Slipped Capital Femoral Epiphysis Surgery

Slipped capital femoral epiphysis (SCFE) was first described by Ernst Müller, who called it Schenkelhalsverbiegungen im Jungesalter ("bending of the femoral neck in adolescence"). The term slipped capital femoral epiphysis is actually a misnomer, because the epiphysis is held in the acetabulum by the ligamentum teres; thus, the metaphysis actually moves proximally and anteriorly while the epiphysis remains in the acetabulum.[1] (See the image below.)

Bilateral slipped capital femoral epiphysis. One side shows evidence of remodeling of the neck and an anterior bone bump that restricts flexion. The other side demonstrates an acute slip as seen by the absence of any evidence of remodeling.

In most patients, SCFE appears radiographically as a varus relation between the head and the neck.[2] Occasionally, the slip appears to be in a valgus position, with the epiphysis displaced superiorly in relation to the neck.[3, 4, 5, 6, 7] In the vast majority of cases, the etiology is unknown, though atypical slips may be associated with a known endocrine disorder, with renal failure osteodystrophy, or with previous radiation therapy.[8, 9, 10, 11, 12]

SCFE is not life-threatening. However, untreated and complicated SCFE can lead to deformity and early osteoarthrosis of the hip and thus can cause considerable morbidity. Factors that increase morbidity include avascular necrosis (AVN) of the hip and chondrolysis.[13] Both of these may result in damage severe enough to warrant a salvage procedure, in the form of an arthrodesis or a total hip arthroplasty. Prompt diagnosis is critical to prevent further deformity and AVN. The diagnosis is often subtle, and symptoms (eg, groin or knee pain) can be misleading.

SCFE develops as a consequence of increased stresses across a weakened physis, with a combination of both biomechanical and biochemical factors contributing to the development of the slip. Factors affecting the stability of the physis include the following:

• Perichondrium - This is thick in children but progressively thins with age
• Perichondrial ring - This is a fibrous ring that spans the physeal plate and extends from the metaphysis to the epiphysis; it also thins with age
• Transphyseal collagen - This weakens because of progressive mineralization; cross-linkage of collagen is affected in osteolathyrism, leading to slippage in these patients
• Mammillary projections - These assume increasing importance as the perichondrial ring thins
• Contour of the growth plate - This is normally convex toward the physis with undulations at the periphery, which contribute to its resistance to linear shear and torque forces
• Thickness of the growth plate - This is mainly affected by biochemical and endocrine factors

Mechanical factors leading to increased stress across the physis[14] include the following:

• Relative femoral retroversion ^{[15, 16, 17, 18]}
• Obesity - This is associated with femoral retroversion, which also increases the stress across the physis ^{[19, 20]} ; the average femoral version of patients who are not obese was found to be 10.6°, compared with 0.40° in patients who are obese ^[15]
• Increased physeal slope - This is an increase in inclination of the physis at the time of rapid skeletal growth around puberty ^[21] ; patients with SCFE have been shown to have a higher physeal inclination even on the opposite side
• Deeper acetabula - The mean center-edge angle of Wiberg is higher in children with SCFE than in control subjects; deeper acetabula lead to increased coverage of the femoral heads and increased stress across the physis ^[22]

SCFE is most common in the peripubertal age group; the effect of the following hormones on the physes may contribute to the likelihood of developing a slip[23] :

• Growth hormone - This causes widening of the physes and consequent weakening
• Sex hormones - Increased physeal width and decreased physeal strength result from testosterone, probably accounting for the increased frequency in boys; narrowing of the physis and increased physeal strength result from estrogen, possibly explaining why slips seldom occur in postpubertal females ^{[24, 25]}
• Thyroid hormone - The effect of this hormone is not clear, though it is known that slips can occur in patients with hypothyroidism and those receiving thyroid hormone replacements for hypothyroidism

Even though most children with SCFE do not have an overt endocrinopathy, they may very well have some subtle endocrine disorder.[26, 27, 28, 29, 30] A delay in bone age with respect to chronologic age in some of these children lends further credence to this theory.[24, 25]

Shear stresses across a physis made vulnerable by the biomechanical and biochemical factors outlined above leads to the slip. The displacement is determined by the direction of the deforming force. Posteroinferior displacement of the head (anterosuperior migration of the neck) is the most common pattern, though in rare cases, the head may displace posterosuperiorly, giving rise to an apparent valgus slip (see the image below).[3, 4]

Valgus slip (rare).

