Cell-based tissue engineered flexor tendon allograft: A canine in vivo study.

This study aimed to compare the clinically established autologous extrasynovial tendon graft to a newly developed tissue-engineered allograft (Eng-allograft) in terms of functional outcomes following flexor tendon reconstruction in a canine model. The second and fifth flexor digitorum profundus (FDP) tendons from 16 dogs were transected and repaired in Zone II. After 6 weeks of cage activity, the repaired tendons were intentionally ruptured, creating a clinically relevant model for reconstruction. The re-ruptured FDP tendons were then reconstructed using either the clinically standard autologous extrasynovial tendon graft or the Eng-allograft, which had been revitalized with autologous bone marrow-derived mesenchymal stem cells (BMSCs) and synovialized using carbodiimide derivatized synovial fluid (cd-SYN). Following 12 weeks of postoperative rehabilitation, the functional outcomes of the surgical digits were evaluated. The Eng-allograft group exhibited improved digital function, including lower digit work of flexion and reduced adhesion status, while maintaining similar tendon gliding resistance compared to the autograft group. However, the failure load of both the distal and proximal host/graft conjunctions in the Eng-allograft group was significantly lower than that of the autograft group with higher graft rupture at the host-graft junction. In conclusion, the decellularized allogenic intrasynovial tendon, when revitalized BMSCs and synovialized with cd-SYN, demonstrates positive effects on digital function improvement and adhesion reduction. However, the healing at both proximal and distal graft/host junctions is far lower than the autograft. Further research is needed to enhance the healing capacity of allograft conjunctions, aiming to achieve a comparable level of healing seen with autografts.

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.

Relationship Between the Changes of Tendon Elastic Moduli With Ultrasound Shear Wave Elastography and Mechanical Compression Test.

OBJECTIVE: The purpose of this study was to investigate the consistency of the changes in the elastic modulus measured with ultrasound shear wave elastography (SWE) with changes measured through mechanical testing using tendons that were artificially altered by chemical modifications. METHODS: Thirty-six canine flexor digitorum profundus tendons were used for this experiment. To mimic tendon mechanical property changes induced by tendinopathy conditions, tendons were treated with collagenase to soften the tissue by collagen digestion or with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) to stiffen the tissues through chemical crosslinking. Tendons were randomly assigned to one of three groups: immersion in phosphate-buffered saline (PBS) as a control group (n = 12), collagenase treatment (n = 12) or EDC treatment (n = 12). Immediately following SWE measurement of each tendon, mechanical compression testing was performed as a gold standard to validate the SWE measurement. Both tests were conducted before and after treatment. RESULTS: The compressive modulus and SWE shear modulus significantly decreased after collagenase treatment. Conversely, both moduli significantly increased after EDC treatment. There was no significant difference in either modulus before or after PBS treatment. As a result of a regression analysis with the percentage change of the compressive modulus as the dependent variable and SWE shear modulus as the independent variable, the best-fit regression was found to be an exponential function and the coefficient of determination was 0.687. CONCLUSION: The changes in the compressive moduli and SWE shear moduli in tendons induced by chemical treatments were correlated by approximately 70%.

Enhancing Functional Recovery after Segmental Nerve Defect Using Nerve Allograft Treated with Plasma-Derived Exosome.

BACKGROUND: Nerve injuries can result in detrimental functional outcomes. Currently, autologous nerve graft offers the best outcome for segmental peripheral nerve injury. Allografts are alternatives, but do not have comparable results. This study evaluated whether plasma-derived exosome can improve nerve regeneration and functional recovery when combined with decellularized nerve allografts. METHODS: The effect of exosomes on Schwann cell proliferation and migration were evaluated. A rat model of sciatic nerve repair was used to evaluate the effect on nerve regeneration and functional recovery. A fibrin sealant was used as the scaffold for exosome. Eighty-four Lewis rats were divided into autograft, allograft, and allograft with exosome groups. Gene expression of nerve regeneration factors was analyzed on postoperative day 7. At 12 and 16 weeks, rats were subjected to maximum isometric tetanic force and compound muscle action potential. Nerve specimens were then analyzed by means of histology and immunohistochemistry. RESULTS: Exosomes were readily taken up by Schwann cells that resulted in improved Schwann cell viability and migration. The treated allograft group had functional recovery (compound muscle action potential, isometric tetanic force) comparable to that of the autograft group. Similar results were observed in gene expression analysis of nerve regenerating factors. Histologic analysis showed no statistically significant differences between treated allograft and autograft groups in terms of axonal density, fascicular area, and myelin sheath thickness. CONCLUSIONS: Plasma-derived exosome treatment of decellularized nerve allograft may provide comparable clinical outcomes to that of an autograft. This can be a promising strategy in the future as an alternative for segmental peripheral nerve repair. CLINICAL RELEVANCE STATEMENT: Off-the-shelf exosomes may improve recovery in nerve allografts.

