Twenty-five years of tendon and ligament research

Short-term vancomycin and buffer soaking does not change rabbit achilles tendon tensile material properties

BACKGROUND

Allograft tendons are commonly used during orthopedic surgery to reconstruct tissue that is severely damaged. Soaking the tendon in an antibiotic solution, specifically vancomycin, has been shown to lower the risk of post-operative infections. While some material properties of tendon and ligament after antibiotic soaking have previously been characterized, extensive sub-failure allograft tendon material properties after soaking in antibiotic solutions have not.

METHODS

Forty tendons were dissected from rabbits and soaked in either a phosphate buffered saline (PBS) only solution or vancomycin and PBS solution for five or 30 min. Immediately after soaking, quasi-static tensile experiments were performed in a materials testing system.

FINDINGS

Tissue nominal stress, Lagrange strain, toe-region properties and elastic modulus were characterized. For all forty tendons, the average elastic modulus was found to be 455 ± 37 MPa, the average transition strain (from toe-region to linear elastic region) was 0.0487 ± 0.0035, and the average transition stress was 9.71 ± 0.79 MPa. No statistically significant differences in any of these material properties were found across soaking medium or soaking time.

INTERPRETATION

From these results, we conclude that soaking an allograft tendon in antibiotic solution for up to 30 min prior to implantation does not change the tensile material properties of tendons, supporting current clinical practice.

Advanced Gene Therapy Strategies for the Repair of ACL Injuries

The anterior cruciate ligament (ACL), the principal ligament for stabilization of the knee, is highly predisposed to injury in the human population. As a result of its poor intrinsic healing capacities, surgical intervention is generally necessary to repair ACL lesions, yet the outcomes are never fully satisfactory in terms of long-lasting, complete, and safe repair. Gene therapy, based on the transfer of therapeutic genetic sequences via a gene vector, is a potent tool to durably and adeptly enhance the processes of ACL repair and has been reported for its workability in various experimental models relevant to ACL injuries in vitro, in situ, and in vivo. As critical hurdles to the effective and safe translation of gene therapy for clinical applications still remain, including physiological barriers and host immune responses, biomaterial-guided gene therapy inspired by drug delivery systems has been further developed to protect and improve the classical procedures of gene transfer in the future treatment of ACL injuries in patients, as critically presented here.

Targeting immunometabolism of neoplasms by interleukins: A promising immunotherapeutic strategy for cancer treatment

In recent years, tumor metabolism has become a prevalent research topic for scientists and pharmaceutical companies. As research in the field has progressed, the metabolism-based therapy of tumors has ushered in new opportunities. Most tumors emerge and evolve under selective pressure from their microenvironment, which promotes the diversification of both neoplastic and non-neoplastic compartments of the tumor microenvironment (TME), and finally reaches a certain degree of intratumoral heterogeneity. As a result of the tumor intratumoral heterogeneity, tumor cells often possess a complex energy metabolism phenotype. During tumor progression, the metabolism for both tumor parenchyma and stroma is reprogrammed. The tumor stroma mainly consists of the extracellular matrix, fibroblasts, and immune cells. Interestingly, tumor-infiltrating immune cells utilize different metabolites based on their subtype and function, and these immunometabolic pathways can be modified in the TME. In particular, interleukins play a vital role in the activation and differentiation of immune cells and have exhibited multiple effects on tumor cell neoplasia, invasion, and metastasis. In this review, we summarize the common mechanisms of interleukins affecting the tumor and tumor-infiltrating immune cells metabolically and discuss how these mechanisms may lead to novel therapeutic opportunities. This review might contribute to the novel development of cancer immunotherapy.

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

Background

Animal models are one of the first steps in translation of basic science findings to clinical practice. For tendon healing research, transgenic mouse models are important to advance therapeutic strategies. However, the small size of the structures complicates surgical approaches, histological assessment, and biomechanical testing. In addition, available models are not standardized and difficult to compare. How surgery itself affects the healing outcome has not been investigated yet. The focus of the study was to develop a procedure that includes a transection and microsurgical reconstruction of the Achilles tendon but, unlike other models, preserves the sciatic nerve. We wanted to examine how distinct parts of the technique influenced healing.

