Molecular pathology of human knee arthrofibrosis defined by RNA sequencing

Dynamic strain and β-catenin mediated suppression of interferon responsive genes in quiescent mesenchymal stromal/stem cells

Multipotent bone marrow mesenchymal stromal/stem cells (MSCs) respond to mechanical forces. MSCs perceive static and dynamic forces through focal adhesions, as well as cytoskeletal and intranuclear actin. Dynamic strain stimulates nuclear β-catenin (Ctnnb1) that controls gene expression and suppresses osteogenesis. The sensitivity of MSCs to external mechanical forces may be altered by cessation of proliferation, when MSCs begin to express extracellular matrix (ECM) proteins and generate cell/cell contact. Therefore, we assessed whether and how gene expression of proliferating versus quiescent MSCs responds to mechanical stimuli. We used RNA-seq and RT-qPCR to evaluate transcriptomes at 3 h after dynamic strain (200 cycles × 2 % for 20 min) once daily during a two-day time course in naïve (uninduced) MSCs. Transcriptomes of untreated MSCs show that cells become quiescent at day 2 when proliferation markers are downregulated, and ECM related genes are upregulated. On both day 1 and day 2, dynamic strain stimulates expression of oxidative stress related genes (e.g., Nqo1, Prl2c2, Prl2c3). Strikingly, in quiescent MSCs, we observe that dynamic strain suppresses multiple interferon (IFN) responsive genes (e.g., Irf7, Oasl2 and Isg15). IFN responsive genes are activated in MSCs depleted of β-catenin using siRNAs, indicating that β-catenin normally suppresses these genes. Our data indicate that the functional effects of dynamic strain and β-catenin on IFN responsive genes in MSCs are mechanistically coupled. Because dynamic strain and β-catenin reduce the osteogenic potential of MSCs, our findings suggest that IFN responsive genes are novel biomarkers and potential regulators of mechanical responses at early stages of lineage-commitment in post-proliferative MSCs.

Research progress of knee fibrosis after anterior cruciate ligament reconstruction

Anterior cruciate ligament (ACL) injury is a common sports injury, and ACL reconstruction is an effective surgery for this trauma. Most cases gain good recovery after surgery, while some patients may experience knee stiffness, which is characterized by joint fibrosis, leading to reduced joint mobility, pain, and dysfunction. Currently, various research studies have been conducted to unveil the mechanisms underlying this condition, identifying pre-, intra-, and post-operative risk factors, and testify the efficacy of different therapeutic methods against it. In this review, we summarize the current progress regarding the advancements in knee fibrosis after ACL reconstruction. The risk factors associated with knee fibrosis are systematically delineated, accompanied by an evaluation of the efficacy of various treatment modalities for both the prevention and mitigation of fibrosis. Furthermore, recommendations for future research directions are proposed, offering a foundational basis for subsequent investigations.

Efficacy of ADIPOR1 and ADIPOR2 peptide-agonist AdipoRon in preventing contracture in a rabbit model of arthrofibrosis

AdipoRon is an adiponectin receptor 1, 2 (ADIPOR1 and ADIPOR2) agonist with potential antifibrotic effects. Whether AdipoRon can mitigate joint stiffness in a rabbit model of arthrofibrosis is unknown. We examined the efficacy of intravenous (IV) AdipoRon at mitigating contracture in a rabbit model of knee arthrofibrosis. Fifty-six female New Zealand White rabbits were divided into three dosing groups: vehicle (dimethyl sulfoxide, DMSO), 2.5 mg/kg AdipoRon, and 5 mg/kg AdipoRon. AdipoRon, in DMSO, was administered IV preoperatively and for 5 days postoperatively (30 rabbits, Aim 1). AdipoRon was again dosed similarly after Kirschner wire (K-wire) removal at 8 weeks (26 rabbits; Aim 2). The primary outcome of joint passive extension angle (PEA,°) was measured at 8, 10, 12, 16, and 24 weeks following index surgery. At 24 weeks, rabbits were euthanized and limbs were harvested to measure posterior capsular stiffness (N cm/°). In Aim 1, the 5 mg/kg treated rabbits had a significant increase in PEA when compared to controls at 16-week (p < 0.05). In Aim 2, the 5 mg/kg treated rabbits had a significant increase in PEA when compared to controls at 10-week (p < 0.05). In both aims, no significant differences were observed at later time points. Capsular stiffness was no different in any group. We are the first to report the efficacy of IV AdipoRon in a rabbit model of arthrofibrosis. We identified a significant dose-dependent decrease in joint PEA at early time points; however, no differences were observed between groups at later time points. Clinical Significance: The present investigation provided the first assessment of AdipoRon's efficacy in mitigating knee stiffness in the current gold standard rabbit model of arthrofibrosis. Results of this investigation provided further evidence as to the potential role of AdipoRon as a preventative for arthrofibrosis in large mammals.

Exploring the molecular mechanisms and shared potential drugs between rheumatoid arthritis and arthrofibrosis based on large language model and synovial microenvironment analysis

Rheumatoid arthritis (RA) and arthrofibrosis (AF) are both chronic synovial hyperplasia diseases that result in joint stiffness and contractures. They shared similar symptoms and many common features in pathogenesis. Our study aims to perform a comprehensive analysis between RA and AF and identify novel drugs for clinical use. Based on the text mining approaches, we performed a correlation analysis of 12 common joint diseases including arthrofibrosis, gouty arthritis, infectious arthritis, juvenile idiopathic arthritis, osteoarthritis, post infectious arthropathies, post traumatic osteoarthritis, psoriatic arthritis, reactive arthritis, rheumatoid arthritis, septic arthritis, and transient arthritis. 5 bulk sequencing datasets and 4 single-cell sequencing datasets of RA and AF were integrated and analyzed. A novel drug repositioning method was found for drug screening, and text mining approaches were used to verify the identified drugs. RA and AF performed the highest gene similarity (0.77) and functional ontology similarity (0.84) among all 12 joint diseases. We figured out that they share the same key pathogenic cell including CD34 + sublining fibroblasts (CD34-SLF) and DKK3 + sublining fibroblasts (DKK3-SLF). Potential therapeutic target database (PTTD) was established with the differential expressed genes (DEGs) of these key pathogenic cells. Based on the PTTD, 15 potential drugs for AF and 16 potential drugs for RA were identified. This work provides a new perspective on AF and RA study which enhances our understanding of their pathogenesis. It also shed light on their underlying mechanism and open new avenues for drug repositioning studies.

