Summary

Tissue-Engineered Augmentation of A Rotator Cuff Tendon Using A Novel Bio-Inductive Biocomposite Scaffold

Abstract

Introduction

Surgical repair of torn rotator cuff tendons has been associated with a high degree of re-tears. Recent studies have shown that augmenting the repair through the induction of new host tissue can prevent gapping or re-tears by increasing the thickness of the tendon. This study investigated the ability of a novel, bio-inductive, biocomposite (high porosity collagen with PLLA microfilaments) scaffold to support the rapid proliferation, maturation, and remodeling of new host tissue in an animal model of rotator cuff tendon repair. The bio-inductive scaffold was hypothesized to rapidly increase the thickness of the repaired tendon through the addition of functional host tissue.

Methods

The porosity of the bio-inductive, biocomposite (collagen-PLLA) scaffold (BioBrace, Biorez Inc.) was measured using mercury porosimetry. Arthroscopic surgical technique of an augmented rotator cuff repair was evaluated using human cadaveric shoulders. Following Institutional Animal Care and Use Committee approval, a mid-portion detachment of the infraspinatus tendon (IST) was created and repaired in 18 sheep using a double row suture bridge, and augmented using the biocomposite scaffold, mimicking human cadaveric technique. Nine animals were humanely euthanized at either 6 or 12 weeks for radiography, micro-computed tomography, MRI, histology, or biomechanical testing.

Results

Mercury Porosimetry: The biocomposite scaffold had an average porosity of 80%, median pore diameter of 19.4 micron, and pore volume of 4.2 cm3/gram. Surgical Technique: The implant could be introduced into the joint arthroscopically and incorporated using a double row suture bridge): The mean thickness in the IST of non-operated animals was 3.5 mm while the mean thickness of the repaired ISTs was 10.0 mm at six weeks and 9.8 mm at twelve weeks . Histology: At six weeks the bio-inductive scaffold was infiltrated by host fibroblasts and fibrovascular tissue. Dense, regularly oriented connective tissue was also observed on the superior and inferior surfaces of the scaffold which added to the overall thickness of the healing tendon . By 12 weeks there was maturation and remodeling of the fibrovascular connective tissue within the scaffold as well as on its inferior and superior surfaces. Scattered foreign body giant cells (arrows) were observed at both 6 and 12 weeks and were associated with the PLLA fibers . Mechanical testing: The ultimate tensile strength (UTS) of the repaired IST construct significantly increased between 0 (1163 + 303N) and 6 weeks (1740 + 338N) (p=0.01), and 6 (1740 + 338N) and 12 weeks (2463 +484N) (p=0.01) . There was no significant difference in UTS between repaired (2463 + 484N) and contralateral control tendons (2707 + 605N) at 12 weeks (p=0.35).

Discussion

The collagen-PLLA biocomposite scaffold increased the thickness of a repaired rotator cuff tendon through the rapid induction of host-generated dense, regularly-oriented connective tissue. The new host tissue demonstrated functional remodeling over time resulting in a repair that was as strong as the unoperated control by 12 weeks.

SIGNIFICANCE/CLINICAL RELEVANCE: Healing of rotator cuff repairs has been a challenging clinical problem. In addition, functional outcomes are improved with integrity of the rotator cuff after repair. This study shows that a biocomposite scaffold induced a proliferative healing response that improved the thickness of the repair tissue, and was as strong as controls. This has strong potential as an adjunct for rotator cuff repair.