Duration of postoperative immobilization affects MMP activity at the healing graft-bone interface: Evaluation in a mouse ACL reconstruction model

Surgical restabilization reduces the progression of post-traumatic osteoarthritis initiated by ACL rupture in mice

OBJECTIVE

People who sustain joint injuries such as anterior cruciate ligament (ACL) rupture often develop post-traumatic osteoarthritis (PTOA). In human patients, ACL injuries are often treated with ACL reconstruction. However, it is still unclear how effective joint restabilization is for reducing the progression of PTOA. The goal of this study was to determine how surgical restabilization of a mouse knee joint following non-invasive ACL injury affects PTOA progression.

DESIGN

In this study, 187 mice were subjected to non-invasive ACL injury or no injury. After injury, mice underwent restabilization surgery, sham surgery, or no surgery. Mice were then euthanized on day 14 or day 49 after injury/surgery. Functional analyses were performed at multiple time points to assess voluntary movement, gait, and pain. Knees were analyzed ex vivo with micro-computed tomography, RT-PCR, and whole-joint histology to assess articular cartilage degeneration, synovitis, and osteophyte formation.

RESULTS

Both ACL injury and surgery resulted in loss of epiphyseal trabecular bone (-27-32%) and reduced voluntary movement at early time points. Joint restabilization successfully lowered OA score (-78% relative to injured at day 14, p < 0.0001), and synovitis scores (-37% relative to injured at day 14, p = 0.042), and diminished the formation of chondrophytes/osteophytes (-97% relative to injured at day 14, p < 0.001, -78% at day 49, p < 0.001).

CONCLUSIONS

This study confirmed that surgical knee restabilization was effective at reducing articular cartilage degeneration and diminishing chondrophyte/osteophyte formation after ACL injury in mice, suggesting that these processes are largely driven by joint instability in this mouse model. However, restabilization was not able to mitigate the early inflammatory response and the loss of epiphyseal trabecular bone, indicating that these processes are independent of joint instability.

Presoaking Grafts in Vancomycin Does Not Impair Graft-Bone Healing in a Rat Anterior Cruciate Ligament Reconstruction Model

BACKGROUND

The vancomycin presoaking technique (wherein grafts are treated with a vancomycin solution [VS] for anterior cruciate ligament reconstruction [ACLR]) reduces the infection rate after ACLR. However, the effects of this technique on graft-bone healing have not been fully elucidated.

PURPOSE

To investigate the effects of vancomycin presoaking on graft-bone healing in a rat ACLR model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Long flexor digitorum longus tendons were obtained from 9 Wistar rats, and each was randomly allocated to the normal saline (NS) or VS groups. The grafts were immersed in sterile saline for 30 minutes in the NS group and in a 5-mg/mL VS in the VS group. The presence of time-zero graft bacterial contamination was confirmed, and the grafts were incubated in Fluidised Thioglycollate Broth for 2 weeks. ACLR was performed on the right knees of 65 male Wistar rats using the flexor digitorum longus tendons. Each graft was similarly treated. Biomechanical testing, micro-computed tomography, and histological evaluations were performed 4 and 12 weeks postoperatively.

RESULTS

The VS group showed significantly reduced graft contamination at time zero (P = .02). The mean maximum loads to failure were 13.7 ± 8.2 N and 11.6 ± 4.8 N in the NS and VS groups, respectively, at 4 weeks (P = .95); and 23.2 ± 13.2 N and 30.4 ± 18.0 N in the NS and VS groups, respectively, at 12 weeks (P = .35). Regarding micro-computed tomography, the mean bone tunnel volumes were 3.76 ± 0.48 mm3 and 4.40 ± 0.58 mm3 in the NS and VS groups, respectively, at 4 weeks (P = .41); and 3.51 ± 0.38 mm3 and 3.67 ± 0.35 mm3 in the NS and VS groups, respectively, at 12 weeks (P = .54). Histological semiquantitative examination revealed no clear between-group differences at any time point.

CONCLUSION

Presoaking grafts in vancomycin in a rat ACLR model demonstrated no discernible adverse effects on short- and midterm biomechanical, radiological, and histological investigations.

CLINICAL RELEVANCE

The findings provide guidance for surgeons when considering this technique.

