Differences in proliferative rate and collagen lattice contraction between endotenon and synovial fibroblasts

Tensile load on the flexor digitorum profundus tendon during palmar and lateral blocking exercises: Influence on blocking force and distal interphalangeal joint flexion angle

STUDY DESIGN

This is a basic science research.

INTRODUCTION

Isolating excursion of the flexor digitorum profundus (FDP) in zones I and II is common practice in the current management after flexor tendon repair. During this procedure, the proximal interphalangeal joint is sometimes fully extended with unmeasured external forces at the middle phalanx when the distal interphalangeal joint is actively flexed.

PURPOSE OF THE STUDY

The purpose of the study was to investigate the incremental effect of external force with palmar blocking versus lateral blocking and increased angles of flexion on internal tendon forces at the repair site for a safer application of force by the treating therapist.

METHODS

Eight human cadaveric fingers were studied. To simulate palmar or lateral finger blocking, a compression force of blocking was applied from 5N (510 grams) to 25N (2,550 grams) on the skin surface of the palmar or the lateral aspect of each of these middle phalanges in 5N increments. The tensile load on the FDP tendon during distal interphalangeal joint flexion from 0° to 60° was measured in 10° increments.

RESULTS

During palmar blocking, the tensile load was significantly increased with increases in palmar blocking force. However, no significant increase in the tensile load on the FDP tendon was observed at any lateral blocking.

DISCUSSION

Lateral blocking exercise can be performed with less tensile force on the FDP tendon when performing blocking exercise after flexor tendon injury repair.

CONCLUSIONS

This study supports the concept that lateral blocking with incremental joint angles allows a safer application of force for the healing tendon.

Improved tendon healing by a combination of Tanshinone IIA and miR-29b inhibitor treatment through preventing tendon adhesion and enhancing tendon strength

Background: Despite significant advances in the materials and methods development used in surgical repair and postoperative rehabilitation, the adhesion formation remains the most common clinical problem in tendon injuries. Therefore, the development of novel therapies is necessary for targeting at preventing tendon adhesion formation and improving tendon strength. Methods: We used rat fibroblasts for in vitro experiments to determine the optimal concentration of TSA in rats, and then set up negative control group, TSA intervention group, mir-29b interference adenovirus intervention group and TSA and mir-29b interference adenovirus co-intervention group. By comparing cell proliferation and protein expression in different group, we verified the effect and mechanism of drugs on fibroblast function. At the same time, the Sprague-Dawley rat Achilles tendon model in vivo was established in this study, which was divided into sham operation group and operation group. Afterwards in the operation group, mir-29b inhibitor and placebo were injected every 3 days respectively. Then the injection inhibitor group was divided into 5 groups which mean TSA was injected into the marked area at 0, 6, 24 and 72 hours after operation for 1 week, finally all of the rats were died at 3 weeks after operation. Through the observation of general properties, histological observation of Achilles tendon injury, biomechanical test and cell and protein expression in rats' tendon cell, the effect of drugs on tendon adhesion formation was analyzed. Results: We demonstrated that the combination of miR-29b inhibitor and tanshinone IIA(TSA) could prevent tendon adhesion and also enhance tendon strength. Mechanically, the miR-29b inhibitor could activate the TGF-β/Smad3 pathway to trigger endogenous pathways and induce a high proliferation of fibroblast. Subsequently, we also found adding TSA after 6 hours of miR-29b treatment gave less cell cytotoxicity in our rat model with better outcome of less tendon adhesion and enhanced strength. Conclusion: We conclude that the use of miR-29b inhibitor at the end of the tendon break could initiate endogenous repair mechanism and subsequently use of TSA should be able to inhibit the exogenous repair mechanism. Therefore, the combination of both treatments could prevent tendon adhesion and ensure tendon strength. Our findings suggested that this approach would be a feasible approach for tendon repair.

Role of a combination dietary supplement containing mucopolysaccharides, vitamin C, and collagen on tendon healing in rats

Objective

The aim of this study was to investigate the effect of mucopolysaccharide, vitamin C, and collagen supplementation on the healing of Achilles tendon in rats.

Methods

Sixteen rats were separated into 2 groups. Both Achilles tendons of all rats were transected 5 mm above the insertion and repaired using a Kessler suture. After the surgical repair, the study group received the daily recommended amount of the supplement by gastric gavage, while the control group received a placebo. At the end of the third week, the animals were sacrificed. The biomechanical properties of the groups were compared with ultimate tensile strength and stiffness tests. The biological properties of the 2 groups were assessed with a histomorphometric comparison to determine the amount of collagen type I (COL1), proliferating cell nuclear antigen (PCNA), and transforming growth factor β1 (TGF-β1) expression in 3 different tissue subgroups (collagen matrix, tenocytes, and endotenon fibroblasts).

Results

Analysis of histomorphometric results revealed that the rats receiving dietary supplements demonstrated a significant increase in PCNA (mean value of 86 in the control group and 168.85 in the trial group; p < 0.05) and TGF-β1 (mean value of 87.57 in the control group and 161.85 in the trial group; p < 0.05) in the endotenon fibroblasts of the repair site. However, there was no difference between the groups in PCNA or TGF-β1 when the collagen matrix and the tenocytes of the repair site were examined. Furthermore, no significant difference could be found between groups in COL1 in any of the 3 tissue subgroups (collagen matrix, tenocytes, and endotenon fibroblasts). The statistical analysis also indicated that the rats receiving supplements did not demonstrate a significant increase in the ultimate tendon tensile strength or stiffness.

Conclusion

The results of this study revealed no advantage to the oral administration of the trial supplement in collagen synthesis or biomechanical properties in rats after 3 weeks using the presented study design. However, the increased expression of PCNA and TGFβ1 seen in the endotenon fibroblasts of the repair site might play a role in the continuum of tendon healing.

