The most common cause of a limp in a child is trauma, so when a mechanism of injury is missing from the history then the differential for diagnosis can be intimidating. Components of the history and physical exam can help guide imaging and the urgency for management since the causes of atraumatic limp can vary from common inflammatory conditions to orthopaedic emergencies.
History questions should focus on clarifying characteristics of the limp including the following:
- How long has the child been limping?
- Has the limp been consistent or intermittent?
- Is the limp associated with pain?
- Is the limp and/or pain worse at any specific time of the day or with activity?
- Does anything aggravate or alleviate the limp?
Additional essential questions also should include:
- Has the patient had a fever?
- Any history of recent illness or antibiotic use?
- Has the patient tried NSAIDs and were they effective?
- Any abdominal or back pain?
In younger patients, it may be difficult to isolate the source of the limp. This can be further complicated by the potential for referred pain. Hip pathology can commonly present in children as referred pain to the knee. Physical examination requires a thorough evaluation starting with inspection for swelling, erythema, eccymosis, rashes, etc. Systematic palpation of the spine and lower extremities should asses for warmth, masses, or pain. Observation of the gait pattern can help determine the affected joint but comparing range of motion will typically provide some of the most helpful guidance. Hip conditions can easily be detected with range of motion testing both supine and prone. Internal rotation should be compared prone with the knees bent. Other causes of limp could span from the spine to the foot and all require full assessment during the physical examination. If a specific joint is already suspected as the source, then it should be saved to be examined last.
The differential diagnosis for atraumatic limp in a child can be significant. Common causes include apophysitis such as Sever (calcaneal) or Osgood-Schlatter (tibial tuberosity) disease which are easily diagnosed based on clinical presentation. Underlying hip conditions such as Legg-Calvé-Perthes or Developmental Dysplasia of the Hip (DDH) may present with a limp as the conditions progress and can typically be differentiated from other causes with plain radiographs. Other considerations may include tumors, rheumatologic conditions, spinal abnormalities, or GI/GU concerns depending on the overall clinical presentation. Differentials that shouldn’t be missed are slipped capital femoral epiphysis (SCFE) and septic hip, as these are both orthopaedic emergencies.
Both SCFE and septic hip will demonstrate asymmetry during range of motion testing of the hips. SCFE is typically diagnosed based on clinical presentation and following plain radiographs including AP pelvis and frog-leg laterals. Early SCFE can be diagnosed on MRI if clinical suspicion warrants advanced imaging. Septic hip, on the other hand, will typically present with an ill-appearing and febrile patient. Radiographs are not diagnostic and emergent laboratory tests include WBC, ESR, and CRP. Transient synovitis of the hip can mimic signs of a septic hip but patients typically appear well, without a fever, and may have a recent history of upper respiratory infection. NSAIDs can be valuable in determining the likelihood of transient synovitis since patient will typically improve, whereas in septic hip NSAIDs will have little to no effect on the patient’s pain. If there is any suspicion for septic hip then laboratory work is required and Kocher criteria can further guide management options. Both SCFE and septic hip require emergent orthopaedic consultation and immediate hospitalization for further work-up, advanced imaging, and management.