Pathological mechanisms and therapeutic outlooks for arthrofibrosis

Effect of Trainee Level on Surgical Time and Postoperative Complications of Anterior Cruciate Ligament Reconstruction

PURPOSE

The objective of this study was to investigate the association between trainee level and surgical time and postoperative complications of anterior cruciate ligament reconstruction (ACLR).

METHODS

A retrospective chart review of patients who underwent ACLR at an academic orthopaedic ambulatory surgery center collected demographic and clinical information, including the number of trainees present and trainee level. Unadjusted and adjusted regression analyses assessed the association between trainee number and level with surgical time (time from skin incision to closure) and postoperative complications.

RESULTS

Of 799 patients in this study operated on by one of five academic sports surgeons, 87% had at least one trainee involved. The average surgical time overall was 93 ± 21 minutes and by trainee level was 99.7 (junior resident), 88.5 (senior residents), 96.6 (fellows), and 95.6 (no trainees). Trainee level was significantly associated with surgical time (P = 0.0008), with increased surgical time in cases involving fellows (0.0011). Fifteen complications (1.9%) were observed within 90 days of surgery. No notable risk factors of postoperative complications were identified.

CONCLUSION

Resident trainee level does not have a notable effect on surgical time or postoperative complications for ACLR at an ambulatory surgery center, although cases involving fellows had longer surgical times. Trainee level was not associated with risk of postoperative complications.

Metformin improves fibroblast metabolism and ameliorates arthrofibrosis in rats

Background

Emerging studies have suggested an essential role of fibroblast metabolic reprogramming in the pathogenesis of arthrofibrosis. The metabolic modulator metformin appears to be a therapeutic candidate for fibrotic disorders. However, whether metformin could alleviate arthrofibrosis has not been defined. In this study we have determined if treatment with metformin has beneficial effect on arthrofibrosis and its underlying mechanism.

Methods

Articular capsule samples were collected from patients with/without arthrofibrosis to perform gene and protein expression analysis. Arthrofibrosis animal model was established to examine the anti-fibrotic effect of metformin. Cell culture experiments were conducted to determine the mechanism by which metformin inhibits fibroblast activation.

Results

We found that glycolysis was upregulated in human fibrotic articular capsules. In an arthrofibrosis animal model, intra-articular injection of metformin mitigated inflammatory reactions, downregulated expression of both fibrotic and glycolytic markers, improved range of motion (ROM) of the joint, and reduced capsular fibrosis and thickening. At the cellular level, metformin inhibited the activation of fibroblasts and mitigated the abundant influx of glucose into activated fibroblasts. Interestingly, metformin prompted a metabolic shift from oxidative phosphorylation to aerobic glycolysis in activated fibroblasts, resulting in the anti-fibrotic effect of metformin.

Conclusion

Metformin decreased glycolysis, causing a metabolic shift toward aerobic glycolysis in activated fibroblasts and has beneficial effect on the treatment of arthrofibrosis.The translational potential of this article: The findings of this study demonstrated the therapeutic effect of metformin on arthrofibrosis and defined novel targets for the treatment of articular fibrotic disorders.

Exercise builds the scaffold of life: muscle extracellular matrix biomarker responses to physical activity, inactivity, and aging

Skeletal muscle extracellular matrix (ECM) is critical for muscle force production and the regulation of important physiological processes during growth, regeneration, and remodelling. ECM remodelling is a tightly orchestrated process, sensitive to multi-directional tensile and compressive stresses and damaging stimuli, and its assessment can convey important information on rehabilitation effectiveness, injury, and disease. Despite its profound importance, ECM biomarkers are underused in studies examining the effects of exercise, disuse, or aging on muscle function, growth, and structure. This review examines patterns of short- and long-term changes in the synthesis and concentrations of ECM markers in biofluids and tissues, which may be useful for describing the time course of ECM remodelling following physical activity and disuse. Forces imposed on the ECM during physical activity critically affect cell signalling while disuse causes non-optimal adaptations, including connective tissue proliferation. The goal of this review is to inform researchers, and rehabilitation, medical, and exercise practitioners better about the role of ECM biomarkers in research and clinical environments to accelerate the development of targeted physical activity treatments, improve ECM status assessment, and enhance function in aging, injury, and disease.

The combined effects of treadmill exercise and steroid administration on anterior cruciate ligament reconstruction-induced joint contracture and muscle atrophy in rats

Rehabilitation protocols to treat joint contracture and muscle atrophy following anterior cruciate ligament (ACL) reconstruction have not been established. In this study, we examined the combined effects of exercise therapy and steroid administration on joint contracture and muscle atrophy following ACL reconstruction. Rats received ACL transection and reconstructive surgery in one knee. After surgery, they were divided into four groups: no intervention, treadmill exercise (started from day three post-surgery, 12 m/min, 60 min/d, 6 d/week), treatment with the steroidal drug dexamethasone (250 μg/kg on days 0-5, 7, and 9 post-surgery), and dexamethasone treatment plus treadmill exercise. Age-matched untreated rats were used as controls. At day 10 or 30 post-surgery, we assessed ACL-reconstruction-induced joint contracture, joint capsule fibrosis, osteophyte formation, and muscle atrophy of the rectus femoris and gastrocnemius. Treadmill exercise after ACL reconstruction improved several indicators of muscle atrophy in both muscles, but it did not have positive effects on joint contracture. Dexamethasone treatment after ACL reconstruction improved joint contracture and joint capsule fibrosis at both timepoints and partially attenuated osteophyte formation at day 10 post-surgery, but delayed recovery from atrophy of the rectus femoris at day 30 post-surgery. The two treatments combined improved both joint contracture and atrophy of the rectus femoris and gastrocnemius. Exercise therapy combined with steroid administration may therefore be a novel therapeutic strategy for joint contracture and muscle atrophy following ACL reconstruction.

Rheumatoid arthritis treatment with zoledronic acid, a potentialinhibitorofGWAS-derived pharmacogenetics STAT3 and IL2 targets

Rheumatoid arthritis (RA) is an inflammatory condition that primarily affects the joints and progress to affect other vital organs. Variety of drugs are being recommended to control the disease progression that benefits patients to perform day-to-day activities. Few of these RA drugs have noticeable side effects; therefore, it's crucial to choose the appropriate drug for treating RA with an understanding of the disease's pathophysiology. Herein, we investigated the RA genes from GWAS data to construct protein-protein interaction (PPI) network and to define appropriate drug targets for RA. The predicted drug targets were screened with the known RA drugs based on molecular docking. Further, the molecular dynamics simulations were performed to comprehend the conformational changes and stability of the targets upon binding of the selected top ranked RA drug. As a result, our constructed protein network from GWAS data revealed, STAT3 and IL2 could be potential pharmacogenetics targets that interlink most of the RA genes encoding proteins. These interlinked proteins of both the targets showed involvement in cell signaling, immune response, and TNF signaling pathway. Among the 192 RA drugs investigated, zoledronic acid had the lowest binding energy that inhibit both STAT3 (-6.307 kcal/mol) and IL2 (-6.231 kcal/mol). Additionally, STAT3 and IL2 trajectories on zoledronic acid binding exhibit notable differences in MD simulations as compared to a drug-free environment. Also, the in vitro assessment with the zoledronic acid confirms the outcome of our computational study. Overall, our study identify zoledronic acid could be potential inhibitor against these targets, that will benefits patients with RA. Comparative efficiency assessments between the RA drugs through clinical trials are needed to validate our findings in the treatment of RA.

Motion lubrication suppressed mechanical activation via hydrated fibrous gene patch for tendon healing

Mechanical activation of fibroblasts, caused by friction and transforming growth factor-β1 recognition, is one of the main causes of tissue adhesions. In this study, we developed a lubricated gene-hydrogel patch, which provides both a motion lubrication microenvironment and gene therapy. The patch's outer layer is composed of polyethylene glycol polyester hydrogel. The hydrogel forms hydrogen bonds with water molecules to create the motion lubrication layer, and it also serves as a gene delivery library for long-term gene silencing. Under the motion lubricated microenvironment, extracellular signal-regulated kinase-small interfering RNA can silence fibroblasts and enhance the blocking effect against fibroblast activation. In vitro, the proposed patch effectively inhibits fibroblast activation and reduces the coefficient of friction. In vivo, this patch reduces the expression of vimentin and α-smooth muscle actin in fibroblasts. Therefore, the lubricated gene-hydrogel patch can inhibit the mechanical activation of fibroblasts to promote tendon healing.

Effectiveness of losartan on infrapatellar fat pad/synovial fibrosis and pain behavior in the monoiodoacetate-induced rat model of osteoarthritis pain

Infrapatellar fat pad (IFP)/ synovial fibrosis is closely associated with the clinical symptoms of joint pain and stiffness, which contribute to locomotor restriction in osteoarthritis (OA) patients. Hence, this study was designed to gain insight on whether losartan, a selective angiotensin II type 1 receptor (AT1R) antagonist, has therapeutic benefit to reverse IFP/synovial fibrosis and secondarily to attenuate pain behavior. In male Wistar rats with monoiodoacetic acid (MIA)-induced IFP/synovial fibrosis, a possible role for increased AT1R expression in the pathogenesis of IFP/synovial fibrosis was assessed over an 8-week period. Pain behavior comprised static weight bearing and von Frey paw withdrawal thresholds (PWTs), which were assessed once or twice weekly, respectively. Groups of MIA-rats received oral losartan (30-mg/kg; n = 8 or 100-mg/kg; n = 9) or vehicle (n = 9) for 28-days according to a prevention protocol. Animals were euthanized on day 28 and various tissues (IFP/synovium, cartilage and lumbar dorsal root ganglia (DRGs)) were collected for histological, immunohistochemical and western blot analyses. Administration of once-daily losartan for 28-days dose-dependently attenuated the development of static weight bearing. This was accompanied by reduced IFP/synovial fibrosis and suppression of TGF-β1 expression. Chronic treatment of MIA-rats with losartan had an anti-fibrotic effect and it attenuated pain behavior in this animal model.