Various causative factors for SCFE have been identified.[31] Factors related to body habitus include the following:

• Obesity - At least 50% of patients are above the 95th percentile for weight ^[32]
• Excessive tallness or thinness

If the patient's height is below the 10th percentile, the likelihood of an underlying endocrinopathy is high.[33, 34] Endocrinopathies that may be present include the following:

• Hypothyroidism
• Acromegaly
• Hypogonadism (adiposogenital syndrome)
• Hyperparathyroidism

Radiation therapy, especially for childhood leukemias or lymphomas, may be involved in the development of SCFE:

• This cause of SCFE tends to occur in young children
• Affected children are also light and thus tend to have mild slips

Finally, renal failure is an important factor:

• There is a high incidence of simultaneous bilateral presentations (~87%)
• The highest incidence of severe slips is in these patients
• There are two distinct patient subgroups: those whose disease is controlled early (less hyperparathyroidism) tend to have mild slips, and those with poorly controlled disease (significant hyperparathyroidism) tend to have severe slips

United States and international statistics

The prevalence of SCFE varies widely even within the continental United States. It has been reported to be 2.13 cases per 100,000 population in the southwestern United States and 10.08 cases per 100,000 population in the northeastern United States[19] ; it is lowest in the mountain and Great Plains states. In Asia, the reported prevalence is quite low, with just 0.2 cases per 100,000 children affected in eastern Japan.[35]

Age-, sex-, and race-related demographics

The mean age at diagnosis is 13.5 years in boys (range, 13-15 years) and 12 years in girls (range, 11-13 years).[20]  This corresponds to the period of maximum skeletal growth. Juvenile SCFE (in children < 10 years) should raise the suspicion of an underlying cause (eg, an endocrinopathy). Radiation-associated slips tend to occur in young children.

Males are affected more commonly than females are; the male-to-female ratio is 2-5:1.

A race predilection exists for SCFE, as follows[20] :

• Whites - 1.0
• Pacific Islanders - 4.5
• Blacks - 2.2
• American Indians and Hispanic individuals - 1.05
• Indonesian-Malay peoples (eg, Chinese, Japanese, Thai, Vietnamese) - 0.5
• Indo-Mediterranean peoples (those of Near East, North African, or Indian subcontinent ancestry) - 0.1

If the SCFE is mild or moderate in severity and is maintained between the femoral head and the acetabulum, long-term outcome is good, and AVN and chondrolysis do not develop. Hips with a severe SCFE and those with AVN or chondrolysis undergo more rapid deterioration with degenerative changes and ultimately require reconstructive procedures.

Murgier et al carried out a single-center retrospective study assessing clinical and radiographic outcomes of in-situ fixation for SCFE in 11 hips followed for a mean of 26 years (range, 10-47 years).[36]  They found that in moderate-to-severe SCFEs, in-situ fixation yielded poor functional results, substantial hip osteoarthritis, and potential femoroacetabular impingement, whereas with minor displacement, it yielded satisfactory functional and radiographic results. The cutoff point for considering other treatment options appeared to be about 30° of slippage.

Nectoux et al performed a multicenter retrospective study evaluating the clinical and radiologic evolution of 222 hips treated with in-situ fixation and followed for a mean of 11.2 years.[37]  In cases of moderate-to-severe initial epiphyseal displacement, in-situ fixation led to hip impingement; however, in cases of lesser displacement, it yielded satisfactory function scores, with no clinical or radiologic evidence of impingement. The threshold seemed to be about 35° of slippage; the authors suggested that beyond this value, other surgical options should be considered.

Bond et al studied long-term outcome scores in 63 SCFE patients and attempted to determine whether there was a threshold level of deformity beyond which outcomes were predictably poor outcomes after in-situ pinning.[38]  Of the 63 patients, 14% had poor functional outcomes, 29% had intermediate outcomes, and 57% had good outcomes. Patients with a posterior slope angle greater than 40° were found to have a higher chance of a poor outcome.

