Chapter 108: The Limping Child

• In a child with a limp that occurs after trauma, localized radiographs or radiographs of the tibia on the affected side are most likely to reveal the diagnosis.

• Suspect hip pathology in a child with a limp and knee or thigh pain.

• Septic arthritis should be suspected in a child with fever, painful limp, elevated C-reactive protein (CRP) >2 mg/dL or erythrocyte sedimentation rate (ESR) >40, and a white cell count >12 × 10⁹/L.

• In a child presenting with a limp and without a history of trauma, fever or systemic symptoms, commence imaging with a hip ultrasound followed by radiographs if the ultrasound is negative.

• An MRI should be performed early in the diagnostic process if infection is a possible cause for a limp in a child.

• A history of trauma and the presence of fever are important symptoms to consider when ordering an expanded diagnostic workup for a limp.

A limp is a jerky, uneven, or laborious gait, usually caused by pain, weakness, or deformity The development of a child's gait is important to identifying the etiology of a limp. Children begin to crawl at 9 months, independently walk at 12 to 15 months and run at 18 months. At 1 year of age, the normal infant has a broad-based gait and moves the limbs rapidly with short steps with the arms flexed and without reciprocal arm movement. The foot makes contact with the ground all at once. By 3 years most adult kinematic patterns are developed. With subsequent changes in velocity and step length an adult gait pattern is achieved at 7 years. The adult gait consists of a stance phase and a swing phase. The stance phase (60% of the gait cycle) begins when the heel of one foot strikes the ground and bears all the weight, advances to a foot flat position during midstance and progresses to push-off by the toes as weight gets transferred from the heel to the forefoot. The swing phase begins when the opposite foot pushes off the ground; the leg is swung forward with the foot clearing the ground until the heel makes contact with the ground. The most common cause for a limp is trauma; Table 108-1 lists other causes. The differential diagnosis is influenced by the duration and type of limp, age of the child, and the anatomic site affected.

A limp of recent onset (<2 weeks) is usually due to trauma, acute infection, or neoplastic causes. A long-standing limp is more likely to be due to developmental dysplasia of the hip (DDH), a neuromuscular or rheumatologic problem, overuse, slipped capital femoral epiphysis (SCFE) or Perthes disease. In contrast to rheumatologic disorders in which the limp is worse in the morning and gradually improves as the day progresses, in muscle disorders there is a gradually increasing muscle fatigue over the course of the day leading to a worsening of the limp.

A history of trauma should be explored. The diagnosis may be difficult if the injury is not witnessed, or the alleged mechanism is inconsistent with the sustained injuries as in nonaccidental trauma. In one study, one-third of children with osteomyelitis of the long bones reported a history of trauma demonstrating that a history of trauma may confuse the diagnosis if the etiology of the limp is infectious.¹ Similarly, the presence of fever may confuse the clinician when trauma is a cause of a limp.

Fever may be present in septic arthritis, osteomyelitis, pyomyositis, soft-tissue infections, fasciitis, discitis, or psoas abscess or may be part of a viral prodrome as in transient synovitis. Other causes of fever include rheumatologic disorders and neoplastic disorders (e.g., leukemia, osteosarcoma, Ewing sarcoma, Langerhans cell histiocytosis, and osseous metastatic disease).

Determine the characteristics of pain, such as the location, type, severity, radiation, aggravating and relieving factors. Pain may be referred from the lower back to the buttocks and lateral thigh, or it may be referred from the hip to the groin, thigh, or knee. Unrelenting, severe pain is a feature of osteomyelitis, septic arthritis, sickle cell vasoocclusive crisis, displaced bone fractures, and compartment syndrome. Intermittent pain or pain of a lesser severity is usually seen with transient synovitis, juvenile idiopathic arthritis, Legg–Calvé–Perthes disease, SCFE, Osgood–Schlatter disease. Pain that worsens with activity is seen in overuse injury, stress fractures, and hypermobility syndromes. In patients with rheumatologic conditions or complex regional pain syndrome, pain improves after activity. Discordance between the history and the intensity of the pain experienced is observed in complex regional pain syndrome. A history of nighttime pain may accompany neoplastic conditions such as leukemia, osteogenic sarcoma, Ewing sarcoma, or benign tumors such as osteoid osteoma. Muscle pain is a feature of myositis.

