Stable Slipped Capital Femoral Epiphysis



Stable Slipped Capital Femoral Epiphysis





FUNDAMENTAL PRINCIPLES OF SLIPPED CAPITAL FEMORAL EPIPHYSIS


Epidemiology and Etiology

Slipped capital femoral epiphysis (SCFE) is a disorder of the proximal femur in which the capital femoral epiphysis displaces in a posterior and inferior direction about the metaphysis. SCFE is the most common hip disorder affecting adolescents. The overall incidence of SCFE is 10.8 in 100 000, and it is more predominant in males.1 The average age of presentation is 12 years for boys and 11 for girls.2

The etiology of SCFE is thought to be multifactorial with biologic, endocrine, and mechanical factors playing a role. Historically, SCFE is associated with obesity. However, only recently, one study confirmed a causal association between obesity and SCFE.3 Another study showed that high levels of leptin, a polypeptide hormone secreted by adipocytes that has been shown to weaken the growth plate, are present in patients with SCFE independent of obesity.4 The etiology of SCFE involves mechanical predisposition related to the morphology of the proximal femur. Femoral retroversion and increased posterior tilt of the capital femoral epiphysis are well-accepted factors associated with the etiology of SCFE.5 Contemporary studies have proposed a rotational mechanism of SCFE, whereas the epiphysis rotates around the metaphysis with the epiphyseal tubercle serving as a fulcrum.6


Clinical Evaluation

The typical clinical presentation is of an adolescent with a history of knee, hip, or groin pain with a slight limp. The diagnosis may be delayed because patients can initially complain of knee or anterior thigh pain instead of actual hip pain. SCFE should be in the differential diagnosis in an adolescent who presents with unspecific thigh or knee pain, and, at minimum, a dedicated hip examination is recommended. Clinical evaluation includes assessment of patient’s standing posture and gait pattern. Outward rotation of the involved lower extremity and a slight limp with the foot externally rotated can be observed at initial presentation. Direct examination of the hip may reveal abnormal range of motion. Flexion and internal rotation are the most commonly restricted and could elicit pain. Given the reduced femoral anteversion of the femur in SCFE, flexion of the hip requires external rotation, the so-called obligatory external rotation sign.

SCFE can be classified according to the timing of presentation, severity of the deformity, and stability of the capital femoral epiphysis. In regard to the time of presentation, SCFE is classified as acute if symptoms have been present for 3 weeks or less, chronic if symptoms have been present for more than 3 weeks, and acute on chronic when symptoms are present for more than 3 weeks but there is an acute exacerbation.7 According to Loder and colleagues,8 a slip is classified as unstable if the patient has such severe pain that walking is not possible even with crutches, regardless of the duration of the symptoms. The slip is classified as stable if walking and weight bearing are still possible with or without crutches. The severity of the slip displacement is classified using specific radiographic criteria.

The diagnosis of SCFE requires radiographic imaging, including an anteroposterior pelvic plain film and a lateral film of the femur. Although the frog-leg view is our preferred lateral radiograph, in acute and unstable slips, pain may limit the ability to obtain the adequate image, and a cross-table lateral view should be obtained to avoid pain and further epiphyseal displacement. Because of the high occurrence of bilateral SCFE, an anteroposterior pelvic film and bilateral lateral radiographs are recommended in the initial evaluation even in patients with unilateral symptoms. The radiographic appearance of SCFE varies according to the chronicity of the disease and the severity of the epiphyseal displacement. Radiographic classification of the displacement is performed by measuring the Southwick angle.9 The Southwick angle measures the alignment of the femoral head in relation to the diaphysis. SCFE can, therefore, be classified as mild when the angle is less than 30°, moderate if the angle is between 30° and 60°, and severe when the Southwick angle is higher than 60° (Figure 6.1). Slight widening of the physis and lucency around the
epiphyseal tubercle (peritubercle lucency sign) are the early radiographic signs that may be present in the early preslip phase and in mild SCFE. With further displacement, the superior aspect of the femoral neck (Klein line) does not cross the epiphysis, and the alignment of the epiphysis assessed by the Southwick angle and the epiphyseal tilt or posterior slope becomes posteriorly oriented. Magnetic resonance imaging (MRI) and computed tomography (CT) are helpful to determine the extent of cartilage damage and the severity of deformity and to plan for femoral realignment osteotomy when indicated. Three-dimensional (3-D) printed modeling is a promising technique that improves the surgeon’s ability to treat a severe SCFE deformity.






