Slipped capital femoral epiphysis (SCFE) is a common hip disorder among adolescents, whereby the epiphysis is displaced posteriorly and inferiorly to the metaphysis. Treatment modalities aim to stabilize the epiphysis, prevent further slippage, and avoid complications associated with long-term morbidity, such as osteonecrosis and chondrolysis. Controversy exists with SCFE regarding prophylactic fixation of the contralateral, painless, normal hip, the role of femoroacetabular impingement with SCFE, and whether in situ fixation is the best treatment method for SCFE. This article presents and discusses the latest diagnostic and treatment modalities for SCFE.
Key points
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Stabilization of the epiphysis, prevention of slip progression, and avoidance of complications are the desired goals with stabilization of SCFE.
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The controversy on prophylactic fixation derives from the inability to predict which patients will sustain a contralateral slip.
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32-mm partially threaded and fully threaded screws are valid options for in situ fixation as additional threads in the metaphysis may increase the biomechanical strength.
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The modified Dunn procedure has an incidence of osteonecrosis of up to 26% in the latest series.
Introduction
Slipped capital femoral epiphysis (SCFE) is the most common hip disorder affecting the adolescent population, with an overall incidence of 10.8 per 100,000. It is characterized by anterosuperior displacement of the metaphysis while the epiphysis remains in the acetabulum. The typical patient afflicted with this disorder is an overweight adolescent boy with groin, thigh, or knee pain, and a limp. Physical examination findings include decreased range of motion (ROM) of the hip, obligate external rotation with hip flexion, and pain with internal rotation. A frog-leg lateral radiograph confirms the diagnosis of SCFE. The etiology of SCFE is usually idiopathic, but can also be seen in patients with endocrine disorders, renal failure, or radiation therapy. Patients with bilateral SCFE initially present with involvement of both hips approximately 50% to 60% of the time. Prophylactic contralateral pinning is controversial among pediatric orthopedic surgeons. SCFE is classified according to 2 methods: the traditional time-based method or the method based on physeal stability and ability to ambulate. The classification system based on physeal stability as described by Loder and colleagues is predictive of prognosis. The unstable SCFE has been reported to have up to 50% incidence of osteonecrosis, compared with a stable SCFE that has nearly 0% incidence of osteonecrosis. Early treatment of SCFE has been supported in the literature as a means to prevent progression of the slip. The classic treatment for stable SCFE has been in situ fixation with a single screw in the center-center position of the epiphysis. Recently, however, there has been a shift in the treatment of SCFE, with the modified Dunn procedure via a surgical hip dislocation emerging as a treatment option for severe SCFE. This method restores the anatomic alignment of the proximal femur and potentially will avoid the sequelae from femoroacetabular impingement. Other treatment options under investigation to improve the outcome of SCFE include computer navigation assistance during in situ fixation, use of an arthrogram during in situ fixation, and arthroscopic-assisted osteoplasty after in situ fixation. The purpose of this article is to present and discuss the latest diagnostic and treatment modalities for SCFE.
