Functional tissue engineering of ligament healing

Loss of periostin function impairs ligament fibroblast activity and facilitates ROS-mediated cellular senescence

Anterior cruciate ligament (ACL) injuries pose a significant challenge due to their limited healing potential, often resulting in premature arthritis. The factors and mechanisms contributing to this inadequate healing process remain elusive. During the acute phase of injury, ACL tissues express elevated periostin levels that decline over time. The functional significance of periostin in ligament biology remains understudied. In this study, we investigated the functional and mechanistic implications of periostin deficiency in ACL biology, utilizing ligament fibroblasts derived from patients and a murine model of ACL rupture. Our investigations unveiled that periostin knockdown compromised fibroblast growth characteristics, hindered the egress of progenitor cells from explants, and arrested cell-cycle progression, resulting in the accumulation of cells in the G0/G1 phase and moderate apoptosis. Concurrently, a significant reduction in the expression of cell-cycle and matrix-related genes was observed. Moreover, periostin deficiency triggered apoptosis through STAT3Y705/p38MAPK signaling and induced cellular senescence through increased production of reactive oxygen species (ROS). Mechanistically, inhibition of ROS production mitigated cell senescence in these cells. Notably, in vivo data revealed that ACL in Postn-/- mice exhibited a higher tearing frequency than wild-type mice under equivalent loading conditions. Furthermore, injured ACL with silenced periostin expression, achieved through nanoparticle-siRNA complex delivery, displayed an elevated propensity for apoptosis and senescence compared to intact ACL in C57BL/6 mice. Together, our findings underscore the pivotal role of periostin in ACL health, injury, and potential for healing.

Posterior cruciate ligament repair seems safe with low failure rates but more high level evidence is needed: a systematic review

PURPOSE

To discuss recent literature on posterior cruciate ligament (PCL) repair and report on the clinical and radiological outcomes.

METHODS

A systematic review was conducted according to the PRISMA guidelines. In August 2022, three databases (PubMed, Scopus, and Cochrane Library) were searched for studies on PCL repair by two independent reviewers. Articles published between January 2000 and August 2022 focussing on the clinical and/or radiological outcomes, following PCL repair, were included. Patient demographic data, clinical evaluations, patient‑reported outcome measures, post-operative complications and radiological outcomes were extracted.

RESULTS

Nine studies met the inclusion criteria, covering 226 patients with a mean age ranging from 22.4 to 38.8 years and mean follow-up periods ranging from 14 to 78.6 months. Seven studies (77.8%) were level IV and two studies (22.2%) were level III. Arthroscopic PCL repair was performed in four studies (44.4%) while the remaining five studies (55.6%) described open PCL repair. In four studies (44.4%) additional suture augmentation was applied. Arthrofibrosis affected a combined total of 24 patients (11.7%; range 0-21.0%) making it the most common complication and the overall failure rate was 5.6%, ranging from 0 to 15.8%. Two studies (22.2%) performed post-operative MRI and confirmed PCL healing.

CONCLUSION

This systematic review indicates that PCL repair can be a safe procedure with an overall failure rate of 5.6%, ranging from 0% to 15.8%. However, more high quality research is necessary before widespread clinical implementation is warranted.

LEVEL OF EVIDENCE

IV.

Oxo-M and 4-PPBP Delivery via Multi-Domain Peptide Hydrogel Toward Tendon Regeneration

We have recently identified novel small molecules, Oxo-M and 4-PPBP, which specifically stimulate endogenous tendon stem/progenitor cells (TSCs), leading to potential regenerative healing of fully transected tendons. Here, we investigated an injectable, multidomain peptide (MDP) hydrogel providing controlled delivery of the small molecules for regenerative tendon healing. We investigated the release kinetics of Oxo-M and 4-PPBP from MDP hydrogels and the effect of MDP-released small molecules on tenogenic differentiation of TSCs and in vivo tendon healing. In vitro, MDP showed a sustained release of Oxo-M and 4-PPBP and a slower degradation than fibrin. In addition, tenogenic gene expression was significantly increased in TSC with MDP-released Oxo-M and 4-PPBP as compared to the fibrin-released. Invivo, MDP releasing Oxo-M and 4-PPBP significantly improved tendon healing, likely associated with prolonged effects of Oxo-M and 4-PPBP on suppression of M1 macrophages and promotion of M2 macrophages. Comprehensive analyses including histomorphology, digital image processing, and modulus mapping with nanoindentation consistently suggested that Oxo-M and 4-PPBP delivered via MDP further improved tendon healing as compared to fibrin-based delivery. In conclusion, MDP delivered with Oxo-M and 4-PPBP may serve as an efficient regenerative therapeutic for in situ tendon regeneration and healing.

