Area, length and mineralization content of new bone at bone-tendon junction predict its repair quality

Rapamycin facilitates healing of the tendon-bone interface in an aging rat model of chronic rotator cuff injury

BACKGROUND

Tendon-bone interface (TBI) healing in chronic rotator cuff injury (CRCI) in older individuals is a common clinical challenge due to cellular senescence, as well as decreased tissue repair and regeneration. Many studies have demonstrated the antiaging, improved tissue repair, and bone regeneration properties of rapamycin (RPM) in multiple age-related diseases. This study aimed to explore the effects of RPM on TBI healing after CRCI in an aging rat model.

METHODS

A CRCI model was established in 60 Sprague-Dawley rats (24 months old). Rats were then randomly allocated into the control, 0.1 μg RPM, and 1 μg RPM groups. At 4 and 8 weeks postreconstructive surgery, the supraspinatus tendon-humerus complexes were harvested for biomechanical, microimaging, histological, and immunohistochemical evaluations.

RESULTS

Biomechanical testing results demonstrated that the failure load, ultimate strength, and stiffness of the 2 RPM groups were significantly higher than those of the control group at 4 and 8 weeks postoperatively. Microradiographically, both RPM groups had significantly higher values of bone mineral density and the ratio of trabecular bone volume to total volume than controls at each time point. Moreover, the RPM groups had higher histological scores and showed better regenerated TBI, characterized by better organizational tissue, more fibrocartilage cells, and more bone formation. Immunohistochemical evaluations showed that RUNX2-, SOX9-, and SCX-positive cells were significantly more in the 2 RPM groups than in the controls at each time point.

CONCLUSIONS

RPM may effectively enhance CRCI healing after reconstruction by facilitating osteogenesis, tenogenesis, and fibrocartilage reformation at the TBI, as well as improving biomechanical properties.

Local Administration of Metformin Improves Bone Microarchitecture and Biomechanical Properties During Ruptured Canine Achilles Tendon-Calcaneus Interface Healing

BACKGROUND

Tendon-bone interface (TBI) healing is a clinical dilemma that is closely relevant to new bone formation and remodeling at the repair site. Previous studies showed that metformin is an osteogenic inducer for stem cells in vitro and capable of stimulating bone regeneration in vivo.

HYPOTHESIS

Metformin would be effective for promoting TBI healing by enhancing new bone formation and remodeling.

STUDY DESIGN

Controlled laboratory study.

METHODS

Canine bone marrow stem cells (BMSCs) were cultured with various concentrations of metformin (0, 10, 50, 100, 200 μM). The effect of metformin on the osteogenic differentiation of canine BMSCs was evaluated via alizarin red staining and osteogenic gene expression. Eighteen mature beagles were included in a bilateral Achilles tendon-calcaneus (ATC) interface injury model. The right interface was reattached via surgical repair only, while the left was surgically reattached after implanting a fibrin glue containing metformin. At postoperative week 4 or 8, the healing quality of the wounded ATC interfaces was evaluated.

RESULTS

In vitro experiments determined that metformin was an osteogenic inducer for canine BMSCs. In vivo experiments showed that the metformin-treated ATC interfaces were repaired with significantly greater failure load and stiffness than was the no-metformin control site (P < .05 for all). Micro-computed tomography analysis showed that the metformin-treated specimens presented significantly higher bone volume/total volume and trabecular thickness than did the no-metformin control specimens (P < .05 for all), as confirmed via hematoxylin and eosin staining. Immunohistochemical staining showed that significantly more osteocalcin-positive cells were located at the newly formed bones treated with metformin than at the no-metformin control site at week 4 (P < .05). Masson trichrome staining showed that significantly more oriented collagen fibers anchored into the newly formed bone of the metformin-treated site than the no-metformin control site (P < .05).

CONCLUSION

Metformin induced the osteogenesis of canine BMSCs in vitro, and local administration of metformin provided an improvement of bone microarchitecture at the calcaneus as well as an increase in the tensile properties of the repaired ATC interfaces in canines.

CLINICAL RELEVANCE

Findings of the study indicate that local administration of metformin may be an effective strategy for TBI healing in clinic.

Effect of Low-Intensity Pulsed Ultrasound on the Graft-Bone Healing of Artificial Ligaments: An In Vitro and In Vivo Study

BACKGROUND

As many researchers have focused on promoting the graft-bone healing of artificial ligaments, even with numerous chemical coatings, identifying a biosafe, effective, and immediately usable method is still important clinically.

PURPOSE

(1) To determine whether a low-intensity pulsed ultrasound system (LIPUS) promotes in vitro cell viability and osteogenic differentiation and (2) to assess the applicability and effectiveness of LIPUS in promoting the graft-bone healing of artificial ligaments in vivo.

STUDY DESIGN

Controlled laboratory study.

METHODS

Polyethylene terephthalate (PET) sheets and grafts were randomly assigned to control and LIPUS groups. MC3T3-E1 preosteoblasts were cultured on PET sheets. Cell viability and morphology were evaluated using a live/dead viability assay and scanning electron microscopy. Alkaline phosphatase activity, calcium nodule formation, and Western blot were evaluated for osteogenic differentiation. For in vivo experiments, the effect of LIPUS was evaluated via an extra-articular graft-bone healing model in 48 rabbits: the osteointegration and new bone formation were tested by micro-computed tomography and histological staining, and the graft-bone bonding was tested by biomechanical testing.

