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

Abstract

Purpose Knotless repairs have demonstrated encouraging performance regarding retear rate reduction, but literature aiming at identifying the specific variables responsible for these results is scarce and conflictive. The purpose of this paper was to evaluate the effect of the material (tape or wire suture) and medial tendon passage (single or double passage) on the contact force, pressure and area at the tendon bone interface in order to identify the key factors responsible for this repairs´ success. Methods A specific knotless transosseous equivalent cuff repair was simulated using 2 tape or suture wire loaded medial anchors and 2 lateral anchors, with controlled lateral suture limb tension. The repair was performed in a previously validated sawbones® mechanical model. Testing analyzed force, pressure and area in a predetermined and constant size “repair box” using a Tekscan® sensor, as well as peak force and pressure, force applied by specific sutures and force variation along the repair box. Results Tapes generate lower contact force and pressure and double medial passage at the medial tendon is associated with higher contact area. Suture wires generate higher peak force and pressure on the repair and higher mean force in their tendon path and at the medial bearing row. Force values decrease from medial to lateral and from posterior to anterior independently of the material or medial passage. Conclusion Contrary to most biomechanical literature, suture tape use lowers the pressure and force applied at the tendon bone junction, while higher number of suture passage points medially increases the area of contact. These findings may explain the superior clinical results obtained with the use uf suture tapes because its smaller compressive effect over the tendon may create a better perfusion environment healing while maintaining adequate biomechanical stability.

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

“…have advantageous implications on the biological process of healing [45]. These results are aligned with our previous report [29], which demonstrated that in knotless TOE repairs with medial row sliding anchors, passing sutures individually (DP) significantly increases the contact area when compared to combined passage of suture limbs in a single pilot hole (SP).…”

“…Also as previously reported [29], results also demonstrated that at higher lateral tension values, single‐hole passage in the medial cuff significantly increases peak force, which may provide higher focal stability but also hamper biological healing in that specific location [22], usually quite close or at the MBR [29]. Of specific interest, looking at McCarron et al [31] description of failure in continuity in which regardless of tendon healing, some tissue retraction always occurs, excessive contact force at the MBR or near it prevents this phenomenon and can, hypothetically, increase the risk of type 2 retears.…”

“…Our study has some strengths that should be highlighted. First, by avoiding the use of biological specimens, we obtained a more reproducible evaluation of the mechanical data, and reduced experimental variability, like reported by other authors [13, 17, 29, 43]. Second, the use of a template and a single sized needle for suture passage increased the homogeneity of anchor placement, suture passage location, and mock tendon damage.…”

“…We chose to evaluate the results at 25 and 50 N taking into consideration Park´s 90 N threshold [37], that if surpassed did not translate into further contact area to the tendon bone interface. Also, in a previous work [29] the use of 75 N of lateral tension generated TBI pressure values that largely exceeded the arterial and capillary pressure and in addition, we also experienced some anchor pullout at 75 N during our preliminary trials, so 25 and 50 N of lateral tension seemed adequate values for the purpose of this part of the study which was to assess the mechanical effect at the TBI of a specific and quantified increase in lateral row tension.…”

“…As previously reported [29], a flexible plastic template was used to ensure that each anchor was placed in a consistent fashion and that all sutures had the same distance among them in each trial. We used the same single-sized needle for tape passage in each trial, regardless of the medial row configuration.…”