When a person is in a seated position, his or her weight typically rests on a section of bone called the ischial tuberosity. There are two of these bony swellings, sometimes called the sitting bones, located at the front of the superior ramus of the ischium, which is the lower back portion of the hip bone. The gluteus maximus muscle lies over it when a person is standing; however, when he or she sits down, the muscle shifts to a position behind it and the tuberosity bears the majority of the weight.
This bone is an attachment point for several muscles and ligaments. Three of the hamstring muscles — the semimembranosus, the biceps femoris, and the semitendinosus — start there. The adductor magnus, a large muscle in the thigh that lies next to the hamstrings, also originates at the tuberosity. The sacrotuberous ligament connects it to the sacrum.
Due to the number of leg muscles attached to the ischial tuberosity, sports-related injuries are fairly common in this area. Sports such as running, soccer, and cycling, where a high level of strain is put on the thighs, are often the culprit. Muscles can be pulled or damaged from overuse, and tendinitis can also develop. In extreme cases, fractures of the bone or even the detachment of muscles may occur, though this is relatively rare.
Extended periods of sitting on hard surfaces may also lead to damage in the area. One of the most common outcomes is a condition called ischial bursitis. A fluid-filled sac called the bursa lies over the tuberosity, acting as a cushion between the pelvis and nearby tendons to keep them from being damaged. Prolonged sitting may lead to inflammation of the bursa. Symptoms may include pain and tenderness in the hips and buttocks, and possibly sciatica, where pain and numbness can spread down into the leg.
Treatment for ischial tuberosity injuries typically involves rest to allow the area to heal and medication to manage pain. Ice applied to the area may help reduce swelling and inflammation, as well as the use of NSAIDs. In some cases, physical therapy to stretch and strengthen the muscles may be useful. Those with bursitis are often instructed to sit on a padded surface, such as a doughnut cushion. In cases where damage is severe, corticosteroid injections may be necessary, or as a last resource, surgery may need to be performed.