The novel epiligament theory: differences in healing failure between the medial collateral and anterior cruciate ligaments

According to current literature, 90% of knee ligament injuries involve the medial collateral ligament or the anterior cruciate ligament. In contrast to the medial collateral ligament, which regenerates relatively well, the anterior cruciate ligament demonstrates compromised healing. In the past, there were numerous studies in animal models that examined the healing process of these ligaments, and different explanations were established. Although the healing of these ligaments has been largely investigated and different theories exist, unanswered questions persist.

Therefore, the aim of this article is 1) to review the different historical aspects of healing of the medial collateral ligament and present the theories for healing failure of the anterior cruciate ligament; 2) to examine the novel epiligament theory explaining the medial collateral ligament healing process and failure of anterior cruciate ligament healing; and 3) to discuss why the enveloping tissue microstructure of the aforementioned ligaments needs to be examined in future studies.

We believe that knowledge of the novel epiligament theory will lead to a better understanding of the normal healing process for implementing optimal treatments, as well as a more holistic explanation for anterior cruciate ligament healing failure.

The Role of Mesenchymal Stem Cells (MSCs) in Veterinary Medicine and Their Use in Musculoskeletal Disorders

Regenerative medicine is a dynamically developing field of human and veterinary medicine. The animal model was most commonly used for mesenchymal stem cells (MSCs) treatment in experimental and preclinical studies with a satisfactory therapeutic effect. Year by year, the need for alternative treatments in veterinary medicine is increasing, and other applications for promising MSCs and their biological derivatives are constantly being sought. There is also an increase in demand for other methods of treating disease states, of which the classical treatment methods did not bring the desired results. Cell therapy can be a realistic option for treating human and animal diseases in the near future and therefore additional research is needed to optimize cell origins, numbers, or application methods in order to standardize the treatment process and assess its effects. The aim of the following work was to summarize available knowledge about stem cells in veterinary medicine and their possible application in the treatment of chosen musculoskeletal disorders in dogs and horses.

Functional and Radiographic Outcomes of Intraoperatively Decreasing the Coracoclavicular Distance to 50% of the Unaffected Side in Stabilization of Acute Acromioclavicular Joint Injury: A Retrospective Evaluation

Background:

The postoperative failure rate of acromioclavicular (AC) joint fixation using the coracoclavicular (CC) stabilization technique is high. Studies have reported that compared with normal intraoperative anatomic reduction, intraoperative overreduction of the AC joint is more successful in achieving a satisfactory anatomic radiographic outcome at 1- to 2-year follow-up.

Purpose:

To evaluate the functional and radiographic outcomes and complications in patients with acute AC joint injury who underwent combined CC stabilization and AC capsular repair in which the CC distance was intraoperatively decreased to 50% of the unaffected side.

Study Design:

Case series; Level of evidence, 4.

Methods:

In this retrospective study, we collected and analyzed the data of patients with an acute AC joint injury (Rockwood type 5) who underwent combined CC stabilization and AC capsular repair during which the CC distance was decreased 50% compared with the unaffected side. At 2-year follow-up, we evaluated functional outcomes (American Shoulder and Elbow Surgeons [ASES] score), radiographic outcomes (alignment of the AC joint in the vertical and horizontal planes, tunnel widening), and complications (infection, clavicular fracture).

Results:

The study included 20 patients with a mean ± SD age of 42.20 ± 10.10 years. The mean follow-up period was 33.75 ± 11.50 months. At the 2-year follow-up, the mean ASES score was 95.13 ± 5.61. The overreduction alignment, anatomic alignment, and loss reduction alignment rates were 0% (0/20 patients), 95% (19/20 patients), and 5% (1/ 20 patients), respectively. No statistically significant difference was found in the mean CC distance between the affected and unaffected sides on radiographic evaluation. The mean medial clavicular tunnel width and lateral clavicular tunnel width were 5.03 ± 0.68 mm and 4.47 ± 0.67 mm, respectively. None of the patients experienced fractures or infections.

Conclusion:

Excellent functional and radiographic outcomes and no complications were seen at 2-year follow-up in patients with acute AC joint injury who underwent combined CC stabilization and AC capsular repair with the CC distance intraoperatively decreased to 50% of the unaffected side.