Synovial Fluid Inflammatory Profiles did not Differ between Isolated Anterior Cruciate Ligament and Multi-ligament Knee Injuries

Objective and design

The purpose of this study was to compare synovial concentrations of pro- and anti-inflammatory cytokines between multiple-ligament knee injured (MLKI) and anterior cruciate ligament (ACL)-injured patients.

Subjects

14 patients with MLKI and 10 patients with isolated ACL injury.

Methods

Synovial fluid was aspirated from the operative knee at the time of surgery and the concentrations of pro- and anti-inflammatory markers in the synovial fluid were determined. Structures injured, the time between injury and surgery, and demographic factors were collected. Linear regressions were used to determine the association between injury pattern and synovial inflammatory markers when controlling for age, BMI, and time between injury and surgery.

Results

When adjusting for group differences in age, BMI and the time between injury and surgery, no group differences were detected (interferon gamma (p = 0.11), interleukin-1beta (IL-1b, p = 0.35), IL-2 (p = 0.28), IL-4 (p = 0.64), IL-6 (p = 0.37), IL-8 (p = 0.54), IL-10 (p = 0.25), IL-12p70 (p = 0.81), IL-13 (p = 0.31), and tumor necrosis factor-alpha (p = 0.90)).

Conclusion

Synovial fluid inflammatory markers did not differ between MLKI and isolated ACL injuries. MLKIs have a greater prevalence of postoperative arthrofibrosis when compared to isolated ACL injuries; however, this may be due in part to factors other than the inflammatory status of the joint.

IFN-α-2b Reduces Postoperative Arthrofibrosis in Rats by Inhibiting Fibroblast Proliferation and Migration through STAT1/p21 Signaling Pathway

Objective

To investigate the effect of IFN-α-2b in preventing postoperative arthrofibrosis in rats, its antiproliferation effect on fibroblasts in vitro, and its molecular mechanism.

Methods

The rat model of arthrofibrosis was established and treated with different concentrations of drugs. Knee specimens were collected for histological and immunohistochemical staining to observe the effect of IFN-α-2b on arthrofibrosis in rats. The biological information was further mined according to the database data, and the possible regulatory mechanism of IFN-α-2b on fibroblasts was analyzed. The inhibitory effect of IFN-α-2b on fibroblast proliferation and migration in vitro was detected by cell counting kit-8 (CCK-8), immunofluorescence analysis, cell cycle test, EdU assay, wound healing test, and Transwell method, and the analysis results were verified by Western blotting method.

Results

The test results of rat knee joint specimens showed that IFN-α-2b significantly inhibited the degree of fibrosis after knee joint surgery, the number of fibroblasts in the operation area was less than that of the control group, and the expression of collagen and proliferation-related proteins decreased. In vitro experimental results show that IFN-α-2b can inhibit the proliferation and migration of fibroblasts. According to the results of database analysis, it is suggested that the STAT1/P21 pathway may be involved, and it has been verified and confirmed by Western blotting and other related methods.

Conclusion

IFN-α-2b can reduce surgery-induced arthrofibrosis by inhibiting fibroblast proliferation and migration, which may be related to the regulation of STAT1/p21 signaling pathway.

Relaxin in fibrotic ligament diseases: Its regulatory role and mechanism

Fibrotic ligament diseases (FLDs) are diseases caused by the pathological accumulation of periarticular fibrotic tissue, leading to functional disability around joint and poor life quality. Relaxin (RLX) has been reported to be involved in the development of fibrotic lung and liver diseases. Previous studies have shown that RLX can block pro-fibrotic process by reducing the excess extracellular matrix (ECM) formation and accelerating collagen degradation in vitro and in vivo. Recent studies have shown that RLX can attenuate connective tissue fibrosis by suppressing TGF-β/Smads signaling pathways to inhibit the activation of myofibroblasts. However, the specific roles and mechanisms of RLX in FLDs remain unclear. Therefore, in this review, we confirmed the protective effect of RLX in FLDs and summarized its mechanism including cells, key cytokines and signaling pathways involved. In this article, we outline the potential therapeutic role of RLX and look forward to the application of RLX in the clinical translation of FLDs.

Arthrofibrosis is a common but poorly defined complication in multiligament knee injuries: a systematic review

PURPOSE

The purpose of this study is to systematically review multiligament knee injury (MLKI) outcome studies to determine definitions of arthrofibrosis (AF) and provide information about incidence, management as well as potential risk factors.

METHODS

A systematic literature search was performed (PubMed and Cochrane library) following the PRISMA guidelines of operatively treated MLKI (Schenck II-IV) studies reporting the incidence of AF. Twenty-five studies met the inclusion criteria. Injury pattern, timing of surgery, surgical technique, treatment of AF, rehabilitation programs and PROMS were inquired. Risk of bias and quality of evidence were assessed using the Coleman methodological score.

RESULTS

Twenty-five studies with a total of 709 patients with a mean age of 33.6 ± 4.8 years were included and followed 47.2 ± 32.0 months. The majority of studies (22/25) used imprecise and subjective definitions of AF. A total of 86 patients were treated for AF, resulting in an overall prevalence of 12.1% (range 2.8-57.1). Higher-grade injuries (Schenck III-IV), acute treatment and ROM (range of motion) limiting rehabilitation programs were potential risk factors for AF. The time from index surgery to manipulation anesthesia (MUA) and arthroscopic lysis of adhesions (LOA) averaged at 14.3 ± 8.8 and 27.7 ± 12.8 weeks. Prior to MUA and LOA, the ROM was 51.7° ± 23.5 and 80.2° ± 17.0, resulting in a total ROM gain after intervention of 65.0° ± 19.7 and 48.0° ± 10.6, respectively; with no reports of any complication within the follow-up. The overall methodological quality of the studies was poor as measured by the Coleman score with average 56.3 ± 12.5 (range 31-84) points.

CONCLUSIONS

AF is a common but poorly defined complication particularly in high-grade MLKI. Early postoperative and intensified physiotherapy is important to reduce the risk of AF. MUA and LOA are very effective treatment options and result in good clinical outcome. Prospective studies with bigger study population are needed to optimize treatment algorithms of further patients after MLKI. The protocol of this systematic review has been prospectively registered with PROSPERO (CRD42021229187, January 4th, 2021).

Risk of Postoperative Stiffness Following Multiligamentous Knee Injury Surgery Is Not Affected by Obesity: A Multicenter Study

PURPOSE

The purpose of this study was to examine the relationship between obesity and postoperative stiffness following surgical management of multiligamentous knee injuries (MLKIs) using a large two-center cohort, by both 1) using binary cutoffs at various body mass indexes (BMIs) and 2) a linear regression model.

METHODS

190 consecutive patients who underwent surgical management of MLKIs between January 2001 and March 2020 were reviewed at two level 1 academic trauma centers. Patient demographics, surgical characteristics, and manipulation under anesthesia (MUA)/lysis of adhesions (LOA) were reviewed. Patients were stratified by obesity grades: grade 1 (BMI 30 to <35) grade 2 (BMI 35 to <40); grade 3 (BMI >40), and compared with a nonobese comparison group with BMI <30. Multivariate logistic regressions were performed, including the covariates of age, gender, BMI, acute versus chronic injury, external fixator, vascular injury, knee dislocation, and Schenck Classification. Fisher's exact test was used to compare rate of MUA between grades of obesity. Analyses were performed with R. Statistical significance was set at P < .05.

RESULTS

The mean BMI of the cohort was 29.2 kg/m². The mean overall follow-up was 27.2 ± 7.2 months (range: 14-142 months). There were 55 (29.1%) MUA procedures observed at a mean 3.77 ± 2.18 months (range: 1.8-9.7 months) after final MLKI surgery. No significant difference was found in BMI of patients who underwent a MUA compared to patients who did not (30.2 vs 28.8; P = .67). There was no significant difference in rate or time to MUA following MLKI surgery between groups, with logistic regression demonstrating no significance (P = .144). Use of external fixation at the index surgery (OR = 3.3 [95% CI: 2.2, 4.7; P < .0001]) and vascular injury (OR = 6.2 [95% CI: 1.8, 24.5; P = .005]) were found to be independent predictors for need for MUA.

CONCLUSION

No difference in risk for postoperative stiffness requiring MUA following surgery for MLKI was found based on BMI. At all BMI levels, there were no significant increase in need for postoperative MUA, suggesting at minimum a neutralizing effect of obesity on postoperative stiffness. In addition, patients with external fixator use and vascular injury at index surgery were found to be at significantly higher risk for postoperative stiffness requiring MUA following surgery for MLKI. Surgeons should be aware of the risk factors for arthrofibrosis when proceeding with surgical repair or reconstruction of two or more ligaments of the knee.

LEVEL OF EVIDENCE

III, multicenter retrospective cohort study.

RANTES Concentration at the Time of Surgery Is Associated With Postoperative Stiffness in Patients Undergoing ACL Reconstruction

BACKGROUND

Patients undergoing anterior cruciate ligament (ACL) reconstruction have been shown to be at risk for postoperative arthrofibrosis. Diagnostic biomarkers associated with the development of postoperative stiffness are unknown.

