Calcific tendinitis is caused by calcium hydroxyapatite deposition in a tendon and may affect as many as 3% of adults at some location. The most commonly affected sites are the shoulder, hip, elbow, wrist, and knee.
The cause of calcium hydroxyapatite crystal deposition in or near a tendon is unclear. It may be related to degeneration of a tendon with age, as a result of recurrent trauma, local hypoxia or metabolic factors. The leading theory at present is that calcific tendinitis is a primary disorder in susceptible tendons. The final pathway is likely to be local hypoxia leading to fibrocartilaginous metaplasia and subsequent calcification. Cortical reaction is caused by the local inflammatory response incited by the deposition of calcium in the affected tendon insertions. The periosteal reaction may have an aggressive appearance that can be confused with malignancy, particularly juxtacortical lesions.
This is an acute inflammatory condition, producing a rapid onset of severe pain with tenderness. The pain is localised just below the hip and it is not relieve by lying still. There may be several episodes taking a week or two to settle. Between time the area is tender to deep palpation.
Plain x-rays can be difficult to interpret as the calcified area overlies the bone on standard projections. Additionally there may be cortical reaction to the tendonitis mimicking other pathology. Therefore it is not unusual for a bone scan to show increased uptake.
MRI scans may also be difficult to interpret as the clarification is not well seen and if there is cortical/marrow involvement the appearances can mimic a malignancy. If there is doubt a CT scan is justified, this is not the first line investigation due to the dose of radiation involved.
Conservative measures are usually all that is needed; rest, time, NSAID. Occasionally a targeted steroid injection may be indicated, and for severe pain the calcific lesion can be excised.
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