Causes / typical injury mechanism: Calcific tendonitis is an inflammatory condition caused by the deposition of carbonate apatite crystals in or surrounding a tendon, most commonly the tendons of the rotator cuff in the shoulder. The supraspinatus tendon is affected in the majority of cases, although deposits may also develop in other tendons in the shoulder, hip, or other anatomic locations. The condition is one of the leading causes of nontraumatic pain in the shoulder.

Classic history and presentation: Approximately half of all patients with calcific deposits are symptomatic. The resorptive phase of the condition, characterized by the spontaneous resorption of the deposits via an inflammatory process, is generally associated with the majority of pain and dysfunction symptoms. Patients often describe atraumatic pain ranging from chronic, mild pain to acute periods of severe discomfort in the affected tissue. In the shoulder, pain is frequently localized anteriorly or posteriorly (depending on the affected tendon) and may radiate toward the insertion of the deltoid. Pain at rest is variable, but discomfort with arm abduction and overhead motion is common. Increased pain during the night or in the morning is often reported, and patients generally have difficulty lying or sleeping on the affected shoulder. Mild swelling and warmth in the affected area may also accompany acute episodes of calcific tendonitis. Systemic symptoms such as fever and malaise are not uncommon. This acute phase typically lasts for 2 weeks or less, and it is generally followed by significant clinical improvement. In milder cases, symptoms normally resolve spontaneously within 6 months, but they may persist for a year or longer. In general, the acuity and severity of the symptoms correlates with their duration.

Prevalence:

• Calcific tendonitis predominately affects individuals between the ages of 30 and 60 years.
• It is slightly more common in women than men.
• Bilateral involvement occurs in 10%-25% of patients.

Risk factors:

• Endocrine diseases including diabetes mellitus and disorders of thyroid and estrogen metabolism have been associated with calcific tendonitis.
• Additionally, the HLA-A1 gene may confer a genetic predisposition to the disease.
• The condition has not been linked to strenuous manual labor or overuse. Patients with a sedentary occupation appear to be at higher risk.

Pathophysiology: The etiology of calcific tendonitis is still not completely understood, but the condition is commonly described as progressing through 3 phases: precalcific, calcific (subphases: formative, resting, and resorptive), and postcalcific.

• The precalcific phase is characterized by fibrocartilaginous metaplasia in the tendon with introduction of chondrocyte-like cells.
• The calcific stage involves the formation of calcific deposits in the transformed tissue, eventually followed by vascularization at the periphery of the deposits and phagocytic infiltration and resorption of the deposits.
• In the postcalcific phase, fibroblasts remodel the affected regions of the tendon by laying down collagen.