RESULTS

Cell viability was significantly higher in the LIPUS group as compared with control (living and dead compared between control and LIPUS groups, P = .0489 vs P = .0489). Better adherence of cells and greater development of extracellular matrix were observed in the LIPUS group. Furthermore, LIPUS promoted alkaline phosphatase activity, calcium nodule formation, and the protein expression of collagen 1 (P = .0002) and osteocalcin (P = .0006) in vitro. Micro-computed tomography revealed higher surrounding bone mass at 4 weeks and newly formed bone mass at 8 weeks in the LIPUS group (P = .0014 and P = .0018). Histological analysis showed a narrower interface and direct graft-bone contact in the LIPUS group; the surrounding bone area at 4 weeks and the mass of newly formed bone at 4 and 8 weeks in the LIPUS group were also significantly higher as compared with control (surrounding bone, P < .0001; newly formed bone, P = .0016 at 4 weeks and P = .005 at 8 weeks). The ultimate failure load in the LIPUS group was significantly higher than in the control group (P < .0001 at 4 weeks; P = .0008 at 8 weeks).

CONCLUSION

LIPUS promoted the viability and osteogenic differentiation of MC3T3-E1 preosteoblasts in vitro and enhanced the graft-bone healing of PET artificial ligament in vivo.

CLINICAL RELEVANCE

LIPUS is an effective physical stimulation to enhance graft-bone healing after artificial ligament implantation.

The Role of Biodegradable Magnesium and Its Alloys in Anterior Cruciate Ligament Reconstruction: A Systematic Review and Meta-Analysis Based on Animal Studies

Objective: The actual efficacy of magnesium and its alloy in anterior cruciate ligament reconstruction (ACLR) was systematically evaluated to reduce the risk of translation from animal experiments to the clinic.

Methods: Databases of PubMed, Ovid-Embase, Web of Science, CNKI, Wanfang, VIP, and CBM were searched for literature in July 2021. Screening of search results, data extraction, and literature quality evaluation were undertaken independently by two reviewers.

Results and discussion: Seven articles were selected for the meta-analysis. The results showed that the mechanical properties of the femoral-tendon graft–tibia complex fixed with magnesium and its alloys were comparable to those fixed with titanium and its alloys, and magnesium and its alloys were superior to titanium and its alloys in promoting new bone formation. In addition, the unique biodegradability made magnesium and its alloys an orthopedic implant with significant therapeutic potential. However, whether the degradation rate of magnesium and its alloy can match the rate of bone-tendon integration, and whether the bioconjugation of bone-tendon after degradation can meet the exercise load still needs to be explored in further detail. Simultaneously, it is necessary for future research to improve and standardize experimental design, result measurement, etc., so as to minimize the risk of transforming animal experimental results into clinical practice.

Treadmill running initiation times and bone-tendon interface repair in a murine rotator cuff repair model

Postoperative exercise has been demonstrated to be beneficial for bone-tendon interface (BTI) healing, yet the debate regarding the optimal time to initiate exercise after tendon enthesis repair is ongoing. This study aimed to evaluate the initiation times for exercise after enthesis repair. A total of 192 C57BL/6 mice underwent acute supraspinatus tendon injury repair. The animals were then randomly assigned to four groups: free cage activity after repair (control group); treadmill running started on postoperative day 2 (2-day delayed group); treadmill running started on postoperative day 7 (7-day delayed group), and treadmill running started on postoperative day 14 (14-day delayed group). Mice were euthanized at 4 and 8 weeks postoperatively, and histological, biomechanical, and bone morphometric tests were performed. Higher failure loads and bone volume fractions were found for the 7-day delayed group and the 14-day delayed group at 4 weeks postoperatively. The 7-day delayed group had better biomechanical properties and higher bone volume fractions than the 2-day delayed group at 4 weeks postoperatively. Histologically, the 7-day delayed group exhibited lower modified tendon-to-bone maturity scores than the control group and the 2-day delayed group at 4 and 8 weeks postoperatively. Quantitative reverse-transcription polymerase chain reaction results showed that the 7-day delayed group had higher expressions of chondrogenic- and osteogenic-related genes. Statement of clinical significance: Postoperative treadmill running initiated on postoperative day 7 had a more prominent effect on BTI healing than other treatment regimens in this study and could accelerate BTI healing and rotator cuff repair.

Calcitonin Gene-Related Peptide Influences Bone-Tendon Interface Healing Through Osteogenesis: Investigation in a Rabbit Partial Patellectomy Model

Background:

Calcitonin gene-related peptide (CGRP), which has been shown to play an important role in osteogenesis during fracture repair, is also widely distributed throughout the tendon and ligament. Few studies have focused on the role of CGRP in repair of the bone-tendon interface (BTI).

Purpose:

To explore the effect of CGRP expression on BTI healing in a rabbit partial patellectomy model.

Study Design:

Controlled laboratory study.

Methods:

A total of 60 mature rabbits were subjected to a partial patellectomy and then randomly assigned to CGRP, CGRP-antagonist, and control groups. In the CGRP-antagonist group, the CGRP receptor antagonist BIBN4096BS was administered to block CGRP receptors. The patella–patellar tendon complex was harvested at 8 and 16 weeks postoperatively and subjected to radiographic, microlaser Raman spectroscopy, histologic, and biomechanical evaluation.