Patients with slipped capital femoral epiphysis (SCFE) may present with the following symptoms:

• Pain - The presenting feature is hip (groin) pain in most patients; as many as 46% of patients with chronic slips may present with thigh pain or knee pain (eg, referred pain, obturator nerve)
• Limp
• Inability to bear weight in acute slips
• History of irradiation, renal failure, endocrinopathy (eg, hypothyroidism and treatment thereof, acromegaly, short stature [growth hormone supplementation])

Either side may be affected. The left hip is involved in 60% of unilateral cases. In most studies, 18-50% of cases are bilateral, though some studies have reported the prevalence of bilaterality to be as high as 80%.[39, 40, 41]  Bilateral involvement may be evident at the time of initial presentation.[20]  Most patients who subsequently develop a contralateral slip do so within 18-24 months of initial symptoms, though slips may occur until physeal closure.[20, 25, 39, 42, 43, 44, 45]

Management of the patient who presents with unilateral involvement is controversial. Significant morbidity can occur if the other side slips and displaces. Early recognition of a preslip on the contralateral side would help determine which patients are at greater risk. A scoring system has been developed to predict the risk of a contralateral slip.[46]

The following physical signs may be present:

• Externally rotated attitude of the affected lower limb
• In varus slips, restriction of flexion, abduction, and internal rotation of the affected hip
• In valgus slips, restriction of flexion, adduction, and internal rotation
• Obligatory external rotation on flexion (this is a diagnostic clue)
• In chronic slips, wasting of the thigh
• True supratrochanteric shortening (Bryant triangle, Nélaton line)
• Trendelenburg sign and gait possible; antalgic gait in acute or acute-on-chronic slips

Typically, knee examination and radiographic findings are normal in individuals with SCFE. All children with knee pain should have their hips evaluated.

A renal panel in patients with renal failure–associated slips may reveal elevated blood urea nitrogen (BUN) and creatinine levels.

An endocrine panel is appropriate if endocrinopathy is suspected. Hypothyroidism is a common endocrinopathy associated with slipped capital femoral epiphysis (SCFE). In cases where hypothyroidism is suspected, triiodothyronine, thyroxine, and thyrotropin levels must be obtained. Other endocrinopathies also may be associated with SCFE (see Pathophysiology). In these cases, the appropriate investigations must be performed.

In the preslip stage (see Classification), the only positive findings on radiography are a widening and irregularity of the physis with rarefaction of its juxtaepiphysial portion.

Early diagnosis is made by using a Lauenstein (frog-leg) lateral view (see the image below) or true lateral view of the hip because small slips may be missed on the anteroposterior (AP) view.[47]  A frog-leg lateral view should not be attempted in persons with acute or unstable slips, because it may cause further displacement.

Frog-leg (Lauenstein) lateral view, showing a mild slip that can easily be missed on an anteroposterior view.

The Klein line, a line along the superior border of the femoral neck, intersects less of the femoral head than it does on the opposite side (Trethowan sign) on the AP radiograph (see the image below).[48]  Green et al, in a study of the diagnosis of SCFE using the Klein-line AP radiograph or the frog-leg lateral radiograph, found that the classic Klein line failed to identify 60% of slips; a modification of the Klein line by the authors increased sensitivity to 79%.[48]

Klein line (line drawn along the superior border of the neck intersects less of the capital epiphysis than on the unaffected side).

Localized rarefaction of the inferior medial metaphysis of the neck may be evident. The so-called metaphyseal blanch of Steel is a crescent-shaped area of increased density overlying the metaphysis adjacent to the physis on the AP radiograph.[49]  This is an early sign of a posterior slip without significant medial slip and indicates the need for a lateral radiograph to identify the slip.

In moderate-to-severe slips, the overlap of the head and the metaphysis is visible.

Remodeling in chronic slips is seen as callus on the posteroinferior portion of the neck and rounding-off of the anterosuperior bare area of the neck, which is seen as a rounded hump.

Bone scanning[50]  can be used to identify patients at high risk for avascular necrosis (AVN). A cold bone scan (demonstrating an absence of vascularity) essentially is seen only in unstable cases. When a patient has such a bone scan finding, the risk that AVN will subsequently develop is 80-100%.

Bone scans help in the early detection of AVN (ie, decreased activity/uptake on the femoral side). These scans also help in the early detection of chondrolysis (ie, increased activity/uptake on both the acetabular and the femoral sides).

Computed tomography (CT) can be used to measure the amount of retroversion and the degree of slip. Three-dimensional imaging of the upper femur, which may be useful in the preoperative planning of osteotomies, is also possible. CT scans may incidentally reveal asymptomatic, mild contralateral slips.

On ultrasonography (US), the presence of an effusion indicates an unstable slip, whereas the presence of remodeling indicates a stable slip.

Magnetic resonance imaging (MRI) is used for early detection of AVN.

