Effects of Interleukin-1ß Inhibition on Incident Hip and Knee Replacement : Exploratory Analyses From a Randomized, Double-Blind, Placebo-Controlled Trial.

BACKGROUND: Osteoarthritis is a common inflammatory disorder with no disease-modifying therapies. Whether inhibition of interleukin-1ß (IL-1ß) can reduce the consequences of large joint osteoarthritis is unclear. OBJECTIVE: To determine whether IL-1ß inhibition with canakinumab reduces incident total hip or knee replacement (THR/TKR). DESIGN: Exploratory analysis of a randomized trial. (ClinicalTrials.gov: NCT01327846). SETTING: 1091 clinical sites in 39 countries. PARTICIPANTS: 10 061 CANTOS (Canakinumab Anti-inflammatory Thrombosis Outcomes Study) participants. INTERVENTION: Random allocation to placebo or canakinumab (50, 150, or 300 mg) subcutaneously once every 3 months. MEASUREMENTS: The primary and secondary outcomes were time to first incident THR/TKR and time to first occurrence of an osteoarthritis-related adverse event (AE). Data were obtained through blinded ascertainment of trial clinical and safety databases. RESULTS: Median follow-up was 3.7 years. For the individual canakinumab dose groups, compared with placebo, hazard ratios (HRs) for incident THR/TKR during follow-up were 0.60 (95% CI, 0.38 to 0.95) for the 50-mg group, 0.53 (CI, 0.33 to 0.84) for the 150-mg group, and 0.60 (CI, 0.38 to 0.93) for the 300-mg group. Thus, in the pooled canakinumab groups, compared with the placebo group, incidence rates for THR/TKR were 0.31 and 0.54 events per 100 person-years (HR, 0.58 [CI, 0.42 to 0.80]; P = 0.001), respectively. The HR for the secondary end point of osteoarthritis-related AEs was 0.73 (CI, 0.61 to 0.87). Similar findings were observed in analyses restricted to participants with a history of osteoarthritis. LIMITATION: Because the parent trial was not designed to examine the efficacy of IL-1ß inhibitors in osteoarthritis, information on structural joint outcomes was not collected. CONCLUSION: Findings from this exploratory analysis of a randomized controlled trial support further investigation of IL-1ß inhibition for treatment of large joint osteoarthritis. PRIMARY FUNDING SOURCE: Novartis Pharmaceuticals.

Orthotopic Bone Formation by Streamlined Engineering and Devitalization of Human Hypertrophic Cartilage.

Most bones of the human body form and heal through endochondral ossification, whereby hypertrophic cartilage (HyC) is formed and subsequently remodeled into bone. We previously demonstrated that HyC can be engineered from human mesenchymal stromal cells (hMSC), and subsequently devitalized by apoptosis induction. The resulting extracellular matrix (ECM) tissue retained osteoinductive properties, leading to ectopic bone formation. In this study, we aimed at engineering and devitalizing upscaled quantities of HyC ECM within a perfusion bioreactor, followed by in vivo assessment in an orthotopic bone repair model. We hypothesized that the devitalized HyC ECM would outperform a clinical product currently used for bone reconstructive surgery. Human MSC were genetically engineered with a gene cassette enabling apoptosis induction upon addition of an adjuvant. Engineered hMSC were seeded, differentiated, and devitalized within a perfusion bioreactor. The resulting HyC ECM was subsequently implanted in a 10-mm rabbit calvarial defect model, with processed human bone (Maxgraft®) as control. Human MSC cultured in the perfusion bioreactor generated a homogenous HyC ECM and were efficiently induced towards apoptosis. Following six weeks of in vivo implantation, microcomputed tomography and histological analyses of the defects revealed an increased bone formation in the defects filled with HyC ECM as compared to Maxgraft®. This work demonstrates the suitability of engineered devitalized HyC ECM as a bone substitute material, with a performance superior to a state-of-the-art commercial graft. Streamlined generation of the devitalized tissue transplant within a perfusion bioreactor is relevant towards standardized and automated manufacturing of a clinical product.

Osteoinductivity of engineered cartilaginous templates devitalized by inducible apoptosis.