Local administration of Trolox, a vitamin E analog, reduced tendon adhesion in a chicken model of flexor digitorum profundus tendon injury

Background

Hand flexor tendon injuries are compromised with tendon adhesion. Tendon adhesion forms between flexor tendon and tendon sheath, reduces the range of motion of fingers, and affects their function. Oxidative stress is increased in flexor tendon after injury and might play a role in tendon adhesion formation. Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), a water-soluble analog of vitamin E, is antioxidative. Trolox reduced oxidative stress and the expression of fibrotic cytokines in the bile gut ligation animal model. Vitamin C and Trolox are strong antioxidants, but they might also have prooxidant properties. The prooxidant properties of vitamin C and Trolox are different. In this study, our aim was to determine the effect of Trolox in reducing tendon adhesion formation.

Methods

Flexor digitorum profundus tendon injury was induced in 54 Kai-Mei Chicken according to a well-established protocol. After wound closure, an injection of 50 μL saline, 10mM Trolox, or 100mM Trolox was administered into the wound area. At 2 weeks or 6 weeks after the surgery, chicken feet were harvested for gliding test, high-resolution ultrasound measurement on a fibrotic area, and histology.

Results

At Week 2 after the surgery, Trolox has no effect on the flexion angle and gliding resistance, whereas a significant improvement was observed in the flexion angle and gliding resistance in the Trolox-treated groups at Week 6. However, no dose response was observed. In the ultrasound measurement, there was no significant difference in the fibrotic mass in the Trolox-treated group as compared to the saline group at Week 2. At Week 6, fibrotic mass was significantly reduced in both Trolox-treated groups. From the histological examination, the Trolox-treated groups presented a higher cellularity at Week 2 as compared to the saline group, and reduced fibrosis and adhesion at Week 6.

Conclusion

Our results suggest that local administration of Trolox can reduce tendon adhesion, and a higher dose of Trolox did not have negative effects.

Clinical Significance

Trolox solution might be feasible to reduce tendon adhesion via intraoperative injection at the wound area during tendon repair.

Erythropoietin stimulates patellar tendon healing in rats

BACKGROUND

Erythropoietin (EPO), regulating erythropoiesis, is used to provide protective and regenerative activity in non-haematopoietic tissues. There is insufficient knowledge about the role of EPO activity in tendon healing. Therefore, we investigated the effect of EPO treatment on healing in rat patellar tendons.

METHODS

One hundred and twenty-six, four-month-old male Sprague-Dawley rats were randomly assigned to three experimental groups: 1, no treatment; 2, treatment with isotonic saline (NaCl) and 3, treatment with EPO. Each group was randomly subdivided into two groups for sacrifice at three (1a, 2a, 3a) or six weeks (1b, 2b, 3b). Complete incision of the left patellar tendon from the distal patellar pole was performed. We applied body casts for 20 days after the incised edges of the patellar tendon were brought together with a surgical technique. Both legs were harvested and specimens from each group underwent histological, biomechanical, and protein mRNA expression analyses.

RESULTS

There were statistically significant differences in the ultimate breaking force between the EPO group and others at both weeks three and six (p<0.05); significant differences in fibroblast proliferation, capillary vessel formation, and local inflammation were found between groups 1a and 3a, and 2a and 3a (p<0.05). There were statistical differences between 1a, 3a and 2a, 3a for Col III, TGF-β1, and VEGF and between 1b, 3b and 2b, 3b for Col I, Col III, TGF-β1, and VEGF mRNA expressions.

CONCLUSION

EPO had an additive effect with surgery on the injured tendon healing process in rats compared to the control groups biomechanically, histopathologically and with tissue protein mRNA expression.

CLINICAL RELEVANCE

This is the first experimental study to analyze the relationship between EPO treatment and the patellar tendon repair process by biomechanical, histopathological, and tendon tissue mRNA expression methodologies.

Biological augmentation of rotator cuff repair using bFGF-loaded electrospun poly(lactide-co-glycolide) fibrous membranes

Clinically, rotator cuff tear (RCT) is among the most common shoulder pathologies. Despite significant advances in surgical techniques, the re-tear rate after rotator cuff (RC) repair remains high. Insufficient healing capacity is likely the main factor for reconstruction failure. This study reports on a basic fibroblast growth factor (bFGF)-loaded electrospun poly(lactide-co-glycolide) (PLGA) fibrous membrane for repairing RCT. Implantable biodegradable bFGF-PLGA fibrous membranes were successfully fabricated using emulsion electrospinning technology and then characterized and evaluated with in vitro and in vivo cell proliferation assays and repairs of rat chronic RCTs. Emulsion electrospinning fabricated ultrafine fibers with a core-sheath structure which secured the bioactivity of bFGF in a sustained manner for 3 weeks. Histological observations showed that electrospun fibrous membranes have excellent biocompatibility and biodegradability. At 2, 4, and 8 weeks after in vivo RCT repair surgery, electrospun fibrous membranes significantly increased the area of glycosaminoglycan staining at the tendon-bone interface compared with the control group, and bFGF-PLGA significantly improved collagen organization, as measured by birefringence under polarized light at the healing enthesis compared with the control and PLGA groups. Biomechanical testing showed that the electrospun fibrous membrane groups had a greater ultimate load-to-failure and stiffness than the control group at 4 and 8 weeks. The bFGF-PLGA membranes had the highest ultimate load-to-failure, stiffness, and stress of the healing enthesis, and their superiority compared to PLGA alone was significant. These results demonstrated that electrospun fibrous membranes aid in cell attachment and proliferation, as well as accelerating tendon-bone remodeling, and bFGF-loaded PLGA fibrous membranes have a more pronounced effect on tendon-bone healing. Therefore, augmentation using bFGF-PLGA electrospun fibrous membranes is a promising treatment for RCT.