Methods

For this animal model study, we used 96 wild-type male C57BL/6 mice aged 8–12 weeks. We evaluated different suture techniques and macroscopically confirmed the optimal combination of suture material and technique to minimize tendon gap formation. A key element is the detailed, step-by-step illustration of the surgery. In addition, we assessed histological (Herovici and Alcian blue staining) outcome parameters at 1–16 weeks postoperatively. Microcomputed tomography (micro-CT) was performed to measure the bone volume of heterotopic ossifications (HOs). Biomechanical analyses were carried out using a viscoelastic protocol on the biomechanical testing machine LM1.

Results

A modified 4-strand suture combined with a cerclage for immobilization without transection of the sciatic nerve reliably eliminated gap formation. The maximal dorsal extension of the hindlimb at the upper ankle joint from the equinus position (limited by the immobilization cerclage) increased over time postoperatively (operation: 28.8 ± 2.2°; 1 week: 54 ± 36°; 6 weeks: 80 ± 11.7°; 16 weeks: 96 ± 15.8°, p > 0.05). Histological staining revealed a maturation of collagen fibres within 6 weeks, whereas masses of cartilage were visible throughout the healing period. Micro-CT scans detected the development of HOs starting at 4 weeks and further progression at 6 and 16 weeks (bone volume, 4 weeks: 0.07604 ± 0.05286 mm³; 6 weeks: 0.50682 ± 0.68841 mm³; 16 weeks: 2.36027 ± 0.85202 mm³, p > 0.001). In-depth micro-CT analysis of the different surgical elements revealed that an injury of the tendon is a key factor for the development of HOs. Immobilization alone does not trigger HOs. Biomechanical properties of repaired tendons were greatly altered and remained inferior 6 weeks after surgery.

Conclusion

With this study, we demonstrated that the microsurgical technique greatly influences the short- and longer-term healing outcome. When the sciatic nerve is preserved, the best surgical reconstruction of the tendon defect is achieved by a 4-strand core suture in combination with a tibiofibular cerclage for postoperative immobilization. The cerclage promotes a gradual increase in the range of motion of the upper ankle joint, comparable with an early mobilization rehabilitation protocol. HO, as a key mechanism for poor tendon healing, is progressive and can be monitored early in the model.

The translational potential of this article

The study enhances the understanding of model dependent factors of healing. The described reconstruction technique provides a reproducible and translational rodent model for future Achilles tendon healing research. In combination with transgenic strains, it can be facilitated to advance therapeutic strategies to improve the clinical results of tendon injuries.

Appropriate Tensile Mode and Timing of Applying Tension to Promote Tendon Gel Regeneration

"Tendon gel" secreted from a parent tendon is regenerated for tendon repair by applying tension. However, the details of the tensile stimulus have not been clarified. This study aimed to evaluate an appropriate tensile stimulus mode and the optimal timing of applying tension to promote tendon gel regeneration. Tendon gel was prepared using a film model method in mice and was preserved in vivo for 3, 5, and 10 days. Unlike tendon gel on day 3 or day 5, a fibrous structure developed in the tendon gel on day 10 when tension was applied. Infrared spectroscopy revealed that characteristic peaks appearing for the tendon gel on days 3 and 5 disappeared on day 10. Disappearance of the peaks indicated maturity of the tendon gel, and it showed the optimal timing for tension application to the tendon gel. The effect of tensile load on tendon gel preserved for 10 days was investigated using a tensile test, a creep test, or a cycle test. In the tensile test, tendon gel was elongated into a thin cord of collagen fibers with an increase in stress, and the maximum diameter of the collagen fiber was approximately 50 times larger than that in the normal Achilles tendon of mice. The results suggest that the diameter of the oriented collagen fiber is controllable by adjusting the applied load and the time in mature tendon gel.

