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Zimmer Collagen Repair Patch and Platelet-Rich Plasma Fibrin Matrix for Achilles Tendon Repair in Sheep

1Sarrafian TL, 1Hackett EK, 2Wang H, 2Yao JQ, 3Shih M, 3Ramsay HL, 1Turner AS 1Colorado State University, Animal Medical Center, Ft Collins, CO; 2Zimmer Orthobiologics, Inc., Austin, TX; 3MDS Pharma Services, Bothell, WA

RESULTS • All operated tendons appeared healed with no

apparent fibrosis.

• Group 1 (Fig 2a): all specimens had identifiable surgical separation sites. Healing occurred by increasing tendon width and bridging the defect.

• Group 2 (Fig 2b): healing occurred with new tendon fiber bundles directly across the separation, without increasing total tendon width.

• Group 3 (Fig 2c): complete bridging of gap in all specimens.

• In Groups 2 and 3, integration of the patch to new and existing tendons was found in peripheral zones with ingrowth of vasculature

• Surgical sites of two animals in Groups 2, 3 were indiscernible with polarization microscopy.

• Group 3 also demonstrated occasional blend-in of new fibers within peripheral portions of patch.

• No significant difference among groups undergoing biomechanical testing

• Group 2 had values in extension closest to that of normal limb with mean % difference of 4.69% from contralateral limb (Fig 3).

ACKNOWLEDGEMENTS This work was supported by Zimmer Orthobiologics, Inc., Austin, TX. © 2008 Zimmer Orthobiologics, Inc.; Zimmer is a registered trademark of Zimmer, Inc.

INTRODUCTION • Surgical repair is the best option for regaining

strength, power, and function of the muscle-tendon-bone complex when the Achilles tendon is injured.

• Zimmer Collagen Repair Patch (cross-linked acellular porcine dermal patch; APD) holds promise as a means to augment healing and regeneration of such lesions.

• The primary goal is to evaluate ultimate potential of APD for Achilles tendon repair in a sheep model.

• A secondary goal is to assess the ability of platelet rich plasma fibrin matrix (PRPFM) to augment healing process and final repair strength.

METHODS • 18 skeletally mature ewes assigned to 3 groups (n=6). The animal acted as own control. Group 1 : tendon sutures only Group 2 : tendon sutures + APD patch Group 3 : APD patch + PRPFM + 1.5cm

gap • Under general anesthesia, the larger branch of gastrocnemius tendon transected (Fig 1: a, b). Two ends anastamosed using Kessler locking loop pattern (Group 1 or 2), or gap left (Group 3).

• APD patch applied for reinforcement (Group 2) or bridging (Group 3, Fig 1: c). Remnant gap filled with autogenously harvested PRPFM (Fig 1: d).

• Sheep housed in pens until humanely euthanized at 24 w. post-op.

• Biomechanical testing evaluated tensile strength in a longitudinal direction.

• All sections examined under transmitted and polarized light microscopy.

• Statistical analysis performed using one-way ANOVA with paired analysis with significance reported at p < 0.05.

DISCUSSION • These findings support use of both PRPFM

and APD in combination, to augment healing of a severed Achilles tendon in sheep model.

• Based on histological data, healing was best achieved in Group 3, despite a 1.5cm gap.

• Group 2 showed closer extension value to that of the contralateral control than the other two groups (Fig 3).

• There were noticeable differences between healing in Groups 1 and 2, with increased healing correlated to APD application.

• The combination of APD patch and PRPFM could serve as a therapeutic regimen for clinical condition when resection of torn tendon is necessary to aid with quality and strength of healing.

• The benefits of an augmentation matrix may be more evident in chronic injury model and need to be investigated.

Figure 1. Intraoperative photographs of a) isolation of Achilles tendon and b) applicaion of APD patch with preparation for transection of Achilles and c) two tendon ends present beneath sutured patch with gap present and d) placement of PRPFM into gap

c d

b a

a b

c d

Figure 2. Photomicrographs (4x) of a) suture only (Group 1) and b) suture + APD (Group 2) and c) APD + PRPFM + gap (Group 3) and d) contralateral limb

Figure 3. Mean extension (mm) for operated and unoperated Achilles tendons

Extension

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

Operated (Left Achilles) Unoperated (Right Achilles)

Ext

ensi

on (m

m)

Treatment Group 1Treatment Group 2Treatment Group 3