The Chitranjan S. Ranawat Award: Manipulation Under Anesthesia to Treat Postoperative Stiffness After Total Knee Arthroplasty: A Multicenter Randomized Clinical Trial

BACKGROUND

Manipulation under anesthesia (MUA) occurs in 4% of patients after total knee arthroplasty (TKA). Anti-inflammatory medications may target arthrofibrosis pathogenesis, but the data are limited. This multicenter randomized clinical trial investigated the effect of adjuvant anti-inflammatory medications with MUA and physical therapy on range of motion (ROM) and outcomes.

METHODS

There were 124 patients (124 TKAs) who developed stiffness after primary TKA for osteoarthritis enrolled across 15 institutions. All received MUA when ROM was < 90° at 4 to 12 weeks postoperatively. Randomization proceeded via a permuted block design. Controls received MUA and physical therapy, while the treatment group also received one dose of pre-MUA intravenous dexamethasone (8 mg) and 14 days of oral celecoxib (200 mg). The ROM and clinical outcomes were assessed at 6 weeks and 1 year. This trial was registered with ClinicalTrials.gov.

RESULTS

The ROM significantly improved a mean of 46° from a pre-MUA ROM of 72 to 118° immediately after MUA (P < .001). The ROM was similar between the treatment and control groups at 6 weeks following MUA (101 versus 99°, respectively; P = .35) and at one year following MUA (108 versus 108°, respectively; P = .98). Clinical outcomes were similar at both end points.

CONCLUSIONS

In this multicenter randomized clinical trial, the addition of intravenous dexamethasone and a short course of oral celecoxib after MUA did not improve ROM or outcomes. However, MUA provided a mean ROM improvement of 46° immediately, 28° at 6 weeks, and 37° at 1 year. Further investigation in regards to dosing, duration, and route of administration of anti-inflammatory medications remains warranted.

LEVEL OF EVIDENCE

Level 1, RCT.

Emerging roles of non-coding RNAs in fibroblast to myofibroblast transition and fibrotic diseases

The transition of fibroblasts to myofibroblasts (FMT) represents a pivotal process in wound healing, tissue repair, and fibrotic diseases. This intricate transformation involves dynamic changes in cellular morphology, gene expression, and extracellular matrix remodeling. While extensively studied at the molecular level, recent research has illuminated the regulatory roles of non-coding RNAs (ncRNAs) in orchestrating FMT. This review explores the emerging roles of ncRNAs, including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), in regulating this intricate process. NcRNAs interface with key signaling pathways, transcription factors, and epigenetic mechanisms to fine-tune gene expression during FMT. Their functions are critical in maintaining tissue homeostasis, and disruptions in these regulatory networks have been linked to pathological fibrosis across various tissues. Understanding the dynamic roles of ncRNAs in FMT bears therapeutic promise. Targeting specific ncRNAs holds potential to mitigate exaggerated myofibroblast activation and tissue fibrosis. However, challenges in delivery and specificity of ncRNA-based therapies remain. In summary, ncRNAs emerge as integral regulators in the symphony of FMT, orchestrating the balance between quiescent fibroblasts and activated myofibroblasts. As research advances, these ncRNAs appear to be prospects for innovative therapeutic strategies, offering hope in taming the complexities of fibrosis and restoring tissue equilibrium.

Removal of the infrapatellar fat pad and associated synovium benefits female guinea pigs in the Dunkin Hartley model of idiopathic osteoarthritis

Background

Several tissues contribute to the onset and advancement of knee osteoarthritis (OA). One tissue type that is worthy of closer evaluation, particularly in the context of sex, is the infrapatellar fat pad (IFP). We previously demonstrated that removal of the IFP had short-term beneficial effects for a cohort of male Dunkin-Hartley guinea pigs. The present project was designed to elucidate the influence of IFP removal in females of this OA-prone strain. It was hypothesized that resection of the IFP would reduce the development of OA in knees of a rodent model predisposed to the disease.

Methods

Female guinea pigs (n=16) were acquired at an age of 2.5 months. Surgical removal of the IFP and associated synovium complex (IFP/SC) was executed at 3 months of age. One knee had the IFP/SC resected; a comparable sham surgery was performed on the contralateral knee. All animals were subjected to voluntary enclosure monitoring and dynamic weight-bearing, as well as compulsory treadmill-based gait analysis monthly; baseline data was collected prior to surgery. Guinea pigs were euthanized at 7 months. Knees from eight animals were evaluated via histology, mRNA expression, and immunohistochemistry (IHC); knees from the remaining eight animals were allocated to microcomputed tomography (microCT), biomechanical analyses (whole joint testing and indentation relaxation testing), and atomic absorption spectroscopy (AAS).

Results

Fibrous connective tissue (FCT) replaced the IFP/SC. Mobility/gait data indicated that unilateral IFP/SC removal did not affect bilateral hindlimb movement. MicroCT demonstrated that osteophytes were not a significant feature of OA in this sex; however, trabecular thickness (TbTh) in medial femorae decreased in knees containing the FCT. Histopathology scores were predominantly influenced by changes in the lateral tibia, which demonstrated that histologic signs of OA were increased in knees containing the native IFP/SC versus those with the FCT. Similarly, indentation testing demonstrated higher instantaneous and equilibrium moduli in the lateral tibial articular cartilage of control knees with native IFPs. AAS of multiple tissue types associated with the knee revealed that zinc was the major trace element influenced by removal of the IFP/SC.

