Quantitative variation in vascular endothelial growth factor mRNA expression during early flexor tendon healing: an investigation in a canine model

Bevacizumab promotes tenogenic differentiation and maturation of rat tendon-derived cells in vitro

Previous work suggested that tenogenic differentiation of tendon stem/progenitor cells (TSPCs) was suppressed by upregulated expression of the angiogenic marker vascular endothelial growth factor (VEGF). The purpose of this study was to test the hypothesis that anti-VEGF antibody, bevacizumab, promotes in vitro tenogenic differentiation and maturation of two distinct types of TSPCs, tendon proper-derived cells (TDCs), and paratenon-derived cells (PDCs) originating from rat Achilles tendon. TDCs and PDCs were isolated from the tendon proper and the paratenon of rat Achilles tendons. TDCs and PDCs were cultured for 3 days on plates with or without VEGF. TDCs and PDCs were also cultured in collagen gel matrix, and the blocking effect of VEGF was examined by the addition of 100 ng/mL of bevacizumab. Effects of bevacizumab on tenogenic differentiation were assessed using real-time PCR, immunofluorescent staining, and western blotting. VEGF significantly attenuated expression of the Tnmd gene in both PDCs and TDCs (P<0.05). Expressions of the Scx, Tnmd, and Col1a1 genes were significantly upregulated by the addition of bevacizumab (P<0.05). Immunofluorescent staining showed that the percentage of tenomodulin-positive PDCs and TDCs was significantly higher with bevacizumab treatment than in control cultures (P<0.05). Western blotting showed that bevacizumab suppressed pVEGFR-2 protein expression in both PDCs and TDCs. Bevacizumab promoted the in vitro tenogenic differentiation and maturation of two distinct TSPCs derived from rat Achilles tendon. Since the previous studies demonstrated that TSPCs have a potential to contribute to tendon repair, attenuating VEGF levels in TSPCs by administration of bevacizumab is a novel candidate therapeutic option for promoting tendon repair.

VEGFA-Enriched Exosomes from Tendon-Derived Stem Cells Facilitate Tenocyte Differentiation, Migration, and Transition to a Fibroblastic Phenotype

Tendon-derived stem cells (TDSCs) play a vital role in repair of rotator cuff tear injuries by secreting paracrine proteins that regulate resident cell functions. Secreted exosomes may play a role in tendon injury repair by mediating intercellular communication; however, the detailed mechanisms by which TDSC-derived exosomes affect tenocyte development remain unknown. Here, we examined the effects of exosomes isolated from conditioned medium of TDSCs on tenocyte differentiation, migration, and transition to a fibroblastic phenotype in vitro. Successful isolation of exosomes from TDSCs was confirmed by high expression levels of CD81, CD63, CD9, and TSG101. Treatment with TDSC-derived exosomes promoted the growth and migration of cultured rat tenocytes, and increased the levels of the fibrosis markers collagen I, collagen III, scleraxis, tenascin C, and α-smooth muscle actin. Furthermore, vascular endothelial growth factor A (VEGFA) expression was higher in TDSC-derived exosomes than in TDSCs, and genetic knockdown of VEGFA suppressed the stimulatory effect of TDSC-derived exosomes on tenocyte development. Overall, these results demonstrate that VEGFA-enriched exosomes isolated from TDSCs promote differentiation and migration of cultured tenocytes and their transition to a fibroblastic phenotype. These data provide a new potential clinical treatment strategy for tendon injury.

Growth Factor Expression During Healing in 3 Distinct Tendons

Purpose

We investigated unique tendon growth-factor expression profiles over time in response to simultaneous, similar injuries. Characterizing these genetic differences lays the foundation for creating targeted, tendon-specific therapies and provides insight into why current growth-factor treatments have success in some applications but not others.

Methods

The left fourth digital flexor, triceps, and supraspinatus tendons in 24 rats were cut to 50% of their transverse width at the midbelly under anesthesia. On postoperative days 1, 3, 5, 7, and 14, randomly selected rats were sacrificed, and the damaged tendons were excised and flash-frozen in liquid nitrogen. The expressional fibroblast growth factor 1, bone morphogenic protein 13, and transforming growth factor β-1 were measured at each time point and compared to their respective, uninjured levels with real-time polymerase chain reaction.

Results

The digital flexor tendon showed exponentially elevated expression of all 3 factors over the preinjury baseline values. Expression in the triceps and supraspinatus had more variation over time. The triceps tendon showed a considerable decrease of transforming growth factor β-1 and bone morphogenic protein 13 expression. The supraspinatus tendon had statistically significant increases of both transforming growth factor β-1 and bone morphogenic protein 13 expression relative to preoperative, uninjured levels, with a nonstatistically significant decrease of fibroblast growth factor 1.

Conclusions

Our study suggests different tendons express their own unique growth-factor profiles after similar, simultaneous injuries. The digital flexor showed particularly high, sustained levels of growth-factor expression in comparison to the supraspinatus and triceps, suggesting that variable dosing may be necessary for growth-factor therapies aimed at supplementing innate responses in these different tendon types.

Clinical relevance

These data show different tendons express unique trends of growth-factor expression over time in response to injury, suggesting each unique tendon may require specific dosing or knockdown therapies. These observations serve as a foundation for more tendon-specific questioning, experimentation, and therapeutic design.

The Role of Vascular Endothelial Growth Factor in Tendon Healing

Angiogenesis is crucial to facilitate tendon healing, such as delivering oxygen and nutrients, removing waste products, and controlling immune responses. Vascular endothelial growth factor (VEGF) is one of the most vital angiogenic factors that regulate blood vessel formation in tendon healing. Recently, biological therapies, including the application of exogenous VEGF, have been attracting increasing attention. However, at present, the effect of the application of exogenous VEGF in tendon healing is controversial, as the role of endogenous VEGF in tendons has also not been fully elucidated. This article will summarize the role of both endogenous and exogenous VEGF in tendon healing and discuss possible reasons for the controversy. The present review shows that tendon repair is facilitated only by proper angiogenesis and VEGF at the early stage, whereas the persistent high VEGF expression and prolonged presence of blood vessels may impair tendon repair at a later stage.

