Abstract
To determine the healing potential and healing process of torn supraspinatus tendons, in situ hybridization was used to localize cells containing α1 type‐I procollagen mRNA. Biopsy specimens of torn supraspinatus tendons from 19 patients with complete‐thickness tears and 13 patients with incomplete‐thickness tears were obtained during surgery. Four macroscopically normal supraspinatus tendons were obtained to serve as normal controls. Specimens were fixed in 10% buffered formalin and embedded in paraffin. A 22‐mer oligonucleotide probe was labeled with digoxigenin and used as an in situ marker. The labeled cells were mainly composed of tenocytes and undifferentiated mesenchymal cells. In complete‐thickness tears, the labeled cells at the proximal tendon stumps in the specimens that were obtained less than 4 months after trauma were significantly more abundant than in the specimens obtained 4 months or more after trauma. However, the number of labeled cells was maintained at the torn portion even in long‐standing incomplete‐thickness tears. The labeled cells at the margins of concomitant intratendinous extensions of the tears were detected even in the long‐standing tears. The intratendinous extensions exhibited more labeled cell than were bursal‐side or joint‐side layers of the tendon substance in the incomplete‐thickness tears (p < 0.05). The torn supraspinatus tendon may possess an intrinsic healing capability in the intermediate and late phases of tendon healing. Incomplete‐thickness tears and concomitant intratendinous extensions can continue to rupture after the initial injury.