Conclusions

Our data suggest that the IFP/SC is a significant component driving knee OA in female guinea pigs and that resection of this tissue prior to disease has short-term benefits. Specifically, the formation of the FCT in place of the native tissue resulted in decreased cartilage-related OA changes, as demonstrated by reduced Osteoarthritis Research Society International (OARSI) histology scores, as well as changes in transcript, protein, and cartilage indentation analyses. Importantly, this model provides evidence that sex needs to be considered when investigating responses and associated mechanisms seen with this intervention.

AdipoRon reduces TGFβ1-mediated collagen deposition in vitro and alleviates knee stiffness in vivo

Arthrofibrosis, which causes joint motion restrictions, is a common complication following total knee arthroplasty (TKA). Key features associated with arthrofibrosis include myofibroblast activation, knee stiffness, and excessive scar tissue formation. We previously demonstrated that adiponectin levels are suppressed within the knee tissues of patients affected by arthrofibrosis and showed that AdipoRon, an adiponectin receptor agonist, exhibited anti-fibrotic properties in human mesenchymal stem cells. In this study, the therapeutic potential of AdipoRon was evaluated on TGFβ1-mediated myofibroblast differentiation of primary human knee fibroblasts and in a mouse model of knee stiffness. Picrosirius red staining revealed that AdipoRon reduced TGFβ1-induced collagen deposition in primary knee fibroblasts derived from patients undergoing primary TKA and revision TKA for arthrofibrosis. AdipoRon also reduced mRNA and protein levels of ACTA2, a key myofibroblast marker. RNA-seq analysis corroborated the anti-myofibrogenic effects of AdipoRon. In our knee stiffness mouse model, 6 weeks of knee immobilization, to induce a knee contracture, in conjunction with daily vehicle (DMSO) or AdipoRon (1, 5, and 25 mg/kg) via intraperitoneal injections were well tolerated based on animal behavior and weight measurements. Biomechanical testing demonstrated that passive extension angles (PEAs) of experimental knees were similar between vehicle and AdipoRon treatment groups in mice evaluated immediately following immobilization. Interestingly, relative to vehicle-treated mice, 5 mg/kg AdipoRon therapy improved the PEA of the experimental knees in mice that underwent 4 weeks of knee remobilization following the immobilization and therapy. Together, these studies revealed that AdipoRon may be an effective therapeutic modality for arthrofibrosis.

Computational screening of biomarkers and potential drugs for arthrofibrosis based on combination of sequencing and large nature language model

Background

Arthrofibrosis (AF) is a fibrotic joint disease resulting from excessive collagen production and fibrous scar formation after total knee arthroplasty (TKA). This devastating complication may cause consistent pain and dramatically reduction of functionality. Unfortunately, the conservative treatments to prevent the AF in the early stage are largely unknown due to the lack of specific biomarkers and reliable therapeutic targets.

Methods

In this study, we extracted1782 fibrosis related genes (FRGs) from 373,461published literature based on the large natural language processing models (ChatGPT) and intersected with the 2750 differential expressed genes (DEGs) from mRNA microarray (GSE135854). A total of 311 potential AF biomarker genes (PABGs) were obtained and functional analysis were performed including gene ontology (GO) annotation and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses. Subsequently, we accomplished validation in AF animal models with immobilization of the unilateral knee joints of 16 rabbits for 1-week, 2-weeks, 3-weeks and 4-weeks. Finally, we tested the biomarkers in a retrospective cohort enrolled 35 AF patients and 35 control group patients.

Results

We identified G-protein-coupled receptor 17 (GPR17) as a reliable therapeutic biomarker for AF diagnosis with higher AUC (0.819) in the ROC curve. A total of 21 potential drugs targeted to GPR17 were screened. Among them, pranlukast and montelukast have achieved therapeutic effect in animal models. In addition, we established an online AF database for data integration (https://chenxi2023.shinyapps.io/afdbv1).

Conclusions

These results unveiling therapeutic biomarkers for AF diagnosis, and provide potential drugs for clinical treatment.

The translational potential of this article

Our study demonstrated that GPR17 holds significant promise as a potential biomarker and therapeutic target for arthrofibrosis. Moreover, pranlukast and montelukast targeted to GPR17 that could be instrumental in the treatment of AF.

Arthrofibrosis After Total Knee Arthroplasty: A Critical Analysis Review

» Arthrofibrosis after total knee arthroplasty (TKA) is the new formation of excessive scar tissue that results in limited ROM, pain, and functional deficits.» The diagnosis of arthrofibrosis is based on the patient's history, clinical examination, absence of alternative diagnoses from diagnostic testing, and operative findings. Imaging is helpful in ruling out specific causes of stiffness after TKA. A biopsy is not indicated, and no biomarkers of arthrofibrosis exist.» Arthrofibrosis pathophysiology is multifactorial and related to aberrant activation and proliferation of myofibroblasts that primarily deposit type I collagen in response to a proinflammatory environment. Transforming growth factor-beta signaling is the best established pathway involved in arthrofibrosis after TKA.» Management includes both nonoperative and operative modalities. Physical therapy is most used while revision arthroplasty is typically reserved as a last resort. Additional investigation into specific pathophysiologic mechanisms can better inform targeted therapeutics.

Arthrofibrosis risk factors after anterior cruciate ligament reconstruction

Introduction

Knee arthrofibrosis is a disabling complication after anterior cruciate ligament reconstruction (ACLr). Different risk factors have been studied but are still controversial because of a diagnosis made only during reoperations for the treatment of the stiffness, which underestimates the occurrence rate. We aimed to confirm risk factors of arthrofibrosis after ACLr in case of clinically made diagnoses.

Methods

Ninety-two athletes with clinically diagnosed arthrofibrosis, complicating a primary ACLr, were compared to 482 athletes with ACLr without any complications. Usually considered risk factors were studied: age under 18, female, Body Mass Index (BMI ≥ 25), high sport level, time from ACL injury to ACLr < 1 month, Bone-Patella-Tendon-Bone surgical procedure (BPTB), meniscal repair, and intensive rehabilitation. Binary logistic regression was carried out to confirm or refute these risk factors.