Traditional classification

The traditional classification of SCFE is as follows:

• Preslip - Discomfort (pain and restricted internal rotation) is mild; the diagnosis is based primarily on radiologic findings, with widening and irregularity of the physis and generalized osteopenia in the affected hemipelvis ^[51] ; a scoring system for staging a preslip on the contralateral side has been developed ^[46]
• Acute slip (10-15% of cases) - The duration of symptoms is less than 3 weeks, with no evidence of remodeling on the radiograph (see the image below) ^{[43, 52]}
• Chronic slip (85% of cases) - Symptoms persist for more than 3 weeks ^[43]
• Acute on chronic - An acute-on-chronic SCFE is one associated with chronic symptoms initially and subsequent development of acute symptoms, as well as a sudden increase in the degree of slip, usually with minor trauma

Bilateral slipped capital femoral epiphysis. One side shows evidence of remodeling of the neck and an anterior bone bump that restricts flexion. The other side demonstrates an acute slip as seen by the absence of any evidence of remodeling.

This traditional classification system may not be accurate and is not useful for prognosis.[53, 54, 52, 55, 56]

Classifications based on stability

The focus of classification has shifted to determining the stability of the slip because stability significantly affects the prognosis. The classification into stable and unstable categories is important because it is predictive of the prognosis. The traditional classification of slips as acute or chronic is misleading in that it does not take into account the stability of the hip, which is highly predictive of the development of AVN.

The Loder classification categorizes SCFE as follows[57] :

• SCFE is considered stable when the child is able to walk with or without crutches
• SCFE is considered unstable when the child cannot walk with or without crutches

The Kallio classification is a radiographic categorization that depends on the presence or absence of a hip effusion on US, as follows[58, 59] :

• If the ultrasonograms demonstrate the absence of metaphyseal remodeling and the presence of an effusion, an acute event is likely to have occurred, and the SCFE is considered unstable
• If the ultrasonograms demonstrate metaphyseal remodeling and the absence of an effusion, an acute event has not occurred, and the SCFE is considered stable

Classifications based on severity

One approach to a severity-based classification of SCFE makes use of the epiphyseal-metaphyseal angle. On a true lateral radiograph, the capital femoral epiphysis and the femoral neck usually lie at right angles to each other (up to 87° is considered normal). The physeal-neck angle decreases in proportion to the amount of slip. Categories are as follows:

• Mild - The neck is displaced less than one third the diameter of the femoral head
• Moderate - One third to one half of the diameter of the femoral head is displaced
• Severe - Displacement is more than one half the diameter of the femoral head

Another approach uses the epiphyseal-shaft angle (angular measurement method), as follows:

• Mild - Angle < 30°
• Moderate - Angle of 30-60°
• Severe - Angle >60°

Depending on the epiphyseal-shaft angle (slip angle of Southwick), this classification is probably most important with regard to long-term prognosis (see the image below).[60, 48]  Mild and moderate slips have an excellent long-term prognosis when treated with in-situ pinning, whereas severe slips are associated with a more rapid decline in hip function over time.[61, 62, 63]

Southwick head-shaft angle (angle between the metaphyseal surface of the physis and the shaft of the femur on a frog leg lateral view). Difference from the opposite side is used to grade the severity of the slip.

In SCFE, the zone of hypertrophy is thickened, and the normal columnar arrangement of chondrocytes is lost. Chondrocyte clustering and disarray are evident.[64, 65]

Anatomically, the slip occurs in the layer of cartilage adjacent to the zone of provisional calcification (unlike a type 1 Salter-Harris injury, which occurs between the proliferating zone and the hypertrophic zone). However, the plane of cleavage may be irregular and may pass through different zones of the physis.

Ultrastructural studies show defective collagen fibrils and defects in collagen banding in the zone of hypertrophy and changes in the proteoglycan and glycoprotein concentrations in the zone of proliferation, with increased glycoprotein staining in the territorial matrix and increased proteoglycan staining in the extraterritorial matrix.[66]

Treatment of slipped capital femoral epiphysis (SCFE) is essentially surgical.[67] The main principles of treatment are as follows:

• Stabilization of the slip to prevent progression
• Promotion of closure of the upper femoral physis

Although surgery should be performed promptly, it is elective; therefore, any severe underlying medical conditions (eg, renal failure or endocrinopathies) that would significantly increase surgical risk should be addressed.

