AVASCULAR NECROSIS OF FEMORAL HEAD

Introduction

Bone is a living tissue and it needs blood supply to survive. If there is damage to one of the blood supply, bone may depend on the accessory blood supply for the survival. But certain bones in our body have precarious unidirectional blood supply like Head of femur, scaphoid, and talus.
When there is damage to blood supply to the head of femur it results in the death of cells in the femoral head. Gradually there is collapse of femoral head with loss of sphericity. This condition is referred to as Avascular necrosis of femoral head or Osteonecrosis (bone death) of femoral head.

How AVN develops in femoral head?

Hip joint is a ball and socket type of synovial joint. The socket is formed by cup shaped acetabulum which surrounds the ball (femoral head - upper end of thigh bone). The surface of femoral head and socket is lined by thick articular cartilage and then lined by synovial membrane. All together with the surrounding joint capsule and muscles form a hip joint.

The ball of hip joint receives most of its blood supply through the neck of thigh bone. If there is damage to this blood supply there is no accessory blood supply to the femoral head.
There is gradual death of cells in femoral head due to loss of blood supply. Due to death of bone cells, there is no reparative process of bone formation and resorption. Gradually the bony structure in the femoral head weakens and starts to collapse. When AVN develops in the head femur, the weight bearing area of the head is the first place to collapse. The rounded contour of the femoral head is lost and it becomes flattened causing abnormal movement in the hip joint.
Secondary osteoarthritis develops, as there is gradual wear in ball and socket of the hip joint.

Causes:
Many causes have been identified

Trauma: Fractures
Damage to the blood supply of femoral head usually occurs following a trauma or fractures to the bones in and around the hip joint.
 Fracture of Femoral neck, Femoral head
 Hip Dislocations
 Bad fractures of acetabulum
AVN can develop months or some times after initial injury.

Drugs:
Steroids:
Some steroids like cortisone, prednislone or methyprednisolone are known to cause AVN. In certain conditions like bronchial asthma, skin diseases, some auto immune disorders, inflammatory arthritis and in cases of organ transplant to prevent rejection, use of steroids is must to control or treat these conditions. Orally prescribed steroid are notorious in producing AVN of femoral head. There have been studies to show that steroid given in the form of injections into the joints or bursa does not cause any AVN of femoral head.

Blood disorders:
Some blood diseases like sickle cell disease, Leukemia’s, Gauchers disease and diseases related to blood coagulation can cause AVN of femoral head.

Lifestyle:
Studies have shown that alcohol and smoking can cause AVN in femoral head. Chronic alcohol intake can damage blood vessels leading to AVN. Smoking cause narrowing of small blood vessels and thereby reducing blood supply to the femoral head.

Others:
Deep see divers and miners are more prone develop AVN. Due to high atomospheric pressure tiny air bubbles are formed inside the blood stream which can block the tiny blood vessels in the femoral head there by resulting in AVN.

Symptoms

What does AVN feel like?
1. Pain:
Initially patient complains of pain in the affected hip which gradually increases on weight bearing. As the disease progresses patient complains of pain at rest and at night.
2. Limping
3. Stiffness
4. Difficulty in sitting cross legged and squatting
5. Shortening of affected limb

Diagnosis

How do doctors identify the condition?
1. History: doctor enquires about
- Occupation
- Medical problems and any medications like steroids
- Alcohol and smoking

2. Examination: doctor examines hip for
- Range of movements
- Stiffness

3. X-rays:
X - rays do not show any changes of AVN in the early stages of disease even though patient is having pain in the hip. It may take few months to observe changes of AVN and make diagnosis on X - ray.

4. MRI:
MRI can detect early changes of AVN in the femoral head that cannot be seen on X- ray. It helps to detect damaged areas of blood supply to the hip. AVN of femoral head can be graded as mild, moderate and severe depending on the size location of these damaged areas and if any collapse has occurred in the MRI images. MRI can also help to detect AVN changes in the opposite hip even though there are no symptoms.

5. Bone scan:
Bone scan involves injecting a radioactive chemical into the blood. Hours after injection a special camera is used to take pictures of your skeleton. The picture shows blank spot in the areas of femoral head which is devoid of blood supply. MRI has replaced Bone scan in diagnosing the cases of AVN of femoral head.

Treatment
What are the treatment options for AVN of femoral head?
AVN of femoral head is irreversible resulting in arthritic hip. Some drugs and salvage procedures can help in delaying the progress of disease. The choice of treatment depends upon the stage of the disease. Some factors like age of the patient, general health of patient and activity level also determines the treatment methods.

Nonoperative treatment:

If avascular necrosis of femoral head is diagnosed in early stages, some of following treatment methods can help in delaying the progress

1. Protected weight bearing on the affected limb with the help of crutches or walker can help reduce pain. The idea behind it is, it permits healing and prevents further damage.
2. Exercises and stretches prevent stiffness in the hip and helps to maintain range of motion.
3. Medications:
A. Bisphosphnates : This group of drugs help to reduce the risk of femoral head collapse in patients with Avascular necrosis.
B. Blood thinners: They are given in view of improving blood circulation to the femoral head.
C. Anti-inflammatory medications / simple analgesics to reduce pain.