Carbodiimide-Derivatized Synovial Fluid for Tendon Graft Coating Improves Long-Term Functional Outcomes of Flexor Tendon Reconstruction.

BACKGROUND: Flexor digitorum profundus (FDP) tendon injury is common in hand trauma, and flexor tendon reconstruction is one of the most challenging procedures in hand surgery because of severe adhesion that exceeds 25% and hinders hand function. The surface properties of a graft from extrasynovial tendons are inferior to those of the native intrasynovial FDP tendons, which has been reported as one of the major causations. Improved surface gliding ability of the extrasynovial graft is needed. Thus, this study used carbodiimide-derivatized synovial fluid and gelatin (cd-SF-gel) to modify the surface of the graft, thus improving functional outcomes using a dog in vivo model. METHODS: Forty FDP tendons from the second and fifth digits of 20 adult women underwent reconstruction with a peroneus longus (PL) autograft after creation of a tendon repair failure model for 6 weeks. Graft tendons were either coated with cd-SF-gel ( n = 20) or not. Animals were euthanized 24 weeks after reconstruction, and digits were collected after the animals were euthanized for biomechanical and histologic analyses. RESULTS: Adhesion score (cd-SF-gel, 3.15 ± 1.53; control, 5 ± 1.26; P < 0.00017), normalized work of flexion (cd-SF-gel, 0.47 ± 0.28 N-mm/degree; control, 1.4 ± 1.45 N-mm/degree; P < 0.014), and distal interphalangeal joint motion (cd-SF-gel, 17.63 ± 6.77 degrees; control, 7.07 ± 12.99 degrees; P < 0.0015) in treated grafts all showed significant differences compared with nontreated grafts. However, there was no significant difference in repair conjunction strength between the two groups. CONCLUSION: Autograft tendon surface modification with cd-SF-gel improves tendon gliding ability, reduces adhesion formation, and enhances digit function without interfering with graft-host healing. CLINICAL RELEVANCE STATEMENT: The authors demonstrate a clinically relevant and translational technology by using the patient's own synovial fluid to "synovialize" an autologous extrasynovial tendon graft to improve functional outcomes following flexor tendon reconstruction.

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.

Effects of purified exosome product on rotator cuff tendon-bone healing in vitro and in vivo.

Exosomes have multiple therapeutic targets, but the effects on healing rotator cuff tear (RCT) remain unclear. As a circulating exosome, purified exosome product (PEP) has the potential to lead to biomechanical improvement in RCT. Here, we have established a simple and efficient approach that identifies the function and underlying mechanisms of PEP on cell-cell interaction using a co-culture model in vitro. In the in vivo trial, adult female Sprague-Dawley rats underwent unilateral surgery to transect and repair the supraspinatus tendon to its insertion site with or without PEP. PEP promoted the migration and confluence of osteoblast cells and tenocytes, especially during direct cell-cell contact. Expression of potential genes for RCT in vitro and in vivo models were consistent with biomechanical tests and semiquantitative histologic scores, indicating accelerated strength and healing of the RC in response to PEP. Our observations suggest that circulating exosomes provide an effective option to improve the healing speed of RCT after surgical repair. The regeneration of enthesis following PEP treatment appears to be related to a mutually reinforcing relationship between direct cell-cell contact and PEP activity, suggesting a dual approach to the healing process.

Characterization of a purified exosome product and its effects on canine flexor tenocyte biology.