Known data on applied regenerative medicine in tendon healing

Tendons and ligaments are important structures in the musculoskeletal system. Ligaments connect various bones and provide stability in complex movements of joints in the knee. Tendon is made of dense connective tissue and transmits the force of contraction from muscle to bone. They are injured due to direct trauma in sports or roadside accidents. Tendon healing after repair is often poor due to the formation of fibro vascular scar tissues with low mechanical property. Regenerative techniques such as PRP (platelet-rich plasma), stem cells, scaffolds, gene therapy, cell sheets, and scaffolds help augment repair and regenerate tissue in this context. Therefore, it is of interest to document known data (repair process, tissue regeneration, mechanical strength, and clinical outcome) on applied regenerative medicine in tendon healing.

Long noncoding RNA H19 accelerates tenogenic differentiation by modulating miR-140-5p/VEGFA signaling

Rotator cuff tear (RCT) is a common tendon injury, but the mechanisms of tendon healing remain incompletely understood. Elucidating the molecular mechanisms of tenogenic differentiation is essential to develop novel therapeutic strategies in clinical treatment of RCT. The long noncoding RNA H19 plays a regulatory role in tenogenic differentiation and tendon healing, but its detailed mechanism of action remains unknown. To elucidate the role of H19 in tenogenic differentiation and tendon healing, tendon-derived stem cells were harvested from the Achilles tendons of Sprague Dawley rats and a rat model of cuff tear was established for the exploration of the function of H19 in promoting tenogenic differentiation. The results showed that H19 overexpression promoted, while H19 silencing suppressed, tenogenic differentiation of tendon-derived stem cells (TDSCs). Furthermore, bioinformatic analyses and a luciferase reporter gene assay showed that H19 directly targeted and inhibited miR-140-5p to promote tenogenic differentiation. Further, inhibiting miR-140-5p directly increased VEGFA expression, revealing a novel regulatory axis between H19, miR-140-5p, and VEGFA in modulating tenogenic differentiation. In rats with RTC, implantation of H19-overexpressing TDSCs at the lesion promoted tendon healing and functional recovery. In general, the data suggest that H19 promotes tenogenic differentiation and tendon-bone healing by targeting miR-140-5p and increasing VEGFA levels. Modulation of the H19/miR-140-5p/VEGFA axis in TDSCs is a new potential strategy for clinical treatment of tendon injury.

Basic Research on Tendon Repair: Strategies, Evaluation, and Development

Tendon is a fibro-elastic structure that links muscle and bone. Tendon injury can be divided into two types, chronic and acute. Each type of injury or degeneration can cause substantial pain and the loss of tendon function. The natural healing process of tendon injury is complex. According to the anatomical position of tendon tissue, the clinical results are different. The wound healing process includes three overlapping stages: wound healing, proliferation and tissue remodeling. Besides, the healing tendon also faces a high re-tear rate. Faced with the above difficulties, management of tendon injuries remains a clinical problem and needs to be solved urgently. In recent years, there are many new directions and advances in tendon healing. This review introduces tendon injury and sums up the development of tendon healing in recent years, including gene therapy, stem cell therapy, Platelet-rich plasma (PRP) therapy, growth factor and drug therapy and tissue engineering. Although most of these therapies have not yet developed to mature clinical application stage, with the repeated verification by researchers and continuous optimization of curative effect, that day will not be too far away.

Biologics in the Treatment of Achilles Tendon

The treatment of Achilles tendinitis from conservative to minimally invasive to surgery gives patients a wide range of treatment options for this common pathology. The use and role of biologics to augment this treatment is emerging. The use of biologics may enhance the healing potential of the Achilles tendon when conservative treatment fails. There are a handful of biologics being investigated to obtain if improved outcomes can be maximized.

In Vitro Innovation of Tendon Tissue Engineering Strategies

Tendinopathy is the term used to refer to tendon disorders. Spontaneous adult tendon healing results in scar tissue formation and fibrosis with suboptimal biomechanical properties, often resulting in poor and painful mobility. The biomechanical properties of the tissue are negatively affected. Adult tendons have a limited natural healing capacity, and often respond poorly to current treatments that frequently are focused on exercise, drug delivery, and surgical procedures. Therefore, it is of great importance to identify key molecular and cellular processes involved in the progression of tendinopathies to develop effective therapeutic strategies and drive the tissue toward regeneration. To treat tendon diseases and support tendon regeneration, cell-based therapy as well as tissue engineering approaches are considered options, though none can yet be considered conclusive in their reproduction of a safe and successful long-term solution for full microarchitecture and biomechanical tissue recovery. In vitro differentiation techniques are not yet fully validated. This review aims to compare different available tendon in vitro differentiation strategies to clarify the state of art regarding the differentiation process.

Flexor Tendon: Development, Healing, Adhesion Formation, and Contributing Growth Factors

Management of flexor tendon injuries of the hand remains a major clinical problem. Even with intricate repair, adhesion formation remains a common complication. Significant progress has been made to better understand the mechanisms of healing and adhesion formation. However, there has been slow progress in the clinical prevention and reversal of flexor tendon adhesions. The goal of this article is to discuss recent literature relating to tendon development, tendon healing, and adhesion formation to identify areas in need of further research. Additional research is needed to understand and compare the molecular, cellular, and genetic mechanisms involved in flexor tendon morphogenesis, postoperative healing, and mechanical loading. Such knowledge is critical to determine how to improve repair outcomes and identify new therapeutic strategies to promote tissue regeneration and prevent adhesion formation.

Biologics in the Treatment of Achilles Tendon Pathologies

Regenerative medicine is gaining more and more space for the treatment of Achilles pathologic conditions. Biologics could play a role in the management of midportion Achilles tendinopathy as a step between conservative and surgical treatment or as an augmentation. Higher-level studies are needed before determining a level of treatment recommendation for biologic strategies for insertional Achilles tendinopathy. Combining imaging with patient's functional requests could be the way to reach a protocol for the use of biologics for the treatment of midportion Achilles tendinopathy and, for this perspective, the authors describe the Foot and Ankle Reconstruction Group algorithm of treatment.

Ultrasound Evaluation of Anti-Vascular Endothelial Growth Factor-Induced Changes in Vascular Response Following Tendon Injury

While vascular ingrowth is necessary for tendon healing, hypervascularization following tendon injury is not always believed to be beneficial, and there is now evidence showing beneficial results of anti-angiogenic treatments in the context of tendon healing. However, the dose-dependency of anti-angiogenic-altered vascular response, as well as methods for evaluating these changes in vivo, has not been fully investigated. Therefore, the objective of this study was to evaluate if in vivo ultrasound imaging can detect dose-dependent, anti-angiogenic treatment-induced changes in vascularity in rat Achilles tendon after injury. Color Doppler ultrasound revealed an increase in vascularity in a low-dosage group, while photoacoustic imaging demonstrated a decrease in vascularity in mid- and high-dosage groups. Histologic staining supported the decrease in vascularity observed in the mid-dosage group. This study demonstrates dose-dependent vascular alterations from the delivery of an anti-angiogenic factor after tendon injury that can be detected through ultrasound imaging methods.

