Why are tapes better than wires in knotless rotator cuff repairs? An evaluation of force, pressure and contact area in a tendon bone unit mechanical model

Comparison of the mechanical properties and mechanical damages to tendon tissue in three suspensory fixation techniques

Background

Anterior cruciate ligament (ACL) injury is the most common traumatic injury to the knee joint. Suspensory fixation has become popular in ACL reconstruction because of its high primary stability, less invasiveness, and surgical convenience. There are two common types of suspensory fixation devices: those with fixed-length and those with adjustable-length loops. Owing to structural differences and differences in initial tensioning techniques, it is expected that mechanical property and damage to the tendons will vary from device to device; however, no literature has examined this so far. The main purpose of this study was to evaluate the damage caused to the tendon by three different suspensory fixation devices. An effective mechanical test was carried out as a prerequisite.

Methods

First, the mechanical properties of simple loop device (SLD) as fixed-length loop device, first-generation, and second-generation adjustable devices (AD1 and AD2) as adjustable-length loop devices were tested (isolated device testing). Second, each device was tested using bovine extensor tendons (specimen testing). Cyclic testing included 2000 cycles; the devices were subsequently displaced until failure, and the ultimate tensile strength was determined using isolated device testing. Six samples of 3 devices were used in each testing experiment. After specimen testing, the surface structure of the tendon was evaluated quantitatively using optical coherence tomography (OCT) and our original histological scoring system.

Results

During isolated device testing, SLD demonstrated the least cyclic displacement, followed by AD1 and AD2. The highest ultimate tensile strength was observed in AD2, followed by SLD and AD1. In specimen testing, the least cyclic displacement was observed in SLD, followed by AD1 and AD2. Histologically, AD1 demonstrated a significantly lower score, with damaged surface morphology, than SLD and AD2. OCT values were significantly higher, with a more disturbing tendon surface structure, in AD1 than in SLD and AD2.

Conclusions

The first-generation adjustable loop device exhibited greatest graft tissue damage at the suspensory site in a clinically relevant setting. The thinner adjustable loop mechanism may have elevated graft damage by frictional stresses during loop adjustment or by repetitive tensioning stresses.

Mechanical consequences at the tendon-bone interface of different medial row knotless configurations and lateral row tension in a simulated rotator cuff repair

Purpose

Little is known about the direct influence of different technical options at the rotator cuff tendon-bone interface (TBI) and, more specifically, at the medial bearing row (MBR), regarding local contact force, area and pressure. We evaluated the mechanical repercussions of different medial row anchor configurations for that setting using different values of tension in the lateral row anchors.

Methods

Knotless transosseous equivalent (TOE) rotator cuff repairs with locked versus nonlocked medial anchors and single versus double-hole suture passage were tested in a synthetic rotator cuff mechanical model, using 2 different values of lateral row tension. Contact force, area, pressure, peak force and MBR force were compared at the simulated TBI using a pressure mapping sensor.

Results

When compared to locked anchors, medial row sliding configurations generate lower values for all the above-mentioned parameters.

The use of double-hole suture passage in the medial cuff generated slightly higher values contact area regardless of lateral row tension. At higher lateral row tension values, lower values of the remaining parameters, including MBR force, were found when compared to single-hole suture passage.

Lateral row anchor tension increase induced an increase of all parameters regardless of the medial row configuration and TBI contact force and MBR force were the most susceptible parameters, regardless of the medial row pattern.

Conclusion

Medial row mechanism, suture configuration and lateral row tension interfere with the mechanical force, area and pressure at by TBI. Lateral row tension increase is a major influencer in those parameters.

These results can help surgeons choose the right technique considering its mechanical effect at the TBI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40634-022-00536-1.