Establishment of an in vivo turkey model for the study of flexor tendon repair

The effect of the number of strands and knot throws of core suture techniques on the mechanical properties of the repaired flexor tendon

Flexor tendon injury is a common hand trauma that requires surgical repair. The objective was to compare the repaired strength and gliding resistance with a varied number of repair strands and of square knots using a two-strand-overhand locking (TSOL) knot. First, isolated suture loops with different number of suture strands and number of closing knots were compared in mechanical strength and failure mode. Then, 90 flexor digitorum profundus (FDP) tendons from turkey digits were used for the tendon repair experiment. Both phases followed a similar 3 × 3 matrix comparing the knot type including TSOL+1SK (square knot), TSOL+2SK, and TSOL+3 SK and repair techniques including two-, four-, and six-strand repairs techniques respectively. The repaired tendons were tested for tendon resistance against pulley (friction), maximum force, force at 2 mm displacement, stiffness, and failure mode. Increasing the number of strands and closing square knots increases the tensile strength and stiffness of flexor tendon repairs and isolated suture loops without a significant effect on tendon friction. An increase in the number of square knots have shown increased strength only in Pennington repair, which correlated with the increased number of knot unraveling, a weak knot failure model. Our data demonstrated that increasing the number of strands is effective for improving the overall strength of tendon repair. When a two-strand repair is chosen, increasing knot number can improve repair strength. However, the number of knots appears not affecting repair strength in six-strand repair technique.

Pentamidine-loaded gelatin decreases adhesion formation of flexor tendon

Background

Prevention of adhesion formation following flexor tendon repair is essential for restoration of normal finger function. Although many medications have been studied in the experimental setting to prevent adhesions, clinical application is limited due to the complexity of application and delivery in clinical translation.

Methods

In this study, optimal dosages of gelatin and pentamidine were validated by gelatin concentration test. Following cell viability, cell migration, live and dead cell, and cell adhesion assay of the Turkey tenocytes, a model of Turkey tendon repair was established to evaluate the effectiveness of the Pentamidine-Gelatin sheet.

Results

Pentamidine carried with gelatin, a Food and drug administration (FDA) approved material for drug delivery, showed good dynamic release, biocompatibility, and degradation. The optimal dose of pentamidine (25ug) was determined in the in vivo study using tenocyte viability, migration, and cell adhesion assays. Further biochemical analyses demonstrated that this positive effect may be due to pentamidine downregulating the Wnt signaling pathway without affecting collagen expression.

Conclusions

We tested a FDA-approved antibiotic, pentamidine, for reducing adhesion formation after flexor tendon repair in both in vitro and in vivo using a novel turkey animal model. Compared with the non-pentamidine treatment group, pentamidine treated turkeys had significantly reduced adhesions and improved digit function after six weeks of tendon healing.

The translational potential of this article

This study for the first time showed that a common clinical drug, pentamidine, has a potential for clinical application to reduce tendon adhesions and improve tendon gliding function without interfering with tendon healing.

Correction of a Hyperflexed Hallux in a Saker Falcon (Falco cherrug) by Hemisectioning the Deep Digital Flexor Tendon

A 3-year-old male saker falcon (Falco cherrug) was presented with a history of hyperflexion of the first digit of the left pelvic limb with what appeared to be a hypercontracted distal end of the deep digital flexor tendon (m. flexor hallucis longus). Conservative treatment, bandaging, and splinting techniques failed to resolve the hypercontraction of the deep digital flexor tendon and improve digit function. Intraoperatively, the deep digital flexor tendon was found to have formed adhesions with the tendon sheath as well as the bone and soft tissue structures underneath it, impeding its ability to move freely within the tendon sheath. The adhesions were surgically resolved, and the tendon was lengthened by hemisectioning the deep digital flexor tendon at its distal end. Postsurgically, the digit was maintained in an extended position by bandaging. Mild physiotherapy was provided at 5-day intervals to retain function and prevent adhesions. Digit extensibility and function were restored to nearly normal levels after 4 weeks.

