Objectives: Calcified tendinitis of the shoulder joint is a common painful condition. Resorption of the calcium deposits is one of the key events in the pathogenesis of this disease. The aim of this study was to examine whether the multinucleated giant cells that appear in this condition have osteoclast phenotypes.
Methods: Immunohistochemical and RNA in situ hybridization analysis of cathepsin K, a marker for osteoclasts, was performed in human surgical samples.
Results: The multinucleated cells located near the calcium deposits were positive for cathepsin K protein and mRNA. Reverse transcription-polymerase chain reaction using human cathepsin K-specific oligonucleotide primers confirmed that synthesis of cathepsin K mRNA occurs in the tissues of calcified rotator cuffs.
Conclusion: The multinucleated giant cells which appear in the resorption area of calcium deposits in calcified tendinitis have the osteoclast phenotype.