The causes of<unk> ing 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<unk> ing 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<unk>  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<unk> . Deliberate abuse is important to consider. Slipped capital femoral epiphysis Slipped capital femoral epiphysis (SCFE) 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<unk>  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<unk>  may be due to a number of mechanical conditions including hip dysplasia and leg length differences. Inflammatory Transient synovitis 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. Juvenile rheumatoid arthritis Juvenile rheumatoid arthritis presents gradually with early morning stiffness, fatigue, and weight loss. Vascular Legg–Calvé–Perthes syndrome Legg–Calvé–Perthes syndrome is a degenerative disease of the head of the femur which results in bone loss and deformity. It usually presents as a chronic condition. Neoplastic Cancers including acute lymphocytic leukemia, osteosarcoma, and Ewing’s sarcoma may result in a gradual onset of<unk> ing in children. It is often associated with night sweating, easy bruising, weight loss, and pain most prominent at night.
Limp
IPrEx
Cll1
SCALPEL
Sparx 
Basigin
CoWIN
Clathrin