Laboratory Workup For Children Who Present With Extremity Pain

Laboratory studies are unnecessary for most extremity pain. However, if the history and physical examination do not lead to a definitive diagnosis, if they raise suspicion of a systemic or an infectious disease, or if the pain persists longer than anticipated, then screening laboratory
tests are in order.

A basic evaluation should include

• a complete blood cell count (CBC),
• a sedimentation rate, 
• a C-reactive protein, and 
• a sickle cell preparation or
• hemoglobin electrophoresis when indicated. 

Appropriate serologies should be considered if features of the physical examination are consistent with rheumatologic disease.

•  An elevated sedimentation rate raises suspicion of an infectious or inflammatory disorder or, occasionally, of a neoplasm.
• A CBC may reveal anemia or may suggest an infectious disease. 
• With leukemia, the white blood cell (WBC) count varies, but immature forms may be present in the differential WBC count or thrombocytopenia may be present. 
• A creatine phosphokinase determination is occasionally indicated if muscular pain or weakness is suspected.

Imaging

Radiologic studies are often unnecessary in evaluating limb pain. However, because of the plasticity of children’s bones, traumatic injury that would ordinarily cause only a sprain in an adult is more likely to result in a greenstick or buckle fracture in a child. 

The presence of point tenderness or gross deformity in an extremity or pain on motion of the involved limb increases the likelihood of fracture. 

In an effort to minimize the use of radiographic studies after traumatic injury to the knee and ankle, The Ottawa Criteria have been developed for use in adults. These criteria have also now been validated for use in children older than 5 years. 

When no clear history of trauma is revealed, when symptoms persist, and when associated systemic complaints are present, radiographs can help identify bony tumors, pathological fractures, some metabolic defects, and a significant number of orthopedic conditions.

Indication for Plain Radiograph Evaluation After Trauma Using the Ottawa Ankle and Knee Rules

Radiograph of the knee is indicated after trauma if 

• Age older than 55 years

• Isolated tenderness of patella

• Tenderness at the head of the fibula

• Inability to flex the knee to 90 degrees

• Inability to bear weight both immediately and at medical evaluation

Radiograph of the ankle is indicated after trauma in cases of 

• Pain in the malleolar zone and 

(1) tenderness of the tip of the medial malleolus or bone tenderness of the distal 6 cm of posteriortibia, OR 

(2) tenderness of the tip of the lateral malleolus or bone tenderness of the distal 6 cm of the posterior fibula, OR 

(3) inability to bear weight immediately after injury and at the time of medical evaluation.

Radiograph of the foot is indicated after trauma in cases of

• Pain in the midfoot zone and 

(1) tenderness at the base of the fifth metatarsal, OR

(2) tenderness at the navicular bone, OR

(3) inability to bear weight immediately after injury and at the time of medical evaluation.

A bone scan is a useful diagnostic tool in evaluating limb pain and should be considered when a stress fracture, osteomyelitis, or malignancy is suspected. Bone scans are more sensitive than plain-film radiography for establishing these diagnoses. 

Increasingly, magnetic resonance imaging (MRI) is being used as a replacement for bone scans in the diagnosis of osteomyelitis. Th e combined use of T1, T2, and short-tau inversion-recovery images effectively rules out osteomyelitis, with a negative predictive value approaching 100%..  MRI

offers the additional advantage of excellent visualization of soft-tissue and joint disease. There may still be a role for bone scan in the evaluation for osteomyelitis when need for sedation is a concern and when the area of potential involvement cannot be adequately narrowed based on physical examination.