Current treatment methods for a patient with an SCFE include the following:

• Hip spica cast immobilization ^[68]
• In-situ stabilization with single or multiple pins or screws ^{[54, 56, 69, 70]}
• Open epiphysiodesis with autograft or allograft bone ^{[71, 72, 73]}
• Open reduction with a corrective osteotomy through the physis and internal fixation with multiple pins ^{[74, 75]}
• Compensatory basilar neck osteotomy with in-situ stabilization with multiple-pin fixation ^{[76, 77]}
• Intertrochanteric osteotomy with internal fixation ^[78]

Treatment of unstable SCFE is controversial. Whether to use one or two pins for stabilization is debated, and some authors advocate open reduction maneuvers. Parsch et al treated 64 consecutive cases of unstable SCFE (20 mild, 24 moderate, and 20 severe) with capsulotomy, evacuation of intra-articular effusion or hematoma, gentle reduction, and fixation with unthreaded Kirschner wires (K-wires).[63] Reduction was successful in 61 cases, without development of avascular necrosis (AVN). Three patients did develop AVN (two with moderate slips and one with a severe slip).

Prophylactic pinning of the contralateral hip, which has long been the practice in some countries, is now being considered more frequently in North America.

The duration of hip spica casting is usually approximately 12 weeks. Advantages are as follows:

• It avoids the complications of anesthesia and surgery
• It also provides prophylactic treatment for the opposite hip; bilateral slips are seen in 20-40% of cases ^{[20, 39, 40, 41]}

Disadvantages are as follows:

• It does not stabilize the SCFE, and most investigators have reported progression of the slip in 5-10% of patients, despite immobilization in the cast ^{[68, 79]}
• The frequency of chondrolysis appears to be higher than with surgical treatment ^{[68, 79]}
• It is cumbersome, especially if the patient is obese, and restricts the mobility of the patient; it can also cause cast sores

For all of these reasons, the authors do not recommend a hip spica cast for treatment of SCFE. Routine use of a hip spica cast in the treatment of SCFE is no longer recommended.

For this procedure, the patient lies supine on a fracture table or a radiolucent-top table. Excellent intraoperative imaging is absolutely essential. In acute slips, positioning of the patient's affected limb in slight flexion and internal rotation may result in an incidental reduction. An aggressive reduction maneuver should be avoided.

A screw or screws are inserted percutaneously under fluoroscopic guidance as described previously by other authors.[72, 80]  Use of 7.3-mm cannulated screws is recommended. For a stable slip, a single screw is preferred; for an unstable slip, the question of whether to use one or two screws is controversial. Use of more than two screws is not recommended, because it increases the risk of iatrogenic damage to the vascularity of the femoral head.

The entry point must be at or above the level of the lesser trochanter to avoid subtrochanteric fracture. It also should be anterolateral, as opposed to the lateral entry point used in fixation of fractures around the hip. Screws are directed from anterolateral to posteromedial.

Care is taken to remain in the center of the capital epiphysis and perpendicular to the physis on AP and lateral views.[80]  Posterosuperior placement in the epiphysis is to be avoided at all costs so as to prevent damage to the lateral epiphyseal vessels.[42, 81]  At least 2.5 threads should engage the epiphysis for a good hold. (See the images below.)

Pin placement (anteroposterior view). A: The entry point must be at or above the level of the lesser trochanter to avoid the risk of subtrochanteric fracture. B: The pin (screw) should be in the center of the epiphysis. C: At least 2.5 threads engaging the epiphysis should be used for a secure hold.

Pin placement (lateral view). Arrow shows entry point in the anterolateral cortex.

Screw position must be confirmed. Although temporary penetration of guide pins into the joint has not been shown to be associated with chondrolysis, hardware that remains in the joint must be avoided to decrease the risk of chondrolysis and joint degeneration.

Advantages to pinning are as follows:

• It is a simple, short procedure
• Blood loss is minimal
• Success rates are high, and rates of slippage and complications are low ^{[19, 80, 82]}

Disadvantages are as follows:

• It may be technically difficult in patients with severe slips
• It is associated with a risk of pin penetration into the joint, especially if multiple pins are used

Single-screw fixation in patients with SCFE has yielded gratifying results. Aronson and Carlson reported excellent or good results in 36 (95%) of 38 mild slips, 10 of 11 moderate slips, and eight of nine severe slips. AVN developed in only one patient (2%) with an unstable SCFE, and chondrolysis developed in no patients.[54]

Ward et al reported on 42 patients (53 hips) with an SCFE treated with single-screw fixation.[56]  After a mean duration of follow-up of 32 months, 92% of the patients demonstrated physeal fusion and were able to participate in full activities. Neither chondrolysis nor AVN developed in any patient.

