Pediatric Limp Workup

Laboratory testing may be indicated if a serious or systemic cause of limp is suspected. Comprehensive testing is typically not necessary; investigations should be used to exclude or confirm suspected diagnoses based on history and physical examination. CBC count and erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP) level are usually the most helpful and often are requested by consultants.

Complete blood cell count

Any abnormal value in the WBC count, hemoglobin or hematocrit, or platelet count warrants further investigation, especially for signs of neoplastic disease. Bone pain, which may cause a limp, can be a subtle but early and important sign of neoplastic disease in children, namely, leukemia or osteosarcoma.

A markedly elevated ESR may be suggestive of an underlying rheumatoid condition if no clear infectious source or supportive clinical findings are found.

A WBC count greater than 12,000 cells/mm and ESR greater than 40 mm/h in combination with an inability to bear weight and history of fever, commonly known as the Kocher criteria, have been suggested as diagnostic criteria to distinguish septic arthritis from transient synovitis in patients with acute hip pain. ^[5]

These criteria are widely used by orthopedic surgeons in determining which patients require hip arthrocentesis. Note that external validation in another retrospective cohort showed diminished performance of these criteria, ^[6] and they have not been prospectively validated to date. A retrospective study suggests that even in cases in which transient synovitis is believed to be the diagnosis, hip joint aspiration may provide faster pain relief, earlier return to normal gait pattern, and earlier hospital discharge, as compared with traditional treatment with rest and NSAIDs. ^[7] Thus, hip aspiration may be a reasonable treatment for any patient with severe disability from limp and a significant joint effusion seen on ultrasound.

Blood culture

A blood culture should be considered for patients with limp and fever.

Serum chemistries

Serum electrolytes and liver function tests are of little diagnostic value but may be obtained if a systemic/metabolic cause of limp is a concern.

Urinalysis

Urinalysis may be obtained.

Hematuria may be associated with endocarditis, HSP, acute glomerulonephritis, and SLE.

Pyuria often is associated with appendicitis or salpingitis, both of which may result in a shuffling or vaulting gait.

The presence of uric acid crystals may support the diagnosis of gout. Obtain serum uric acid level if gout is suspected. Although an uncommon pediatric diagnosis, it may be seen in renal transplant patients who often have asymptomatic hyperuricemia.

Stool cultures

Salmonella enteritis and Yersinia infection may cause joint symptoms. ^[8]

Plain radiographs are the minimal imaging workup necessary on the initial ED visit to evaluate for obvious bony pathology. Other imaging studies may be scheduled or obtained on an inpatient basis depending on the severity of diseases being considered.

Radiography

Plain films should include views of the entire limb, bearing weight when possible. ^[9] Films of the bones/joints above and below the site of suspected pathology may be required in the toddler or nonverbal child who poorly localizes pain. Consider obtaining films of the contralateral, unaffected side if a pediatric radiologist is not available for immediate interpretation, as multiple growth plates and ossification centers in developing children can make interpretation difficult. Spine films may be indicated with back pain, midline tenderness, or any neurologic complaints.

Bone scan

Intravenous technetium 99m–labeled methylene diphosphonate tracer accumulates in areas of increased cellular activity, blood flow, and bone turnover. A 3-phase scan consisting of a blood flow, blood pool, and delayed imaging phases is the current recommended protocol.

Scintigraphy is useful in detecting early Legg-Calve-Perthes disease, osteomyelitis, diskitis, stress fractures, and osteoid osteomas. Scintigraphy is 84-100% sensitive and 70-96% specific for osteomyelitis. It also has an adjunctive role to the skeletal survey for nonaccidental trauma.

Bone scans deliver a relatively high radiation dose, an important consideration in children. Other diagnostic modalities including plain films and ultrasonography should be considered first, especially when anatomic site of pathology is easily located by physical examination.

Timing of scintigraphy in the evaluation of the limping child may pose a diagnostic dilemma. False-negative results may be produced by scanning too early, as results may not become positive until 48-72 hours into an inflammatory process. ^[10] Further complicating the matter is that procedures such as joint aspiration, which should be performed as soon as possible in suspected septic arthritis, may cause false-positive scintigraphy results. It is therefore up to the clinician’s judgment as to how to orchestrate these procedures in a limping patient with suspected serious pathology.

