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A Patient’s Guide to Avascular Necrosis of the Hip

Introduction

Bones are living tissue, and like all living tissue they rely on blood vessels to bring blood to keep them alive. Most living tissues have blood vessels that come from many directions into the tissue. If one blood vessel is damaged it may not cause problems, since there may be a backup blood supply coming in from a different direction. But certain joints of the body have only a few blood vessels that bring in blood. One of these joints is the hip. This document will describe what happens when this blood supply is damaged and results in what is called avascular necrosis (AVN) of the hip.

This guide will help you understand

  • how AVN develops
  • how doctors diagnose the condition
  • what treatments are available

Anatomy

Where does AVN develop?

The hip joint is one of the true ball-and-socket joints of the body. The hip socket is called the acetabulum and forms a deep cup that surrounds the ball of the upper thigh bone. The thigh bone itself is called the femur, and the ball on the end is the femoral head. Thick muscles of the buttock at the back and the thick muscles of the thigh in the front surround the hip.

The surface of the femoral head and the inside of the acetabulum are covered with articular cartilage. This material is about one-quarter of an inch thick in most large joints. Articular cartilage is a tough, slick material that allows the surfaces to slide against one another without damage.

All of the blood supply comes into the ball that forms the hip joint through the neck of the femur (the femoral neck), a thinner area of bone that connects the ball to the shaft. If this blood supply is damaged, there is no backup. Damage to the blood supply can cause death of the bone that makes up the ball portion of the femur. Once this occurs, the bone is no longer able to maintain itself.

Living bone is always changing. To maintain a bone’s strength, bone cells are constantly repairing the wear and tear that affects the bone tissue. If this process stops the bone can begin to weaken, just like rust can affect the metal structure of a bridge. Eventually, just like a rusty bridge, the bone structure begins to collapse.

When AVN occurs in the hip joint, the top of the femoral head (the ball portion) collapses and begins to flatten. This occurs because this is where most of the weight is concentrated. The flattening creates a situation where the ball no longer fits perfectly inside the socket. Like two pieces of a mismatched piece of machinery, the joint begins to wear itself out. This leads to osteoarthritis of the hip joint, and pain.

Causes

Why do I have this problem?

There are many causes of AVN. Anything that damages the blood supply to the hip can cause AVN.

Injury to the hip itself can damage the blood vessels. Fractures of the femoral neck (the area connecting the ball of the hip joint) can damage the blood vessels. A dislocation of the hip out of the socket can tear the blood vessels. It usually takes several months for AVN to show up, and it can even become a problem up to two years following this type of injury.

Some medications are known to cause AVN. Cortisone is the most common drug known to lead to AVN. This is usually only a problem in patients who must take cortisone every day due to other diseases, such as advanced arthritis, or to prevent rejection of an organ transplant. Sometimes there is no choice, and cortisone has to be prescribed to treat a condition, knowing full well that AVN could occur. AVN has not been proven to be caused by short courses of treatment with cortisone, such as one or two injections into joints to treat arthritis or bursitis.

A clear link exists between AVN and alcoholism. Excessive alcohol intake somehow damages the blood vessels and leads to AVN. Deep sea divers and miners who work under great atmospheric pressures also are at risk for damage to the blood vessels. The pressure causes tiny bubbles to form in the blood stream which can block the blood vessels to the hip, damaging the blood supply.

Symptoms

What does AVN feel like?

The first symptom of AVN is pain when weight is placed on the hip. The pain can be felt in the groin area, the buttock area, and down the front of the thigh. As the problem progresses, the symptoms include development of a limp when walking and stiffness in the hip joint. Eventually, the pain will also be present at rest and may even interfere with sleep.

Diagnosis

How do doctors identify the condition?

The diagnosis of AVN begins with a history and physical examination. Your doctor will want to know about your occupation, what other medical problems you have, and your medication use. You’ll be asked whether you drink alcohol. A physical examination will be done to determine how much stiffness you have in the hip and whether you have a limp. Once this is done, X-rays will most likely be ordered.

X-rays will usually show AVN if it has been present for long enough. In the very early stages, it may not show up on X-rays even though you are having pain. In the advanced stages, the hip joint will be very arthritic, and it may be hard to tell whether the main problem is AVN or advanced osteoarthritis of the hip. Either way, the treatment is basically the same.

