Effects of low-intensity pulsed ultrasound on tendon-bone healing in an intra-articular sheep knee model

Comparison of Structural Properties Between Postnatal and Adult Tendon Insertion with FIB/SEM Tomography in Rat

OBJECTIVE

The repaired tendon-bone interface after rotator cuff (RC) repair has been identified as a mechanical weak point, which may contribute to re-tearing. Analyzing the postnatal development of a normal tendon insertion in detail may be useful in helping to promote the regeneration of a normal tendon insertion. We verified the morphological differences between postnatal and adult tendon insertions in terms of the cellular structural properties using FIB/SEM tomography.

MATERIALS AND METHOD

SPostnatal and adult Sprague-Dawley rats were used as a model of tendon insertion. The morphological structure of the insertion was evaluated using hematoxylin and eosin (HE) staining, and the 3D ultrastructure of the cells in the insertion was evaluated using FIB/SEM tomography. Additionally, the volume of the cell bodies, nuclei, and cytoplasm were measured and compared in a quantitative analysis.

RESULTS

On conventional histology, the boundary line between the fibrocartilage and mineralized cartilage was flat in the adult insertions; however, the boundary line between the mineralized cartilage and bone formed deep interdigitations. The morphology of the cells among the collagen bundles in the adult insertions was completely different from those in the postnatal insertions at the 3D ultrastructural level. The cellular structural properties were statistically different between the postnatal and adult insertions.

CONCLUSIONS

In the present study, the morphological differences between postnatal and adult tendon insertion in terms of the ultrastructural cellular properties were clarified. These findings may aid in determining how to regenerate a clinically stable tendon insertion at the tendon-bone interface after RC repair.

Low-Intensity Pulsed Ultrasound Augments Tendon, Ligament, and Bone-Soft Tissue Healing in Preclinical Animal Models: A Systematic Review

PURPOSE

To appraise the available animal and human studies investigating low-intensity pulsed ultrasound stimulation (LIPUS) on tendon, ligament, and bone-soft tissue (B-ST) junction healing.

METHODS

A systematic review of PUBMED, EMBASE, and the Cochrane Library was performed for animal and human studies investigating the effects of LIPUS on tendon, ligament, and B-ST junction healing. The systematic search was performed using the key term "low intensity pulsed ultrasound" and any of the following: "tendon," "ligament," "tendon-bone," and "bone-tendon." Inclusion criteria consisted of (1) randomized controlled trials assessing the effect of LIPUS on bone, tendon, and soft tissue in animals or humans and (2) English-language articles.

RESULTS

A total of 28 animal and 2 human studies met inclusion criteria. Animal studies utilized various models, including Achilles and patellar tendon transections, medial collateral ligament transections, and surgical repair of patellar tendon, rotator cuff tendon, and anterior cruciate ligament, to evaluate the effects of LIPUS. Animal studies demonstrated significantly improved collagen content and organization, bone formation, fibrocartilage remodeling, and mechanical strength with LIPUS treatment compared with controls. In human trials, LIPUS treatment of chronic tendinopathies did not improve clinical outcomes.

CONCLUSIONS

In acute injury animal models, LIPUS augmented healing of acute tendon, ligament, and B-ST junction injuries through increased collagen content and organization; increased anti-inflammatory cellular signaling; and increased angiogenesis. However, in 2 human studies investigating chronic tendinopathy, LIPUS did not lead to superior outcomes compared with controls.

CLINICAL RELEVANCE

Animal models suggest that LIPUS may be a promising noninvasive treatment modality for accelerating patient recovery after acute tendon and ligament injuries, as well as after surgical repair of B-ST junction injuries, but this has not been demonstrated in human studies. Randomized clinical trials evaluating LIPUS for acute tendon and ligament injuries are warranted.

Bone marrow mesenchymal stem cell-derived exosomes promote rotator cuff tendon-bone healing by promoting angiogenesis and regulating M1 macrophages in rats

BACKGROUND

Rotator cuff tears (RCTs) often require reconstructive surgery. Tendon-bone healing is critical for the outcome of rotator cuff reconstruction, but the process of tendon-bone healing is complex and difficult. Mesenchymal stem cells (MSCs) are considered to be an effective method to promote tendon-bone healing. MSCs have strong paracrine, anti-inflammatory, immunoregulatory, and angiogenic potential. Recent studies have shown that MSCs achieve many regulatory functions through exosomes. The purpose of this study was to explore the role of bone marrow mesenchymal stem cell-derived exosomes (BMSC-Exos) in tendon-bone healing.

METHODS

Our study found that BMSC-Exos promote the proliferation, migration, and angiogenic tube formation of human umbilical vein endothelial cells (HUVECs). The mechanism by which BMSC-Exos achieve this may be through the regulation of the angiogenic signaling pathway. In addition, BMSC-Exos can inhibit the polarization of M1 macrophages and inhibit the secretion of proinflammatory factors by M1 macrophages. After rotator cuff reconstruction in rats, BMSC-Exos were injected into the tail vein to analyze their effect on the rotator cuff tendon-bone interface healing.

RESULTS

It was confirmed that BMSC-Exos increased the breaking load and stiffness of the rotator cuff after reconstruction in rats, induced angiogenesis around the rotator cuff endpoint, and promoted growth of the tendon-bone interface.

CONCLUSION

BMSC-Exos promote tendon-bone healing after rotator cuff reconstruction in rats by promoting angiogenesis and inhibiting inflammation.

[Research progress of structured repair of tendon-bone interface]

In sports system, the tendon-bone interface has the effect of tensile and bearing load, so the effect of healing plays a crucial role in restoring joint function. The process of repair is the formation of scar tissue, so it is difficult to achieve the ideal effect for morphology and biomechanical strength. The tissue engineering method can promote the tendon-bone interface healing from the seed cells, growth factors, and scaffolds, and is a new direction in the field of development of the tendon-bone interface healing.

Biological augmentation of graft healing in anterior cruciate ligament reconstruction: a systematic review

Aims

The success of anterior cruciate ligament reconstruction (ACLR) depends on osseointegration at the graft-tunnel interface and intra-articular ligamentization. Our aim was to conduct a systematic review of clinical and preclinical studies that evaluated biological augmentation of graft healing in ACLR.