Bioinspired Scaffold Designs for Regenerating Musculoskeletal Tissue Interfaces

The musculoskeletal system works at a very advanced level of synchrony, where all the physiological movements of the body are systematically performed through well-organized actions of bone in conjunction with all the other musculoskeletal soft tissues, such as ligaments, tendons, muscles, and cartilage through tissue-tissue interfaces. Interfaces are structurally and compositionally complex, consisting of gradients of extracellular matrix components, cell phenotypes as well as biochemical compositions and are important in mediating load transfer between the distinct orthopedic tissues during body movement. When an injury occurs at interface, it must be re-established to restore its function and stability. Due to the structural and compositional complexity found in interfaces, it is anticipated that they presuppose a concomitant increase in the complexity of the associated regenerative engineering approaches and scaffold designs to achieve successful interface regeneration and seamless integration of the engineered orthopedic tissues. Herein, we discuss the various bioinspired scaffold designs utilized to regenerate orthopedic tissue interfaces. First, we start with discussing the structure-function relationship at the interface. We then discuss the current understanding of the mechanism underlying interface regeneration, followed by discussing the current treatment available in the clinic to treat interface injuries. Lastly, we comprehensively discuss the state-of-the-art scaffold designs utilized to regenerate orthopedic tissue interfaces.

Does Manual Drilling Improve the Healing of Bone-Hamstring Tendon Grafts in Anterior Cruciate Ligament Reconstruction? A Histological and Biomechanical Study in a Rabbit Model

Background:

Heat necrosis due to motorized drilling during anterior cruciate ligament (ACL) reconstruction could be a factor in delayed healing at the bone–tendon graft interface.

Hypothesis:

The process of osteointegration could be enhanced using manual drilling. It reduces the invasiveness of mechanical-thermal stress normally caused by the traditional motorized drill bit.

Study Design:

Controlled laboratory study.

Methods:

ACL reconstruction using semitendinosus tendon autografts was performed in 28 skeletally mature female New Zealand white rabbits, which were randomly divided into 3 groups. In group A (n = 12), the tunnels were drilled using a motorized device; in group B (n = 12), the tunnels were drilled using a manual drill bit; and group C (n = 4) served as a control with sham surgical procedures. The healing process in the tunnels was assessed histologically at 2, 4, 8, and 12 weeks and graded according to the Tendon–Bone Tunnel Healing (TBTH) scoring system. In addition, another 25 rabbits were used for biomechanical testing. The structural properties of the femur–ACL graft–tibia complex, from animals sacrificed at 8 weeks postoperatively, were determined using uniaxial tests. Stiffness (N/mm) and ultimate load to failure (N) were determined from the resulting load-elongation curves.

Results:

The time course investigation showed that manual drilling (group B) had a higher TBTH score and improved mechanical behavior, reflecting better organized collagen fiber continuity at the bone–fibrous tissue interface, better integration between the graft and bone, and early mineralized chondrocyte-like tissue formation at all the time points analyzed with a maximum difference at 4 weeks (TBTH score: 5.4 [group A] vs 12.3 [group B]; P < .001). Stiffness (23.1 ± 8.2 vs 17.8 ± 6.3 N/mm, respectively) and ultimate load to failure (91.8 ± 60.4 vs 55.0 ± 18.0 N, respectively) were significantly enhanced in the specimens treated with manual drilling compared with motorized drilling (P < .05 for both).

Conclusion:

The use of manual drilling during ACL reconstruction resulted in better tendon-to-bone healing during the crucial early weeks. Manual drilling was able to improve the biological and mechanical properties of bone–hamstring tendon graft healing and was able to restore postoperative graft function more quickly. Tunnel drilling results in bone loss and deficient tendon-bone healing, and heat necrosis after tunnel enlargement may cause mechanical stress, contributing to a delay in healing. Manual drilling preserved the bone stock inside the tunnel, reduced heat necrosis, and offered a better microenvironment for faster healing at the interface.

Clinical Relevance:

Based on study results, manual drilling could be used successfully in human ACL reconstruction, but further clinical studies are needed. A clinical alternative, called the original “all-inside” technique, has been developed for ACL reconstruction. In this technique, the femoral and tibial tunnels are manually drilled only halfway through the bone for graft fixation, reducing bone loss. Data from this study suggest that hamstring tendon–to–bone healing can be improved using a manual drilling technique to form femoral and tibial tunnels.

