Leg pain can be caused by injury or stress that affects the mechanical operation of the lower body (hip, leg, knee or foot). Leg pain can occur from circulatory problems, especially in the calf area at the back of the lower leg, or rarely from inflammation of veins called thrombophlebitis. 

Arthritis, most commonly osteoarthritis, may also cause leg pain, particularly in the knees and hips. Rheumatoid arthritis may affect the feet, ankles, knees and, in later stages, the hips. Pseudogout often causes knee pain, and gout can cause excruciating pain in the big toe. Reiter’s syndrome and ankylosing spondylitis can affect the knee, ankle, foot and other parts of the leg.

Other causes of leg pain include:

• Circulatory problems. Disorders of the circulatory system in the legs can cause leg pain. Peripheral artery disease (PAD) affects blood vessels in the legs, resulting in blockage of blood flow, causing swelling and leg pain. This pain, called intermittent claudication, usually is located in the calves, normally occurs while walking and is alleviated with rest. PAD, by definition, refers to any obstructed artery outside the heart, but most commonly occurs in the leg and results in pain.

  

• Deep vein thrombosis (DVT). Blood clots in the venous blood vessels that usually develop in the legs. When these blood clots remain in the legs, they can cause pain and swelling. If the blood clot is left untreated, it may dislodge and travel to a lung, causing a life-threatening condition called pulmonary embolism. Prolonged periods of sitting, leg trauma, inactivity or smoking while on certain contraceptives may predispose a person to a higher risk for DVT.
  
  
• Other vein problems. Smaller blood clots or inflammation near the surface of the legs indicate a condition called phlebitis, which may cause leg pain. Varicose veins, although more frequently a cosmetic problem, have also been linked to pain in the legs. They result from malfunctioning valves in leg veins that cause blood to pool, resulting in enlarged, often painful, veins.
  
  
• Traumatic injuries. Sudden falls or unusual movements can injure the legs, resulting in bone fractures, joint dislocations, muscle strains, or sprains or tears to ligaments. Fractures of the femur most often occur from high-impact injuries in automobile accidents and workplace traumas. Longtime strain can cause femoral neck stress fractures, incomplete fractures that are most common in runners. In the United States, femur fractures occur in about three of every 10,000 people. They usually require surgery, extensive healing time and rehabilitation.
  
  Any femur fracture from a low-impact fall may indicate that the bone has been weakened by osteoporosis or cancer. Fractures of the lower leg typically involve both bones (tibia and fibula). The tibia is one of the most common leg bones to be fractured, often with breakage through the skin (compound fracture). In general, fractured bones in the legs have a good prognosis for healing.
  
  
  Contusions are another common cause of leg pain. For example, a blow to the side of the hip may injure the iliac crest of the pelvic bone and nearby tissues. This acute injury, known as hip pointer, occurs most often during football or other contact sports.

• Overuse and soft tissue injuries. Leg cramps (charley horse) may be caused by muscle fatigue from overuse, dehydration or loss of such body chemicals as potassium or sodium. Leg cramps often occur during sleep and may be related to dehydration or mineral deficiencies.

Shin splints can occur after periods of inactivity or after exercise intensity is increased. Excessive exercise may cause small, painful cracks on the surface of the leg bones called stress fractures. Inflammation of the tendons (tendinitis), bursa (bursitis) or entheses (sites where tendons or ligaments attach to bone; enthesitis) in the legs, knees, feet or hips may cause leg pain. Poor posture and ergonomics can contribute to back, hip and leg pain.

• Nerve problems. A pinched nerve resulting from conditions such as spinal stenosis, degenerative disc disease or a herniated disc can cause pain from the back down the leg. Sciatica refers to pain along the sciatic nerves, which run from the pelvic bone down the back of each leg. Compression at the roots of these nerves in the lower spine causes the pain, which is also known as radiculopathy. This pain may involve one or both legs with associated numbness.

Neuropathy is another form of nerve damage that can cause pain in the legs. Neuropathy is common in diabetes patients and is believed to be related to high glucose (blood sugar). It can result in unsteady gait, numbness, tingling and mild to excruciating pain in the legs. Other conditions may also cause neuropathy, including alcohol abuse, certain vitamin deficiencies or rare hereditary conditions.

