Tendon Gap Formation Research Articles

Rotator Cuff Repair and Overlay Augmentation by Direct Interlocking of a Nonwoven Polyethylene Terephthalate Patch Into the Tendon: Evaluation in an Ovine Model

Background: Arthroscopic repair of large rotator cuff tendon tears is associated with high rates of retear. Construct failure often occurs at the suture-tendon interface. Patch augmentation can improve mechanical strength and healing at this interface. Purpose: To introduce a novel technique for suture-free attachment of an overlaid patch and evaluate its biomechanical strength and biological performance. Study Design: Descriptive and controlled laboratory studies. Methods: An established ovine model of partial infraspinatus tendon resection and immediate repair was used. After a nonwoven polyethylene terephthalate patch was overlaid to the resected tendon, a barbed microblade was used to draw fibers of the patch directly into the underlying tissue. In vivo histological assessment of healing was performed at 6 and 13 weeks after implantation. Ex vivo models were used to characterize primary repair strength of the suture-free patch fixation to tendon. Additional ex vivo testing assessed the potential of the technique for patch overlay augmentation of suture-based repair. Results: The in vivo study revealed no macroscopic evidence of adverse tissue reactions to the interlocked patch fibers. Histological testing indicated a normal host healing response with minimal fibrosis. Uniform and aligned tissue ingrowth to the core of the patch was observed from both the tendon and the bone interfaces to the patch. There was no evident retraction of the infraspinatus muscle, lengthening of the tendon, or tendon gap formation over 13 weeks. Ex vivo testing revealed that direct patch interlocking yielded tendon purchase equivalent to a Mason-Allen suture (150 ± 58 vs 154 ± 49 N, respectively; P = .25). In an overlay configuration, fiber interlocked patch augmentation increased Mason-Allen suture retention strength by 88% (from 221 ± 43 N to 417 ± 86 N; P < .01) with no detectable difference in repair stiffness. Conclusion: Testing in an ovine model of rotator cuff tendon repair suggested that surgical interlocking of a nonwoven medical textile can provide effective biomechanical performance, support functional tissue ingrowth, and help avoid musculotendinous retraction after surgical tendon repair. Clinical Relevance: The novel technique may facilitate patch augmentation of rotator cuff repairs.

No Significant Difference Between Intramedullary and Extramedullary Button Fixation for Distal Biceps Brachii Tendon Rupture After Cyclic Loading in a Cadaver Model

PurposeTo biomechanically compare intramedullary (IM) versus extramedullary (EM) distal biceps button fixation under cyclic loading conditions, which is most representative of postoperative physiologic status.MethodsThis controlled laboratory study used 13 fresh-frozen matched paired cadaver elbows. One specimen from each pair was randomized to either IM (unicortical) or EM (bicortical) distal biceps button fixation via onlay technique. A servohydraulic actuator was used to cycle each specimen from full extension to 90° of flexion at 0.5 Hz for 3,000 cycles. All specimens were subsequently loaded to failure to simulate an acute postoperative load.ResultsDuring cyclic loading, the mean change in force from cycle 5 to cycle 3000 was 2.1 ± 3.2 N for the IM group and 0.6 ± 4.2 N for the EM group (P = .19). The increase in tendon gap for the IM group was 1.02 mm and for the EM group was 1.83 mm (P = .37). During failure loading, the IM group had a mean failure load of 154.9 ± 44.5 N and the EM group a mean failure load of 191.1 ± 62.6 N (P = .16).ConclusionsNo significant differences exist between the IM and EM techniques in loss of force and tendon gap formation under cyclic loading or load to failure conditions. Thus, IM fixation may adequately facilitate optimal bone-tendon apposition, with less risk of iatrogenic injury to the posterior interosseous nerve that can be seen with bicortical extramedullary fixation.Clinical RelevanceThe most common major complication following distal biceps repair is PIN palsy. IM fixation may be sufficient in facilitating optimal bone-tendon apposition and healing with onlay technique, while minimizing risk of iatrogenic PIN injury associated with EM fixation.

