Thigh pain is a common symptom and can be caused by a large number of different conditions from lower back pain to more local problems. The type of thigh pain present is indicated by the position of the pain in the thigh and the nature of the symptoms.
Anterior (front) thigh pain can be a symptom of hip pain from hip arthritis and some people to go to the doctor with thigh and knee pain end up getting hip pain relief by having a hip replacement instead of the knee treatment they expected. A nerve root compression of the third lumbar nerve, a form of sciatica in the front of the thigh, can also be a cause of anterior thigh pain, although this is often severe and disabling and difficult to mistake for any other diagnosis. Front thigh pain can also be caused by a contusion of the muscle such as from a blow in sport, or a quadriceps muscle strain.
Posterior (rear) thigh pain can be part of typical sciatica or nerve root compression of one of the lumbar nerves, but in these cases the pain goes beyond the knee into the calf and foot. Referred pain from the lower back pain structures can also be referred to the posterior thigh, with sacroiliac joint dysfunction also referring to this area. A hamstring strain will also cause pain at the back of the thigh but is easy to diagnose as the pain comes on suddenly with exertion.
Lateral thigh pain can be part of lateral hip pain secondary to hip arthritis, meralgia paraesthetica or iliotibial band syndrome. Hip bursitis, also known as trochanteric bursitis was presumed to be a common cause of this type of pain but recent research has indicated that degenerative changes in the hip muscle tendons is more likely to be the cause. The inflammation of bursitis may not occur in most of these cases and one of the commonest causes of lateral hip pain is hip pain running, usually overdoing the distances too soon.
Iliotibial band syndrome is pain from the iliotibial band, a ligamentous band down the outside of the thigh, as it rubs against the bony prominence of the greater trochanter. It again can be related to distance running.
Meralgia paraesthetica is a condition where pain and hypersensitivity are present on the side and front of the thigh, caused by compression of a nerve as it enters the thigh from the pelvis. Injection or operation to decompress the nerve are management options
Sportsinjuryclinic.net has a page on thigh pain with links to further relevant pages and wrongdiagnosis.com also has some interesting information about thigh pain and gives all the possible causes of thigh pain.