Results:

Radiographic data showed that local CGRP expression improved the growth parameters of newly formed bone, including area and volumetric bone mineral density (P < .05 for both). Raman spectroscopy revealed that the relative bone mineral composition increased in the CGRP group compared with in the control group and the CGRP-antagonist group (P < .05 for both). Histologic testing revealed that the CGRP group demonstrated better integration, characterized by well-developed trabecular bone expansion from the residual patella and marrow cavity formation, at the 8- and 16-week time points. Mechanical testing demonstrated that the failure load, ultimate strength, and stiffness in the CGRP group were significantly higher than those in the control group (P < .05 for all), whereas these parameters in the CGRP-antagonist group were significantly lower compared with those in the control group at 16 weeks after surgery (P < .05 for all).

Conclusion:

Increasing the local concentration of CGRP in the early stages of BTI healing enhanced osteogenesis in a rabbit partial patellectomy model and promoted healing of the BTI injury, whereas treatment using a CGRP antagonist had the opposite effect. However, exogenous CGRP expression did not induce novel bone remolding.

Clinical Relevance:

CGRP may have potential as a new therapy for BTI injuries or may be added to postoperative regimens to facilitate healing.

Effect of Exercise Intensity on the Healing of the Bone-Tendon Interface: A Mouse Rotator Cuff Injury Model Study

BACKGROUND

Injuries at the bone-tendon interface (BTI) are common findings in clinical practice. Rehabilitation procedures after BTI surgery are important but are controversial.

PURPOSE

To investigate the effects of different exercise intensities on BTI healing by means of an established mouse rotator cuff injury model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 150 specific pathogen free male C57BL/6 mice, with supraspinatus insertion injury, were randomly assigned to 1 of 5 groups according to postoperative rehabilitation of different exercise intensities: (1) control group, (2) low-intensity exercise group, (3) moderate-intensity exercise group, (4) high-intensity exercise group, and (5) increasing-intensity exercise group (IG). The specimens were harvested 4 or 8 weeks postoperatively for microarchitectural, histological, molecular biological, and mechanical evaluations.

RESULTS

Histological test results showed that the degrees of tissue fusion and polysaccharide protein distribution at the healing interface at 4 and 8 weeks after surgery were significantly better in the IG than in the other 4 groups. Synchrotron radiation micro-computed tomography showed that the quantity of subchondral bone at the enthesis (bone volume/total volume fraction, trabecular thickness, trabecular number) was higher and trabecular separation was lower in the IG than in the other 4 groups. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis revealed that the healing interface in the IG expressed more transcription factors, such as sox 9, runx 2, and scleraxis, than the interfaces in the other groups. Although no significant difference was seen in the cross-sectional area between the groups at postoperative weeks 4 and 8 (P > .05), the tensile load, ultimate strength, and stiffness of the specimens in the IG were significantly better than those in the other 4 groups (P < .05).

CONCLUSION

The rehabilitation program with increasing-intensity exercise was beneficial for BTI healing.

CLINICAL RELEVANCE

The results of this study provide evidence supporting the use of a simple and progressive exercise rehabilitation program after rotator cuff surgery.

Sustained release of collagen-affinity SDF-1α from book-shaped acellular fibrocartilage scaffold enhanced bone-tendon healing in a rabbit model

Rapid and functional bone-tendon (B-T) healing remains a difficulty in clinical practice. Tissue engineering has emerged as a promising strategy to address this problem. However, the majority of tissue engineering scaffolds are loaded with stem cells to enhance the regenerability in B-T healing, which is complicated and inconvenient for clinical application. Accordingly, developing a cell-free scaffold with chemotactic function and chondrogenic inducibility may be an effective approach. In this study, a collagen affinity peptide derived from the A3 domain of von Willebrand factor (a hemostasis factor) was fused into the C-terminal of a stromal cell-derived factor-1α (SDF-1α) to synthesize a recombinant SDF-1α capable of binding collagen and chemotactic activity. The recombinant SDF-1α was then tethered on the collagen fibers of a book-shaped acellular fibrocartilage scaffold (BAFS), thus fabricating a novel scaffold (C-SDF-1α/BAFS) with chemotactic function and chondrogenic inducibility. In vitro tests determined that this scaffold was noncytotoxic and biomimetic, could attract stem cells migrating to the scaffold using sustainably released C-SDF-1α, and inducedthe interacting stem cells down the chondrogenic lineage. In vivo, the C-SDF-1α/BAFS significantly enhanced the B-T healing in a rabbit partial patellectomy model, as shown by the larger cartilaginous metaplasia region, better fibrocartilage regeneration, additional bone formation, and improved biomechanical properties. Therefore, the findings of the study demonstrate that the C-SDF-1α/BAFS could potentially be applied for B-T healing.

Recombinant human bone morphogenetic protein-4 enhances tendon-to-bone attachment healing in a murine model of rotator cuff tear

Background

Injuries of tendon-to-bone attachments (TBA) are common clinical challenges. Bone morphogenetic protein-4 (BMP-4) is potent in chondrogenesis. However, studies focusing on the influence of BMP-4 on the healing of TBA are scarce. Thus, this study's objective was to explore the effect of BMP-4 on the healing of TBA in a murine model of rotator cuff tear.

Methods

An injury model of the supraspinatus tendon (SST) insertion was established on a total of 120 mature C57 black (BL)/6 mice (12 weeks old), who were then randomly allocated into 3 groups: BMP-4, noggin (an inhibitor of all BMP activities), and control, At weeks 2 and 4 after surgery, the supraspinatus tendon-humerus complexes (SSTHC) were harvested for microradiographic, histologic, immunofluorescent, and biomechanical evaluations.