Ultrasonography

Ultrasonography is useful for diagnosing soft tissue and joint pathology. ^[11] A key advantage of ultrasonography is that anatomic structures can be evaluated both statically and dynamically. It is particularly useful in younger children in whom the skeleton is incompletely ossified; for example, it can make the diagnosis of DDH in infants. Ultrasonography can confirm the presence of a joint effusion and can guide diagnostic or therapeutic aspiration. Although classically the domain of radiologists, ultrasonography of the hip by the emergency physician may have developing role for guiding bedside management of limping patients. ^{[12, 13]}  

Computed tomography scan

Judicious use of CT scanning may be indicated for the limping pediatric patient. In the absence of neurologic or musculoskeletal examination findings, intra-abdominal pathology becomes a greater concern. Atypical appendicitis, psoas abscesses, and GU tract abnormalities may be visualized.

CT scan gives better resolution of bone and soft tissues than plain films and has the advantage of multiplanar imaging capabilities. CT can also help identify periosteal abscesses or pyomyositis in association with osteomyelitis.

CT scan can aid in diagnosing joint effusions. However, given the adverse effects of radiation exposure and the availability of other diagnostic modalities, CT should not be used for this purpose.

Tarsal coalition, the abnormal union of two or more bones of the hindfoot and midfoot, is one disorder that has been better studied since the advent of CT scanning.

Magnetic resonance imaging

MRI is an excellent imaging modality to evaluate bony and soft tissue pathology and has the advantage of multiplanar imaging capabilities and no radiation exposure.

MRI is the imaging modality of choice for evaluating internal joint derangement, soft tissue or bony infection, tumors, and osteonecrosis. It is also helpful for imaging the brain and spinal cord.

Disadvantages of MRI include expense, relatively poor availability, and long duration. The prolonged scan time can result in significant motion artifact and may necessitate sedation in younger children. Contraindications to MRI include pacemakers, intracranial surgical clips, metallic foreign bodies, particularly in the eye, and indwelling pumps or stimulator devices.

Synovial fluid analysis remains the criterion standard for diagnosis of suspected septic arthritis. It can also help define other joint problems that may be the cause of an acute limp, such as hemarthrosis, gout, and pseudogout. See Aspiration Techniques and Indications for Surgery, Septic Arthritis for a detailed explanation of synovial fluid interpretation.

A cerebrospinal fluid (CSF) analysis should be obtained if meningitis is strongly suspected (ie, symptoms including fever, headache, meningismus). Meningitis has been associated with limping, probably due to meningismus. ^[14]

Other tests (informational), such as the following, usually are obtained on subsequent visits (not on the first ED visit) to investigate chronic, progressive, or recurrent causes of limp.

• Sickle cell preparation

• Lupus erythematosus (LE) preparation

• Lupus antibodies

• Antinuclear antibody (ANA)

• Anti-DNA (rheumatoid arthritis, scleroderma, SLE)

• Antimuscle antibodies (myasthenia gravis)

• Human leukocyte antigen (HLA) (Specific HLA types are associated with various rheumatoid disorders.)

• Rheumatoid factors

• Creatinine phosphokinase (myositis)

• Aldolase (some forms of muscular dystrophy)

• Serologies such as Lyme disease, parvovirus, or antistreptolysin-O (ASLO)

Arthrocentesis

Aspiration of synovial fluid from the hip, knee, ankle, metatarso-phalangeal, or interphalangeal joints should be performed as clinically indicated. See Arthrocentesis, Ankle and Arthrocentesis, Knee. In cases of septic hip, a retrospective case series suggests that ultrasound guided aspiration can be performed by the bedside by trained orthopedic surgeons, and serial aspiration is a treatment modality that can obviate the need for hip arthrotomy. ^[15]

Bone aspirates

Fine needle aspiration or open biopsy may be indicated in the nonemergent setting to confirm suspected diagnoses of malignancy causing limp, such as osteosarcoma or Ewing sarcoma, and to identify other bony or soft tissue lesions.

Sputum aspirates

Tuberculous arthritis is rare but becoming more common in association with immune deficiency states. Pott disease may be an insidious cause of limp but would more likely be associated with systemic symptoms of tuberculosis.