Mechanical stimulation improves rotator cuff tendon-bone healing via activating IL-4/JAK/STAT signaling pathway mediated macrophage M2 polarization

Background

It is well known that appropriate mechanical stimulation benefits tendon-bone (T-B) healing, however, the mechanisms behind this are still uncovered completely. Here, we aimed to explore whether the IL-4/JAK/STAT signaling pathway mediated macrophage polarization was involved in mechanical stimulation induced T-B healing.

Method

C57BL/6 mice rotator cuff (RC) repair model was established, and the mice were randomly allocated to the following group. 1. Mice were allowed for free cage activities after surgery (FC group); 2. Mice received treadmill running initiated on postoperative day 7 (TR group); 3. Mice only received a local injection of hydrogel containing IL-4 neutralizing antibody without postoperative intervention (FC ​+ ​AF-404-SP group); 4. Mice received a local injection of hydrogel containing IL-4 neutralizing antibody and postoperative treadmill running (TR ​+ ​AF-404-SP group). The expression of IL-4 within supraspinatus tendon (SST) enthesis was measured by Enzyme-linked immunosorbent assay (ELISA). In addition, the activation of JAK/STAT signaling pathway in macrophages and identification of macrophage phenotype at the RC insertion site was detected by Flow cytometry and qRT-PCR. T-B healing quality in this RC repair model was evaluated by histological staining, Micro-computed tomography (Micro-CT) scanning, and biomechanical testing.

Result

In this study, using the RC repair model, we confirmed that generation of IL-4, activation of the JAK/STAT signaling pathway in macrophages, the ability of macrophages to polarize towards M2 subtype, and T-B healing quality were significantly enhanced in TR group compared to FC group. When comparing FC ​+ ​AF-404-SP group with TR ​+ ​AF-404-SP group, it was found that the mechanical stimulation induced this effect was depleted following the blockade of the IL-4/JAK/STAT signaling pathway.

Conclusion

Our finding suggested that mechanical stimulation could accelerate T-B healing via activating the IL-4/JAK/STAT signaling pathway that modulates macrophages to polarize towards M2 subtype.

The translational potential of this article

This is the first study to reveal a significant role of mechanical stimulation in the IL-4/JAK/STAT signaling pathway activation and macrophage polarization during RC T-B healing, which highlights the IL-4/JAK/STAT signaling pathway as a potential target to mediate macrophage M2 polarization and improves T-B healing for RC repair.

Effects of Joint Immobilization and Treadmill Exercise on Articular Cartilage After ACL Reconstruction in Rats

Background:

The development of osteoarthritis after anterior cruciate ligament (ACL) reconstruction (ACLR) is an important issue. However, the appropriate rehabilitation protocol to prevent cartilage degeneration due to postoperative osteoarthritis is unclear.

Purpose:

To examine the effects of joint immobilization and treadmill exercise on articular cartilage after ACLR.

Study Design:

Controlled laboratory study.

Methods:

A total of 55 rats received unilateral knee ACL transection and reconstruction surgery using tail tendon autografts. After surgery, rats were reared without intervention, with joint immobilization, or with daily treadmill exercise (12 m/minute, 60 minutes/day, 6 days/week). Treadmill exercise was initiated at 3 or 14 days postoperatively. After 2 weeks of immobilization, the fixation device was removed from some of the immobilized rats, and the knee was allowed to move freely for 2 weeks. Untreated, age-matched rats (n = 8) were used as controls. At 2 or 4 weeks after starting the experiment, cartilage degeneration in the medial tibial plateau was histologically assessed using a modified Mankin score, cartilage thickness, chondrocyte density, and immunohistochemistry for cyclooxygenase-2 (COX-2) in the anterior, middle, and posterior regions.

Results:

After ACLR, cartilage degeneration in the anterior region characterized by increased Mankin score, accompanied with increased COX-2 expression, was detected. Joint immobilization after ACLR facilitated cartilage degeneration, which is detected by histological changes such as reductions in cartilage thickness, chondrocyte density, and high Mankin scores. Enhanced COX-2 expression in all degenerated cartilage regions was also detected. It was found that 2 weeks of remobilization could not restore cartilage degeneration induced by 2 weeks of immobilization after ACLR. Treadmill exercise after ACLR did not affect most articular cartilage parameters, regardless of the timing of exercise.