The role of cell-free extracellular matrix (ECM) in triggering tissue and organ regeneration has gained increased recognition, yet current approaches are predominantly based on the use of ECM from fully developed native tissues at nonhomologous sites. We describe a strategy to generate customized ECM, designed to activate endogenous regenerative programs by recapitulating tissue-specific developmental processes. The paradigm was exemplified in the context of the skeletal system by testing the osteoinductive capacity of engineered and devitalized hypertrophic cartilage, which is the primordial template for the development of most bones. ECM was engineered by inducing chondrogenesis of human mesenchymal stromal cells and devitalized by the implementation of a death-inducible genetic device, leading to cell apoptosis on activation and matrix protein preservation. The resulting hypertrophic cartilage ECM, tested in a stringent ectopic implantation model, efficiently remodeled to form de novo bone tissue of host origin, including mature vasculature and a hematopoietic compartment. Importantly, cartilage ECM could not generate frank bone tissue if devitalized by standard "freeze & thaw" (F&T) cycles, associated with a significant loss of glycosaminoglycans, mineral content, and ECM-bound cytokines critically involved in inflammatory, vascularization, and remodeling processes. These results support the utility of engineered ECM-based devices as off-the-shelf regenerative niches capable of recruiting and instructing resident cells toward the formation of a specific tissue.

Thoracic Outlet Syndrome in the Overhead Athlete: A Report of 2 Cases of Subclavius Posticus Muscle.

Subclavius posticus muscle is a supernumerary anatomical variation of the subclavius muscle. The aim of this study was to show the possible contribution of the posticus muscle in the development of unilateral thoracic outlet syndrome (TOS) in overhead athletes, presenting hypertrophy of the dominant arm due to their sport activity. Reported here are 2 young overhead athletes complaining pain, paresthesia, weakness in the dominant upper limb, although presenting none of the main shoulder and neurological disorders. After developing subclavian vein thrombosis, TOS was suspected and finally diagnosed by dynamic magnetic resonance angiography, which also showed bilateral subclavius posticus muscle in both patients. Despite bilateral subclavius posticus, TOS was only evident in the dominant limb in which the association of hypertrophy of lateral cervical muscles, resulting from the overhead sport activity, to the subclavius posticus likely led to a significant reduction of the upper thoracic outlet space.

One-step surgery with multipotent stem cells and Hyaluronan-based scaffold for the treatment of full-thickness chondral defects of the knee in patients older than 45 years.

PURPOSE: The aim of this study is to prospectively evaluate the medium-term effectiveness and regenerative capability of autologous adult mesenchymal stem cells, harvested as bone marrow aspirate concentrate (BMAC), along with a hyaluronan-based scaffold (Hyalofast) in the treatment of ICRS grade 4 chondral lesions of the knee joint, in patients older than 45 years. METHODS: A study group of 20 patients with an age >45 years (mean 50.0 ± 4.1 years) was compared to a control group of 20 patients with an age <45 years (mean 36.6 ± 5.0). Patients were prospectively evaluated for 4 years. All patients were evaluated with MRI, KOOS, IKDC, VAS and Tegner scores preoperatively and at two-year and final follow-up. RESULTS: At final follow-up, all scores significantly improved (P < 0.001) as follows: all KOOS score categories; Tegner 2 (range 0-4) to 6 (range 4-8) and 3 (range 0-6) to 6 (range 3-10); IKDC subjective (39.2 ± 16.5 to 82.2 ± 8.9) and (40.8 ± 13.9 to 79.4 ± 14.6), in the study and control group respectively. In addition, we show that results are affected by lesion size and number but not from concomitant surgical procedures. MRI showed complete filling in 80 % of patients in the study group and 71 % of patients in the control group. Histological analysis conducted in three patients from the study and two patients from the control group revealed good tissue repair with a variable amount of hyaline-like tissue. CONCLUSION: Treatment of cartilage lesions with BMAC and Hyalofast is a viable and effective option that is mainly affected by lesion size and number and not by age. In particular, it allows to address the >45 years population with functional outcomes that are comparable to younger patients at final follow-up. LEVEL OF EVIDENCE: Prospective cohort study, Level II.

Engineering of a functional bone organ through endochondral ossification.