Augmenting tendon and ligament repair with platelet-rich plasma (PRP)

Tendon and ligament injuries (TLI) commonly occur in athletes and non-athletes alike, and remarkably debilitate patients' athletic and personal abilities. Current clinical treatments, such as reconstruction surgeries, do not adequately heal these injuries and often result in the formation of scar tissue that is prone to re-injury. Platelet-rich plasma (PRP) is a widely used alternative option that is also safe because of its autologous nature. PRP contains a number of growth factors that are responsible for its potential to heal TLIs effectively. In this review, we provide a comprehensive report on PRP. While basic science studies in general indicate the potential of PRP to treat TLIs effectively, a review of existing literature on the clinical use of PRP for the treatment of TLIs indicates a lack of consensus due to varied treatment outcomes. This suggests that current PRP treatment protocols for TLIs may not be optimal, and that not all TLIs may be effectively treated with PRP. Certainly, additional basic science studies are needed to develop optimal treatment protocols and determine those TLI conditions that can be treated effectively.

The effects of 5-fluorouracil on flexor tendon healing by using a biodegradable gelatin, slow releasing system: experimental study in a hen model

This study investigated the effects of 5-fluorouracil in a slow-release biodegradable gelatin system on tendon healing. Gelatin blocks prepared in a size of 10 × 20 × 1 mm were loaded with 10, 20, and 30 mg of 5-fluorouracil, and 30 adult white Leghorn chickens were used. The tendons to the third and fourth toes were severed and repaired. The extremities were casted for three weeks. After sacrifice, the tendons were examined histologically and biomechanically for adhesion formation. The 10 mg-loaded gelatin group showed a decrease in adhesion formation when compared with the operative control group; the 20 and 30 mg groups showed signs of severe inflammation. Low doses of 5-fluorouracil applied via a slow-release gelatin system reduced adhesion formation in flexor tendon healing.

Prevention of Tendon Adhesions by ERK2 Small Interfering RNAs

Tendon adhesions are one of the most concerning complications after surgical repair of flexor tendon injury. Extracellular signal-regulated kinase (ERK) 2 plays crucial roles in fibroblast proliferation and collagen expression which contributes to the formation of tendon adhesions after flexor tendon surgery. Using a chicken model, we have examined the effects of a small interfering RNA (siRNA) targeting ERK2 delivered by a lentiviral system on tendon adhesion formation with an adhesion scoring system, histological assessment, and biomechanical evaluation. It was found that ERK2 siRNA effectively suppressed the increase of fibroblasts and the formation of tendon adhesions (p < 0.05 compared with the control group). Moreover, no statistically significant reduction in breaking force was detected between the ERK2 siRNA group and the control group. These results show that the lentiviral-mediated siRNA system is effective in preventing tendon adhesion formation but not to tendon healing, and may be used for tendon repair after confirmation and improvement by future detailed studies.

Cell migration after synovium graft interposition at tendon repair site

BACKGROUND

We have recently reported that interpositional synovium grafts from tendon sheath have a potential to accelerate tendon healing when implanted at the repair site. The purpose of this study was to investigate the effect of orientation of the synovium after synovium graft transplantation, by comparing the ability of cells from the visceral and parietal surfaces to migrate into the tendon in a canine tissue culture model.

METHODS

The synovium graft was placed within a complete tendon laceration, with either the visceral or parietal surface facing the proximal end of the lacerated tendon. The number of migrating cells was quantified by a cell migration assay. Qualitative immunohistochemistry and confocal laser microscopy were also used at day 10.

RESULTS

Many labeled synovial cells were observed within the tendon to which the visceral surface of the synovium graft was facing. Migrated cells were also observed on the parietal side, but there were fewer cells compared to visceral surface cells. Migrating cells all expressed α-smooth muscle actin.

CONCLUSION

We found that graft orientation affected cell migration. Whether this finding has clinical significance awaits in vivo study.

Managing the injured tendon: current concepts

Despite advances in understanding of the mechanical aspects of tendon management with improved suture technique and early stress application with postoperative therapy, clinical results remain inconsistent after repair, especially within the synovial regions. Complementary research to enhance the intrinsic pathway of healing, suppress the extrinsic pathway of healing, and manipulate frictional resistance to tendon gliding is now the focus of current basic science research on tendons. In the future, application of these new biologic therapies may increase the "safety zone" (or tolerance for load and excursion without dysfunctional gapping) as therapists apply stress to healing tendons and may alter future rehabilitation protocols by allowing greater angles of motion (and thus tendon excursion), increased external load, and decreased time in protective orthoses (splints). However, at this time, the stronger repair techniques and the application of controlled stress remain the best and most well-supported intervention after tendon injury and repair in the recovery of functional tendon excursion and joint range of motion. The hand therapist's role in this process remains a critical component contributing to satisfactory outcomes.

The attachment of intrinsic and extrinsic, mobilized and immobilized adhesion cells to collagen and fibronectin

This study investigated the attachment of intrinsic and extrinsic, mobilized and immobilized adhesion cells to the extracellular matrix. Five New Zealand White rabbit forepaws were dissected to isolate the flexor tendon core, tendon surface and synovial sheath, which were explanted separately. A further 10 animals were subjected to flexor tendon injuries, randomized to either mobilization or immobilization, and adhesions were explanted at 2 weeks. Cell groups were tested for attachment to collagen type-I or fibronectin and morphometric analysis was made. The attachment of intrinsic tendon cells and adhesion cells from mobilized tendons to both matrix proteins was statistically significantly greater than that of extrinsic tendon cells and adhesion cells from immobilized tendons. Adhesion cells from mobilized tendons were statistically significantly more elongated, which may correlate with the deposition of a more organized matrix. Because the synovial sheath cells were least attached to matrix proteins, selective treatments that reduce cell attachment may be used to exclude them, without inhibiting intrinsic tendon healing.