Results

Radiographic data showed that BMP-4 was able to improve the quality of subchondral bone, manifested as higher bone volume fraction (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), and lower trabecular spacing (Tb.Sp). Histologically, the BMP-4 group at week-2 and -4 showed a better TBA healing interface, characterized by better organizational integration and remodeling, thicker fibrocartilage layer, and more fibrocartilage cells. Immunofluorescence evaluation demonstrated that the number of SOX 9 positive cells in the BMP-4 group was significantly more than that in the control or noggin groups at postoperative weeks 2 and 4 (P<0.05 for all). Mechanical testing results at postoperative weeks 4 demonstrated the failure load, and stiffness in the BMP-4 group were significantly higher (P<0.05 for both), while in the noggin group were significantly lower (P<0.05 for both), compared to the control group.

Conclusions

The BMP-4 might enhance TBA healing by promoting the regeneration of fibrocartilaginous enthesis and mineralization, while this process was inhibited by noggin. Thus, BMP-4 may be a potential therapy to augment TBA healing and finally lead to more rapid rehabilitation and reduce recurrent injury risk.

Functional decellularized fibrocartilaginous matrix graft for rotator cuff enthesis regeneration: A novel technique to avoid in-vitro loading of cells

Rapid and functional enthesis regeneration after rotator cuff tear (RCT) remains a challenge in clinic. Current tissue-engineering strategies for solving this challenge are focused on developing grafts with the mode of in-vitro loading cells on a scaffold. However, this mode is complicated and time-inefficient, moreover the preservation of this graft outside a cell incubator is highly inconvenient, thus limiting their clinical application. Developing a cell-free graft with chemotaxis to recruit postoperative injected cells may be a promising approach to solve these problems. Herein, we prepared a recombinant SDF-1α (termed as C-SDF-1α) capable of binding collagen and chemotaxis, which were then tethered on the collagen fibers of book-shaped decellularized fibrocartilage matrix (BDFM) to fabricate this cell-free graft (C-SDF-1α/BDFM). This C-SDF-1α/BDFM is noncytotoxicity and low-immunogenicity, allows synovium-derived mesenchymal stem cells (SMSCs) attachment and proliferation, and shows superior chondrogenic inducibility. More importantly, C-SDF-1α/BDFM released the tethered SDF-1α with a sustained release profile in-vitro and in-vivo, thus steadily recruiting chemokine (C-X-C motif) receptor 4 positive (CXCR4⁺) cells. Rats with RCT were repaired acutely with C-SDF-1α/BDFM together with postoperative CXCR4⁺SMSCs injection (C-SDF-1α/BDFM + CXCR4⁺SMSCs), BDFM in-vitro pre-loaded CXCR4⁺SMSCs (BDFM/CXCR4⁺SMSCs), or direct suture only (CTL). At postoperative 14-day, compared with BDFM/CXCR4⁺SMSCs, C-SDF-1α/BDFM + CXCR4⁺SMSCs showed a little more CXCR4⁺SMSCs at the healing site. At postoperative week 4 or 8, rats treated with C-SDF-1α/BDFM + CXCR4⁺SMSCs presented a similar RC healing quality as BDFM/CXCR4⁺SMSCs, both of which were significantly better than the CTL. Collectively, compared with conventional BDFM/CXCR4⁺SMSCs, C-SDF-1α/BDFM, as a cell-free graft with chemotaxis, could recruit postoperative injected CXCR4⁺cells into the healing site to participating RC healing, thus avoiding the complex process of in-vitro loading cells on a scaffold and necessitating immense care for the graft outside cell incubator, making it very convenient for clinical application.

Comparison of bone surface and trough fixation on bone-tendon healing in a rabbit patella-patellar tendon injury model

BACKGROUND

Many orthopedic surgical procedures involve reattachment between tendon and bone. Whether bone-tendon healing is better facilitated by tendon fixation on a bone surface or within a tunnel is unknown. The purpose of this study was to comparatively evaluate the effects of bone surface versus bone trough fixation on bone-tendon healing in a rabbit patella-patellar tendon (PPT) injury model.

METHODS

The rabbits underwent partial patellectomy with patellar-tendon fixation on the osteotomy surface (bone surface fixation, BSF group) (n = 28) or within a bone trough (bone trough fixation, BTF group) (n = 28). The PPT interface was evaluated by macroscopic observation, micro-computed tomography scanning, histological analysis, and biomechanical testing at postoperative week 8 or week 16.

RESULTS

Macroscopically, no signs of infection or osteoarthritis were observed, and the regenerated tissue bridging the residual patella and patellar tendon showed no obvious difference between the two groups. There were significantly higher bone mineral density ​and trabecular thickness ​in BSF group compared with BTF group at week 8 (p ​< ​0.05 for both). However, the bone volume fraction (BVF), bone mineral density and trabecular thickness in BSF group were significantly lower than those in BTF group (p ​< ​0.05 for all) at week 16. Histological analysis demonstrated that new bone was formed at the proximal patella and reattached to the residual patellar tendon through a regenerated fibrocartilage-like tissue in both groups. There was more formation and better remodelling of fibrocartilage-like tissue in BTF group than BSF group at week 8 and week 16 (p ​< ​0.05 for both). Biomechanical testing revealed that there was higher failure load and stiffness at the PPT interface in BTF group than BSF group at week 16 (p ​< ​0.05 for both).

