HISTORY OF PRESENT ILLNESS
A 14-year-old boy presented to the emergency department complaining of left knee pain. Three days prior to this visit he noted left knee pain after playing basketball and began to limp. This knee pain improved over the next few days. However, on the day of presentation, he slipped and fell while walking across a wooden floor. As soon as he stood up, he again noted pain in his left knee that occasionally radiated to the left hip. There was no other bone pain. He did not strike his head and did not report headache, blurry vision, or loss of consciousness. There was no fever, weight loss, myalgias, or malaise.
The patient required overnight hospitalization at 8 years of age for disorientation following a car accident. His symptoms resolved fully. At the age of 10, he developed poststreptococcal glomerulonephritis and was treated with a short course of corticosteroids. He did not report taking any medications, currently. There was no family history of endocrine or autoimmune disorders.
T 37.1°C; HR 105 bpm; RR 24/min; BP 125/80 mmHg
Weight 101 kg
Physical examination revealed an obese boy without visible evidence of head trauma. He was alert and cooperative. Heart and lung sounds were normal. The abdomen was soft without organomegaly. There was no deformity of either lower extremity. Passive flexion of the left hip accompanied by internal and external rotation significantly worsened the left knee pain. Internal rotation of the left hip was limited compared to the right hip. There was no tenderness, swelling, or erythema of the left knee. There was full range of motion of the left knee without discomfort when this joint was tested in isolation. There was no sign of knee ligament instability. The right lower extremity was normal. He had an antalgic gait and preferred not to place weight on the left leg due to pain.
The complete blood count revealed the following: 8600 white blood cells/mm3 (65% segmented neutrophils, 30% lymphocytes, and 5% monocytes); hemoglobin 13.1 g/dL; and 204 000 platelets/mm3. C-reactive protein was 0.7 mg/dL and the erythrocyte sedimentation rate (ESR) was 12 mm/h. Serum electrolytes and calcium were normal.
COURSE OF ILLNESS
Radiographs of the left knee were normal. Hip radiographs revealed the diagnosis (Figure 5-3).
FIGURE 5-3. Antero-posterior (AP) radiographs of the hip.
DISCUSSION CASE 5-3
Diagnosing the cause of knee pain in an adolescent can be difficult. Since knee pain may actually be pain referred from the hip via the obturator nerve, diagnostic considerations should include problems involving either the knee or the hip. In this case, although the patient was adamant in his complaint of pain localized to the knee, examination of the knee was normal. The lack of physical findings localized to the knee makes septic arthritis of the knee and fracture of the distal femur, patella, proximal tibia, and fibula unlikely. Antecedent trauma raises the possibility of knee hyper-extension or patellar dislocation but the normal knee examination places these possibilities lower on the differential diagnosis. Osgood-Schlatter disease typically presents with localized tenderness and swelling over the tibial tuberosity, findings that were absent in this case.
Hip disorders to consider in an adolescent boy include avascular necrosis of the femoral head, septic arthritis of the hip, femoral or pelvic osteomyelitis, femoral neck fracture, chronic developmental hip dysplasia, inguinal hernia, slipped capital femoral epiphysis, Ewing sarcoma, and osteogenic sarcoma. Avascular necrosis of the femoral head can be caused by corticosteroid use and also occurs in children with sickle cell disease (SCD) and idiopathically (Legg-Calvé Perthes disease). The absence of fever combined with a normal C-reactive protein and ESR makes acute septic arthritis and osteomyelitis unlikely. In this case, radiographs of the hip narrowed the above differential diagnosis even further.
Antero-posterior (AP) radiographs of the hip (Figure 5-3) demonstrated inferior displacement of the left femoral head relative to the femoral neck. On the lateral frog leg view this displacement appeared posterior and medial relative to the femoral neck. These findings confirmed the diagnosis of slipped capital femoral epiphysis (SCFE). The patient underwent percutaneous screw fixation (Figure 5-4). Prophylactic screw fixation of the contralateral hip was also performed.
FIGURE 5-4. Percutaneous screw fixation.
