# Rotator Cuff Repair Augmentation by Direct Interlocking of an Overlayed Nonwoven Polyethylene Terephthalate Patch Substantially Increases Repair Strength: A Biomechanical Comparison in Ovine Shoulders

## TL;DR

A new surgical technique using a special patch improves the strength of rotator cuff repairs in sheep, potentially reducing retear rates in humans.

## Contribution

A novel interlocking patch design significantly enhances biomechanical properties of rotator cuff repairs compared to conventional methods.

## Key findings

- Direct interlocked patch augmentation increased ultimate tensile strength to 587 ± 109 N, significantly higher than conventional and nonaugmented repairs.
- Interlocked patch repairs showed higher cyclic stiffness (44 ± 3 N/mm) compared to conventional (25 ± 2 N/mm) and nonaugmented (29 ± 2 N/mm) repairs.
- Linear stiffness was also significantly improved with interlocked patches (34 ± 6 N/mm) compared to conventional patch-augmented repairs (22 ± 2 N/mm).

## Abstract

Despite advancements in surgical treatment of rotator cuff tears, such as the implementation of patches to reinforce repairs, the rate of retears remains high. Construct failure often occurs at the suture-tendon interface.

The purpose of this study was to compare the biomechanical properties of 3 types of rotator cuff repair (RCR): a nonaugmented transosseous-equivalent (TOE) repair, a conventional patch–augmented TOE repair, and a TOE repair augmented with a polyethylene terephthalate (PET) patch that directly interlocks with the underlying tendon across its entire interface. It was hypothesized that interlocked patch augmentation of RCR is biomechanically superior to conventional TOE.

Controlled laboratory study.

A total of 18 ovine infraspinatus tendons were detached, repaired (with TOE), and tested in 3 groups (n = 6): (1) nonaugmented TOE, (2) conventional patch–augmented TOE, and (3) interlocked patch–augmented TOE. In the second group, a commercial synthetic polyester patch was attached to the tendon via No. 2 FiberWire sutures and laterally attached to the humerus using No. 2 FiberWire sutures and 2 knotless anchors. In the third group, an interwoven patch-tendon interface was created using a microblade to push the fibers of the patch directly into the underlying tissue and to the humerus as described above. Each specimen underwent cyclic loading, followed by pull-to-failure testing. Ultimate tensile strength, cyclic and linear stiffness, peak-to-peak elongation, and gap formation were measured.

Direct patch interlocking resulted in significantly higher tendon purchase during pull to failure (587 ± 109 N vs 222 ± 48 N and 211 ± 52 N) as well as cyclic stiffness testing (44 ± 3 N/mm vs 25 ± 2 N/mm and 29 ± 2 N/mm) compared with the conventional patch–augmented and nonaugmented TOE, respectively (P < .0001 for all comparisons). Linear stiffness was also significantly higher compared with the conventional patch–augmented TOE (34 ± 6 N/mm vs 22 ± 2 N/mm; P = .007).

While limiting but not eliminating tendon retraction, augmentation of a conventional TOE with direct interlocking of a nonwoven PET patch provided biomechanically superior results compared with conventionally augmented and nonaugmented TOE RCRs. The interlocked patch not only significantly improved time-zero force to failure but, compared with a conventional commercial patch design, also increased linear stiffness.

Higher construct stiffness suggests that micromotion and gap formation were minimized, an aspect that is crucial for tendon-bone healing and for reducing early tendon retraction, thereby offering potential to improve retear rates in future clinical applications.