Bone overgrowth: Description, Causes and Risk Factors:
Bony overgrowth rarely extends more than a few millimeters and is mostly of no consequence. However, at critical sites, particularly in the shoulder and spine, it may be a significant problem.
The extent of bone overgrowth is influenced by the level of local mechanical stress, genetic predisposing factors, the passage of time, and, probably, age related changes such as the menopause. In very crude terms the size of an osteophyte may be given by local mechanical stress x time x genetic tendency.
When bone overgrowth occurs in the absence of any local defect in articular cartilage it tends to be uniform and symmetrical. When bone overgrowth is accelerated by cartilage defects it is local to the site of cartilage damage. The subchondral bone shows local "reactive" sclerosis and a local osteophyte appears.
There appear to be many genetic factors which accelerate bone overgrowth, in a variety of anatomical patterns. In the average individual by the age of 80, in the absence of cartilage damage, there is slight flaring of most bone ends, particular those that are flat or concave - vertebral endplates, the tibial plateau, the proximal end of the distal phalanges etc. Greater degrees of bone overgrowth can be divided into those dominated by osteophytes and those by syndesmophytes. An outgrowth which increases the area of a joint surface is an osteophyte. An outgrowth which extends into a ligament is a syndesmophyte. They are not always totally distinct.
A common familial pattern of osteophytic overgrowth is termed peripheral generalized osteoarthropathy (PGOA). This term is of practical value in that it describes a reasonably homogeneous clinical syndrome of overgrowth at DIP (distal interphalangeal), first carpometacarpal, and knee joints. Clinically, hard swellings are most prominent at the DIP joints and are known as a Heberden's node. Heberden's nodes usually appear sequentially over a period of a few years, after the age of 40. This pattern of overgrowth is consistently associated with loss of articular cartilage in the affected hand joints, and sometimes the knee. Cartilage may disintegrate because of the changes in underlying bone. There may also be an element of cartilage ossification as part of the bone overgrowth. A vicious cycle of bone growth and cartilage loss may be set up, and although it is not clear how this starts, everything points to bone rather than cartilage.
A less common but highly specific pattern is erosive osteoarthropathy (EOA) which produces florid bony swellings most marked in PIP (proximal interphalangeal) joints. Cartilage is lost and there is a net increase in bone. However, irregular bony defects ("erosions") occur at the joint line, unlike typical subchondral cysts. The mechanism is not understood and may in fact be a synovitis with an unusual bone and cartilage reaction. Joints may undergo bony fusion.
Other patterns of osteophytosis are not well defined but gross osteophytosis at the knee seems to be more common in west Africans. Rare patterns of bone overgrowth (Mseleni disease, Kashin-Beck disease) may relate to geographically localized environmental factors.
Osteophytosis in the elderly is often associated with mineralization of soft tissues and cartilage involving calcium pyrophosphate and/or hydroxyapatite.
In diffuse idiopathic skeletal hyperostosis (DISH), widespread bone overgrowth occurs at ligament and tendon insertions around joints and spinal discs. New bone forms wispy streaks along ligaments and at muscular attachments. These growths are best viewed as syndesmophytes. There are probably many subtypes, some being purely spinal (Forestier's disease) and others affecting tendon and muscle attachments peripherally.
Ankylosing spondylitis is characterized by widespread bone overgrowth. It is usually viewed as a disorder of the immune system and is certainly related to MHC Class I. However, the division between connective tissue matrix homeostasis and the inflammatory response may not be as clear as is often implied.
In acromegaly, both bone and cartilage grow inappropriately in adult life. Cartilage disintegration frequently supervenes.
If the bone growth presses on a nerve, you may experience symptoms of numbness or tingling and muscle weakness. Bone overgrowth in the neck and back can often put pressure on the nerves that control the arms, legs and also digestion.
Over time, bone overgrowth that rubs on other bone or tissue can create swelling and inflammation. This can lead to tears of the ligament, tendon or muscle it rubs against, if not treated. If the bone growth is in your neck and facing inwards, it can interfere with breathing and swallowing.
Even when a patient experiences apparent nerve compression symptoms, it doesn't necessarily indicate the presence of a bone overgrowth. A number of degenerative spine conditions can produce back or neck pain, including herniated discs, bulging discs, or the thickening of spinal ligaments. Part of confirming an initial bone overgrowth diagnosis is eliminating the possibility that symptoms might be caused by a different condition.
The first step in the diagnostic process is to answer a doctor's questions about medical history, symptom severity, and symptom location. This will usually be followed by a physical and neurological exam, in which the doctor will test range of motion and reflexes. Often, an X-ray and blood tests will be ordered, sometimes in conjunction with one or more of the following:
Magnetic resonance imaging - an MRI produces clear pictures of the interior of the body without the use of X-ray.
- Computed topography scan - a CT scan uses computers and X-rays to produce cross-sectional images of the body.
- Bone scan - radioactive material injected into the body collects in the bones, pooling in areas affected by an abnormality.
- Electromyography - in EMG, muscle activity is monitored by very fine needles that measure response to brain signals.
When bone overgrowth leads to friction on soft tissues it may seem logical to remove the bony outgrowth. However, such outgrowths form an integral part of the cortical shell and may be sites for ligament attachment. Removal may weaken the bone and generate instability. Bone tends to bleed profusely when cut and heals by the formation of a mass of surrounding callus. In many cases removal is impractical. However, there are exceptions. Removal of new bone compressing nerve roots or spinal cord in the spine is the clearest example. Trimming of bone causing impingement on the rotator cuff tendon of the shoulder can also be successful in relieving pain.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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