Microsurgical reconstruction affects the outcome in a translational mouse model for Achilles tendon healing.

SummaryBackgroundAnimal models are one of the first steps in translation of basic science findings to clinical practice. For tendon healing research, transgenic mouse models are important to advance therapeutic strategies. However, the small size of the structures complicates surgical approaches, histological assessment, and biomechanical testing. In addition, available models are not standardized and difficult to compare. How surgery itself affects the healing outcome has not been investigated yet. The focus of the study was to develop a procedure that includes a transection and microsurgical reconstruction of the Achilles tendon but, unlike other models, preserves the sciatic nerve. We wanted to examine how distinct parts of the technique influenced healing.MethodsFor this animal model study, we used 96 wild-type male C57BL/6 mice aged 8–12 weeks. We evaluated different suture techniques and macroscopically confirmed the optimal combination of suture material and technique to minimize tendon gap formation. A key element is the detailed, step-by-step illustration of the surgery. In addition, we assessed histological (Herovici and Alcian blue staining) outcome parameters at 1–16 weeks postoperatively. Microcomputed tomography (micro-CT) was performed to measure the bone volume of heterotopic ossifications (HOs). Biomechanical analyses were carried out using a viscoelastic protocol on the biomechanical testing machine LM1.ResultsA modified 4-strand suture combined with a cerclage for immobilization without transection of the sciatic nerve reliably eliminated gap formation. The maximal dorsal extension of the hindlimb at the upper ankle joint from the equinus position (limited by the immobilization cerclage) increased over time postoperatively (operation: 28.8 ± 2.2°; 1 week: 54 ± 36°; 6 weeks: 80 ± 11.7°; 16 weeks: 96 ± 15.8°, p > 0.05). Histological staining revealed a maturation of collagen fibres within 6 weeks, whereas masses of cartilage were visible throughout the healing period. Micro-CT scans detected the development of HOs starting at 4 weeks and further progression at 6 and 16 weeks (bone volume, 4 weeks: 0.07604 ± 0.05286 mm3; 6 weeks: 0.50682 ± 0.68841 mm3; 16 weeks: 2.36027 ± 0.85202 mm3, p > 0.001). In-depth micro-CT analysis of the different surgical elements revealed that an injury of the tendon is a key factor for the development of HOs. Immobilization alone does not trigger HOs. Biomechanical properties of repaired tendons were greatly altered and remained inferior 6 weeks after surgery.ConclusionWith this study, we demonstrated that the microsurgical technique greatly influences the short- and longer-term healing outcome. When the sciatic nerve is preserved, the best surgical reconstruction of the tendon defect is achieved by a 4-strand core suture in combination with a tibiofibular cerclage for postoperative immobilization. The cerclage promotes a gradual increase in the range of motion of the upper ankle joint, comparable with an early mobilization rehabilitation protocol. HO, as a key mechanism for poor tendon healing, is progressive and can be monitored early in the model.The translational potential of this articleThe study enhances the understanding of model dependent factors of healing. The described reconstruction technique provides a reproducible and translational rodent model for future Achilles tendon healing research. In combination with transgenic strains, it can be facilitated to advance therapeutic strategies to improve the clinical results of tendon injuries.

Stem cell-derived extracellular vesicles attenuate the early inflammatory response after tendon injury and repair.

Adipose-derived stem cells (ASCs) have the potential to enhance tendon repair via paracrine regulation of the inflammatory response to injury. Extracellular vesicles (EVs), which are secreted by ASCs, have shown promise in mediating this process. This study was designed to evaluate the effect of ASC EVs on early tendon healing using a mouse Achilles tendon injury and repair model. EVs were isolated from the conditioned medium of naïve and interferonγ-primed ASCs and applied to the repair site via a collagen sheet. Tendon healing was assessed in nuclear factor-κB (NF-κB)-luciferase reporter mice up to 7 days after suture repair. As anticipated, repair site NF-κB activity increased greater than twofold following tendon repair. Treatment with EVs from primed but not naïve ASCs effectively suppressed the response. Accordingly, the pro-inflammatory genes Il1b and Ifng were both dramatically increased in repaired tendons, while primed, but not naïve ASC EVs attenuated the response. Compared with control repairs, primed ASC EVs further reduced the rate of post-repair tendon gap formation and rupture and facilitated collagen formation at the injury site. Additional experiments demonstrated that EVs target macrophages and that primed ASC EVs were most effective in blocking macrophage NF-κB activity. Collectively, the findings of this study demonstrate that primed ASC EVs, similar to ASCs, attenuate the early tendon inflammatory response after injury via modulation of the macrophage inflammatory response. Statement of clinical significance: These findings introduce a new cell-free therapy, derived from stem cells, for tendon repair with the potential for improved therapeutic efficacy and safety. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:117-127, 2020.

