Avascular necrosis (AVN) of the hip is a progressive disorder in which the blood supply to the head of the femur is diminished. This leads to the deterioration of bone that causes a progressive collapse of the femoral head.1 The bony collapse ultimately results in arthritis, causing inflammation and pain in the affected hip joint.2 This disorder most commonly affects men between the ages of 25 and 50 years. There are 2 etiologic factors associated with AVN: traumatic and atraumatic.2
Traumatic AVN occurs when the head of the femur sustains physical damage or injury, while atraumatic refers to systemic diseases or exogenous causative factors.2 Femoral head fractures are the most common traumatic etiologies of AVN of the hip, but studies have demonstrated that they are actually uncommon injuries.3 In order to fracture the femoral head, high-energy trauma to the hip must occur.3
In a majority of patients, atraumatic factors are more likely to cause AVN of the hip. Atraumatic causes include chronic use of alcohol or glucocorticoids, history of smoking tobacco products, and hematologic disorders such as sickle cell anemia, thalassemia, polycythemia, hemophilia, myeloproliferative disorders, and metabolic disorders.1 Clinicians must be able to distinguish the exact etiology of the disorder in order to prevent further injuries and to determine the potential risk factors associated with AVN of the hip.
Signs and Symptoms of AVN of the Hip
Patients with AVN of the hip will typically present with pain that is achy and throbs. They especially feel tenderness and pain in the groin and are usually unaware of what may have caused the onset of pain.4 Patients will report that the pain is aggravated with physical activities such as prolonged walking, climbing stairs, and getting up and down from a seated position.4
Physical examination will reveal limited range of motion especially with internal forced rotation.5 Unfortunately, these clinical manifestations also present with osteoarthritis of the hip.6
Clinicians must take a thorough history by questioning their patients on chronic alcohol and tobacco use, previous history of glucocorticoid use, any history of hematologic disorders, and any past trauma to the affected hip. Taking a thorough history may give the clinician a better understanding of what is causing the pain. While AVN of the hip may not be as common as osteoarthritis of the hip, it should be on a clinician’s list of differential diagnosis when a patient presents with hip pain.7 The pathophysiology of osteoarthritis and AVN are entirely different, and clinicians must be able to distinguish between them (Figures 1 and 2).8,9
Assessment of AVN of the Hip
Diagnosis of AVN of the hip from history and physical evaluation may be difficult; therefore, clinicians must be well-trained and have knowledge on which imaging modality may provide the best and most accurate results.
Due to its availability, decreased risk of complications, and fairly inexpensive cost, radiographs are the initial imaging study performed.9 Radiographs of the hip and pelvis will be able to reveal any abnormalities that may be present. The downside of this imaging technique is that it is insensitive in the earlier stages of the disease; it may take up to 3 months after the initial onset of symptoms to reveal AVN of the hip on film.9 In advanced stages of AVN, however, radiographs may detect subchondral fracture with collapse of the femoral head. This typically presents with radiolucent lines called “crescent sign”.10
The use of magnetic resonance imaging (MRI) removes the delay in diagnosis. An MRI is considered the gold standard for diagnosing AVN of the hip because it can detect the disease more quickly than radiography.9 It has a sensitivity of more than 99%, can detect crescent signs earlier, and is capable of detecting bone marrow changes including edema and sclerosis sooner than plain radiographs.9 Additionally, MRI will be able to help clinicians rule out labral tears and/or any soft tissue impingement problems and complications in which a radiograph cannot.1,2
However, there are several disadvantages of MRI, including increased cost, prolonged wait time for results, and the extended time where patients must stay idle during the imaging study. Regardless of the drawbacks associated with MRI, it can be concluded that it is still the best imaging modality due to its high sensitivity rate and ability to diagnose the patient quickly. Unfortunately, the pain associated with AVN of the hip progressively worsens and can be extremely debilitating to the patient. Therefore, the sooner the patient is diagnosed, the sooner treatment may begin.