Results

Female, time from ACL injury to ACLr < 1 month, BPTB procedure, meniscal repair, and BMI ≥ 25 were not confirmed as risk factors. Previous competitive sport level assessed by Tegner score was the only risk factor identified, OR: 3.56 (95%IC: 2.20-5.75; p = 0.0001). Age < 18, OR: 0.40 (95%IC: 0.19-0.84; p = 0.015) and inpatient rehabilitation program, OR: 0.28 (95%IC: 0.17-0.47; p = 0.0001), were protective factors.

Discussion

Competitive athletes are at risk of arthrofibrosis after ACLr and should benefit from protective inpatient rehabilitation program.

Single-cell and bulk tissue sequencing unravels the heterogeneity of synovial microenvironment in arthrofibrosis

Arthrofibrosis (AF) is a debilitating complication that occurs after trauma or surgery, leading to functional impairment and surgical failures worldwide. This study aimed to uncover the underlying mechanism of AF. A total of 141 patients were enrolled, and synovial samples were collected from both patients and animal models at different time points. Single-cell RNA-sequencing (scRNA-seq) and bulk tissue RNA sequencing (bulk-seq) were employed to profile the distinct synovial microenvironment. This study revealed changes in cell proportions during AF pathogenesis and identified Engrailed-1 (EN1) as a key transcription factor strongly associated with disease severity and clinical prognosis. Additionally, the researchers discovered a specific type of synovial fibroblast called DKK3-SLF, which played a critical role in driving AF development. These findings shed light on the composition and heterogeneity of the synovial microenvironment in AF, offering potential avenues for identifying therapeutic targets and developing clinical treatments for AF and other fibrotic diseases.

Understanding of arthrofibrosis: New explorative insights into extracellular matrix remodeling of synovial fibroblasts

Arthrofibrosis following total knee arthroplasty is a fibroproliferative joint disorder marked by dysregulated biosynthesis of extracellular matrix proteins, such as collagens and proteoglycans. The underlying cellular events remain incompletely understood. Myofibroblasts are highly contractile matrix-producing cells characterized by increased alpha-smooth muscle actin expression and xylosyltransferase-I (XT-I) secretion. Human XT-I has been identified as a key mediator of arthrofibrotic remodeling. Primary fibroblasts from patients with arthrofibrosis provide a useful in vitro model to identify and characterize disease regulators and potential therapeutic targets. This study aims at characterizing primary synovial fibroblasts from arthrofibrotic tissues (AFib) regarding their molecular and cellular phenotype by utilizing myofibroblast cell culture models. Compared to synovial control fibroblasts (CF), AFib are marked by enhanced cell contractility and a higher XT secretion rate, demonstrating an increased fibroblast-to-myofibroblast transition rate during arthrofibrosis. Histochemical assays and quantitative gene expression analysis confirmed higher collagen and proteoglycan expression and accumulation in AFib compared to CF. Furthermore, fibrosis-based gene expression profiling identified novel modifier genes in the context of arthrofibrosis remodeling. In summary, this study revealed a unique profibrotic phenotype in AFib that resembles some traits of other fibroproliferative diseases and can be used for the future development of therapeutic interventions.

The epigenetic regulator BRD4 is required for myofibroblast differentiation of knee fibroblasts

Arthrofibrosis, which is characterized by excessive scar tissue and limited motion, can complicate the daily functioning of patients after total knee arthroplasty (TKA). Molecular hallmarks of arthrofibrosis include pathologic accumulation of myofibroblasts and disproportionate collagen deposition. Epigenetic mechanisms, including posttranslation modification of histones, control gene expression and may regulate fibrotic events. This study assessed the role of the bromodomain and extra-terminal (BET) proteins on myofibroblast differentiation. This group of epigenetic regulators recognize acetylated lysines and are targeted by a class of drugs known as BET inhibitors. RNA-seq analysis revealed robust mRNA expression of three BET members (BRD2, BRD3, and BRD4) while the fourth member (BRDT) is not expressed in primary TKA knee outgrowth fibroblasts. RT-qPCR and western blot analyses revealed that BET inhibition with the small molecule JQ1 impairs TGFβ1-induced expression of ACTA2, a key myofibroblast marker, in primary outgrowth knee fibroblasts. Similarly, JQ1 administration also reduced COL3A1 mRNA levels and collagen deposition as monitored by picrosirius red staining. Interestingly, the inhibitory effects of JQ1 on ACTA2 mRNA and protein expression, as well as COL3A1 expression and collagen deposition, were paralleled by siRNA-mediated depletion of BRD4. Together, these data reveal that BRD4-mediated epigenetic events support TGFβ1-mediated myofibroblast differentiation and collagen deposition as seen in arthrofibrosis. To our knowledge, these are the first studies that assess epigenetic regulators and their downstream events in the context of arthrofibrosis. Future studies may reveal clinical utility for drugs that target epigenetic pathways, specifically BET proteins, in the prevention and treatment of arthrofibrosis.

Inflammatory Treatment Used to Mimic Osteoarthritis and Patients' Synovial Fluid Have Divergent Molecular Impact on Chondrocytes In Vitro

Osteoarthritis (OA) is a chronic disease characterized by joint tissue disruption and inflammation with a paucity of therapeutic options. Chondrocyte in vitro models are commonly used as the first step in evaluating new approaches and rely on the stimulation of an OA-like phenotype with inflammation often the method of choice. Inflammatory priming is frequently based on cytokines used at concentrations very far from the reality in the patients' synovial fluid (SF). The aim of this work was to compare the transcriptional response of chondrocytes to different inflammatory conditions: the high levels of IL1β that are used for standardized inflammation protocols, OA-SF, IL1β, IL6 and IFNγ at SF-like concentrations both individually and simultaneously to mimic a simplified "in vitro" SF. Both high IL1β and OA-SF strongly influenced chondrocytes, while SF-like concentrations of cytokines gave weak (IL1β alone or in combination) or no (IL6 and IFNγ alone) outcomes. Chondrocytes under the two most powerful polarizing conditions had a clearly distinct fingerprint, with only a shared albeit molecularly divergent effect on ECM stability, with IL1β mainly acting on ECM degrading enzymes and OA-SF accounting for a higher turnover in favor of fibrous collagens. Moreover, OA-SF did not induce the inflammatory response observed with IL1β. In conclusion, although partially similar in the endpoint phenotype, this work intends to encourage reflection on the robustness of inflammation-based in vitro OA models for molecular studies on chondrocytes.