Unicortical Versus Bicortical Button Fixation For Distal Biceps Brachii Tendon Rupture: A Cadaveric Biomechanical Study

Objectives: Acute distal biceps tendon rupture is an increasingly common and more recognized injury affecting active adults. Operative repair is the preferred treatment, particularly for restoration of elbow function and strength. No prior study has biomechanically compared unicortical versus bicortical distal biceps button fixation under cyclic loading, which is most representative of postoperative physiologic conditions. We hypothesized there would be no difference in loss of force, tendon gap formation, or ultimate failure load following cyclic loading between unicortical and bicortical button techniques for the repair of distal biceps tendon rupture. Methods: Experimental testing with 13 fresh-frozen matched paired cadaver elbows was conducted. One specimen from each pair was randomized to either unicortical or bicortical distal biceps button fixation techniques, with contralateral specimen assigned to the alternate technique. In both arms of the experiment, the distal 2.5 cm of the biceps tendon was whipstitched and the free suture ends threaded in opposite directions through a 2.6 x 12 mm titanium cortical button. A 3.2 mm guide pin was drilled through the central aspect of the radial tuberosity from anterior to posterior, aiming approximately 20° in the ulnar direction. The button was inserted and deployed for either unicortical or bicortical fixation and the free suture limbs tensioned to advance tendon down to bone for final fixation. Loading was performed using an MTS servohydraulic actuator. A 25-N distal biceps preload was applied and each specimen cycled from full extension to 90° of flexion at 0.5 Hz for 3000 cycles using a displacement controlled protocol. All specimens were subsequently loaded to failure at 2 mm/s to simulate an acute postoperative load. Outcome measures were a loss of force from cycle 5 to cycle 3000, tendon gapping during cyclic loading, and ultimate failure load. Results: During cyclic loading, the mean change in force from cycle 5 to cycle 3000 was -0.33 N for the unicortical fixation group and 0.36 N for the bicortical fixation group (p=0.21). The increase in tendon gap for the unicortical fixation group was 1.02 mm and for the bicortical fixation group was 1.83 mm (p=0.37). During failure loading, the unicortical button fixation group had a mean failure load of 170.45 N and the bicortical button fixation group a mean failure load of 181.25 N (p=0.89). Conclusion: No significant differences exist between the two techniques in loss of force and tendon gap formation under cyclic loading conditions. This indicates that both unicortical and bicortical distal biceps button techniques maintained an equivalent stabilization during a simulated 3 month postoperative healing period. Additionally, there was no significant difference in failure load between the two groups indicating an equivalent response in the event of an acute injury. Clinical Relevance: Distal biceps button fixation strength and tendon gap behavior under physiologic cyclic load support the implementation of early postoperative elbow range of motion, imperative in the prevention of elbow stiffness. Unicortical fixation may be sufficient in facilitating optimal bone-tendon apposition and healing, while minimizing risk of iatrogenic injury associated with bicortical fixation.