FIGURE 6.1. Diagram representing different severity of slipped capital femoral epiphysis displacement as mild, moderate, and severe. The epiphysis displaces in an inferior and posterior direction creating a retroversion deformity of the proximal femur, with the metaphysis being externally rotated about the epiphysis. Illustration by Nathan Billington.



Treatment Algorithm for Stable Slipped Capital Femoral Epiphysis

For stable SCFE, the procedure performed most often is in situ fixation of the epiphysis (Figure 6.2). In situ pinning has been proven to allow for good long-term outcomes in mild SCFE; however in severe SCFE, there is a higher risk of deformity, causing FAI and long-term osteoarthritis.13
Historically, multiple pins have been used for the treatment of SCFE; however, contemporary fixation can be performed using guided fluoroscopy imaging and a cannulated screw system. In situ pinning is a universally applied surgical technique. Traditionally, the goal has been to provide stabilization of the epiphysis while allowing for closure of the growth plate. However, in situ pinning using nontransphyseal screw devices allows for femoral neck growth, increased remodeling of the deformity with an overall improvement of the femoral head-neck offset, and avoidance of FAI in mild SCFE.






FIGURE 6.3. Diagram representing the mechanism of femoroacetabular impingement (FAI) in slipped capital femoral epiphysis. A, With progressive displacement of the epiphysis posteriorly and inferiorly, a metaphyseal prominence develops at the femoral head-neck junction (black arrow). B, Impaction type of impingement: the metaphyseal prominence abuts against the acetabular rim, deforming the acetabular labrum (in light blue). C, Inclusion type of impingement: with remodeling of the femoral head-neck junction, the metaphyseal prominence does not block motion. Instead, the metaphyseal bone enters the joint and impinges against the acetabular cartilage, causing damage represented in red. Illustration by Nathan Billington.

In situ fixation has a long-term prognosis that is benign for patients with a mild deformity; however, with increasing deformity, there is a higher risk of degeneration changes of the hip and development of osteoarthritis secondary to cam-type FAI.10,11,12 Even in mild SCFE at the early stages of the disease, cartilage damage can be present. Cartilage damage occurs because of impingement from the metaphysis into the acetabular rim. In SCFE, the impingement is thought to be an impact between the metaphyseal prominence into the acetabular rim, but with time and remodeling of the deformity, the metaphysis would enter the joint and damage the cartilage, which is called an inclusion type of impingement14 (Figure 6.3). Because of the risk of cartilage damage associated even with mild SCFE, early resection of the metaphyseal prominence during in situ pinning may be of benefit. In moderate and severe unstable SCFE, in situ pinning may allow for resolution of symptoms in the short term with stabilization of the physis. However, the severity of the deformity is unlikely to allow for complete remodeling, and FAI would persist with a high likelihood of articular cartilage damage and osteoarthritis in the long term.11,12,13 Treatment of moderate and severe SCFE, therefore, is often traditionally performed by in situ pinning alone with close monitoring for patients developing symptoms of FAI with further treatment by a proximal femoral realignment osteotomy. We, however, favor acute correction of the moderate and severe SCFE deformity. Realignment of severe SCFE can be performed at the subcapital level, base of the femoral neck, and intertrochanteric and subtrochanteric level. Although controversy surrounds the best level for deformity correction, most authors accept that close to anatomic realignment is only possible at the subcapital level. We favor subcapital realignment in moderate and severe SCFE using the modified Dunn technique through a surgical hip dislocation approach as in patients with wide-open growth plate. In skeletally mature patients with closed proximal femoral growth plates and moderate or severe SCFE deformity leading to FAI, our preferred technique is the surgical hip dislocation approach with osteochondroplasty of the femoral head-neck junction in association with an intertrochanteric flexion derotational osteotomy.