Cytokines in rotator cuff degeneration and repair

The pathogenesis of rotator cuff degeneration remains poorly defined, and the incidence of degenerative tears is increasing in the aging population. Rates of recurrent tear and incomplete tendon-to-bone healing after repair remain significant for large and massive tears. Previous studies have documented a disorganized, fibrous junction at the tendon-to-bone interface after rotator cuff healing that does not recapitulate the organization of the native enthesis. Many biologic factors have been implicated in coordinating tendon-to-bone healing and maintenance of the enthesis after rotator cuff repair, including the expression and activation of transforming growth factor-β, basic fibroblast growth factor, platelet-derived growth factor-β, matrix metalloproteinases, and tissue inhibitors of metalloproteinases. Future techniques to treat tendinopathy and enhance tendon-to-bone healing will be driven by our understanding of the biology of this healing process after rotator cuff repair surgery. The use of cytokines to provide important signals for tissue formation and differentiation, the use of gene therapy techniques to provide sustained cytokine delivery, the use of stem cells, and the use of transcription factors to modulate endogenous gene expression represent some of these possibilities.

Effects of antisense transforming growth factor-beta1 gene transfer on the biological activities of tendon sheath fibroblasts

Recent studies have shown the importance of transforming growth factor-beta (TGF-beta) in flexor tendon wound healing. Decreased adhesion formation and increased range of motion after the administration of TGF-beta antibodies after tendon repair have been shown. But TGF-beta antibodies have a short biologic half-life, and continuous supplementation of exogenous TGF-beta antibodies is not practical. Transfer of growth factor genes to tenocytes provides an alternative to protein therapeutics, and a gene therapy approach will prolong the availability of therapeutic proteins.We investigated the biological activities effects of rabbit tendon sheath fibroblasts transfected by antisense TGF-beta1 gene. Tendon sheath fibroblasts were isolated from New Zealand white rabbits and transfected by antisense TGF-beta1 gene with Lipofectin (Invitrogen, Carlsbad, California). Reverse transcription polymerase chain reaction was used to measure collagen I, collagen III, and TGF-beta1 expression, and Western blot was used to measure collagen protein I expression in tendon sheath fibroblasts after being transfected by antisense TGF-beta1 gene. Reverse transcription polymerase chain reaction displayed that tendon sheath fibroblasts transfected with antisense TGF-beta1 gene showed marked decrease collagen I, collagen III, and TGF-beta1 mRNA expression. Western blot showed that tendon sheath fibroblasts transfected with antisense TGF-beta1 gene showed marked decrease expression of collagen I protein, and there was significant difference compared with the untransfected and empty transfected groups (P<.01). Tendon sheath fibroblasts can transfect with antisense TGF-beta1 gene successfully and can decrease production of collagen I, collagen III, and TGF-beta1, which were factors of tendon adhere formation.

Effects of cell concentration and collagen concentration on contraction kinetics and mechanical properties in a bone marrow stromal cell-collagen construct

A cell-collagen construct is commonly used to investigate the phenomenon of wound healing and to estimate the variables for tissue engineering. The purpose of this study was to assess the effects of cell concentration and collagen concentration on the contraction kinetics and mechanical properties of bone marrow stromal cell (BMSC) seeded collagen lattices. To investigate the effects of both variables on the contraction kinetics, the construct contraction was monitored up to 13 days. Incremental stress- relaxation tests were carried out after a 2-week incubation to obtain the stress-strain profiles, which were subsequently assessed in a quasilinear viscoelastic (QLV) model. During contraction, aligned BMSCs were observed first in the interior portion of the ring, followed by the middle portion and finally in the exterior portion. Constructs seeded with a higher initial cell concentration (higher than 1 x 10(5) cells/mL) or lower initial collagen concentration (lower than 2 mg/mL) exhibited faster contraction, higher ultimate stress, and superior elasticity and reduced relaxation behavior (p < 0.05). The cell-collagen model was successfully used to yield information regarding the initial cell concentration and the initial collagen concentration on contraction kinetics and mechanical behavior, which may have possible application in tissue engineering.

Effects of synovial interposition on healing in a canine tendon explant culture model

PURPOSE

To investigate whether synovium interposition between repaired tendon ends can integrate into the tendon repair and improve tendon healing strength in a canine tendon explant culture model.

METHODS

We used 80 flexor digitorum profundus tendons from 10 mixed-breed dogs for this study. The flexor digitorum profundus tendons were assigned to 2 groups: repaired tendons with synovium implanted between the cut tendon ends and repaired tendons without any implantation between the tendon ends. The repaired tendons were cultured for either 2 or 4 weeks and then assessed mechanically for rupture strength and histology.

RESULTS

The strength of the repaired tendons with the synovium interposition was significantly higher (p < .001) than the repaired tendons without interposition at both 2 and 4 weeks. The strength of the repaired tendons at 4 weeks was significantly higher than that at 2 weeks in both groups.

CONCLUSIONS

Interpositional synovial grafts have the potential to accelerate tendon healing when they are implanted at the repair site. The exact mechanism of this effect remains to be elucidated.

Twenty-five years of tendon and ligament research

Twenty-five years ago, the Journal of Orthopaedic Research published its first volume, which included five articles covering topics in tendon and ligament research. Since then, the body of tendon and ligament research has continued to increase exponentially. This review summarizes major advancements in tendon and ligament research since the initial publication of this journal. The purpose of this article is not to provide an in-depth review of all of tendon and ligament research, but instead to provide a concise literature review of some of the major and recurring areas of research. The general topics covered over the last 25 years include tissue properties, tendinopathy, healing, and engineered scaffolds.

