lesion) on the femoral head and is most likely the cause of osteoarthritis in later life. The abrasion on the anterior part of the acetabulum caused by the cam-type lesion is observed intraoperatively and on MRI. The question arises whether FAI is correlated with a worse clinical outcome on the long-term.
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