Unhas Suture, A Novel Tendon Repair Technique: An In Vitro Experimental Study Comparing Unhas Suture and Bunnell Suture in Tensile Strength and Gap Formation

Purpose: Developing a simple and yet strong repair technique that allows smooth gliding of the tendon within the tendon sheath has remained a challenge to meet the biomechanical needs of early active rehabilitation. Our Objective was to compare Unhas and Bunnell suture technique in terms of strength and gap resistance in tendon repair. Materials and Methods: Thirty feet of healthy roosters Gallus domesticus were harvested and assigned randomly into 2 groups of 15 feet each. The tendons were repaired using Unhas suture and Bunnell suture utilizing monofilament nylon 4-0. Every specimens were tested by using repaired tendon gap formation apparatus and then measured when it produced an initial gap and 2-mm gap at the repair site. The measurements were then analyzed for statistical significance. Results: Significant difference in initial gap was detected between repaired tendon using Unhas suture and Bunnell suture. Two-millimeter gap forces were tested and Unhas suture group was also significantly higher compared with Bunnell suture group. Conclusions: Unhas suture was proven to be able to resist gap forces either in initial gap or 2-mm gap compared with Bunnell suture Clinical Relevance: Unhas suture may be a reliable alternative in tendon repair that provides tensile strength, gapping resistance and also provide easiness which can be performed with conventional suture material and less operating time.

The use of suture-tape and suture-wire in arthroscopic rotator cuff repair: A comparative biomechanics study

BackgroundRotator cuff repair surgery aims to create a secure, pressurized tendon-bone footprint to permit re-establishment of the fibrovascular interface and tendon healing. Flat-braided suture-tape is an alternative suture material to traditional suture-wire that has potential to reproduce a larger repair construct contact area. The objective of this study was to compare contact pressure, area as well as the mechanical fatigue strength between suture-wire and suture-tape Suture-bridge repair constructs in an ovine model. MethodsSixty lamb infraspinatus tendons were harvested and randomly allocated to three- and four-anchor Suture-bridge repairs performed using either suture-wire or suture-tape. Thirty-two specimens were cyclically loaded for 200 cycles in an Instron testing machine, while tendon gap formation was recorded using a high speed digital motion analysis system. Loading to failure was then performed to evaluate construct ultimate tensile strength and stiffness. The remaining 28 specimens were assessed for repair contact pressure and area using pressure-sensitive film. ResultsThere was a significantly greater average tendon contact pressure (mean difference: 0.064 MPa, p = 0.04) and area (mean difference: 2.71 mm2, p = 0.03) in fiber-tape repair constructs compared to those in fiber-wire constructs for the three-anchor Suture-bridge configuration. The four-anchor suture-tape constructs had a significantly larger ultimate tensile strength than that of the four-anchor suture-wire constructs (mean difference: 56.4 N, p = 0.04). There were no significant differences in gap formation or stiffness between suture-tape and suture-wire constructs (p > 0.05). ConclusionSuture-tape offers greater pressurised tendon-bone contact than suture-wire in three-anchor Suture-bridge repairs, while greater mechanical strength is achieved with the use of suture-tape in four-anchor Suture-bridge constructs.

The validity and reliability of ultrasound on identifying supraspinatus tears during passive external rotation from 0° to 30°: a pilot project.

Controversy exists regarding how much external rotation should be allowed following rotator cuff repair. Clinicians may use ultrasound imaging (USI) to visualize the supraspinatus (SSp) tendon during passive external rotation. However, the validity and reliability of USI used to assess supraspinatus tendon gap formation during external rotation needs to be established prior to using this technique in patient cohorts. Ten subjects with magnetic resonance imaging (MRI) confirmation of full-thickness SSp tears were matched to 10 control subjects. Images of the SSp were obtained at 0°, 10°, 20° and 30° of external rotation by a blinded tester on two occasions to establish both validity and reliability of the measure. Validity was established as 70% agreement between the USI and MRI confirmed SSp tear group; reliability was established at greater than 0.90 at all positions of external rotation measured. USI may be used to detect SSp tears with 70% validity, and the technique is reliable in all positions of external rotation.