Substrate adhesion affects contraction and mechanical properties of fibroblast populated collagen lattices

Fibroblasts can condense a hydrated collagen lattice to a tissue-like structure. The purpose of this study was to evaluate the effect of substrate adhesion on the contraction and mechanical properties of fibroblast populated collagen lattices. Bacteriological grade polystyrene (BGPS) plates and tissue culture polystyrene (TCPS) plates were used as substrates for incubation of fibroblast populated collagen lattices. Hydrophobicity of the polystyrene surfaces was measured by the static sessile contact angle method. Collagen lattice contraction was recorded for 2 weeks, after which the lattices were mechanically tested. The BGPS culture plate had a significantly larger contact angle and was more hydrophobic than the TCPS culture plate. Both hydrophobicity and peripheral detachment of the collagen gel significantly decreased the time lag before initiation of gel contraction and increased the strength of the fibroblast populated collagen lattices. Substrate adhesion affects the contractility and strength of cell seeded collagen gels. This information may be useful in developing tissue engineered tendons and ligaments.

Factors related to contraction and mechanical strength of collagen gels seeded with canine endotenon cells

Fibroblasts can construct a hydrated collagen lattice to a tissue-like structure that is greatly influenced by initial culture conditions. The purpose of this study was to investigate the effects of cell concentration and collagen concentration on the contraction kinetics and mechanical properties of resultant endotenon-derived fibroblast-seeded collagen lattice. The experiment was designed to evaluate the effect of cell concentration (0, 0.25, 0.5, and 1.0 x10(6) cells/mL) and collagen concentration (0.5, 1.0, 1.5, and 2.0 mg/mL). Collagen lattice contraction was recorded for 42 days, after which time the lattices were mechanically tested. The collagen lattices seeded with higher initial cell concentration had a shorter contraction lag phase (p < 0.01), and exhibited a higher ultimate stress (p < 0.01) and instantaneous and equilibrium modulus (p < 0.01) than those seeded with a lower initial cell concentration. The collagen lattices cultured with a lower initial collagen concentration also had a shorter contraction lag phase, and exhibited greater instantaneous and equilibrium modulus (p < 0.01) than those cultured with higher initial collagen concentration. The collagen lattices of initial 0.5 mg/mL collagen concentration had the highest value of ultimate stress (p < 0.03).

The inflammatory response and hyaluronan synthases in the rabbit flexor tendon and tendon sheath following injury

Using a rabbit model of flexor tendon injury, mRNA levels for a subset of relevant molecules involved in inflammatory and fibrotic processes were assessed by reverse transcriptase-polymerase chain reaction 3, 6, 12 and 24 days after injury. Increased levels of COX-2, IL-1beta, MMP-13 and TIMP-1 mRNA were detected in both tendon and tendon sheath following injury, with each molecule exhibiting tissue and time-dependent changes. MMP-13 and TIMP-1 mRNA levels were markedly upregulated in both tissues, whereas COX-2 and IL-1beta predominantly increased in tendon. Both hyaluronan synthase (HAS) 2 and 3 exhibited increases in mRNA levels in tendon tissue after injury, HAS 2 being more pronounced. These findings support the concept that healing in the flexor tendon and the sheath involve different molecular events and that each tissue may require unique modifications if healing is to be enhanced and adhesions reduced.

A comparison of tenocytes and mesenchymal stem cells for use in flexor tendon tissue engineering

PURPOSE

Tissue-engineered tendon grafts will meet an important clinical need. To engineer tendons, we used acellularized allogeneic tendon as scaffold material. To determine the ideal cell type to seed the scaffolds, we studied in vitro characteristics of epitenon tenocytes, tendon sheath fibroblasts, bone marrow-derived mesenchymal stem cells (BMSCs), and adipoderived mesenchymal stem cells (ASCs). Subsequently, we implanted reseeded acellularized tendons in vivo as flexor tendon grafts.

METHODS

Tenocytes, sheath fibroblasts, BMSCs, and ASCs were obtained from adult rabbits. For all cell lines, collagen 1, 2, and 3 immunocytochemistry was performed, and proliferation was assessed by hemacytometry and senescence by beta-galactosidase staining. Flexor tendons were acellularized after harvest. Tendons were assessed by histology after in vitro reseeding with each of the cell types after 1, 4, and 8 weeks. Finally, reseeded tendons and controls were implanted in a flexor profundus tendon defect. After 6 weeks, the reseeded tendons were harvested and assessed by histology. Statistical analysis for cell proliferation was performed using analysis of variance and t-tests with Bonferroni correction.

RESULTS

All cell types had similar collagen expression. Cell proliferation was higher in ASCs in late passage compared with early passage and in ASCs compared with epitenon tenocytes at late passage. The other cell types were similar in growth characteristics. No senescence was detected. In vitro assessment of reseeded constructs showed the presence of cells on the construct surface. In vivo assessment after implantation showed viable cells seen within the tendon architecture in all cell types.

CONCLUSIONS

This study suggests that the four cell types may be successfully used to engineer tendons. Adipoderived mesenchymal stem cells proliferate faster in cell culture, but the cell types were similar in other respects. All could be used to successfully repopulate acellularized tendon in vivo as flexor tendon grafts.

Modulation of peritendinous adhesion formation by alginate solution in a rabbit flexor tendon model

To examine the antiadhesive effect of an alginate solution following tendon surgery, unilateral subtotal laceration of the flexor digitorum communis tendon was created in one hind limb while the other side was left intact in 32 Japanese white rabbits. The lesion was coated with alginate solution in 16 animals and not coated in the other 16. Degree of adhesion formation was assessed histologically and biomechanically by measuring the flexion angle of the first toe when the flexor digitorum tendon was pulled with a specified force at 4 weeks postoperatively. When compared with the control group, the alginate-treated group demonstrated significantly greater toe flexion, with less scar tissue formation at the repair site. Histologically, complete tendon healing with longitudinal remodeling of collagen fibers was observed in the alginate-treated group, while a random pattern of fibers was observed in the control group. Reduction in adhesion formation using alginate solution represents a novel strategy for the management of tendon injury and repair in the clinical setting.