HYPOTHESIS

Biomarkers found in the synovial fluid at the time of surgery are associated with the development of postoperative arthrofibrosis in a cohort of patients undergoing ACL reconstruction.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

Patients undergoing ACL reconstruction were prospectively enrolled. Synovial fluid was collected before surgical incision. A cohort of patients with postoperative stiffness requiring manipulation under anesthesia (MUA) and/or lysis of adhesions (LOA) was retrospectively identified. Matching of cases to controls was performed using a 1:2 pair matching algorithm. Risk factor-adjusted single-biomarker and multivariable models were used to assess the association of synovial fluid biomarkers with postoperative stiffness requiring MUA/LOA. Stepwise logistic regression controlling for clinical risk factors was used to identify biomarkers that are possible predictors of postoperative stiffness.

RESULTS

A total of 11 cases (3 male, 8 female) were identified and matched with 21 controls (6 male, 15 female) with no significant differences in age, sex, smoking history, or days from injury to surgery. Concentrations of the biomarker regulated upon activation, normal T-cell expressed and presumably secreted (RANTES) were significantly higher in patients requiring MUA/LOA versus controls (694.20 pg/mL [interquartile range, 214.75-3428.79] vs 113.04 pg/mL [interquartile range, 32.81-517.91], respectively; P = .034). On single-biomarker models, RANTES (odds ratio, 2.28; 95% CI, 1.29-5.37; P = .019) and basic fibroblast growth factor (bFGF) (odds ratio, 1.91; 95% CI, 1.07-3.99; P = .047) were associated with increased risk of postoperative stiffness requiring MUA/LOA after ACL reconstruction. Stepwise logistic regression identified 3 biomarkers that are possible predictors of postoperative stiffness, which were included in the final model: Interleukin 1 receptor antagonist (IL-1RA) (P = .198), bFGF (P = .157), and RANTES (P = .046).

CONCLUSION

Higher concentrations of synovial fluid biomarkers bFGF and RANTES were associated with increased risk for stiffness requiring intervention after ACL reconstruction. Interleukin 6 (IL-6), vascular endothelial growth factor A (VEGF-A), tissue inhibitor of metalloproteinases 1 (TIMP-1), interleukin 1 receptor antagonist (IL-1RA), matrix metalloproteinase 3 (MMP-3), monocyte chemotactic protein 1 (MCP-1), and macrophage inflammatory protein 1B (MIP-1B) were not associated with the development of postoperative arthrofibrosis.

Perlecan: Roles in osteoarthritis and potential treating target

Osteoarthritis (OA) is the most common joint disease, affecting hundreds of millions of people globally, which leads to a high cost of treatment and further medical care and an apparent decrease in patient prognosis. The recent view of OA pathogenesis is that increased vascularity, bone remodeling, and disordered turnover are influenced by multivariate risk factors, such as age, obesity, and overloading. The view also reveals the gap between the development of these processes and early stage risk factors. This review presents the latest research on OA-related signaling pathways and analyzes the potential roles of perlecan, a typical component of the well-known protective structure against osteoarthritic pericellular matrix (PCM). Based on the experimental results observed in end-stage OA models, we summarized and analyzed the role of perlecan in the development of OA. In normal cartilage, it plays a protective role by maintaining the integrin of PCM and sequesters growth factors. Second, perlecan in cartilage is required to not only activate vascular epithelium growth factor receptor (VEGFR) signaling of endothelial cells for vascular invasion and catabolic autophagy, but also for different signaling pathways for the catabolic and anabolic actions of chondrocytes. Finally, perlecan may participate in pain sensitization pathways.

Anticoagulant Usage After Anterior Cruciate Ligament Reconstruction Is Associated With Increased Rate of Manipulation Under Anesthesia

BACKGROUND

Arthrofibrosis after anterior cruciate ligament reconstruction (ACLR) is a notable but uncommon complication of ACLR. To improve range of motion after ACLR, aggressive physical therapy, arthroscopic/open lysis of adhesions, and revision surgery are currently used. Manipulation under anesthesia (MUA) is also a reasonable choice for an appropriate subset of patients with inadequate range of motion after ACLR. Recently, the correlation between anticoagulant usage and arthrofibrosis after total knee arthroplasty has become an area of interest. The purpose of this study was to determine whether anticoagulant use has a similar effect on the incidence of MUA after ACLR.

METHODS

The Mariner data set of the PearlDiver database was used to conduct this retrospective cohort study. Patients with an isolated ACLR were identified by using Current Procedural Terminology codes. Patients were then stratified by MUA within 2 years of ACLR, and the use of postoperative anticoagulation was identified. In addition, patient demographics, medical comorbidities, and timing of ACLR were recorded. Univariate and multivariable analyses were used to model independent risk factors for MUA.

RESULTS

We identified 216,147 patients who underwent isolated ACLR. Of these patients, 3,494 (1.62%) underwent MUA within 2 years. Patients who were on anticoagulants after ACLR were more likely to require an MUA (odds ratio [OR]: 2.181; P < 0.001), specifically low-molecular-weight heparin (OR: 2.651; P < 0.001), warfarin (OR: 1.529; P < 0.001), and direct factor Xa inhibitors (OR: 1.957; P < 0.001).

DISCUSSION

In conclusion, arthrofibrosis after ACLR is associated with the use of preoperative or postoperative thromboprophylaxis. Healthcare providers should be aware of increased stiffness among these patients and treat them aggressively.

Sex-based differences in the severity of radiation-induced arthrofibrosis

As cancer survivorship increases, so does the number of patients that suffer from the late effects of radiation therapy. This includes arthrofibrosis, the development of stiff joints near the field of radiation. Previous reports have concentrated on skin fibrosis around the joint but largely ignored the deeper tissues of the joint. We hypothesized that fat, muscle, and the joint tissues themselves would play a more significant role in joint contracture after radiation than the skin surrounding the joint. To address this hypothesis, we irradiated the right hind flanks of mice with fractionated and unfractionated dose schedules, then monitored the mice for 3 months postradiotherapy. Mice were euthanized and physiological indications of arthrofibrosis including limb contracture and joint resting position were assessed. Stifle (knee) joints demonstrated significant arthrofibrosis, but none was observed in the hock (ankle) joints. During these studies, we were surprised to find that male and female mice showed a significantly different response to radiation injury. Female mice developed more injuries, had significantly worse contracture, and showed a greater difference in the expression of all markers studied. These results suggest that women undergoing radiation therapy might be at significantly greater risk for developing arthrofibrosis and may require specific adjustments to their care.

Use of Supplemental Home Oxygen is Associated With Early Postoperative Complications Following Total Knee Arthroplasty

BACKGROUND

The objective of this study is to evaluate preoperative supplemental home oxygen use as a potential risk factor for both medical and surgical complications following primary elective total knee arthroplasty (TKA) in patients who have respiratory disease (RD).

METHODS

Patients with a diagnosis of RD who underwent elective TKA from 2010 to 2020 were identified using a national database. The rates of postoperative medical and surgical complications, hospital readmissions, and emergency room visits were calculated for RD patients who used supplemental home oxygen and those who did not. Additionally, reimbursements and lengths of stay were determined. Both cohorts were then compared to matched cohorts who did not have RD using logistic regression analyses.

RESULTS

A total of 41,418 patients who underwent TKA with RD on home oxygen and 138,635 patients who had RD without home oxygen use were compared with matched cohorts. The RD cohort with home oxygen use had a significantly higher incidence of periprosthetic joint infection (5.78% versus 2.69%, odds ratio [OR] 1.42, P < .0001), pneumonia (3.95% versus 0.69%, OR 4.44, P < .0001), venous thromboembolism (3.17% versus 2.10%, OR 1.12, P = .007), and periprosthetic fracture (0.82% versus 0.34%, OR 1.72, P < .0001) compared to the matched control cohort. Additionally, the RD with home oxygen cohort had a significantly higher incidence of periprosthetic joint infection (5.78% versus 3.77%, OR 1.15, P < .0001), pneumonia (3.95% versus 1.63%, OR 1.99, P < .0001), and several other medical complications compared to RD patients without home oxygen use.

CONCLUSION

Preoperative supplemental home oxygen use is associated with significantly increased risk of postoperative surgical and medical complications following elective TKA. This finding can help guide risk assessment and the informed consent process prior to surgery.

Minimally invasive, sustained-release relaxin-2 microparticles reverse arthrofibrosis

Substantial advances in biotherapeutics are distinctly lacking for musculoskeletal diseases. Musculoskeletal diseases are biomechanically complex and localized, highlighting the need for novel therapies capable of addressing these issues. All frontline treatment options for arthrofibrosis, a debilitating musculoskeletal disease, fail to treat the disease etiology-the accumulation of fibrotic tissue within the joint space. For millions of patients each year, the lack of modern and effective treatment options necessitates surgery in an attempt to regain joint range of motion (ROM) and escape prolonged pain. Human relaxin-2 (RLX), an endogenous peptide hormone with antifibrotic and antifibrogenic activity, is a promising biotherapeutic candidate for musculoskeletal fibrosis. However, RLX has previously faltered through multiple clinical programs because of pharmacokinetic barriers. Here, we describe the design and in vitro characterization of a tailored drug delivery system for the sustained release of RLX. Drug-loaded, polymeric microparticles released RLX over a multiweek time frame without altering peptide structure or bioactivity. In vivo, intraarticular administration of microparticles in rats resulted in prolonged, localized concentrations of RLX with reduced systemic drug exposure. Furthermore, a single injection of RLX-loaded microparticles restored joint ROM and architecture in an atraumatic rat model of arthrofibrosis with clinically derived end points. Finally, confirmation of RLX receptor expression, RXFP1, in multiple human tissues relevant to arthrofibrosis suggests the clinical translational potential of RLX when administered in a sustained and targeted manner.

