Most of us know what happens in a heart attack or in a stroke: the blood supply to a segment of the heart or brain gets clogged, leading to tissue damage. You may or may not know that certain regions of the skeleton can also suffer the same process: the blood supply to a segment of the bone is blocked, resulting in a “bone attack”, or a “bone stroke”. The term “avascular necrosis” is used to name this condition, “necrosis” meaning tissue death, “avascular” meaning “no blood supply”. Avascular necrosis is particularly common in certain joints, such as the hip, ankle, knee, and shoulder. This condition is abbreviated AVN.
What happens exactly?
The shoulder joint is formed by a sphere (humeral head) and a socket (glenoid). Shoulder avascular necrosis typically involves the humeral head. Thick layers of articular cartilage cover the surfaces of the humeral head and the glenoid. Articular cartilage is very smooth. The motion of two opposing surfaces of cartilage has been compared to gliding an ice-cube against another ice-cube; friction is minimal, which protects against wear. The bone on the humeral head is the foundation supporting articular cartilage.
Bone is alive and dynamic; it needs to be bathed by blood. Blood vessels enter the humerus in various locations, and branch out inside the humeral head towards the periphery. In avascular necrosis, the blood supply to a segment of the humeral head is lost, and that segment dies. If the segment is relatively small, the condition may go unnoticed, however larger areas of bone necrosis becomes brittle and collapses. The foundation supporting the articular cartilage is thus gone, and the cartilage may break and collapse as well. In addition, the articular cartilage on the surface of the humeral head becomes rough, and will eventually wear out the cartilage on the socket side.
Any risk factors?
Avascular necrosis of the humeral head may happen to some individuals out of the blue, for no apparent reason. However, a number of predisposing factors are identified in some. The most common risk factors include treatment with corticosteroid medications, excessive alcohol intake, kidney or bone marrow transplant, and some relatively rare diseases that make individuals more prone to form blood clots. Avascular necrosis may also complicate certain fractures of the proximal humerus. Interestingly, ocean divers who ascend to the surface too rapidly may also develop avascular necrosis.
How is it diagnosed?
Most patients with avascular necrosis of the humeral head suffer with deep-seated pain present at rest, with activity, and at night. With time, shoulder motion becomes limited to some extent. Early on, plain radiographs will not show any abnormalities. At this stage, magnetic resonance is required for the diagnosis: the segment of avascular necrosis appears excessively bright. As the condition worsens, radiographs show progressive changes: first, the area of necrosis becomes dense and looks brighter; next, bone and cartilage collapse and the outline of the humeral head looks interrupted, fractured; with time, the whole joint degenerates. Most likely, your shoulder specialist will inquire about possible risk factors as well as symptoms in other joints, such as the opposite shoulder and the hips. In fact, magnetic resonance evaluation of other joints may be suggested.
What is the prognosis?
In most individuals with avascular necrosis of the humeral head, pain and stiffness get worse over time as the condition progresses. When avascular necrosis is related to excessive alcohol intake or chronic treatment with steroids, interrupting consumption of alcohol/steroids is recommended to hopefully prevent further necrosis at the affected shoulder and more importantly in other joints. Some individuals may be able to handle their symptoms using a combination of acetaminophen and non-steroidal anti-inflammatory drugs. However, in many the pain and functional limitations become unbearable, and surgery becomes the only reliable solution, especially once the humeral head collapses.
If you need surgery…
Shoulder replacement is the best surgical procedure for avascular necrosis. As discussed in a previous post, the shoulder joint can be replaced with either anatomic or reverse prostheses. Anatomic components are almost universally recommended for most patients with shoulder AVN, unless the socket is severely damaged or the rotator cuff muscles are tendons are also badly torn, which is very uncommon in avascular necrosis. When surgery is performed prior to the articular cartilage of the socket being damaged, replacing just the sphere, and not the socket, is best (the term hemiarthroplasty or partial shoulder replacement is used to describe this procedure). Otherwise, both the ball and the socket are replaced (anatomic total shoulder arthroplasty). Your shoulder surgeon may need to decide between a partial and a total replacement depending on how good or bad the cartilage on the socket looks at the time of surgery. Many individuals with avascular necrosis need to undergo shoulder replacement at a young age; preservation of bone is extremely important in case further surgery becomes necessary in the future.