The Epiligament: Structure, Postnatal Development and Role in Ligament Healing

While much is known about the ligament, the precise morphology and function of the thin layer of connective tissue lining its surface, termed the epiligament, have not been fully studied yet. Herein, we aimed at reviewing the recent findings on the structural and functional significance of the epiligament in both animal models and human tissue. The epiligament is made up of various connective tissue cells such as fibroblasts, fibrocytes, mast cells, and adipocytes and contains a number of neurovascular bundles. Arrangement of collagen fibers in the epiligament is rather chaotic, in multiple directions, which allows for greater mobility and resistance to stress. Differences in the collagen content and types of enzymes of the group of matrix metalloproteinases between the epiligament and the underlying ligament tissue have been reported and are reviewed herein. While the ligament tissue mainly contains collagen type I, the epiligament is also rich in collagen types III and V. As suggested by a number of studies, the epiligament plays a key role in ligament repair as a donor of cells and matrix metalloproteinases, particularly matrix metalloproteinase-2 and 9, which are essential for scar tissue remodeling. In conclusion, future studies will likely reveal additional functional aspects of the epiligament, which may allow scientists to devise more suitable treatment strategies for damaged ligaments in a world where injuries resulting from sports activities or daily routine have long merited their due attention.

A Combination of Oxo-M and 4-PPBP as a potential regenerative therapeutics for tendon injury

Tendons injuries frequently result in scar-like tissue with poor biochemical structure and mechanical properties. We have recently reported that CD146+ perivascular originated tendon stem/progenitor cells (TSCs), playing critical roles in tendon healing. Here, we identified highly efficient small molecules that selectively activate endogenous TSCs for tendon regeneration. Methods: From a pool of ERK1/2 and FAK agonists, Oxo-M and 4-PPBP were identified, and their roles in tenogenic differentiation of TSCs and in vivo tendon healing were investigated. Controlled delivery of Oxo-M and 4-PPBP was applied via PLGA µS. Signaling studies were conducted to determine the mechanism for specificity of Oxo-M and 4-PPBP to CD146+ TSCs. Results: A combination of Oxo-M and 4-PPBP synergistically increased the expressions of tendon-related gene markers in TSCs. In vivo, delivery of Oxo-M and 4-PPBP significantly enhanced healing of fully transected rat patellar tendons (PT), with functional restoration and reorganization of collagen fibrous structure. Our signaling study suggested that Oxo-M and 4-PPBP specifically targets CD146+ TSCs via non-neuronal muscarinic acetylcholine receptors (AChR) and σ1 receptor (σ1) signaling. Principal conclusions: Our findings demonstrate a significant potential of Oxo-M and 4-PPBP as a regenerative therapeutics for tendon injuries.

Biomimetic substrate control of cellular mechanotransduction

Extracellular mechanophysical signals from both static substrate cue and dynamic mechanical loading have strong potential to regulate cell functions. Most of the studies have adopted either static or dynamic cue and shown that each cue can regulate cell adhesion, spreading, migration, proliferation, lineage commitment, and differentiation. However, there is limited information on the integrative control of cell functions by the static and dynamic mechanophysical signals. For example, a majority of dynamic loading studies have tested mechanical stimulation of cells utilizing cultures on flat surfaces without any surface modification. While these approaches have provided significant information on cell mechanotransduction, obtained outcomes may not correctly recapitulate complex cellular mechanosensing milieus in vivo. Several pioneering studies documented cellular response to mechanical stimulations upon cultures with biomimetic substrate modifications. In this min-review, we will highlight key findings on the integrative role of substrate cue (topographic, geometric, etc.) and mechanical stimulation (stretch, fluid shear) in modulating cell function and fate. The integrative approaches, though not fully established yet, will help properly understand cell mechanotransduction under biomimetic mechanophysical environments. This may further lead to advanced functional tissue engineering and regenerative medicine protocols.

Positive effects of an extracellular matrix hydrogel on rat anterior cruciate ligament fibroblast proliferation and collagen mRNA expression

Background/Objective

We have previously shown that an extracellular matrix (ECM) bioscaffold derived from porcine small intestine submucosa (SIS) enhanced the healing of a gap injury of the medial collateral ligament as well as the central third defect of the patellar tendon. With the addition of a hydrogel form of SIS, we found that a transected goat anterior cruciate ligament (ACL) could also be healed. The result begs the research question of whether SIS hydrogel has positive effects on ACL fibroblasts (ACLFs) and thus facilitates ACL healing.