Articular cartilage delamination at eight years following cellular-based repair procedures: a case reports

This report describes two cases of late cartilage delamination in two young adults after two different autologous cell-based techniques for cartilage restoration: 1. Matrix-assisted autologous chondrocyte implantation (MACI) and 2. Hyaluronic acid-bone marrow aspirate concentrate (HA-BMAC). Both cases demonstrate that even in patients who do not present with any ongoing symptoms after primary surgery, a cellular-based graft's subsequent delamination can occur later. It is possible that regardless of the technique used or the time passed since the surgery, a graft failure may occur at some level, causing delamination of a previously asymptomatic cartilage restoration graft and a traumatic event with long-term follow-up. Surgeons must be alert to this injury and describe histologic findings to determine where failure occurs.

Inflammation and Fibrosis Induced by Joint Remobilization, and Relevance to Progression of Arthrogenic Joint Contracture: A Narrative Review

Joint immobilization is frequently administered after fractures and ligament injuries and can cause joint contracture as a side effect. The structures responsible for immobilization-induced joint contracture can be roughly divided into muscular and articular. During remobilization, although myogenic contracture recovers spontaneously, arthrogenic contracture is irreversible or deteriorates further. Immediately after remobilization, an inflammatory response is observed, characterized by joint swelling, deposit formation in the joint space, edema, inflammatory cell infiltration, and the upregulation of genes encoding proinflammatory cytokines in the joint capsule. Subsequently, fibrosis in the joint capsule develops, in parallel with progressing arthrogenic contracture. The triggers of remobilization-induced joint inflammation are not fully understood, but two potential mechanisms are proposed: 1) micro-damage induced by mechanical stress in the joint capsule, and 2) nitric oxide (NO) production via NO synthase 2. Some interventions can modulate remobilization-induced inflammatory and subsequent fibrotic reactions. Anti-inflammatory treatments, such as steroidal anti-inflammatory drugs and low-level laser therapy, can attenuate joint capsule fibrosis and the progression of arthrogenic contracture in remobilized joints. Antiproliferative treatment using the cell-proliferation inhibitor mitomycin C can also attenuate joint capsule fibrosis by inhibiting fibroblast proliferation without suppressing inflammation. Conversely, aggressive exercise during the early remobilization phases is counterproductive, because it facilitates inflammatory and then fibrotic reactions in the joint. However, the adverse effects of aggressive exercise on remobilization-induced inflammation and fibrosis are offset by anti-inflammatory treatment. To prevent the progression of arthrogenic contracture during remobilization, therefore, care should be taken to control inflammatory and fibrotic reactions in the joints.

Imperatorin Inhibits Proliferation, Migration, and Inflammation via Blocking the NF-κB and MAPK Pathways in Rheumatoid Fibroblast-like Synoviocytes

Rheumatoid arthritis (RA) is a chronic joint inflammatory disease associated with the aberrant activation of fibroblast-like synoviocytes (FLSs). Searching for natural compounds that may suppress the activation of FLSs has become a complementary approach for RA treatment. Here, we investigated the effects and mechanisms of imperatorin (IPT) on proliferation, migration, and inflammation in primary cultured arthritic FLSs. We found that IPT significantly suppressed TNFα-induced proliferation and migration of arthritic FLSs, but showed little effect on survival and apoptosis. In addition, IPT treatment significantly reduced the TNFα-induced expression of pro-inflammatory cytokines (IL-1β, TNFα, IL-6, and IL-8) in arthritic FLSs. Further mechanism studies suggested that IPT inhibited the activations of p38 and extracellular signal-regulated kinase (ERK). Also, IPT blocked the nuclear factor of κB (NF-κB) activation by suppressing the phosphorylation and degradation of IκBα, thereby preventing the translocation of p65. Collectively, our results demonstrated that IPT could inhibit the over-activated phenotypes of arthritic FLSs via the mitogen-activated protein kinase (MAPK) (p38 and ERK) and NF-κB pathways leading to the down-regulation of pro-inflammatory cytokines, which might be beneficial to the anti-proliferative and anti-migratory activities of FLS cells. These findings suggest that IPT has the potential to be developed as a novel agent for RA treatment.

A new mouse model of post-traumatic joint injury allows to identify the contribution of Gli1+ mesenchymal progenitors in arthrofibrosis and acquired heterotopic endochondral ossification

Complex injury and open reconstructive surgeries of the knee often lead to joint dysfunction that may alter the normal biomechanics of the joint. Two major complications that often arise are excessive deposition of fibrotic tissue and acquired heterotopic endochondral ossification. Knee arthrofibrosis is a fibrotic joint disorder where aberrant buildup of scar tissue and adhesions develop around the joint. Heterotopic ossification is ectopic bone formation around the periarticular tissues. Even though arthrofibrosis and heterotopic ossification pose an immense clinical problem, limited studies focus on their cellular and molecular mechanisms. Effective cell-targeted therapeutics are needed, but the cellular origin of both knee disorders remains elusive. Moreover, all the current animal models of knee arthrofibrosis and stiffness are developed in rats and rabbits, limiting genetic experiments that would allow us to explore the contribution of specific cellular targets to these knee pathologies. Here, we present a novel mouse model where surgically induced injury and hyperextension of the knee lead to excessive deposition of disorganized collagen in the meniscus, synovium, and joint capsule in addition to formation of extra-skeletal bone in muscle and soft tissues within the joint capsule. As a functional outcome, arthrofibrosis and acquired heterotopic endochondral ossification coupled with a significant increase in total joint stiffness were observed. By employing this injury model and genetic lineage tracing, we also demonstrate that Gli1+ mesenchymal progenitors proliferate after joint injury and contribute to the pool of fibrotic cells in the synovium and ectopic osteoblasts within the joint capsule. These findings demonstrate that Gli1+ cells are a major cellular contributor to knee arthrofibrosis and acquired heterotopic ossification that manifest after knee injury. Our data demonstrate that genetic manipulation of Gli1+ cells in mice may offer a platform for identification of novel therapeutic targets to prevent knee joint dysfunction after chronic injury.

Perioperative Use of Antifibrotic Medications Associated With Lower Rate of Manipulation After Primary TKA: An Analysis of 101,366 Patients

BACKGROUND

Several commonly prescribed medications have known antifibrotic properties and have been shown to reduce postoperative scar formation in other clinical areas, but it is unknown whether the use of such medications perioperatively in patients undergoing TKA may improve rates of postoperative stiffness.

METHODS

A large US employer-sponsored healthcare database (Truven Marketscan) was queried for patients who underwent elective primary TKA for primary osteoarthritis between 2015-2019. Demographic information and comorbidities were recorded, along with whether patients were prescribed one of several medications with known antifibrotic properties during the three months before or after surgery.

RESULTS

Complete data were available for 101,366 patients undergoing TKA, of which 4,536 underwent MUA (4.5%). Perioperative use of any antifibrotic medication was associated with a lower likelihood of undergoing MUA (P < .001). When controlling for age, sex, comorbidities, opioid use, length of stay, among other variables, perioperative use of specific ACE inhibitors (OR 0.91, CI 0.84-1, P = .042), COX-2 inhibitors (OR 0.88, CI 0.81-0.96, P = .002), and angiotensin II receptor blockers, specifically losartan (OR 0.80, CI 0.70-0.91, P = .007) all remained significantly associated with lower rates of MUA.

CONCLUSION

This study, spanning over a hundred thousand primary TKA procedures over a recent five-year period, demonstrates an association between perioperative use of specific medications with antifibrotic properties and a decreased rate of MUA. These data will help inform future studies aimed to prospectively evaluate the potential of antifibrotic medications in preventing postoperative stiffness in high-risk patients undergoing knee arthroplasty.

Low-level laser therapy attenuates arthrogenic contracture induced by anterior cruciate ligament reconstruction surgery in rats

Therapeutic approaches to treat joint contracture after anterior cruciate ligament (ACL) reconstruction have not been established. Arthrofibrosis accompanied by joint inflammation following ACL reconstruction is a major cause of arthrogenic contracture. In this study, we examined whether anti-inflammatory treatment using low-level laser therapy (LLLT) can prevent ACL reconstruction-induced arthrogenic contracture. Rats underwent ACL transection and reconstruction surgery in their right knees. Unoperated left knees were used as controls. After surgery, rats were reared with or without daily LLLT (wavelength: 830 nm; power output: 150 mW; power density: 5 W/cm2; for 120 s/day). We assessed the passive extension range of motion (ROM) after myotomy at one and two weeks post-surgery; the reduction in ROM represents the severity of arthrogenic contracture. ROM was markedly decreased by ACL reconstruction at both time points; however, LLLT partially attenuated the decrease in ROM. One week after ACL reconstruction, the gene expression of the proinflammatory cytokine interleukin-1beta in the joint capsule was significantly upregulated, and this upregulation was significantly attenuated by LLLT. Fibrotic changes in the joint capsule, including upregulation of collagen type I and III genes, shortening of the synovium, and thickening were caused by ACL reconstruction and seen at both time points. LLLT attenuated these fibrotic changes as well. Our results indicate that LLLT after ACL reconstruction could attenuate the formation of arthrogenic contracture through inhibition of inflammation and fibrosis in the joint capsule. Thus, LLLT may become a novel therapeutic approach for ACL reconstruction-induced joint contracture.