Mechanobiology of tendon

Tendons are able to respond to mechanical forces by altering their structure, composition, and mechanical properties--a process called tissue mechanical adaptation. The fact that mechanical adaptation is effected by cells in tendons is clearly understood; however, how cells sense mechanical forces and convert them into biochemical signals that ultimately lead to tendon adaptive physiological or pathological changes is not well understood. Mechanobiology is an interdisciplinary study that can enhance our understanding of mechanotransduction mechanisms at the tissue, cellular, and molecular levels. The purpose of this article is to provide an overview of tendon mechanobiology. The discussion begins with the mechanical forces acting on tendons in vivo, tendon structure and composition, and its mechanical properties. Then the tendon's response to exercise, disuse, and overuse are presented, followed by a discussion of tendon healing and the role of mechanical loading and fibroblast contraction in tissue healing. Next, mechanobiological responses of tendon fibroblasts to repetitive mechanical loading conditions are presented, and major cellular mechanotransduction mechanisms are briefly reviewed. Finally, future research directions in tendon mechanobiology research are discussed.

The future of flexor tendon surgery

Clinical outcomes following flexor tendon repair have made significant improvements in the last 50 years. In that time standard treatment has evolved from secondary grafting to primary repair with postoperative rehabilitation protocols. Unfortunately, excellent results are not yet attained universally following treatment. Improving understanding of tendon healing at the cellular, molecular, and genetic levels will likely enable surgeons to modulate the normal repair process. We now look toward biologic augmentation of flexor tendon repairs to address the problems of increasing tensile strength while reducing adhesion formation following injury and operative repair.

Expression of Growth Factors in Canine Flexor Tendon After Laceration in Vivo

Growth factors, transforming growth factor beta (TGF-beta), epidermal growth factor (EGF), platelet-derived growth factor (PDGF), insulin-like growth factor (IGF), basic fibroblast growth factor (bFGF), and vascular endothelial growth factor (VEGF), are critical components of the cutaneous wound healing process. Little is known, however, about the expression of these growth factors in normal flexor tendon healing. In this study, we wished to examine which of these growth factors are present at 10 days following tendon injury in a canine flexor tendon repair model. Using immunohistochemical analysis, we found positive staining for all growth factors in both timing groups. TGF-beta was detected around the repair site and proximal to it. PDGF-AA, PDGF-BB and VEGF appeared in the whole tendon section following repair. EGF, IGF and bFGF were not seen in tenocytes but were present in inflammatory cells surrounding the repair site. These findings provide evidence that TGF-beta, EGF, PDGF-AA, PDGF-BB, IGF, bFGF and VEGF are all expressed at 10 days after tendon injury but by different cell types and in different locations. The time course of growth factor expression is an important element in wound healing, and a better understanding of where and when such factors are expressed may help in the development of methods to manipulate this expression, accelerate healing, and reduce adhesions.

Clinical implications of growth factors in flexor tendon wound healing

Recent research has focused on the role of growth factors in flexor tendon wound healing. These basic science reports have described the identification and quantification of various growth factors in in vitro and in vivo models. Although these reports have begun to piece together the cascade of events involved in flexor tendon wound healing, the clinical relevance for the practicing hand surgeon is unclear. Growth factors are cell-secreted proteins that regulate cellular functions. These growth factors are involved in cell differentiation and growth, including the normal processes of development and tissue repair. Several growth factors recently have been identified as playing roles in tendon healing including vascular endothelial growth factor (VEGF), insulin-like growth factor (IGF), platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF), and transforming growth factor beta (TGF-beta). In addition, the transcription factor NF-kappaB has been implicated in the signaling pathways of these growth factors. The purpose of this article is to describe what is known about the molecular basis of flexor tendon wound healing, to review the most commonly studied growth factors, and to summarize likely clinical applications of these growth factors to flexor tendon repair.

Inhibition of TGF-beta-induced collagen production in rabbit flexor tendons

PURPOSE

Postoperative adhesions frequently compromise the success of flexor tendon repair. Manipulation of growth factors responsible for scar formation may be a method of decreasing adhesion formation. Transforming growth factor beta (TGF-beta) is a key cytokine in the pathogenesis of tissue fibrosis. The purpose of this study was to examine the effectiveness of TGF-beta neutralizing antibody in blocking TGF-beta-induced collagen I production in rabbit flexor tendons in vitro.

METHODS

Sheath fibroblasts, epitenon tenocytes, and endotenon tenocytes were obtained from rabbit flexor tendons. Each cell culture was supplemented with 1 ng/mL of TGF-beta along with increasing doses of TGF-beta neutralizing antibody (0.1-2.0 microg/mL). Collagen I production was measured by enzyme-linked immunoabsorbent assay and TGF-beta bioactivity was measured by the luciferase assay. Results were compared with TGF-beta alone and unsupplemented controls.

RESULTS

The addition of neutralizing antibody significantly reduced TGF-beta-induced collagen I production in a dose-dependent manner in all 3 cell cultures. TGF-beta bioactivity was also reduced by its neutralizing antibody.

CONCLUSIONS

This study shows that TGF-beta inhibition through its neutralizing antibody was effective in cultured flexor tendon cells. The results encourage further experiments that use such agents to modulate flexor tendon wound healing in in vivo models in the hope of eventually blocking the effect of TGF-beta on flexor tendons clinically.

Synovial sheath cell migratory response to flexor tendon injury: an experimental study in rats

PURPOSE

We aimed to investigate the degree of participation of synovial sheath cells in the process of tendon healing by selective cell labeling and direct observation of migrational pathways.

METHODS

We designed a novel rat animal model that employed vital dye staining of synovial sheath cells. The flexor digitorum profundus (FDP) tendon was removed from its sheath and vital dye was applied directly to the synovial sheath cells. A window was cut in the removed tendon before being returned to the sheath, thus placing a tendon injury adjacent to the labeled synovial sheath cells. The synovium remained intact at all times, and labeling was confirmed to be localized to the synovium. The migrational response of the synovial sheath cells to the tendon injury was observed by harvesting the tendons at 1, 3, 5, and 7 days (n = 6 for each time period) after injury and assessing tendon response with frozen sections under ultraviolet microscopy.