Embryonic development, lengthening, and repair of most bones proceed by endochondral ossification, namely through formation of a cartilage intermediate. It was previously demonstrated that adult human bone marrow-derived mesenchymal stem/stromal cells (hMSCs) can execute an endochondral program and ectopically generate mature bone. Here we hypothesized that hMSCs pushed through endochondral ossification can engineer a scaled-up ossicle with features of a "bone organ," including physiologically remodeled bone, mature vasculature, and a fully functional hematopoietic compartment. Engineered hypertrophic cartilage required IL-1ß to be efficiently remodeled into bone and bone marrow upon subcutaneous implantation. This model allowed distinguishing, by analogy with bone development and repair, an outer, cortical-like perichondral bone, generated mainly by host cells and laid over a premineralized area, and an inner, trabecular-like, endochondral bone, generated mainly by the human cells and formed over the cartilaginous template. Hypertrophic cartilage remodeling was paralleled by ingrowth of blood vessels, displaying sinusoid-like structures and stabilized by pericytic cells. Marrow cavities of the ossicles contained phenotypically defined hematopoietic stem cells and progenitor cells at similar frequencies as native bones, and marrow from ossicles reconstituted multilineage long-term hematopoiesis in lethally irradiated mice. This study, by invoking a "developmental engineering" paradigm, reports the generation by appropriately instructed hMSC of an ectopic "bone organ" with a size, structure, and functionality comparable to native bones. The work thus provides a model useful for fundamental and translational studies of bone morphogenesis and regeneration, as well as for the controlled manipulation of hematopoietic stem cell niches in physiology and pathology.

Unlocking the full potential of rare disease drug development: exploring the not-for-profit sector's contributions to drug development and access.

This commentary provides a comprehensive overview of the challenges and opportunities in the field of drug development for rare diseases and especially of gene therapy products for ultra-rare diseases. It discusses the limited market size, reimbursement and scientific complexities that deter pharmaceutical investment in this field. Highlighting the pivotal role of charitable organizations like Fondazione Telethon, it showcases their efforts in funding research and ensuring access to innovative therapies. This commentary also addresses the challenges in therapy distribution, particularly regarding sustainability and global access. It outlines Fondazione Telethon's operational model to try to address these challenges. Finally, it appeals to governments and regulatory bodies to implement policies and incentives aimed at further fostering innovation and accessibility in rare disease drug development and access.

Meniscus repair and regeneration: review on current methods and research potential.

Meniscus regeneration is an unsolved clinical challenge. Despite the wide acceptance of the degenerative consequences of meniscectomy, no surgical procedure has succeeded to date in regenerating a functional and long-lasting meniscal fibrocartilage. Research proposed a number of experimental approaches encompassing all the typical strategies of regenerative medicine: cell-free scaffolds, gene therapy, intra-articular delivery of progenitor cells, biological glues for enhanced bonding of reparable tears, partial and total tissue engineered meniscus replacement. None of these approaches has been completely successful and can be considered suitable for all patients, as meniscal tears require specific and patient-related treatments depending on the size and type of lesion. Recent advances in cell biology, biomaterial science and bioengineering (e.g., bioreactors) have now the potential to drive meniscus regeneration into a series of clinically relevant strategies. In this tutorial paper, the clinical need for meniscus regeneration strategies will be explained, and past and current experimental studies on meniscus regeneration will be reported.

Recapitulation of endochondral bone formation using human adult mesenchymal stem cells as a paradigm for developmental engineering.

Mesenchymal stem/stromal cells (MSC) are typically used to generate bone tissue by a process resembling intramembranous ossification, i.e., by direct osteoblastic differentiation. However, most bones develop by endochondral ossification, i.e., via remodeling of hypertrophic cartilaginous templates. To date, endochondral bone formation has not been reproduced using human, clinically compliant cell sources. Here, we aimed at engineering tissues from bone marrow-derived, adult human MSC with an intrinsic capacity to undergo endochondral ossification. By analogy to embryonic limb development, we hypothesized that successful execution of the endochondral program depends on the initial formation of hypertrophic cartilaginous templates. Human MSC, subcutaneously implanted into nude mice at various stages of chondrogenic differentiation, formed bone trabeculae only when they had developed in vitro hypertrophic tissue structures. Advanced maturation in vitro resulted in accelerated formation of larger bony tissues. The underlying morphogenetic process was structurally and molecularly similar to the temporal and spatial progression of limb bone development in embryos. In particular, Indian hedgehog signaling was activated at early stages and required for the in vitro formation of hypertrophic cartilage. Subsequent development of a bony collar in vivo was followed by vascularization, osteoclastic resorption of the cartilage template, and appearance of hematopoietic foci. This study reveals the capacity of human MSC to generate bone tissue via an endochondral program and provides a valid model to study mechanisms governing bone development. Most importantly, this process could generate advanced grafts for bone regeneration by invoking a "developmental engineering" paradigm.

Interleukin-1ß modulates endochondral ossification by human adult bone marrow stromal cells.