Conclusion:

Our results indicated that (1) immobilization after ACLR accelerates cartilage degeneration, even when applied only for 2 weeks, and (2) mild exercise during early phases after ACLR does not facilitate cartilage degeneration.

Clinical Relevance:

To reduce cartilage degeneration, periods of joint immobilization after ACLR should be minimized. Mild exercise during the early phases after ACLR will not negatively affect articular cartilage.

Development of a novel knee contracture mouse model by immobilization using external fixation

AIMS

Several studies have used animal models to examine knee joint contracture; however, few reports detail the construction process of a knee joint contracture model in a mouse. The use of mouse models is beneficial, as genetically modified mice can be used to investigate the pathogenesis of joint contracture. Compared to others, mouse models are associated with a lower cost to evaluate therapeutic effects. Here, we describe a novel knee contracture mouse model by immobilization using external fixation.

METHODS

The knee joints of mice were immobilized by external fixation using a splint and tape. The passive extension range of motion (ROM), histological and immunohistochemical changes, and expression levels of fibrosis-related genes at 2 and 4 weeks were compared between the immobilized (Im group) and non-immobilized (Non-Im group) groups.

RESULTS

The extension ROM at 4 weeks was significantly lower in the Im group than in the Non-Im group (p < 0.01). At 2 and 4 weeks, the thickness and area of the joint capsule were significantly greater in the Im group than in the Non-Im group (p < 0.01 in all cases). At 2 weeks, the mRNA expression levels of the fibrosis-related genes, except for the transforming growth factor-β1, and the protein levels of cellular communication network factor 2 and vimentin in the joint capsule were significantly higher in the Im group (p < 0.01 in all cases).

CONCLUSION

This mouse model may serve as a useful tool to investigate the etiology of joint contracture and establish new treatment methods.

Tackling the Challenges of Graft Healing After Anterior Cruciate Ligament Reconstruction-Thinking From the Endpoint

Anterior cruciate ligament (ACL) tear is common in sports and accidents, and accounts for over 50% of all knee injuries. ACL reconstruction (ACLR) is commonly indicated to restore the knee stability, prevent anterior–posterior translation, and reduce the risk of developing post-traumatic osteoarthritis. However, the outcome of biological graft healing is not satisfactory with graft failure after ACLR. Tendon graft-to-bone tunnel healing and graft mid-substance remodeling are two key challenges of biological graft healing after ACLR. Mounting evidence supports excessive inflammation due to ACL injury and ACLR, and tendon graft-to-bone tunnel motion negatively influences these two key processes. To tackle the problem of biological graft healing, we believe that an inductive approach should be adopted, starting from the endpoint that we expected after ACLR, even though the results may not be achievable at present, followed by developing clinically practical strategies to achieve this ultimate goal. We believe that mineralization of tunnel graft and ligamentization of graft mid-substance to restore the ultrastructure and anatomy of the original ACL are the ultimate targets of ACLR. Hence, strategies that are osteoinductive, angiogenic, or anti-inflammatory should drive graft healing toward the targets. This paper reviews pre-clinical and clinical literature supporting this claim and the role of inflammation in negatively influencing graft healing. The practical considerations when developing a biological therapy to promote ACLR for future clinical translation are also discussed.

Platelet-rich plasma injections induce disease-modifying effects in the treatment of osteoarthritis in animal models

PURPOSE

The mechanisms of action and disease-modifying potential of platelet-rich plasma (PRP) injection for osteoarthritis (OA) treatment are still not fully established. The aim of this systematic review of preclinical evidence was to determine if PRP injections can induce disease-modifying effects in OA joints.

METHODS

A systematic review was performed on animal studies evaluating intra-articular PRP injections as treatment for OA joints. A synthesis of the results was performed investigating the disease-modifying effects of PRP by evaluating studies that compared PRP with OA controls or other injectable products, different PRP formulations or injection intervals, and the combination of PRP with other products. The risk of bias was assessed according to the SYRCLE's tool.

RESULTS

Forty-four articles were included, for a total of 1251 animals. The publication trend remarkably increased over time. PRP injections showed clinical effects in 80% and disease-modifying effects in 68% of the studies, attenuating cartilage damage progression and reducing synovial inflammation, coupled with changes in biomarker levels. Evidence is limited on the best PRP formulation, injection intervals, and synergistic effect with other injectables. The risk of bias was low in 40%, unclear in 56%, and high in 4% of items.