The effect of age on hamstring passive properties after a 10-week stretch training

[Purpose] Degenerative changes take place in the musculoskeletal system of elderly people, resulting in a reduced range of motion. For this reason, stretch training is recommended for elderly individuals. To date, there have been no studies of the adaptations of the passive properties of muscles following long-term stretch training. The aim of this study is to investigate the hamstring elasticity of elderly people following a 10-week stretch training and compare the results to a younger cohort. [Subjects and Methods] The experimental groups consisted of 15 younger (24.0 ± 4.0 years) and 14 older (65.1 ± 7.9 years) individuals. Both experimental groups undertook a standardised 10-week static passive hamstring stretch training. Passive properties of the hamstring were measured with an instrumented Straight Leg Raise Test. [Results] After a 10-week stretch training, there were increases in range of motion, passive resistive force and passive elastic energy in both age groups. Passive elastic stiffness decreased. Changes of hamstring passive properties did not differ significantly between age groups after a 10-week stretch training. [Conclusion] Increasing age has a negative effect on muscle passive properties, but older individuals benefit from regular stretch training, just as younger individuals do.

Unveil the mysterious mask of cytokine-based immunotherapy for melanoma

Melanoma is the leading cause of death among all skin cancers and its incidence continues to rise rapidly worldwide in the past decades. The available treatment options for melanoma remain limited despite extensive clinical research. Melanoma is an immunogenic tumor and great advances in immunology in recent decades allow for the development of immunotherapeutic agents against melanoma. In recent years, immunotherapy utilizing cytokines has been particularly successful in certain cancers and holds promise for patients with advanced melanoma. In this review, an overview of the current status and emerging perspectives on cytokine immunotherapy for melanoma are discussed in details. Such a study will be helpful to unveil the mysterious mask of cytokine-based immunotherapy for melanoma.

On the accuracy and fitting of transversely isotropic material models

Fiber reinforced structures are central to the form and function of biological tissues. Hyperelastic, transversely isotropic material models are used widely in the modeling and simulation of such tissues. Many of the most widely used models involve strain energy functions that include one or both pseudo-invariants (I4 or I5) to incorporate energy stored in the fibers. In a previous study we showed that both of these invariants must be included in the strain energy function if the material model is to reduce correctly to the well-known framework of transversely isotropic linear elasticity in the limit of small deformations. Even with such a model, fitting of parameters is a challenge. Here, by evaluating the relative roles of I4 and I5 in the responses to simple loadings, we identify loading scenarios in which previous models accounting for only one of these invariants can be expected to provide accurate estimation of material response, and identify mechanical tests that have special utility for fitting of transversely isotropic constitutive models. Results provide guidance for fitting of transversely isotropic constitutive models and for interpretation of the predictions of these models.

From repair to regeneration: biomaterials to reprogram the meniscus wound microenvironment

When the field of tissue engineering first arose, scaffolds were conceived of as inert three-dimensional structures whose primary function was to support cellularity and tissue growth. Since then, advances in scaffold and biomaterial design have evolved to not only guide tissue formation, but also to interact dynamically with and manipulate the wound environment. At present, these efforts are being directed towards strategies that directly address limitations in endogenous wound repair, with the goal of reprogramming the local wound environment (and the cells within that locality) from a state that culminates in an inferior tissue repair into a state in which functional regeneration is achieved. This review will address this approach with a focus on recent advances in scaffold design towards the resolution of tears of the knee meniscus as a case example. The inherent limitations to endogenous repair will be discussed, as will specific examples of how biomaterials are being designed to overcome these limitations. Examples will include design of fibrous scaffolds that promote colonization by modulating local extracellular matrix density and delivering recruitment factors. Furthermore, we will discuss scaffolds that are themselves modulated by the wound environment to alter porosity and modulate therapeutic release through precise coordination of scaffold degradation. Finally, we will close with emerging concepts in local control of cell mechanics to improve interstitial cell migration and so advance repair. Overall, these examples will illustrate how emergent features within a biomaterial can be tuned to manipulate and harness the local tissue microenvironment in order to promote robust regeneration.

Tendon response to pharmaco-mechanical stimulation of the chronically retracted rotator cuff in sheep

PURPOSE

Chronic tearing of tendons is associated with molecular and structural alterations causing biomechanical changes, which compromise musculotendinous function and become limiting factors for tendon repair. This study investigated the histological response of chronically retracted sheep rotator cuff tendons to mechanical and pharmacological stimulation in view of tendon repair.

