An Introduction to Hip Problems in Children Marlis Sabo, Meds 2005 Children are susceptible to a variety of hip problems throughout the period of skeletal maturation. Some are emergencies, while others are self-limited and relatively benign. Some are also linked to the developmental stage of the child. It is important to recognize those conditions requiring timely treatment and referral. The following is a brief discussion of some of the conditions that must be considered in approaching a child with a lower limb complaint. INTRODUCTION The hip in childhood is a highly dynamic and developing structure. For optimal hip growth and function into adulthood, the head of the femur and the cup of the acetabulum must be maintained in correct contact. Furthermore, unique properties of the hip during early development make it susceptible to certain conditions present only in childhood. Assessing the hip in children can be difficult. In addition to poor symptom description on the part of the child, the symptoms may be misleading (such as knee pain in hip pathology) or confusing (such as recent trauma that may be irrelevant to the diagnosis). Important information includes a correct characterization of any pain present (location, day vs night pain, duration, severity, ability to weight bear), duration of any limp, the child’s past medical and developmental history, other symptoms (fever, rashes, weight loss, decreased movement of the leg in infants), and family history.1 The physical examination is of great importance, and should include an examination of gait, inspection, palpation of the hip and pelvis, and assessment of range of motion.1 Both hips should be examined, as should the knee and lumbar spine. Attention should also be given to vital signs such as temperature, body habitus, and skin rashes. Appropriate investigations depend on the clinical presentation, but in nearly every case, plain film radiography forms the starting point. The differential for limp and hip/leg pain is long and varied, and can be imposing. This paper discusses some of the more common and important disease entities of the paediatric hip. SEPTIC ARTHRITIS OF THE HIP Hips are the second most common joint to be infected, with the incidence of infection decreasing with the age of the child.2 The child’s presentation depends somewhat on age, but includes anterior hip and thigh pain, pseudoparalysis (unwillingness to move the limb), fever, recent infection (such as pharyngitis), and possibly a history of trauma.2 On examination, the child would hold the hip in external rotation, abduction and slight flexion as this maximizes the space inside the capsule, which would be full of purulent material.2 Pain would be elicited with internal rotation, extension, and flexion more than 60º.2 Muscle guarding may be evident, and one should palpate both hip and pelvis for tenderness.2 An abdominal exam is indicated as a psoas abscess (although rare) could present similarly.2 Appropriate investigations include a CBC and differential, ESR, CRP, blood cultures, and serum glucose. The white cell count may be misleadingly low depending on the age of the child.2 The joint itself should also be aspirated emergently for material that can be cultured (positive in 50-80%), Gram stained, and assessed for white cell count and glucose. Compared with plasma, the aspirate glucose is reduced.2 A white cell count greater than 50,000/mL (>90% polymorphonuclear cells)2,3 is also highly suggestive. Plain films show soft tissue edema, loss of tissue planes, widening of the joint space, capsular distension, UWOMJ 74(2) 2006 43 Table 1: Considerations on the differential of pain and limp in children1, 2, 10 Condition Pain Septic Hip + Acute Hematogenous Osteomyelitis + Slipped Capital Femoral Epiphysis + Legg-Calvé-Perthes Disease +/– Developmental Dysplasia Irritable Hip + Post-Infectious Arthritis + Juvenile Chronic Arthritis + Collagen Vascular Diseases + Henoch-Schonlein Purpura + Leukemia + Bone Tumors +/– Psoas Abscess + Pyomyositis + Sickle Cell Disease + Fracture + Dislocation + Low back disorders + Knee disorders + Foot and Ankle disorders + Neuromuscular disorders - Limp +/Pseudoparalysis + + + + + + + + +/– +/– +/– +/No WB +/No WB + + + + subluxation, and possibly an osteomyelitis.2 Ultrasound can be used to differentiate a septic hip from an irritable hip.2 Bone scintigraphy with gallium can also help sort out difficult cases.2 A septic hip is an urgent issue in a child, and requires surgical drainage and IV antibiotics.2 The common pathogens are somewhat age-dependent, but overall, Staph. aureus and streptococcus species are implicated in most cases.2 Complications include premature physeal closure, growth abnormalities, pseudoarthrosis, subluxation or dislocation of the femoral head, and acetabular dysplasia.2 Risk factors for a poor outcome include age under 6 months, delay of more than 4 days to treatment, associated osteomyelitis, and Staph. aureus infection.2 ACUTE HEMATOGENOUS OSTEOMYELITIS Acute hematogenous osteomyelitis affects roughly 1:5,000 children under age 13, with 50% of these occurring in children under 5 years old.4 The femur is the site of infection in 27% of cases. Like septic arthritis, the common pathogens are Staph. aureus and streptococcus species.4 It is important to note that because of the unique blood supply and capsular