Materials and Methods

In all, 1879 studies were identified across three databases. Following assessment against strict criteria, 112 studies were included (20 clinical studies; 92 animal studies).

Results

Seven categories of biological interventions were identified: growth factors, biomaterials, stem cells, gene therapy, autologous tissue, biophysical/environmental, and pharmaceuticals. The methodological quality of animal studies was moderate in 97%, but only 10% used clinically relevant outcome measures. The most interventions in clinical trials target the graft-tunnel interface and are applied intraoperatively. Platelet-rich plasma is the most studied intervention, but the clinical outcomes are mixed, and the methodological quality of studies was suboptimal. Other biological therapies investigated in clinical trials include: remnant-augmented ACLR; bone substitutes; calcium phosphate-hybridized grafts; extracorporeal shockwave therapy; and adult autologus non-cultivated stem cells.

Conclusion

There is extensive preclinical research supporting the use of biological therapies to augment ACLR. Further clinical studies that meet the minimum standards of reporting are required to determine whether emerging biological strategies will provide tangible benefits in patients undergoing ACLR. Cite this article: Bone Joint J 2018;100-B:271-84.

Demineralized Bone Matrix to Augment Tendon-Bone Healing: A Systematic Review

Background:

Following injury to the rotator cuff and anterior cruciate ligament, a direct enthesis is not regenerated, and healing occurs with biomechanically inferior fibrous tissue. Demineralized bone matrix (DBM) is a collagen scaffold that contains growth factors and is a promising biological material for tendon and ligament repair because it can regenerate a direct fibrocartilaginous insertion via endochondral ossification.

Purpose:

To provide a comprehensive review of the literature investigating the use of DBM to augment tendon-bone healing in tendon repair and anterior cruciate ligament reconstruction (ACLR).

Study Design:

Systematic review.

Methods:

Electronic databases (MEDLINE and EMBASE) were searched for preclinical and clinical studies that evaluated the use of DBM in tendon repair and ACLR. Search terms included the following: (“demineralized bone matrix” OR “demineralized cortical bone”) AND (“tissue scaffold” OR “tissue engineering” OR “ligament” OR “tendon” OR “anterior cruciate ligament” OR “rotator cuff”). Peer-reviewed articles written in English were included, and no date restriction was applied (searches performed February 10, 2017). Methodological quality was assessed with peer-reviewed scoring criteria.

Results:

The search strategy identified 339 articles. After removal of duplicates and screening according to inclusion criteria, 8 studies were included for full review (tendon repair, n = 4; ACLR, n = 4). No human clinical studies were identified. All 8 studies were preclinical animal studies with good methodological quality. Five studies compared DBM augmentation with non-DBM controls, of which 4 (80%) reported positive findings in terms of histological and biomechanical outcomes.

Conclusion:

Preclinical evidence indicates that DBM can improve tendon-bone healing, although clinical studies are lacking. A range of animal models of tendon repair and ACLR showed that DBM can re-create a direct fibrocartilaginous enthesis, although the animal models are not without limitations. Before clinical trials are justified, research is required that determines the best source of DBM (allogenic vs xenogenic) and the best form of DBM (demineralized cortical bone vs DBM paste) to be used in them.

Low Intensity Ultrasound for Promoting Soft Tissue Healing: A Systematic Review of the Literature and Medical Technology

Therapeutic ultrasound has been studied and used for the past seven decades to treat musculoskeletal injuries. Recently, a significant body of animal and human research has focused on the biomechanical effects of daily-applied, low intensity therapeutic ultrasound (LITUS) on soft tissue recovery. We performed a systematic review of the last two decades of LITUS literature to examine the effects on tendon, skeletal muscle, ligament, and tendon-bone junction injuries. LITUS facilitated tendon healing, with increased tensile strength and improved collagen alignment. For skeletal muscle and ligament injuries, LITUS increased cell proliferation during myoregeneration and improved tissue biomechanics (ultimate load, stiffness, energy absorption). LITUS aided tendon-bone junction healing through improved tissue function. Scientific evidence supports the use of LITUS to treat soft tissue injuries, and improve outcomes for musculoskeletal injuries and post-operative recovery. Lastly, we discuss the use of LITUS devices facilitating daily applied therapy in the home setting.

Biological enhancement of graft-tunnel healing in anterior cruciate ligament reconstruction

The sites where graft healing occurs within the bone tunnel and where the intra-articular ligamentization process takes place are the two most important sites of biological incorporation after anterior cruciate ligament (ACL) reconstruction, since they help to determine the mechanical behavior of the femur-ACL graft-tibia complex. Graft-tunnel healing is a complex process influenced by several factors, such as type of graft, preservation of remnants, bone quality, tunnel length and placement, fixation techniques and mechanical stress. In recent years, numerous experimental and clinical studies have been carried out to evaluate potential strategies designed to enhance and optimize the biological environment of the graft-tunnel interface. Modulation of inflammation, tissue engineering and gene transfer techniques have been applied in order to obtain a direct-type fibrocartilaginous insertion of the ACL graft, similar to that of native ligament, and to accelerate the healing process of tendon grafts within the bone tunnel. Although animal studies have given encouraging results, clinical studies are lacking and their results do not really support the use of the various strategies in clinical practice. Further investigations are therefore needed to optimize delivery techniques, therapeutic concentrations, maintenance of therapeutic effects over time, and to reduce the risk of undesirable effects in clinical practice.

Histomorphometric and ultrastructural analysis of the tendon-bone interface after rotator cuff repair in a rat model

Successful rotator cuff repair requires biological anchoring of the repaired tendon to the bone. However, the histological structure of the repaired tendon-bone interface differs from that of a normal tendon insertion. We analysed differences between the normal tendon insertion and the repaired tendon-bone interface after surgery in the mechanical properties, histomorphometric analysis, and 3-dimensional ultrastructure of the cells using a rat rotator cuff repair model. Twenty-four adult Sprague-Dawley (SD) rats underwent complete cuff tear and subsequent repair of the supraspinatus tendon. The repaired tendon-bone interface was evaluated at 4, 8, and 12 weeks after surgery. At each time point, shoulders underwent micro-computed tomography scanning and biomechanical testing (N = 6), conventional histology and histomorphometric analysis (N = 6), and ultrastructural analysis with focused ion beam/scanning electron microscope (FIB/SEM) tomography (N = 4). We demonstrated that the cellular distribution between the repaired tendon and bone at 12 weeks after surgery bore similarities to the normal tendon insertion. However, the ultrastructure of the cells at any time point had a different morphology than those of the normal tendon insertion. These morphological differences affect the healing process, partly contributing to re-tearing at the repair site. These results may facilitate future studies of the regeneration of a normal tendon insertion.