If the X-rays fail to show AVN, you may have a bone scan done to determine if the pain in your hip is coming from early AVN. A bone scan involves injecting tracers into your blood stream. Several hours later, a large camera is used to take a picture of the bone around the hip joint. If there is no blood supply to the femoral head, the picture will show a blank spot where the femoral head should be outlined on the film.

The bone scan has pretty much been replaced with magnetic resonance imaging (MRI) today. The MRI scan is probably the most common test used to look for AVN of the hip. The MRI scanner uses magnetic waves instead of radiation. Multiple pictures of the hip bones are taken by the MRI scanner. The images look like slices of the bones. The MRI scan is very sensitive and can show even small areas of damage to the blood supply of the hip, even just hours after the damage has occurred.

Treatment for Avascular Necrosis of the Hip

What can be done for the condition?

Once AVN has occurred, the treatment choices are determined by how far along the problem is and your symptoms. While the symptoms may be reduced with pain medications and anti-inflammatory medications, no medical treatments will restore the blood supply to the femoral head and reverse the AVN.

Nonsurgical Treatment

If AVN is caught early, keeping weight off the sore-side foot when standing and walking may be helpful. Patients are shown how to use a walker or crutches to protect the hip. The idea is to permit healing and to prevent further damage to the hip. Patients may be shown stretches to avoid a loss of range of motion in the hip. Anti-inflammatory medicine is often used to ease pain. In some cases, surgeons also prescribe an electrical stimulator in an attempt to get the bone to heal. Sometimes these measures may help delay the need for surgery, but they rarely reverse the problem.

Surgery

If the femoral head has not begun to collapse, your surgeon may suggest an operation to try to increase the blood supply to the femoral head. Several operations have been designed to do this.

Decompressing the Femoral Head

The simplest operation is to drill one or several holes through the femoral neck and into the femoral head, trying to reach the area that lacks blood supply. The drill bores out a plug of bone within the femoral head. This operation is thought to do two things: (1) it creates a channel for new blood vessels to quickly form into the area that lacks blood supply, and (2) it relieves some of the pressure inside the bone of the femoral head. Relieving this pressure seems to help decrease the pain patients experience from AVN.

This operation is done through a very small incision in the side of the thigh. The surgeon watches on a fluoroscope as a drill is used. A fluoroscope is a type of X-ray that shows the bones on a TV screen. The surgeon uses the fluoroscope to guide the drill where it needs to go. This operation is usually done as an outpatient procedure, and you will be able to go home with crutches the same day.

Fibular Bone Graft

A more complicated procedure to try to increase the blood supply to the femoral head is a vascularized fibular bone graft procedure. This is actually a tissue transplant. The graft is taken from the fibula (the thin bone that runs next to the shin bone). The graft is vascularized, meaning it has a blood supply of its own. Because it supports the femoral head, the graft is also referred to as a strut graft.

The surgeon removes a piece of the small bone in your lower leg (the fibula) along with the blood vessels to the bone. The surgeon then drills a hole through the side of the femur and into the femoral head. The surgeon attaches the blood vessels from the fibula to one of the blood vessels around the hip. This creates instant blood flow into the bone graft and into the head of the femur. This operation does two things: (1) it brings blood flow to the femoral head through the bone graft, and (2) the fibular bone graft is strong and keeps the femoral head from collapsing as the bone heals itself. This procedure is an inpatient procedure and will require you to stay in the hospital for several days.

This is a very complicated operation and is not commonly done. It is not always successful because the blood supply to the graft is fragile and may not form completely.

Artificial Hip Replacement

When AVN is in the advanced stages, the condition is no different from osteoarthritis of the hip joint. Your surgeon will probably recommend replacing the hip with an artificial hip joint.

Rehabilitation

What should I expect following treatment?

Nonsurgical Rehabilitation

You may work with a physical therapist who will show you ways to safely move and stretch your hip. The goal is to keep your hip mobile and to avoid losing range of motion. Your therapist will also instruct you to use a walker or crutches. Keeping weight off your hip while you are standing or walking may help the bone to heal while protecting the femur from further damage.

After Surgery

After a simple drilling operation, you will probably use crutches for six weeks or so. The drill holes weaken the bone around the hip, making it possible to fracture the hip. Using crutches allows the bone to heal safely and reduce the risk that you may fracture your hip. Patients who have had bone and blood vessels grafted are required to limit how much weight they place on the hip for up to six months.

When you are safe in putting full weight through the leg, your doctor may have you work with a physical therapist to help regain hip range of motion and strength.