structure of the developing hip, a femoral osteomyelitis can erode into the hip and cause a comorbid septic arthritis. The most common historical features are fever, pain, and limited use of the extremity.4 Lethargy and anorexia are less common. On examination, there may be point tenderness. Swelling is age-dependent such that a very small child with a thinner periosteum may have a great deal more swelling than an older child. Range of motion is reduced, and there may be cellulitis overlying an abscess. As with septic arthritis, a CBC and differential, ESR, CRP, blood culture, and direct aspiration for culture are indicated. Plain 44 UWOMJ 74(2) 2006 film radiographs begin to show changes at 48 hours with soft tissue swelling.4 Periosteal new bone formation becomes visible at 5-7 days, while osteolytic changes don’t appear until 10-14 days after onset. On bone scintigraphy, cold spots (ischemia) are more predictive than hot spots. MRI is most useful for defining the marrow of long bones and for planning surgical debridement. Management is mainly medical, with surgery reserved for cases requiring decompression, debridement, and facilitation of antibiotic delivery. Current opinion on antibiotics suggests that at least three weeks of IV and PO antibiotics are required, with neonates receiving the entire course by IV. Complications include recurrent or chronic infection, pathological fracture, growth disturbances, and side effects of the antibiotics including rash, GI upset, and neutropenia. Given delays in diagnosis or inadequate treatment, adverse outcomes are as common as 6% of cases.4 IRRITABLE HIP (TRANSIENT SYNOVITIS) Transient synovitis of the hip is the most common cause of a childhood limp aside from traumatic events.3 Its incidence is 14/1000, peaking between 3 and 8 years of age. There is also a seasonal variation in cases. Boys and Caucasian children are more commonly affected, with neither side affected more. In 5% of cases, the synovitis is bilateral. The child presents with hip pain, limp, and may have had a preceding illness. The presentation can mimic that of septic hip, but the symptoms and findings are less severe. As a result, labs such as CBC, ESR and CRP are done more to rule out other serious conditions.3 Plain AP and frog-leg views of the hip are taken, also to rule out more serious problems. Ultrasound of both hips can help to distinguish between irritable hip and septic hip. The key findings are echo-free joint effusion2 and widening of the medial joint space more than 1 mm compared with the other hip.3 Since this is a self-limiting condition, once other conditions requiring therapy have been ruled out, observation is adequate. LEGG-CALVÉ-PERTHES DISEASE Perthes disease is a condition of femoral head necrosis, collapse, and regeneration most commonly found in boys between the ages of 4 and 10 years (although girls are also affected).5 The etiology is unknown, although a variety of theories have been postulated. Children present with mild pain, often referred to thigh or knee, and a limp. The patient may also present with a history of trauma. On physical exam, the child may appear small for their age, have an antalgic gait, a positive Trendelenburg sign, limited internal rotation, quadriceps atrophy, and adduction contracture leading to the appearance of a short leg.5 The hallmark diagnostic test are AP and frog-leg radigraphs of the hip and pelvis showing such signs as widened cartilage, sclerosis, collapse of the femoral head, and the cresecent sign of subchondral fracture. A variety of classification systems exist, based on the severity of involvement of the femoral head. In the very young with limited involvement, observation may be adequate therapy. In others with more severe disease, the basic principle of therapy is maintaining containment of the femoral head within the acetabulum, achieved with casting, bracing, or surgical intervention.5 Sequelae include degenerative arthritis, coxa magna, and growth disturbance. SLIPPED CAPITAL FEMORAL EPIPHYSIS Slipped capital femoral epiphysis (SCFE) is a condition in which the femoral head slides posteromedially off the femoral neck through the growth plate.6 The prevalence is 2/100,000, and is more common in boys than girls. Because it occurs in the gap between the onset of rapid growth and the onset of sex hormone production, this is a disease of early adolescence (averaging 13 years old in girls, 15 years old in boys). Children with SCFE are often obese (>95th percentile for weight), or, less commonly, have some endocrinopathy such as hypothyroidism, hypogonadism, hypopituitarism, or renal osteodystrophy. Two types of slips occur: stable and unstable. In stable slips, the pain is located in the hip and groin, and is much worse with walking. On exam, an antalgic gait with the leg in external rotation is observed, and loss of internal rotation, flexion and abduction can be demonstrated.6 In acute slips, a history of trauma is sometimes present, and the child will not be able to bear weight on the affected side. The hallmark investigation for SCFE is a set of AP and frog-leg lateral radiographs.6 The femoral head will be posteromedial to its correct location, demonstrated by drawing a line along the femoral neck (Klein’s line). In SCFE, the line will no longer intersect the femoral epiphysis. In unstable slips, reduction is