Approach to a limp (pediatrics): Clinical sciences

A limp is a gait abnormality that’s usually caused by pain, weakness, or deformity, and if it goes unrecognized, it can lead to permanent disfigurement and loss of function.

Based on history, exam, and imaging findings, you can differentiate between a painful limp, which is typically associated with infectious, traumatic, inflammatory, or mechanical causes; and a painless limp, which can occur due to mechanical or developmental causes.

When a child presents with a limp, begin by obtaining a focused history and physical exam, including a thorough musculoskeletal and neurologic exam. Keep in mind that young children may not be able to describe their pain well, so in non-verbal children, look for indicators of pain, such as irritability, crying, or refusal to stand or walk.

Okay, now your first step when evaluating a limp is to assess for pain. If the patient is presenting with a painful limp, your next step is to assess the onset of the limp, which could be either sudden or gradual. Any painful limp with a sudden onset, should make you consider infection, so assess for the presence of fever. If fever is present, the main causes to consider include septic arthritis, meaning an infection of the joint, and osteomyelitis, which is an infection of the bone.

First, let’s discuss septic arthritis. These individuals may report joint swelling and pain, with refusal to bear weight on the affected extremity. The physical exam might reveal joint tenderness, effusion, and warmth, as well as a limited range of motion. In addition, you may observe that the child "guards" the joint. At this point, consider septic arthritis and order labs, including a CBC, CRP, ESR, and a blood culture. Additionally, perform a joint aspiration to collect synovial fluid for analysis and culture.

The labs will typically show elevated WBCs, CRP, and ESR, and sometimes, blood cultures might reveal a causative pathogen. The synovial fluid will likely appear purulent, with WBCs greater than 50,000, and possible growth on culture. With these findings, you can confirm the diagnosis of septic arthritis.

Now, let's switch gears and discuss osteomyelitis. This is usually associated with localized bony pain. There may also be a history of immunosuppression. Physical exam will reveal point tenderness with localized warmth and swelling. In addition, the child will have pain on weight bearing, usually felt over the metaphysis. These findings should make you consider osteomyelitis, so again, order CBC, CRP, ESR, and a blood culture. In addition, order an X-ray, and, if needed, MRI for better visualization. Labs will reveal an elevated WBC, CRP, and ESR with possible growth on blood culture; while imaging studies will show evidence of osteolysis and bone destruction, and if there is still uncertainty, nuclear imaging can be done. At this point, diagnose osteomyelitis.

Now, let’s go back and consider the causes of a sudden painful limp in which there’s no fever; starting with bone fractures. The child may present with localized pain and inability to bear weight on the affected leg after a known trauma. Physical exam could reveal point tenderness or an area of swelling or bruising. Additionally, you might notice a visible deformity of the affected limb. These findings should make you consider bone fracture. Your next step is to order an X-ray, which will show the location and severity of bone fracture, confirming that what’s causing the limp is indeed a fracture.

Next is soft tissue injury. This child will also complain of localized pain, but they may also describe a sudden “pop” at the time of injury. There will be localized tenderness and swelling, and they might have ligamentous laxity. All of these findings should lead you to consider a soft tissue injury. Depending on the suspected injury, your next step might be to order an MRI, which will help you identify injury of the muscle, ligament, or tendon, and confirm the diagnosis of soft tissue injury.

Let’s move on to non-accidental trauma, which can be challenging to diagnose. A worrisome sign of non-accidental trauma is any injury that’s out of proportion to the mechanism described. Red flags on physical exam include unusual or patterned bruising, such as of the auricle of the ear; any type of oral injury; or burn marks on the skin. If you see any of these, you must consider non-accidental trauma. Your next step is to order a skeletal survey to look for evidence of previous injuries. If you detect multiple fractures in various stages of healing, then you can diagnose non-accidental trauma.

Now, here’s a clinical pearl! Non-accidental trauma is not limited to bones only, so be sure to evaluate for intracranial bleeding, abdominal trauma, and other signs of maltreatment or neglect.

Okay, now, let’s go back and take a look at individuals with a sudden painful limp, with no fever or trauma, which should make you think of transient synovitis. These patients typically present with hip pain and a recent upper respiratory tract infection. On the exam, the child is well-appearing with their hip abducted and externally rotated because internal hip rotation is painful. In this case, consider transient synovitis of the hip, and order a CBC, CRP, and ESR; as well as a bilateral hip ultrasound. Unlike in septic arthritis, the WBC, CRP, and ESR will be normal, with possible unilateral or bilateral hip effusion on ultrasound. Based on these findings, you can diagnose transient synovitis.