Samuelson and Olney, using a similar percutaneous technique, reported excellent results in seven patients treated with two Knowles pins and in 17 patients treated with a single Knowles pin.[29]

Castaneda et al studied 105 patients with a slip greater than 60º who were treated with in-situ pinning with a single cannulated screw to determine functional outcome. There were excellent results in 52 patients, good results in 28, fair results in 16, and bad results in nine (resulting from inadequate pin placement). Better results were found to have occurred in patients younger than 12 years.[83]

Remodeling or adaptation may occur after pinning, and the loss of internal rotation often improves. Pinning is currently the method of choice for stabilization of all slips.

Controversies include the following:

• Single pins are preferred for stable slips, but there is no consensus on the number of pins to use for unstable slips
• The data are not yet sufficient to determine whether early reduction and stabilization in unstable slips provides more benefit than delayed surgery ^{[57, 84, 85]}
• Prophylactic pinning of the contralateral hip is recommended in noncompliant patients and when follow-up is not ensured, as well as in patients with endocrinopathy or renal disease in whom the risk of contralateral slip is very high, ^{[86, 87]}  but the indications in other patients are less well defined; the modified Oxford bone scoring system may help determine who should be treated prophylactically ^[46]

This procedure was first reported by Ferguson and Howorth in 1931.[88]  The hip is exposed via the iliofemoral approach. A rectangular window of bone is removed from the anterior aspect of the femoral neck. A cylindrical tunnel is created across the physis, and multiple corticocancellous strips of iliac crest bone graft are driven into the tunnel as bone pegs across the proximal femoral physis in an attempt to promote early closure of the physis. A cortical strut allograft, for structural support, also may be used.[73]

Advantages include the following:

• The risk of damaging the vascularity of the femoral head is reduced because the graft usually is inserted at a proper angle
• The risk of the graft being inserted too deeply and causing joint penetration is also reduced
• The complications of internal fixation, including unrecognized pin penetration and hardware failure, are avoided
• Rapid, reliable closure of the physis is achieved

Disadvantages include the following:

• The curettage may make the slip even more unstable, and the fixation afforded by bone graft is not as solid as that provided by pins; a risk of additional slippage remains
• The operating time and the duration of anesthesia are longer
• Blood loss is increased
• The incision is larger
• A spica cast is needed

Weiner et al reported on their 30-year experience with this technique, which they used to treat 159 patients (185 hips) who had an SCFE. Additional slipping developed in four hips (2%), AVN developed in one (1%), and chondrolysis developed in none.[72]

Rao et al reported on evaluations of 43 patients (64 hips) treated by open bone-peg epiphysiodesis. At the time of healing, 27 hips (42%) had additional slipping. AVN developed in four hips (6%), chondrolysis developed in three (5%), and additional complications developed in 14 (22%).[71]

Schmidt et al reported on evaluations of 31 patients (38 hips; mean follow-up, 3.5 years) and stated that the Harris hip rating was excellent for 35 hips, good for one, and fair for two. Six patients (19%) had a major complication: AVN, chondrolysis, femoral neck fracture, subtrochanteric hip fracture, bilateral coxa vara deformity, and unilateral coxa vara deformity occurred in one patient each.[73]  Despite these complications, the authors still recommended this technique, particularly for a patient with a severe SCFE.

Osteotomies for patients with SCFE are recommended most commonly as secondary procedures after clinically significant residual deformity develops. They are aimed at altering the arc of motion and at attempting to retard the onset of osteoarthrosis.

The osteotomies can be performed through the physis, neck, or subtrochanteric regions. As the osteotomies move from proximal to distal, the correction moves further from the point of deformity, but the risk of AVN decreases. (See the image below.)

Osteotomies in slipped capital femoral epiphysis (SCFE). A: Subcapital osteotomy. B: Base of the neck compensatory osteotomy. C: Intertrochanteric compensatory osteotomy. Note that the amount of correction increases from subcapital to intertrochanteric osteotomies.

Open reduction with corrective osteotomy through physis and internal fixation with multiple pins

In this procedure, as described by Fish[89] and by Dunn and Angel[90] (see the image below), the hip is exposed via the anterior Smith-Petersen or anterolateral approach.[74, 75]  A wedge of bone is removed from the metaphysis of the femoral neck, allowing the epiphysis to be repositioned anatomically on the metaphysis without creating tension on the epiphyseal vasculature. After the femoral neck is shortened sufficiently, the epiphysis is reduced and internally fixed with three pins.