Modulating tibiofemoral contact force in the sheep hind limb via treadmill walking: Predictions from an opensim musculoskeletal model

Sheep are a predominant animal model used to study a variety of orthopedic conditions. Understanding and controlling the in-vivo loading environment in the sheep hind limb is often necessary for investigations relating to bone and joint mechanics. The purpose of this study was to develop a musculoskeletal model of an adult sheep hind limb and investigate the effects of treadmill walking speed on muscle and joint contact forces. We constructed the skeletal geometry of the model from computed topography images. Dual-energy x-ray absorptiometry was utilized to establish the inertial properties of each model segment. Detailed dissection and tendon excursion experiments established the requisite muscle lines of actions. We used OpenSim and experimentally-collected marker trajectories and ground reaction forces to quantify muscle and joint contact forces during treadmill walking at 0.25 m• s(-1) and 0.75 m• s(-1) . Peak compressive and anterior-posterior tibiofemoral contact forces were 20% (0.38 BW, p = 0.008) and 37% (0.17 BW, p = 0.040) larger, respectively, at the moderate gait speed relative to the slower speed. Medial-lateral tibiofemoral contact forces were not significantly different. Adjusting treadmill speed appears to be a viable method to modulate compressive and anterior-posterior tibiofemoral contact forces in the sheep hind limb. The musculoskeletal model is freely-available at www.SimTK.org.

Direct bone-to-bone integration between recombinant human bone morphogenetic protein-2-injected tendon graft and tunnel wall in an anterior cruciate ligament reconstruction model

PURPOSE

This study was performed to evaluate one-stage anterior cruciate ligament (ACL) reconstruction using a semitendinosus tendon graft injected with bone morphogenetic protein 2 (BMP-2) in a rabbit model.

METHODS

We injected recombinant human BMP-2 (rhBMP-2) in the experimental group and phosphate-buffered saline in the control group at two sites of the semitendinosus tendon (15 μg in each site) to replace tendon with bone in the bone tunnel. Twenty minutes later, the injected tendon graft was transplanted for ACL reconstruction by passing the graft through the bone tunnel. The animals were harvested at four, eight, or 12 weeks postoperatively and examined by histological and biomechanical methods.

RESULTS

Histological analysis revealed that the tendon graft was replaced with new bone in the tunnel of the experimental group. Characteristic features identical to the regenerated direct insertion morphology at the bone-tendon junction were acquired at eight or 12 weeks in the experimental group. Biomechanical pull-out testing revealed greater stiffness in the experimental than control group at 12 weeks, although the maximum load to failure showed no significant difference between the two groups at four, eight, or 12 weeks.

CONCLUSION

These results indicate the potential for ACL reconstruction with regenerated direct insertion morphology.

Tissue engineering of ligaments for reconstructive surgery

PURPOSE

The use of musculoskeletal bioengineering and regenerative medicine applications in orthopaedic surgery has continued to evolve. The aim of this systematic review was to address tissue-engineering strategies for knee ligament reconstruction.

METHODS

A systematic review of PubMed/Medline using the terms "knee AND ligament" AND "tissue engineering" OR "regenerative medicine" was performed. Two authors performed the search, independently assessed the studies for inclusion, and extracted the data for inclusion in the review. Both preclinical and clinical studies were reviewed, and the articles deemed most relevant were included in this article to provide relevant basic science and recent clinical translational knowledge concerning "tissue-engineering" strategies currently used in knee ligament reconstruction.

RESULTS

A total of 224 articles were reviewed in our initial PubMed search. Non-English-language studies were excluded. Clinical and preclinical studies were identified, and those with a focus on knee ligament tissue-engineering strategies including stem cell-based therapies, growth factor administration, hybrid biomaterial, and scaffold development, as well as mechanical stimulation modalities, were reviewed.

CONCLUSIONS

The body of knowledge surrounding tissue-engineering strategies for ligament reconstruction continues to expand. Presently, various tissue-engineering techniques have some potential advantages, including faster recovery, better ligamentization, and possibly, a reduction of recurrence. Preclinical research of these novel therapies continues to provide promising results. There remains a need for well-designed, high-powered comparative clinical studies to serve as a foundation for successful translation into the clinical setting going forward.

LEVEL OF EVIDENCE

Level IV, systematic review of Level IV studies.

Intermittently administered parathyroid hormone [1-34] promotes tendon-bone healing in a rat model

The objective of this study was to investigate whether intermittent administration of parathyroid hormone [1–34] (PTH[1–34]) promotes tendon-bone healing after anterior cruciate ligament (ACL) reconstruction in vivo. A rat model of ACL reconstruction with autograft was established at the left hind leg. Every day, injections of 60 μg PTH[1–34]/kg subcutaneously were given to the PTH group rats (n = 10) for four weeks, and the controls (n = 10) received saline. The tendon-bone healing process was evaluated by micro-CT, biomechanical test, histological and immunohistochemical analyses. The effects of PTH[1–34] on serum chemistry, bone microarchitecture and expression of the PTH receptor (PTH1R) and osteocalcin were determined. Administration of PTH[1–34] significantly increased serum levels of calcium, alkaline phosphatase (AP), osteocalcin and tartrate-resistant acid phosphatase (TRAP). The expression of PTH1R on both osteocytes and chondrocyte-like cells at the tendon-bone interface was increased in the PTH group. PTH[1–34] also enhanced the thickness and microarchitecture of trabecular bone according to the micro-CT analysis. The results imply that systematically intermittent administration of PTH[1–34] promotes tendon-bone healing at an early stage via up-regulated PTH1R. This method may enable a new strategy for the promotion of tendon-bone healing after ACL reconstruction.

