13.19 Slipped capital femoral epiphysis

Slipped capital femoral epiphysis (SCFE) is a condition that occurs during a period of rapid growth in adolescence, when shear forces, particularly in the obese individual, increase across the proximal femoral growth plate resulting in a posteromedial displacement of the epiphysis relative to the femoral metaphysis.

Delay in diagnosis remains the major problem because of the failure to associate knee and thigh pain in the adolescent with hip pathology. AP pelvic radiographs are easily misinterpreted in the early stages.

Most slips can be treated by cannulated single screw stabilization. There is continuing debate about the necessity for prophylactic contralateral fixation and the management of the acute unstable slip.

The reported incidence varies from 1–7 per 100 000. Males are affected three times more than females. Bilateral slips occur in approximately 20% of cases.

The typical phenotype of obesity and possible hypogonadism implicates an endocrine cause. There is a clear association with hypothyroidism and with growth hormone treatment and pathological values of follicle stimulating hormone, luteinizing hormone, and testosterone have been identified. Cases are also seen in association with metabolic bone disease such as renal rickets and in survivors of childhood malignancy who had received chemo- or radiotherapy. Perhaps more worryingly, recent evidence has highlighted a close correlation between rising childhood obesity and increasing incidence of SCFE. There is also a link between SCFE and femoral retroversion.

Ultrastructural studies of SCFE growth plates have shown diminished cellularity and marked distortion of the architecture in both the proliferative and hypertrophic zones. The diminished cell number has been shown to be due to abnormal frequency and distribution of chondrocytes undergoing apoptosis. In this context the concept of ‘preslip’ has been confirmed by magnetic resonance imaging.

There are various classifications related to onset of symptoms (temporal), ability to weight bear (functional), and extent of epiphyseal displacement relative to the neck (morphological).

An acute SCFE is one that occurs in a patient with prodromal symptoms of 3 weeks or less followed by an acute event often after minor trauma, considered to be too insignificant to cause a type I physeal fracture.

The chronic SCFE is the more common presentation. There is usually several months’ history of vague groin, thigh, and knee pain with increasing limp and out-toeing gait. Radiographs reveal signs of remodelling.

In the acute-on-chronic slip, there has been a history of prodromal symptoms for more than 3 weeks followed by a sudden exacerbation of pain.

The concept of stability popularized by Loder relates to the patient’s ability to weight bear after the acute event. Both acute and acute-on-chronic slips may be categorized further in this way. Patients with an unstable slip are in such severe pain that they are unable to weight bear.

The degree of displacement is assessed on radiographs. Lines are drawn corresponding to the axis of the femoral shaft and the base of the capital epiphysis. It is not necessary to obtain a computed tomography scan. A grade I slip is 0–30°, grade II 30–60° and grade III 60–90+°.

The symptoms and physical findings vary according to the type of slip. In a stable chronic SCFE the presenting complaint is usually of groin pain and/or vague anteromedial thigh and knee pain. This localization of the pain continues to cause diagnostic delay and confusion. The relationship between delay in diagnosis and increased slip severity has been confirmed and there have been calls for a more robust educational strategy, particularly for allied health professionals.

The early physical signs are perhaps subtle, with loss of internal rotation of the hip progressing to limb shortening and external rotation deformity. Acute unstable or acute-on-chronic slips will usually present with sudden pain and inability to bear weight.

The standard radiographs of an anteroposterior (AP) pelvis and lateral views of the hips are usually sufficient for diagnosis. The earliest sign is a widening of the physis (pre-slip). The diagnosis may be difficult to detect on the AP view. A line drawn parallel to the superior femoral neck (Klein’s line) will intersect the lateral portion of the epiphysis but not in an early slip (Trethowan’s sign). Steel described the ‘metaphyseal blanch sign’ that corresponds to increased density caused by overlapping of the femoral head and displaced epiphysis (Figure 13.19.1 and Box 13.19.2). An ultrasound scan may demonstrate an effusion and confirm an early/mild slip.

The primary aims of treatment are to stabilize the epiphysis and prevent further slip. Prevention of avascular necrosis (AVN) and chondrolysis are secondary aims. A treatment algorithm is presented in Figure 13.19.2 (and see Figure 13.19.1).