Preclinical tendon and ligament models: Beyond the 3Rs (replacement, reduction, and refinement) to 5W1H (why, who, what, where, when, how)

Several tendon and ligament animal models were presented at the 2022 Orthopaedic Research Society Tendon Section Conference held at the University of Pennsylvania, May 5 to 7, 2022. A key objective of the breakout sessions at this meeting was to develop guidelines for the field, including for preclinical tendon and ligament animal models. This review summarizes the perspectives of experts for eight surgical small and large animal models of rotator cuff tear, flexor tendon transection, anterior cruciate ligament tear, and Achilles tendon injury using the framework: "Why, Who, What, Where, When, and How" (5W1H). A notable conclusion is that the perfect tendon model does not exist; there is no single gold standard animal model that represents the totality of tendon and ligament disease. Each model has advantages and disadvantages and should be carefully considered in light of the specific research question. There are also circumstances when an animal model is not the best approach. The wide variety of tendon and ligament pathologies necessitates choices between small and large animal models, different anatomic sites, and a range of factors associated with each model during the planning phase. Attendees agreed on some guiding principles including: providing clear justification for the model selected, providing animal model details at publication, encouraging sharing of protocols and expertise, improving training of research personnel, and considering greater collaboration with veterinarians. A clear path for translating from animal models to clinical practice was also considered as a critical next step for accelerating progress in the tendon and ligament field.

Knotless Tendon Repair with a Resorbable Barbed Suture: An In-vivo Comparison in the Turkey Foot

Background: Un-knotted barbed suture constructs are postulated to decrease repair bulk and improve tension loading along the entire repair site resulting in beneficial biomechanical repair properties. Applying this repair technique to tendons has shown good results in ex-vivo experiments previously but thus far no in-vivo study could confirm these. Therefore, this current study was conducted to assess the value of un-knotted barbed suture repairs in the primary repair of flexor tendons in an in-vivo setting. Methods: Two groups of 10 turkeys (Meleagris gallapovos) were used. All turkeys underwent surgical zone II flexor tendon laceration repairs. In group one, tendons were repaired using a traditional four-strand cross-locked cruciate (Adelaide) repair, while in group two, a four-strand knotless barbed suture 3D repair was used. Postoperatively repaired digits were casted in functional position, and animals were left free to mobilise and full weight bear, resembling a high-tension post-op rehabilitation protocol. Surgeries and rehabilitations went uneventful and no major complications were noted. The turkeys were monitored for 6 weeks before the repairs were re-examined and assessed against several outcomes, such as failure rate, repair bulk, range of motion, adhesion formation and biomechanical stability. Results: In this high-tension in-vivo tendon repair experiment, traditionally repaired tendons performed significantly better when comparing absolute failure rates and repair stability after 6 weeks. Nevertheless, the knotless barbed suture repairs that remained intact demonstrated benefits in all other outcome measures, including repair bulk, range of motion, adhesion formation and operating time. Conclusions: Previously demonstrated ex-vivo benefits of flexor tendon repairs with resorbable barbed sutures may not be applicable in an in-vivo setting due to significant difference in repair stability and failure rates. Level of Evidence: Level IV (Therapeutic).

The Effects of the TSOL Knot on the Repair Strength and Gliding Resistance Following Flexor Tendon Repair

BACKGROUND

The stability of a suture knot construct has been realized as an important parameter that affects the strength of flexor tendon repairs. A novel 2-strand-overhand-locking (TSOL) knot, which is not commonly used in the clinical setting, recently was reported to increase repair strength and to decrease tendon gliding resistance in a 2-strand repair technique. The purpose of the present study was to investigate the effect of the TSOL knot on tendon repair strength and gliding resistance compared with a typical surgical knot in both 2-strand and 4-strand repair techniques using an in vitro turkey flexor tendon model.

METHODS

Sixty flexor digitorum profundus tendons from the long digit of the turkey foot were divided evenly into 4 groups and repaired with the following techniques: (1) a 2-strand modified Pennington repair with a square knot, (2) a 2-strand modified Pennington repair with a TSOL knot, (3) a 4-strand grasping cruciate repair with a square knot, and (4) a 4-strand grasping cruciate repair with a TSOL knot. Repaired tendons were tested for failure mode, gliding resistance, and repair strength at failure.