Flexor tendon injuries and tendinopathy are very common but remain challenging in clinical treatment. Exosomes-based cell-free therapy appears to be a promising strategy for tendon healing, while limited studies have evaluated its impacts on tenocyte biology. The objective of this study was to characterize a novel purified exosome product (PEP) derived from plasma, as well as to explore its cellular effects on canine tenocyte biology. The transmission electron microscope revealed that exosomes of PEP present cup-shaped structures with the diameters ranged from 80 to 141 nm, and the NanoSight report presented that their size mainly concentrated around 100 nm. The enzyme-linked immunosorbent assay kits analysis showed that PEP was positive for CD63 and AChE expression, and the cellular uptake of exosomes internalized into tenocyte cytoplasm was observed. The cell growth assays displayed that tenocyte proliferation ability was enhanced by PEP solution in a dose-dependent manner. Tenogenic phenotype was preserved as is evident by that tendon-related genes expression (SCX, COL1A, COL3A1, TNMD, DCN, and MKX) were expressed insistently in a high level, while tenocytes were treated with 5% PEP solution. Furthermore, migration capability was maintained and total collagen deposition was increased. More interesting, dexamethasone-induced cellular apoptosis was attenuated during the incubation of tenocytes with a 5% PEP solution. These findings will provide the basic understandings about the PEP, and support the potential use of this biological strategy for tendon healing.

Calculation of flexor pollicis longus moment arm for wrist motion in a cadaver model validates the tenodesis effect for therapy.

INTRODUCTION: Synergies of fingers and wrist motion have been incorporated into therapies for finger flexor tendon injuries to improve repair outcomes. Similar synergistic therapy strategies have not been well documented for the thumb. PURPOSE OF THE STUDY: The purpose of this study was to investigate the extent to which wrist motion enables a synergistic effect at the thumb in a cadaveric model by measuring flexor pollicis longus excursion and calculating the moment arm of this tendon at the wrist joint. STUDY DESIGN: This is a basic science research. METHODS: Eight fresh-frozen cadaveric arms were obtained from our anatomical bequest program. The proximal arm was fixed in neutral pronation/supination position, and motion of the wrist was guided through either flexion/extension or radial/ulnar deviation. Fingers were fixed in extension, thumb interphalangeal and metacarpophalangeal joints were fixed in neutral extension, and the carpometacarpal joint was fixed at 30° palmar abduction. The flexor pollicis longus tendon was exposed proximal to the wrist crease and connected to a rotary potentiometer to measure tendon excursion. Optical markers were attached to the hand to capture kinematics. Wrists were moved from a neutral position over the range of flexion and extension and then from the neutral position through the range of radial to ulnar deviation. Moment arms were calculated. RESULTS: Moment arm calculation indicated that the flexor pollicis longus acts as a wrist flexor over the entire motion range and as a weak radial deviator at ulnarly-deviated positions. CONCLUSIONS: This study provides a mechanistic rationale for passive interphalangeal joint motion in varying wrist positions when treating thumb flexor tendon injuries, with benefits seen primarily for wrist extension.

Engineered tendon-fibrocartilage-bone composite and bone marrow-derived mesenchymal stem cell sheet augmentation promotes rotator cuff healing in a non-weight-bearing canine model.

Reducing rotator cuff failure after repair remains a challenge due to suboptimal tendon-to-bone healing. In this study we report a novel biomaterial with engineered tendon-fibrocartilage-bone composite (TFBC) and bone marrow-derived mesenchymal stem cell sheet (BMSCS); this construct was tested for augmentation of rotator cuff repair using a canine non-weight-bearing (NWB) model. A total of 42 mixed-breed dogs were randomly allocated to 3 groups (n = 14 each). Unilateral infraspinatus tendon underwent suture repair only (control); augmentation with engineered TFBC alone (TFBC), or augmentation with engineered TFBC and BMSCS (TFBC + BMSCS). Histomorphometric analysis and biomechanical testing were performed at 6 weeks after surgery. The TFBC + BMSCS augmented repairs demonstrated superior histological scores, greater new fibrocartilage formation and collagen fiber organization at the tendon-bone interface compared with the controls. The ultimate failure load and ultimate stress were 286.80 ± 45.02 N and 4.50 ± 1.11 MPa for TFBC + BMSCS group, 163.20 ± 61.21 N and 2.60 ± 0.97 MPa for control group (TFBC + BMSCS vs control, P = 1.12E-04 and 0.003, respectively), 206.10 ± 60.99 N and 3.20 ± 1.31 MPa for TFBC group (TFBC + BMSCS vs TFBC, P = 0.009 and 0.045, respectively). In conclusion, application of an engineered TFBC and BMSCS can enhance rotator cuff healing in terms of anatomic structure, collagen organization and biomechanical strength in a canine NWB model. Combined TFBC and BMSCS augmentation is a promising strategy for rotator cuff tears and has a high potential impact on clinical practice.

