A limp is a type of asymmetric abnormality of the gait. Limping may be caused by pain, weakness, neuromuscular imbalance, or a skeletal deformity. The most common underlying cause of a painful limp is physical trauma; however, in the absence of trauma, other serious causes, such as septic arthritis or slipped capital femoral epiphysis, may be present. The diagnostic approach involves ruling out potentially serious causes via the use of X-rays, blood tests, and sometimes joint aspiration. Initial treatment involves pain management. A limp is the presenting problem in about 4% of children who visit hospital emergency departments. Definition 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 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 (a bacterial infection spread by deer ticks) and osteomyelitis (an infection of the bone). 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