SLIPPED CAPITAL FEMORAL EPIPHYSIS
Slipped capital femoral epiphysis refers to the displacement of the epiphysis of the femoral head. It occurs most commonly in boys 10 to 17 years of age (average age at onset is 12 years). The initial examination reveals bilateral involvement in about one third of patients, but patients with unilateral involvement have little risk of a subsequent slip on the contralateral side.
The etiology of slipped capital femoral epiphysis is unclear, although various traumatic, inflammatory, and endocrine factors have been proposed. For example, the position of the growth plate of the proximal femur normally changes from horizontal to oblique during preadolescence and adolescence. Thus, the weight increase that occurs during the adolescent growth spurt puts extra strain on the growth plate.
|PHYSICAL EXAMINATION AND CLASSIFICATION OF SLIPPED CAPITAL FEMORAL EPIPHYSIS|
The disorder is often accompanied by rapid growth and is often associated with adiposogenital dystrophy, a condition characterized by obesity and deficient gonadal development. These findings suggest an endocrine basis for the skeletal problem. The major complications of slipped capital femoral epiphysis are avascular necrosis, chondrolysis, and, later, degenerative osteoarthritis.
Clinical Manifestations. The severity and onset of symptoms reflect the three categories of slipped capital femoral epiphysis. Most common is the stable slip (>90% of cases), which causes persistent pain referable to the hip or distal medial thigh, and often as far as the knee. In some patients, the pain is restricted to the area of the vastus medialis muscle and the slip itself is over-looked. Limp, pain, and loss of hip motion are the other usual presenting manifestations. The most important diagnostic finding is the loss of internal rotation (see Plate 2-40). This is easily detected on examination because, as the hip is flexed, it rolls into external rotation and abduction; restricted abduction becomes more pronounced as the slip increases.
An unstable slip (<5% of patients), which occurs after some traumatic event, produces the sudden onset of pain severe enough to prevent weight bearing even with aids. Patients usually report minimal or no previous symptoms.
Patients with a third type of slip first experience a persistent aching in the hip, thigh, or knee and sometimes a limp that is the result of a stable slip. Subsequent trauma—even a minor accident—causes an unstable slip superimposed on the chronic slip. The unstable slip is heralded by sudden, severe pain.
Radiographic Findings. Slipped capital femoral epiphysis produces classic radiographic features. In the earliest stages, there is a widening of the epiphyseal line (representing the growth plate). An anteroposterior radiograph of a normal hip shows the epiphysis of the femoral head projecting above and lateral to the superior border of the femoral neck. A slip must be suspected if a straight (Klein) line drawn up the lateral surface of the femoral neck does not touch the femoral head. Because the anteroposterior view does not always reveal the initial slip, which is usually posterior, a frog-leg radiograph is essential for the diagnosis.
A three-grade classification of slipped capital femoral epiphysis is helpful in the radiographic evaluation (see Plate 2-40). Grade I refers to displacement of the epiphysis up to one third the width of the femoral neck.
Grade II represents a slip greater than one third but less than one half of the width of the neck. Grade III includes slips of greater than one half of the width of the neck.
Treatment. The primary goals of treatment are to stop displacement and keep the proximal femoral deformity to a minimum while maintaining a close to normal range of hip motion and to delay the onset of osteoarthritis.
Stable Slip. Bed rest and urgent in situ fixation is the gold standard for treatment of the stable slip. Placement of a single partially threaded cannulated screw under image intensification is the most advocated and simplest technique with the lowest complication rate. Postoperatively, the patient can bear weight as tolerated with aids as needed for comfort for around 4 to 6 weeks’ time. They can then progress to activities as tolerated. Symptoms usually resolve soon after screw stabilization of the physis.
Radiographic follow-up is necessary to ensure physeal closure (usually between 9 and 12 months postoperatively) and for surveillance of complications (avascular necrosis) and contralateral disease.
Unstable Slip. Urgent in situ fixation of the slip with a single partially threaded screw remains the gold standard of treatment. Forceful attempts at reduction should not be attempted because they may lead to avascular necrosis of the femoral head, which is a greater threat to the hip than incomplete reduction. Urgent surgical dislocation with visualization of the femoral head vasculature has been advocated by some authors to treat the unstable slip. It is much more invasive and technically demanding but can provide near-normalization of the proximal femoral anatomy with less risk of avascular necrosis.
Incorrect placement of pins is the most common error in surgical management. Because of the minor but real risk of segmented avascular necrosis, screws are placed to avoid the weight-bearing area of the femoral head. The best possible construct is a single screw placed across the proximal femoral physis such that the tip of the screw lies in the center of the femoral head in both the anteroposterior and lateral radiograph. Five threads should cross the physis if possible to avoid the epiphysis growing off the physis.
|PIN FIXATION IN SLIPPED CAPITAL FEMORAL EPIPHYSIS|
In a grade III slip, visible on both anteroposterior and frog-leg radiographs, the epiphysis and metaphysis overlap only 25% of the width of the femoral neck, leaving very little room for a screw to cross from the femoral neck to the head. Screw placement through the anterior aspect of the base of the neck and directing them posteromedially allows them to engage the head without leaving the bone (see Plate 2-41). This technique is applicable to slips of any grade. Care must be taken in more severe slips to avoid leaving the head of the screw in a position too anterior that creates impingement on the acetabulum.
Pinning is the initial treatment of choice for all grades of slip. After closure of the growth plate, re-constructive procedures such as intertrochanteric osteotomy may be performed if needed. Osteotomy of the femoral neck is never indicated, because it often leads to avascular necrosis. Osteoplasty may also help late symptoms after physeal closure. This can be accomplished through a surgical dislocation with either a mini-open or arthroscopic approach.
Chondrolysis. Treatment comprises traction, range-of-motion exercises, and use of anti-inflammatory medications, which help decrease joint reaction and increase hip motion. After resolution, range-of-motion exercises and walking with a crutch should be continued for a prolonged period. After the initial loss of articular cartilage, there may be a gradual improvement in the joint space and hip movement may improve slightly. Fortunately, chondrolysis has been seen far less frequently since the advent of intraoperative fluoroscopy, because inadvertent pin or screw penetration of the joint is the most likely cause.