Avascular Necrosis Flashcards
Definition/Description
Avascular necrosis/Osteonecrosis is a degenerative bone condition characterised by death of cellular components of bone secondary to an interruption of the subchondral blood supply. It typically affects the epiphysis of long bones at weight-bearing joints. Advanced disease may result in subchondral collapse which threatens the viability of the joint involved. Non-traumatic cases will typically present with mechanical pain of variable onset and severity and often difficult to localize. In early disease, the physical examination is often normal which inevitably causes a delay in diagnosis.
Causes
Osteonecrosis is most common in the hip, but also seen in the humerus, knee, and talus and more rarely seen in the smaller bones of the wrist such as the lunate or scaphoid.
It can be caused by trauma or non traumatic events
Joint or bone trauma
An injury, such as a dislocated joint, might damage nearby blood vessels.
A fracture in a bone eg femoral head.
Cancer treatments involving radiation also can weaken bone and harm blood vessels.
2. Non-traumatic
heavy drinking and steroid abuse have been identified as major risk factors
Numerous studies have also concluded that hyperlipidemia in the femoral head, induced by steroid and alcohol use, are associated with osteonecrosis.
Both of these factors precipitate an increase in fat volume in bone marrow and blood lipid levels, thereby increasing deposition of fat and interrupting blood flow to the femoral head.
Glucocorticoid intake was found to have an even stronger association than alcohol use.
Cigarette smoking: due to changes in nitric oxide bioavailability, there is an increased oxidative stress level and endothelial dysfunction
Obesity: osteonecrosis is positively associated with BMI. Overweight and obesity are, just like steroid and alcohol use, often associated with hyperlipidemia.
A medical condition, such as sickle cell anemia or Systemic Lupus Erythematosus.
Studies show that there is a higher prevalence among males, this could be attributed to higher levels of smoking and alcohol use. Greater fluctuations in climate temperatures may also contribute to higher rates of non-traumatic osteonecrosis
Clinical Presentation
Symptoms include pain and decreased range of motion in the affected joint. In some cases, the condition is diagnosed during routine x-ray imaging, due to a lack of overt symptoms. The most common location for this condition to manifest, is the head or neck of the femur or humerus, and the knee joint
In the beginning, this disease is asymptomatic. It is also plausible there is a segmental collapse present and the patient doesn’t feel it. As the disease progresses, the hip can become stiffer, which is visible in the gait of the patient when he starts to limp. Pain is also observed by support on the leg, in the buttock, groin and thigh.
Avascular necrosis can be classified into five different stages:
Stage 1: Radiographic changes are absent or show minor osteopaenia. An MRI scan is required for identification (can show oedema). The onset of this disease is asymptomatic.
Stage 2: First stage with radiographic changes. This stage is characterized by sclerosis of the superior central portion of the joint head and/or osteopenia and/or subchondral cysts.
Stage 3: In this stage, the articular surface is depressed so that the round contour is compromised, without being significantly deformed. This leads to a joint space narrowing. Plain radiograph shows a crescent sign.
Stage 4: This stage is characterized by a wide collapse of the subchondral bone and destruction of the underlying trabecular pattern. This can lead to secondary arthritis.
Stage 5: The final stage where both articular surfaces are affected, which leads to a dysfunctional joint.
For example, if a case presents itself where the patient has has osteonecrosis of the femoral head. Avascular necrosis most commonly affects the hip in more than 72% of the cases. The patient will have mild chronic pain in the hip, the groin, around the buttocks and at the antero-medial thigh, with normal radiograph, they should undergo observation for ONFH and a Hip joints MRI. This pain is most commonly aggravated by activity and internal rotation in flexion. As the disease progresses, the pain may also become present at rest. Without treatment 85% will progress to the collapse of the articular surface and will eventually require total hip arthroplasty.
Diagnostic Procedures
Osteonecrosis can be diagnosed with a thorough check of the historical background of the patient combined with physical examination. Steroid exposure and alcohol abuse are important risk factors. The age of the patient can also provide clues to the disease, because patients with osteonecrosis are generally younger than those with osteoarthritis.
Locking, popping, or a painful click during mobilization of the affected joint can point to the presence of loose osteochondral fragments. In further stages of the disease, loss of mobilization and increased pain can be detected. Once osteonecrosis is detected, the physician should assess other joints that may be at risk, such as the hip, shoulder and knee
The double line sign is an MRI finding seen at the periphery of a region of osteonecrosis. It consists of an inner bright line representing granulation tissue and an outer dark line representing sclerotic bone. Measurement of the size and location of the necrotic lesion is a crucial prognostic parameter to predict collapse and can be better defined on an MRI.
