Purpose: A major challenge in repairing injured digital flexor tendon is the weak intrinsic healing capacity of tendon, which is responsible for rerupture of repaired tendon after primary repair. In an experimental model of transection and surgical repair of the digital flexor tendon in chicken toes, we aim to test the effectiveness of introducing the vascular endothelial growth factor (VEGF) gene through an adeno-associated virus (AAV) vector to enhance tendon healing strength. Materials and Methods: One hundred and eighteen flexor digitorum profundus (FDP) tendons in the long chicken toes were completely transected the in zone 2 and surgically repaired using 2-strand modified Kessler method. These toes were divided into two groups: 58 FDP tendons (group 1) were injected with 2 × 109 particles of AAV2-VEGF per tendon and 62 tendons (group 2) after injection with saline. The toes were immobilized in semiflexed position for the first 3 weeks and then released for free toe motion. At postoperative 1, 2, 3, 4, 6, and 8 weeks, the ultimate strengths of the healing tendons were tested in an Instron tensile testing machine. At weeks 4, 6, and 8, the work of digital flexion (WOF) was also recorded and adhesions around the repair site scored. We also supplemented a group (20 toes) in which only empty AAV2 vector was injected to the tendon, and tendon strength and adhesions were recorded at weeks 2 and 4. Results: Delivery of AAV2-VEGF significantly increased ultimate strength of the healing tendons at postoperative weeks 3, 4, 6, and 8 (P < .05 or P < .01). At week 4, the tendon strength was 12.4 ± 8.6 N after AAV2-VEGF injection, but 5.7 ± 1.1 N after saline injection. At week 6, the strength was 46.4 ± 19.2 N after AAV2-VEGF injection, but 27.1 ± 8.9 N after saline injection. At week 6 and 8, the adhesion scores and WOF of the toes after AAV2-VEGF injected were not increased. We found no significant increases in the strength of the tendon after injection of sham vector compared with that in saline control group. Conclusions: The results of this study show the therapeutic efficacy of AAV2-VEGF for improvement of tendon healing strength without aggravating adhesion formation after surgical tendon repair. AAV2-VEGF therapy appears to be a promising method of biological modulation of healing of the digital flexor tendons.