CONCLUSIONS

These results suggested that raptured tendon fixation in a bone trough resulted in superior bone-tendon healing in comparison with tendon fixation on bone surface in a rabbit PPT injury model.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

Although the structural and functional difference of knee joint between human and rabbit limit the results to be directly used in clinical, our research does offer a valuable reference for the improvement of reattachment between bone and tendon.

Comparative Evaluation of the Book-Type Acellular Bone Scaffold and Fibrocartilage Scaffold for Bone-Tendon Healing

Bone-tendon (B-T) healing is a clinical challenge due to its limited regeneration capability. Fibrocartilage regeneration and bone formation at the healing site are two critical factors for B-T healing. Promoting fibrocartilage regeneration and bone formation by tissue-engineering may be a promising treatment strategy. In this study, we innovatively fabricated two kinds of acellular scaffolds from bone or fibrocartilage tissues, namely the book-type the acellular bone scaffold (BABS) and the book-type acellular fibrocartilage scaffold (BAFS). Histologically, the two scaffolds well preserved the native extracellular matrix (ECM) structure without cellular components. In vitro studies showed BABS is superior in osteogenic inducibility, while BAFS has good chondrogenic inducibility. To comparatively investigate the efficacy on B-T healing, the BABS or BAFS were, respectively, implanted into a rabbit partial patellectomy model. Macroscopically, a regenerated bone-tendon insertion (BTI) was bridging the residual patella and patellar-tendon with no signs of infection and osteoarthritis. Radiologically, more new bone was formed at the healing interface in the BABS group as compared with the BAFS or control (CTL) groups (p < 0.05). Histologically, at postoperative week 16, histological scores were significantly better for regenerated fibrocartilage in the BAFS group or BABS group compared with the CTL group, but the BAFS group showed a significantly larger score than the BABS groups (p < 0.05). Biomechanical evaluation indicated a higher failure load and stiffness were shown in the BAFS group than those in the BABS or CTL groups at week 16 (p < 0.05). This study indicated that the BAFS is a more promising scaffold for B-T healing in comparison with the BABS. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1709-1722, 2019.

Autologous Freeze-Dried, Platelet-Rich Plasma Carrying Icariin Enhances Bone-Tendon Healing in a Rabbit Model

BACKGROUND

Tendon-bone interface (TBI) injuries are common in sports activities. Owing to the limited regenerative ability of the TBI, its functional healing remains a difficulty in clinical practice. Icariin (ICA) provides strong stimulation for osteogenesis. Platelet-rich plasma (PRP) can be used as a carrier for bioactive molecules, although its ability to provide sustained release for such molecules needs improvement.

HYPOTHESIS

Freeze-dried PRP (FD-PRP) as a carrier for ICA can provide sustained release of ICA into the tendon-bone (T-B) healing site, thus accelerating T-B healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 84 New Zealand rabbits with partial patellectomy in the hindlimb were randomly allocated into 3 different treatments: ICA incorporated with FD-PRP (ICA/FD-PRP), FD-PRP alone (FD-PRP), or saline control (CTL). The rabbit patella-patellar tendon (PP) interfaces were postoperatively harvested at postoperative week 8 or 16 for gross, radiological, histological, and mechanical evaluations.

RESULTS

Our results showed that FD-PRP can act as a carrier for sustained release of ICA into the T-B healing site. Macroscopically, no signs of infection or osteoarthritis were shown in the regenerated PP interfaces, and the area of cartilaginous metaplasia in the FD-PRP and ICA/FD-PRP groups at postoperative week 16 was significantly larger than that of the CTL group (P < .05 for all). Radiologically, micro-computed tomography showed that new bone which formed at the healing site in the ICA/FD-PRP group was significantly increased, remodeled, and mineralized in comparison with the CTL group (P < .05 for all). Histologically, the ICA/FD-PRP group exhibited a significant native PP interface, as shown by the enlargement and remodeling of new bone, well-organized collagen fibers, and robust production of proteoglycans in the regenerated fibrocartilage. The mechanical strength of the regenerated PP interface was significantly improved in the ICA/FD-PRP group. Significantly higher failure load and stiffness were shown in the ICA/FD-PRP group compared with the CTL and FD-PRP groups, respectively (P < .05 for all).

CONCLUSION

FD-PRP is a suitable sustained-release carrier for ICA, and ICA/FD-PRP can provide sustained release of ICA into the T-B healing site, thus effectively accelerating T-B healing.

CLINICAL RELEVANCE

Findings of this study demonstrate the feasibility of using FD-PRP as a carrier for ICA to improve T-B healing and provide a foundation for future clinical application.

Effect of Low-Intensity Pulsed Ultrasound After Autologous Adipose-Derived Stromal Cell Transplantation for Bone-Tendon Healing in a Rabbit Model

BACKGROUND

Low-intensity pulsed ultrasound (LIPUS), as a safe biophysiotherapy, can enhance bone-tendon (B-T) healing in vivo and induce osteogenic or chondrogenic differentiation of mesenchymal stromal cells in vitro. This study aimed to determine whether LIPUS can improve the efficacy of transplanted mesenchymal stromal cells on B-T healing.