Introduction
Slipped capital femoral epiphysis (SCFE) is the most common hip disorder affecting the adolescent population, with an overall incidence of 10.8 per 100,000. It is characterized by anterosuperior displacement of the metaphysis while the epiphysis remains in the acetabulum. The typical patient afflicted with this disorder is an overweight adolescent boy with groin, thigh, or knee pain, and a limp. Physical examination findings include decreased range of motion (ROM) of the hip, obligate external rotation with hip flexion, and pain with internal rotation. A frog-leg lateral radiograph confirms the diagnosis of SCFE. The etiology of SCFE is usually idiopathic, but can also be seen in patients with endocrine disorders, renal failure, or radiation therapy. Patients with bilateral SCFE initially present with involvement of both hips approximately 50% to 60% of the time. Prophylactic contralateral pinning is controversial among pediatric orthopedic surgeons. SCFE is classified according to 2 methods: the traditional time-based method or the method based on physeal stability and ability to ambulate. The classification system based on physeal stability as described by Loder and colleagues is predictive of prognosis. The unstable SCFE has been reported to have up to 50% incidence of osteonecrosis, compared with a stable SCFE that has nearly 0% incidence of osteonecrosis. Early treatment of SCFE has been supported in the literature as a means to prevent progression of the slip. The classic treatment for stable SCFE has been in situ fixation with a single screw in the center-center position of the epiphysis. Recently, however, there has been a shift in the treatment of SCFE, with the modified Dunn procedure via a surgical hip dislocation emerging as a treatment option for severe SCFE. This method restores the anatomic alignment of the proximal femur and potentially will avoid the sequelae from femoroacetabular impingement. Other treatment options under investigation to improve the outcome of SCFE include computer navigation assistance during in situ fixation, use of an arthrogram during in situ fixation, and arthroscopic-assisted osteoplasty after in situ fixation. The purpose of this article is to present and discuss the latest diagnostic and treatment modalities for SCFE.
Prediction of the contralateral SCFE
Controversy exists among pediatric orthopedic surgeons as to when it is appropriate to stabilize the painless, radiographically normal contralateral hip in a patient who presents with unilateral SCFE. The controversy derives from the inability to predict which patients will sustain a contralateral slip. Those in favor of prophylactic pinning refer to the high incidence of slip in the contralateral hip and the associated devastating complications of osteonecrosis or chondrolysis, in addition to the prevalence of the asymptomatic “silent” slip, resulting in the development of osteoarthritis being reported in up to 40% of cases. The counterargument accounts for the potential surgical complications, including infection, implant complication, chondrolysis, and osteonecrosis.
Riad and colleagues determined that chronologic age was a significant predictor of contralateral slip. In their series of 70 patients with unilateral SCFE, 16 (23%) developed a contralateral SCFE. All girls younger than 10 and boys younger than 12 years developed a contralateral SCFE. Twenty-five percent of girls younger than 12 and 37% of boys younger than 14 years developed a contralateral SCFE ( Fig. 1 ). The investigators therefore recommended prophylactic screw fixation in all girls younger than 10 and boys younger than 12 years. To assist in predicting contralateral slips in other patients aside from the very young, 2 methods have recently been reported in the literature: the posterior sloping angle and the modified Oxford bone age score.
Posterior sloping angle as a predictor of contralateral SCFE
The posterior sloping angle (PSA) of the physis is the angle measured on the Lauenstein axial view between the intersection of the plane of the physis and a line perpendicular to the longitudinal neck-diaphyseal axis ( Fig. 2 ). Barrios and colleagues established that the PSA most accurately demonstrates the physeal vertical shear forces that place patients at risk for developing SCFE. In their study of 47 patients, the PSA was found to be 5° in the control group, 12° in patients with unilateral SCFE, and 18° in patients with bilateral SCFE. The investigators concluded that patients presenting with unilateral SCFE demonstrating a PSA of greater than 12° should undergo prophylactic pinning of the contralateral side.
Zenios and colleagues tested the intraobserver and interobserver reliability of PSA, and their study demonstrated a good to excellent reliability of this measurement. Thirteen of their 47 patients in the study group developed a contralateral slip with mean PSA values of 18.8°. Those who did not go on to develop a contralateral hip showed PSA values of 13.9°, and the control group showed a PSA of 3.9°. The investigators concluded that patients with a PSA of greater than 14.5° should undergo prophylactic pinning of the contralateral hip.
Park and colleagues demonstrated the reliability of PSA in a larger series, and also found a difference between sexes, with greater predictability in girls. Phillips and colleagues continued to show the utility of the PSA in the largest study to date in the literature in a predominately Maori population, which is particularly susceptible to SCFE. This study showed that if a PSA of 14° was used as an indication for prophylactic fixation, 83% of contralateral slips would have been prevented and only 21% would have been pinned unnecessarily.