Augmentation of tendon-to-bone healing

Tendon-to-bone healing is vital to the ultimate success of the various surgical procedures performed to repair injured tendons. Achieving tendon-to-bone healing that is functionally and biologically similar to native anatomy can be challenging because of the limited regeneration capacity of the tendon-bone interface. Orthopaedic basic-science research strategies aiming to augment tendon-to-bone healing include the use of osteoinductive growth factors, platelet-rich plasma, gene therapy, enveloping the grafts with periosteum, osteoconductive materials, cell-based therapies, biodegradable scaffolds, and biomimetic patches. Low-intensity pulsed ultrasound and extracorporeal shockwave treatment may affect tendon-to-bone healing by means of mechanical forces that stimulate biological cascades at the insertion site. Application of various loading methods and immobilization times influence the stress forces acting on the recently repaired tendon-to-bone attachment, which eventually may change the biological dynamics of the interface. Other approaches, such as the use of coated sutures and interference screws, aim to deliver biological factors while achieving mechanical stability by means of various fixators. Controlled Level-I human trials are required to confirm the promising results from in vitro or animal research studies elucidating the mechanisms underlying tendon-to-bone healing and to translate these results into clinical practice.

Genes responsive to low-intensity pulsed ultrasound in MC3T3-E1 preosteoblast cells

Although low-intensity pulsed ultrasound (LIPUS) has been shown to enhance bone fracture healing, the underlying mechanism of LIPUS remains to be fully elucidated. Here, to better understand the molecular mechanism underlying cellular responses to LIPUS, we investigated gene expression profiles in mouse MC3T3-E1 preosteoblast cells exposed to LIPUS using high-density oligonucleotide microarrays and computational gene expression analysis tools. Although treatment of the cells with a single 20-min LIPUS (1.5 MHz, 30 mW/cm(2)) did not affect the cell growth or alkaline phosphatase activity, the treatment significantly increased the mRNA level of Bglap. Microarray analysis demonstrated that 38 genes were upregulated and 37 genes were downregulated by 1.5-fold or more in the cells at 24-h post-treatment. Ingenuity pathway analysis demonstrated that the gene network U (up) contained many upregulated genes that were mainly associated with bone morphology in the category of biological functions of skeletal and muscular system development and function. Moreover, the biological function of the gene network D (down), which contained downregulated genes, was associated with gene expression, the cell cycle and connective tissue development and function. These results should help to further clarify the molecular basis of the mechanisms of the LIPUS response in osteoblast cells.

Low-intensity pulsed ultrasound therapy: a potential strategy to stimulate tendon-bone junction healing

Incorporation of a tendon graft within the bone tunnel represents a challenging clinical problem. Successful anterior cruciate ligament (ACL) reconstruction requires solid healing of the tendon graft in the bone tunnel. Enhancement of graft healing to bone is important to facilitate early aggressive rehabilitation and a rapid return to pre-injury activity levels. No convenient, effective or inexpensive procedures exist to enhance tendon-bone (T-B) healing after surgery. Low-intensity pulsed ultrasound (LIPUS) improves local blood perfusion and angiogenesis, stimulates cartilage maturation, enhances differentiation and proliferation of osteoblasts, and motivates osteogenic differentiation of mesenchymal stem cells (MSCs), and therefore, appears to be a potential non-invasive tool for T-B healing in early stage of rehabilitation of ACL reconstruction. It is conceivable that LIPUS could be used to stimulate T-B tunnel healing in the home, with the aim of accelerating rehabilitation and an earlier return to normal activities in the near future. The purpose of this review is to demonstrate how LIPUS stimulates T-B healing at the cellular and molecular levels, describe studies in animal models, and provide a future direction for research.

The effects of low-intensity pulsed ultrasound on tendon-bone healing in a transosseous-equivalent sheep rotator cuff model

PURPOSE

The purpose of this study was to examine the effects Low-intensity Pulsed Ultrasound has on initial tendon-bone healing in a clinically relevant extra-articular transosseous-equivalent ovine rotator cuff model.

METHODS

Eight skeletally mature wethers, randomly allocated to either control group (n = 4) or treatment group (n = 4), underwent rotator cuff surgery following injury to the infraspinatus tendon. All animals were killed 28 days post surgery to allow examination of early effects of Low-intensity Pulsed Ultrasound treatment.

RESULTS

General improvement in histological appearance of tendon-bone integration was noted in the treatment group. Newly formed woven bone with increased osteoblast activity along the bone surface was evident. A continuum was observed between the tendon and bone in an interdigitated fashion with Sharpey's fibres noted in the treatment group. Low-intensity Pulsed Ultrasound treatment also increased bone mineral density at the tendon-bone interface (p < 0.01), while immunohistochemistry results revealed an increase in the protein expression patterns of VEGF (p = 0.038), RUNX2 (p = 0.02) and Smad4 (p = 0.05).

CONCLUSIONS

The results of this study indicate that Low-intensity Pulsed Ultrasound may aid in the initial phase of tendon-bone healing process in patients who have undergone rotator cuff repair. This treatment may also be beneficial following other types of reconstructive surgeries involving the tendon-bone interface.

Effects of demineralized bone matrix on tendon-bone healing in an intra-articular rodent model

BACKGROUND

Techniques to improve and accelerate tendon-bone healing could be advantageous in anterior cruciate ligament (ACL) reconstruction. Effects of demineralized bone matrix (DBM) on intra-articular tendon-bone healing have not been examined.

HYPOTHESIS

Demineralized bone matrix has the potential to convey osteoinductive growth proteins to the site of healing at the tendon-bone interface. We hypothesized that the presence of DBM will result in more bone formation and hasten tendon-bone healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

Fifty-six female athymic rnu/rnu (nude) rats were used. Rats were randomly allocated into 2 groups (control or treatment). The control group underwent an ACL reconstruction, while the treatment group had human DBM implanted in the tendon graft and bone tunnel before reconstruction. Rats were sacrificed at 2 (n = 8), 4 (n = 24), and 6 (n = 24) weeks for histological, and immunohistochemical (t = 2, 4, and 6 weeks), and biomechanical testing and micro-computed tomography (t = 4 and 6 weeks) end points.