HYPOTHESIS

LIPUS can induce lineage-specific differentiation of transplanted adipose-derived stromal cells (ASCs) at the B-T healing site, thus resulting in superior healing quality when compared with LIPUS or ASCs alone.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 112 mature rabbits with partial patellectomy in the hindlimb were randomly assigned into mock sonication without ASCs (control), ultrasonication without ASCs (LIPUS), mock sonication with ASCs (ASCs), and ultrasonication with ASCs (LIPUS + ASCs). The treatment time of the mock sonication or ultrasonication was 20 minutes per day. Autologous ASCs were transplanted to the healing site by fibrin glue during the operation, and LIPUS was delivered daily starting at postoperative day 3 until euthanasia. The patella-patellar tendon junctions were postoperatively harvested at 8 and 16 weeks for radiological, histological, and mechanical evaluations. Additionally, 9 animals were used for ASC tracking with mCherry protein.

RESULTS

Radiologically, there was more new bone formation and remodeling in the LIPUS + ASCs group as compared with the other groups. Synchrotron radiation micro-computed tomography showed that the LIPUS + ASCs group significantly increased bone volume fraction, trabecular thickness, and trabecular number at the healing site as compared with the other groups at postoperative 8 weeks ( P < .05 for all). Histologically, immunohistochemical staining confirmed that the transplanted mCherry-ASCs can differentiate into osteoblasts and fibrochondrocytic-like cells. Meanwhile, as compared with the other groups, the LIPUS + ASCs group showed more formation and maturity of the fibrocartilage layer and new bone at postoperative weeks 8 and 16 ( P < .05 for all). Biomechanically, the LIPUS + ASCs group showed significantly higher failure load and stiffness versus the other groups at postoperative weeks 8 and 16 ( P < .05 for all).

CONCLUSION

Autologous ASC transplantation stimulated with LIPUS can result in superior B-T healing quality when compared with LIPUS or ASCs alone.

CLINICAL RELEVANCE

This study demonstrates the effectiveness of using ASC transplantation stimulated with LIPUS for B-T healing and provides a foundation for future clinical studies.

The effect of low-intensity pulsed ultrasound on bone-tendon junction healing: Initiating after inflammation stage

The purpose of this study was to explore the effect of low-intensity pulsed ultrasound (LIPUS) treatment initiating after inflammation stage on the process of bone-tendon junction (BTJ) healing in a rabbit model. Thirty-six rabbits undergoing partial patellectomy were randomly divided into two groups: control and LIPUS. The period of initial inflammatory stage is 2 weeks. So LIPUS treatment was initiated at postoperative week 2 and continued until the patella-patellar tendon (PPT) complexes were harvested at postoperative weeks 4, 8, and 16. At each time point, the PPT complexes were harvested for qRT-PCR, histology, radiographs, synchroton radiation micro computed tomography (SR-µCT), and biomechanical testing. The qRT-PCR results showed that LIPUS treatment beginning at postoperative week 2 played an anti-inflammatory role in BTJ healing. Histologically, the LIPUS group showed more advanced remodeling of the lamellar bone and marrow cavity than the control group. The area and length of the new bone in the LIPUS group were significantly greater than the control group at postoperative weeks 8 and 16. SR-µCT demonstrated that new bone formation and remodeling in the LIPUS group were more advanced than the control group. Biomechanical test results demonstrated that the failure load, ultimate strength and energy at failure were significantly higher than those of the control group. In conclusion, LIPUS treatment beginning at postoperative week 2 was able to accelerate bone formation during the bone-tendon junction healing process and significantly improved the healing quality of BTJ injury. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1697-1706, 2016.

Initiation Timing of Low-Intensity Pulsed Ultrasound Stimulation for Tendon-Bone Healing in a Rabbit Model

BACKGROUND

Low-intensity pulsed ultrasound stimulation (LIPUS) has been proven to be a beneficial biophysical therapy for tendon-bone (T-B) healing. However, the optimal time to initiate LIPUS treatment has not been determined yet. LIPUS initiated at different stages of the inflammatory phase may profoundly affect T-B healing.

PURPOSE

An established rabbit model was used to preliminarily investigate the effect of LIPUS initiation timing on T-B healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 112 mature rabbits that underwent partial patellectomy were randomly assigned to 4 groups: daily mock sonication (control group) and daily ultrasonication started immediately postoperatively (immediate group), on postoperative day 7 (7-day delayed group), or on postoperative day 14 (14-day delayed group). Peripheral leukocyte counts at the inflammatory phase were used to assess postoperative inflammation. The rabbits were sacrificed at 8 or 16 weeks postoperatively for microarchitectural, histological, and mechanical evaluations of the patella-patellar tendon (PPT) junction.

RESULTS

The biomechanical properties of the PPT junction were significantly improved in the LIPUS-treated groups. Significantly higher ultimate strength and stiffness were seen in the 7-day delayed group compared with the other groups at 8 weeks postoperatively (P < .05 for all). Newly formed bone expansion from the remaining patella in the ultrasonic treatment groups was significantly increased and remodeled compared with the control group. Micro-computed tomography analysis showed that the 7-day delayed group had significantly more bone volume and bone mineral content at the interface as compared with the other groups at 8 weeks postoperatively (P < .05 for all). Histologically, the ultrasonic treatment groups exhibited a significantly better PPT junction, as shown by more formation and remodeling of the fibrocartilage layer and newly formed bone. Additionally, peripheral leukocyte counts displayed a significant increase from postoperative day 1 to day 3 in the immediate group as compared with the other groups. Furthermore, postoperative hydrarthrosis was more likely in the immediate group.