Methods

In the study, ECM-SIS hydrogel was fabricated from the digestion of decellularised and sterilised sheets of SIS derived from αGal-deficient (GalSafe) pigs. As a comparison, a pure collagen hydrogel was also fabricated from commercial collagen type I solution. The morphometrics of hydrogels was assessed with scanning electron microscopy. The ECM-SIS and collagen hydrogels had similar fibre diameters (0.105 ± 0.010 μm vs. 0.114 ± 0.004 μm), fibre orientation (0.51 ± 0.02 vs. 0.52 ± 0.02), and pore size (0.092 ± 0.012 μm vs. 0.087 ± 0.008 μm). The preservation of bioactive properties of SIS hydrogel was assessed by detecting bioactive molecules sensitive to processing and enzyme digestion, such as growth factors fibroblast growth factor-2 (FGF-2) and transforming growth factor-beta 1 (TGF-β1), with enzyme-linked immunosorbent assay. ACLFs were isolated and expanded in culture from explants of rat ACLs (n = 3). The cells were then seeded on the hydrogels and cultured with 0%, 1%, and 10% foetal bovine serum (FBS) for 3 days and 7 days. Cell attachment was observed using a light microscope and scanning electron microscopy, whereas cell proliferation and matrix production (collagen types I and III) were examined with bromodeoxyuridine assays and reverse transcription-polymerase chain reaction, respectively.

Results

The results showed that FGF-2 and TGF-β1 in the SIS hydrogel were preserved by 50% (65.9 ± 26.1 ng/g dry SIS) and 90% (4.4 ± 0.6 ng/g dry SIS) relative to their contents in ECM-SIS sheets, respectively. At Day 3 of culture, ACLFs on the SIS hydrogel were found to proliferate 39%, 31%, and 22% more than those on the pure collagen hydrogel at 0%, 1%, and 10% FBS, respectively (p < 0.05). Collagen type I mRNA expression was increased by 150%, 207%, and 100%, respectively, compared to collagen hydrogel (p < 0.05), whereas collagen type III mRNA expression was increased by 123% and 132% at 0% and 1% FBS, respectively (all p < 0.05) but not at 10% FBS. By Day 7, collagen type I mRNA expression was still elevated by 137% and 100% compared to collagen hydrogel at 1% and 10% FBS, respectively (p < 0.05). Yet, collagen type III mRNA levels were not significantly different between the two groups at any FBS concentrations.

Conclusion

Our data showed that the ECM-SIS hydrogel not only supported the growth of ACLFs, but also promoted their proliferation and matrix production relative to a pure collagen hydrogel. As such, ECM-SIS hydrogel has potential therapeutic value to facilitate ACL healing at the early stage after injury.

Harnessing endogenous stem/progenitor cells for tendon regeneration

Current stem cell-based strategies for tissue regeneration involve ex vivo manipulation of these cells to confer features of the desired progenitor population. Recently, the concept that endogenous stem/progenitor cells could be used for regenerating tissues has emerged as a promising approach that potentially overcomes the obstacles related to cell transplantation. Here we applied this strategy for the regeneration of injured tendons in a rat model. First, we identified a rare fraction of tendon cells that was positive for the known tendon stem cell marker CD146 and exhibited clonogenic capacity, as well as multilineage differentiation ability. These tendon-resident CD146+ stem/progenitor cells were selectively enriched by connective tissue growth factor delivery (CTGF delivery) in the early phase of tendon healing, followed by tenogenic differentiation in the later phase. The time-controlled proliferation and differentiation of CD146+ stem/progenitor cells by CTGF delivery successfully led to tendon regeneration with densely aligned collagen fibers, normal level of cellularity, and functional restoration. Using siRNA knockdown to evaluate factors involved in tendon generation, we demonstrated that the FAK/ERK1/2 signaling pathway regulates CTGF-induced proliferation and differentiation of CD146+ stem/progenitor cells. Together, our findings support the use of endogenous stem/progenitor cells as a strategy for tendon regeneration without cell transplantation and suggest this approach warrants exploration in other tissues.

Overrepresentation of the COL3A1 AA genotype in Polish skiers with anterior cruciate ligament injury

Although various intrinsic and extrinsic risk factors for anterior cruciate ligament (ACL) rupture have been identified, the exact aetiology of the injury is not yet fully understood. Type III collagen is an important factor in the repair of connective tissue, and certain gene polymorphisms may impair the tensile strength. The aim of this study was to examine the association of the COL3A1 rs1800255 polymorphism with ACL rupture in Polish male recreational skiers. A total of 321 male Polish recreational skiers were recruited for this study; 138 had surgically diagnosed primary ACL ruptures (ACL-injured group) and 183 were apparently healthy male skiers (control group – CON) who had no self-reported history of ligament or tendon injury. Both groups had a comparable level of exposure to ACL injury. Genomic DNA was extracted from the oral epithelial cells. All samples were genotyped on a real-time polymerase chain reaction instrument. The genotype distribution in the ACL-injured group was significantly different than in CON (respectively: AA=10.1 vs 2.2%, AG=22.5 vs 36.1, GG=67.4 vs 61.8%; p=0.0087). The AA vs AG+GG genotype of COL3A1 (odds ratio (OR)=5.05; 95% confidence interval (CI), 1.62-15.71, p=0.003) was significantly overrepresented in the ACL-injured group compared with CON. The frequency of the A allele was higher in the ACL-injured group (21.4%) compared with CON (20.2%), but the difference was not statistically significant (p=0.72). This study revealed an association between the COL3A1 rs1800255 polymorphism and ACL ruptures in Polish skiers.