Limiting angiogenesis to modulate scar formation

Angiogenesis, the process of new blood vessel formation from existing blood vessels, is a key aspect of virtually every repair process. During wound healing an extensive, but immature and leaky vascular plexus forms which is subsequently reduced by regression of non-functional vessels. More recent studies indicate that uncontrolled vessel growth or impaired vessel regression as a consequence of an excessive inflammatory response can impair wound healing, resulting in scarring and dysfunction. However, in order to elucidate targetable factors to promote functional tissue regeneration we need to understand the molecular and cellular underpinnings of physiological angiogenesis, ranging from induction to resolution of blood vessels. Especially for avascular tissues (e.g. cornea, tendon, ligament, cartilage, etc.), limiting rather than boosting vessel growth during wound repair potentially is beneficial to restore full tissue function and may result in favourable long-term healing outcomes.

Acute and Long-Term Effects of Mechanotherapy on the Outcome After an Achilles Repair: A Prospective Cohort Study With Historical Controls

OBJECTIVES

To evaluate the effects of vibration on Achilles' tendon microcirculation and characteristics following surgical repair of Achilles' tendon rupture.

DESIGN

Cohort study with historical controls.

SETTING

A university institute.

PARTICIPANTS

Participants (N=32), including 19 (16 men, 3 women; median [range] age: 43.0 [25.0-57.0] years) and 13 (10 men, 3 women; 44.00 [29.0-60.0] years) in the vibration (application to the ball of the foot, 30Hz, 2mm amplitude, 4kg pressure, and self-administration) and control groups, respectively, who underwent unilateral Achilles' tendon repairs were recruited.

INTERVENTION

A 4-week vibration intervention in the vibration group.

MAIN OUTCOME MEASUREMENTS

The tendon microcirculation was measured after the first session of vibration. The participants were evaluated repeatedly with bilateral follow-up measurements of tendon stiffness, 3 functional outcome tests, and a questionnaire survey.

RESULTS

Acute effects of the vibration were observed immediately after the 5-minute vibration (P≤.001). Lower total hemoglobin and oxygen saturation were respectively observed (P=.043) in the repaired legs 3 and 6 months postsurgery in the vibration group as compared with the control group. The vibration group also showed greater tendon stiffness, heel raising height and hopping distance 3 or 6 months postoperation in both the repaired and noninjured legs (all P<.05). The microcirculatory characteristics 2 months postoperation were correlated with the outcomes at 6 months postoperation.

CONCLUSIONS

Differences in microcirculatory characteristics and better rehabilitation outcomes were observed in the legs with an Achilles repair that underwent the early vibration intervention.

Biologic and mechanical aspects of tendon fibrosis after injury and repair

Tendon injuries of the hand that require surgical repair often heal with excess scarring and adhesions to adjacent tissues. This can compromise the natural gliding mechanics of the flexor tendons in particular, which operate within a fibro-osseous tunnel system similar to a set of pulleys. Even combining the finest suture repair techniques with optimal hand therapy protocols cannot ensure predictable restoration of hand function in these cases. To date, the majority of research regarding tendon injuries has revolved around the mechanical aspects of the surgical repair (i.e. suture techniques) and postoperative rehabilitation. The central principles of treatment gleaned from this literature include using a combination of core and epitendinous sutures during repair and initiating motion early on in hand therapy to improve tensile strength and limit adhesion formation. However, it is likely that the best clinical solution will utilize optimal biological modulation of the healing response in addition to these core strategies and, recently, the research in this area has expanded considerably. While there are no proven additive biological agents that can be used in clinical practice currently, in this review, we analyze the recent literature surrounding cytokine modulation, gene and cell-based therapies, and tissue engineering, which may ultimately lead to improved clinical outcomes following tendon injury in the future.

Selectively activated PRP exerts differential effects on tendon stem/progenitor cells and tendon healing

To understand the variable efficacy with platelet rich plasma (PRP) treatments for tendon injury, we determined the differential effects of proteinase-activated receptor (PAR)1- or PAR4-activated PRP (PAR1-PRP, PAR4-PRP) from humans on human patellar tendon stem/progenitor cells (TSCs) and tendon healing. We show that PAR1-PRP released VEGF, whereas PAR4-PRP released endostatin. Treatment of TSCs with PAR1-PRP increased collagen I expression and matrix metalloproteinase-1 (MMP-1), but cells treated with PAR4-PRP increased less collagen I and higher MMP-2 expression. The wound area treated with PAR4-PRP formed tendon-like tissues with well-organized collagen fibers and fewer blood vessels, while PAR1-PRP treatment resulted in the formation of blood vessels and unhealed tissues. These findings indicate that differential activation of PRP leads to different effects on TSCs and tendon healing. We suggest that based on acute or chronic type of tendon injury, selective activation of PRP should be applied in clinics in order to treat injured tendons successfully.

Growth Factor and Intense Pulse Light in Flexor Tendon Repair: A Biomechanical Study at Strength and Gap Resistance

BACKGROUND

Flexor tendon injuries are extremely common and they are usually the result of incised traumatic glass or knife injury. The process of tendon healing is a complicated and exceptionally-regimented mechanism that is originated and monitored by a vast number of diverse molecules. One of the most pivotal groups of mediators that are crucial to the healing process are growth factors (GF). Intense pulse light (IPL) can lead to evidence of new collagen formation with associated clinical improvement in tissue healing. The biological benefit of Intense pulse light (IPL) relies on judicious photothermolysis, where heat driven radiation is dissipated and focused at the cellular level. The aims of this study is to set out the effect of growth factor and IPL on healing following a tendon repair.

METHODS

Bovine common digital extensor tendons (CDET) were used as an ex vivo model. 44 tendon repairs were performed by the lead author using 2.5 × magnification loupes and standard instruments. Clamped tendons were assigned into the following groups; control, IPL, GF, IPL and GF. After culturing, biomechanical testing was carried out using monotonic tensile testing with displacement-controlled uniaxial tension to failure.

