Key points

Introduction

Slipped capital femoral epiphysis (SCFE) is a condition of the young hip in which mechanical overload of the proximal femoral physis results in anterior and superior displacement of the femoral metaphysis relative to the epiphysis. A varus and external rotation deformity usually results, although a valgus deformity may be present in up to 10%. Although the incidence in the United States is approximately 10 in 100,000 people, variations by region have been reported. The cause of SCFE is often multifactorial, including both biochemical and biomechanical forces acting at the physis of the proximal femur in a susceptible individual. SCFE has been classified as either stable, in which the patient can walk with or without an assistive device, or unstable, in which walking is not possible. The natural history of untreated SCFE is slip progression and subsequent hip deformity, which can lead directly to adjacent cartilage damage and degenerative changes of the hip joint. The treatment of SCFE requires surgical stabilization of the proximal femoral epiphysis, but the optimal technique and timing of care remain controversial. Although the goal of treatment is to minimize complications, the overall complication rate of SCFE remains high. The purpose of this article is to review those complications. Among the more reported complications are osteonecrosis (ON) of the femoral head, chondrolysis, SCFE-induced impingement with associated articular cartilage damage and labral injury, fixation failure and deformity progression, growth arrest, and development of bilateral disease.

Introduction

Slipped capital femoral epiphysis (SCFE) is a condition of the young hip in which mechanical overload of the proximal femoral physis results in anterior and superior displacement of the femoral metaphysis relative to the epiphysis. A varus and external rotation deformity usually results, although a valgus deformity may be present in up to 10%. Although the incidence in the United States is approximately 10 in 100,000 people, variations by region have been reported. The cause of SCFE is often multifactorial, including both biochemical and biomechanical forces acting at the physis of the proximal femur in a susceptible individual. SCFE has been classified as either stable, in which the patient can walk with or without an assistive device, or unstable, in which walking is not possible. The natural history of untreated SCFE is slip progression and subsequent hip deformity, which can lead directly to adjacent cartilage damage and degenerative changes of the hip joint. The treatment of SCFE requires surgical stabilization of the proximal femoral epiphysis, but the optimal technique and timing of care remain controversial. Although the goal of treatment is to minimize complications, the overall complication rate of SCFE remains high. The purpose of this article is to review those complications. Among the more reported complications are osteonecrosis (ON) of the femoral head, chondrolysis, SCFE-induced impingement with associated articular cartilage damage and labral injury, fixation failure and deformity progression, growth arrest, and development of bilateral disease.

Osteonecrosis

ON is perhaps the most feared complication related to SCFE and is associated with poorer outcomes ( Fig. 1 ). The etiology of ON is not entirely elucidated, but is likely related to a combination of direct damage of the retinacular vessels that supply the femoral head and an intracapsular tamponade caused by hemorrhage. Loder and colleagues established a relationship between unstable slips and ON in their series of 55 patients treated with internal fixation: 47% (14 of 30) of unstable slips developed ON. Twenty years later, in a review of the literature, Loder reported an overall incidence of 21% (88 of 417) of ON in unstable slips.

Osteonecrosis of the left hip in a 12-year-old girl after surgical treatment of an unstable SCFE.

In a separate retrospective study of 240 patients evaluating the factors influencing the development of ON, all 21 hips (8.75%) that had ON were classified as unstable at presentation, whereas none of those classified as stable had ON, regardless of severity. Although the slip severity had no effect in the stable group, the risk of ON in the unstable group increased with increasing slip severity. ON is related to the stability of the slip and, thus, may not be avoidable, regardless of treatment; however, methods to minimize the rate of ON have been developed. In an attempt to determine a cause of ON, 5 unstable slips in Loder’s later study were evaluated with angiography, which found kinking of the epiphyseal vessels, with 1 of 3 hips having a return of the blood supply after a reduction maneuver. In contrast, intracapsular pressure measurements showed an increase from 48 mm Hg to 75 mm Hg after reduction maneuver, which is significantly higher than a normal unaffected hip measurement of 23 mm Hg. After capsulotomy, this pressure decreased significantly to 17 mm Hg. In the presence of chronic changes, a forceful manipulation of an unstable SCFE can cause cessation of flow through the posterior physeal retinacular vessels as they become stretched over posterior callous at the head and neck junction resulting in higher rates of ON.