Management of arthrofibrosis in neuromuscular disorders: a review

Arthrofibrosis, or rigid contracture of major articular joints, is a significant morbidity of many neurodegenerative disorders. The pathogenesis depends on the mechanism and severity of the precipitating neuromuscular disorder. Most neuromuscular disorders, whether spastic or hypotonic, culminate in decreased joint range of motion. Limited range of motion precipitates a cascade of pathophysiological changes in the muscle-tendon unit, the joint capsule, and the articular cartilage. Resulting joint contractures limit functional mobility, posing both physical and psychosocial burdens to patients, economic burdens on the healthcare system, and lost productivity to society. This article reviews the pathophysiology of arthrofibrosis in the setting of neuromuscular disorders. We describe current non-surgical and surgical interventions for treating arthrofibrosis of commonly affected joints. In addition, we preview several promising modalities under development to ameliorate arthrofibrosis non-surgically and discuss limitations in the field of arthrofibrosis secondary to neuromuscular disorders.

Association of circulating gene expression signatures with stiffness following total knee arthroplasty for osteoarthritis: a pilot study

A subset of patients undergoing total knee arthroplasty (TKA) for knee osteoarthritis develop debilitating knee stiffness (reduced range of motion) for poorly understood reasons. Dysregulated inflammatory and immune responses to surgery correlate with reduced surgical outcomes, but the dysregulated gene signatures in patients with stiffness after TKA are poorly defined. As a consequence, we are limited in our ability to identify patients at risk of developing poor surgical outcomes and develop preventative approaches. In this pilot study we aimed to identify perioperative blood gene signatures in patients undergoing TKA for knee osteoarthritis and its association with early surgical outcomes, specifically knee range of motion. To do this, we integrated clinical outcomes collected at 6 weeks after surgery with transcriptomics analyses in blood samples collected immediately before surgery and at 24 h after surgery. We found that patients with stiffness at 6 weeks after surgery have a more variable and attenuated circulating gene expression response immediately after surgery. Our results suggest that patients with stiffness following TKA may have distinct gene expression signatures detectable in peripheral blood in the immediate postoperative period.

The articular cartilage surface is impaired by a loss of thick collagen fibers and formation of type I collagen in early osteoarthritis

Osteoarthritis (OA) is a joint disease affecting millions of patients worldwide. During OA onset and progression, the articular cartilage is destroyed, but the underlying complex mechanisms remain unclear. Here, we uncover changes in the thickness of collagen fibers and their composition at the onset of OA. For articular cartilage explants from knee joints of OA patients, we find that type I collagen-rich fibrocartilage-like tissue was formed in macroscopically intact cartilage, distant from OA lesions. Importantly, the number of thick fibers (>100 nm) has decreased early in the disease, followed by complete absence of thick fibers in advanced OA. We have obtained these results by a combination of high-resolution atomic force microscopy imaging under near-native conditions, immunofluorescence, scanning electron microscopy and a fluorescence-based classification of the superficial chondrocyte spatial organization. Taken together, our data suggests that the loss of tissue functionality in early OA cartilage is caused by a reduction of thick type II collagen fibers, likely due to the formation of type I collagen-rich fibrocartilage, followed by the development of focal defects in later OA stages. We anticipate that such an integrative characterization will be very beneficial for an in-depth understanding of other native biological tissues and the development of sustainable biomaterials. STATEMENT OF SIGNIFICANCE: In early osteoarthritis (OA) the cartilage appears macroscopically intact. However, this study demonstrates that the collagen network already changes in early OA by collagen fiber thinning and the formation of fibrocartilage-like tissue. Both nanoscopic deficiencies already occur in macroscopically intact regions of the human knee joint and are likely connected to processes that result in a weakened extracellular matrix. This study enhances the understanding of earliest progressive cartilage degeneration in the absence of external damage. The results suggest a determination of the mean collagen fiber thickness as a new target for the detection of early OA and a regulation of type I collagen synthesis as a new path for OA treatment.

Early Identification of Arthrofibrosis in Adolescents Following Anterior Cruciate Ligament Reconstruction Is Associated With the Need for Subsequent Surgery: A Matched Case-Control Study

PURPOSE

To identify the postoperative characteristics associated with the need for subsequent surgical intervention in pediatric anterior cruciate ligament reconstruction (ACLR).

METHODS

Patients ≤18 years old who received operative treatment for arthrofibrosis following ACLR versus age- and sex-matched controls with a satisfactory postoperative course were retrospectively reviewed. The range of knee motion preoperatively and at each postoperative visit was recorded. Based on the typical post-operative protocols, visits were categorized into 3 groups: first (first 4 weeks), second (weeks 5-8), and third (weeks 9-16) visits. The deficit in the total arc of range of motion (ROM) in the operative knee relative to the nonoperative knee and the change in ROM between visits were compared. Receiver operating characteristic analysis was performed to determine the time point in which a diagnosis of arthrofibrosis could be predicted with the greatest accuracy.

RESULTS

In total, 18 patients with arthrofibrosis (mean age 14.2 ± 2.7 years, 9 male) and 36 control patients were included in the final analysis. Arthrofibrosis patients had significantly larger ROM deficits at all visits, 93° vs 69° for the first, 69° vs 24° for the second, and 56° vs 2º for the third, compared with controls (P < .001 for all). Pairwise comparisons showed that in arthrofibrosis cases, the total ROM did not change significantly between the second and third visits (P = .77), contrary to the controls. Receiver operating characteristic analysis revealed that the total ROM deficit of 50.7° at the second postoperative visit is 89% sensitive and 92.5% specific for development of arthrofibrosis.

CONCLUSIONS

We found that patients who go on to need manipulation of the knee under anesthesia/arthroscopic lysis of adhesions do not experience a significant improvement in ROM after the first 5-8 weeks, and that a ROM deficit of >50° at the 5- to 8-week mark postoperatively, is associated with ultimately needing operative intervention for arthrofibrosis. Based on these findings, it may be appropriate to intervene earlier if a patient still has a ROM deficit exceeding 50° by the second postoperative month.

LEVEL OF EVIDENCE

Level III, retrospective comparative prognostic trial.

Effect of polycaprolactone scaffolds containing different weights of graphene on healing in large osteochondral defect model

Now it is possible to combine the different biomaterial properties of graphene and 3 D printing scaffolds produced by tissue engineering for cartilage repair. In the study graphene-containing (1, 3, 5, 10 wt%), porous and oriented poly-ε-caprolactone-based scaffolds were prepared by robocasting method to use in the regeneration of large osteochondral defects. The scaffolds were implanted into the full-thickness osteochondral defect in a rabbit model to evaluate the regeneration of the defect in vivo. For this purpose, twenty female New Zealand white rabbits were used and they were euthanized at 4 and 8 weeks of implantation. The reparative osteochondral tissues were harvested from rabbit distal femurs and then processed for gross appearance assessment, radiographic imaging, histopathological, histochemical and immunohistochemical examinations. Results revealed that graphene-containing graft materials caused significant amelioration at the defect areas. Graphene-containing graft materials improved the fibrous, chondroid and osseous tissue regeneration compared to the control group. The expressions of bone morphogenetic protein-2 (BMP-2), collagen-1 (col-1), vascular endothelial growth factor (VEGF) and alkaline phosphatase (ALP) expressions were more prominent in graphene-containing PCL implanted groups (p < .001). Picrosirrius red method was used for to evaluate connective and muscle tissues. Results also revealed that the ameliorative effect of graphene increased by the elevation in concentration. The most prominent healing was observed in 10 wt% graphene-containing PCL based composite scaffold implanted group. This study results showed that graphene-containing PCL scaffolds enhanced the healing significantly in large osteochondral defect areas compared to the control groups.

Effect of Remote Control Augmented Reality Multimedia Technology for Postoperative Rehabilitation of Knee Joint Injury

This study was aimed at exploring the application value of augmented reality (AR) in postoperative rehabilitation training for patients with knee joint injury. 40 patients who underwent knee joint injury surgery were selected as the research objects, and the patients were randomly divided into two groups: an experimental group (20 cases) and a control group (20 cases). Patients in the experimental group were treated with AR-based rehabilitation methods, while those in the control group were treated with traditional rehabilitation methods. Afterwards, the two groups of patients were compared with various indicators such as pain value, swelling, structural and functional recovery, time to complete weight bearing, time to return to work, and X-ray examination results. The main evaluation tools used were Hospital for Special Surgery (HSS) score and Visual Analogue Scale (VAS) score. The results showed that after six weeks, the HSS score of the control group was 82.88 ± 3.07, and the HSS score of the experimental group was 85.46 ± 3.21. The difference between the two groups was statistically significant (P < 0.05). After three months, the HSS score of the control group was 89.96 ± 3.76, and that of the experimental group was 93.21 ± 4.33. The difference between the two groups was statistically significant (P < 0.05). There was a significant difference in pain scores between the two groups at 7 days (3.81 ± 0.48 vs. 5.06 ± 0.66) and 14 days (2.03 ± 0.45 vs. 3.61 ± 0.63) after surgery, with statistical significances (P < 0.05). There were statistically significant differences between the two groups in terms of time to complete weight bearing (7 ± 0.87 weeks vs. 8.82 ± 0.88 weeks) and time to return to work (8.69 ± 0.94 vs. 9.93 ± 0.88 weeks) (P < 0.05). One month after surgery, the X-ray examination results of both groups showed recovery. The AR-based rehabilitation training system showed a good application effect and prospect in the postoperative structural and functional recovery of patients with knee joint injury.