METHODS

Sixteen weeks after experimental release of the infraspinatus tendon in 20 sheep, the retracted musculotendinous unit was subjected to continuous traction either with [anabolic steroids (nandrolone) group/insulin-like growth factor (IGF) group] or without (control group) additional pharmacological treatment during 6 weeks. A new degeneration score for tendinous tissues (DSTT), based on established knowledge on histological changes associated with tendon degeneration, was used for histological analysis at the time of tendon release, at the beginning of continuous re-lengthening and at repair in all animals.

RESULTS

The DSTT score (inter-observer correlation: r = 0.83), quantifiably representing tendon degeneration, improved from 15.5 (SD 1.3) points before to 9.8 (SD 3.8) points after re-lengthening. It improved in a qualitatively and quantitatively similar fashion if pharmacological stimulation was added. The nandrolone group improved from 13.7 (SD 1.6) to 9.8 (SD 1.9) and the IGF group from 13.3 (SD 3.6) to 8.8 (SD 1.8) points.

CONCLUSION

Mechanical stimulation significantly reduced tissue degeneration. However, the addition of a pharmacological stimulation with anabolic steroids or IGF had neither a measurable positive nor negative effect on the degenerative process. Therefore, this investigation does neither support the additional pharmacological use of the anabolic steroid nandrolone or of IGF decanoate for restoration of tendon degeneration, nor otherwise provide evidence for additional tendon damage, if those substances are used to alter the muscular metabolism.

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.

Co-cultured tissue-specific scaffolds for tendon/bone interface engineering

The tendon/ligament-to-bone interface has a complex organization to enable transfer of forces through the tendon/ligament to the bone. The purpose of this study is to create a co-culture environment enabling a tissue-specific tendon region and tissue-specific bone region on a degradable scaffold, using NIH 3T3 fibroblast–deposited extracellular matrix and MC 3T3 osteoblast–deposited extracellular matrix, respectively. Before full characterization of the deposited extracellular matrix coating can be analyzed, co-culture parameters including culture medium and seeding technique should be addressed. An appropriate medium formulation was developed to reduce fibroblast to osteoblast mineralization by adjusting beta-glycerophosphate concentrations. Standard growth medium with fetal bovine serum + 3 mM beta-glycerophosphate + 25 µg/mL ascorbic acid was found to be the most suitable formulation evaluated in these study conditions. Seeding and cell migration studies of co-cultured fibroblast- and osteoblast-specific scaffolds were performed to identify whether tissue regions could be created on the scaffold. Fibroblast and osteoblast regions were successfully seeded and little to no cell migration was observed up to 42 h after seeding. Finally, a preliminary analysis of basic extracellular matrix components was measured in the fibroblast, osteoblast, and transition regions. Tissue-specific DNA, glycosaminoglycan, and collagen were found in uniform amounts on the scaffolds and were not different significantly between scaffold regions. In conclusion, initial steps to create tissue-specific fibroblast and osteoblast regions on a degradable scaffold were successful in preparation for further characterization investigations as a tendon-to-bone interface scaffold.

Endoscopic functional imaging of partial tendon tears--proof of concept and intraoperative feasibility

The ability to quantify the biomechanical integrity of tendons could provide useful information for both clinical diagnostics and for clinical follow-up in tracking functional recovery of the injured tissue. This study develops and characterizes a functional endoscopy approach for intraoperative quantification of tendon tear severity using both ex vivo and in vivo experimental models. We first verified the accuracy of endoscopic strain (i.e., tissue stretch) imaging in an ex vivo tear model by comparing endoscopic measurements against gold standard measurements with research grade optics. We then tested in vivo feasibility by endoscopically quantifying altered tissue strain distributions in a rat supraspinatus model of partial tendon tear. The endoscopic method was able to achieve diagnostically relevant levels of accuracy compared to research grade optics (mean error = 26.2 ± 19.1%), and tissue strain analysis could sensitively discern torn tendon subregions. Applying this approach to free-hand in vivo endoscopic strain measurements, we were similarly able to discern functional changes in partially torn tendons (average maximum principal strains surrounding the lesion: 5.1 ± 2.9% versus intact controls: 1.9 ± 1.4%; p = 0.023). These findings indicate that the functional endoscopic assessment of tendon mechanical integrity is not only possible but could potentially offer intraoperative arthroscopic guidance for management of tendon tears in man.