attempted while in stable slips, fixation of the slip in its existing position are the goals of treatment. Complications include involvement of the contralateral side (in 20-40%, not necessarily simultaneously), avascular necrosis (up to 50% in unstable slips), chondrolysis, and osteoarthritis.6, 7 Because of this, careful follow-up after fixation is required until the child is out of the danger window. INFLAMMATORY ARTHRITIS This is a heterogenous group of disorders including Juvenile Chronic Arthritis (JCA), Ankylosing Spondylitis (AS), Lyme disease, and other inflammatory conditions.2 Juvenile Chronic Arthritis presents in one of three ways: Still’s disease, polyarticular, or pauciarticular joint involvement. The pauciarticular form is most likely to present with single hip involvement. The presentation is not as florid as a septic joint, and may include pain, other joint involvement, fever, weight loss, morning stiffness, or rash.2 Of importance is the high risk of iridocyclitis in the pauciarticular form that could lead to blindness if not treated by steroids. Lyme arthritis can be suspected if the child lives in or has traveled to an endemic area. An attempt to elicit a history of the characteristic erythema migrans occurring 3-21 days after the tick bite is also useful in diagnosing Lyme disease.2 The seronegative arthropathies such as AS present with leg joint involvement in slightly older children. Appropriate investigations include CBC and differential, ESR, CRP, RF, ANA, and Lyme serology.2 In JCA, Rheumatoid Factor (RF) may be positive only in a minority of patients, and these children are usually more severely affected. Complications include differential growth of the affected limb (often larger than the normal side), and destruction of the articular structures.8 DEVELOPMENTAL DYSPLASIA OF THE HIP The incidence of developmental dysplasia (DDH) is 11.5/1,000 live births, with risk factors including female gender, firstborn children, breech presentation, family history, oligohydramnios, and comorbid limb problems such as metatarsus adductus. Patients usually do not present with a history as the disease is usually uncovered on screening physical examination at birth.9 Key physical findings include positive Ortolani (an audible clunk as the hip reduces while being abducted) and Barlow (a posterior dislocation of the hip when posterior pressure is applied on a flexed hip) tests, leg length discrepancy, asymmetric skin folds, and if the child remains undiagnosed at time of walking, a waddling gait and hyperlordosis.9 Ultrasound is an important component of diagnostic testing as the hip is mostly cartilage at this point in life. Plain x-rays, however, can also offer important information. The acetabular index is the angle between a line drawn through the triradiate cartilage of the acetabula and a line connecting the brims of the acetabulum on each side.9 A normal acetabular index is up to 25º degrees. Increased values suggest that the femoral head is not located correctly and corresponding changes are causing a shallowing of the acetabulum. If caught early, a Pavlik harness worn constantly for 6 weeks results in a cure in 95% of cases. From 6 months to 2 years of age, skin traction, closed reduction and casting in a hip spica can keep the head correctly located as well. After two years of age, open reduction is the only effective treatment option. If untreated, pain, degenerative osteoarthritis, and differential limb growth can result.9 SUMMARY The potential causes of hip pain or limp in a child are many and varied, ranging from local disease such as septic hip or DDH to systemic disease such as inflammatory arthritis. Some are true emergencies, while others simply require reassurance and observation. In any event, important diagnoses ought not to be missed, and one should not be fooled by lack of pain in the hip area. An index of suspicion is necessary for timely diagnosis and referral, and to avoid potentially disastrous sequelae. AUTHOR’S NOTE Although several important hip diseases were briefly discussed in this paper, this is by no means a comprehensive discussion of the subject. For more information, please consult the references listed below. REFERENCES 1. Flynn JM, Widmann RF. 2001. The Limping Child: Evaluation and Diagnosis. JAAOS 9(2):89-98. 2. Sucato DJ, Schewnd RM, Gillespie R. 1997. Septic Arthritis of the Hip in Children. JAAOS 5(5):249-60. 3. Benson MKD, Fixsen JA, Macnicol MF, Bleck EE. 1994. Children’s Orthopaedics and Fractures. Churchill Livingstone. Edinburgh. 4. Song KM, Sloboda JF. 2001. Acute Hematogenous Osteomyelitis in Children. JAAOS 9(3):166-75. 5. Skaggs DL, Tolo VT. 1996. Legg-Calvé-Perthes Disease. JAAOS 4(1):916. 6. Aronsson DD, Karol, LA. 1996. Stable Slipped Capital Femoral Epiphysis: Evaluation and Management. JAAOS 4(4):173-81 7. Reynolds RAK. 1999. Diagnosis and treatment of slipped capital femoral epiphysis. Current Opinion in Pediatrics 11(1):80 8. Swann M. 1987. Juvenile Chronic Arthritis. Clinical Orthopedics and Related Research. (219):38-49. 9. Morrissy RT, Weinstein SL. 1996. Lovell and Winter’s Pediatric Orthopedics (4th ed). Lippincott-Raven. Philadelphia. 10. Hollister JR. 2003. Rheumatic Diseases. In Current Pediatric Diagnosis and Treatment (16th ed). Hay WH, Hayward AR, Levin MJ, Sondheimer JM. McGraw Hill. New York. UWOMJ 74(2) 2006 45