Updates in biological therapies for knee injuries: anterior cruciate ligament

There have been many advances in anterior cruciate ligament reconstruction (ACLR) techniques incorporating biological treatment. The aim of this review is to discuss the recent contributions that may enlighten our understanding of biological therapies for anterior cruciate ligament (ACL) injuries and improve management decisions involving these enhancement options. Three main biological procedures will be analyzed: bio-enhanced ACL repair, bio-enhanced ACLR scrutinized under the four basic principles of tissue engineering (scaffolds, cell sources, growth factors/cytokines including platelet-rich plasma, and mechanical stimuli), and remnant-preserving ACLR. There is controversial information regarding remnant-preserving ACLR, since different procedures are grouped under the same designation. A new definition for remnant-preserving ACLR surgery is proposed, dividing it into its three major procedures (selective bundle augmentation, augmentation, and nonfunctional remnant preservation); also, an ACL lesion pattern classification and a treatment algorithm, which will hopefully standardize these terms and procedures for future studies, are presented.

Allografts in soft tissue reconstructive procedures: important considerations

CONTEXT

Allografts offer several important advantages over autografts in musculoskeletal reconstructive procedures, such as anterior cruciate ligament reconstruction. Despite growing widespread use of allograft tissue, serious concerns regarding safety and functionality remain. We discuss the latest knowledge of the potential benefits and risks of allograft use and offer a critical review of allograft tissue regulation, management, and sterilization to enable the surgeon to better inform athletes considering reconstructive surgery options.

EVIDENCE ACQUISITION

A review of sources published in the past 10 years is the primary basis of this research.

STUDY DESIGN

Observational analysis (cohort study).

LEVEL OF EVIDENCE

Level 3.

RESULTS

Comparable outcome data for autografts and allografts do not support universal standards for anterior cruciate ligament reconstruction, and physician recommendation and bias appear to significantly influence patient preference and satisfaction. Sterilization by gamma and electron-beam irradiation diminishes the biomechanical integrity of allograft tissue, but radioprotective agents such as collagen cross-linking and free radical scavengers appear to have potential in mitigating the deleterious effects of irradiation and preserving tissue strength and stability.

CONCLUSION

Allografts offer greater graft availability and reduced morbidity in orthopaedic reconstructive procedures, but greater expansion of their use by surgeons is challenged by the need to maintain tissue sterility and biomechanical functionality. Advances in the radioprotection of irradiated tissue may lessen concerns regarding allograft safety and structural stability.

Emerging Applications of Stem Cell and Regenerative Medicine to Sports Injuries

Background:

The treatment of sports-related musculoskeletal injuries with stem cells has become more publicized because of recent reports of high-profile athletes undergoing stem cell procedures. There has been increased interest in defining the parameters of safety and efficacy and the indications for potential use of stem cells in clinical practice.

Purpose:

To review the role of regenerative medicine in the treatment of sports-related injuries.

Study Design:

Review.

Method:

Relevant studies were identified through a PubMed search combining the terms stem cells and cartilage, ligament, tendon, muscle, and bone from January 2000 to August 2013. Studies and works cited in these studies were also reviewed.

Results:

Treatment of sports-related injuries with stem cells shows potential for clinical efficacy from the data available from basic science and animal studies.

Conclusion:

Cell-based therapies and regenerative medicine offer safe and potentially efficacious treatment for sports-related musculoskeletal injuries. Basic science and preclinical studies that support the possibility of enhanced recovery from sports injuries using cell-based therapies are accumulating; however, more clinical evidence is necessary to define the indications and parameters for their use. Accordingly, exposing patients to cell-based therapies could confer an unacceptable risk profile with minimal or no benefit. Continued clinical testing with animal models and clinical trials is necessary to determine the relative risks and benefits as well as the indications and methodology of treatment.