RESULTS

The mean values for ultimate tensile stress (UTS) for the control group was 53.51 N, for IPL it was 51.15 N, for growth factor was 70.10 N and for combined growth factor and IPL it was 75.16 N.

CONCLUSIONS

This study showed significant improvement in UTS when repaired tendons were cultured with growth factor compared to control and IPL. This would suggest a biomechanical advantage for tendon healing.

Platelet-Rich Plasma Promotes Migration, Proliferation, and the Gene Expression of Scleraxis and Vascular Endothelial Growth Factor in Paratenon-Derived Cells In Vitro

Background:

Platelet-rich plasma (PRP) is a treatment option for tendon injury because of its effective tendon-healing properties. At the early stage of tendon repair, paratenon-derived cells (PDCs) are thought to play a more important role than tendon proper–derived cells (TDCs). However, there has been no study investigating the effects of PRP on PDCs.

Hypothesis:

PRP promotes the migration, proliferation, and differentiation of PDCs in vitro.

Study Design:

Controlled laboratory study.

Methods:

TDCs and PDCs were isolated from the tendon proper and paratenon of rat Achilles tendons and were cultured to the third passage. PRP was prepared from the rats using the double-spin method. Third-passage TDCs and PDCs were cultured in Dulbecco’s modified Eagle medium with 2% fetal bovine serum (control group) or 2% fetal bovine serum plus 5% PRP (PRP group), and cell migration, proliferation, and differentiation were evaluated. The relative mRNA expression levels of scleraxis (Scx), tenomodulin (Tnmd), collagen type I alpha 1 (Col1a1), collagen type III alpha 1 (Col3a1), and vascular endothelial growth factor A (VEGF) were examined by quantitative real-time reverse transcription polymerase chain reaction.

Results:

The cell migration rate was significantly higher in the PDCs of the PRP group than in the control group (1.4-fold increase; P = 0.02). Cell proliferation was significantly higher in the PDCs of the PRP group (2.2-fold increase; P < 0.01). In the PDCs, the gene expression levels of Scx, Col1a1, and VEGF were significantly increased by PRP (Scx: 2.0-fold increase, P = 0.01; Col1a1: 5.3-fold increase, P = 0.01; VEGF: 7.8-fold increase, P = 0.01), but the gene expression level of Tnmd, a factor for tendon maturation, was significantly reduced by PRP (0.11-fold decrease; P = 0.02).

Conclusion:

In vitro PRP promoted migration, proliferation, and tenogenic differentiation with the upregulation of Scx in PDCs. PRP also upregulated the expression of the angiogenic marker VEGF.

Clinical Relevance:

Our results suggest that PRP treatment in vitro may enhance the tendon-healing properties of PDCs at the initial stage of tendon repair.

Rescue plan for Achilles: Therapeutics steering the fate and functions of stem cells in tendon wound healing

Due to the increasing age of our society and a rise in engagement of young people in extreme and/or competitive sports, both tendinopathies and tendon ruptures present a clinical and financial challenge. Tendon has limited natural healing capacity and often responds poorly to treatments, hence it requires prolonged rehabilitation in most cases. Till today, none of the therapeutic options has provided successful long-term solutions, meaning that repaired tendons do not recover their complete strength and functionality. Our understanding of tendon biology and healing increases only slowly and the development of new treatment options is insufficient. In this review, following discussion on tendon structure, healing and the clinical relevance of tendon injury, we aim to elucidate the role of stem cells in tendon healing and discuss new possibilities to enhance stem cell treatment of injured tendon. To date, studies mainly apply stem cells, often in combination with scaffolds or growth factors, to surgically created tendon defects. Deeper understanding of how stem cells and vasculature in the healing tendon react to growth factors, common drugs used to treat injured tendons and promising cellular boosters could help to develop new and more efficient ways to manage tendon injuries.

Tendinopathy: injury, repair, and current exploration

Both acute and chronic tendinopathy result in high morbidity, requiring management that is often lengthy and expensive. However, limited and conflicting scientific evidence surrounding current management options has presented a challenge when trying to identify the best treatment for tendinopathy. As a result of shortcomings of current treatments, response to available therapies is often poor, resulting in frustration in both patients and physicians. Due to a lack of understanding of basic tendon-cell biology, further scientific investigation is needed in the field for the development of biological solutions. Optimization of new delivery systems and therapies that spatially and temporally mimic normal tendon physiology hold promise for clinical application. This review focuses on the clinical importance of tendinopathy, the structure of healthy tendons, tendon injury, and healing, and a discussion of current approaches for treatment that highlight the need for the development of new nonsurgical interventions.

Molecular Biology of Flexor Tendon Healing in Relation to Reduction of Tendon Adhesions

Tendon injuries are encountered after major and minor hand trauma. Despite meticulous repair technique, adhesion formation can occur, limiting recovery. Although a great deal of progress has been made toward understanding the mechanism of tendon healing and adhesions, clinically applicable solutions to prevent adhesions remain elusive. The goal of this paper is to review the most recent literature relating to the tendon healing and adhesion prevention.

Tendon injuries: Basic science and new repair proposals

Tendons connect muscles to bones, ensuring joint movement. With advanced age, tendons become more prone to degeneration followed by injuries. Tendon repair often requires lengthy periods of rehabilitation, especially in elderly patients. Existing medical and surgical treatments often fail to regain full tendon function.

The development of novel treatment methods has been hampered due to limited understanding of basic tendon biology. Recently, it was discovered that tendons, similar to other mesenchymal tissues, contain tendon stem/progenitor cells (TSPCs) which possess the common stem cell properties.

The current strategies for enhancing tendon repair consist mainly of applying stem cells, growth factors, natural and artificial biomaterials alone or in combination. In this review, we summarise the basic biology of tendon tissues and provide an update on the latest repair proposals for tendon tears.

Cite this article: EFORT Open Rev 2017;2:332-342. DOI: 10.1302/2058-5241.2.160075

Characteristics of Intratendinous Microcirculation Shortly After an Achilles Rupture and Subsequent Treatment Outcomes

BACKGROUND

Early microcirculatory responses after experimental tenotomy are critical to the healing of tendons and their ultimate tensile strength. The effects of changes in microcirculation on the outcomes of tendon healing, however, have not been determined.

OBJECTIVES

To assess microcirculation values in injured Achilles tendons in the first 3 months after surgical repair and to correlate the inter-limb microcirculatory changes with functional outcomes at 3 and 6 months after surgery.

DESIGN

Case-control study.

SETTING

A university sports physiotherapy laboratory.

