Differential Diagnosis for a 7-year-old with Leg Discomfort after a Fall
Single most likely diagnosis
- Quadriceps contusion or strain: This is a common injury in children who fall and hit their knee or thigh, leading to pain and difficulty straightening the leg. The absence of swelling or fractures on imaging supports this diagnosis, as soft tissue injuries may not be visible on X-ray or CT.
Other Likely diagnoses
- Muscle sprain: Similar to a quadriceps contusion, a muscle sprain in the thigh or knee area could cause discomfort and stiffness, making it hard to straighten the leg.
- Patellar subluxation or dislocation: Although less common, a patellar subluxation or dislocation could occur without visible fractures or significant swelling, especially if the patella has reduced spontaneously.
- Medial collateral ligament (MCL) or lateral collateral ligament (LCL) sprain: These ligament sprains around the knee could result from a fall and cause pain and instability, potentially making it uncomfortable to straighten the leg.
Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
- Vascular injury: Although rare, a vascular injury (e.g., popliteal artery injury) could occur from a fall and might not present with obvious swelling or fractures. This is a medical emergency requiring prompt intervention.
- Compartment syndrome: This condition, characterized by increased pressure within a muscle compartment, can lead to serious complications if not addressed promptly. It might not be immediately apparent on imaging but is crucial to diagnose early.
- Spinal cord injury: If the fall was significant or involved a mechanism that could affect the spine, a spinal cord injury is possible and must be ruled out, especially if there are any neurological symptoms.
Rare diagnoses
- Osteochondritis dissecans: A rare condition where a piece of cartilage and bone in a joint becomes damaged, potentially causing pain and stiffness. It might not be visible on initial X-rays but could be a consideration if symptoms persist.
- Slipped capital femoral epiphysis (SCFE): More common in older children and adolescents, SCFE is a condition where the ball at the upper end of the femur (thigh bone) slips out of place. It's rare in a 7-year-old but could be considered if there's ongoing pain and limited mobility.
Treatment for the most likely diagnosis, quadriceps contusion or strain, typically involves rest, ice, compression, and elevation (RICE), along with pain management and gradual return to activity. However, the specific treatment should be guided by a thorough clinical evaluation and, if necessary, further diagnostic testing to rule out other potential causes.