The above mentioned treatment modalities may delay the progression of disease, but not completely reverse the Avascular necrosis.

Surgical management:

Salvage procedures: Some surgical procedures can try to decrease the pressure in femoral head and increase the blood supply. The main prerequisite for such surgeries is that there should not be any collapse in the femoral head. Many procedures have been designed to improve the blood supply of femoral head. Your surgeon can choose and suggest appropriate procedure.

Core decompression of femoral head:

The most common surgical procedure is to drill one or several holes into the femoral neck and head trying to enter into areas of poor blood supply. The idea behind this procedure is one that it creates a new path for new blood vessels to grow into areas of poor blood supply and it relieves pressure inside the femoral head. The other advantage of this procedure is that there is pain relief secondary to relieving pressure in the femoral head.
Core decompression of femoral head can be supplemented with bone grafting with or without stem cells injection

Core Decompression and Bone grafting of femoral head:

Following core decompression procedure bone graft is packed into the dead part of femoral head and channel created in the femoral head and neck. The bone graft can be taken from the patient or from the bone bank. The bone graft is made into tiny pieces and packed into the channel created in the femoral head and neck.

Stem cells treatment:

Stem cells obtained from the patient body can be injected into the channel created for core decompression of femoral head. Stem cells injection can be done along with bone grafting also. There are studies showing that stem cells help to stimulate new bone formation in the diseased areas of the femoral head.

Postoperative rehabilitation after core decompression surgery:
This surgical procedure is done through a very small incision from the side of thigh. Surgeon guides the drill into the femoral head with help of intraoperative X - ray machine (C-Arm). This procedure is usually done as outpatient procedure and patient can go back to the house on the same day with help of crutches or walker.

Following core decompression surgery the drill holes in the femoral neck and head may weaken the bone, making it susceptible to fracture. So patients are advised to use crutches or walker to move around for six weeks. After six weeks, patient patients are advised to put full weight on operated leg and take advice of physiotherapist to regain hip range of motion and strength.

Advantages of core decompression surgery:
Core decompression of femoral head is NOT A DEFINITIVE procedure. It is a salvage procedure to delay the process of Avascular necrosis probably by increasing blood supply and also preventing further collapse.
After the core decompression procedure it is necessary to continue, the medications explained above as they also help in delaying the progress of disease.

Core decompression and Vascularized fibular grafting:

In the first step surgeons drills a hole into the femoral neck and head. In the next step surgeon removes small part of fibula (Thin bone by the side of shin bone in leg) along with its blood vessels. This is referred as vascularized fibular graft because it has its own blood supply. Fibular graft is inserted into the channel created in the neck and head of the femur. Vascular surgeon attaches the blood vessels from the fibula to one of the blood vessels in the hip. This procedure does two things
1. Fibular graft acts as structural support preventing collapse of femoral head.
2. The newly connected blood vessels try to increase blood supply to the femoral head.
This is a very complicated procedure and needs special expertise. The success of the surgery depends on the viability of newly created blood supply. It is rarely practiced nowadays.

TOTAL HIP REPLACEMENT:

The process of Avascular necrosis of femoral head invariably ends in arthritic hip. In arthritic hip, joint surfaces of femoral head and acetabulum becomes irregular with loss of motion in the joint. The treatment choice is total hip replacement.

Total hip replacement is procedure in which the surgeon replaces the damaged femoral head and damaged joint surface of acetabulum (socket) with prosthetic components. Damaged femoral head is removed and replaced with metallic stem and ball. Damaged cartilage of the socket of hip joint is replaced with metal socket.

Prosthetic components:
Total Hip replacement can be either cemented or uncemented.

Cemented Total hip replacement: In this procedure, cement is used for fixation of the prosthetic components into the bone.
Uncemented Total Hip replacement: In this technique, the fixation of components is by “pressfit” into the bone which allows bone to grow onto the components.

Prosthetic materials:
Total hip replacement has wide range of designs and materials.
The stem component and socket components in the total hip arthroplasty are invariably medical grade steel or titanium alloys. There is choice of material selection for the prosthetic head and liner of socket. Prosthetic heads can be metallic or ceramic. Socket liners are available in plastic, metallic and ceramic materials.
Different combinations of metal heads and liners can be made depending on needs of the patient.
Metal on plastic (Metal head / Plastic liner)
Ceramic on plastic (Ceramic head / Plastic liner)
Metal on metal (Metal head / Metal liner)
Metal on ceramic (Metal head / ceramic liner)
Ceramic on ceramic (Ceramic head / Ceramic liner)

The decision to use cemented or uncemented components and various combination of head and socket liners are based on various factors such as age, bone quality and sometimes surgeons choice.

RESURFACING ARTHROPLASTY:
In certain patients with limited damage to the part of femoral head surgeon may consider resurfacing arthroplasty. In this procedure surgeon replaces only damaged femoral head with metallic implant.