Abstract

Objectives: To report a rare case of in situ regeneration of the human palmaris longus tendon one year after resection, and to evaluate the structural integrity and mechanical properties of the regenerated tissue using tissue engineering methods. Introduction: Tendons are generally considered to have limited regenerative capacity, and repaired tissue is often regarded as scar tissue rather than true tendon. Although tendon regeneration has been reported in vitro, evidence of in vivo regeneration in humans remains scarce. We observed an in situ regenerated palmaris longus tendon during surgery and investigated its morphological, histological, and biomechanical characteristics. Materials / method: Regenerated tendon tissue was harvested intraoperatively and carefully preserved. Tensile mechanical testing, hematoxylin-eosin staining, polarized light staining, and immunofluorescence staining were performed. The regenerated region was compared with non-regenerated normal tendon tissue to assess similarities and differences in mechanical behavior and histological structure. Results: The regenerated tendon measured approximately 5.20 cm in length, with a long-axis diameter of 0.82 cm and a short-axis diameter of 0.34 cm. Grossly, it retained a tendon-like structure, with a translucent appearance and firm texture. Mechanical testing showed a maximum tensile force of 137.26 N and a maximum displacement of 4.23 mm. Histological analysis demonstrated an orderly arrangement similar to normal tendon tissue, arguing against simple scar formation. Conclusion: This case documents in situ regeneration of a resected human palmaris longus tendon in vivo. The regenerated tissue showed tendon-like morphology, mechanical properties comparable to functional tendon, and expression of tendon-related markers. These findings suggest that the regenerated tissue was structurally and functionally similar to normal tendon.