Core Decompression for Avascular Necrosis of the Hip
Core decompression is a surgical procedure used in the management of the early stages of the avascular necrosis of the head of the femur. The avascular necrosis is also known as osteonecrosis, is a disease caused by disruption of the blood supply to the involved bone. The disruption of the blood supply may lead to bone death or necrosis.
The upper end of the thigh bone forms the ball of the hip joint. The ball known as the head of the femur has a precarious blood supply. Various mechanisms may lead to the disruption of the blood supply. Corticosteroids and alcoholism are the top causes of non-traumatic avascular necrosis of the head of the femur.
Blood supply is vital to maintain the normal surface and structure of the hip joint. Traumatic or nontraumatic causes may lead to a decreased or absent blood supply to parts of the head of the femur. With an absent blood supply, the segment of bone becomes nonviable.
The surrounding bone with blood supply tries to revascularize the dead bone. Vascular tissue lays down new bone in the area which increases the density (visible as increased whiteness in an X-ray.) A small fracture or break may develop between the new bone and the dead bone.
The space in between the break is filled by scar tissue. Overlying cartilage without nourishment softens and decays. The weight bore on the joint leads to small dents or breaks in the cartilage leading to collapse.
The smooth gliding is now lost and the ball grinds with the socket in the area. The process becomes widespread leading to severe arthritis and destruction of the joint surface.
In the early stages (stage 1 and 2 of Ficat & Arlet staging) of avascular necrosis, the surface of the ball and socket joint is smooth. There are no changes visible on an X-ray but changes appear on an MRI or a bone scan. The patients with early stages (pre-collapse) may benefit from core decompression.
In the early stages of osteonecrosis, the pressure inside in the head of the femur is vastly increased. The elevated pressure hampers the revascularisation of dying bone. The increased pressure also further decreases the blood of the head of the femur.
The procedure involves the creation of a small tunnel/tunnels in the head of the femur to slow or stop the osteonecrosis. The patient is laid on the operating table and the leg is placed in a specially designed table for positioning.
An intraoperative X-ray known as C-arm is used for checking the position of the instruments during the surgery. The patient may be given an intravenous sedative, spinal anesthesia, or general anesthesia. A small incision is given on the outer side of the upper thigh.
A small guide wire is passed from the incision to reach the area of the avascular necrosis without breaching the articular cartilage. A small drilling instrument is passed over the guidewire to create a tunnel to the dead bone. The procedure may involve the use of multiple drill holes instead of a single hole.
Usually, bone marrow is injected through the hole in the area of the dead bone. Sometimes bone graft taken from the patient’s body or from a bone bank may be used to fill the tunnel. The incision is closed with a suture and sterile dressing is placed on the site. The creation of a tunnel/tunnels decreases the pressure inside the head of the femur.
The reduction of pressure may lead to revascularisation and therefore repair the area of nonviable bone. The addition of bone marrow or bone graft may provide stem cells which may lead to early repair of the dead bone.
The patients are usually able to go home the same day of the procedure. The patients are usually instructed to bear 50% of the weight on the side of the procedure for the next 3 months. The patients are also instructed to avoid high impact activities.
The patients are usually followed up every 6 months to monitor the progression of osteonecrosis. In the majority of the patients, the disease process slows down or comes to a stop. They may have radiological evidence of repair of the necrotic bone.
Unfortunately, the disease process may progress in some patients. The progress is however slowed down after core decompression. The progressed cases of avascular necrosis and those in advanced stages usually require joint replacement surgery.
A total hip replacement provides excellent relief from pain and the patients are quickly able to get back to the activities they enjoy. The joint replacement surgery has revolutionized the treatment of advanced cases of avascular necrosis of the head of the femur.