PARTICIPANTS

Thirteen subjects (median age: 45 years; range: 34.8-51.9 years) with a repaired Achilles tendon were recruited.

METHODS OR INTERVENTION

Surgical repair.

MAIN OUTCOME MEASUREMENTS

Measurements were obtained at 1, 2, 3, and 6 months after surgery. Bilateral measurements of tendon microcirculation (total hemoglobin [THb] and oxygen saturation [StO₂]) were recorded at the first 3 time points, whereas outcome measures of a Taiwan Chinese version of the Victorian Institute of Sport Assessment Scale-Achilles questionnaire, one-leg hopping distance, the star excursion balance test, and the heel raise index were conducted at the third and fourth time points. Correlations between the inter-limb microcirculatory changes, eg, between the measurements at 2 months and 1 month (2-1) after surgery, at 3 months and 2 months (3-2) after surgery, and at 3 months and 1 month (3-1) after surgery, and the outcome measures were investigated.

RESULTS

Compared with the noninjured tendons, the repaired Achilles demonstrated greater THb (at 1, 2, and 3 months; P = .017, .008, and .012 respectively) and StO₂ (at 3 months; P = .017). Furthermore, the THb2-1 and THb3-2, StO₂ 2-1, and StO₂ 3-2 showed correlations with the heel raise index, differences in the star excursion balance test and one-leg hopping distance between the noninjured leg and injured leg, and Taiwan Chinese version of the Victorian Institute of Sport Assessment Scale-Achilles questionnaire scores (rho -0.921 to 0.855).

CONCLUSIONS

Changes in the inter-limb microcirculation shortly after Achilles repair were correlated with subsequent symptoms and functional symmetry.

LEVEL OF EVIDENCE

III.

Autologous leukocyte-reduced platelet-rich plasma therapy for Achilles tendinopathy induced by collagenase in a rabbit model

Leukocyte-reduced platelet-rich plasma (LR-PRP) is a therapy for tendinopathy of the Achilles tendon (TAT); however, there is scarce information regarding LR-PRP effects in rabbit models of TAT. We compared, at 4 and 12 weeks (w), the LR-PRP and placebo (PBS) effects on ultrasonography, histology and relative gene expression of collagen types I (COL1A1) and III (COL3A1) and vascular endothelial growth factor (VEGF) in 24 rabbits with TAT induced by collagenase. The rabbits (treated with both treatments) were euthanatised after either 4 or 12 w. A healthy group (HG (n = 6)) was included. At 4 and 12 w, the LR-PRP group had a no statistically different histology score to the HG. At w 4, the COL1A1 expression was significantly higher in the LR-PRP group when compared to HG, and the expression of COL3A1from both LR-PRP and PBS-treated tendons was significantly higher when compared to the HG. At w 12, the expression of COL3A1 remained significantly higher in the PBS group in comparison to the LR-PRP group and the HG. At w 4, the LR-PRP group presented a significantly higher expression of VEGF when compared to the PBS group and the HG. In conclusion, LR-PRP treatment showed regenerative properties in rabbits with TAT.

Lipogems Product Treatment Increases the Proliferation Rate of Human Tendon Stem Cells without Affecting Their Stemness and Differentiation Capability

Increasing the success rate of rotator cuff healing remains tremendous challenge. Among many approaches, the possibility of activating resident stem cells in situ, without the need to isolate them from biopsies, could represent valuable therapeutic strategy. Along this line, it has been recently demonstrated that lipoaspirate product, Lipogems, contains and produces growth-factors that may activate resident stem cells. In this study, human tendon stem cells (hTSCs) from the rotator cuff were cocultured in a transwell system with the Lipogems lipoaspirate product and compared to control untreated cells in terms of cell proliferation, morphology, stem cell marker and VEGF expression, and differentiation and migration capabilities. Results showed that the Lipogems product significantly increases the proliferation rate of hTSCs without altering their stemness and differentiation capability. Moreover, treated cells increase the expression of VEGF, which is crucial for the neovascularization of the tissue during the healing process. Overall, this study supports that directly activating hTSCs with the Lipogems lipoaspirate could represent a new practical therapeutic approach. In fact, obtaining a lipoaspirate is easier, safer, and more cost-effective than harvesting cells from tendon or bone marrow biopsies, expanding them in GMP facility and then reinjecting them in the patient.

Does Diabetes Mellitus Affect Tendon Healing?

Diabetes mellitus (DM) is a metabolic disorder resulting from defective insulin production and characterized by chronic hyperglycemia. DM affects around 170 million people worldwide and its incidence is increasing globally. DM can cause a wide range of musculoskeletal disorders such as painful tendinopathies, tendon contracture, tendon rupture, and rotator cuff tear.In patients with diabetes neuropathy, diminished peripheral blood flow and decreased local angiogenesis are reported which probably are results of abnormalities in the production of collagen production, inflammatory mediators, angiogenic and growth factors and also contribute to lack of healing in damaged tissue. Abnormal or delayed wound healing is one of the main complications of both type-I and type-II DM.

Dendrimers as tunable vectors of drug delivery systems and biomedical and ocular applications

Dendrimers are large polymeric structures with nanosize dimensions (1-10 nm) and unique physicochemical properties. The major advantage of dendrimers compared with linear polymers is their spherical-shaped structure. During synthesis, the size and shape of the dendrimer can be customized and controlled, so the finished macromolecule will have a specific "architecture" and terminal groups. These characteristics will determine its suitability for drug delivery, diagnostic imaging, and as a genetic material carrier. This review will focus initially on the unique properties of dendrimers and their use in biomedical applications, as antibacterial, antitumor, and diagnostic agents. Subsequently, emphasis will be given to their use in drug delivery for ocular diseases.

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.

Biologics for tendon repair

Tendon injuries are common and present a clinical challenge to orthopedic surgery mainly because these injuries often respond poorly to treatment and require prolonged rehabilitation. Therapeutic options used to repair ruptured tendons have consisted of suture, autografts, allografts, and synthetic prostheses. To date, none of these alternatives has provided a successful long-term solution, and often the restored tendons do not recover their complete strength and functionality. Unfortunately, our understanding of tendon biology lags far behind that of other musculoskeletal tissues, thus impeding the development of new treatment options for tendon conditions. Hence, in this review, after introducing the clinical significance of tendon diseases and the present understanding of tendon biology, we describe and critically assess the current strategies for enhancing tendon repair by biological means. These consist mainly of applying growth factors, stem cells, natural biomaterials and genes, alone or in combination, to the site of tendon damage. A deeper understanding of how tendon tissue and cells operate, combined with practical applications of modern molecular and cellular tools could provide the long awaited breakthrough in designing effective tendon-specific therapeutics and overall improvement of tendon disease management.