Comparative risk-benefit profiles of weak opioids in the treatment of osteoarthritis: a network meta-analysis of randomized controlled trials

BACKGROUND

Despite their poor tolerance, weak opioids are still the most commonly-prescribed medicine for osteoarthritis (OA)-related pain. The objective of this network meta-analysis was to comparatively examine the efficacy and safety of weak opioids in OA treatment.

METHODS

Databases including PubMed, Embase, Cochrane Library and Web of Science were searched from inception to August 5, 2020 to retrieve randomized controlled trials (RCTs) comparing weak opioids with placebo or between one another in OA patients. Bayesian network meta-analysis was performed on the following outcomes of interest, namely the change-from-baseline score in pain relief, gastrointestinal (GI) adverse events (AEs), central nervous system (CNS) AEs, and total number of AEs (i.e., the number of subjects experiencing any AE for at least once) during follow-up.

RESULTS

A total of 14 RCTs involving four types of weak opioids were included in this meta-analysis. Compared to placebo, tramadol (standardized mean difference [SMD] = -0.34, 95% credible interval [CrI]: -0.53 to -0.18) and codeine (SMD = -0.39, 95% CrI: -0.79 to -0.04) were effective for pain relief, but involved a higher risk of GI AEs, CNS AEs and total number of AEs. Dextropropoxyphene demonstrated a significantly lower risk of GI AEs (OR = 0.28, 95%CrI: 0.17 to 0.51), CNS AEs (OR = 0.29, 95%CrI: 0.11 to 0.78) and total number of AEs (OR = 0.35, 95%CrI: 0.15 to 0.82) compared to codeine. Dihydrocodeine had a better safety profile in CNS AEs (SUCRA = 64.8%) and total number of AEs (SUCRA = 66.6%).

CONCLUSIONS

The results of the present study confirmed that tramadol and codeine were effective drugs for the treatment of OA, but involved considerable safety issues. Dextropropoxyphene and dihydrocodeine exhibited a relatively good safety profile but their efficacy still warrant further investigation.

Aspirin Administered for Venous Thromboembolism Prophylaxis May Protect Against Stiffness Following Total Knee Arthroplasty

BACKGROUND

Aspirin has become the main agent for venous thromboembolism (VTE) prophylaxis following total knee arthroplasty (TKA). This study assessed whether aspirin is associated with less knee stiffness compared to warfarin and other chemoprophylaxis agents.

METHODS

This is a retrospective review of all primary and revision TKAs performed between January 2009 and October 2020 at a high volume institution. Demographics, comorbidity data, and operative variables were extracted from medical records. VTE prophylaxis administered during this time period included aspirin, warfarin, and "others" (factor Xa, unfractionated heparin, low-molecular-weight heparin, fondaparinux, adenosine diphosphate receptor inhibitor, and direct thrombin inhibitor). The primary outcome assessed was manipulation under anesthesia (MUA) performed within 6 months of index surgery. Secondary outcome included major bleeding events. Univariate followed by multivariate regression analyses were performed.

RESULTS

A total of 15,903 cases were included in the study, of which 531 (3.3%) patients developed stiffness that required MUA. The rates of MUA were 2.7% (251/9223) for patients receiving aspirin, 4.2% (238/5709) for patients receiving warfarin, and 4.3% (42/971) for all others (P's < .001). Multivariate regression analysis confirmed that aspirin is associated with lower rates of VTE compared to warfarin (adjusted odds ratio 1.423, 95% confidence interval 1.158-1.747, P < .001) and compared to other anticoagulation medications (adjusted odds ratio 1.742, 95% confidence interval 1.122-2.704, P = .013). Major bleeding events were also significantly lower in patients who received aspirin compared to the other 2 groups (P's = .001).

CONCLUSION

Aspirin prophylaxis is associated with lower rates of MUA following TKA compared to warfarin and other VTE chemoprophylactic agents when grouped together.

Anterior Cruciate Ligament Reconstruction Surgery: Creating a Permissive Healing Phenotype in Military Personnel and Civilians for Faster Recovery

Introduction

Anterior cruciate ligament (ACL) rupture in military personnel and civilians can be a devastating injury. A service member is 10 times more likely to suffer an ACL injury than their civilian counterparts, and despite successful surgical stabilization, 4%-35% will develop arthrofibrosis, over 50% will not return to full active duty, and up to 50% will develop post-traumatic osteoarthritis (PTOA) within 15 years. Equally concerning, woman are 2 to 8 times more likely to experience ACL injuries than men, which represents a major knowledge gap.

Materials and Methods

A comprehensive literature search was performed in December 2021 using structured search terms related to prevalence, risk factors, disease progression, and treatment of ACL injury and reconstruction. The literature search was conducted independently by two researchers using PubMed, Cochrane, and Embase databases, with inclusion of articles with military, civilian, and sex relevance, and exclusion of most papers with a publication date greater than 10 years. The resources used for the review reflect the most current data, knowledge, and recommendations associated with research and clinical findings from reliable international sources.

Results

Currently, there is no effective system-based drug therapy that creates a “permissive environment” to reduce synovial and cartilage stress after ACL injury and reconstruction and prevent secondary complications. We argue that progress in this area has been hampered by researchers and clinicians failing to recognize that (1) an ACL injury is a system’s failure that affects the whole joint, (2) the early molecular events define and perpetuate different injury phenotypes, (3) male and female responses may be different and have a molecular basis, (4) the female phenotype continues to be under-represented in basic and clinical research, and (5) the variable outcomes may be perpetuated by the trauma of surgery itself. The early molecular events after ACL injury are characterized by an overexpression of joint inflammation, immune dysfunction, and trauma-induced synovial stress. We are developing an upstream adenosine, lidocaine, and magnesium therapy to blunt these early molecular events and expedite healing with less arthrofibrosis and early PTOA complications.

Conclusions

ACL injuries continue to be a major concern among military personnel and civilians and represent a significant loss in command readiness and quality of life. The lack of predictability in outcomes after ACL repair or reconstruction underscores the need for new joint protection therapies. The male–female disparity requires urgent investigation.

Multimodal conservative management of arthrofibrosis after total knee arthroplasty compared to manipulation under anesthesia: a feasibility study with retrospective cohort comparison

Background

The ideal treatment of early-stage arthrofibrosis after total knee arthroplasty is unclear. The purpose of this study was to determine the treatment effect, including variability, and feasibility of a multimodal physical therapy program as compared to manipulation under anesthesia.

Methods

This was a prospective feasibility study with a retrospective cohort comparison. Ten consecutive patients (aged 64 ± 9 years, 7 females) with early-stage arthrofibrosis were enrolled 6 weeks after primary total knee arthroplasty and participated in the multimodal physical therapy program. The multimodal physical therapy program consisted of manual therapy, therapeutic exercise, and static progressive splinting delivered over 4 weeks. The outcomes included knee range of motion (ROM), adherence, patient satisfaction, and safety. Data were compared to a retrospective cohort of 31 patients with arthrofibrosis (aged 65 ± 9 years, 20 females) who underwent manipulation under anesthesia followed by physical therapy.

Results

Overall, knee ROM outcomes were similar between multimodal physical therapy (110° ± 14) and manipulation under anesthesia (109° ± 11). Seven out of ten patients achieved functional ROM (≥ 110°) and avoided manipulation under anesthesia with the multimodal physical therapy program. Three out of 10 multimodal physical therapy patients required manipulation under anesthesia secondary to failure to demonstrate progress within 4 weeks of the multimodal physical therapy program. Adherence to the multimodal physical therapy program was 87 ± 9%. The median patient satisfaction with the multimodal physical therapy program was “very satisfied.” Safety concerns were minimal.

Conclusion

The use of the multimodal physical therapy program is feasible for treating early-stage arthrofibrosis after total knee arthroplasty, with 70% of patients avoiding manipulation under anesthesia. Randomized controlled trials are needed to determine the efficacy of the multimodal physical therapy program and to determine the optimal patient selection for the multimodal physical therapy program versus manipulation under anesthesia.

Trial registration

ClinicalTrials.gov, NCT04837872.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40814-022-01026-y.

The Molecular Structure and Role of Humanin in Neural and Skeletal Diseases, and in Tissue Regeneration

Humanin (HN) belongs to a member of mitochondrial-derived peptides (MDPs) which are encoded by mitochondrial genes. HN shares sequence homology with thirteen HN-like proteins, named MTRNR2L1 to MTRNR2L13, which encompass 24–28 amino acid residues in length. HN mediates mitochondrial status and cell survival by acting via an intracellular mechanism, or as a secreted factor via extracellular signals. Intracellularly, it binds Bcl2-associated X protein (BAX), Bim and tBid, and IGFBP3 to inhibit caspase activity and cell apoptosis. When released from cells as a secreted peptide, HN interacts with G protein-coupled formyl peptide receptor-like 1 (FPRL1/2) to mediate apoptosis signal-regulating kinase (ASK) and c-Jun N-terminal kinase (JNK) signalling pathways. Additionally, it interacts with CNTFR-α/gp130/WSX-1 trimeric receptors to induce JAK2/STA3 signalling cascades. HN also binds soluble extracellular proteins such as VSTM2L and IGFBP3 to modulate cytoprotection. It is reported that HN plays a role in neuronal disorders such as Alzheimer’s disease, as well as in diabetes mellitus, infertility, and cardiac diseases. Its roles in the skeletal system are emerging, where it appears to be involved with the regulation of osteoclasts, osteoblasts, and chondrocytes. Understanding the molecular structure and role of HN in neural and skeletal diseases is vital to the application of HN in tissue regeneration.