Inflammatory cytokines present in the milieu of the fracture site are important modulators of bone healing. Here we investigated the effects of interleukin-1ß (IL-1ß) on the main events of endochondral bone formation by human bone marrow mesenchymal stromal cells (BM-MSC), namely cell proliferation, differentiation and maturation/remodelling of the resulting hypertrophic cartilage. Low doses of IL-1ß (50 pg/mL) enhanced colony-forming units-fibroblastic (CFU-f) and -osteoblastic (CFU-o) number (up to 1.5-fold) and size (1.2-fold) in the absence of further supplements and glycosaminoglycan accumulation (1.4-fold) upon BM-MSC chondrogenic induction. In osteogenically cultured BM-MSC, IL-1ß enhanced calcium deposition (62.2-fold) and BMP-2 mRNA expression by differential activation of NF-κB and ERK signalling. IL-1ß-treatment of BM-MSC generated cartilage resulted in higher production of MMP-13 (14.0-fold) in vitro, mirrored by an increased accumulation of the cryptic cleaved fragment of aggrecan, and more efficient cartilage remodelling/resorption after 5 weeks in vivo (i.e., more TRAP positive cells and bone marrow, less cartilaginous areas), resulting in the formation of mature bone and bone marrow after 12 weeks. In conclusion, IL-1ß finely modulates early and late events of the endochondral bone formation by BM-MSC. Controlling the inflammatory environment could enhance the success of therapeutic approaches for the treatment of fractures by resident MSC and as well as improve the engineering of implantable tissues.

An Automatic Foot and Shank IMU Synchronization Algorithm: Proof-of-concept.

When using wearable sensors for measurement and analysis of human performance, it is often necessary to integrate and synchronise data from separate sensor systems. This paper describes a synchronization technique between IMUs attached to the shanks and insoles attached at the feet and aims to solve the need to compute the ankle joint angle, which relies on synchronized sensor data. This will additionally enable concurrent analysis using gait kinematic and kinetic features. A proof-of-concept of the algorithm, which relies on cross-correlation of gyroscope sensor data from the shank and foot, to align the sensor systems is demonstrated. The algorithm output is validated against those signals synchronized using manually annotated heel-strike and toe-off ground-truth signal landmarks, identified in both the shank and feet signals using previously published definitions. Results demonstrate that the developed algorithm is capable of synchronizing both sensor systems, based on IMU data from both healthy participants and participants suffering from knee osteoarthritis, with a mean lag time bias of 25.56ms when compared to the ground truth. A proof-of-concept of technique to synchronise IMUs attached to the shanks and insoles attached at the feet is demonstrated and offers an alternative approach to sensor system synchronisation.

Test-retest reliability of wireless inertial-sensor derived measurements of knee joint kinematics.

Advances in sensor technology have provided an opportunity to measure gait characteristics using body-worn inertial measurement units (IMUs). Whilst research investigating the validity of IMUs in reporting gait characteristics is extensive, research investigating the reliability of IMUs is limited. This study aimed to investigate the inter-session reliability of wireless IMU derived measures of gait (i.e., knee angle, range of motion) taking multiple test administrators into account. Fifteen healthy volunteers (43 ± 15 years) completed two visits. Within each visit, participants were required to perform two sets of 6 gait trials (6-metre walk tests). IMUs were placed on the participant in 7 locations on the lower limbs and waist. A different test administrator (n = 3) applied the IMUs at each set. At visit 2, this procedure was repeated with the same test administrators as visit 1. Kinematic measures of maximum angle (Knee_Max), minimum angle (Knee_Min), and range of motion (RoM) are reported for the left and right knee. The intraclass correlation coefficients (ICC), standard error of measurement (SEM) and minimum detectable change (MDC) are reported to determine IMU reliability. The results confirmed moderate to good inter-session reliability across all features (0.73-0.87). SEM values ranged from 1.21-3.32° and MDC values ranged from 3.37 - 9.21°. Therefore, IMUs appear to be a reliable method to determine inter-session gait characteristics across multiple test administrators.

Angiopoietin-like 3-derivative LNA043 for cartilage regeneration in osteoarthritis: a randomized phase 1 trial.