It remains controversial whether reduction is protective against, promoting of, or neutral for ON. In contrast to Loder’s perfusion findings, Kitano and colleagues found reduction, whether purposeful or inadvertent, to be related to the risk of ON and recommended against such treatment in unstable or acute SCFE. For this reason, they also cautioned against the use of a fracture table. In a comparative study of intracapsular cuneiform osteotomy and in-situ pinning for unstable slips, Walton and colleagues showed the 2 groups had ON rates of 25% and 42%, respectively. In the in situ pinning group, further analysis found a protective role for incomplete rather than complete reduction, with a decrease in the ON rate from 80% to 33%. Partial reduction, to the point at which it was before the acute component of the slip, through an open approach for hip joint decompression (Parsch method) on a regular operating table, has produced rates of ON of less than 10% at 5 years.

Other techniques for anatomic reduction have been described, such as the modified Dunn technique, which allows for resection of posterior callus and reorientation and fixation of the femoral epiphysis via a safe surgical dislocation approach, and have produced rates of ON as low as 8% in some reports, whereas in other reports the incidence of ON with the modified Dunn is as high as 30%. Other recommendations to minimize the risk of complications include the use of the modified Dunn procedure at specialty centers where a higher-volume surgeon experienced with the procedure can be available in the operating room. These investigators also suggested that the modified Dunn be done urgently (<24 hours) only for acute, severe (slip angle >50°) slips with only mild metaphyseal remodeling. Further investigation with randomized, matched groups of unstable slips will be helpful in determining the best treatment for unstable slips to obtain the lowest rate of ON possible.

Chondrolysis

Chondrolysis is suspected if the patient complains of pain and stiffness in the hip and has more than 50% joint space reduction of the involved hip or a joint space measuring less than 3 mm in bilateral cases. The etiology of chondrolysis is unknown, is likely multifactorial, and can occur with or without treatment. The overall incidence of chondrolysis is estimated at 7%, depending on the series but has ranged from 0% to 55%. Persistent pin penetration into the joint surface is most frequently cited as the cause, with a frequency of 88% in a study of 17 hips with a diagnosis of chondrolysis. In contrast, in a series of 14 hips with transient penetration of the joint by a guide pin, screw, or both that was recognized and corrected during the surgical procedure, no patient had chondrolysis at 2-year follow-up. Additionally, in a retrospective review, Dendane did not find transient intra-articular pin penetration to be a risk factor. Moreover, Dendane found that obesity and delay in diagnosis of more than 60 days was significantly associated with the development of chondrolysis after SCFE. An immune reaction has also been suggested as a possible cause based on joint aspirations, but further study is required to validate this hypothesis.

Regardless of its cause, chondrolysis is thought to have better outcomes than the complication of ON. In a long-term (average 14 years) follow-up study, Tudisco and colleagues noted diminishing pain and radiographic restoration of the joint space by 10 months; however, all of their patients had decreased range of motion at final follow-up. Patients with the worst outcomes had severe slippage or ON. Treatment for chondrolysis is aimed at pain reduction and maintenance of range of motion. Patients should be placed on limited activities with diminished weight bearing and started on range-of-motion physical therapy. Surgical interventions such as hinged distraction, periosteal patches, and osteochondral allografts have been performed but require further investigation.

Slipped capital femoral epiphysis–induced impingement

The true incidence of degenerative joint disease (DJD) after SCFE is unclear but is thought to be most closely associated with SCFE-induced impingement. The characteristic deformity produced by SCFE results in cam morphology of the hip and creates a potential geometric conflict between the femoral head and neck and the acetabulum that can lead to femoroacetabular impingement (FAI) ( Fig. 2 ). Acetabular retroversion may be present before the slip and also may contribute to a combined (cam and pincer) FAI. Radiographic assessment of even mild cases of SCFE has found loss of normal head/neck ratios and significant increases in the α angle as measured on the Dunn lateral view. In their series of 121 hips with stable SCFE treated with in situ fixation, Castañeda and colleagues found signs of DJD in all; clinical and radiographic signs of FAI were present in 79% of hips that were followed up for a minimum of 20 years after mild SCFE (grade I, II, or III). A direct correlation was identified between the degree of deformity and the presence of DJD in early adulthood. In a study comparing post-SCFE hips and those with primary osteoarthritis at the time of joint arthroplasty, patients with post-SCFE deformity were 11 years younger than those who had primary osteoarthritis. This finding was attributed to the loss of head/neck offset, abnormal rotation of the femoral head resulting in reorientation of the articular cartilage on the femoral head typical of the abnormal SCFE hips in this study.