• Joint disease in the back. Conditions in a sacroiliac joint or facet joint can cause pain in the back of thighs. Predisposing factors include injury and arthritis.
  

• Infections. Many infectious diseases can cause leg pain, including:
  

• • Shingles (herpes zoster), a viral infection caused by the varicella-zoster virus (VZV), the same virus that causes chickenpox. After a person has had chickenpox, VZV remains in a dormant (inactive) state in the nerve roots for the rest of their life. VZV may reactivate years later in the form of a painful skin rash and postherpetic neuralgia.
    
    
  • Cellulitis, a bacterial infection of the deep layers of the skin that can spread to muscle, blood, lymph nodes and other tissues.
    
    
  • Osteomyelitis, a serious infection of the bone.
    
    
  • Impetigo, a common and highly contagious bacterial skin infection that most often occurs in children.
    
    
  • Scabies, infestation of the skin with a mite whose spread causes intense itching (pruritus).
    
    
  • Restless legs syndrome (RLS). This neurological disorder causes unpleasant leg sensations, ranging from a crawling or burning sensation to pain. The National Institute of Neurological Disorders and Stroke estimate that RLS affects as many as 12 million Americans. It usually occurs when people are sitting or lying down, particularly at night. In addition to discomfort, individuals with RLS have difficulty keeping their legs still and may suffer insomnia. Moving the legs helps relieve the discomfort caused by this condition.
    
    
  • Complex regional pain syndrome. A chronic pain marked by continuous, intense pain that tends to worsen over time. It usually occurs after a significant trauma to an arm or a leg and is characterized by burning or aching pain along with inflammation, skin discoloration, altered temperature, abnormal sweating and hypersensitivity of the affected area. Complex regional pain syndrome may also occur without a known injury or with microscopic injury such as intramuscular injection.
    
    
  • Compartment syndrome. Layers of tissue called fascia divide leg muscles into compartments. Each compartment has a limited amount of space that cannot expand. Any swelling in a compartment (usually in the calf), especially after blunt trauma, may cause the extreme pain of compartment syndrome. Urgent surgery may be necessary to treat this condition.
    
    
  • Osgood-Schlatter disease. A condition that causes swelling and pain at the bony point (tibial tuberosity) just below the knee. It appears most often in young children engaged in athletic activities that stress the muscles and other tissues surrounding this area of the leg.
    
    
  • Coxa saltans (snapping hip). A condition in which a tendon or other connective tissue snaps over pelvic bone when the hip is bent forward or moved in certain other positions. It can be painless at first but can become painful over time. It may be more common in athletes.
    
    
  • Slipped capital femoral epiphysis. An adolescent hip disorder in which the upper end of the thigh bone slips out of place. It is more common in boys than girls, more common in overweight teens than those of normal weight.
    
    
  • Hernia. Intestinal protrusions such as a femoral hernia may cause thigh pain.
    
    
  • Paget’s disease. This involves excessive breakdown of bone and abnormal formation of bone.
    
    
• Cancer. The three most common forms of bone cancer (osteosarcoma, chondrosarcoma and Ewing’s tumor) all occur in the bones of the leg. Additionally, cancer may travel from a different part of the body (metastatic cancer) and be found in the legs. Leg pain is their most frequent symptom, along with swelling and possible growths.
  
  
• Meningitis. Scientists have recently reported that leg pain, cold feet and hands, and abnormal skin coloration can be early indicators of meningitis. These symptoms can appear within hours of infection, long before the onset of better-known signs such as rash, headache and stiffness of the neck.
  
  
• Hypermobile joints. Research suggests that children with very flexible joints might be at increased risk of recurrent leg pain.
  
  
• Pigmented villonodular synovitis. This rare disorder involves abnormal growth of tissue in joints. Joint swelling can damage bone. It most often involves the knee or hip but may also involve the ankle, foot, shoulder, hand or fingers.

In addition, numerous conditions including lupus, fibromyalgia, sarcoidosis, polymyalgia rheumatica, sickle cell anemia, Lyme disease, myositis and chronic fatigue syndrome can cause widespread pain in the joints and may affect the legs.

Many sources of leg pain can lead to gait disturbances, which can in turn worsen or create new types of leg pain.