SURGICAL PROCEDURES


In Situ Pinning


Although in situ pinning can be performed with the patient on a fracture table, it is our preferred method to perform the surgery with the patient in a radiolucent flat table. A gel roll is placed under the patient’s ipsilateral shoulder to allow for slightly trunk rotation, which aligns the lower extremity in neutral rotation with the patella pointing upward. The entire hemipelvis and the lower extremity are prepared and draped free.

Under C-arm fluoroscopy, the anteroposterior trajectory of the guidewire is marked aiming toward the center of the femoral head with an attempt to avoid the superior aspect of the femoral head to avoid the area corresponding to the epiphyseal tubercle and the penetration of the epiphyseal vessels. A line is drawn on the skin in line with the guidewire marking the trajectory of the pin in the anteroposterior view. The skin incision is performed in line with the guidewire mark in the anterolateral aspect of the thigh. Then, Schnidt clamp is introduced through the incision up to the anterolateral aspect of the bone at the level of the entry point. The Schnidt clamp is then spread, which would create a tunnel of the soft tissue (Figure 6.5). We use an 8-gauge bone marrow biopsy needle (Harvest Terumo BCT, Lakewood, Colorado) that is introduced to the desired point in the anterolateral aspect of the proximal femur. The needle is gently tapped into the desired entry point using C-arm fluoroscopy in the anteroposterior view (Figure 6.6). The hip is flexed up to about 45°, whereas the C-arm fluoroscopy view is moved into an oblique view to about 45°, which will allow for adequate visualization of a lateral view of the femur. By flexing the hip and rotating the C-arm, we avoid the popular maneuver to obtain the lateral view placing the hip in abduction and external rotation. Moving the hip in external rotation to allow for lateral view may cause bending of the guidewire. With the C-arm in the lateral view and with the hip flexed, the bone marrow biopsy needle can then be adjusted to aim toward the center of the femoral head (Figure 6.7). Typically, the surgeon’s hand should move slightly posteriorly because the anterior entry point in the femur may create an excessively posterior path through the neck and end in the posterior quadrant of the epiphysis. The needle and later the screw should aim toward the center of the
femoral head avoiding the posterior aspect of the epiphysis again to avoid penetration of the epiphyseal tubercle and the epiphyseal vessels. It is at this point during the procedure that the use of the bone marrow biopsy needle is very helpful. With gentle tapping, the bone marrow biopsy needle can be introduced into the anterolateral aspect of the metaphysis about 3 or 5 mm inside the bone. Slightly adjustments into varus or valgus or anterior or posterior direction are facilitated by the use of the bone marrow biopsy needle. Once the needle is placed in the adequate position, the internal trocar of the needle is removed and a long guidewire for the cannulated screw is introduced through the needle (Figure 6.8). An additional advantage of this technique is that the bone marrow biopsy needle allows for slightly adjustments in varus or valgus or anterior or posterior direction without bending of the guidewire. The wire is then advanced, while confirmation with the C-arm fluoroscopy is made with the anteroposterior view and the lateral view with the hip flex to about 45° and the C-arm machine in the oblique view at 45°. We cannot emphasize enough that to avoid bending of the wire, the hip is flexed up to 45° but is not brought into an external rotation or abduction in the typical figure-of-four or frog-leg lateral position, which is not necessary for perfect placement of the pin. It is our preference to advance the wire just
slightly passed the physis but not penetrating excessively the epiphysis to avoid any inadvertent penetration of the articular cartilage (Figure 6.9). Once the guidewire is in place, then the bone marrow biopsy needle is removed, and the regular soft-tissue protection is placed around the guidewire and the cannulated drill is inserted. It is our preference to drill just barely passed the growth plate into the epiphysis again to avoid inadvertent penetration of the femoral head cartilage while drilling and, more importantly, to avoid excessive heating caused by the drill, which has been identified as a potential cause of focal osteonecrosis of the femoral head (Figure 6.10). The guidewire is then measured, and we prefer to tap the screw path, even though the modern cannulated screws are self-tapping. Using the tap tool may protect from excessive heating while introducing the screw. It is our preference to use a fully threaded screw with a minimum of five threads placed across the growth plate into the epiphysis. For patients aged 10 years and younger, we use a 6.5-mm screw, whereas for patients older than 10 years, we prefer a larger screw of 7.3 mm. After the screw is introduced, a full inspection of the radiographic appearance is confirmed with an anteroposterior, frog-leg lateral, and a 45° Dunn view (Figure 6.11).






