Evaluation of Bioadhesive Mesh Construct to Augment Achilles Tendon Repair in a Rabbit Model

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1 Evaluation of Bioadhesive Mesh Construct to Augment Achilles Tendon Repair in a Rabbit Model Yan Lu, MD 1, Brett Nemke 1, Jackie Kondratko 1, Vicki kalscheur 1, Gino Bradica 2, Ray Vanderby 1, Mark D. Markel 1. 1 UW-Madison, Madison, WI, USA, 2 Kensey Nash Inc., Exton, PA, USA. Disclosures: Y. Lu: None. B. Nemke: None. J. Kondratko: None. V. kalscheur: None. G. Bradica: 3A; Kensey Nash. 4; Kensey Nash. R. Vanderby: 5; Kensey Nash. M.D. Markel: 5; Kensey Nash. Introduction: The Achilles tendon is a commonly injured tendon, usually occurring at a point 4-5 cm proximal to the calcaneus, a zone of poor blood flow in the tendon.(1) Polymer/mesh combinations with patterned coating of the adhesive have been demonstrated to allow soft tissue in-growth and biocompatibility in animal models.(2) The objective of this study was to determine which one of mesh constructs with or without suturing reinforcement was most effective for Achilles tendon healing when compared to control in a rabbit model. Methods: Three constructs used in this rabbit study were 1) ECM: single layer meso (BioMatrix PN 30050); 2) construct 1: ECM coated with M179, and 3) construct 2: ECM coated with M202. They were prepared in dry, sterile and pre-shaped (1.5x0.9 cm) conditions (Fig. 1). One hundred two New Zealand White rabbits were utilized in the study. All experimental protocols were approved by the Institutional Animal Use and Care Committee of University of Wisconsin-Madison. Bilateral transections and re-attachments were performed on each rabbit's Achilles tendons. All operated tendons were divided into 7 treatment groups and each operated tendon randomly received one of 7 treatments: 1) suture only; 2) ECM + suture reinforcements; 3) ECM + suture reinforcements + platelet-rich plasma (PRP); 4) construct 1 + suture markers without reinforcements; 5) construct 1 + suture reinforcements; 6) construct 2 + suture markers without reinforcements, and 7) construct 2 + suture reinforcements. After anesthesia, a rabbit was placed in a prone position and surgically draped. A 3.0 cm lateral skin incision was made in one randomly selected leg to expose the rabbit Achilles tendon. A lateral bundle of the Achilles tendon was separated and sharply transected at the level of 15 mm proximal to the calcaneus insertion, leaving the flexor digitorum superficialis tendon and medial bundle of the Achilles tendon intact. The lateral bundle of Achilles tendon was immediately reattached with a 4-0 non-absorbable nylon suture material in a single locking loop suture. One of 7 treatments was randomly selected to apply to the reattached tendon. The construct (ECM, construct 1 or construct 2) was wrapped around the reattached tendon ends via an umbilical tape and hydrated with saline (2 ml) or PRP (1 ml) for 10 minutes. The both ends of wrapped construct were sutured with a 5-0 braided silk suture material to the tendon as reinforcements or sutured outside the both ends of the construct as markers (Fig. 2). The distance from the calcaneous to the first suture and the first to the second suture were measured. The contralateral Achilles tendon was performed the same procedure and received another 1 of 7 treatments. All rabbits were sacrificed at 7, 14, 28 and 84 days after surgery. All tendon samples were analyzed by gross appearance, biomechanical testing and histology. Postoperative tendon stretch or rupture was determined based on comparing the change in the distance between the two suture markers at the time

2 of surgery and sacrifice. The change in the distance less than 2 mm was defined as a non-stretch, between 2-5 mm defined as a minor stretch, between 5-10 mm defined as a moderate stretch and greater than 10 mm defined as a over stretch. All histologic samples were scored by 3 senior researchers using a custom-designed score table. One way ANOVA was used to determine the significances among groups after surgery. If the significant differences were discovered, a Duncan s Multiple Range Test was used to compare the differences among the groups. Differences were considered to be significant at a probability level of 95% (p<0.05). Results: No construct tearing and peeling were discovered in any repaired tendon in this study. After comparing distances between the 1st and 2nd suture markers at the times of surgery and sacrifice, 10% of all treatment tendons hadn t stretched, 22% had mildly stretched, 52% had moderately stretched, 16% had overly stretched. At 28 days after surgery, group 6 had a significantly greater failure load than groups 2, 4, 5, and 7 (p<0.05). Group 6 also had a trend to have a greater failure load than group 3. Group 6 had a significantly greater stiffness than groups 2, 4 and 5 (p<0.05). There were no significant differences in the stiffness among other groups. At 7 days after surgery, there were no significant differences in the histologic scores among the groups 1, 2, 3, 6 and 7. Groups 1, 2 and 6 had better histologic scores than the group 4. At 14 days, there were no difference among the groups 2, 4, 5, 6 and 7. At 28 days after surgery, group 6 had better histologic scores than groups 3, 4, 5 and 7 (p<0.05). There were no significant differences in histologic scores among groups 6, 1 and 2. At 84 days after surgery, there were no significant differences between the group 6 and other groups (Fig. 3). Discussion: Biomechanical testing and histologic results of the construct 2 (group 6) were correlated and indicated that the construct 2 adhered to the repaired tendon very well and may accelerate tendon healing better than ECM and construct 1 at 28 days after surgery. Addition of PRP treatment and suture reinforcement on the tendon didn t show remarkable advantages in Achilles tendon healing in this rabbit model study. Possible reasons for a high percentage of tendon stretch after repair may be: 1) no external immobilization and protection for the repaired Achilles tendon after surgery; 2) operative procedures for the implantations were more aggressive to increase tensile force of the tendon than the suture only. In summary, based on the biomechanical and histologic results, construct 2 may be an optimal implant for the future Achilles studies. Significance: Construct 2 adhered rabbit tendon tissue well and may be applied for human tendon healing clinically in the future.

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5 ORS 2015 Annual Meeting Poster No: 1349