CONCLUSION

Intra-articular PRP injections showed disease-modifying effects in most studies, both at the cartilage and synovial level. These findings in animal OA models can play a crucial role in understanding mechanism of action and structural effects of this biological approach. Nevertheless, the overall low quality of the published studies warrants further preclinical studies to confirm the positive findings, as well as high-level human trials to demonstrate if these results translate into disease-modifying effects when PRP is used in the clinical practice to treat OA.

LEVEL OF EVIDENCE

Level II.

Immobilization after injury alters extracellular matrix and stem cell fate

Cells sense the extracellular environment and mechanical stimuli and translate these signals into intracellular responses through mechanotransduction, which alters cell maintenance, proliferation, and differentiation. Here we use a mouse model of trauma-induced heterotopic ossification (HO) to examine how cell-extrinsic forces impact mesenchymal progenitor cell (MPC) fate. After injury, single-cell (sc) RNA sequencing of the injury site reveals an early increase in MPC genes associated with pathways of cell adhesion and ECM-receptor interactions, and MPC trajectories to cartilage and bone. Immunostaining uncovers active mechanotransduction after injury with increased focal adhesion kinase signaling and nuclear translocation of transcriptional coactivator TAZ, inhibition of which mitigates HO. Similarly, joint immobilization decreases mechanotransductive signaling, and completely inhibits HO. Joint immobilization decreases collagen alignment and increases adipogenesis. Further, scRNA sequencing of the HO site after injury with or without immobilization identifies gene signatures in mobile MPCs correlating with osteogenesis, and signatures from immobile MPCs with adipogenesis. scATAC-seq in these same MPCs confirm that in mobile MPCs, chromatin regions around osteogenic genes are open, whereas in immobile MPCs, regions around adipogenic genes are open. Together these data suggest that joint immobilization after injury results in decreased ECM alignment, altered MPC mechanotransduction, and changes in genomic architecture favoring adipogenesis over osteogenesis, resulting in decreased formation of HO.

Biomechanical, histologic, and molecular characteristics of graft-tunnel healing in a murine modified ACL reconstruction model

Purpose

The purpose of our study was to introduce and validate a metal-free, reproducible and reliable mouse model of anterior cruciate ligament (ACL) reconstruction (ACLR) surgery as an effective tool for a better understanding of molecular mechanisms of graft-tunnel healing after ACLR.

Methods

A total of 150 C57BL/6 mice were randomly allocated into five Groups: Group 1 (mice with intact ACL), Group 2–4 (mice underwent modified ACLR surgery and sacrificed 1-, 2-, and 4-weeks after surgery), and Group 5 (mice underwent unmodified ACLR surgery and sacrificed 4 weeks after surgery). Micro-computed tomography (CT), biomechanical histological as well as immunohistochemical (IHC) analyses were performed to characterize the modified ACLR.

Results

Micro-CT analysis demonstrated there is a non-significant increase in BV/TV and BMD of the bone tunnel during the tendon-to-bone healing following ACLR. Biomechanical tests showed that the mean load-to-failure forces of Group 3 and 4 are equal to 31.7% and 46.0% of that in Group 1, while the stiffness was 33.1% and 57.2% of that of Group 1, respectively. And no obvious difference in biomechanical parameters was found between Group 4 and 5. Histological analysis demonstrated that formation of fibrovascular tissue in the tibial tunnel and aperture in Groups 4 and 5 and direct junction appeared between tendon graft and tunnel both in Groups 4 and 5. IHC results showed that there are gradually enhanced expression of Patched1, Smoothened and Gli2 concomitant with decreased Gli3 protein in the tendon-bone interface during the tendon-bone healing process.

Conclusion

We introduced a metal-free, reproducible and reliable mouse model of ACLR compared to the unmodified ACLR procedure, and characterized the expression pattern of key molecules in Ihh signaling during the graft healing process.

The translational potential of this article

In the present study we introduced and validated, for the first time, a metal-free, reproducible and reliable ACLR mouse model, which could be used to investigate the detailed molecular mechanisms of graft-tunnel healing after ACLR. We also explored new strategies to promote the healing of tendon-to-bone integration.