Comparison of Autograft and Allograft with Surface Modification for Flexor Tendon Reconstruction: A Canine in Vivo Model.

BACKGROUND: Flexor tendon injury is common, and tendon reconstruction is indicated clinically if the primary repair fails or cannot be performed immediately after tendon injury. The purpose of the current study was to compare clinically standard extrasynovial autologous graft (EAG) tendon and intrasynovial allogeneic graft (IAG) that had both undergone biolubricant surface modification in a canine in vivo model. METHODS: Twenty-four flexor digitorum profundus (FDP) tendons from the second and fifth digits of 12 dogs were used for this study. In the first phase, a model of failed FDP tendon repair was created. After 6 weeks, the ruptured FDP tendons with a scarred digit were reconstructed with the use of either EAG or IAG tendons treated with carbodiimide-derivatized hyaluronic acid and lubricin. At 12 weeks after tendon reconstruction, the digits were harvested for functional, biomechanical, and histologic evaluations. RESULTS: The tendon failure model was a clinically relevant and reproducible model for tendon reconstruction. The IAG group demonstrated improved digit function with decreased adhesion formation, lower digit work of flexion, and improved graft gliding ability compared with the EAG group. However, the IAG group had decreased healing at the distal tendon-bone junction. Our histologic findings verified the biomechanical evaluations and, further, showed that cellular repopulation of allograft at 12 weeks after reconstruction is still challenging. CONCLUSIONS: FDP tendon reconstruction using IAG with surface modification has some beneficial effects for reducing adhesions but demonstrated inferior healing at the distal tendon-bone junction compared with EAG. These mixed results indicate that vitalization and turnover acceleration are crucial to reducing failure of reconstruction with allograft. CLINICAL RELEVANCE: Flexor tendon reconstruction is a common surgical procedure. However, postoperative adhesion formation may lead to unsatisfactory clinical outcomes. In this study, we developed a potential flexor tendon allograft using chemical and tissue-engineering approaches. This technology could improve function following tendon reconstruction.

Revitalized and synovialized allograft for intrasynovial flexor tendon reconstruction in an in vivo canine model.

This study was to test our hypothesis that flexor tendon reconstruction with an allograft revitalized with bone marrow stromal cells (BMSCs) and synovialized with carbodiimide derivatized autologous synovial fluid (cd-SYN) would result in better digit functional restoration than the conventional allograft tendon. A total of 32 flexor digital profundus tendons from the second and fifth digit of 16 dogs were created a repair failure model first. Then, failed-repaired tendons were reconstructed with either a revitalized-synovialized allograft tendon or a clinical standard autograft tendon (control group). The allograft tendon was seeded with autologous BMSCs in multiple slits and the graft surface was coated with cd-SYN. A 6 weeks after tendon reconstruction, the digits were harvested and evaluated for digit function, adhesion status, tendon gliding resistance, attachment strength, cell viability, and histologic factors. The allograft group had significantly improved digit function compared with the control group through decreased work of flexion, increased digit range of motion under 2-Newton force, and less adhesion score (p < .05). However, the distal attachment-site strength and stiffness in the allograft tendon were significantly weaker than the autografts (p < .05). No significant difference was found for gliding resistance. Histologically, allograft tendons coated with allograft had smoother surfaces and showed tendon-to-bone and tendon-to-tendon incorporation. Viable BMSCs were found in the tendon slits 6 weeks after the graft. In conclusion, cellular lubricant-based modification of allograft tendons improved digit function and reduced the adhesions compared with autograft for flexor tendon reconstruction. However, improvement of graft-to-host tendon healing is still challenging. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Kinetic analysis of canine gait on the effect of failure tendon repair and tendon graft.