CONCLUSION

LIPUS started at postoperative day 7 had a more prominent effect on T-B healing compared with the other treatment regimens in this study.

CLINICAL RELEVANCE

The findings of the study may help optimize the initiation timing of LIPUS for T-B healing.

A Comparative Study on the Biomechanical and Histological Properties of Bone-to-Bone, Bone-to-Tendon, and Tendon-to-Tendon Healing: An Achilles Tendon-Calcaneus Model in Goats

BACKGROUND

Surgical repair around the bone-tendon insertion (BTI) may involve bone-to-bone (BB), bone-to-tendon (BT), or tendon-to-tendon (TT) reattachment with varying healing outcome.

HYPOTHESIS

The repair of Achilles tendon-calcaneus (ATC) by reattachment of homogeneous tissue (BB or TT) would heal faster, with respect to tensile properties at the healing complex, than those of reattachment of heterogeneous tissues (BT) over time.

STUDY DESIGN

Controlled laboratory study.

METHODS

Forty-seven adolescent male Chinese goats were divided into BB, BT, and TT groups. Osteotomy of the calcaneus, reattachment of Achilles tendon to the calcaneus after removal of the insertion, and tenotomy of the Achilles tendon were performed to simulate BB, BT, and TT repair, respectively. The ATC healing complexes were harvested at 6, 12, or 24 weeks postoperatively. Mechanical and morphological properties of the healing ATC complexes were assessed by tensile testing and qualitative histology, respectively. The contralateral intact ATC complex was used as the control.

RESULTS

Failure load of BT was 33.4% lower than that of TT (P = .0243) at week 12. Ultimate strength of BT was 50.2% and 45.3% lower than that of TT at weeks 12 (P = .0002) and 24 (P = .0001), respectively. Tissue morphological characteristics of the BB and TT groups showed faster remodeling. The BT group showed limited regeneration of fibrocartilage zone and excessive formation of fibrous tissue at the healing interface.

CONCLUSION

BTI repair between homogeneous tissues (BB and TT healing) showed better healing quality with respect to mechanical and histological assessments than did healing between heterogeneous tissues (BT healing).

CLINICAL RELEVANCE

Anatomic reconstruction of ATC complex injury may be a primary concern when selecting the proper surgical approach. However, it is recommended to select fracture fixation (BB) or tendon repair (TT) instead of bone-tendon reattachment (BT) if possible to ensure better outcome at the healing interface.

Effects of low-intensity pulsed ultrasound on new trabecular bone during bone-tendon junction healing in a rabbit model: a synchrotron radiation micro-CT study

This study was designed to evaluate the effects of low-intensity pulsed ultrasound on bone regeneration during the bone-tendon junction healing process and to explore the application of synchrotron radiation micro computed tomography in three dimensional visualization of the bone-tendon junction to evaluate the microarchitecture of new trabecular bone. Twenty four mature New Zealand rabbits underwent partial patellectomy to establish a bone-tendon junction injury model at the patella-patellar tendon complex. Animals were then divided into low-intensity pulsed ultrasound treatment (20 min/day, 7 times/week) and placebo control groups, and were euthanized at week 8 and 16 postoperatively (n = 6 for each group and time point). The patella-patellar tendon specimens were harvested for radiographic, histological and synchrotron radiation micro computed tomography detection. The area of the newly formed bone in the ultrasound group was significantly greater than that of control group at postoperative week 8 and 16. The high resolution three dimensional visualization images of the bone-tendon junction were acquired by synchrotron radiation micro computed tomography. Low-intensity pulsed ultrasound treatment promoted dense and irregular woven bone formation at week 8 with greater bone volume fraction, number and thickness of new trabecular bone but with lower separation. At week 16, ultrasound group specimens contained mature lamellar bone with higher bone volume fraction and thicker trabeculae than that of control group; however, there was no significant difference in separation and number of the new trabecular bone. This study confirms that low-intensity pulsed ultrasound treatment is able to promote bone formation and remodeling of new trabecular bone during the bone-tendon junction healing process in a rabbit model, and the synchrotron radiation micro computed tomography could be applied for three dimensional visualization to quantitatively evaluate the microarchitecture of new bone in bone-tendon junction.

Enhanced patella-patellar tendon healing using combined magnetic fields in a rabbit model

BACKGROUND

A combined magnetic field (CMF) is a composite of a dynamic sinusoidal magnetic field and a magnetostatic field. Stimuli from CMFs has proved to be an effective tool for healing problem fractures and spinal fusion procedures.

HYPOTHESIS

Combined magnetic field technology will enhance healing of bone-tendon junction repair via endochondral ossification for regeneration of the fibrocartilage zone.

STUDY DESIGN

Controlled laboratory study.

METHODS

Forty-eight mature rabbits were randomly divided into CMF-treated and placebo-treated (control) groups. A partial patellectomy model was created. The CMF-treated group was subjected to CMF stimulation from the third postoperative day for 30 minutes per day up to weeks 8 or 16. At each time point, tissue samples were harvested and evaluated biomechanically and histomorphologically. The area of newly formed bone and the thickness of fibrocartilage were measured in hematoxylin and eosin-stained sections and toluidine blue-stained sections, respectively, while the density of fibrocartilage cells and the amount of proteoglycans were calculated using safranin O-stained sections. A biomechanical analysis was carried out to ascertain tensile strength.

