A limp is a type of asymmetric abnormality of the gait. When due to pain it is referred to as an antalgic gait, in which the foot is in contact with the ground for a shorter duration than usual; in severe cases there may be a refusal to walk. Hip deformities with associated muscular weakness, on the other hand, may present with a Trendelenburg gait, with the body shifted over the affected hip.
Differential diagnosis
The causes of limping are many and can be either serious or non-serious. It usually results from pain, weakness, neuromuscular imbalance, or a skeletal deformity. In 30% of cases, the underlying cause remains unknown after appropriate investigations. The most common underlying cause of limping in children is minor physical trauma. In those with no history of trauma, 40% are due to transient synovitis and 2% are from Legg–Calvé–Perthes syndrome. Other important causes are infectious arthritis, osteomyelitis, and slipped capital femoral epiphysis in children.
Infection
Septic arthritis
can be difficult to separate from less serious conditions such as transient synovitis. Factors that can help indicate septic arthritis rather than synovitis include a WBC count greater than 12×109/l, fever greater than, ESR greater than 40 mm/h, CRP greater than 2.0 mg/dL, and refusal to walk. People with septic arthritis usually look clinically toxic or sick. Even in the absence of any of these factors, however, septic arthritis may be present. Joint aspiration is required to confirm the diagnosis.
Other
Other infections that classically lead to a limp include Lyme disease and osteomyelitis.
Mechanical
Trauma
Accidental or deliberate physical trauma may result in either a fracture, muscle bruising, or a contusion. It is the leading cause of a limp. Deliberate abuse is important to consider.
Slipped capital femoral epiphysis
is a condition in which the growth plate of the head of the femur slips over the underlying bone. It most commonly presents with hip pain in males during puberty and is associated with obesity. The majority of people affected have a painful limp and in half of cases both hips are affected. Nearly a quarter of people present with only knee pain. Treatment involves non-weight-bearing movement and surgery. If not identified early, osteonecrosis or death of the head of the femur may occur.
Other
A non-painful limp may be due to a number of mechanical conditions including hip dysplasia and leg length differences.
Inflammatory
Transient synovitis
is a reactive arthritis of the hip of unknown cause. People are usually able to walk and may have a low grade fever. They usually look clinically nontoxic or otherwise healthy. It may only be diagnosed once all other potential serious causes are excluded. With symptomatic care it usually resolves over one week.
The diagnosis of the cause of a limp is often made based on history, physical exam findings, laboratory tests, and radiological examination. If a limp is associated with pain it should be urgently investigated, while non-painful limps can be approached and investigated more gradually. Young children have difficulty determining the location of leg pain, thus in this population, knee pain equals hip pain. SCFE can usually be excluded by an x-ray of the hips. An ultrasound or x-ray guided aspiration of the hip joint maybe required to rule out an infectious process within the hip.