Femoroacetabular impingement after SCFE.

Milder slips have been treated with in situ pinning with low rates of complications; however, impingement-related articular damage, regardless of slip severity, has been reported. Lee and colleagues found that osteoarthritis rates after SCFE ranged from 24% at 11 years to 92% at 28 years. The long-term natural history of untreated, stable slips includes decreased Iowa Hip Ratings scores with increased slip severity; mild slips are distinct from moderate to severe slips in that the incidence of DJD is only 36% in contrast to 100% in more severe slips.

Surgical treatment of SCFE-induced impingement has increased over the last 10 years and has been focused on preservation of the native joint as an alternative to hip arthroplasty. The decision to operate on a young hip with structural impingement before degenerative symptoms occur remains controversial. Of 89 hips treated with surgical hip dislocation for prearthritic hip disease, Beaulé and colleagues had only 6 hips (7%) that required total joint arthroplasty at 7-year follow-up; however, 38% of these patients required removal of internal fixation hardware, and the authors concluded that less-invasive approaches to the treatment of this condition should be considered. With the treatment evolving for FAI related to SCFE, open surgical hip dislocation remains the gold standard. With improving techniques and further research, arthroscopy may supplant this open technique, especially for the treatment of mild cases of prearthritic impingement after SCFE.

Fixation failure and slip progression

Fixation failure also is a known complication associated with the treatment of SCFE and can lead to hardware-related symptoms or be directly related to slip progression. Smooth pins and cannulated screws are the most common hardware used for fixation, regardless of the procedure chosen. Although smooth pins allow for easier removal and the potential for added growth, pin migration and breakage have been reported. As a result, fixation with 1 or 2 cannulated screws has become the standard fixation at most centers. Multiple clinical studies have shown satisfactory results with single screw constructs, even in higher-grade slips ; however, most of these studies evaluated stable slips of varying degrees of severity and acuity and did not specifically address the challenge presented by an unstable slip. An in vitro study simulating unstable slips in porcine models used single- and double-screw constructs in varying configurations to treat the simulated slips and then tested them mechanically for failure. The investigators did not find a difference in configuration patterns but did find added strength and stiffness in the 2-screw models. Additionally, at degrees of displacement of more than 2 mm, they found significantly higher failure loads in the 2-screw compared with the singe screw-model. Orientation to the physis of those screws, whether perpendicular or oblique, was not found to significantly affect resistance to shear forces. Whether the loads produced in this study can be naturally reproduced in vivo is uncertain. Karol and colleagues found only 33% improved stiffness in a double-screw bovine model and argued that such gain did not outweigh the risk associated with placement of the additional screw. Although 2 screws may be stronger biomechanically, there are risks associated with the placement of a second screw. Another study found that a single screw was adequate in mild slips and avoided the risks associated with additional screws. Blanco and colleagues found a direct correlation between an increasing number of pins and increased rates of complications without a significant difference in time to closure of the proximal femoral physis. Based on these findings, the authors concluded that single-pin or screw fixation provided dependable physeal closure and minimized implant-related complications.

Intra-articular placement of a screw can occur as a result of trying to obtain maximal fixation within the epiphysis. Additionally, determining appropriate screw length based on measurements taken intraoperatively can be a challenge. Although it is desirable to obtain maximal purchase in the epiphysis, it is equally important to avoid intra-articular penetration of the screw tip. Careful measurements of the screw length, use of fluoroscopy in multiple planes during placement, and consideration of the spherical shape of the femoral head will help avoid this complication. A screw that is seen to be too long at insertion can potentially be left prominent on the anterolateral surface of the proximal femur, but a prominence of more than 1.5 cm has been associated with a “windshield wiper” loosening effect caused by the forces exerted on the screw head from the overlying soft tissues. Additionally, placement of the screw tip eccentric to a center-center position can allow for inadequate fixation and further migration of the capital epiphysis.