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.

Biochemical markers of postsurgical knee arthrofibrosis: A systematic review

Introduction

Postsurgical knee arthrofibrosis is a common complication associated with pain and limited range of motion. Although the mechanism is unclear, many biochemical and genetic markers have been identified within arthrofibrotic knees. The purpose of this systematic review is to synthesize the many biochemical and genetic markers that have been associated with surgery-induced knee arthrofibrosis in order to better guide future therapeutic endeavors.

Methods

A thorough search of literature was conducted on April 27, 2022. Seventeen studies met inclusion criteria for this systematic review. Inclusion criteria for this study were as follows: title or abstract discussed biochemical and genetic markers associated with postoperative knee arthrofibrosis, study design included human and/or animal subjects.

Results

A wide variety of genetic biomarkers (mRNA), proteins/enzymes, and cytokines were identified in both animal models and human subjects with postsurgical knee arthrofibrosis. These included various extracellular matrix-encoding mRNA sequences, matrix metalloproteinases, proteins and mRNA sequences involved in Transforming Growth Factor-β signaling, and interleukin-family cytokines to name just a few.

Conclusion

There are many biomarkers found in postsurgical arthrofibrotic knees. TGF-β, and mRNA/proteins that participate in TGF-β signaling (i.e., LOX, SERPINE1, PAI-1/Akt/mTOR, BMP-2), appear to be particularly common. Future comparative studies should aim to determine which of these are most relevant, and therefore, worthwhile therapeutic targets.

Immune cell populations differ in patients undergoing revision total knee arthroplasty for arthrofibrosis

Arthrofibrosis following total knee arthroplasty (TKA) is a debilitating condition typically diagnosed based on clinical findings. To gain insight into the histopathologic immune cell microenvironment of arthrofibrosis, we assessed the extent of tissue fibrosis and quantified immune cell populations in specific tissue regions of the posterior capsule. We investigated specimens from three prospectively-collected, matched cohorts, grouped as patients receiving a primary TKA for osteoarthritis, revision TKA for arthrofibrosis, and revision TKA for non-arthrofibrotic, non-infectious reasons. Specimens were evaluated using hematoxylin and eosin staining, picrosirius red staining, immunofluorescence, and immunohistochemistry with Aperio®-based digital image analysis. Increased collagen deposition and increased number of α-SMA/ACTA2 expressing myofibroblasts were present in the arthrofibrosis group compared to the two non-arthrofibrotic groups. CD163 + macrophages were the most abundant immune cell type in any capsular sample with specific enrichment in the synovial tissue. CD163 + macrophages were significantly decreased in the fibrotic tissue region of arthrofibrosis patients compared to the patients with primary TKA, and significantly increased in adipose tissue region of arthrofibrotic specimens compared to non-arthrofibrotic specimens. Synovial CD117 + mast cells were significantly decreased in arthrofibrotic adipose tissue. Together, these findings inform diagnostic and targeted therapeutic strategies by providing insight into the underlying pathogenetic mechanisms of arthrofibrosis.

Adaptive immune responses in patients requiring revision after total knee arthroplasty

Dissatisfaction occurs in nearly 20% of patients after total knee arthroplasty (TKA); however, there remains only limited understanding of the biologic mechanisms that may contribute to suboptimal postoperative outcomes requiring revision surgery. Expansion of effector T and B cells, could promote an abnormal healing response via local or peripheral immune system mechanisms and contribute to inferior outcomes necessitating revision TKA. In this pilot study, we hypothesized that patients suffering from complications of arthrofibrosis or instability may exhibit differences in adaptive immune function. Patients (n = 31) undergoing revision TKA for an indication of arthrofibrosis or instability were prospectively enrolled. Whole blood and synovial fluid (SF) from the operative knee were collected at time of surgery. Peripheral blood mononuclear cells were isolated and analyzed by flow cytometry. Serum and SF were assessed for immunoglobulin levels by Luminex and antiphospholipid antibodies by enzyme-linked immunoassay. No significant differences were observed in peripheral blood T/B cell populations or serum immunoglobulins levels between groups. SF analysis demonstrated significant differences between the two groups, with higher levels of immunoglobulin G1 (IgG1) (p = 0.0184), IgG3 (p = 0.0084) and antiphosphatidyl serine IgG (p = 0.034) in arthrofibrosis relative to instability patients. Increased levels of both IgG subclasses and antiphospholipid antibodies in the SF suggest that intra-articular T-B cell interactions, potentially triggered by exposure to apoptotic components generated during post-op healing, could be functioning as a source of immune complexes that fuel fibrous tissue growth in arthrofibrotic patients.

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.

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.

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.