RESULTS

Quantitative histological measurements showed that the newly formed bone and regenerated fibrocartilage zone in the CMF-treated group increased by a respective 99.2% and 41.9% compared with the control group at week 8 and a respective 97.8% and 22.8% at week 16. In the CMF-treated group at postoperative week 16, the amount of proteoglycans was 36.9% more than that of the control group, but the density of fibrocartilage cells was just 71.4% of the control group; there were no significant differences at week 8. Mechanical test results showed that energy to failure was not significantly different between the 2 groups at week 8. Yet, at week 16, load to failure, ultimate strength, and energy to failure in the CMF-treated group (311.0 ± 59.4 N, 8.46 ± 1.41 MPa, and 0.87 ± 0.17 J, respectively) were significantly higher than those in the control group (247.1 ± 65.6 N, 6.84 ± 1.12 MPa, and 0.52 ± 0.15 J, respectively).

CONCLUSION

Biophysical stimulation with CMFs enhances healing after bone-tendon junction injuries in a rabbit model.

CLINICAL RELEVANCE

These results demonstrate the feasibility of using CMFs for stimulating bone-tendon healing after repair.

Combined application of low-intensity pulsed ultrasound and functional electrical stimulation accelerates bone-tendon junction healing in a rabbit model

The objective of this study was to elucidate the combined use of low-intensity pulsed ultrasound (LIPUS) and functional electrical stimulation (FES) on patella-patellar tendon (PPT) junction healing using a partial patellectomy model in rabbits. LIPUS was delivered continuously starting day 3 postoperative until week 6. FES was applied on quadriceps muscles to induce tensile force to the repaired PPT junction 5 days per week for 6 weeks since week 7 postoperatively. Forty rabbits with partial patellectomy were randomly divided into four groups: control, LIPUS alone, FES alone, and LIPUS + FES groups. At week 12, the PPT complexes were harvested for histology, radiographs, peripheral quantitative computed tomography, and biomechanical testing. There was better remodeling of newly formed bone and fibrocartilage zone in the three treatment groups compared with the control group. LIPUS and/or FES treatments significantly increased the area and bone mineral content of new bone. The failure load and ultimate strength of PPT complex were also highly improved in the three treatment groups. More new bone formed and higher tensile properties were showed in the LIPUS + FES group compared with the LIPUS or FES alone groups. Early LIPUS treatment and later FES treatment showed the additive effects of accelerating PPT junction healing.

Effects of Sox9 gene therapy on the healing of bone-tendon junction: An experimental study

BACKGROUND

Sox9 is an operon that positively regulates the transcription of type II collagen. The generation of type II collagen plays a critical role in the healing process of the bone-tendon junction (BTJ).

MATERIALS AND METHODS

Sox9 was injected into an established bone-tendon healing model in order to observe its effect on the healing by determining the biomechanical properties of the BTJ. In addition, the recombinant adenovirus Sox9 was used to transduce the animal model samples and in vivo observations of the effect of the adenovirus-mediated Sox9 transduction as well as its promotion of the healing properties were made.

RESULTS

Sox9 was not only able to promote the healing, but also increased the biomechanical strength. The recombinant Sox9 delivered by adenoviral vector can be expressed at a high level in the damaged tissues of the bone-tendon junction, which can stimulate the production of type II collagen and improve the healing of the BTJ.

CONCLUSIONS

Based on the results of this study, we considered that gene therapy may be applicable in the healing process of the bone-tendon junction.

Extracorporeal shockwave therapy for treatment of delayed tendon-bone insertion healing in a rabbit model: a dose-response study

BACKGROUND

Tendon-bone insertion (TBI) consists of both hard and soft tissues. TBI injury with delayed repair is not uncommon. High-dose extracorporeal shockwave (ESW) is effective for treating nonunion fracture, whereas low-dose ESW is used for tendinopathy therapy. The dosing effect of ESW on delayed TBI healing is lacking.

HYPOTHESIS

Low-dose ESW might have a healing enhancement effect comparable to that of high-dose ESW in treating delayed TBI healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

Partial patellectomy was adopted to create a delayed TBI healing model by shielding the healing interface between tendon and bone. Ninety-six female New Zealand White rabbits with unilateral delayed TBI healing at the knee joint were divided into 3 groups: controls, low-dose ESW (LD-ESW; 0.06 mJ/mm(2), 4 Hz, 1500 impulses), and high-dose ESW (HD-ESW; 0.43 mJ/mm(2), 4 Hz, 1500 impulses). The TBI shielding was removed at week 4 after partial patellectomy, followed by treatment with control or ESW at week 6. The rabbits were euthanized at week 8 and week 12 for radiological, microarchitectural, histological, and mechanical assessments of healing tissues.

RESULTS

Radiologically, both the LD-ESW group and the HD-ESW group showed larger new bone area than the controls at week 8 and week 12. Microarchitectural measurements showed that the LD-ESW and HD-ESW groups had larger new bone volume than the controls at week 12. Histological assessments confirmed osteogenesis enhancement. Both the LD-ESW and HD-ESW groups showed significantly higher failure load at the TBI healing complex than the control group at week 12. No significant difference was detected between the 2 ESW treatment groups at week 8 or week 12.

CONCLUSION

Extracorporeal shockwave, a unique noninvasive physical modality, had similar effects between the low and high dose for treating delayed TBI healing.

CLINICAL RELEVANCE

Low-dose ESW for TBI delayed healing might be more desirable and have better compliance in clinical applications.