The pathogenesis of Calcifying Tendinitis (CT) is still not well established. Prognostic factors for outcome could not yet be identified. The purpose of this study was to evaluate the histologic features of calcific deposits (CD) and their correlation with radiologic and clinical findings.

122 patients with a radiologically confirmed CD were prospectively scheduled for arthroscopic shoulder surgery. According to their radiologic appearance (RA) the CD were graded as fluffy or sharply demarcated. Arthroscopic removal of the deposit was performed and biopsies were taken and embedded in methylmethacry-late. Sections were stained and also immunohistology was performed. Shoulder function was assessed with the Constant score (CS) and the SST.

Three distinct histologic stages (HS) of the CDs could be divided: calcification (I), fibrotic organisation (II) and ossification (III). Biopsies revealed 42x (34%) HS I, 18x (15%) HS II and 62x (51%) HS III deposits. 90% of the CD were located in the SSP tendon. 12 months after the operation the CS and the SST showed a significant improvement (p< 0.01). Forty percent of the patients with ossification (III) of the CD underwent unsuccessful shock wave therapy before. The preoperative RA as well as the HS of the CD did not predispose to postoperative outcome.

In this study three definite histologic stages of Calcifying Tendinitis were identified that have not been described previously. We underline the hypothesis that CT is an active cell mediated tissue process which can lead to production of primitive bone.