Kinetic analysis of canine gait has been extensively studied, including normal and abnormal gait. However, no research has looked into how flexor tendon injury and further treatment would affect the walking pattern comparing to the uninjured state. Therefore, this study was aimed to utilize a portable pressure walkway system, which has been commonly used for pedobarographic and kinetic analysis in the veterinary field, to examine the effect of a failed tendon repair and tendon graft reconstruction on canine digit kinetics during gait. 12 mixed breed (mongrel) hound-type female dogs were included in this study and 2nd and 5th digits were chosen to undergo flexor tendon repair and graft surgeries. Kinetic parameters from the surgery leg in stance phase were calculated. From the results, after tendon failure repair, decrease of weight bearing was seen in the affected digits and weight bearing was shifted to the metacarpal pad. After tendon graft reconstruction, weight bearing returned to the affected digits and metacarpal pads. Slight alteration in peak pressure and instant of peak force were identified, but it was estimated to have little influence on post-reconstruction gait. This study could serve as a reference in evaluating canine digit function in flexor tendon injury for future studies.

Turkey model for flexor tendon research: in vitro comparison of human, canine, turkey, and chicken tendons.

BACKGROUND: Flexor tendon injuries are one of the most common hand injuries and remain clinically challenging for functional restoration. Canine and chicken have been the most commonly used animal models for flexor tendon-related research but possess several disadvantages. The purpose of this study was to explore a potential turkey model for flexor tendon research. METHODS: The third digit from human cadaveric hands, canine forepaws, turkey foot, and chicken foot were used for this study. Six digits in each of four species were studied in detail, comparing anatomy of the flexor apparatus, joint range of motion tendon excursion, tendon cross-sectional area, work of flexion, gliding resistance at the level of the A2 pulley, modulus of elasticity, suture retention strength, and histology across species. RESULTS: Anatomically, the third digit in the four species displayed structural similarities; however, the tendon cross-sectional area of the turkey and human were similar and larger than canine and chicken. Furthermore, the turkey digit resembles the human's finger with the lack of webbing between digits, similar vascularization, tendon excursion, work of flexion, gliding resistance, mechanical properties, and suture holding strength. More importantly, human and turkey tendons were most similar in histological appearance. CONCLUSIONS: Turkey flexor tendons have many properties that are comparable to human flexor tendons which would provide a clinically relevant, economical, nonhuman companion large animal model for flexor tendon research.

Effects of lubricant and autologous bone marrow stromal cell augmentation on immobilized flexor tendon repairs.

The purpose of the study was to test a novel treatment that carbodiimide-derivatized-hyaluronic acid-lubricin (cd-HA-lubricin) combined cell-based therapy in an immobilized flexor tendon repair in a canine model. Seventy-eight flexor tendons from 39 dogs were transected. One tendon was treated with cd-HA-lubricin plus an interpositional graft of 8 × 10(5) BMSCs and GDF-5. The other tendon was repaired without treatment. After 21 day of immobilization, 19 dogs were sacrificed; the remaining 20 dogs underwent a 21-day rehabilitation protocol before euthanasia. The work of flexion, tendon gliding resistance, and adhesion score in treated tendons were significantly less than the untreated tendons (p < 0.05). The failure strength of the untreated tendons was higher than the treated tendons at 21 and 42 days (p < 0.05). However, there is no significant difference in stiffness between two groups at day 42. Histologic analysis of treated tendons showed a smooth surface and viable transplanted cells 42 days after the repair, whereas untreated tendons showed severe adhesion formation around the repair site. The combination of lubricant and cell treatment resulted in significantly improved digit function, reduced adhesion formation. This novel treatment can address the unmet needs of patients who are unable to commence an early mobilization protocol after flexor tendon repair.