FIGURE 6.5. A, Intraoperative photography showing the insertion of a Schnidt clamp in the anterolateral aspect of the proximal femur in line with the femoral neck axis previously marked in the skin. B, Intraoperative fluoroscopy imaging corresponding to the placement of the Schnidt clamp in the anterolateral aspect of the femur.






FIGURE 6.6. A, Intraoperative photography showing the insertion of an 8-gauge bone marrow biopsy needle (Harvest Terumo BCT, Lakewood, Colorado) in line with the skin mark. B, Intraoperative fluoroscopy imaging corresponding to the placement of the bone marrow biopsy needle in the anterolateral aspect of the femur.






FIGURE 6.7. A, Intraoperative photography showing the position of the lower extremity for lateral radiograph. The hip is in neutral and flexed to about 45°, whereas the C-arm fluoroscopy is arched about 45°. As the bone marrow biopsy needle has been introduced in the femur, it does not disengage from the bone with simple flexion. B, Intraoperative fluoroscopy imaging in the lateral view showing the bone marrow biopsy needle adequately corrected to aim toward the center of the femoral head.






FIGURE 6.8. Intraoperative fluoroscopy in the anteroposterior view after the internal trocar of the bone marrow biopsy needle has been removed. The needle is confirmed to be pointing toward the center of the femoral head.






FIGURE 6.9. Intraoperative photography showing the introduction of the long guidewire through the bone marrow biopsy needle. In the bottom right corner, the correspondent fluoroscopy view shows the long guidewire introduced through the biopsy needle.






FIGURE 6.10. A, Intraoperative fluoroscopy in the anteroposterior view after the cannulated drill is introduced. Drill is placed just slightly past the physis to avoid excessive heating and inadvertent penetration of the femoral head. B, Intraoperative fluoroscopy imaging in the lateral view showing the tapping tool advanced past the physis into the femoral head.







FIGURE 6.11. A, Final intraoperative anteroposterior view with the C-arm fluoroscopy revealing optimal position of the screw in center of the femoral head with five threads past the physis. B, Final intraoperative frog-leg lateral radiograph revealing optimal position of the screw in the center of the femoral head.

Postoperatively, patients are instructed to be toe-touch weight bearing with two crutches for 6 weeks. A wheelchair is provided for school use and for long distances. We see patients for postoperative check at 2, 6, and 12 weeks when physical therapy may be recommended. Additional follow-up is obtained at 6 and 12 months from surgery when we expect to observe signs of physeal closure. Return to full activities including sports is typically allowed after 12 months from surgery. We followed up patients with SCFE until they achieve skeletal maturity age to monitor for contralateral slip development in those not treated prophylactically. Prophylactic fixation is controversial; however, in general, we offer prophylactic fixation for patients aged 10 years or younger, those with endocrine disorders, and patients with a triradiate cartilage that is wide opened with an unreliable family/social situation to allow for close follow-up (Figure 6.12).






FIGURE 6.12. A, Anteroposterior pelvic radiograph obtained at 2 months postoperatively revealing correct placement of the screw for the right-sided slipped capital femoral epiphysis and for prophylactic fixation of the left hip. The indication for prophylactic fixation was based on age younger than or equal to 10 years. B, Postoperative bilateral frog-leg lateral radiograph revealing correct placement of the screws.