Principle of the Dunn osteotomy. Reduction of the slip after shortening the neck to avoid stretch on the vessels and decrease the risk of avascular necrosis.

The advantage of this procedure is that correction is performed at the site of deformity. The disadvantage is that the procedure is associated with a high risk of AVN.

Fish reported on cuneiform osteotomy in 61 patients (66 hips) and stated that 55 hips (83%) had an excellent result, six (9%) had a good result, two (3%) had a fair result, and three (5%) had a poor result.[89]

DeRosa et al evaluated 23 patients (27 hips) with severe SCFE treated by cuneiform osteotomy.[74]  After a mean follow-up of 8 years 5 months, no hip had an excellent result, 19 (70%) had a good result, four (15%) had a fair result, and four had a poor result. AVN developed in four (15%) and chondrolysis in eight (30%). In addition, two patients (7%) lost fixation and required additional surgery, one developed a skin erosion over a pin and required pin removal, and another had a buttock pressure sore. Despite the 15% AVN rate, the authors would still recommend this osteotomy for patients with severe SCFE.

Velasco et al evaluated 65 patients (66 hips) treated with open reduction for SCFE.[75]  In 60 hips, open reduction of the slip was combined with a cuneiform subcapital wedge resection of the femoral neck according to the Dunn-Angel technique. At a mean of 16 years, chondrolysis had developed in eight hips (12%) and AVN in seven (11%). Of the 48 hips followed for at least 10 years (mean, 20.6), 22 (46%) had a good result, 16 (33%) a moderate result, and 10 (21%) a poor result. Degenerative arthritis was seen in 19 (40%) of the 48 hips.

In a study of 30 children with severe stable SCFE who were treated with either the modified Dunn procedure (n = 15) or in-situ pinning (n = 15), Novais et al found that at a mean follow-up of 2.5 years, the former procedure was superior with respect to proximal femoral radiographic deformity, Heyman and Herndon clinical outcome, complication rate, and number of reoperations after the initial operation.[91]

In a multicenter study of 20 SFCE patients (21 hips) with an average Harris hip score of 76.3 (range, 40-100) who were treated with the modified Dunn procedure, Javier et al found that 65% of patients had good or excellent functional results but that the rate of complications (eg, osteonecrosis and infection) was high.[92]

Compensatory basilar neck osteotomy with in-situ stabilization with multiple-pin fixation

This technique was described by Barmada et al,[76] Crawford,[93] and Kramer et al.[77] The anterosuperior-based wedge osteotomy was described by Kramer et al, and the extracapsular basilar neck osteotomy was described by Barmada et al.[76]

The main advantage is that the prevalence of AVN associated with basilar neck osteotomy is less than that associated with cuneiform osteotomy.

Disadvantages are as follows:

• It shortens the femoral neck, which may result in impingement of the greater trochanter against the lateral aspect of the acetabulum during hip abduction
• If the proximal femoral physis closes prematurely, as is often seen in patients with an SCFE, shortening of the femoral neck may aggravate a limb-length discrepancy
• Only 35-55° of correction is possible with this technique

Kramer et al described an anterosuperior-based wedge osteotomy of the femoral neck in 55 SCFE patients (56 hips) who all had a positive preoperative Trendelenburg test result and had walked with a lurching gait.[77]  They stabilized both the osteotomy site and the SCFE with multiple pins. After the osteotomy, 48 patients (87%) had a negative Trendelenburg test result. Nine hips (16%) had a poor result because of pain, a limp, or a decreased range of motion (ROM). AVN developed in two patients (4%) and chondrolysis in one (2%).

Intertrochanteric osteotomy with internal fixation

This technique was described by Crawford,[81] Schai et al,[94] and Southwick[78]  and was initially proposed by Southwick as the primary treatment for severe slips. It is now used primarily if restricted ROM persists even after remodeling of the slip. The procedure consists of an intertrochanteric osteotomy at the level of the lesser trochanter with flexion, abduction, and internal rotation of the distal fragment. The osteotomy site is fixed with a compression hip screw, blade plate, or other fixation device.