Arthrofibrosis Nightmares: Prevention and Management Strategies

Arthrofibrosis (AF) is an exaggerated immune response to a proinflammatory insult leading to pathologic periarticular fibrosis and symptomatic joint stiffness. The knee, elbow, and shoulder are particularly susceptible to AF, often in the setting of trauma, surgery, or adhesive capsulitis. Prevention through early physiotherapeutic interventions and anti-inflammatory medications remain fundamental to avoiding motion loss. Reliable nonoperative modalities exist and outcomes are improved when etiology, joint involved, and level of dysfunction are considered in the clinical decision making process. Surgical procedures should be reserved for cases recalcitrant to nonoperative measures. The purpose of this review is to provide an overview of the current understanding of AF pathophysiology, identify common risk factors, describe prevention strategies, and outline both nonoperative and surgical treatment options. This manuscript will focus specifically on sterile AF of the knee, elbow, and shoulder.

Arthrofibrosis following primary total hip arthroplasty: a distinct clinical entity

INTRODUCTION

Arthrofibrosis is a relatively frequent complication after total knee arthroplasty. Although stiffness after total hip arthroplasty (THA), because of formation of heterotopic ossification or other causes, is not uncommon, to the authors' best knowledge, arthrofibrosis after THA has not been described. The aim of this study is to describe the arthrofibrosis of the hip after primary THA using an established clinical and histological classification of arthrofibrosis.

MATERIALS AND METHODS

We retrospectively examined all patients who were histologically confirmed to have arthrofibrosis after primary THA during revision surgery by examination of tissue samples in our clinic. Arthrofibrosis was diagnosed according to the histopathological SLIM-consensus classification, which defines seven different SLIM types of the periimplant synovial membrane. The SLIM type V determines the diagnosis of endoprosthesis-associated arthrofibrosis.

RESULTS

The study population consists of 66 patients who were revised due to arthrofibrosis after primary THA. All patients had a limitation in range of motion prior to revision with a mean flexion of 90° (range from 40 to 125), mean internal rotation of 10° (range from 0 to 40) and mean external rotation of 20° (range from 0 to 50). All patients had histological SLIM type V arthrofibrosis, corresponding to endoprosthesis-associated arthrofibrosis. Histological examination revealed that seven patients (10.6%) had particle-induced and 59 patients (89.4%) had non-particle-induced arthrofibrosis.

CONCLUSION

This is the first description of endoprosthetic-associated arthrofibrosis after primary THA on the basis of a well-established histological classification. Our study results could enable new therapeutic and diagnostic opportunities in patients with such an arthrofibrosis. Surgeons should keep arthrofibrosis as a possible cause for stiffness and pain after primary THA in mind.

LEVEL OF EVIDENCE

Diagnostic study, Level of Evidence IV.

Differences in synovial fibrosis relative to range of motion in knee osteoarthritis patients

This study tests if differences exist in the severity of synovial fibrosis between patients undergoing total knee arthroplasty (TKA) for osteoarthritis (OA) to help explain disparate deficits in pre- and postoperative range of motion (ROM) between patient groups. 117 knee OA patients were grouped by women (n = 74) and men (n = 43) or those who self-reported as Black (n = 48) or White (n = 69). ROM was measured pre- and post-TKA. Condyles and synovium collected during TKA were scored histologically for OA severity and synovitis. Fibrosis was measured from picrosirius-stained sections of the synovium. Data were analyzed using Mann-Whitney, parametric, and Spearman's rho tests with alpha at 0.05. We found no significant differences between patient age, BMI, radiographic scores, or deformity type when grouped by sex or race, or between metrics or OA severity when grouped by sex. Notably, higher synovitis was measured in women (p = .039) than men. White patients had greater ROM before (p = 0.46) and after surgery (p = .021) relative to Black patients. Fibrosis, but not OA severity and synovitis scores, for the total patient sample negatively correlated with preoperative (r _s  = -0.330; p = .0003) but not postoperative (r_s  = -0.032; p = .7627) ROM. Black patients manifested more fibrosis than White patients (p = <.0001), without significant differences between sexes. Statement of Clinical Significance: Coupled with histological scoring, measuring perioperative differences in synovial fibrosis against ROM may refine OA classification and justify the in-depth preoperative assessment of the knee as a whole. Such individualized analyses could guide personalized strategies to relieve symptomatic OA when TKA is not readily accessible and promote equitable TKA outcomes.

Cross-Communication Between Knee Osteoarthritis and Fibrosis: Molecular Pathways and Key Molecules

Knee fibrosis is characterized by the presence of excessive connective tissue due to dysregulated fibroblast activation following local or systemic tissue damage. Knee fibrosis constitutes a major clinical problem in orthopaedics due to the severe limitation in the knee range of motion that leads to compromised function and patient disability. Knee osteoarthritis is an extremely common orthopedic condition that is associated with patient disability and major costs to the health-care systems worldwide. Although knee fibrosis and osteoarthritis (OA) have traditionally been perceived as two separate pathologic entities, recent research has shown common ground between the pathophysiologic processes that lead to the development of these two conditions. The purpose of this review was to identify the pathophysiologic pathways as well as key molecules that are implicated in the development of both knee OA and knee fibrosis in order to understand the relationship between the two diagnoses and potentially identify novel therapeutic targets.

Human outgrowth knee fibroblasts from patients undergoing total knee arthroplasty exhibit a unique gene expression profile and undergo myofibroblastogenesis upon TGFβ1 stimulation

Arthrofibrosis is characterized by excessive extracellular matrix (ECM) deposition that results in restricted joint motion after total knee arthroplasties (TKAs). Currently, treatment options are limited. Therefore, an in vitro model of knee-related myofibroblastogenesis is valuable to facilitate investigation of the arthrofibrotic process, diagnostic and therapeutic options. In this study, we obtained intraoperative posterior capsule (PC), quadriceps tendon (QT), and suprapatellar pouch (SP) tissues from the knees of four patients undergoing primary TKAs for osteoarthritis. From these tissues, we isolated primary cells by the outgrowth method and subsequently characterized these cells in the absence and presence of the pro-myofibroblastic cytokine, transforming growth factor beta 1 (TGFβ1). Light microscopy of knee outgrowth cells revealed spindle-shaped cells, and immunofluorescence (IF) analysis demonstrated staining for the fibroblast-specific markers TE-7 and vimentin (VIM). These knee outgrowth fibroblasts differentiated readily into myofibroblasts as reflected by enhanced α-smooth muscle actin (ACTA2) mRNA and protein expression and increased mRNA expression of collagen type 1 (COL1A1) and type 3 (COL3A1) with collagenous matrix deposition in the presence of TGFβ1. Outgrowth knee fibroblasts were more sensitive to TGFβ1-mediated myofibroblastogenesis than adipose-derived mesenchymal stromal/stem cells (MSCs). While outgrowth knee fibroblasts isolated from three anatomical regions in four patients exhibited similar gene expression, these cells are distinct from other fibroblastic cell types (i.e., Dupuytren's fibroblasts) as revealed by RNA-sequencing. In conclusion, our study provides an in vitro myofibroblastic model of outgrowth knee fibroblasts derived from patients undergoing primary TKA that can be utilized to study myofibroblastogenesis and assess therapeutic strategies for arthrofibrosis.

Pleiotropic Long-Term Effects of Atorvastatin on Posttraumatic Joint Contracture in a Rat Model

The antifibrotic effect of atorvastatin has already been demonstrated in several organ systems. In the present study, a rat model was used to investigate the effect of atorvastatin on posttraumatic joint contracture. Forty-eight Sprague Dawley rats were equally randomized into an atorvastatin group and a control group. After initial joint trauma, knee joints were immobilized for intervals of 2 weeks (n = 16) or 4 weeks (n = 16) or immobilized for 4 weeks with subsequent remobilization for another 4 weeks (n = 16). Starting from the day of surgery, animals received either atorvastatin or placebo daily. After euthanasia at week 2, 4 or 8, joint contracture was determined, histological examinations were performed, and gene expression was assessed. The results suggest that the joint contracture was primarily arthrogenic. Atorvastatin failed to significantly affect contracture formation and showed a reduction in myofibroblast numbers to 98 ± 58 (control: 319 ± 113, p < 0.01) and a reduction in joint capsule collagen to 60 ± 8% (control: 73 ± 9%, p < 0.05) at week 2. Gene expression of α-smooth muscle actin (α-SMA), collagen type I, transforming growth factor β1 (TGF-β1) and interleukin-6 (IL-6) was not significantly affected by atorvastatin. Atorvastatin decreases myofibroblast number and collagen deposition but does not result in an improvement in joint mobility.

E8002 Reduces Adhesion Formation and Improves Joint Mobility in a Rat Model of Knee Arthrofibrosis

Knee arthrofibrosis is a common complication of knee surgery, caused by excessive scar tissue, which results in functional disability. However, no curative treatment has been established. E8002 is an anti-adhesion material that contains L-ascorbic acid, an antioxidant. We aimed to evaluate the efficacy of E8002 for the prevention of knee arthrofibrosis in a rat model, comprising injury to the surface of the femur and quadriceps muscle 1 cm proximal to the patella. Sixteen male, 8-week-old Sprague Dawley rats were studied: in the Adhesion group, haemorrhagic injury was induced to the quadriceps and bone, and in the E8002 group, an adhesion-preventing film was implanted between the quadriceps and femur after injury. Six weeks following injury, the restriction of knee flexion owing to fibrotic scarring had not worsened in the E8002 group but had worsened in the Adhesion group. The area of fibrotic scarring was smaller in the E8002 group than in the Adhesion group (p < 0.05). In addition, the numbers of fibroblasts (p < 0.05) and myofibroblasts (p < 0.01) in the fibrotic scar were lower in the E8002 group. Thus, E8002 reduces myofibroblast proliferation and fibrotic scar formation and improves the range of motion of the joint in a model of knee injury.