Biomechanical, histological, and molecular characterization of a new posttraumatic model of arthrofibrosis in rats

Experimental analyses of posttraumatic knee arthrofibrosis utilize a rabbit model as a gold standard. However, a rodent model of arthrofibrosis offers many advantages including reduced cost and comparison with other models of organ fibrosis. This study aimed to characterize the biomechanical, histological, and molecular features of a novel posttraumatic model of arthrofibrosis in rats. Forty eight rats were divided into two equal groups. An immobilization procedure was performed on the right hind limbs of experimental rats. One group was immobilized for 4 weeks and the other for 8 weeks. Both groups were remobilized for 4 weeks. Limbs were studied biomechanically via assessment of torque versus degree of extension, histologically via whole knee specimen, and molecularly via gene expression of posterior capsular tissues. Significant differences were observed between experimental and control limbs at 4 N-cm of torque in the 4-week (knee extension: 115° ± 8° vs. 169° ± 17°, respectively; p = 0.007) and 8-week immobilization groups (knee extension: 99° ± 12° vs. 174° ± 9°, respectively; p = 0.008). Histologically, in each group experimental limbs demonstrated increased posterior capsular thickness and total area of tissue when compared to control limbs (p < 0.05). Gene expression values evaluated in each group were comparable. This study presents a novel rat model of arthrofibrosis with severe and persistent knee contractures demonstrated biomechanically and histologically. Statement of clinical significance: Arthrofibrosis is a common complication following contemporary total knee arthroplasties. The proposed model is reproducible, cost-effective, and can be employed for translational investigations studying the pathogenesis of arthrofibrosis and efficacy of neoadjuvant pharmacologic agents.

Immune and repair responses in joint tissues and lymph nodes after knee arthroplasty surgery in mice

The importance of a local tissue immune response in healing injured tissues such as skin and lung is well established. Little is known about whether sterile wounds elicit lymph node (LN) responses and inflammatory responses after injury of musculoskeletal tissues that are mechanically loaded during the repair response. We investigated LN and tissue immune responses in a tibial implant model of joint replacement surgery where wounded tissue is subjected to movement and mechanical loading postoperatively. Draining inguinal and iliac LNs expanded postoperatively, including increases in regulatory T cells and activation of a subset of T cells. Thus, tissue injury was actively sensed in secondary lymphoid organs, with the potential to activate adaptive immunity. Joint tissues exhibited three temporally distinct immune response components, including a novel interferon (IFN) response with activation of signal transducer and activator of transcription (STAT) and interferon regulatory factor (IRF) pathways. Fibrovascular tissue formation was not associated with a macrophage type 2 (M2) reparative immune response, but instead with delayed induction of interleukin-1 family (IL-1β, IL-33, IL-36), IL-17, and prostaglandin pathway genes concomitant with transforming growth factor (TGF)-β and growth factor signaling, fibroblast activation, and tissue formation. Tissue remodeling was associated with activity of the HOX antisense intergenic RNA (HOTAIR) pathway. These results provide insights into immune responses and regulation of tissue healing after knee arthroplasty that potentially can be used to develop therapeutic strategies to improve healing, prevent arthrofibrosis, and improve surgical outcomes. © 2021 American Society for Bone and Mineral Research (ASBMR).

Acquired Idiopathic Stiffness After Contemporary Total Knee Arthroplasty: Incidence, Risk Factors, and Results Over 25 Years

BACKGROUND

Acquired idiopathic stiffness (AIS) remains a common failure mode of contemporary total knee arthroplasties (TKAs). The present study investigated the incidence of AIS and manipulation under anesthesia (MUA) at a single institution over time, determined outcomes of MUAs, and identified risk factors associated with AIS and MUA.

METHODS

We identified 9771 patients (12,735 knees) who underwent primary TKAs with cemented, modular metal-backed, posterior-stabilized implants from 2000 to 2016 using our institutional total joint registry. Mean age was 68 years, 57% were female, and mean body mass index was 33 kg/m². Demographic, surgical, and comorbidity data were investigated via univariate Cox proportional hazard models and fit to an adjusted multivariate model to access risk for AIS and MUA. Mean follow-up was 7 years.

RESULTS

During the study period, 456 knees (3.6%) developed AIS and 336 knees (2.6%) underwent MUA. Range of motion (ROM) increased a mean of 34° after the MUA; however, ROM for patients treated with MUA was inferior to patients without AIS at final follow-up (102° vs 116°, P < .0001). Significant risk factors included younger age (HR 2.3, P < .001), increased tourniquet time (HR 1.01, P < .001), general anesthesia (HR 1.3, P = .007), and diabetes (HR 1.5, P = .001).

CONCLUSION

Acquired idiopathic stiffness has continued to have an important adverse impact on the outcomes of a subset of patients undergoing primary TKAs. When utilized, MUA improved mean ROM by 34°, but patients treated with MUA still had decreased ROM compared to patients without AIS. Importantly, we identified several significant risk factors associated with AIS and subsequent MUA.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Identification of novel biomarkers for arthrofibrosis after total knee arthroplasty in animal models and clinical patients

Background

Arthrofibrosis is a debilitating complication after total knee arthroplasty (TKA) which becomes a considerable burden for both patients and clinical practitioners. Our study aimed to identify novel biomarkers and therapeutic targets for drug discovery.

Methods

Potential biomarker genes were identified based on bioinformatic analysis. Twelve male New Zealand white rabbits underwent surgical fixation of unilateral knees to mimics the joint immobilization of the clinical scenario after TKA surgery. Macroscopic assessment, hydroxyproline content determination, and histological analysis of tissue were performed separately after 3-days, 1-week, 2-weeks, and 4-weeks of fixation. We also enrolled 46 arthrofibrosis patients and 92 controls to test the biomarkers. Clinical information such as sex, age, range of motion (ROM), and visual analogue scale (VAS) was collected by experienced surgeons

Findings

Base on bioinformatic analysis, transforming growth factor-beta receptor 1 (TGFBR1) was identified as the potential biomarkers. The level of TGFBR1 was significantly raised in the rabbit synovial tissue after 4-weeks of fixation (p<0.05). TGFBR1 also displayed a highly positive correlation with ROM loss and hydroxyproline contents in the animal model. TGFBR1 showed a significantly higher expression level in arthrofibrosis patients with a receiver operating characteristic (ROC) area under curve (AUC) of 0.838. TGFBR1 also performed positive correlations with VAS baseline (0.83) and VAS after 1 year (0.76) while negatively correlated with ROM baseline (-0.76) in clinical patients.

Interpretation

Our findings provided novel biomarkers for arthrofibrosis diagnosis and uncovered the role of TGFBR1. This may contribute to arthrofibrosis prevention and therapeutic drug discovery.