RESULTS

Our findings suggest that in the presence of DBM, tendon-bone healing is augmented by increased woven bone formation and enhanced bone remodeling as indicated by histology and micro-computed tomography. This ultimately resulted in a statistically significant increase in peak load to failure of the tendon-bone interface at 4 weeks (DBM group: 5.96 ± 1.36 N; control group: 2.86 ± 0.7 N) and 6 weeks (DBM group: 9.13 ± 0.97 N; control group: 5.81 ± 1.1 N).

CONCLUSION

Demineralized bone matrix at the tendon-bone interface promotes healing between the tendon and bone in a rodent ACL model.

CLINICAL RELEVANCE

Introduction of osteoinductive DBM at the tendon-bone interface during ACL reconstructive surgery may improve short-term 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.

ACL reconstruction using bone-tendon-bone graft engineered from the semitendinosus tendon by injection of recombinant BMP-2 in a rabbit model

We attempted to generate a bone-tendon-bone structure by injecting human-type recombinant human bone morphogenetic protein-2 (rhBMP-2) into the semitendinosus tendon, and an anterior cruciate ligament (ACL) defect was reconstructed by grafting the engineered bone-tendon-bone graft. Two ossicles with a separation distance of 1 cm were generated within the left semitendinosus tendon of a rabbit 6 weeks after the injection of rhBMP-2 (15 µg at each site). The engineered bone-tendon-bone graft was transplanted in order to reconstruct the ACL by passing the graft through the bone tunnels. In the control group, the ACL was reconstructed with the semitendinosus tendon without BMP-2 using the same methods as those used in the experimental group. The animals were harvested at 4 or 8 weeks after surgery and examined by radiographic, histological, and biomechanical methods. In the experimental group, ossicles in the bone-tendon-bone graft were successfully integrated into the host bone of the femur and tibia. Histological analysis revealed that characteristic features identical to the normal direct insertion morphology had been restored. Biomechanical pull-out testing showed that the ultimate failure load and stiffness of the reconstructed ACL in the experimental group were significantly higher than those in the control group at both 4 and 8 weeks (p < 0.05). These results indicate the potential of regenerative reconstruction of the ACL, and the reconstruction resulted in the restoration of morphology and function equivalent to those of the normal ACL.

Labeling and tracing of bone marrow mesenchymal stem cells for tendon-to-bone tunnel healing

PURPOSE

To investigate the effects of bone marrow mesenchymal stem cells (BMSCs) on tendon-to-bone tunnel healing and provide experimental evidence for labeling and tracing of stem cells.

METHODS

Rat BMSCs were harvested using the adherence separation technique and labeled by super paramagnetic iron oxide (SPIO) and 1,1-Dioctadecyl-3,3,3,3-tetramethylindocarbocyanine perchlorate (Dil) particles. Thirty-nine male Sprague-Dawley (SD) rats aged 8 weeks were randomly divided into two groups: experimental (n = 21) and control (n = 18). Rats from the experimental group were injected with SPIO- and Dil-labeled BMSCs and Pluronic F-127, and rats from the control group were only injected with Pluronic F-127. At 2, 4, and 8 weeks after surgery, biomechanical analysis was performed to evaluate tendon-to-bone tunnel healing. The transplanted BMSCs were observed by fluorescence microscope at 2, 4, and 8 weeks after surgery and traced by magnetic resonance (MR) imaging at 0, 3, and 7 days after surgery.

RESULTS

BMSCs were labeled effectively by SPIO and Dil particles. At 2, 4, and 8 weeks after surgery, Dil-labeled cells were observed at tendon-bone interface by fluorescence microscope. In the experimental group, no obvious signal changes of tendon-bone interface were observed by MR imaging. The maximum biomechanical pull-out strength was not statistically different between experimental and control groups at 2 weeks, but significantly higher in the experimental group at 4 and 8 weeks after surgery (P < 0.05).

CONCLUSION

The present study indicated that the transplanted BMSCs could promote tendon-to-bone tunnel healing at 4-8 weeks postoperatively. Dil- and SPIO-labeled transplanted BMSCs distributed at the tendon-bone interface and might play a role in promoting tendon-to-bone tunnel healing, which may be translated into practical cytotherapy for patients those who need earlier rehabilitation for ligament reconstruction surgery in clinic.

Biology and augmentation of tendon-bone insertion repair

Surgical reattachment of tendon and bone such as in rotator cuff repair, patellar-patella tendon repair and anterior cruciate ligament (ACL) reconstruction often fails due to the failure of regeneration of the specialized tissue ("enthesis") which connects tendon to bone. Tendon-to-bone healing taking place between inhomogenous tissues is a slow process compared to healing within homogenous tissue, such as tendon to tendon or bone to bone healing. Therefore special attention must be paid to augment tendon to bone insertion (TBI) healing. Apart from surgical fixation, biological and biophysical interventions have been studied aiming at regeneration of TBI healing complex, especially the regeneration of interpositioned fibrocartilage and new bone at the healing junction. This paper described the biology and the factors influencing TBI healing using patella-patellar tendon (PPT) healing and tendon graft to bone tunnel healing in ACL reconstruction as examples. Recent development in the improvement of TBI healing and directions for future studies were also reviewed and discussed.

Osteointegration of soft tissue grafts within the bone tunnels in anterior cruciate ligament reconstruction can be enhanced

Anterior cruciate ligament reconstruction with a soft tissue autograft (hamstring autograft) has grown in popularity in the last 10 years. However, the issues of a relatively long healing time and an inferior histological healing result in terms of Sharpey-like fibers connection in soft tissue grafts are still unsolved. To obtain a promising outcome in the long run, prompt osteointegration of the tendon graft within the bone tunnel is essential. In recent decades, numerous methods have been reported to enhance osteointegration of soft tissue graft in the bone tunnel. In this article, we review the current literature in this research area, mainly focusing on strategies applied to the local bone tunnel environment. Biological strategies such as stem cell and gene transfer technology, as well as the local application of specific growth factors have been reported to yield exciting results. The use of biological bone substitute and physical stimulation also obtained promising results. Artificially engineered tissue has promise as a solution to the problem of donor site morbidity. Despite these encouraging results, the current available evidence is still experimental. Further clinical studies in terms of randomized control trial in the future should be conducted to extrapolate these basic science study findings into clinical practice.