Implantation of a novel biologic and hybridized tissue engineered bioimplant in large tendon defect: an in vivo investigation

Surgical reconstruction of large Achilles tendon defects is technically demanding. There is no standard method, and tissue engineering may be a valuable option. We investigated the effects of 3D collagen and collagen-polydioxanone sheath (PDS) implants on a large tendon defect model in rabbits. Ninety rabbits were divided into three groups: control, collagen, and collagen-PDS. In all groups, 2 cm of the left Achilles tendon were excised and discarded. A modified Kessler suture was applied to all injured tendons to retain the gap length. The control group received no graft, the treated groups were repaired using the collagen only or the collagen-PDS prostheses. The bioelectrical characteristics of the injured areas were measured at weekly intervals. The animals were euthanized at 60 days after the procedure. Gross, histopathological and ultrastructural morphology and biophysical characteristics of the injured and intact tendons were investigated. Another 90 pilot animals were also used to investigate the inflammatory response and mechanism of graft incorporation during tendon healing. The control tendons showed severe hyperemia and peritendinous adhesion, and the gastrocnemius muscle of the control animals showed severe atrophy and fibrosis, with a loose areolar connective tissue filling the injured area. The tendons receiving either collagen or collagen-PDS implants showed lower amounts of peritendinous adhesion, hyperemia and muscle atrophy, and a dense tendon filled the defect area. Compared to the control tendons, application of collagen and collagen-PDS implants significantly improved water uptake, water delivery, direct transitional electrical current and tissue resistance to direct transitional electrical current. Compared to the control tendons, both prostheses showed significantly increased diameter, density and alignment of the collagen fibrils and maturity of the tenoblasts at ultrastructure level. Both prostheses influenced favorably tendon healing compared to the control tendons, with no significant differences between collagen and collagen-PDS groups. Implantation of the 3D collagen and collagen-PDS implants accelerated the production of a new tendon in the defect area, and may become a valuable option in clinical practice.

Healing of the goat anterior cruciate ligament after a new suture repair technique and bioscaffold treatment

Primary suture repair of the anterior cruciate ligament (ACL) has been used clinically in an attempt to heal the ruptured ACL. The results, however, were not satisfactory, which in retrospect can be attributed to the used suturing technique and the suboptimal healing conditions. These constraining conditions can be improved by introducing a new suturing technique and by using small intestinal submucosa (SIS) as a bioscaffold. It is hypothesized that the suturing technique keep the torn ends together and that SIS enhance and promote the healing of the ACL. The goat was used as the study model. In the Suture group, the left ACL was transected and suture repaired with a new locking suture repair technique (n=5) allowing approximation and fixation under tension. The Suture-SIS group underwent the same procedure with the addition of SIS (n=5). The right ACL served as control. After 12 weeks of healing, anterior-posterior translation and in situ force of the healing ACL were measured, followed by the measurement of the cross-sectional area and structural stiffness. Routine histology was performed on tissue samples. Gross morphology showed that the healing ACL was continuous with collagenous tissue in both groups. The cross-sectional area of the Suture and the Suture-SIS group was 35% and 50% of the intact control, respectively. The anterior-posterior translations at different flexion angles were statistically not different between the Suture group and the Suture-SIS group. Only the in situ force at 30° in the Suture-SIS group was higher than in the Suture group. Tensile tests showed that the stiffness for the Suture group was not different from the Suture-SIS group (31.1±8.1 N/mm vs. 41.9±18.0 N/mm [p>0.05]). Histology showed longitudinally aligned collagen fibers from origo to insertion. More fibroblasts were present in the healing tissue than in the control intact tissue. The study demonstrated the proof of concept of ACL repair in a goat model with a new suture technique and SIS. The mechanical outcome is not worse than previously reported for ACL reconstruction. In conclusion, the approach of using a new suture technique, with or without a bioscaffold to heal the ACL is promising.

The Essex-Lopresti lesion

The Essex-Lopresti lesion represents a severe injury of the forearm unit. In the 1940s, it’s pathology and consequences have already been mentioned by several authors. Over the course of time, the pathophysiology of the lesion was displayed in more detail. Therefore, an intensive analysis of the involved anatomic structures was done. The interosseous membrane was shown to play a major role in stabilising the forearm unit, in the situation of a fractured radial head, which is the primary stabiliser of the longitudinal forearm stability. Moreover, biomechanical analyses showed a relevant attribution of the distal radio-ulnar joint to the forearm stability. If, in the case of a full-blown Essex-Lopresti lesion, the radial head, the interosseous membrane and the distal radio-ulnar joint are injured, proximalisation of the radius will take place and will come along with secondary symptoms at the elbow joint and the wrist. According to actual studies, the lesion seems to occur more often than realised up to now. Thus, to avoid missing the complex injury, subtle clinical diagnosis combined with adequate imaging has to be undertaken. If the lesion is confirmed, several operative treatment options are available, yet not proofed to be sufficient.