Patients who require artificial hip joint replacement follow a structured program of physical therapy beginning shortly after surgery.

In-depth Information for Avascular Necrosis of the Hip

Basics
Description
  • AVN is osteonecrosis, or death of the bone.
    • All major joints can be affected.
    • In the pediatric population, this condition is called Legg-Calve-Perthes disease and, in general, has a better prognosis than osteonecrosis in the adult.
  • AVN of the hip is osteonecrosis of the femoral head.
  • Synonyms: Osteonecrosis; Aseptic necrosis; Chandler disease
  • Classification:
    • Ficat and Arlet described 4 stages:
      • Stage I: No changes on radiograph, changes noted on MRI
      • Stage II: Sclerotic or cystic changes on radiographs in the femoral head, no collapse
      • Stage III: Subchondral fracture, crescent sign on radiographs
      • Stage IV: Degenerative changes in the hip joint with involvement of the femoral head
    • Steinberg et al. modification of the Ficat and Arlet classification (all stages except stage 0 + advanced degenerative changes):
      • Stage 0: Normal radiograph, normal bone scan
      • Stage I: Normal radiograph, abnormal bone scan
      • Stage II: Sclerosis or cyst formation in the femoral head (A = mild, <20%; B = moderate, 20-40%; C = severe, >40%)
      • Stage III: Subchondral collapse (crescent sign) without flattening (A = mild, <15%; B = moderate, 15-30%; C = severe, >30%)
      • Stage IV: Flattening of the head without joint narrowing or acetabular involvement (A = mild, <15% of surface and <2 mm of depression; B = moderate, 15-30% of surface or 2-4 mm of depression)
      • Stage V: Flattening of head with joint narrowing or acetabular involvement (A = mild; B = moderate; C = severe [acetabular involvement])
    • One of the most predictive findings on radiography or MRI is the actual size of the lesion.
General Prevention
  • Limited systemic corticosteroid use
  • Avoidance of alcohol abuse
  • Early fixation of femoral neck fractures or reduction of hip dislocations
Epidemiology
  • Most common in young adults 20-40 years old and in children 6-10 years old.
  • The average age of patients with osteonecrosis who require hip arthroplasty is 38 years.
  • The distribution between males and females is equal.
  • Patients with atraumatic osteonecrosis of one hip have a >50% chance of developing osteonecrosis of the contralateral side.
Prevalence
~2.5% of total hip replacements are performed for the diagnosis of AVN.
 
Risk Factors
  • Femoral neck fractures
  • Steroid use
  • Alcohol abuse
  • Hemoglobinopathies (e.g., sickle cell anemia)
  • Clotting abnormalities
  • Dysbarism (bends)
  • Ionizing radiation
  • Pancreatitis
  • Gout
Genetics
A genetic pattern may be related to a clotting disorder with protein S deficiency.
 
Etiology
  • Osteonecrosis is most commonly alcohol-related or induced by incremental and cumulative doses of corticosteroids (90%).
    • Alcohol: The threshold of alcohol ingestion reported to be associated with osteonecrosis is the equivalent of 400 mL or more per week of 100% ethyl alcohol (~3 beers per day).
    • Corticosteroids:
      • A total dose of 2,800 mg of oral prednisone over 4 months significantly increases the risk of bone infarction.
      • Some researchers believe that patients who have idiosyncratic reactions to steroids, with systemic changes such as acute weight gain or moon faces, have an increased risk of developing osteonecrosis.
  • Other causes include:
    • Traumatic injuries such as hip fractures
    • Subclinical clotting disorders
    • Exposure to atmospheric pressure variations
Associated Conditions
  • Hip fracture
  • Hemoglobinopathy
  • Alcohol abuse
  • Perthes disease
Diagnosis
Signs and Symptoms
  • Onset of pain in the hip without antecedent trauma
  • Pain is usually in the groin.
History
  • The patient often initially complains of vague pain in the groin for 4-6 months before evaluation.
  • Pain increases with internal rotation of the hip.
  • A high index of suspicion should exist in a young patient with hip pain and other risk factors.
Physical Exam
  • Look for groin pain with ROM of the hip (internal rotation), which is not typically tender with direct palpation.
  • The patient has a limp but a normal neurologic examination.
  • The combination of history and physical examination should lead to a suspicion of osteonecrosis of the hip.
Tests
Lab
  • Complete blood count
  • ESR
  • Coagulation profile (research tool at present)
Imaging
  • Plain radiographs, including AP and lateral projections of the hip
  • MRI of the hip is the single best test for diagnosing osteonecrosis of the hip (specificity, 98%).
Pathological Findings
  • Although osteonecrosis has many possible causes, a common final pathway leads to the typical pathologic findings, including death of the osteoblast and osteocytes with empty lacunae in the trabecula of the necrotic area.
  • An area of sclerotic margin also commonly is present in the area of necrosis.
Differential Diagnosis
  • Fracture
  • Infection
  • Transient osteoporosis of the hip
  • Neurogenic pain
  • Sports hernia
  • Acetabular labral tear
  • Psoas bursitis
  • Synovitis or adhesions of the capsule
Treatment for Avascular Necrosis of the Hip
General Measures
  • The diagnosis of osteonecrosis of the hip should be made as early as possible.
  • Other joints, including the contralateral hip, knees, shoulders, and ankles, should be evaluated.
  • Patients with this diagnosis should be evaluated by an orthopaedic surgeon who is experienced in treating osteonecrosis of the hip.
  • Nonoperative treatment typically is not successful for symptomatic lesions.
    • The failure rate is ~80%, depending on the size and classification of the lesion.
  • Small lesions have a higher rate of spontaneous resolution than do large lesions.
Special Therapy
Physical Therapy
Physical therapy can be useful for maintaining ROM but usually is of little benefit.
 
