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Unni G. Narayanan, M.D.
Assistant Professor, Division of Orthopaedics,
The Hospital for Sick Children, University of Toronto
Toronto, ON Introduction
Slipped capital femoral epiphysis (SCFE) is the most common disorder of the hip in adolescents. It is characterized by the posterior displacement of the proximal femoral epiphysis on the femoral neck (Figure 1). Obesity, mechanical factors (e.g., reduced anteversion), minor trauma, endocrinopathies and inflammatory factors have been implicated in the etiology of this condition. It is more common in the black population.
 | | Figure 1. The epiphysis "slips" posteriorly, forcing the hip into external rotation and creates an apparent varus deformity. | Presentation & Classification
SCFE most commonly presents as intermittent pain in the anterior hip or groin of insidious onset. It is associated with an antalgic gait and limitation of internal rotation of the affected hip. The pain may be referred to the medial thigh or knee, which sometimes leads to missed diagnosis of SCFE. Ten percent of the time, the presentation may be acute with more severe pain and limited ability to bear weight. The affected limb is externally rotated and may be shortened. In severe slips, passive flexion of the affected hip forces it into external rotation.
The classification of SCFE based on the duration of symptoms has been replaced with a prognostically more useful classification system based on presumed slip stability1. A slip is labeled unstable if the patient is in sufficient discomfort to prevent walking even with crutches, whereas the patient is able to walk with a stable slip. Diagnosis is by anteroposterior and frog-leg lateral (cross-table lateral for "unstable" presentation) radiographs of both hips, since up to 40% of patients have bilateral hip involvement, half of which present concurrently2. The severity of the slip, based on the magnitude of displacement or slip angle, also has prognostic significance.
Goals of Treatment
SCFE is associated with late osteoarthritis related to slip seve-rity and deformity3. Unstable and/or severely displaced slips are more likely to result in avascular necrosis, femoral head collapse and accelerated secondary osteoarthritis. The goals of treatment, therefore, are to arrest slip progression by obtaining premature epiphyseodesis in order to prevent significant deformity, and to avoid osteonecrosis. This can best be accomplished by in situ fixation of the femoral epiphysis with a single cannulated screw placed across the physis along the central axis of the femoral head. Treatment is instituted urgently, pending which further slip is prevented with protected weight-bearing or bed rest.
 |  | | Figure 2. Single crew across the centre of the physis and perpendicular to it. Note the bone entry site is in the anterior part of the femoral neck. | Technique
The patient is positioned on a fracture table with the affected limb in neutral rotation without a deliberate attempt at redu-cing the slip. The c-arm is positioned between the affected limb and the flexed and abducted contralateral limb to obtain antero-posterior and cross-table lateral views of the proximal femur. The pin entry site is determined by the intersection of two lines drawn along a guide pin laid on the skin, corresponding to the central axis of the femoral head as determined from AP and lateral views of the hip4. A guide pin is advanced percutaneously following the plane of both lines, with bone entry point on the neck of the femur above the level of the lesser trochanter to avoid a stress riser. The more severe the slip, the more posterior is the epiphysial displacement, necessitating a more anterior entry point on the femoral neck. The pin should cross the centre of the physis perpendicular to it and into the centre of the epiphysis (Figure 2). A partially threaded cannulated screw between 6.5 and 7.5 mm is advanced over the guide pin until there are at least 3-4 threads on either side of the physis. The tip of the screw should remain about 5 mm from the subchondral surface, verified by the so-called "approach-withdraw" test5. Under the image intensifier, the hip is rotated in varying degrees of flexion to confirm that the tip of the screw does not breach the articular surface. Following these guidelines, the risk of unrecognized joint penetration and subsequent chondrolysis, and the rates of iatrogenic osteonecrosis have been reduced dramatically6. The use of two screws may be indicated in some unstable slips for stronger fixation.
Postoperative Surveillance
Protected weight-bearing with crutches is usually recommended for six weeks. Clinical and radiographic follow-up of both hips is typically continued for 18-24 months. Physeal closure may take as long as 12-14 months on the affected side. The vast majority of non-concurrent contralateral slips occur within 18 months of the initial presentation2. Removal of the screw is unnecessary and indeed may be associated with complications. Removal of the screw may be indicated in the presence of osteonecrosis and impending femoral head collapse to avoid intra-articular penetration of the screw tip. Chondrolysis is characterized by hip pain and progressive loss of motion associated with narrowing of the hip joint. Management includes protected weight-bearing, NSAIDs, and physiotherapy for active and passive motion.
Controversies
Should unstable slips be reduced or fixed in situ?
The rationale for reduction is to prevent significant deformity and late osteoarthritis. It is unclear whether osteonecrosis is related to the reduction or the instability and/or severity of the slip in the first place. Although some have advocated open reduction to correct deformity, the most common practice in North America remains "gentle" reduction by positioning the limb in neutral rotation and in situ fixation. The residual deformity is addressed secondarily with corrective osteotomy.
Should the contralateral hip be pinned prophylactically?
Prophylactic pinning has been advocated when the risk of bila-terality is high (e.g., endocrinopathy). It has the advantage of keeping the leg lengths equal. Although a recent decision ana-lysis recommends routine prophylactic pinning7, most would choose to avoid potentially unnecessary surgery and follow patients until skeletal maturity to ensure that a contraleteral slip is not missed.
Summary
The possibility of SCFE should be considered in a limping child between 10 and 16 years of age. The hip should always be assessed in the presence of medial thigh or knee pain. Using the guidelines above, SCFE can be managed safely and successfully. The issues of controversy will require prospective cohort studies and multicentre trials to resolve.
References
- Loder R.T., Richards B.S., Shapiro P.S., Reznick L.R. Acute slipped capital femoral epiphysis: the importance of physeal stability. J Bone Joint Surg 1993; 75A:1134-1140.
- Loder R.T., Aronson D.D., Greenfield M.L. The epidemiology of bilateral slipped capital femoral epiphysis: A study of children in Michigan. J Bone Joint Surg 1993; 75A:1141-1147.
- Carney B.T., Weinstein S.L., Noble J. Long term follow-up of slipped capital femoral epiphysis. J Bone Joint Surg 1991; 73A:667-674.
- Lindaman L.M., Canale T.S., Beaty J.H., Warner W.C. A fluoroscopic technique for determining the incision site for percutaneous fixation of slipped capital femoral epiphysis. J Pediatr Orthop 1991; 11:397-401.
- Moseley C. The "approach-withdraw" phenomenon in the pinning of slipped capital femoral epiphysis. Orthop Trans 1985; 9:497.
- Aronson D.D., Carlson W.E. Slipped capital femoral epiphysis: A prospective study of fixation with a single screw. J Bone Joint Surg 1992; 74A:810-819.
- Schulz W.R., Weinstein S.L., Smith B.G. Prophylactic pinning of the contralateral slip in slipped capital femoral epiphysis. Evaluation of long-term outcome for the contralateral hip with use of decision analysis. J Bone Joint Surg 2002; 84A:1305-1314.
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