Conduct a review of systems to search for systemic causes for a limp. A sore throat may precede acute rheumatic fever with arthritis. Reactive joint pain and swelling may appear 1 to 2 weeks after a diarrheal illness. Back pain is present in discitis, spondylolisthesis, or vertebral osteomyelitis. Urticaria and fever may accompany the arthritis of serum sickness. Bleeding gums and ecchymosis are seen in vitamin C deficiency (scurvy) and poor growth, motor delay, bow legs or knock knees observed in vitamin D deficiency (rickets). These conditions may cause bone pain and the gradual inability to walk. Henoch–Schonlein disease has a characteristic rash.

Vital Signs: Fever is likely to be associated with an infectious etiology but may be absent in 18% to 28%^2,3 of patients with septic arthritis.

General: Toddlers with painful foot conditions may crawl or ambulate on their knees. A child with a painful limb will be apprehensive and less active. Acute abdominal processes such as appendicitis and painful groin conditions such as testicular torsion and obstructed inguinal hernia may cause limping. Inspect the child's limbs from the waist down, examining the skin for contusions, puncture wounds, deformity, pustules or abscesses, retained foreign bodies, and ecchymosis or bruises as seen in accidental or nonaccidental trauma, hemophilia, or bleeding disorders with hematoma or Henoch–Schonlein purpura. Ingrown toenails, calluses caused by tight-fitting shoes, retained foreign bodies, and puncture wounds may cause a painful limp.

Musculoskeletal: Compare both lower limbs and evaluate for warmth, point tenderness, soft-tissue or joint swelling, deformity, limb-length discrepancy, and differences in girth. Leg-length discrepancy is seen in developmental conditions (limb hypoplasia, developmental hip dysplasia, and club foot), hemihypertrophy syndromes, or posttraumatic physeal injury. Arthritis causes pain on movement of the joint. The position of comfort for the hip joint is abduction and external rotation. Severe pain and swelling in the setting of a crush injury may suggest compartment syndrome. In the absence of fever, trauma, and systemic symptoms, pain on palpation of the tendon and fascia insertion sites suggest conditions such as Osgood–Schlatter disease (tibial tubercle apophysitis), Sever disease (calcaneal apophysitis), or plantar fasciitis. Compare active and passive ranges of motion of the joints on the affected and nonaffected sides, starting with the sacroiliac joints, hips, and knees to the ankles and toes (Table 108-2; Figs. 108-1 to 108-5).

A history of trauma and localized pain will point toward the injured area. However, in toddlers with a limp, a history of trauma may be absent, or there may not be localized tenderness. A useful radiographic screening strategy has been described for five types of fractures in the lower extremity.⁴ Type 1 is a spiral fracture of the tibia, which may be subtle and may be seen only on an oblique radiograph. It is diagnosed when you elicit pain upon twisting the leg while holding the knee and ankle. Hyperextension causes another type of fracture (Type 2) diagnosed when pain is elicited by holding the tibia and hyperextending the knee. Findings on imaging include a hairline fracture of the upper tibia often accompanied by a buckle fracture of the lateral or medial tibial cortex, buckling of the anterior, upper tibial cortex and/or increased concavity of the notch for the tibial tubercle on lateral view, and anterior tilting of the epiphyseal plate. Buckle fractures of the distal tibia and fibula (Type 3) should be suspected when squeezing and wobbling of the ankle while holding the ankle with a thumb and forefinger, causes pain. Type 4 or bunk-bed foot and ankle fractures are impaction-buckle fracture of the base of the first metatarsal and a compression fracture of the cuboid bone. This occurs when a child lands on the forefoot in a hyperflexed position. Point tenderness will be present when you press directly on the base of the first metatarsal and the cuboid bone Finally, fractures of the upper femur are usually nondisplaced Salter–Harris Type I fractures. Pain is elicited by holding the leg at the knee and rotating the hip (see Chapter 31 for fractures of the lower extremity).

It may be challenging to differentiate between a psoas abscess and septic arthritis of the hip. Patients with a psoas abscess may have a palpable abdominal mass and a positive psoas sign (Table 108-1); scoliosis, sciatica, and femoral nerve neuropathy may be present. Unlike children with septic arthritis, in whom range of motion is markedly limited in all directions due to pain, flexing the hip of a child with a psoas abscess will decrease the pain and internal and external rotation of the hip can be performed easily.

Examine the muscle groups for tenderness, strength, and tone. Proximal muscle weakness will be seen in muscle dystrophy and myopathies. In peripheral neuropathy or radiculopathy (Guillain–Barré syndrome), the reflexes will be depressed whereas they will be exaggerated in upper motor neuron disease with spasticity. Spinal dysraphism may present with midline abnormalities such as a dimple or tuft of hair.