Are Patients Taking Benzodiazepines at Increased Risk for Complications Following Primary Total Knee Arthroplasty?

BACKGROUND

Benzodiazepines are commonly taken by patients who are undergoing total knee arthroplasty (TKA), but there is a paucity of studies evaluating any associations. Therefore, we hoped to study if patients taking preoperative benzodiazepines would have increased complications following TKA.

METHODS

Using a nationwide database, from 2010 to 2019, we evaluated patients undergoing primary TKA who either did or did not have a preoperative record of benzodiazepine prescription. We performed a multivariable logistic regression analysis, adjusting for multiple variables (age, gender, obesity, and Charlson comorbidity index), to determine the association of preoperative benzodiazepine use and adverse events in a matched cohort. Furthermore, we stratified patients by one vs multiple preoperative benzodiazepine prescription(s). We evaluated 90-day and 2-year rates of revision, resection, femur fracture fixation, manipulation under anesthesia (MUA), and delirium.

RESULTS

Patients filling more than one preoperative benzodiazepine prescription had increased adjusted odds of 90-day (odds ratio [OR] = 1.198, confidence interval [CI] = 1.086-1.320) and 2-year (OR = 1.188, CI = 1.125-1.254) revision; 90-day resection (OR = 1.430, CI = 1.125-1.817); 90-day (OR = 1.639, CI = 1.255-2.141) and 2-year (OR = 1.646, CI = 1.412-1.919) femur fracture fixation; and 2-year delirium (OR = 2.288, CI = 1.564-3.382). Preoperative benzodiazepine users had decreased adjusted odds of 90-day (OR = 0.670, CI = 0.639-0.702) and 2-year (OR = 0.702, CI = 0.671-0.734) MUA.

CONCLUSION

After controlling for multiple variables, benzodiazepine use was associated with increased rates of revision, resection, femur fracture fixation, and delirium. Furthermore, benzodiazepine use was also associated with a decreased rate of MUA. Orthopaedic professionals can counsel patients taking this group of medications about the associated adverse events. Future studies should assess the use of other muscle relaxants in the prevention of knee stiffness and MUA.

The Prognosis of Arthrofibroses: Prevalence, Clinical Shortcomings, and Future Prospects

Fibrosis is the dysregulated biosynthesis of connective tissue that results from persistent infection, high serum cholesterol, surgery, trauma, or prolonged joint immobilization. As a disease that impacts connective tissue, it is prevalent across the body and disrupts normal extracellular and tissue organization. Ultimately, fibrosis impairs the tissue structural, mechanical, or biochemical function. This review describes the clinical landscape of joint fibrosis, that is, arthrofibrosis, including the risk factors and causes, as well as current clinical treatments and their shortcomings. Because treating arthrofibrosis remains an unmet clinical challenge, we present several animal models used for exploration of the physiopathology of arthrofibrosis and summarize their use for testing novel treatments. We then discuss therapeutics for the prevention or treatment of arthrofibrosis that are in preclinical development and in ongoing clinical trials. We conclude with recent findings from molecular biological studies of arthrofibroses that shed insight on future areas of research for improved treatments.

Elevated Expression of Plasminogen Activator Inhibitor (PAI-1/SERPINE1) is Independent from rs1799889 Genotypes in Arthrofibrosis

Arthrofibrosis is characterized by excessive extracellular matrix deposition in patients with total knee arthroplasties (TKAs) and causes undesirable joint stiffness. The pathogenesis of arthrofibrosis remains elusive and currently there are no diagnostic biomarkers for the pathological formation of this connective tissue. Fibrotic soft tissues are known to have elevated levels of plasminogen activator inhibitor-1 (PAI-1) (encoded by SERPINE1), a secreted serine protease inhibitor that moderates extracellular matrix remodeling and tissue homeostasis. The 4G/5G insertion/deletion (rs1799889) is a well-known SERPINE1 polymorphism that directly modulates PAI-1 levels. Homozygous 4G/4G allele carriers typically have higher PAI-1 levels and may predispose patients to soft tissue fibrosis (e.g., liver, lung, and kidney). Here, we examined the genetic contribution of the SERPINE1 rs1799889 polymorphism to musculoskeletal fibrosis in arthrofibrotic (n = 100) and non-arthrofibrotic (n = 100) patients using Sanger Sequencing. Statistical analyses revealed that the allele frequencies of the SERPINE1 rs1799889 polymorphism are similar in arthrofibrotic and non-arthrofibrotic patient cohorts. Because the fibrosis related SERPINE1 rs1799889 polymorphism is independent of arthrofibrosis susceptibility in TKA patients, the possibility arises that fibrosis of joint connective tissues may involve unique genetic determinants distinct from those linked to classical soft tissue fibrosis.

Tanshinone IIA regulates fibroblast proliferation and migration and post-surgery arthrofibrosis through the autophagy-mediated PI3K and AMPK-mTOR signaling pathway

Post-surgery arthrofibrosis is one of the most restrictive factors in the development of intra-articular surgery and has presented tremendous obstacles for most orthopaedic surgeons. Tanshinone IIA (Tan IIA), a key active ingredient of Den-shen, has been used to treat fibrosis-related diseases, such as pulmonary, hepatic and myocardial fibrosis. In the present study, we aimed to investigate the effects of Tan IIA on post-surgery arthrofibrosis in vivo and in vitro. Histological analysis indicated that topical application of Tan IIA (10 mg/mL) could significantly alleviate postsurgery arthrofibrosis in rabbits. Immunohistochemistry results showed that proliferating cell nuclear antigen (PCNA) and tubulin protein expression was inhibited, whereas LC3 was activated in vivo. In vitro, EdU and flow cytometry assays demonstrated that Tan IIA could inhibit fibroblast proliferation by arresting cells in G2 phase. Scratch, Transwell and cytoskeleton protein immunofluorescence assays revealed that fibroblast migration was attenuated. Interestingly, LC3 immunofluorescence staining and transmission electron microscopy indicated that autophagy flux could be induced in fibroblasts by Tan IIA. However, the inhibitory effects of Tan IIA against fibroblast proliferation and migration were partially restored when fibroblast autophagy was suppressed after combined treatment with the autophagy inhibitor 3-methyladenine (3-MA). Finally, the expression of p-mTOR was suppressed in a dose-dependent manner after Tan IIA treatment but partially restored when Tan IIA treatment was combined with 3-MA intervention. The inhibitory effect of Tan IIA against fibroblast proliferation and migration may be related to autophagy induction mediated by the PI3K and AMPK-mTOR signaling pathway.