Osteoarthritis (OA) is a common, debilitating, chronic disease with no disease-modifying drug approved to date. We discovered LNA043-a derivative of angiopoietin-like 3 (ANGPTL3)-as a potent chondrogenesis inducer using a phenotypic screen with human mesenchymal stem cells. We show that LNA043 promotes chondrogenesis and cartilage matrix synthesis in vitro and regenerates hyaline articular cartilage in preclinical OA and cartilage injury models in vivo. LNA043 exerts at least part of these effects through binding to the fibronectin receptor, integrin α5ß1 on mesenchymal stem cells and chondrocytes. In a first-in-human (phase 1), randomized, double-blinded, placebo-controlled, single ascending dose, single-center trial ( NCT02491281 ; sponsored by Novartis Pharmaceuticals), 28 patients with knee OA were injected intra-articularly with LNA043 or placebo (3:1 ratio) either 2 h, 7 d or 21 d before total knee replacement. LNA043 met its primary safety endpoint and showed short serum pharmacokinetics, cartilage penetration and a lack of immunogenicity (secondary endpoints). Post-hoc transcriptomics profiling of cartilage revealed that a single LNA043 injection reverses the OA transcriptome signature over at least 21 d, inducing the expression of hyaline cartilage matrix components and anabolic signaling pathways, while suppressing mediators of OA progression. LNA043 is a novel disease-modifying OA drug candidate that is currently in a phase 2b trial ( NCT04864392 ) in patients with knee OA.

Posterior spinal instrumentation: biomechanical study on the role of rods on hardware response to axial load.

Posterior spinal instrumentation is frequently used for the treatment of spine disorders. Importantly, different requirements have to be considered for the optimal use of these systems in various clinical scenarios. In this work, we focused on the role of rods diameter on hardware's stiffness. For this purpose, we established an in vitro model and compared the response to axial load of a posterior stabilization system, characterized by rods of different diameter (4, 5, 6 mm), with that of Dynesys®. Intuitively, the higher the stiffness of the hardware, the lower the load is transferred to the disc. However, the 4 hardware tested showed a different trend in the response to the load regimens: when increasing the load, more flexible systems display a progressive reduction in the percentage of load which is transferred to the disc while more rigid system display the opposite trend. Considering that the load which is transferred, and not by-passed by the hardware, influences the healing of a fracture; the integration of a bone graft or a cage; the fusion process, these data have a relevant impact on clinical practice and highlight features that have to be considered in the choice for the optimal posterior spinal instrumentation.

Surgical treatment of thoracic outlet syndrome in young adults: single centre experience with minimum three-year follow-up.

Thoracic outlet syndrome is an often misdiagnosed syndrome which consists of a neurovascular compression at the upper thoracic outlet. The clinical presentation can be variable, ranging from mild symptoms to venous thrombosis and muscle atrophy. Many aetiologies, both congenital and acquired, related either to bony or soft tissue anomalies, have been associated with this syndrome. As a consequence, the diagnosis is often challenging and sometimes it can be obtained only with surgical exploration. Additionally, no specific clinical test is considered diagnostic of thoracic outlet syndrome. However, the recent advances in imaging techniques together with a careful clinical evaluation give the surgeon the chance to recognize the constricting anatomy before surgery in many cases. No standard surgical procedure has been identified; however, in literature the largest series have been treated with transaxillary first rib resection. Here we report our experience in the surgical treatment of this syndrome with a minimum follow-up of three years. Our approach consists of performing a supraclavicular decompression without routine first rib resection. This allows for identifying and removing the constricting anatomy in most cases, with satisfactory results in 96.9% of patients and a low complication rate.

Effect of in vitro culture on a chondrocyte-fibrin glue hydrogel for cartilage repair.

Research in tissue engineering has been focused on articular cartilage repair for more than a decade. Some pioneristic studies involved the use of hydrogels such as alginate and fibrin glue which still possess valuable potential for cartilage regeneration. One of the main issues in cartilage tissue engineering is represented by the ideal maturation of the construct, before in vivo implantation, in order to optimize matrix quality and integration. The present study was focused on the effect of in vitro culture on a fibrin glue hydrogel embedding swine chondrocytes. We performed an evaluation of the immunohistochemical and biochemical composition and of the biomechanical properties of the construct after 1 and 5 weeks of culture. We noticed that chondrocytes survived in the fibrin glue gel and enhanced their synthetic activity. In fact, DNA content remained stable, while all indices of cartilage matrix production increased (GAGs content, immunohistochemistry for collagen II and safranin-o staining). On the other hand, the biomechanical properties remained steady, indicating a gradual substitution of the hydrogel scaffold by cartilaginous matrix. This demonstrates that an optimal preculture could provide the surgeon with a better engineered cartilage for implantation. However, whether this more mature tissue will result in a more efficient regeneration of the articular surface still has to be evaluated in future investigations.