Using low-intensity pulsed ultrasound to improve muscle healing after laceration injury: an in vitro and in vivo study

The purpose of this study was to determine whether low-intensity pulsed ultrasound (LIPUS) could enhance the regeneration of myofibers and shorten the healing time in injured muscle. NIH C2C12 cells, a well-known myoblastic cell line, are subclones derived from the mouse myoblast cell line established from normal adult C3H mouse leg muscle. The cells differentiate rapidly and produce extensive contracting myotubes expressing characteristic muscle proteins. We exposed C2C12 cells to LIPUS therapy using the EXOGEN 2000+ system ultrasound apparatus (Exogen Inc., Piscataway, NJ, USA) with a total treatment of 20 min every 24 h. At intervals of 2, 4, 6 and 8 days, cell growth was measured by the increase in cell number and western blot analysis of myogenin and actin. Forty mice (C57BL10J+/+) were divided into five groups of eight animals each and used in the published laceration injury model. The gastrocnemius muscle of the left leg was lacerated in all the animals. The control group (sham ultrasound) did not undergo LIPUS therapy. The ultrasound 7-, 14-, 21- and 28-day groups (only changing the number of days during which the ultrasound was applied to the injured muscle) were treated with LIPUS (20 min/day) for 7, 14, 21 and 28 consecutive days, respectively. All animals were sacrificed at 4 weeks after the injury. Evaluation methods included muscle regeneration and muscle contractile properties. LIPUS therapy produced a significantly higher proliferative rate and cell number at days 6 and 8 (p < 0.05). Densitometric evaluation revealed an increase in myogenin and actin proteins in cells treated with LIPUS in the 4-, 6- and 8-day groups. The regeneration of myofibers, fast-twitch and tetanus of LIPUS-treated muscles (21 and 28 days) was significantly greater relative to control muscles. There was no major strength difference between the normal non-injured muscle and the group treated with LIPUS for 28 days. In conclusion, this was the first experimental study to show that LIPUS therapy is able to enhance the regeneration of myofibers with better physiologic performance in injured mice muscles after laceration, especially prior to postoperative week 4. Findings of this study demonstrate a scientific basis for future clinical trials and establish an indication for LIPUS in enhancing muscle healing after laceration injury.

Graft healing in anterior cruciate ligament reconstruction

Successful anterior cruciate ligament reconstruction with a tendon graft necessitates solid healing of the tendon graft in the bone tunnel. Improvement of graft healing to bone is crucial for facilitating an early and aggressive rehabilitation and ensuring rapid return to pre-injury levels activity. Tendon graft healing in a bone tunnel requires bone ingrowth into the tendon. Indirect Sharpey fiber formation and direct fibrocartilage fixation confer different anchorage strength and interface properties at the tendon-bone interface. For enhancing tendon graft-to-bone healing, we introduce a strategy that includes the use of periosteum, hydrogel supplemented with periosteal progenitor cells and bone morphogenetic protein-2, and a periosteal progenitor cell sheet. Future studies include the use of cytokines, gene therapy, stem cells, platelet-rich plasma, and mechanical stress for tendon-to-bone healing. These strategies are currently under investigation, and will be applied in the clinical setting in the near future.

The effect of tunnel placement on bone-tendon healing in anterior cruciate ligament reconstruction in a goat model

BACKGROUND

Misplacement of the bone tunnels is one of the main causes of graft failure of anterior cruciate ligament surgery.

HYPOTHESIS

Anatomic tunnel placement in anterior cruciate ligament surgery reconstruction will lead to improved outcomes, including biological ingrowth and biomechanical properties, when compared with nonanatomic tunnel placement.

STUDY DESIGN

Controlled laboratory study.

METHODS

Anterior cruciate ligament surgery reconstructions were performed on 3 different groups of goats (1 anatomic tunnel placement group and 2 different nonanatomic tunnel placement groups, with 10 goats in each group). For each group of 10 knees, 3 knees were used for histologic evaluation (bone tunnel enlargement, number of osteoclasts at the bone tendon interface, and revascularization of the graft) and 7 knees were used for biomechanical testing (anterior tibial translation, in situ force, cross-sectional area, and ultimate failure load). Animals were sacrificed at 12 weeks after surgery.

RESULTS

The anatomic tunnel placement group showed less tunnel enlargement on the tibial side, fewer osteoclasts on both the tibial and femoral sides, and more vascularity in the femoral side when compared with the 2 nonanatomic reconstruction groups. Biomechanically, the anatomic tunnel placement group demonstrated less anterior tibial translation and greater in situ force than both nonanatomic tunnel placement groups.

CONCLUSION

Anatomic tunnel placement leads to superior biological healing and biomechanical properties compared with nonanatomic placement at 12 weeks after anterior cruciate ligament surgery reconstruction in a goat model.

CLINICAL RELEVANCE

The findings of this study demonstrate the importance of anatomic tunnel placement in anterior cruciate ligament surgery reconstruction.

Tendon bone healing can be enhanced by demineralized bone matrix: a functional and histological study

Rotator cuff repair surgery has high failure rates, with tendon reattachment to bone remaining a challenging clinical problem. Increasing the integrity of the healing tendon-bone interface has been attempted by adopting a number of different augmentation strategies. Because of chondrogenic and osteogenic properties we hypothesise that demineralized bone matrix (DBM) augmentation of a healing tendon-bone interface will result in improved function, and a morphology that more closely resembles that of a normal enthesis, compared with nonaugmented controls in an ovine patellar tendon model. The right patellar tendon was detached from its insertion and reattached to an osteotomized bone bed using suture anchors. Two groups were analyzed, the control group (without augmentation) and the DBM group (DBM interposed between the tendon and bone). Animals were sacrificed at 12 weeks. Force plate, mechanical, and histomorphometric analyses were performed. Tendon repairs failed at a rate of 33 and 0% for the control and DBM groups, respectively. DBM augmentation resulted in significantly improved functional weight bearing and increased amounts of fibrocartilage and mineralized fibrocartilage. This study shows that DBM enhances tendon-bone healing and may reduce the high failure rates associated with rotator cuff repair clinically.