Medication
First Line
  • Anticoagulants, antihypertensives, and lipid-lowering agents are all being investigated for the treatment of early-stage disease.
  • Currently, use of these pharmacologic agents should be considered experimental.
  • Evidence exists that diphosphonate may be helpful in preventing collapse.
Surgery
  • Surgery for the treatment of osteonecrosis of the hip can be divided into procedures that preserve the femoral head and arthroplasty options.
  • Head-preserving techniques:
    • Core decompression:
      • Indicated for small- to medium-sized precollapse lesions
      • Weightbearing should be protected for 5 weeks after surgery to avoid fracture.
      • Variable satisfactory outcomes have been reported (range, 40-90%).
    • Osteotomy: Rotates the affected area of the head away from the weightbearing portion.
    • Vascularized fibular grafts: 1 study indicated an 83% success at 17-year follow-up in specialized centers.
    • Nonvascularized bone-graft:
      • Dead bone is removed and replaced with bone graft through a trapdoor in the femoral neck.
      • Reported success rate of 80-83% at 2.5-5 years follow-up
  • Arthroplasty options:
    • Resurfacing arthroplasty:
      • Indicated for patients with severe femoral head collapse and minimal acetabular changes
      • Variable results have been reported.
    • Total hip arthroplasty:
      • Indicated for patients with femoral head collapse and acetabular involvement
      • A lower success rate is reported for patients with osteonecrosis than patients with osteoarthritis.
Follow-up
Prognosis
  • <50% of asymptomatic hips progress to end-stage disease requiring hip arthroplasty.
  • Nonoperative treatment of symptomatic lesions result in 79% failure rate.
  • Patients with diagnoses or risk factors thought to contribute to the development of osteonecrosis have worse outcomes with head-preserving procedures.
Complications
  • Progressive collapse of the hip can lead to debilitating arthritis and the need for total hip arthroplasties.
  • Risk of fracture exists with weightbearing after core decompression.
    • Risk is increased if the core tract is made through diaphyseal bone.
  • Risk of donor site morbidity exists with vascularized fibular grafting.
  • Hip arthroplasty in patients with osteonecrosis has a higher failure rate, owing to loosening, than in patients with osteoarthritis (20% versus 5%, respectively, at 10 years).
    • With modern implants, bearing surfaces may become the limiting factor of replacements in younger patients.
Patient Monitoring
  • Serial radiographs are used to note any progression of joint involvement every 3-4 months.
  • Clinical symptoms are equally important, especially if nonoperative management is selected with the end point of total hip arthroplasty.
Miscellaneous
Codes
ICD9-CM
733.42 Osteonecrosis (aseptic necrosis), femoral head
 
Patient Teaching
Patients are counseled on the natural history of the disease and are asked to call the physician’s attention to bone or joint pain.
 
FAQ
Q: Will osteonecrosis of the hip get better?
A: Spontaneous resolution occurs more often in patients with small lesions. Larger lesions and those that have collapsed are unlikely to improve spontaneously.
 
Q: Which patients should have total hip replacement?
Collapse of the femoral head and arthritic changes in the joint are indications for arthroplasty.

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