Avascular necrosis (AVN), otherwise known as osteonecrosis, is the death of bone tissue due to a lack of blood supply. Because bone is living tissue that requires a blood supply, tiny breaks in the bone can occur in the affected area and the bone can eventually collapse. The most common area where AVN occurs is in the hips causing pain on the groin, thigh, or buttock. However, AVN can occur in the shoulders, knees, hands, and feet as well.
The cause of AVN can vary from a dislocation or a fracture, chronic use of corticosteroids, a common anti-inflammatory drug for pain management, excessive alcohol use, damage to the surrounding arteries, or other health conditions such as piriformis syndrome. A dislocation or fracture that leads to AVN is known as trauma-related AVN. This type of injury can affect the blood supply to the bone. All other causes of AVN are known as non-traumatic AVN. Chronic corticosteroid use can interfere with the body's ability to break down fatty substrates. When these substrates collect in the blood vessels it can make them narrower and therefore reduce the amount of blood supply to that area. Similar to anti-inflammatory drugs or pain killers, excessive alcohol use may also cause fatty substrates to build up in the blood vessels and lead to a reduced blood supply. Blood clots, damage to the arteries and local inflammation can also block blood flow to the bones. The cause of AVN may also lead to the development of hip osteoarthritis. Bone on bone hip osteoarthritis can further aggravate the pain in the hip area making the symptoms of AVN worse.
If osteonecrosis has caused extensive damage to the femur and the bone has begun to collapse causing significant pain in the hip or knee, a total joint replacement may be recommended.
Piriformis syndrome is a condition when the Piriformis muscle contracts and spasms compressing and irritating the sciatic nerve. This causes sciatic pain along the path of the sciatic nerve descending down the lower thigh and into the leg. Piriformis muscle spasms also compress the superior and inferior gluteal nerve and arteries beneath the muscle causing contractions of other muscles in the buttocks and cause symptoms of hip muscle pain, coldness, tightness, tingling, and numbness in the buttocks. Hip muscle contraction and tightening further compress the femoral artery and its branch, the profunnda femoris, the main artery supplying blood to the hip joint capsule and the femur neck, resulting in restricted blood supply and causing hip joint cartilage degeneration, hip osteoarthritis, and femur neck bone death leading to AVN.
The cause of Piriformis syndrome is due to prolonged stress. Our body's fight-or-flight response to a stressor such as a perceived harmful event, attack, or threat to survival involves tightening of the Piriformis muscle which is the most important muscle in the lower body involved in balance, posture and movement. Its contraction moves the body in different directions. Under a prolonged stress condition, the piriformis muscle continually contracts which can eventually lead to Piriformis syndrome. Besides for the Piriformis muscle, the shoulder muscle and the smooth muscle of the stomach also contract in the fight-or-flight response to stress causing reduced blood flow to these areas. It is common for AVN patients to also have shoulder problems and stomach conditions including acid reflux, GERD, poor digestion, or stomach ulcers due to poor blood supply.