RESULTS

Labeled synovial sheath cells were observed within the substance of the healing tendon 24 hours after injury, with numbers increasing with time for up to 5 days, but decreasing by day 7.

CONCLUSIONS

This study confirms that in the rat model synovial sheath cells move into the healing tendon area and then migrate into the tendon core.

Tissue engineering of flexor tendons

Despite technical advances in suture methods and rehabilitation protocols, challenges remain in the field of flexor tendon repair. This article reviews the state-of-the-art research in the tissue engineering of flexor tendons. These early published data will hopefully lay the foundation for molecular methods and materials that can be used to reconstruct tendons to restore normal form and function in the hand.

Differences in morphology, cytoskeletal architecture and protease production between zone II tendon and synovial fibroblasts in vitro

Fibroblast migration is an integral component of the processes resulting in the formation of restrictive adhesions in the injured tendon, especially in Zone II. Pre-requisites for cell migration are an intact cytoskeleton and an ability to biochemically degrade the extra-cellular matrix. The relative characteristics of fibroblasts from the fibro-osseus sheath (SC), the tissue surrounding the tendon in Zone II, and the endotenon (TC) with respect to morphology, cytoskeletal structure and ability to produce matrix metalloproteinases (MMPs) 2 and 9 were compared in vitro. It was found that SCs were larger in size and demonstrated greater amounts of intra-cellular alpha-smooth muscle actin (alpha-SMA) and intra-membranous vinculin. Filamentous actin (F-actin) fibres in SCs were more densely packed and concentrated, resulting in stress fibres. The SCs also produce greater amounts of MMP-2 and MMP-9 compared to TCs. These observations imply that SCs play an active role in adhesion formation and should be specifically targeted to inhibit or treat tendon adhesions.

The early surface cell response to flexor tendon injury

PURPOSE

The migratory response of surface fibroblasts to flexor tendon injury was studied by their selective labeling with a vital dye.

METHOD

The surfaces of 30 rat deep flexor tendons were bathed in 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine percholate (DiI), a vital dye for 5 minutes. The residual dye was removed by thorough irrigation. A partial tenotomy was made in the stained section by cutting out a central window. Semiquantitative cell counts and position of stained fibroblasts were noted by examination under fluorescent light at 0, 1, 3, 5, and 7 days.

RESULTS

The surface fibroblasts readily took up the vital dye at day 0. By day 1 dyed cells had moved into the cut. By day 3 they had migrated laterally into the core substance of the tendon. Core dyed cell counts at days 1, 3, 5, and 7 were significantly different compared with day 0 core dyed cell counts.

CONCLUSIONS

This cell migration from the surface of the cut to the tendon core is likely to be vital in the early stages of tendon healing.

Inhibition of cell migration from tendon explants into fibrin clots by extracts derived from cheese whey is largely due to transforming growth factor-beta

Whey-derived growth factor extract (WGFE) and the acid-activated form (WGFE-a) were tested for their ability to influence the migration of cells from chicken flexor tendon biopsies into fibrin clots. When added to the medium surrounding clots, both extracts significantly inhibited migration relative to controls (P<0.05) in a dose-dependent manner when measurements were made after seven days of incubation. WGFE-a was approximately ten times more potent than WGFE. Since transforming growth factor (TGF)-beta1 and -beta2 activity of WGFE-a is much higher than in WGFE we hypothesized that TGF-beta was responsible for the inhibition of tendon cell migration. Neutralizing anti-TGF-beta monoclonal antibody was added to the medium bathing tendon biopsies in fibrin clots along with WGFE-a. WGFE-a alone inhibited migration by 51% and this was reversed by the antibody in a dose-dependent manner. Furthermore, recombinant human TGF-beta1 and -beta2 significantly inhibited tendon cell migration with similar dose-dependent potency when tested in the assay. These results indicate that TGF-beta is largely responsible for the inhibition of tendon cell migration by WGFE-a. This sheds further light on the functions of this growth factor during the early events in tendon repair.

Biomimetic approaches to tendon repair

The linear organization of collagen fibers in tendons results in optimal stiffness and strength at low strains under tensile load. However, this organization makes repairing ruptured or lacerated tendons extremely difficult. Current suturing techniques to join split ends of tendons, while providing sufficient mechanical strength to prevent gapping, are inadequate to carry normal loads. Immobilization protocols necessary to restore tendon congruity result in scar formation at the repair site and peripheral adhesions that limit excursion. These problems are reviewed to emphasize the need for novel approaches to tendon repair, one of which is the development of biomimetic tendons. The objective of the empirical work described here was to produce biologically-based, biocompatible tendon replacements with appropriate mechanical properties to enable immediate mobilization following surgical repair. Nor-dihydroguaiaretic acid (NDGA), a di-catechol from creosote bush, caused a dose dependent increase in the material properties of reconstituted collagen fibers, achieving a 100-fold increase in strength and stiffness over untreated fibers. The maximum tensile strength of the optimized NDGA treated fibers averaged 90 MPa; the elastic modulus of these fibers averaged 580 MPa. These properties were independent of strain rates ranging from 0.60 to 600 mm/min. Fatigue tests established that neither strength nor stiffness were affected after 80 k cycles at 5% strain. Treated fibers were not cytotoxic to tendon fibroblasts. Fibroblasts attached and proliferated on NDGA treated collagen normally. NDGA-fibers did not elicit a foreign body response nor did they stimulate an immune reaction during six weeks in vivo. The fibers survived 6 weeks with little evidence of fragmentation or degradation. The polymerization scheme described here produces a fiber-reinforced NDGA-polymer with mechanical properties approaching an elastic solid. The strength, stiffness and fatigue properties of the NDGA-treated fibers are comparable to those of tendon. These fibers are biocompatible with tendon fibroblasts and elicit little rejection or antigenic response in vivo. These results indicate that NDGA polymerization may provide a viable approach for producing collagenous materials that can be used to bridge gaps in ruptured or lacerated tendons. The tendon-like properties of the NDGA-fiber would allow early mobilization after surgical repair. We predict that timely loading of parted tendons joined by this novel biomaterial will enhance mechanically driven production of neo-tendon by the colonizing fibroblasts and result in superior repair and rapid return to normal properties.