Comparison of intra-articular administration of adenosine, lidocaine and magnesium solution and tranexamic acid for alleviating postoperative inflammation and joint fibrosis in an experimental model of knee arthroplasty

BACKGROUND

Dysregulated inflammatory responses are implicated in the pathogenesis of joint stiffness and arthrofibrosis following total knee arthroplasty (TKA). The purpose of this study was to compare the effects of intra-articular (IA) administration of tranexamic acid (TXA), an anti-fibrinolytic commonly used in TKA, and ALM chondroprotective solution on postoperative inflammation and joint tissue healing in a rat model of knee implant surgery.

METHODS

Male Sprague-Dawley rats (n = 24) were randomly divided into TXA or ALM treatment groups. The right knee of each rat was implanted with titanium (femur) and polyethylene (tibia) implants. An IA bolus (0.1 ml) of TXA or ALM was administered after implantation and capsule closure, and before skin closure. Postoperative coagulopathy, haematology and systemic inflammatory changes were assessed. Inflammatory and fibrotic markers were assessed in joint tissue, 28 days after surgery.

RESULTS

Haemostasis was comparable in animals treated with TXA or ALM after knee implant surgery. In contrast to ALM-treated animals, systemic inflammatory markers remained elevated at day 5 (IL-6, IL-12, IL-10, platelet count) and day 28 (IL-1β, IL-10) following surgery in TXA-treated animals. At day 28 following surgery, the extension range of motion of operated knees was 1.7-fold higher for ALM-treated animals compared to the TXA group. Key inflammatory mediators (NF-κB, IL-12, IL-2), immune cell infiltration (CD68+ cells) and markers of fibrosis (α-SMA, TGF-β) were also lower in capsular tissue of ALM-treated knees at day 28.

CONCLUSION

Data suggest that IA administration of ALM is superior to TXA for reducing postoperative systemic and joint inflammation and promoting restoration of healthy joint tissue architecture in a rat model of TKA. Further studies are warranted to assess the clinical translational potential of ALM IA solution to improve patient outcomes following arthroplasty.

Interleukin-1 receptor antagonist inhibits arthrofibrosis in a post-traumatic knee immobilization model

BACKGROUND

Therapies for arthrofibrosis after knee surgery are needed to prevent loss of joint function. Interleukin-1 receptor antagonists (IL-1RA) have shown promise in treating established arthrofibrosis in pilot clinical studies. The objective of this study was to evaluate the ability of intra-articular injection of IL-1RA to prevent knee joint contracture in a post-traumatic knee immobilization model.

METHODS

20 male Sprague Dawley rats were block randomized into two groups: control and IL-1RA. Rats underwent intra-articular surgical trauma of the right knee with placement of an immobilization suture, securing the knees in 150° flexion. On post-operative days 1 and 8, each group received a 0.1 ml intra-articular injection of either saline (control) or anakinra (IL-1RA:single dosage; 2.63 mg/kg). Rats were euthanized fourteen days after surgery and the immobilization femorotibial angles were measured on the operative limbs with the suture and musculature intact. Subsequently, musculature was removed and femorotibial angles were measured in the operative and non-operative limbs with a defined extension moment applied with the posterior capsule intact or cut. A contracture angle was calculated as the angular difference between the operative and non-operative limb.

RESULTS

The immobilization knee flexion angle did not differ (P = 0.761) between groups (control: 152 ± 9; IL-1RA: 150 ± 11). The joint contracture angles (smaller angle = improved outcome) were reduced by 12 degrees on average in the IL-1RA group compared to the control for both the capsule intact (P = 0.024) and cut (P = 0.019) states.

CONCLUSIONS

Intra-articular IL-1RA injection was found to diminish knee extension deficits associated with arthrofibrosis in a post-traumatic joint immobilization model.

Does Flipping the Tubercle for Improved Cartilage Repair Exposure Increase the Risk for Arthrofibrosis?

OBJECTIVE

We sought to determine whether rates of postoperative arthrofibrosis following tibial tuberosity osteotomy (TTO) with complete mobilization of the fragment (TTO-HD) are comparable to TTOs where the hinge remained intact (TTO-HI).

DESIGN

Patients who underwent TTO with concomitant cartilage repair procedure between January 2007 and May 2017, with at least 2 years of follow-up were included in this study. Postoperative reinterventions following TTO-HD and TTO-HI were assessed and multivariant logistic regression models were used to identify whether postoperative reinterventions can be attributed to either technique when controlled for defect size or defect number.

RESULTS

A total of 127 patients (TTO-HD, n = 80; TTO-HI, n = 47) were included in this study. Significantly more patients in the TTO-HD group (31.2%) developed postoperative arthrofibrosis compared with TTO-HI (6.4%; P < 0.05). Multivariant logistic regression revealed that TTO-HD is an independent risk factor for predicting postoperative arthrofibrosis (OR 6.5, CI = 1.7-24.2, P < 0.05).

CONCLUSION

Patients who underwent TTO with distal hinge detachment and a proximally flipped tubercle for better exposure during concomitant cartilage repair were at a significantly higher risk of postoperative arthrofibrosis than patients with similar size and number of defects treated without mobilization of the tubercle. While certain procedures can benefit from larger exposure, surgeons should be aware of the increased risk of postoperative arthrofibrosis.

LEVEL OF EVIDENCE

Level III, case-control study.

The Potential Use of Cannabis in Tissue Fibrosis

Fibrosis is a condition characterized by thickening or/and scarring of various tissues. Fibrosis may develop in almost all tissues and organs, and it may be one of the leading causes of morbidity and mortality. It provokes excessive scarring that excels the usual wound healing response to trauma in numerous organs. Currently, very little can be done to prevent tissue fibrosis, and it is almost impossible to reverse it. Anti-inflammatory and immunosuppressive drugs are among the few treatments that may be efficient in preventing fibrosis. Numerous publications suggest that cannabinoids and extracts of Cannabis sativa have potent anti-inflammatory and anti-fibrogenic properties. In this review, we describe the types and mechanisms of fibrosis in various tissues and discuss various strategies for prevention and dealing with tissue fibrosis. We further introduce cannabinoids and their potential for the prevention and treatment of fibrosis, and therefore for extending healthy lifespan.

Proteoglycan-4 is an essential regulator of synovial macrophage polarization and inflammatory macrophage joint infiltration

BACKGROUND

Synovial macrophages perform a multitude of functions that include clearance of cell debris and foreign bodies, tissue immune surveillance, and resolution of inflammation. The functional diversity of macrophages is enabled by distinct subpopulations that express unique surface markers. Proteoglycan-4 (PRG4) is an important regulator of synovial hyperplasia and fibrotic remodeling, and the involvement of macrophages in PRG4's synovial role is yet to be defined. Our objectives were to study the PRG4's importance to macrophage homeostatic regulation in the synovium and infiltration of pro-inflammatory macrophages in acute synovitis and investigate whether macrophages mediated synovial fibrosis in Prg4 gene-trap (Prg4GT/GT) murine knee joints.

METHODS

Macrophage phenotyping in Prg4GT/GT and Prg4+/+ joints was performed by flow cytometry using pan-macrophage markers, e.g., CD11b, F4/80, and surface markers of M1 macrophages (CD86) and M2 macrophages (CD206). Characterizations of the various macrophage subpopulations were performed in 2- and 6-month-old animals. The expression of inflammatory markers, IL-6, and iNOS in macrophages that are CD86+ and/or CD206+ was studied. The impact of Prg4 recombination on synovial macrophage populations of 2- and 6-month-old animals and infiltration of pro-inflammatory macrophages in response to a TLR2 agonist challenge was determined. Macrophages were depleted using liposomal clodronate and synovial membrane thickness, and the expression of fibrotic markers α-SMA, PLOD2, and collagen type I (COL-I) was assessed using immunohistochemistry.

RESULTS

Total macrophages in Prg4GT/GT joints were higher than Prg4+/+ joints (p<0.0001) at 2 and 6 months, and the percentages of CD86+/CD206- and CD86+/CD206+ macrophages increased in Prg4GT/GT joints at 6 months (p<0.0001), whereas the percentage of CD86-/CD206+ macrophages decreased (p<0.001). CD86+/CD206- and CD86+/CD206+ macrophages expressed iNOS and IL-6 compared to CD86-/CD206+ macrophages (p<0.0001). Prg4 re-expression limited the accumulation of CD86+ macrophages (p<0.05) and increased CD86-/CD206+ macrophages (p<0.001) at 6 months. Prg4 recombination attenuated synovial recruitment of pro-inflammatory macrophages in 2-month-old animals (p<0.001). Clodronate-mediated macrophage depletion reduced synovial hyperplasia, α-SMA, PLOD2, and COL-I expressions in the synovium (p<0.0001).

CONCLUSIONS

PRG4 regulates the accumulation and homeostatic balance of macrophages in the synovium. In its absence, the synovium becomes populated with M1 macrophages. Furthermore, macrophages exert an effector role in synovial fibrosis in Prg4GT/GT animals.