Calcium hydroxyapatite deposition disease is a condition where there is a deposition of calcium phosphate crystals, mainly hydroxyapatite in the soft tissues around the joint. The depositions occur, especially in tendons. The condition is commonly known as calcific tendinitis and seen when the deposition involves supraspinatus tendon.
But the deposits also occur in structures other than tendons and the term calcific periarthritis is suggested for broader involvement.
Peritendinitis calcarea, hydroxyapatite rheumatism etc. are other names for this condition.
Calcium hydroxyapatite deposition disease is a type of crystal deposition like gout and calcium pyrophosphate dihydrate deposition disease and there appears to be considerable overlap among these crystal deposition diseases.
Pathogenesis of Calcium Hydroxyapatite Deposition Disease
Calcium hydroxyapatite is the most abundant form of calcium in human bone. The deposition of hydroxyapatite (and other basic calcium phosphate crystals) occurs mainly as a primary or idiopathic entity (without any cause).
The periarticular deposition has been found nearly all joints as well as in a number of tendon insertions remote from joints.
The shoulder is the most commonly involved joint followed by hip, elbow, wrist, and knee.
It can also occur as a secondary process in a number of conditions like
- End-stage renal disease
- Collagen vascular diseases
- Vit D intoxication
- Tumoral calcinosis
- Dystrophic calcifications
The pathogenesis is still not clear.
The following initiating factors have been suggested
- Abnormal pressure
- Decreased local vascularity
- Local hypoxia [decreased oxygen levels]
- Preexisting tissue degeneration
Stages of Process of Deposition
Three phases of the condition have been identified. Here the description is of the shoulder joint.
- Initial phase
- Calcium deposit is completely contained within the tendon
- The deposit is sharply circumscribed
- Patients do not have any symptoms.
- Enlargement of the deposits
- The deposit is still within the tendon
- May produce impingement like symptoms
- Liquefaction may occur causing an increase in pressure
- The rupture causes bursitis which can be very painful
- Occur as late stage with substantial destruction
- Pain and stiffness occur
- Variable sized calcium deposits within a rotator cuff
- Cause destructive changes.
Middle-aged people are most commonly affected with slight male preponderance. Calcific tendinitis typically affects a single site but bilateral shoulder [and rarely hip] involvement is known.
The affected patients could be without symptoms. In some patients, these might be discovered incidentally on x-ray.
The patients who have symptoms, the symptoms may be chronic or acute.
The shoulder region is the commonest site for calcium hydroxyapatite deposition but the deposits can occur in the number of other sites.
The patients who have symptoms have recurrent pain and stiffness of varying degrees. There could be an inability to use the joint.
Sometimes, the patient may present with acute onset of pain in the joint region.
The results of laboratory tests are usually normal.
Electron microscopy may be used to identify calcium hydroxyapatite crystals. But this is a specialized investigation and can have limited access.
X-rays show deposits as homogenous amorphous densities. They are roughly ovoid in shape or linear or triangular with smooth and ill-defined margins. These can be differentiated from heterotropic ossification by a lack of trabeculations.
Occasionally, calcific periarthritis may produce erosions of bone immediately beneath the insertion of the involved tendon. The cause of the erosions is not known.
CT or MRI may can be used to differentiate the lesions from other conditions. But these are not commonly done for the purpose of diagnosis.
CT has similar findings as in an x-ray. Tissue edema is better visualized by CT.
MRI findings depend on the inflammation and stage of calcification. In acute inflammation, there is acute phase soft tissue edema surrounding the calcification is present. The calcifications themselves appear as heterogeneous signals on T1 sequences of MRI.
Chondrocalcinosis may be noted.
- Metastatic calcification
- Tumor and tumor-like conditions [sucha as synovial osteochondromatosis]
- Synovial sarcoma
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 steroids appear to shorten the duration and intensity of symptoms.
Intraarticular Calcium hydroxyapatite Deposition Disease [Milwaukee Shoulder]
In this, there is intraarticular deposits lead to apatite associated destructive arthritis. This is associated with chronic tears of the rotator cuff and joint effusions
Though the cause is not exactly clear, the deposition of crystals is thought to release the enzymes like collagenases, serine proteases, elastases, and interleukin-1. It leads to a painful and swollen joint.
X-rays reveal glenohumeral joint destruction with or wihtout subluxation of humerus.
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- V. Sansone, O. Consonni, E. Maiorano, R. Meroni, and A. Goddi, “Calcific tendinopathy of the rotator cuff: the correlation between pain and imaging features in symptomatic and asymptomatic female shoulders,” Skeletal Radiology. 2016, vol. 45, no. 1, pp. 49–55.
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