RESULTS

The repair strength and stiffness of the 4-strand repairs were significantly higher than those of the 2-strand repairs, regardless of knot type (p < 0.05). The repair strength at failure of the TSOL knot was significantly greater than that of the square knot in 2-strand repairs (p < 0.05) but not in 4-strand repairs. The gliding resistance of the TSOL knot was significantly decreased compared with that of the square knot in both 2-strand and 4-stand repairs (p < 0.05). With regard to failure mode, the TSOL knot was less likely to fail due to knot unravelling.

CONCLUSIONS

In this in vitro biomechanical study involving the use of turkey flexor tendons to compare gliding resistance and repair strength characteristics for knot-inside 2 and 4-strand repairs, the TSOL knot was associated with decreased repaired tendon gliding resistance, regardless of the number of strands used. Although the TSOL knot also increased the repair strength, the difference was only significant when 2-strand repairs were used. The results of our study support the use of the TSOL knot in the clinical setting of flexor tendon repair using 2 or 4-strand, knot-inside methods.

CLINICAL RELEVANCE

In surgical repair of flexor tendons, there is substantial interest in maximizing strength while minimizing friction. This study shows the potential utility of the TSOL knot to increase repair strength while decreasing gliding resistance, particularly in 2-strand repairs.

An In Vivo Comparison: Novel Mesh Suture Versus Traditional Suture-Based Repair in a Rabbit Tendon Model

Purpose

Despite advancements in surgical techniques, suture pull-though and rupture continue to limit the early range of motion and functional rehabilitation after flexor tendon repairs. The aim of this study was to evaluate a suturable mesh compared with a commonly used braided suture in an in vivo rabbit intrasynovial tendon model.

Methods

Twenty-four New Zealand female rabbits (3–4 kg) were injected with 2 units/kg botulinum toxin evenly distributed into 4 sites in the left calf. After 1 week, the animals underwent surgical tenotomy of the flexor digitorum tendon and were randomized to repair with either 2-0 Duramesh suturable mesh or to 2-0 Fiberwire using a 2-strand modified Kessler and 6-0 polypropylene running epitendinous suture. Rabbits were killed at 2, 4, and 9 weeks after surgery.

Results

Grouping across time points, 58.3% (7 of 12) of Duramesh repairs were found to be intact for the explant compared with 16.7% (2 of 12) of Fiberwire repairs (P = .09). At 2 weeks, the mean Duramesh repairs were significantly stronger than the Fiberwire repairs with a mean failure load of 50.7 ± 12.7 N compared to 14.8 ± 18.3 N (P = .02). The load supported by the Duramesh repairs at 2 weeks (mean 50.7 ± 12.7 N) was similar to the load supported by both Fiberwire (52.2 ± 13.6 N) and Duramesh (57.6 ± 22.3 N) at 4 weeks. The strength of repair between Fiberwire and Duramesh at 4 weeks and 9 weeks was not significantly different.

Conclusions

The 2-strand tendon repair with suturable mesh achieved significantly greater strength at 2 weeks than the conventional suture material. Future studies should evaluate the strength of repair prior to 2 weeks to determine the strength curve for this novel suture material.

Clinical Relevance

This study evaluates the utility of a novel suturable mesh for flexor tendon repair in an in vivo rabbit model compared with conventional suture material.

Isolation and characterization of turkey bone marrow-derived mesenchymal stem cells

Flexor tendon injury is often associated with suboptimal outcomes and results in substantial digit dysfunction. Stem cells have been isolated from several experimental animals for the growing interest and needs of utilizing cell-based therapies. Recently, turkey has been developed as a new large animal model for flexor tendon research. In the present study, we reported the isolation and characterization of bone marrow-derived mesenchymal stem cells (BMSCs) from 8- to 12-month-old heritage-breed turkeys. The isolated cells demonstrated fibroblast-like morphology, clonogenic capacity, and high proliferation rate. These cells were positive for surface antigens CD90, CD105, and CD44, but were negative for CD45. The multipotency of turkey BMSCs was determined by differentiating cells into osteogenic, adipogenic, chondrogenic, and tenogenic lineages. There was upregulated gene expression of tenogenic markers, including mohawk, tenomodulin, and EGR1 as well as increased collagen synthesis in BMP12 induced cells. The successful isolation and verification of bone marrow-derived MSCs from turkey would provide opportunities of studying cell-based therapies and developing new treatments for tendon injuries using this novel preclinical large animal model. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1419-1428, 2019.