The Effect of Suture Preloading on the Force to Failure and Gap Formation After Flexor Tendon Repair

Gap formation is a common and severe complication after flexor tendon repair that can affect the outcome and prolong tendon healing. The purpose of this study was to investigate the effect that a pretensional force applied to the suture during tendon repair has on the repair strength and force that causes gap formation. We used a total of 48 flexor digitorum profundus tendons from 12 human cadaver hands. We employed a core tendon suture, using the modified Pennington technique, and a running suture for flexor tendon repair. Before tying the knots of the core suture, we preloaded the sutures in each tendon end 0, 5, 10, or 15 N for 10 seconds to compare the effect of loading magnitude on repaired tendon peak force to failure and force causing gap formation. The force to form a gap of 2 mm in the 15-N preload group was significantly increased compared with the 0-N and 5-N preload groups. At the 3-mm gap formation, the force of all preload groups was significantly higher than the nonpreload group. The peak force with a preload of 10 N and 15 N was significantly higher than 0-N preload. These findings suggest that pretensioning with 10 to 15 N at the suture-tendon interface before tying the knot has a beneficial effect on both the tendon gap formation and the peak force to failure. When the surgeons perform tendon repair, pretensioning at the suture-tendon conjunction will increase the repair strength.

Emerging Ideas: Soft Tissue Applications of Radiostereometric Analysis

Currently, the movement that occurs at the site of soft tissue repair cannot be measured accurately in vivo. Radiostereometric analysis (RSA) is the gold standard for measuring movement between two skeletal segments in vivo but its application to studying soft tissue migration has been limited by the unknown stability of tantalum beads in tendons and ligaments and their ability to define rigid bodies in these structures. RSA can be used to accurately measure movement between two tendon segments or between a bony and a tendon segment in vivo. The stability of tantalum beads and the ability to use such beads to define rigid bodies in some soft tissues will be investigated in animal models of tendon repair. Several tantalum bead insertion techniques will be tested using in vivo RSA measurements of bead movement followed by morphologic studies of the repaired tendon and soft tissue reaction to the tantalum beads. RSA performed on tantalum beads encapsulated in muscles and tendons could be a powerful new tool to study the in vivo motion at the site of soft tissue repairs, for instance, the tendon gap formation. If RSA could be used to evaluate the efficiency of different tendon repair techniques in vivo, enhanced rehabilitation protocols could be developed and complications associated with prolonged protection or failure of repair could be reduced.

The Biomechanical Effects of Dynamic External Rotation on Rotator Cuff Repair Compared to Testing with the Humerus Fixed

Background Biomechanical testing without humeral motion is a standard method for evaluating rotator cuff repair constructs. This cannot elucidate the effects of dynamic external rotation on the repair, which is a common postoperative motion. Hypothesis Biomechanical properties and gap formation of rotator cuff repairs will be different when dynamic external rotation is allowed to occur during loading. Study Design Controlled laboratory study. Methods In 6 matched pairs of human cadaveric shoulders, a commonly used single-row rotator cuff repair was performed. In 6 shoulders, a materials testing machine and a custom testing apparatus that permits cyclic rotation (0°-30°) were employed (group 1). In contralateral shoulders, the apparatus was fixed to prevent humeral rotation (group 2). All repairs were cyclically loaded from 0 to 60 N at a displacement rate of 1 mm/s for 30 cycles. The constructs were then loaded to failure. Repair strength, gap formation, and strain were compared between groups. Results Cyclic loading revealed no difference in linear stiffness between testing conditions. Hysteresis was significantly greater when dynamic external rotation was allowed to occur. With load to failure, there were no differences in yield or ultimate load. Anterior tendon gap formation was greater at end rotation (30° of humeral external rotation) and at yield load, and strain on the posterior tendon was less with dynamic external rotation. With dynamic external rotation, gap formation and tendon strain were significantly greater in the anterior region of the supraspinatus tendon compared with the posterior region. Discussion External rotation using postoperative physiologic loads affects gap formation and tendon strain between anterior and posterior supraspinatus tendon regions. Previous testing models without humeral rotation may underestimate gap formation and anterior tendon strain and overestimate posterior tendon strain. Clinical Relevance Understanding regional differences with respect to these variables, depending on quality of repair, may provide the surgeon a framework from which to prescribe guidelines for postoperative rehabilitation.