INCIDENCE AND EPIDEMIOLOGY
The term SCFE refers to displacement of the femoral head relative to the femoral neck through the physis (growth plate). This displacement results from either cumulative normal stresses acting on a weakened physis or by an acute traumatic event on a normal or previously weakened physis. SCFE occurs with an annual incidence of 2-3 cases per 100 000 persons. It typically develops during the adolescent growth spurt, occurring in boys 10-16 years of age and girls 10-13 years of age. The incidence is approximately 2.5 times greater in boys compared with girls. The incidence is also higher in African-Americans compared with Caucasians. Obesity is a predisposing factor. One-half to two-thirds of children with SCFE have weight-for-height profiles greater than the 95th percentile. Obesity may contribute by creating increased shear forces across the weakened physis during ambulation. Underlying endocrine or metabolic disorders that delay skeletal maturation, such as primary or secondary hypothyroidism, panhypopituitarism, and hypogonadism, should be suspected in children who fall outside the typical age or weight range for SCFE. In this case, corticosteroids the patient received at 10 years of age were not thought to be a contributing factor in the development of SCFE.
There are often considerable delays in the diagnosis of SCFE. Patients frequently complain of symptoms 3-4 months before diagnosis. Therefore, clinicians should have a high level of suspicion for the diagnosis of SCFE even in adolescents with vague complaints of hip, thigh, or knee pain.
Patients with SCFE usually complain of pain in the affected hip or groin. Pain perceived in the medial thigh and knee is due to referred hip pain along the sensory distribution of the femoral and obturator nerves. Isolated knee pain is the sole presenting feature in up to 15% of children diagnosed with SCFE. Early in the course, pain is usually associated with exercise, but as the slip progresses, the symptoms become more persistent and severe.
On physical examination, patients complain of pain with rotation of the hip. The pain is most prominent at the extremes of rotation. Internal rotation may be noticeably decreased. Furthermore, as the hip is flexed, the thigh rotates externally. This finding, when present, is nearly pathognomonic for SCFE in an obese adolescent. Thigh or gluteal muscle atrophy occurs with long-standing symptoms and disuse.
AP and frog leg lateral hip radiographs. On the AP view, a line drawn along the superior femoral neck (Klein’s line) normally intersects a portion of the femoral head. In SCFE, the femoral head will be located below this line. On the frog leg lateral view, the femoral head is displaced posterior and medial to the femoral neck. In the early stages of SCFE, the only finding may be a widened and blurred physis. In chronic cases (symptoms present longer than 3 weeks), radiographs may reveal bony remodeling along the posterior and medial aspects of the femoral neck. Both hips should be examined since SCFE will be bilateral in 25% of cases. Approximately 20% to 50% of those with known unilateral involvement ultimately develop SCFE in the contralateral hip. Radiographs also allow exclusion of conditions with similar manifestations such as femoral neck fracture.
Additional imaging. Hip ultrasound, computed tomography, and magnetic resonance imaging have been used to confirm the diagnosis when hip radiographs are inconclusive.
Other studies. Consider evaluating thyroid and pituitary function in children outside the typical age or weight range for SCFE, as hypothyroidism and growth hormone deficiency also predispose to SCFE. Complete blood count, C-reactive protein, and ESR should be obtained when osteomyelitis or septic arthritis are diagnostic considerations.
The goals of treatment are to prevent further slippage and restore function. The patient should not be allowed to bear weight on the affected extremity once the diagnosis has been confirmed. An untreated stable slip may progress to a more severe unstable slip, leading to increased morbidity. The most common surgical treatment involves percutaneous fixation of the displaced femoral head with one or more metallic pins or screws.
Prophylactic treatment of the asymptomatic contralateral hip is controversial. Complications of prophylactic pinning such as avascular necrosis, peri-implant femur fracture, and pain requiring hardware removal occur in approximately 5% of cases. However, the incidence of eventual bilateral involvement is relatively high, ranging from 15% to 40%. Among 133 patients with unilateral SCFE undergoing unilateral repair, 20 (15%) developed SCFE in the contralateral hip within 2 years. Therefore, some surgeons advocate for treatment of the contralateral hip at the time of initial surgery. Some orthopedic surgeons recommend fixation of an asymptomatic contralateral hip only in patients who are at highest risk of developing SCFE of the contralateral hip, such as those with known endocrine or metabolic disorders. The modified Oxford Bone Age Score may improve identification of children at greatest risk for contralateral SCFE who may benefit most from prophylactic pinning.
Outcome after repair is generally good but depends on the degree of abnormality prior to repair. Subsequent avascular necrosis of the femoral head complicates 15% of cases. Avascular necrosis is most often a consequence of vascular injury associated with initial femoral head displacement rather than a consequence of the repair. Patients with a moderate or severe degree of femoral head displacement at presentation are also more likely to develop associated osteoarthritis. Chondrolysis or destruction of cartilage may occur after pin placement but has also occurred in patients without any surgical therapy. Leg length discrepancy may result from incomplete reduction, avascular necrosis, or chondrolysis. Early recognition and treatment of SCFE prevents many of these complications.
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