Mechanical Properties of Polyglycolide-trimethylene Carbonate and Polydioxanone Monofilament Sutures in Vivo Used for Flexor Tendon Repair

INTRODUCTION Braided polyester suture materials have been commonly used for flexor tendon repair in the clinical setting. However, knotted braided polyester lost approximately 50% of its tensile strength according to a study by Trail et al.(1) Accordingly, 4 or 5 throws are needed to prevent slippage for a secure knot, which may result in stitch granuloma. The use of absorbable sutures avoids problems associated with long-term foreign body implantation such as excessive fibrosis and stitch granuloma that could affect the critical smooth running of the tendons. However, many surgeons do not use absorbable sutures for flexor tendon repair, not only because they fear a loss in tensile strength but also because of an inflammatory response. Several studies have analyzed polyglycolide-trimethylene carbonate monofilament and polydioxanone monofilament sutures for flexor tendon repair and demonstrated that these materials possess adequate strength under conditions of immobilization.(2,3) It remains unclear whether tendons repaired using these absorbable sutures are able to withstand postoperative mobilization. We evaluated the effectiveness of absorbable flexor tendon repair in combination with active mobilization. Polydioxanone and polyglycolide-trimethylene carbonate monofilament sutures were used and compared in this study. MATERIALS AND METHODS Forty-eight canine flexor digitorum profundus (FDP) tendons from 24 mongrel adult dogs were used in this study. 12 fresh canine cadaver FDP tendons from 6 mongrel adult dogs that had been sacrificed primarily for other purposes were used as a day-0 control. The specimens were divided into two equal groups, according to whether a polyglycolide-trimethylene carbonate (Group 1) or a polydioxanone (Group 2) monofilament suture would be used. Operative procedure Each animal was initially tranquilized with Ketamine (10 mg/kg body weight, injected intramuscularly) and subsequently anesthetized with pentobarbital (15 mg/kg body weight, injected intravenously) as necessary to maintain appropriate anesthesia levels. Under tourniquet control, an Lshaped lateral longitudinal incision was made adjacent to the paw pad. The flexor sheath was excised between the proximal and distal pulleys to expose the FDP tendons in zone 2. The FDP tendons were sharply lacerated and repaired utilizing the technique (Fig.1), which consisted of the 2-strand locking Kessler core suture in combination with the simple circumferential suture. A 5-0 polyglycolide-trimethylene carbonate monofilament (Maxon; Davis & Geck, Danbury, CT) and a 5-0 polydioxanone monofilament (PDS2; Ethicon, Somerville, NJ, USA) were used as the core suture, and a 6-0 polypropylene monofilament (Prolene; Ethicon, Somerville, NJ, USA) was used as the circumferential suture. The sheaths were not repaired. After surgery, the dogs were allowed active mobilization immediately under a 45° wrist extension block shoulder-elbow-forearm spica cast control. Repaired tendons were harvested at 7, 14 and 28 days for biomechanical testing.