Effect of transosseous application of low-intensity ultrasound at the tendon graft-bone interface healing: gene expression and histological analysis in rabbits

The present study investigates the effect of transosseous low-intensity pulsed ultrasound (LiUS) on the healing at tendon graft-bone interface, in molecular and histological level. The anterior cruciate ligament (ACL) in both knees of 52 New Zealand White rabbits was excised and replaced with the long digital extensor. A custom-made ultrasound transducer was implanted onto the medial tibial condyle, adjacent to the surface of the bone tunnel at both knees of the rabbits. The LiUS-treated right knees received 200-mus bursts of 1 MHz sine waves at a pulse repetition rate of 1 kHz and with 30 mW/cm(2) spatial-average temporal-average intensity for 20 min daily (study group), while the left knee received no LiUS (control group). Thirty-six rabbits were used to perform semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis from both study and control groups for transforming growth factor-beta1 (TGF-beta1), biglycan and collagen I. RT-PCR products showed statistically significant upregulation of biglycan and collagen I gene expression in the study group, while TGF-beta1 gene expression exhibited a bimodal profile. Histological examination performed in 16 rabbits from both groups supported the findings of the molecular analysis, indicating a faster healing rate and a more efficient ligamentization process after ultrasound treatment. These findings suggest that transosseous application of LiUS enhances the healing rate of the tendon graft-bone interface, possibly by affecting the expression levels of genes significant for the tendon to bone healing process.

The effects of LIPUS on soft-tissue healing: a review of literature

INTRODUCTION

Ultrasound is widely used for imaging purposes and as an adjunct to physiotherapy. Low-intensity pulsed ultrasound (LIPUS), having removed the thermal component found at higher intensities, is used to improve bone healing. However, its potential role in soft-tissue healing is still under investigation.

MATERIAL AND METHODS

We searched on Medline using the keywords: low-intensity pulsed ultrasound, LIPUS and LIPUS and soft-tissue healing. Thirty-two suitable articles were identified.

RESULTS

Research, mainly pre-clinical, so far has shown encouraging result, with LIPUS able to promote healing in various soft tissues such as cartilage, inter-vertebral disc, etc. The effect on the bone-tendon junction, however, is primarily on bone. The role of LIPUS in treating tendinopathies is questionable. Adequately powered human studies with standardisation of intensities and dosages of LIPUS for each target tissue are needed.

High-intensity focused ultrasound ablation of ex vivo bovine achilles tendon

Small tears in tendons are a common occurrence in athletes and others involved in strenuous physical activity. Natural healing in damaged tendons can result in disordered regrowth of the underlying collagen matrix of the tendon. These disordered regions are weaker than surrounding ordered regions of normal tendon and are prone to re-injury. Multiple cycles of injury and repair can lead to chronic tendinosis. Current treatment options either are invasive or are relatively ineffective in tendinosis without calcifications. High-intensity focused ultrasound (HIFU) has the potential to treat tendinosis noninvasively. HIFU ablation of tendons is based on a currently-used surgical analog, viz., needle tenotomy. This study tested the ability of HIFU beams to ablate bovine tendons ex vivo. Two ex vivo animal models were employed: a bare bovine Achilles tendon (deep digital flexor) on an acoustically absorbent rubber pad, and a layered model (chicken breast proximal, bovine Achilles tendon central and a glass plate distal to the transducer). The bare-tendon model enables examination of lesion formation under simple, ideal conditions; the layered model enables detection of possible damage to intervening soft tissue and consideration of the possibly confounding effects of distal bone. In both models, the tissues were degassed in normal phosphate-buffered saline. The bare tendon was brought to 23 degrees C or 37 degrees C before insonification; the layered model was brought to 37 degrees C before insonification. The annular array therapy transducer had an outer diameter of 33 mm, a focal length of 35 mm and a 14-mm diameter central hole to admit a confocal diagnostic transducer. The therapy transducer was excited with a continuous sinusoidal wave at 5.25 MHz to produce nominal in situ intensities from 0.23-2.6 kW/cm(2). Insonification times varied from 2-10 s. The focus was set over the range from the proximal tendon surface to 7 mm deep. The angle of incidence ranged from 0 degrees (normal to the tissue surface) to 15 degrees . After insonification, tendons were dissected and photographed, and the dimensions of the lesions were measured. Transmission electron micrographs were obtained from treated and untreated tissue regions. Insonification produced lesions that mimicked the shape of the focal region. When lesions were produced below the proximal tendon surface, no apparent damage to overlying soft tissue was apparent. The low intensities and short durations required for consistent lesion formation, and the relative insensitivity of ablation to small variations in the angle of incidence, highlight the potential of HIFU as a noninvasive treatment option for chronic tendinosis.

Histologic and biomechanical analysis of anterior cruciate ligament graft to bone healing in skeletally immature sheep

PURPOSE

It was our aim to establish an animal model and to investigate the tendon graft-to-bone and physis healing process in skeletally immature sheep after reconstruction of the anterior cruciate ligament (ACL).

METHODS

Thirty-two immature sheep aged 4 months underwent a fully transphyseal ACL reconstruction by use of a soft-tissue graft. The animals were subsequently killed after 3, 6, 12, and 24 weeks and analyzed histologically and biomechanically.

RESULTS

There was a transient hypertrophy of the physis tissue at the passing site of the graft. Anchoring Sharpey-like fibers evolved as early as 3 weeks after surgery. A strong expression of collagen III messenger ribonucleic acid within the first 6 weeks preceded this anchoring process. The maximum load to failure of the tendon graft in the reconstructed knees initially decreased to 37.8 +/- 17.8 N after 3 weeks and was restored to 522.9 +/- 113 N after 24 weeks. Tendon graft stiffness was restored to 86% when compared with the control knees.