The majority of slips are chronic and can be treated with single cannulated screw fixation. The screw thread should traverse the physis into the centre of the epiphysis. Recent biomechanical studies have indicated that there should be equal distribution of threads across the physis for optimum stability. Joint penetration should be avoided to reduce the risk of chondrolysis. It is not necessary to employ a reverse cutting thread to facilitate screw removal, since there is now a consensus that screws should not be removed because of the associated morbidity.

Single screw fixation is reliable but in the more severely displaced slips, knowledge of the pathoanatomy is required for accurate anterior placement of the screw. Remodelling will occur and often the external rotation deformity will resolve but there is concern among some about long-term femoroacetabular impingement.

In younger patients with endocrine disease, smooth pins may be inserted and subsequently removed if it is anticipated that healing will occur with endocrine replacement therapy, for example in hypothyroidism.

The primary treatment of the acute unstable slip remains controversial mainly because of the incidence of AVN as a consequence of the injury to the epiphyseal blood supply. Many support the proposition that the displaced epiphysis should be gently repositioned on the operating table and stabilized with single screw fixation (some authors believe two point fixation with two screws is preferable). One study performed such a manoeuvre in acute slips within the first 24h and no cases of AVN were encountered whilst another report documented a 7% incidence of AVN for reductions less than 24h from presentation, but 20% if treatment was delayed. This author advocates a period of traction for 3 weeks in those acute slips that present after 24h before any subsequent intervention followed by a femoral neck osteotomy or screw in situ if possible.

In acute on-chronic slips no attempt should be made to reposition the epiphysis beyond its acute displacement and full correction should be avoided. In situ screw fixation is used.

There are protagonists who believe that anatomical realignment of the capital epiphysis should be attempted in severe slips in order to improve function and to reduce the risk of later osteoarthritis. They therefore advocate osteotomy or open reduction in acute slips to correct the deformity with single or double screw stabilization.

Reference has already been made to the capacity for femoral neck remodelling but recent studies have drawn attention to femoroacetabular impingement as a cause of early structural abnormalities in the acetabular rim and late osteoarthritis.

Some surgeons advocate surgical dislocation of the hip and osteochondroplasty at the femoral neck junction, even for minor slips but conventionally, neck osteotomies at the level of the physis are performed. The cuneiform neck osteotomy of Fish results in complete excision of the physis from the metaphysis and epiphysis allowing bone on bone apposition and healing. The AVN rate is variable (4.5–35%). Chondrolysis has an incidence of 10–30%. The high complication rate leads many to advise primary screw stabilization and a subsequent osteotomy to correct deformity if necessary (vide infra).

It remains debatable whether the contralateral normal hip should undergo prophylactic screw fixation. The development of AVN or chondrolysis in such a hip is a devastating complication. A systematic review of the literature identified the probability of contralateral SCFE occurring as 19%. They concluded that the overall optimum decision path is observation. When the probability of contralateral slip exceeds 27%, for example in endocrinopathies, or when reliable follow-up is not feasible, screw stabilization is favoured.

Delayed bone age does not appear to be a predictor for a contralateral slip.

Residual deformity can be managed by subsequent intertrochanteric osteotomy. Southwick described a triplane osteotomy at the level of the lesser trochanter. It is technically difficult and corrects the deformity a long distance from the site of the deformity. The osteotomy described by Dunn (and that by Fish) is performed at the site of deformity but the complication rate is higher. Such osteotomies do increase hip range of movement but may not provide improvement in functional outcome. Furthermore the influence of such osteotomies on late onset osteoarthritis, and the ease with which subsequent arthroplasties can be performed, remains uncertain.

AVN is the most common complication but radiological changes may take 18 months to become evident. The acute unstable slip has a relatively high incidence (up to 35%). The risk factors for AVN include open reduction, femoral neck osteotomies, manipulation of stable slips, forcible manipulation (late) of unstable hips and Down syndrome. Many hips with AVN will require early arthroplasty.

Chondrolysis is defined as narrowing of greater than 50% of the joint space. Hip spica cast treatment increases the incidence. The aetiology is not exactly known but appears to be related to immune system activation. Historically, there may be an association with joint penetration of implants. Maximum joint space narrowing occurs in the first year and improvement in up to 50% of cases can occur for up to 3 years. Some hips will require joint replacement.