Advantages are as follows:

• It improves hip motion
• It is rarely associated with AVN

Disadvantages are as follows:

• It results in shortening and limb-length discrepancy
• The correction is limited to 45° on the anteroposterior (AP) radiograph and to 60° on the lateral radiograph, as measured by the Southwick method ^[95]

Schai et al evaluated 51 patients who had an SCFE of 30-60° that was treated with an intertrochanteric osteotomy and followed for a mean of 24 years.[94]  Moderate osteoarthritis developed in 14 patients (27%) and severe osteoarthritis in nine (18%). Thirty-five patients (69%) had a shorter limb on the affected side, and two (4%) had a limb-length equalization procedure. AVN developed in only one patient (2%).

In stable slips, partial weightbearing with axillary crutches can be started as soon as the patient is comfortable after pinning, with progression to full weightbearing as tolerated. In unstable slips, toe-touch weightbearing with axillary crutch protection is used for 6 weeks after pinning. The patient may be discharged on the day after pinning and after 3-5 days for uncomplicated osteotomies.

In patients with unilateral slips, the patient must return for an evaluation if any pain develops on the contralateral side.

Avascular necrosis

AVN is the most devastating complication of SCFE.[96] Factors responsible for the development of AVN include the following[3, 42, 74, 81, 89, 97, 63] :

• Acute, unstable SCFE
• Overreduction of an acute SCFE
• Attempted reduction of the chronic component of an acute-on-chronic SCFE
• Placement of pins in the superolateral quadrant of the femoral head
• Femoral neck osteotomy, especially if performed before physeal closure

Clinical features include pain in the groin or knee. On physical examination, loss of motion of the hip, particularly internal rotation, is evident, and the hip is irritable upon passive internal and external rotation.

Plain radiographs are unremarkable early in the course of the disorder, but changes diagnostic of AVN (collapse of the femoral head with cyst formation and sclerosis) develop after a few months. All cases of AVN after SCFE are radiographically apparent within 1 year. Early bone scanning or magnetic resonance imaging (MRI) often reveals asymmetry between the femoral heads, predicting the eventual development of AVN.[98]

Symptomatic treatment includes nonweightbearing walking with crutches, ROM exercises, traction, and anti-inflammatory medication. The radiographic evaluation should reassess the position of the hardware, which can protrude into the hip joint with femoral head collapse. Clearly, this should be backed out of the joint or removed if the physis is closed. In severe cases, a hip arthrodesis or joint arthroplasty may be needed.

A multicenter study by Kohno et al suggested that the timing of surgery in the setting of unstable SFCE may be related to the risk of AVN; they found that AVN rates were highest when the time to surgery was between 24 hours and 7 days.[99]

Chondrolysis

The factors responsible for chondrolysis are unknown. The possible role of an autoimmune phenomenon or some factor interfering with cartilage nutrition is yet to be defined. Risk factors for developing chondrolysis include the following:

• Immobilization in a cast
• Unrecognized permanent pin penetration
• Severe SCFE

The prevalence of chondrolysis is 5-7%.[20] It is not increased in the black population, as has previously been reported.[20, 47, 65, 69] Clinical features include pain in the groin or knee and a loss of hip motion, particularly internal rotation.

Radiographs demonstrate a greater than 50% decrease in the width of the joint space as compared with the uninvolved side or, in patients who have bilateral involvement, a joint space of less than 3 mm. Hips that demonstrate increased uptake with premature closure of the greater trochanter on an early bone scan have been associated with an increased risk for the development of chondrolysis.[98]

Symptomatic treatment is similar to that of AVN. Early and aggressive physical therapy may help regain ROM. Some authors have recommended surgical interventions, such as extensive releases or distraction with external fixation.

Device penetration into joint

The frequency of problems related to internal fixation devices (slip progression, pin breakage, and joint penetration by the pins) is decreasing with the use of fluoroscopic guidance and cannulated single-screw fixation. The risk of fracture through an unused pinhole can be avoided by using fluoroscopy to position the guide pin and by entering the bone proximal to the lesser trochanter.

Iatrogenic hip instability

A report by the International SFCE Study Group assessed the modified Dunn procedure in 406 patients with severe, chronic SFCE at eight institutions and found iatrogenic anterolateral hip instability to be a potentially devastating, albeit uncommon, complication.[100] The authors suggested that maintaining anterior hip precautions for several weeks postoperatively in an abduction brace or broomstick cast might help prevent this complication.

The following consultations may be useful:

• A consultation with a pediatric endocrinologist may be useful when an underlying endocrinopathy is suspected
• A consultation with a pediatric nephrologist is useful for management of renal failure
• A dietitian may be consulted for a graduated weight-loss program; at least 50% of patients are above the 95th percentile for weight