Despite the overwhelming evidence showing the PSA of the physis as a predictor of contralateral SCFE, its use has not been widely used in the treatment of SCFE, probably because of lack of awareness or reliability on other proven methods of predicting a future slip.
The modified Oxford bone age score as a predictor of contralateral SCFE
The modified Oxford bone age score, as originally described by Stasikelis and colleagues, scored 3 consecutive stages of maturation for 5 radiographic features on anteroposterior pelvic and frog-leg lateral views of patients with idiopathic SCFE. The score ranges from 16 to 26. The lower the number, the younger the patient and the higher the risk of developing a contralateral slip ( Fig. 3 ). The iliac apophysis, triradiate cartilage, proximal femoral epiphysis, greater trochanter, and lesser trochanter were the features measured. In their study of 260 patients, 24% of whom developed a contralateral slip, Popejoy and colleagues showed that a modified Oxford bone age score of 16, 17, or 18 had a positive predictive value of developing a contralateral slip of 96% and a negative predictive value of 92%. The study demonstrated that the modified Oxford bone age score and a triradiate score of 1 were significant for prediction of a contralateral slip, with the modified Oxford score being a better indicator ( Fig. 4 ). Despite good intraobserver and interobserver reliability, the scoring system of the modified Oxford score is difficult to recall, owing to its basis on 3 continuous stages of maturation. Zide and colleagues modified the scoring system of the 3 stages of maturation to 0, 1, and 2, resulting in an easier ability for clinicians to recall the scoring system and thereby enhancing the use of the modified Oxford score by clinicians. Overall, the modified Oxford score was found to be a reliable predictor of developing a contralateral SCFE.
Treatment updates with slipped capital femoral epiphysis
Stabilization of the epiphysis, prevention of slip progression, and avoidance of complications such as avascular necrosis and chondrolysis are the desired goals with stabilization of SCFE. Single in situ screw fixation for stable slips has developed into the most accepted treatment method. Using fluoroscopy, a single cannulated screw is inserted in the center-center position of the epiphysis without progressing closer than 5 mm from the subchondral bone. This method is minimally invasive, not technically demanding, and has a high success rate. In their series, Aronson and Carlson showed excellent to good results in 95% of hips with mild SCFE, 91% of hips with moderate SCFE, and 86% of hips with severe SCFE. Loder and Dietz recently reviewed 65 articles to determine the best evidence for treatment of stable SCFE, which demonstrated that single in situ screw fixation was the best method of treatment.
The type of operating table has also been questioned, as some investigators prefer the radiolucent table to the typically used fracture table. Studies have shown mixed results regarding radiation time, accuracy, and operating time.
With regard to slip progression, Carney and colleagues reviewed 37 children with 46 slips treated with in situ single-screw fixation. In this study, 9 hips demonstrated slip progression, and this progression was linked to the number of threads engaged in the epiphysis. Fewer than 5 screw threads demonstrated progression. Dragoni and colleagues compared 16-mm and 32-mm partially threaded screws and fully threaded screws in a biomechanical porcine model to further evaluate whether the type of screw used during in situ fixation contributed to stability. There was no significant difference detected with the cycles to failure between the different screws used. The 16-mm partially threaded screw did demonstrate a higher frequency of femoral neck fracture, leading the investigators to conclude that both 32-mm partially threaded and fully threaded screws were valid options for in situ fixation, and that the additional threads in the metaphysis may increase the biomechanical strength of the femoral neck.
Arthrogram-assisted in situ screw fixation
Arthrogram-assisted fixation of SCFE has recently been described in the literature as improving screw placement ( Fig. 5 ). Wright and colleagues reported that the screwtip-to-articular surface distance was significantly smaller in the arthrogram-assisted group in comparison with patients in whom only fluoroscopy was used (2.8 mm vs 5.2 mm). The investigators concluded that arthrogram-assisted fixation was an effective method to improve screw placement and visualization, especially when the patient’s body habitus makes fluoroscopic imaging difficult to obtain.