Spine: Examine the spine for kyphosis or scoliosis and range of movement. A patient with a painful spinal condition will resist bending the spine. The differentiation between discitis and vertebral osteomyelitis in children can be difficult. In vertebral osteomyelitis, the child is usually ill-appearing, and the fever is usually higher and present for a longer duration. It may involve any part of the spine, as opposed to the lumbar area in discitis. In discitis, children may have fever, fussiness, or refusal to walk or sit, and there may be poor localizing signs. Plain radiographs may not show any changes early in the condition, and the diagnosis may be delayed. Older children with spondylolisthesis will experience lumbosacral pain on extension of the spine.

Gait: Evaluate the gait after completing the physical examination. As young children may refuse to walk for the examiner, ask the parents to beckon the child after they have moved some distance away. Examine the stance for pelvic tilting, scoliosis, knee flexion, leg asymmetry, or rotation of the foot. Pay attention to the overall motion, the stride length, and stance and swing phases. Also look at the pelvis, hips, thighs, knees, legs, ankles, and feet. Examine the shoes for wear and tear. Conditions, which cause foot drop, will lead to the foot “slapping” the ground during swing phase on the affected side. Test muscle strength by having the patient climb stairs, squatting, and heel and toe walking.

The most common gait abnormality is an antalgic gait. It is caused by a painful condition on the affected limb or referred pain from the back. Weight-bearing is reduced on account of the pain, and the stance phase gets shortened. The swing on the unaffected limb may lengthen. Gait due to limb-length discrepancy is manifested by a downward tilting of the trunk and pelvis during the stance phase on the shortened limb and circumduction of the longer leg during the swing phase of that side. Some children may walk on the toes of the shortened side. A circumduction gait is seen in a child with spastic hemiparesis or with an ankle or foot problem. The spastic limb is moved outwards in a half circle during the swing phase to allow the toes to clear the ground. A Trendelenburg gait occurs due to weakness in the hip abductors or in DDH. Here, the pelvis tilts towards the unaffected side during the stance phase of the affected side since the hip abductors on the affected side are not strong enough to counter the weight of the opposite side. If the weakness is bilateral, the patient will demonstrate a waddling gait as the pelvis tilts alternately on either side during walking. In a “steppage gait,” due to an inability to dorsiflex the foot, the hip and knee joints are flexed during the swing phase to allow the toes to clear the ground.

Laboratory studies are not usually necessary in a patient with a limp caused by trauma with no history of fever. If the child has systemic complaints such as fever, anemia, or weakness, CBC with differential, peripheral blood smear, ESR, and CRP tests should be ordered.

Kocher et al.² prospectively evaluated the performance of four predictors in the diagnostic phase of a clinical prediction model to differentiate between transient synovitis and septic arthritis of the hip joint: the combined presence of fever, non–weight-bearing, ESR >40, and a WBC >12 × 10⁹/L. In validating the rule in a new cohort, Kocher described a decreased diagnostic performance (93% probability of septic arthritis if all four factors were present)⁵ as have other validation studies (59%).³ Caird et al.⁶ added a CRP of >2.0 mg/dL to Kocher's criteria and was able to predict septic arthritis in 93% of patients if four factors were present and 97.5% if five factors were present. Currently, there is no clinical prediction rule that has been validated by a multicenter prospective study involving large patient numbers. The CRP is elevated earlier than the ESR and is a more sensitive indicator for infection and a better independent predictor of septic arthritis. CRP is a better negative predictor than a positive predictor of disease. If the CRP is <1.0 mg/dL, the probability of the patient not having septic arthritis is 87%.⁷

Joint pain may be observed in childhood leukemia. Leukemia may present with musculoskeletal symptoms such as pain and swelling even before the appearance of blasts in the peripheral blood. A retrospective study compared acute lymphoblastic leukemia (ALL) and juvenile rheumatoid arthritis: a low white blood cell count (<4 × 10⁹/L), low-normal platelet count (150–250 × 10⁹/L), and history of nighttime pain had a sensitivity and specificity of 100% and 85% respectively for a diagnosis of ALL.⁸ Order other tests for specific conditions: Lyme titers for Lyme disease, antinuclear antibody (ANA) test for juvenile idiopathic arthritis, and creatine phosphokinase (CPK) test for myositis.

