The hip is composed of two bones, the head of the femur (ball on top of thigh bone) and the acetabulum (socket) that is a portion of the pelvis. The ends of these bones that move about each other have a layer of cartilage, which forms the surface of the joint.
In avascular necrosis, or hip AVN, the blood supply to the femoral head is disrupted. This in turn causes death of the bone beneath the cartilage, which may compromise the structural integrity of the femoral head. In advanced cases the bone will collapse leaving a defect under the cartilage that causes an abnormal shape of the head. This will give rise to abnormal mechanics within the hip socket leading to degeneration and mechanical failure of the cartilage and thus results in hip arthritis. Some patients may be indicated for a hip steroid injection. There are also surgeries, which attempt to decrease pressure inside the femoral head that is thought to contribute to the pain that is experienced with AVN. This surgery is called a core decompression, or hip decompression. Severe cases may be indicated for a minimally invasive anterior approach total hip replacement surgery or total hip arthroplasty.
Discomfort and pain are described by patients as a dull, aching throb that is deep in the hip. This typically is located in the groin fold in front of the hip and will radiate down the front of the thigh toward the inner aspect of the knee and toward the buttock region.
In fact, many patients may have the sensation that their knee hurts; however, it may just be radiating pain from hip joint problems. Many will also describe a sharp, stabbing type of pain that is equilibrated to being “stabbed by an icepick”. Pain can also elicit a feeling of weakness in the muscles around the hip, which can result in the leg buckling or giving way. The pain typically increases whenever the hip joint is bent during activities like squatting, sitting and stairs. Athletic activities such as running and jumping, which require hip flexion, will also aggravate these symptoms. Activities that also require rotation through the hip, such as golf and pickleball may also increase these symptoms.
Stiffness is a common finding in patients with hip avascular necrosis. This is described as stiffness in the morning, when they first get out of bed or when they rise from a seated position where they have been stationary for a long time. I commonly hear “it takes me a minute or two to get my joints warmed up before I start walking”.
Swelling can be recurrent in people with AVN. This is likely due to inflammation of the synovium, or joint lining, that produces fluid. This is described as “having too much fluid inside the hip.”
A person’s range of motion, or movement, of the hip will also be affected. This effectively decreases ones ability to fully bend or straighten the hip. Patients typically have difficulty tying shoes or picking up objects from low-lying places.
In severe cases, a person may be able to feel or hear the hip joint moving and grinding. This may be a result of damaged cartilage and bone moving about each other or perhaps from loose fragments floating in the hip or a flap from a concomitant labrum tear catching on the overlying bone.
Common risk factors for the development of avascular necrosis include excessive alcohol intake, corticosteroid use and certain prescription drug use. Previous trauma such as a hip fracture or dislocation may also cause a disruption of the blood supply to the femoral head. Genetic mutations or predispositions may also alter one’s metabolism of homocysteine. Homocysteine levels have been found to be elevated in hip avascular necrosis.