A Potential Theragnostic Regulatory Axis for Arthrofibrosis Involving Adiponectin (ADIPOQ) Receptor 1 and 2 (ADIPOR1 and ADIPOR2), TGFβ1, and Smooth Muscle α-Actin (ACTA2)

(1) Background: Arthrofibrosis is a common cause of patient debility and dissatisfaction after total knee arthroplasty (TKA). The diversity of molecular pathways involved in arthrofibrosis disease progression suggest that effective treatments for arthrofibrosis may require a multimodal approach to counter the complex cellular mechanisms that direct disease pathogenesis. In this study, we leveraged RNA-seq data to define genes that are suppressed in arthrofibrosis patients and identified adiponectin (ADIPOQ) as a potential candidate. We hypothesized that signaling pathways activated by ADIPOQ and the cognate receptors ADIPOR1 and ADIPOR2 may prevent fibrosis-related events that contribute to arthrofibrosis. (2) Methods: Therefore, ADIPOR1 and ADIPOR2 were analyzed in a TGFβ1 inducible cell model for human myofibroblastogenesis by both loss- and gain-of-function experiments. (3) Results: Treatment with AdipoRon, which is a small molecule agonist of ADIPOR1 and ADIPOR2, decreased expression of collagens (COL1A1, COL3A1, and COL6A1) and the myofibroblast marker smooth muscle α-actin (ACTA2) at both mRNA and protein levels in basal and TGFβ1-induced cells. (4) Conclusions: Thus, ADIPOR1 and ADIPOR2 represent potential drug targets that may attenuate the pathogenesis of arthrofibrosis by suppressing TGFβ-dependent induction of myofibroblasts. These findings also suggest that AdipoRon therapy may reduce the development of arthrofibrosis by mediating anti-fibrotic effects in joint capsular tissues.

Human Fibrosis: Is There Evidence for a Genetic Predisposition in Musculoskeletal Tissues?

BACKGROUND

Pathologic fibrosis is characterized by dysregulation of gene expression with excessive extracellular matrix production. The genetic basis for solid organ fibrosis is well described in the literature. However, there is a paucity of evidence for similar processes in the musculoskeletal (MSK) system. The purpose of this review is to provide an overview of existing evidence of genetic predisposition to pathologic fibrosis in the cardiac, pulmonary, and MSK systems, and to describe common genetic variants associated with these processes.

METHODS

A comprehensive search of several databases from 2000 to 2019 was conducted using relevant keywords in the English language. Genes reported as involved in idiopathic fibrotic processes in the heart, lung, hand, shoulder, and knee were recorded by 2 independent authors.

RESULTS

Among 2373 eligible studies, 52 studies investigated genetic predisposition in terms of variant analysis with the following organ system distribution: 36 pulmonary studies (69%), 15 hand studies (29%), and 1 knee study (2%). Twenty-two percent of gene variants identified were associated with both pulmonary and MSK fibrosis (ie, ADAM, HLA, CARD, EIF, TGF, WNT, and ZNF genes). Genetic variants known to be involved in the MSK tissue development or contractility properties in muscle were identified in the pulmonary fibrosis.

CONCLUSION

Despite shared genetic variations in both the lung and hand, there remains limited information about genetic variants associated with fibrosis in other MSK regions. This finding establishes the necessity of further studies to elucidate the genetic determinants involved in the knee, shoulder, and other joint fibrotic pathways.

LEVEL OF EVIDENCE

Level III.

Quantification of intra-articular fibrosis in patients with stiff knee arthroplasties using metal-reduction MRI

AIMS

Stiffness is a common complication after total knee arthroplasty (TKA). Pathogenesis is not understood, treatment options are limited, and diagnosis is challenging. The aim of this study was to investigate if MRI can be used to visualize intra-articular scarring in patients with stiff, painful knee arthroplasties.

METHODS

Well-functioning primary TKAs (n = 11), failed non-fibrotic TKAs (n = 5), and patients with a clinical diagnosis of fibrosis1 (n = 8) underwent an MRI scan with advanced metal suppression (Slice Encoding for Metal Artefact Correction, SEMAC) with gadolinium contrast. Fibrotic tissue (low intensity on T1 and T2, low-moderate post-contrast enhancement) was quantified (presence and tissue thickness) in six compartments: supra/infrapatella, medial/lateral gutters, and posterior medial/lateral.

RESULTS

Fibrotic tissue was identified in all patients studied. However, tissue was significantly thicker in fibrotic patients (4.4 mm ± 0.2 mm) versus non-fibrotic (2.5 mm ± 0.4 mm) and normal TKAs (1.9 mm ± 0.2 mm, p = < 0.05). Significant (> 4 mm thick) tissue was seen in 26/48 (54%) of compartments examined in the fibrotic group, compared with 17/30 (57%) non-fibrotic, and 10/66 (15%) normal TKAs. Although revision surgery did improve range of movement (ROM) in all fibrotic patients, clinically significant restriction remained post-surgery.

CONCLUSION

Stiff TKAs contain intra-articular fibrotic tissue that is identifiable by MRI. Studies should evaluate whether MRI is useful for surgical planning of debridement, and as a non-invasive measurement tool following interventions for stiffness caused by fibrosis. Revision for stiffness can improve ROM, but outcomes are sub-optimal and new treatments are required. Cite this article: Bone Joint J 2020;102-B(10):1331-1340.