Repair process of the rat Achilles tendon after tenotomy

アキレス腱の修復能力と修復過程について詳細に調べるために,ラットのアキレス腱を切断して,後肢を固定せずに,最長6カ月後まで修復過程を観察した.3日後には腱の断端間(修復部)は,柔らかい結合組織で充たされ,1週後には断端が索状の結合組織で連絡していた.切断した腱の残存部には,線状の細い核を持ち細胞質が乏しい線維芽細胞(腱細胞)に混じって,核が楕円形で細胞質が豊富な線維芽細胞(腱芽細胞)が,3日後に少数出現し,1,2週後には増加したが,4週後以降は減少した.血管は,3日後には修復部の周辺に少数観察され,次第に増加して分布も広がり,2週後には修復部や切断された腱の内部にも多数観察されたが,4週後以降は減少した.修復部の線維芽細胞と膠原線維は,3日後には乏しかったが,1,2週後には増加し,4週後には多数が長軸に沿って配列して腱の断端と再生した腱との区別は困難だった.4週後以降には一部の再生腱で軟骨が見られ,3,6カ月後にはすべての再生腱で骨が観察された. 本実験で,アキレス腱の修復には腱内部と周囲結合組織の線維芽細胞が関わり,2週後に最も修復が盛んになることが示唆された.また,4週後ないし遅くとも6週後までに腱はおおむね修復されることが明らかになった.ラットとヒトでは異なるが,アキレス腱が高い修復能力を持ち比較的短期間に修復が進むことは,アキレス腱断裂に対する治療法を選択するうえで参考になり,リハビリテーションの開始時期を早めることができる可能性を示唆する.To investigate the regenerating ability and healing process of the rat Achilles tendon, the tendon was cut and its repair process was observed up to 6 months without hindlimb casting. The gap between severed tendons was filled with soft connective tissue at 3 days postoperatively and bridged by fibrous connective tissue at 1 week. By light microscopy, tendons showed a small number of tenoblasts with an ovoid nucleus and rich cytoplasm among tenocytes which contained a thin nucleus and scanty cytoplasm at 3 days. Tenoblasts increased in number at 1 and 2 weeks, and decreased at 4 weeks onward. Blood vessels were located at the peripheries of the regenerating portion at 3 days, increased in number and distribution throughout the regenerating portion and tendon at 2 weeks, and decreased at 4 weeks afterwards. Fibroblasts and collagen fibers at the regenerating portion were small in number at 3 days, increased at 1 and 2 weeks, and oriented along the long axis of tendon at 2 and 4 weeks. It was difficult to discriminate between severed tendon and the regenerated portion at 4 weeks. Cartilage was observed in some specimens at 4 weeks, and bones were found in all specimens at 3 and 6 months. These findings indicate that fibroblasts derived from both tendon and surrounding connective tissues are involved in repair, and that the repair process of tendon seems most active at 2 weeks after surgery. Regenerated tendons are considered to restore principal tendon structure at 4 or, at the latest, 6 weeks. Thus, Achilles tendon has an intrinsic ability to repair within several weeks, which provides a rationale for consideration of medical treatment and planning of early rehabilitation