Flexor tendon wound healing in vitro: the effect of lactate on tendon cell proliferation and collagen production

Flexor tendon repair in zone II is complicated by adhesions to the surrounding fibro-osseous sheath. Lactate is an early mediator of wound healing known to play an important role in stimulation of collagen production after cellular injury. Little attention has been paid to the role of lactate in flexor tendon wound healing. In this study tendon and tendon sheath were excised from rabbit forepaws. We examined proliferation of tendon sheath fibroblasts, epitenon tenocytes, and endotenon tenocytes; collagen production by each of these 3 cell types; and effects of lactate on cell proliferation and collagen production. Three cell lines, tendon sheath, epitenon, and endotenon, were isolated and cultured. Tendon sheath fibroblasts showed the greatest proliferation. All 3 cell lines produced collagen I, II, and III. Lactate significantly increased collagen production by all 3 cell lines. We show that cells of the tendon sheath, epitenon, and endotenon produce collagen in vitro. Modulation of lactate levels may provide a means to modulate collagen production.

Reduction in matrix metalloproteinase production by tendon and synovial fibroblasts after a single exposure to 5-fluorouracil

This study investigated the effect of treatment with 5min exposures to 5-fluorouracil (5-FU) on the production of matrix metalloproteinases (MMPs) by endotenon and synovial fibroblasts. Fibroblasts were grown from the flexor tendons of New Zealand White rabbits and were then exposed to varying concentrations (ranging from 0.25 mg x ml(-1)to 25 mg x ml(-1)of 5-FU for 5 min. The treated fibroblasts were suspended in a three-dimensional collagen lattice. The conditioned media from these collagen lattices were then analysed for MMP production using gelatin zymography on days 1, 3 and 7 after treatment. In the majority of cases this treatment produced a dose- and time-dependent reduction in total MMP production by both cell lines, specifically in the production of MMPs 2 and 9. This reduction was significant for most concentrations (P< or =0.01-P< or =0.05) when compared to phosphate-buffered-saline-treated controls. We conclude that 5-FU may reduce adhesions by limiting the migratory capacity of synovial fibroblasts (extrinsic healing).

The cell and developmental biology of tendons and ligaments

We have sought to create, for the first time in a single comprehensive review, a modern synthesis of opinion on the cell, developmental, and molecular biology of tendons, ligaments, and their associated structures (tendon sheaths, vinculi, and retinacula). Particular attention has been paid to highlighting new data on the early development of tendons, the signaling molecules involved in their patterning, and the diversity of specialized regions (entheses, wrap-around regions, and myotendinous junctions) that characterize fully formed tendons and ligaments. We have emphasized the complexities of adult tendon and ligament cell shape and related these to their early development. The importance of gap junctions in allowing cell communication throughout an extensive extracellular matrix (ECM) has also been highlighted, particularly in relation to understanding how tendon and ligament cells respond to changes in mechanical load. Finally, we have considered the influence of growth factors and related molecules on cell proliferation and ECM synthesis.

Effects of 5-fluorouracil on flexor tendon repair

This study was performed to assess the effects of a single 5-minute exposure of 5-fluorouracil (5-FU) applied topically at the time of flexor tendon repair in an attempt to reduce postoperative adhesions. The flexor digitorum profundus tendon to the long and fourth toe of Leghorn chickens was lacerated and primarily repaired using a 2-strand technique. The repair site was then exposed to a single 5-minute application of 5-FU in concentrations of 5, 25, or 50 mg/mL. Legs were casted for 3 weeks. After death the tendon was examined for the work of flexion using a tensile testing machine and examined with light microscopy, scanning electron microscopy, and transmission electron microscopy for morphologic and histologic differences in adhesion formation. Forty-seven chickens were examined. Average work of flexion values were 0.12 J for normal tendon, 0.31 J for operative controls, 0.34 J for the 5 mg/mL group, 0.15 J for the 25 mg/mL group, and 0.19 J for the 50 mg/mL group. The work of flexion was significantly reduced in the 25 and 50 mg/mL groups compared with the operative controls (p =.008 and p =.03, respectively). Histologic sections as graded by a blinded pathologist revealed decreased adhesion formation in all the 5-FU-treated animals (p <.008). Histologic examination showed that the highest concentration of 5-FU was not as effective at reducing adhesions as the 25 mg/mL dose. This appeared to be due to increasing inflammatory changes seen around and within the tendons of the 50 mg/mL group. Overall, a single intraoperative application of 5-FU at concentrations of 25 mg/mL appears to be an effective mechanism for reducing postoperative flexor tendon adhesions.

Differential cellular response within the rabbit tendon unit following tendon injury

The cellular changes in the epitenon, endotenon and synovial sheath were investigated in a rabbit model after a partial transverse laceration was made on the plantar aspect of the flexor digitorum profundus proximal to the synovial sheath (which was not injured). Fibroblasts, macrophages and mast cells within the epitenon, endotenon and synovial sheath were counted on electron micrographs. The epitenon and uninjured synovial sheath became engorged with fibroblasts and macrophages following injury. The number of synovial fibroblasts showed the greatest increase during the first week after injury. In comparison, the endotenon exhibited a delay in cellular response with initial apoptosis, as judged by positive P53 staining. However, hypercellular activity was seen within the endotenon at 12 weeks postoperatively.