Synovial Fluid Analysis: Septic arthritis is suspected in a patient with joint swelling, inflammation, severe pain, and markedly reduced range of movements or in a febrile child with an effusion of the hip joint. Synovial fluid obtained from joint aspiration should be sent for white blood cell count, protein and glucose, Gram stain, and aerobic and anaerobic cultures. Blood cultures should be sent in all children suspected of having septic arthritis. The sensitivity and specificity of white cell count in the synovial fluid above 40,000 per mm³ exceeds 90% in differentiating septic arthritis and other causes.⁹ Although a positive synovial fluid culture is diagnostic, synovial fluid analysis with >50,000 cells per mm³ with predominance (>90%) of polymorphonuclear cells suggests septic arthritis. However, synovial cultures may be negative despite clinical and laboratory features of septic arthritis due to fastidious organisms or pretreatment with antibiotics. Synovial fluid obtained from a sexually active teenager with unilateral arthritis should be tested for Neisseria gonorrhoeae.

Parenteral antibiotics should be withheld until the joint aspirate has been sent for Gram stain and culture in a case with suspected bacterial arthritis unless the child is gravely ill. Pathogens include Staphylococcus aureus, Kingella kingae, Streptococcal species, Haemophilus influenzae type B in incompletely immunized children, and Salmonella species in patients with sickle cell anemia. K. kingae is being increasingly recognized as a common cause of pediatric osteoarticular infections, including previously healthy children under age 4 years. It may affect older children with underlying medical conditions. A high index of suspicion is required since the clinical presentation is often subtle, and there may be normal levels of acute phase reactants.¹⁰

Imaging: Obtain plain radiographs of the injured area if there is a history of trauma and localized bony pain but avoid a strategy of imaging the entire lower extremity as this has a low yield. Fractures are seen in 4% to 20% of lower extremity radiographs obtained for trauma of which fractures of the tibia are the most common.¹¹ In one study, 14% of children with non–weight-bearing and nonfocal examinations had tibial fractures on initial radiology, and only one child had a nontibial fracture on total extremity imaging.¹² The findings suggest that imaging may be limited to the tibia in these groups of patients to avoid unnecessary radiation. The authors recommend that if the initial examination is negative, follow-up instructions, and a repeat evaluation may be necessary in patients with persistent symptoms.

Nonaccidental trauma should be considered if there is an implausible explanation for soft-tissue or skeletal injuries that are identified on examination. A radiographic skeletal survey is recommended in all children under age 2 years with suspicion for abuse. For older children up to age 5 years, the need for a skeletal survey should be based on the presence of other clinical findings, unexplained craniocerebral or abdominal injuries or fractures that are suspicious for abuse.¹³

Ultrasound (USG) is very useful in detecting hip effusions in children but cannot differentiate between septic arthritis and transient synovitis It is radiation-free and can be performed quickly but is operator dependent. False-negative results of up to 5% can occur because of inadequate examinations or very early scanning.¹⁴ It is more sensitive than plain radiography in diagnosing a hip effusion.¹⁵ USG may also uncover soft-tissue abscess.

The radionuclide scan may be useful in evaluating young children who present with a limp but have a nonfocal examination. It is sensitive in detecting bone and soft-tissue abnormalities but is not specific enough to differentiate between conditions such as osteomyelitis, discitis, avascular necrosis, malignant bone conditions, or stress fractures. The MRI is a better test to distinguish between these conditions. Although bone scintigraphy can detect injuries, given the radiation and cost involved, it is not the preferred test in evaluating a child with trauma.

The CT scan has a limited role in the workup for a limping child because of ionizing radiation and the availability of other more efficacious imaging modalities. It may be useful for diagnosing osteoid osteoma, and detecting osteopenia in early tibial stress fractures.¹⁶

MRI has no ionizing radiation and is highly sensitive in detecting musculoskeletal injury and inflammation. It is very useful in differentiating osteomyelitis and pyomyositis¹⁷ and to detect stress fractures.¹⁶ The drawbacks of MRI are its cost and the need for sedation in young children. It is the preferred imaging modality for the investigation of pediatric community-acquired S. aureus (CA-SA) musculoskeletal infections because it offers superior sensitivity for osteomyelitis compared to bone scintigraphy (98% vs. 53%) and can also detect extraosseous complications that occur in a substantial proportion of these patients.¹⁸ Contrast enhanced MRI is useful in diagnosing skeletal infection caused by CA-SA in infants and young children where there is a propensity for involvement of the unossified growth cartilage. Unenhanced MRI sequences may miss occult cartilage and bone marrow involvement in these children (Fig. 108-6)¹⁹