Effect of wrist and interphalangeal thumb movement on zone T2 flexor pollicis longus tendon tension in a human cadaver model.

INTRODUCTION: Therapy after flexor pollicis longus (FPL) repair typically mimics finger flexor management, but this ignores anatomic and biomechanical features unique to the FPL. PURPOSE OF THE STUDY: We measured FPL tendon tension in zone T2 to identify biomechanically appropriate exercises for mobilizing the FPL. METHODS: Eight human cadaver hands were studied to identify motions that generated enough force to achieve FPL movement without exceeding hypothetical suture strength. RESULTS: With the carpometacarpal and metacarpophalangeal joints blocked, appropriate forces were produced for both passive interphalangeal (IP) motion with 30° wrist extension and simulated active IP flexion from 0° to 35° with the wrist in the neutral position. DISCUSSION: This work provides a biomechanical basis for safely and effectively mobilizing the zone T2 FPL tendon. CONCLUSION: Our cadaver study suggests that it is safe and effective to perform early passive and active exercise to an isolated IP joint. LEVEL OF EVIDENCE: NA.

Surface Modification with Chemically Modified Synovial Fluid for Flexor Tendon Reconstruction in a Canine Model in Vivo.

BACKGROUND: Functional restoration is the major concern after flexor tendon reconstruction in the hand. The purpose of the present study was to investigate the effects of modifying the surface of extrasynovial tendon autografts with carbodiimide-derivatized synovial fluid with gelatin (cd-SF-G) on functional outcomes of flexor tendon reconstruction using a canine model. METHODS: The second and fifth flexor digitorum profundus tendons from eleven dogs were transected and repaired in zone II. The dogs then had six weeks of free activity leading to tendon rupture and scar formation (the repair-failure phase). In the reconstruction phase, two autologous peroneus longus tendons from each dog were harvested; one tendon was coated with cd-SF-G and the other, with saline solution, as a control. A non-weight-bearing rehabilitation protocol was followed for six weeks after reconstruction. The digits were then harvested and evaluations of function, adhesion status, gliding resistance, attachment strength, cell viability, and histology were performed. RESULTS: The tendons coated with cd-SF-G demonstrated significantly lower values (mean and standard deviation) compared with the saline-solution group for work of flexion (0.63 ± 0.24 versus 1.34 ± 0.42 N-mm/deg), adhesion score (3.5 ± 1.6 versus 6.1 ± 1.3), proximal adhesion breaking force (8.6 ± 3.2 versus 20.2 ± 10.2 N), and gliding resistance (0.26 ± 0.08 versus 0.46 ± 0.22 N) (p < 0.05). There was no significant difference between the cd-SF-G and saline-solution groups (p > 0.05) in distal attachment-site strength (56.9 ± 28.4 versus 77.2 ± 36.2 N), stiffness (19 ± 7.5 versus 24.5 ± 14.5 N/mm), and compressive modulus from indentation testing (4.37 ± 1.26 versus 3.98 ± 1.24 N/mm). Histological analysis showed that tendons coated with cd-SF-G had smoother surfaces and demonstrated tendon-to-bone and tendon-to-tendon incorporation. No significant difference in viable cell count between the two groups was observed on tendon culture. CONCLUSIONS: Modification of the flexor tendon surface with cd-SF-G significantly improved digital function and reduced adhesion formation without affecting graft healing and stiffness. CLINICAL RELEVANCE: This study used native synovial fluid as a basic lubricating reagent to treat a tendon graft in vivo, a novel avenue for improving clinical outcomes of flexor tendon reconstruction. This methodology may also apply to other surgical procedures where postoperative adhesions impair function.

Biomechanical evaluation of flexor tendon graft with different repair techniques and graft surface modification.