CONCLUSIONS

The early anchoring by Sharpey fibers was found at 3 weeks with continued maturation to 24 weeks. This development of anchoring fibers corresponded to that of biomechanical strength, starting with 5% of the normal knee at 3 weeks and then 15.2% at 6 weeks, 41.2% at 12 weeks, and 69% at 24 weeks. Tendon graft-to-bone and physis healing in skeletally immature sheep is further characterized by a transient hypertrophy of the physis cartilage. The physis recovers well from the trauma of drilling and placement of a soft-tissue graft. The early development of Sharpey-like fibers results in a solid integration of the graft into bone in a timely manner.

CLINICAL RELEVANCE

ACL reconstruction in skeletally immature individuals is still controversial. This study describes in detail the histologic and biomechanical stages of tendon graft healing to the bone and physis. These data enrich the existing knowledge of previous studies in adult sheep and may provide a basis for further research in the controversial field of ACL reconstruction during growth.

Augmentation of tendon-to-bone healing with a magnesium-based bone adhesive

BACKGROUND

Healing of an anterior cruciate ligament graft in a bone tunnel occurs by formation of fibrous scar tissue, which is weaker than the normal fibrocartilaginous insertion.

HYPOTHESIS

We hypothesized that a magnesium-based bone adhesive would improve tendon-to-bone healing in a rabbit anterior cruciate ligament reconstruction model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Thirty-five New Zealand White rabbits underwent bilateral anterior cruciate ligament reconstructions with semitendinosus autografts. A total of 12.5 g of bone adhesive was placed in the intraosseous tunnel around the graft in one limb, while the tunnels in the contralateral limb received no implant. Sixteen animals each were sacrificed at 3 weeks and at 6 weeks (12 biomechanical testing/4 histology). Outcomes included semiquantitative histologic analyses for new cartilage formation and fibrous tissue formation in the tendon-bone interface, microcomputed tomography to quantify new bone formation along the bone tunnel, and biomechanical testing of load-to-failure and stiffness. Three animals were sacrificed at time 0 to confirm adequate tunnel fill with the bone adhesive on microcomputed tomography.

RESULTS

All specimens had adequate tunnel fill with the bone adhesive at time 0. Application of the bone adhesive resulted in more cartilage formation and less fibrous tissue formation at the tendon-bone interface at 6 weeks compared with controls (P < .05). There was significantly more bone formation in the tibia of the treated limbs at 6 weeks (P = .01). The load-to-failure was significantly higher in the treated group at 6 weeks (71.8 +/- 31.8 N vs 43.4 +/- 14.8 N; P = .04). There were no differences in stiffness at either time point, and there were no differences at 3 weeks in any outcome variable.

CONCLUSION

The magnesium-based bone adhesive improves tendon-to-bone healing based on histologic and biomechanical testing at 6 weeks in a rabbit model of anterior cruciate ligament reconstruction.

CLINICAL RELEVANCE

Further studies are needed to investigate the clinical potential of this bone adhesive to enhance healing and decrease recovery time in soft-tissue ligament reconstruction.

Biological augmentation of rotator cuff tendon repair

A histologically normal insertion site does not regenerate following rotator cuff tendon-to-bone repair, which is likely due to abnormal or insufficient gene expression and/or cell differentiation at the repair site. Techniques to manipulate the biologic events following tendon repair may improve healing. We used a sheep infraspinatus repair model to evaluate the effect of osteoinductive growth factors and BMP-12 on tendon-to-bone healing. Magnetic resonance imaging and histology showed increased formation of new bone and fibrocartilage at the healing tendon attachment site in the treated animals, and biomechanical testing showed improved load-to-failure. Other techniques with potential to augment repair site biology include use of platelets isolated from autologous blood to deliver growth factors to a tendon repair site. Modalities that improve local vascularity, such as pulsed ultrasound, have the potential to augment rotator cuff healing. Important information about the biology of tendon healing can also be gained from studies of substances that inhibit healing, such as nicotine and antiinflammatory medications. Future approaches may include the use of stem cells and transcription factors to induce formation of the native tendon-bone insertion site after rotator cuff repair surgery.

Strategies to improve anterior cruciate ligament healing and graft placement

Recent improvements in anterior cruciate ligament (ACL) reconstruction have been notable for strategies to improve ACL healing and to improve graft placements. The controversial choice of 1-bundle or 2-bundle grafts requires an advanced knowledge of native ACL insertional anatomy and an appreciation for the kinematic effects of graft placements. Understanding the limitations of surgical techniques to place tunnels is important. Once grafts are placed, new biologic strategies to promote intra-articular and intraosseous healing are evolving. Although these biologic engineering strategies are currently experimental, they are projected for clinical application in the near future.

Comparison of poly-L-lactide and polylactide carbonate interference screws in an ovine anterior cruciate ligament reconstruction model

PURPOSE

The purpose of this study was to compare polylactide carbonate (PLC) interference screws with poly-L-lactide (PLLA) screws in an ovine anterior cruciate ligament reconstruction model.

METHODS

A PLC screw or PLLA screw was placed in the center of a 4-strand soft-tissue autograft fixating the graft within the tibial tunnel. Assessments were made at 6 and 12 weeks for fixation strength and at time points of 6, 12, 26, and 52 weeks via computed tomography and histology.

RESULTS

No adverse or inflammatory reactions were noted for either material at any time point. Mechanical fixation strength increased from 6 to 12 weeks for both the PLC and PLLA screws, with no significant differences in fixation strength being found between the 2 groups. By 26 weeks, the PLC screw was partially replaced by new bone, a process that was completed by 52 weeks. The PLLA screws were intact and surrounded by a fibrous layer at 52 weeks with no obvious resorption. New bone formation within the tendon construct located in the bone tunnel proximal to the interference screw was also noted in the PLC screw group but was not observed in the PLLA group.

CONCLUSIONS

This study has supported the hypothesis that this bioabsorbable composite has sufficient mechanical properties and strength retention to function successfully as an interference screw but also stimulates a biologic healing response, enabling replacement by bone and tunnel healing.

CLINICAL RELEVANCE

This study shows both the satisfactory mechanical characteristics and osteoconductive nature of PLC used in an interference screw in an ovine anterior cruciate ligament reconstruction model.