Flexor tendon injury, repair and rehabilitation

Injuries to the flexor tendons remain among the most difficult problems in hand surgery. Historically, lacerations to the intrasynovial portion of the flexor tendons were thought to be unsuitable for primary repair. Despite continuing advances in our knowledge of flexor tendon biology, repair, and rehabilitation, good results following primary repair of flexor tendons remain challenging to achieve.

Expression of tenocyte lineage-related factors in regenerated tissue at sites of tendon defect

BACKGROUND

The healing mechanism of ruptured or injured tendons is poorly understood. To date, some lineage-specific factors, such as scleraxis and tenomodulin, have been reported as markers of tenocyte differentiation. Because few studies have focused on tenocyte lineage-related factors with respect to the repaired tissue of healing tendons, the aim of this study was to investigate their expression during the tendon healing process.

METHODS

Defects were created in the patellar tendons of rats, and the patellae and patellar tendons were harvested at 3 days and at 1, 2, 3, 6, 12, and 20 weeks after surgery. They were studied using micro-computed tomography, and paraffin-embedded sections were then prepared for histological evaluation. Reverse transcription-polymerase chain reactions were performed to analyze the expression of genes related to the tenocyte lineage, chondrogenesis, and ossification.

RESULTS

Repaired tissue became increasingly fibrous over time and contained a greater number of vessels than normal tendons, even in the later period. Safranin O staining revealed the existence of proteoglycan at 1 week and its persistence through 20 weeks. Ossification was detected in all tendons at 12 weeks. The expression of tenocyte lineage-related genes was high at 1 and 2 weeks. Chondrogenic genes were up-regulated until 6 weeks. Runt-related transcription factor 2, an osteogenic gene, was up-regulated at 20 weeks.

CONCLUSIONS

In our tendon defect model, cells participating in the tendon healing process appeared to differentiate toward tenocyte lineage only in the early phase, and chondrogenesis seemed to occur from the early phase onward. To improve tendon repair, it will be necessary to promote and maintain tenogenesis and to inhibit chondrogenesis, especially in the early phase, in order to avoid erroneous differentiation of stem cells.

Gene expression of catabolic inflammatory cytokines peak before anabolic inflammatory cytokines after ACL injury in a preclinical model

Background

The response of the joint to anterior cruciate ligament (ACL) injury has not been fully characterized. In particular, the characterization of both catabolic factors, including interleukin-6 (IL-6), interleukin-8 (IL-8), and markers of ongoing tissue damage (CRP), and anabolic factors, including vascular endothelial growth factor (VEGF), transforming growth factor β-induced (TGFβI), and the presence of CD163+ macrophages, have not been well defined. In this study, we hypothesized ACL injury would catalyze both catabolic and anabolic processes and that these would have different temporal profiles of expression.

Methods

Adolescent Yucatan minipigs were subjected to ACL transection. Within the joint, gene expression levels of IL-6, IL-8, VEGF, and TGFβI were quantified in the synovium, ligament, and provisional scaffold located between the torn ligament ends at days 1, 5, 9, and 14 post-injury. Macrophage infiltration was also assessed in the joint tissues over the two week period. Serum C-reactive protein (CRP) levels were measured at multiple time points between 1 hour to 14 days after injury.

Results

Increases in IL-6 and IL-8 gene expression peaked at day 1 after injury in the synovium and ligament. CRP levels were significantly increased at day 3 before returning to pre-injury levels. VEGF and TGFβI gene expression did not significantly increase until day 9 in the synovium and were unchanged in the other tissues. CD163+ macrophages increased in the ligament and synovium until day 9.

Conclusion

Taken together, these results suggest that the response within the joint is primarily catabolic in the first three days after injury, switching to a more anabolic phase by nine days after injury. The effect of medications which alter these processes may thus depend on the timing of administration after injury.

Tendon and ligament regeneration and repair: clinical relevance and developmental paradigm

As dense connective tissues connecting bone to muscle and bone to bone, respectively, tendon and ligament (T/L) arise from the somitic mesoderm, originating in a recently discovered somitic compartment, the syndetome. Inductive signals from the adjacent sclerotome and myotome upregulate expression of Scleraxis, a key transcription factor for tenogenic and ligamentogenic differentiation. Understanding T/L development is critical to establishing a knowledge base for improving the healing and repair of T/L injuries, a high-burden disease due to the intrinsically poor natural healing response. Current treatment of the three most common tendon injuries-tearing of the rotator cuff of the shoulder, flexor tendon of the hand, and Achilles tendon-include mostly surgical repair and/or conservative approaches, including biophysical modalities such as rehabilitation and cryotherapy. Unfortunately, the fibrovascular scar formed during healing possesses inferior mechanical and biochemical properties, resulting in compromised tissue functionality. Regenerative approaches have sought to augment the injured tissue with cells, scaffolds, bioactive agents, and mechanical stimulation to improve the natural healing response. The key challenges in restoring full T/L function following injury include optimal combination of these biological agents as well as their delivery to the injury site. A greater understanding of the molecular mechanisms involved in T/L development and natural healing, coupled with the capability of producing complex biomaterials to deliver multiple biofactors with high spatiotemporal resolution and specificity, should lead to regenerative procedures that more closely recapitulate T/L morphogenesis, thereby offering future patients the prospect of T/L regeneration, as opposed to simple tissue repair.

The growth factors involved in flexor tendon repair and adhesion formation

Flexor tendon injuries remain a significant clinical problem, owing to the formation of adhesions or tendon rupture. A number of strategies have been tried to improve outcomes, but as yet none are routinely used in clinical practice. Understanding the role that growth factors play in tendon repair should enable a more targeted approach to be developed to improve the results of flexor tendon repair. This review describes the main growth factors in tendon wound healing, and the role they play in both repair and adhesion formation.

Increased vascularization during early healing after biologic augmentation in repair of chronic rotator cuff tears using autologous leukocyte- and platelet-rich fibrin (L-PRF): a prospective randomized controlled pilot trial

HYPOTHESIS

We hypothesized that arthroscopic rotator cuff repairs using leukocyte- and platelet-rich fibrin (L-PRF) in a standardized, modified protocol is technically feasible and results in a higher vascularization response and watertight healing rate during early healing.

