Calcium Hydroxyapatite Deposition Disease

Idiopathic Perriarticular Calcium Hydroxyapatite Deposition Disease

Calcium hydroxyapatite deposition disease is a condition where there is  deposition of  calcium phosphate crystals, mainly hydroxyapatite in the  soft tissues around the joint especially tendons.

Calcific tendinitis is the term given to it in the shoulder when the deposition involves involves supraspinatus tendon.  However the term calcific periarthritis denotes the condition better as the deposits may also be found in tissues other than tendons.

Other names in use for this condition are peritendinitis calcarea, hydroxyl apatite rheumatism etc.

Calcium hydroxyapatite is most abundant form of calcium in human bone and the deposition of hydroxyapatite and other basic calcium phosphate crystals, occurs as a primary or idiopathic entity and as secondary process in  number of conditions like end stage renal disease, collagen vascular diseases, vit D intoxication, tumoral calcinosis. Dystrophic calcifications are also largely Calcium hydroxyapatite.

Calcium  hydroxyapatite deposition disease is a type of  crystal deposition like gout and calcium pyrophosphate dehydrate deposition disease and there appears to be considerable overlap among these crystal deposition diseases.

Calcific Tendinitis caused By Hydroxyapatite deposition disease

Calcific Tendinitis caused By Hydroxyapatite deposition disease, Image Wikipedia GNU License

Pathogenesis of Calcium Hydroxyapatite Deposition Disease

Pathogenesis of is still not clear. Trauma, abnormal pressure and compression, decreased local vascularity, local hypoxia and preexisting tissue degeneration have been suggested as possible initiating factors.

Three  phases of condition have been identified. Here the description is of shoulder joint.

Silent phase

This is initial phase in which calcium deposit is completely contained within the tendon which appear sharply defined circumscribed . Patients do not have any symptoms in this phase.

Mechanical Phase

The mechanical phase is characterized by enlargement of the deposits which may produce impingement like symptoms. Liquefaction of the deposits occurs leading to increase in pressure and bursitis. The deposit is still within the tendon.

Recurrent bursitis may lead to rupture of the deposit, either under or inside the bursa.  This stage is characterized by acute painful attacks.

Adhesive Periarthritis

It is a late stage, is characterized by general debility, pain, limitation of motion. Variable sized calcium deposits within a rotator cuff that shows considerable destructive changes.


Calcium hydroxyapatite Deposition Disease or Calcific periarthritis most commonly affects middle aged person.

Males are slightly more affected than females.  The patients with these deposits  could be asymptomatic or may present recurrent symptoms of pain and disability of varying severity. Acute presentation is also known.

Although the shoulder region by far the common site for Calcium hydroxyapatite deposition, these deposits occur in number of other sites.

Periarticular deposition has been found nearly all joints as well as in number of tendon insertion remote form joints. Shoulder is most commonly involved joint followed by   hip, elbow, wrist and knee.

Tendinous Calcium hydroxyapatite deposits loosely occur close to the site of tendon insertion near the joint though distant deposits  have been noted. For example  example in the gluteus maximus insertiona, adductor magnus insertion and pectolis  major insertion.

Lab Investigations

Results of laboratory tests are usually normal.

Individual calcium hydroxyapatite are small  and they not visible with light microscopy except as aggregates which may appear glossy but nobirefrigerant in polarized light.

Transmission electron microscopy of electron diffraction studies may be used to specifically identify Calcium hydroxyapatite crystals but have limited access.


On x-rays, calcium hydroxyapatite deposits are homogenous amorphous densities and lack trabeculations which allows them to be different from heterotrpoic ossification or accessory bones. Size could be variable. They are roughly ovoid in shape or linear or triangular with smooth and ill defined margins.

CT or MRI may be needed for differentiation of lesions from other conditions. Chondrocalcinosis may be noted

Occasionally, calcific periarthritis may produce erosions of bone immediately beneath insertion of the involved tendon.  The cause of the erosions is not known.

Intrarticular Calcium hydroxyapatite Depostion Disease [Milwaukee Shoulder]

This is also called apatite  associated destructive arthritis. This is destructive arthropathy of the shoulder associated with chronic tears of the rotator cuff and joint effusions containing hydroxyapatite crystals activated collagenases, neutral proteases.

Most commonly affected patients are elderly women and usually involves dominant shoulder.

Though cause is not exactly clear, it is thought that crystal deposition in the joint causes the release enzymes like  collagenases, serine proteases, elastases, and interleukin-1.  This leads to decrease in joint function and degradation of joint anatomy.

The involved shoulder is usually swollen and may be painless or painful. Aspiration of the joint may yield large amounts of synovial fluid, frequently tinged with blood. The fluid contains hydroxyapatite  crystals in aggregates, activated collagenases, neutral proteases and particulate collagen.

View An Image Of Milwaukee Shoulder

Sometimes calcium pyrophosphate dihydrate crystals are also often found in the fluid supporting the theory that Milwaukee shoulder syndrome may represent a mixed disease.

Xrays reveal destroyed joint, gleohumeral joint destruction, narrowing and sclerosis with ossification cyst formation. Upward subluxation of the humeral head due to disruption of rotator cuff may be evident.

Knee involvement is common in patients with Milwaukee shoulder syndrome [50%] where radiographic appearance at this site is very similar to that calcium pyrophosphate arthropathy and distinguishing could be difficult. The  two may  also coexist as a mixed crystal deposition disease.

Differential Diagnosis of Calcium Hydroxyapatite Deposition Disease

Other crystal deposition like pseudogout [calcium pyrophosphate dihydrate deposition disease] and gout may be similar in presentation and imaging to calcium hydroxyapatite deposition disease and may have periarticular depositions.

Meatastatic calcifications may occur in periarticular locations in a number of diseases with end stage renal disease and renal osteodystrophy,  hyperparathyroidism, hypervitaminosis D and tumoral calcinosis.

The underlying disease or large size of the calcifictions should allow differential from calcium hydroxyapatite deposition disease

Collagen vascular diseases such as scleroderrma and dermatomysositis may show  soft tissue calcifications.

Heterotropic ossifications secondary to trauma may occur in periarticular locations.  Trabeulcae may be present unlike calcium hydroxyapatite deposition disease

Tumor and tumor like conditions like synovial osteochondromatois may be associated  with cacifications within periarticular soft tissue masses. The presence of the significant soft tissue mass and possible articular erosion may help distinguish this entities.

Synovial sarcomas arise in perarticular locations and contain calcifications in one third of cases. Bone erosions may be present.

Treatment of Calcium hydroxyapatite Depostion Disease

Treatment of calcium hydroxyapatite deposition disease is nonspecific.

Acute attacks of synovitis may be self-limiting, resolving in from days to several weeks.

Aspiration of effusions and the use of either nonsteroidal anti-inflammatory agents is the prescribed treatment.

Oral colchicines for 2 weeks or of intraarticular injection of steroid appear to shorten the duration and intensity of symptoms.

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