Tendon detects remaln a realol concern in plastic surgery because of the limlted availalailicv of tertdon autografts. Whereas immune rejection prohibits the use of tendon allografts, most prosthetic replacements also fail to achieve a sausfactory long-term result of tendon repair. The tissue engineering technique however.can generare differet tissues using autologous cells and thus provide an optimal approach to address this concern. The Purpose of this study was to test the feasibility of engineering tendon tissues with autologous tenocytes to bridge a tendon defect in either atendon sheath open model or a partial open model in the hen. In a total of 40 Leghorn hens, flexor tendons were harvested from the left feet and were digested with 0.25% type II collagenase. The isolated tenocytes were expanded in vitro and mixed with unwoven polyglycolic acid fibers to form a cell-caffold construct in the shape of a tendon. The constructs were wrapped with intestinal submucosa and then cultured in Dulbeecco's Modified Eagle Medium plus 10% fetal bovine serum for 1 week before in vivo transplantation. On the feet. a defect of 3 to 4cm was created at tile second flexor digitorum profundus tendon by resetting a tendon fragment. The defects were bridged either with a cell-scaffold, construce in the experlmental group (n=20) or with scaffold material alone in the control group (n=20). Specimens were harvested at 8, 12, and 14 weeks postrepair for gross and histologic examinaltion and for biomechanical analysis. In the experimental group, a cordlike tissue hridging the rendon defect was formed at 8 weeks postrepair. At 14 weeks, the engineered tendons resembled the natural tendons grossly in both color and texture. Histologic examination at 8 weeks showed that the neo-tendon contained abundant tenocytes and collagen; most collagen bundles were randomly arranged. The undegraded polyglycolic acid tibers surrounded by inflammatory cells were also observed At 12 weeks, tenocytes and collagen fibers became longitudinally aligned, with good interface healing to normal tendon. At 14 weeks, the engineered tendons di■ played a typical tendon structure hardly distinguishab■ from that of normal tendons. Biomecfianical analysis den■ onstrated increased breaking strength of the engineere■ tendons with dine, which reached 83 percent of norm■ tendon strength at 14 weeks. In the control group, pol■ glycollc acid constructs were mostly degraded at 8 wee■ and disappeared at 14 weeks. However the breakir■ strength of the scaffold materials accounted for only ■ percent of normal tendon strength.The results of this study indicated that tendon tisst■ could be engineered in vivo to bridge a tendon dcfect. T■ engineered tendoms resembled natural tendons not on■ in gross appearance and histologic structure but also ■ biomechanical properties.