METHODS

Twenty patients with chronic rotator cuff tears were randomly assigned to 2 treatment groups. In the test group (N = 10), L-PRF was added in between the tendon and the bone during arthroscopic rotator cuff repair. The second group served as control (N = 10). They received the same arthroscopic treatment without the use of L-PRF. We used a double-row tension band technique. Clinical examinations including subjective shoulder value, visual analog scale, Constant, and Simple Shoulder Test scores and measurement of the vascularization with power Doppler ultrasonography were made at 6 and 12 weeks.

RESULTS

There have been no postoperative complications. At 6 and 12 weeks, there was no significant difference in the clinical scores between the test and the control groups. The mean vascularization index of the surgical tendon-to-bone insertions was always significantly higher in the L-PRF group than in the contralateral healthy shoulders at 6 and 12 weeks (P = .0001). Whereas the L-PRF group showed a higher vascularization compared with the control group at 6 weeks (P = .001), there was no difference after 12 weeks of follow-up (P = .889). Watertight healing was obtained in 89% of the repaired cuffs.

DISCUSSION/CONCLUSIONS

Arthroscopic rotator cuff repair with the application of L-PRF is technically feasible and yields higher early vascularization. Increased vascularization may potentially predispose to an increased and earlier cellular response and an increased healing rate.

Bilateral quadriceps rupture: results with and without platelet-rich plasma

This article presents a 46-year-old man with bilateral atraumatic quadriceps rupture that occurred while he was descending stairs. The patient underwent surgery the day after the accident. In the left knee, quadriceps reinsertion was performed using a conventional technique. In the right knee, platelet-rich plasma (PRP), both in its liquid and semisolid patterns, was added intraoperatively. Ultrasonography and magnetic resonance imaging evaluations were performed 1, 6, and 24 months postoperatively. At 6 and 24 months postoperatively, clinical and functional evaluations also were performed. Clinical examination showed no differences between the knees, and functional scores were the same for both knees. Ultrasonographic evaluation showed bilateral persistent tendon thickening and gross echotexture abnormalities, with no side-to-side differences. Magnetic resonance imaging showed signals of vascularized granulation tissue in both knees, which was more evident in the right (PRP) knee at 1 month postoperatively, along with a better signal of scar tissue in the right knee at 6 and 24 months postoperatively. The use of PRP yielded no better clinical or functional results than the lack of its use. However, a more intense and significant reparative healing process occurred where the PRP was used, thus suggesting a more rapid completion of the healing process, although this effect seems to remain only a radiographic finding with no clinical correlation.

Augmentation of tendon healing with butyric acid-impregnated sutures: biomechanical evaluation in a rabbit model

BACKGROUND

Butyric acid (BA) has been shown to be angiogenic and to enhance transcriptional activity in tissue. These properties of BA have the potential to augment biological healing of a repaired tendon.

PURPOSE

To evaluate this possibility both biomechanically and histologically in an animal tendon repair model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A rabbit Achilles tendon healing model was used to evaluate the biomechanical strength and histological properties at 6 and 12 weeks after repair. Unilateral tendon defects were created in the middle bundle of the Achilles tendon of each rabbit, which were repaired equivalently with either Ultrabraid BA-impregnated sutures or control Ultrabraid sutures.

RESULTS

After 6 weeks, BA-impregnated suture repairs had a significantly increased (P < .0001) Young's modulus and ultimate tensile strength relative to the control suture repairs. At 12 weeks, no statistical difference was observed between these measures. The histological data at 6 weeks demonstrated significantly increased (P < .005) vessel density within 0.25 mm of the repair suture in the BA-impregnated group. There was also an associated 42% increase in the local number of myofibroblasts in the BA samples relative to the controls at this time. By 12 weeks, these differences were not observed.

CONCLUSION

Tendons repaired with BA-impregnated sutures demonstrated improved biomechanical properties at 6 weeks relative to control sutures, suggesting a neoangiogenic mechanism of enhanced healing through an increased myofibroblast presence.

CLINICAL RELEVANCE

These findings demonstrate that a relatively simple alteration of suture material may augment early tendon healing to create a stronger repair construct during this time.

Engaging stem cells for customized tendon regeneration

The need for a consistent therapeutic approach to tendon injury repair is long overdue. Patients with tendon microtears or full ruptures are eligible for a wide range of invasive and non invasive interventions, often subjectively decided by the physician. Surgery produces the best outcomes, and while studies have been conducted to optimize graft constructs and to track outcomes, the data from these studies have been inconclusive on the whole. What has been established is a clear understanding of healthy tendon architecture and the inherent process of healing. With this knowledge, tissue regeneration efforts have achieved immense progress in scaffold design, cell line selection, and, more recently, the appropriate use of cytokines and growth factors. This paper evaluates the plasticity of bone-marrow-derived stem cells and the elasticity of recently developed biomaterials towards tendon regeneration efforts. Mesenchymal stem cells (MSCs), hematopoietic progenitor cells, and poly(1,8-octanediol co-citrate) scaffolds (POC) are discussed in the context of established grafting strategies. With POC scaffolds to cradle the growth of MSCs and hematopoietic progenitor cells, developing a fibroelastic network guided by cytokines and growth factors may contribute towards consistent graft constructs, enhanced functionality, and better patient outcomes.

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.

The role of mechanobiology in tendon healing

Mechanical cues affect tendon healing, homeostasis, and development in a variety of settings. Alterations in the mechanical environment are known to result in changes in the expression of extracellular matrix proteins, growth factors, transcription factors, and cytokines that can alter tendon structure and cell viability. Loss of muscle force in utero or in the immediate postnatal period delays tendon and enthesis development. The response of healing tendons to mechanical load varies depending on anatomic location. Flexor tendons require motion to prevent adhesion formation, yet excessive force results in gap formation and subsequent weakening of the repair. Excessive motion in the setting of anterior cruciate ligament reconstruction causes accumulation of macrophages, which are detrimental to tendon graft healing. Complete removal of load is detrimental to rotator cuff healing; yet, large forces are also harmful. Controlled loading can enhance healing in most settings; however, a fine balance must be reached between loads that are too low (leading to a catabolic state) and too high (leading to microdamage). This review will summarize existing knowledge of the mechanobiology of tendon development, homeostasis, and healing.