The purpose of this study was to investigate the biomechanical properties of modified repair techniques for flexor tendon reconstruction and the effects of surface modification using carbodiimide-derivatized synovial fluid plus gelatin (cd-SF-G), compared to the traditional repair techniques. The second and fifth digits from 16 canine forepaws were randomly divided into 4 groups: (1) traditional graft repairs (TGR group) including distal Bunnell repair and proximal Pulvertaft weave repair; (2) modified graft repairs (MGR group) including distal graft bony attachment repair and proximal step-cut repair; (3) group TGR coated with cd-SF-G (TGR-C group); and (4) group MGR coated with cd-SF-G (MGR-C group). Digit normalized work of flexion (nWOF), ultimate failure strength, and stiffness were measured. The nWOF in MGR group was significantly less than TGR group (p < 0.05). The nWOF in groups treated with cd-SF-G was significantly less than their untreated counterparts (p < 0.05). Ultimate load to failure of the MGR-C group was significantly greater than the TGR-C group (p < 0.05), but no significant difference in stiffness was found between these two groups. The modified techniques cannot only improve tendon gliding abilities but can also improve breaking strength. Additionally, surface modification with cd-SF-G significantly decreased the work of flexion.

Transforming growth factor-ß (TGF-ß) expression is increased in the subsynovial connective tissue in a rabbit model of carpal tunnel syndrome.

Carpal tunnel syndrome (CTS) is an idiopathic disease that results from increased fibrosis of the subsynovial connective tissue (SSCT). A recent study found overexpression of both transforming growth factor-ß (TGF-ß) and connective tissue growth factor (CTGF) in the SSCT of CTS patients. This study investigated TGF-ß and CTGF expression in a rabbit model of CTS, in which SSCT fibrosis is induced by a surgical injury. Levels of TGF-ß1 and CTGF at 6, 12, 24 weeks after injury were determined by immunohistochemistry A significant increase in TGF-ß1 and a concomitant significant increase in CTGF were found at 6 weeks, in addition to higher cell density compared to normal (all p<0.05), Interestingly, CTGF expression was reduced at 12 and 24 weeks, suggesting that an initial insult results in a time limited response. We conclude that this rabbit model mimics the fibrosis found in human CTS, and may be useful to study pathogenetic mechanisms of CTS in vivo.

CORR® ORS Richard A. Brand Award for Outstanding Orthopaedic Research: Engineering flexor tendon repair with lubricant, cells, and cytokines in a canine model.

BACKGROUND: Adhesions and poor healing are complications of flexor tendon repair. QUESTIONS/PURPOSES: The purpose of this study was to investigate a tissue engineering approach to improve functional outcomes after flexor tendon repair in a canine model. METHODS: Flexor digitorum profundus tendons were lacerated and repaired in 60 dogs that were followed for 10, 21, or 42 days. One randomly selected repair from either the second or fifth digit in one paw in each dog was treated with carbodiimide-derivatized hyaluronic acid, gelatin, and lubricin plus autologous bone marrow stromal cells stimulated with growth and differentiation factor 5; control repair tendons were not treated. Digits were analyzed by adhesion score, work of flexion, tendon-pulley friction, failure force, and histology. RESULTS: In the control group, 35 of 52 control tendons had adhesions, whereas 19 of 49 treated tendons had adhesions. The number of repaired tendons with adhesions in the control group was greater than the number in the treated group at all three times (p = 0.005). The normalized work of flexion in treated tendons was 0.28 (± 0.08), 0.29 (± 0.19), and 0.32 (± 0.22) N/mm/° at Day 10, Day 21, and Day 42 respectively, compared with the untreated tendons of 0.46 (± 0.19) at Day 10 (effect size, 1.5; p = 0.01), 0.77 (± 0.49) at Day 21 (effect size, 1.4; p < 0.001), and 1.17 (± 0.82) N/mm/° at Day 42 (effect size, 1.6; p < 0.001). The friction data were comparable to the work of flexion data at all times. The repaired tendon failure force in the untreated group at 42 days was 70.2 N (± 8.77), which was greater than the treated tendons 44.7 N (± 8.53) (effect size, 1.9; p < 0.001). Histologically, treated repairs had a smooth surface with intrinsic healing, whereas control repairs had surface adhesions and extrinsic healing. CONCLUSIONS: Our study provides evidence that tissue engineering coupled with restoration of tendon gliding can improve the quality of tendon healing in a large animal in vivo model. CLINICAL RELEVANCE: Tissue engineering may enhance intrinsic tendon healing and thus improve the functional outcomes of flexor tendon repair.