SLIPPED CAPITAL FEMORAL EPIPHYSIS (SCFE) is one of the most puzzling and unpredictable conditions treated by orthopaedists today. We do not know what causes it nor can we prevent it. In many cases, it may be undetected for a long time. Some very serious complications may occur and, in some instances, may be related to treatment. Treatment options may not be ideal.

Diagnosis
Any patient between ages ten to sixteen years who presents with a history of limp and pain in the hip, thigh, or knee, should be presumed to have a SCFE. On physical exam, the patient usually walks with an antalgic limp or abductor lurch with the leg externally rotated. There is a diminished range of internal rotation of the hip and forcing this rotation is painful. The diagnosis is verified by an AP and lateral x ray of the femoral head and neck. Early changes include widening and irregularity of the physis, decreased epiphyseal height compared to the opposite side, and failure of a line drawn along the superior surface of the femoral neck to intersect the epiphysis. Displacement is more often seen in the lateral view as the direction of the slip is primarily posterior.

Epidemiology
The incidence of SCFE is about 2/100,000 and it occurs two to three times more frequently in males than females. It is the major cause of a limp between the ages of ten to sixteen years and is most frequently seen in those with delayed skeletal maturation and those with obesity. Over half the patients show weights above the 95th percentile for their age and above the 97th percentile for their height. Blacks are more prone to SCFE than whites.

Etiology
There are many hypotheses regarding the cause of SCFE. Trauma seems to play a role but is it primary or secondary? There certainly appears to be a hormonal basis as this condition occurs most frequently at puberty. It has been shown that estrogen increases the strength of the growth plate and that growth hormone and testosterone weaken the plate. Certain endocrine abnormalities, such as hypothyroidism 7 hyper-parathyroidism, hypogonadal conditions and panhypopituitarism have been associated with SCFE as have other conditions which cause weakening of the epiphyseal plate, such as radiation therapy, renal osteodystrophy, nutritional deficiencies and rickets.

There is an hereditary factor with the incidence far greater than expected if a parent had a SCFE. Mechanical factors such as femoral anteversion, sitting posture, and an oblique physis have been implicated, but not proven. Since synovitis always accompanies SCFE and cannot be explained on a mechanical basis in the presence of a small, early slip, abnormalities of the immune system have been sought without conclusive results. It is reasonable to assume that normal weight bearing factors and athletic activities can cause slips only in those patients who have some unexplained problem or weakness in their epiphyseal plates.

Pathology
The microscopic findings in SCFE are well documented, but no one knows if they are primary (causative) or secondary (as a result of the slip). There is a widening of the physis through the hypertrophic zone with cartilage columns disrupted, clusters of unorganized cartilage, scanty endochondral ossification and decreased collagen fibrils. The slip occurs through this zone.

Natural History
Most slips occur slowly (chronic slips), allowing simultaneous remodeling of the femoral neck. If the slip is minimal, it may go undetected. Symptoms usually do not occur until long after the process has started. There is a high incidence of bilaterality, ranging from 20% to 80% in various studies. This may be present when first seen or occur later. There is increasing evidence linking anatomical abnormality of the femoral head after SCFE to incidence of osteoarthritis of the hip in later life.

Classification
Prognosis and treatment are related to the degree of slip. Radiologically, slips are classified as follows: Clinically, slips are chronic if symptoms have been present for more than three weeks with gradual onset and progression. Acute slips present with a history of sudden onset of severe pain and disability. Minimal, vague complaints often precede the acute episode by several weeks.

Treatment
The goals of treatment are to prevent further slipping, to stimulate early closure of the physis, and to prevent complications. There are three methods proposed to accomplish the goal of preventing further slip. In situ pinning is the most widely used and accepted. It has the benefits of being relatively simple with minimal blood loss and does not require opening the hip joint. However, a second operation is necessary to remove the pins and the risks of avascular necrosis (AVN) and chondrolysis are increased. Optimal pin placement in the center of the epiphysis as seen on the AP and lateral views is mandatory. Pin penetration through the femoral head must be avoided since it is related to a higher incidence of chondrolysis. The lateral epiphyseal artery may be compromised by pin placement in the supero lateral portion of the head leading to AVN and collapse. Thus, it is essential that one pin be placed in central position without head penetration. Single pin fixation is all that is necessary in the majority of patients with SCFE.

Epiphysiodesis is a more difficult and extensive procedure which has the advantage of providing quicker closure of the physis, less risk of head penetration, and eliminates the need for a second operation. Postoperative spica cast immobilization for several weeks (until the physis closes) is necessary. Cast immobilization alone is not reliable and rarely used.

Clinically, slips are chronic if symptoms have been present for more than three weeks with gradual onset and progression. Acute slips present with a history of sudden onset of severe pain and disability. Minimal, vague complaints often precede the acute episode by several weeks.

If there is marked displacement as in a Grade III slip, other treatment may be required. Severe deformity of the femoral head is related to an earlier onset of osteoarthritis and to limitation of motion impairing gait. An acute slip can usually be restored to a position of minimal displacement amenable to pinning in situ following gentle manipulation under anesthesia or a period of traction. This is the instance where two pin placement is indicated to prevent rotation or further slipping of the epiphysis. Severe chronic slips may be restored to more normal anatomy by osteotomy, which may be performed in the physeal area, base of the femoral neck, or in the subtrochanteric region. The closer to the physis, the better is the anatomical restoration, but the higher the risk of AVN and chondrolysis and vice versa. Because these complications are often associated with the early onset of painful degenerative hip disease, many orthopaedists will pin in situ all slips, accepting the risk of later onset of osteoarthritis.

Complications
Avascular necrosis does not occur in untreated chronic slips. It is the most frequent complication following acute slips. The risk of AVN is higher in forceful close reductions, femoral neck osteotomies and valgus pin placement in the femoral head. Most cases of AVN will progress to early symptomatic osteoarthritis, but some ma: become asymptomatic after 12 18 months of non weight bearing and gentle range of motion exercises.

Chondrolysis or acute cartilage necrosis occurs in approximately 7% of SCFE cases and the incidence is increased in blacks, females and those treated for long periods in cast immobilization. There is also an increased incidence in those with severe slips or who have had pin penetration of the femoral head. Treatment consists of prolonged non weight bearing, range of motion exercises and removal of penetrating pins, if present. Approximately one third will restore the joint space and recover full function; one third will become asymptomatic with a diminished range of hip motion; and one third will continue with severe disability requiring some type of surgical salvage procedure.

Summary
SCFE is a relatively common orthopaedic disorder, frequently first seen in the office of a primary care physician. It is easily diagnosed if suspected. Despite the risk of serious complications, SCFE is successfully treated in the vast majority of cases. Knowledge of current literature and operative techniques is important.