Growth factor and protease expression during different phases of healing after rabbit deep flexor tendon repair

The purpose of the study was to contribute to the mapping of molecular events during flexor tendon healing, in particular the growth factors insulin-like growth factor-1 (IGF-1), vascular endothelial growth factor (VEGF) and nerve growth factor (NGF), matrix metalloproteinases (MMP-3 and MMP-13) and their inhibitors (tissue inhibitors of metalloproteinases, TIMP-1 and TIMP-3, and the protease cathepsin K. In a rabbit model of flexor tendon injury, the mRNA expression for the growth factors, MMPs and TIMPs were measured in tendon and tendon sheath tissue at several time points (3, 6, 21, and 42 days) representing different phases of the healing process. We found that MMP-13 remained increased during the study period, whereas MMP-3 returned to normal levels within the first week after injury. TIMP-3 was down-regulated in the tendon sheaths. Cathepsin K was up-regulated in tendons and sheaths after injury. NGF was present in both tendons and sheaths, but unaltered. IGF-1 exhibited a late increase in the tendons, while VEGF was down-regulated at the later time points. In conclusion, we have demonstrated the presence of NGF in flexor tendons. MMP-13 expression appears to play a more protracted role in flexor tendon healing than MMP-3. The relatively low levels of endogenous IGF-1 and VEGF mRNA following injury support their potential beneficial role as exogenous modulators to optimize tendon healing and strength without increasing adhesion formation.

What we should know before using tissue engineering techniques to repair injured tendons: a developmental biology perspective

Tendons connect muscles to bones, and serve as the transmitters of force that allow all the movements of the body. Tenocytes are the basic cellular units of tendons, and produce the collagens that form the hierarchical fiber system of the tendon. Tendon injuries are common, and difficult to repair, particularly in the case of the insertion of tendon into bone. Successful attempts at cell-based repair therapies will require an understanding of the normal development of tendon tissues, including their differentiated regions such as the fibrous mid-section and fibrocartilaginous insertion site. Many genes are known to be involved in the formation of tendon. However, their functional roles in tendon development have not been fully characterized. Tissue engineers have attempted to generate functional tendon tissue in vitro. However, a lack of knowledge of normal tendon development has hampered these efforts. Here we review studies focusing on the developmental mechanisms of tendon development, and discuss the potential applications of a molecular understanding of tendon development to the treatment of tendon injuries.

Tissue engineered biological augmentation for tendon healing: a systematic review

INTRODUCTION

Tendon injuries give rise to significant morbidity. In the last few decades, several techniques have been increasingly used to optimize tendon healing.

SOURCES OF DATA

We performed a comprehensive search of PubMed, Medline, Cochrane, CINAHL and Embase databases using various combinations of the commercial names of each scaffold and the keywords 'tendon', 'rotator cuff', 'supraspinatus tendon', 'Achilles tendon', 'growth factors', 'cytokines', 'gene therapy', 'tissue engineering', 'mesenchymal' and 'stem cells' over the years 1966-2009. All articles relevant to the subject were retrieved, and their bibliographies were hand searched for further references in the context to tissue-engineered biological augmentation for tendon healing.

AREAS OF AGREEMENT

Several new techniques are available for tissue-engineered biological augmentation for tendon healing, growth factors, gene therapy and mesenchimal stem cells.

AREAS OF CONTROVERSY

Data are lacking to allow definitive conclusions on the use of these techniques for routine management of tendon ailments.

GROWING POINTS

The emerging field of tissue engineering holds the promise to use new techniques for tendon augmentation and repair. Preliminary studies support the idea that these techniques can provide an alternative for tendon augmentation with great therapeutic potential.

AREAS TIMELY FOR DEVELOPING RESEARCH

The optimization strategies discussed in this article are currently at an early stage of development. Although these emerging technologies may develop into substantial clinical treatment options, their full impact needs to be critically evaluated in a scientific fashion.

Autologous Growth Factors: A Biological Treatment in Sports Medicine

Autologous growth factors have been used in maxillofacial and plastic surgery since the 1990s. The use of preparations rich in growth factors has seen an increase in sports medicine is due to its potential to enhance muscle, tendon, ligament and cartilage healing, and thereby accelerating an athlete's functional return to play. The efficacy of these autologous preparations rich in growth factors has seen varying healing effects for ligament, tendon, muscle, and cartilage injuries. Current clinical evidence is in its infancy with mainly animal and retrospective human studies, but the use of preparations rich in growth factors has increased, given its favourable safety profile and efficient preparation and delivery systems. It is important for physicians to keep abreast with the latest available preparation devices and current clinical evidence looking into the effects of autologous growth factors on tendon, ligament, muscle and cartilage healing.

Molecular events of cellular apoptosis and proliferation in the early tendon healing period

PURPOSE

Cellular proliferation is accompanied by cellular apoptosis. In the healing digital flexor tendon, molecular events concerning cellular apoptosis have not been investigated. This study aimed to investigate the relationship between cellular apoptosis and proliferation in early tendon healing.

METHODS

The flexor digitorum profundus tendons of 50 long toes in 25 chickens were transected and were repaired surgically. On postoperative days 3, 7, 14, 21, and 28, we subjected tendons to in situ terminal deoxynucleotide transferase dUTP nick end labeling (TUNEL) assay to detect apoptotic cells, immunofluorescence staining with antibodies to proliferating cell nuclear antigen to assess proliferation, and Bcl-2, an anti-apoptotic protein, to assess responses suppressive to apoptosis. The positively labeled tenocytes were counted microscopically and compared statistically. We also stained sections with hematoxylin and eosin to observe their healing status. An additional 12 tendons (6 chickens) served as day 0 controls.

RESULTS

Compared with tendons at day 0, the healing tendons had notably greater cellularity in both epitenon and endotenon areas. The total number of cells and number of TUNEL-positive cells peaked at day 3. At days 7 to 21, the number of proliferating cell nuclear antigen-positive cells peaked. At days 7 and 14, the cells positively stained with Bcl-2 peaked. At days 14 to 28, the total number of cells and TUNEL-positive cells decreased significantly compared with those at days 3 and 7, yet the numbers remained greater than those on day 0.

CONCLUSIONS

Apoptosis in the healing tendons peaks at day 3, followed about 10 days later by the peak proliferation period. Because Bcl-2 serves to inhibit apoptosis, a later increase in Bcl-2-positive cells indicates that tendon apoptosis is inhibited. These findings indicate that tenocyte apoptosis is accelerated within several days after injury, followed by increases in cellular proliferation and activation of molecular events to inhibit apoptosis in 2 to 4 weeks.