Effects of mechanical strain on human mesenchymal stem cells and ligament fibroblasts in a textured poly(L-lactide) scaffold for ligament tissue engineering

The purpose of this study was to prove the effect of cyclic uniaxial intermittent strain on the mRNA expression of ligament-specific marker genes in human mesenchymal stem cells (MSC) and anterior cruciate ligament-derived fibroblasts (ACL-fibroblasts) seeded onto a novel textured poly(L-lactide) scaffold (PLA scaffold). Cell-seeded scaffolds were mechanically stimulated by cyclic uniaxial stretching. The expression of ligament matrix gene markers: collagen types I and III, fibronectin, tenascin C and decorin, as well as the proteolytic enzymes matrix metalloproteinase MMP-1 and MMP-2 and their tissue specific inhibitors TIMP-1 and TIMP-2 was investigated by analysing the mRNA expression using reverse transcriptase polymerase chain reaction and related to the static control. In ACL-fibroblasts seeded on PLA, mechanical load induced up-regulation of collagen types I and III, fibronectin and tenascin C. No effect of mechanical stimulation on the expression of ligament marker genes was found in undifferentiated MSC seeded on PLA. The results indicated that the new textured PLA scaffold could transfer the mechanical load to the ACL-fibroblasts and improved their ligament phenotype. This scaffold might be suitable as a cell-carrying component of ACL prostheses.

Structure of retracted tendons after staged repair following continuous traction

PURPOSE

The effect of staged repair involving continuous re-lengthening of the retracted musculotendinous unit after rotator cuff tear is not known. We quantified changes in chronically retracted tendons undergoing no repair or a staged repair involving an initial re-lengthening of the musculotendinous unit by traction in a sheep model of massive rotator cuff tear.

MATERIALS AND METHODS

Infraspinatus tendons of 12 sheep were released and allowed to retract for 4 months. Repair was performed after the retracted musculotendinous unit had been progressively returned to its original length through continuous traction in 8 sheep (group I). In the other 4 sheep (group II) traction was not successful and the tendons remained retracted. Tendon structure was assessed macroscopically, by MRI, histology, and TEM.

RESULTS

Normalized to their contralateral controls, at sacrifice, tendon thickness was unchanged in group I (116%, n.s) and increased in group II (129%, P < 0.05), however with substantial shortening. Increased collagen fiber crimping and disorganization was found in group II, whereas in group I the differences from normal tendon were less pronounced.

CONCLUSION

Retracted musculotendinous units have deteriorated tendons, characterized by increased collagen fiber crimp, and ultrastructural collagen fibril atrophy and disorganization. Continuous traction may arrest and partially restore degenerative changes in retracted tendon. The findings of this study might contribute to new approaches for the treatment of chronic "irreparable" rotator cuff tears.

Mechanisms of collagen fibril alignment in tendon injury: from tendon regeneration to artificial tendon

The process by which collagen fibrils are aligned following tendon injury remains unknown. Therefore, we analyzed the process of tendon regeneration by transmission electron microscopy, using a film model method. In mice, the Achilles tendon of medial head was transected. On day 3, after only the proximal end of the transected tendon was placed on film and kept in vivo, a translucent substance containing granules, called tendon gel, was secreted. On day 5, the granules assembled in a loose (L) layer, and coalesced tightly in a dense (D) layer, forming an L-D-L layered pattern. On day 10, granules showed high electron density in H layers, which developed into D-H-D layers on day 13. The distal end was placed on film to face the proximal end. On day 10, the tendon gel showed a D-H-D layer pattern. On day 11, mechanical stress from muscular constriction changed the tendon gel to aligned collagen fibrils (6 ± 2 nm in diameter). Thereafter, the diameter of the fibrils increased. Tendon gel harvested on day 5 or day 10 was pulled manually or by hanging weights (about 0.6 MPa). Aligned collagen fibrils (32 ± 7 nm in diameter) were created by traction using tendon gel harvested on day 10.