Concise review: the clinical application of mesenchymal stem cells for musculoskeletal regeneration: current status and perspectives

Regenerative therapies in the musculoskeletal system are based on the suitable application of cells, biomaterials, and/or factors. For an effective approach, numerous aspects have to be taken into consideration, including age, disease, target tissue, and several environmental factors. Significant research efforts have been undertaken in the last decade to develop specific cell-based therapies, and in particular adult multipotent mesenchymal stem cells hold great promise for such regenerative strategies. Clinical translation of such therapies, however, remains a work in progress. In the clinical arena, autologous cells have been harvested, processed, and readministered according to protocols distinct for the target application. As outlined in this review, such applications range from simple single-step approaches, such as direct injection of unprocessed or concentrated blood or bone marrow aspirates, to fabrication of engineered constructs by seeding of natural or synthetic scaffolds with cells, which were released from autologous tissues and propagated under good manufacturing practice conditions (for example, autologous chondrocyte implantation). However, only relatively few of these cell-based approaches have entered the clinic, and none of these treatments has become a "standard of care" treatment for an orthopaedic disease to date. The multifaceted reasons for the current status from the medical, research, and regulatory perspectives are discussed here. In summary, this review presents the scientific background, current state, and implications of clinical mesenchymal stem cell application in the musculoskeletal system and provides perspectives for future developments.

Cell- and gene-based approaches to tendon regeneration

Repair of rotator cuff tears in experimental models has been significantly improved by the use of enhanced biologic approaches, including platelet-rich plasma, bone marrow aspirate, growth factor supplements, and cell- and gene-modified cell therapy. Despite added complexity, cell-based therapies form an important part of enhanced repair, and combinations of carrier vehicles, growth factors, and implanted cells provide the best opportunity for robust repair. Bone marrow-derived mesenchymal stem cells provide a stimulus for repair in flexor tendons, but application in rotator cuff repair has not shown universally positive results. The use of scaffolds such as platelet-rich plasma, fibrin, and synthetic vehicles and the use of gene priming for stem cell differentiation and local anabolic and anti-inflammatory impact have both provided essential components for enhanced tendon and tendon-to-bone repair in rotator cuff disruption. Application of these research techniques in human rotator cuff injury has generally been limited to autologous platelet-rich plasma, bone marrow concentrate, or bone marrow aspirates combined with scaffold materials. Cultured mesenchymal progenitor therapy and gene-enhanced function have not yet reached clinical trials in humans. Research in several animal species indicates that the concept of gene-primed stem cells, particularly embryonic stem cells, combined with effective culture conditions, transduction with long-term integrating vectors carrying anabolic growth factors, and development of cells conditioned by use of RNA interference gene therapy to resist matrix metalloproteinase degradation, may constitute potential advances in rotator cuff repair. This review summarizes cell- and gene-enhanced cell research for tendon repair and provides future directions for rotator cuff repair using biologic composites.

Braided nanofibrous scaffold for tendon and ligament tissue engineering

Tendon and ligament (T/L) injuries present an important clinical challenge due to their intrinsically poor healing capacity. Natural healing typically leads to the formation of scar-like tissue possessing inferior mechanical properties. Therefore, tissue engineering has gained considerable attention as a promising alternative for T/L repair. In this study, we fabricated braided nanofibrous scaffolds (BNFSs) as a potential construct for T/L tissue engineering. Scaffolds were fabricated by braiding 3, 4, or 5 aligned bundles of electrospun poly(L-lactic acid) nanofibers, thus introducing an additional degree of flexibility to alter the mechanical properties of individual scaffolds. We observed that the Young's modulus, yield stress, and ultimate stress were all increased in the 3-bundle compared to the 4- and 5-bundle BNFSs. Interestingly, acellular BNFSs mimicked the normal tri-phasic mechanical behavior of native tendon and ligament (T/L) during loading. When cultured on the BNFSs, human mesenchymal stem cells (hMSCs) adhered, aligned parallel to the length of the nanofibers, and displayed a concomitant realignment of the actin cytoskeleton. In addition, the BNFSs supported hMSC proliferation and induced an upregulation in the expression of key pluripotency genes. When cultured on BNFSs in the presence of tenogenic growth factors and stimulated with cyclic tensile strain, hMSCs differentiated into the tenogenic lineage, evidenced most notably by the significant upregulation of Scleraxis gene expression. These results demonstrate that BNFSs provide a versatile scaffold capable of supporting both stem cell expansion and differentiation for T/L tissue engineering applications.