Calcium is found inside the joints in the synovial fluid, which is a viscous fluid with an egg-white consistency, vital for reducing friction between the articular cartilage of synovial joints when they are moved.
The calcium contained in the fluid may crystallize and when this happens the crystals damage the articular surfaces. This results in the breakdown of cartilage by the enzymes released during the damage, leading to swelling and tenderness, inflamed skin over the joint and pain and stiffness in addition to a general feeling of being unwell. In up to 60% of joints that require replacement surgery for osteoarthritis, calcium-containing crystals are found.
Types of Calcium Crystals
The two main types of calcium crystals that can cause painful joint inflammation are calcium pyrophosphate (CPP) crystals and apatite crystals. The problems that these two types of crystals cause may be collectively referred to as calcium crystal diseases. CPP crystals tend to build up in the joint cartilage and cause chondroncalcinosis, also known as cartilage calcification and usually affects people in the late middle-age to elderly.
Apatite crystals tend to occasionally build up in the cartilage but do so mostly in a tendon and cause calcific tendinitis and affects mostly young or middle-aged adults. In both cases, men and women are affected equally. Sometimes cartilage calcification may involve a mixture of both CPP and apatite crystals.
Pathobiology
Calcium accumulation in the tendons is seen especially in the rotator cuff tendons of the shoulder. This pathological accumulation is most often seen where there is tissue or cellular damage of some sort. Moreover, there need not be any involvement of an overuse or traumatic injury in order for calcific tendinitis to occur. Important contributors to determining the severity of the tendinitis include size, location, and number of the calcifications.
Sometimes these calcium accumulations may not cause any symptoms at all, but they can become inflamed and lead to considerable shoulder pain, which may lead to limitation in range of motion.
If crystals embed themselves deep in the tissue and do not come into contact with cells or proteins of the body’s immune system, then no inflammation may be involved. This is usually the case in people who have crystal deposits for many years without having any complications. However, should the crystals go from the cartilage and into the joint cavity or go from the tendon and into the surrounding tissues, significant inflammation may occur.
The process by which crystals are dislodged causing inflammation is known as shedding.
The shedding of CPP crystals into the joint cavity is called acute CPP arthritis. The crystals cause pain and swelling in the joint due to the inflammatory reaction generated. This condition was once called pseudo-gout or false-gout, because the inflammatory reaction resembles that of gout (a disease due to the defective metabolism of uric acid leading to urate crystal accumulation in joints with resultant arthritis).
Apatite crystal shedding causes acute calcific tendinitis in the supraspinatus shoulder tendon or in tendons anywhere in the body.
Diagnosis and Treatment
In diagnosing calcium crystal pathology, other pathologies such as gout and infection must be first ruled out. Tests done include joint fluid sampling, X-rays, and blood and biochemical panels. Non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen ease the pain associated with acute attacks.
Anti-gout drug colchicine may also be used to reduce the interaction between the crystals and the body’s immune system. Joint fluid aspiration may also be used to reduce the pain caused by fluid pressure and long-acting steroids may be injected into the joint. Other therapies include exercise and pain management with ice-packs.
Further Reading
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