Pseudoaneurysm overlying an osteochondroma: a noteworthy complication.

Pseuodaneurysms are an extremely rare complication of osteochondromas. We describe a case of traumatic pseudoaneurysm of the brachial artery presenting as a soft tissue mass in a patient who was treated for an osteochondroma 3 years earlier. This case demonstrates that radiographic follow-up of large osteochondromas is mandatory and that, in patients with soft tissue masses and a history of osteochondroma, pseudoaneurysms should be included in the differential diagnosis.

VEGF Over-Expression by Engineered BMSC Accelerates Functional Perfusion, Improving Tissue Density and In-Growth in Clinical-Size Osteogenic Grafts.

The first choice for reconstruction of clinical-size bone defects consists of autologous bone flaps, which often lack the required mechanical strength and cause significant donor-site morbidity. We have previously developed biological substitutes in a rabbit model by combining bone tissue engineering and flap pre-fabrication. However, spontaneous vascularization was insufficient to ensure progenitor survival in the core of the constructs. Here, we hypothesized that increased angiogenic stimulation within constructs by exogenous VEGF can significantly accelerate early vascularization and tissue in-growth. Bone marrow stromal cells from NZW rabbits (rBMSC) were transduced with a retroviral vector to express rabbit VEGF linked to a truncated version of rabbit CD4 as a cell-surface marker. Autologous cells were seeded in clinical-size 5.5 cm3 HA scaffolds wrapped in a panniculus carnosus flap to provide an ample vascular supply, and implanted ectopically. Constructs seeded with VEGF-expressing rBMSC showed significantly increased progenitor survivival, depth of tissue ingrowth and amount of mineralized tissue. Contrast-enhanced MRI after 1 week in vivo showed significantly improved tissue perfusion in the inner layer of the grafts compared to controls. Interestingly, grafts containing VEGF-expressing rBMSC displayed a hierarchically organized functional vascular tree, composed of dense capillary networks in the inner layers connected to large-caliber feeding vessels entering the constructs at the periphery. These data constitute proof of principle that providing sustained VEGF signaling, independently of cells experiencing hypoxia, is effective to drive rapid vascularization and increase early perfusion in clinical-size osteogenic grafts, leading to improved tissue formation deeper in the constructs.

Assessment of Low-Grade Focal Cartilage Lesions in the Knee With Sodium MRI at 7 T: Reproducibility and Short-Term, 6-Month Follow-up Data.

OBJECTIVES: Several articles have investigated potential of sodium (Na) magnetic resonance imaging (MRI) for the in vivo evaluation of cartilage health, but so far no study tested its feasibility for the evaluation of focal cartilage lesions of grade 1 or 2 as defined by the International Cartilage Repair Society. The aims of this study were to evaluate the ability of Na-MRI to differentiate between early focal lesions and normal-appearing cartilage, to evaluate within-subject reproducibility of Na-MRI, and to monitor longitudinal changes in participants with low-grade, focal chondral lesions. MATERIALS AND METHODS: Thirteen participants (mean age, 50.1 ± 10.9 years; 7 women, 6 men) with low-grade, focal cartilage lesions in the weight-bearing region of femoral cartilage were included in this prospective cohort study. Participants were assessed at baseline, 1 week, 3 months, and 6 months using morphological MRI at 3 T and 7 T, compositional Na-MRI at 7 T, and the Knee Injury and Osteoarthritis Outcome Score (KOOS) questionnaire. Na signal intensities corrected for coil sensitivity and partial volume effect (Na-cSI) were calculated in the lesion, and in weight-bearing and non-weight-bearing regions of healthy femoral cartilage. Coefficients of variation, repeated measures analysis of covariance models, and Pearson correlation coefficients were calculated to evaluate within-subject reproducibility as well as cross-sectional and longitudinal changes in Na-cSI values. RESULTS: The mean coefficients of variation of Na-cSI values between the baseline and 1-week follow-up were 5.1% or less in all cartilage regions. Significantly lower Na-cSI values were observed in lesion than in weight-bearing and non-weight-bearing regions at all time points (all P values ≤ 0.002). Although a significant decrease from baseline Na-cSI values in lesion was found at 3-month visit (P = 0.015), no substantial change was observed at 6 months. KOOS scores have improved in all subscales at 3 months and 6 months visit, with a significant increase observed only in the quality of life subscale (P = 0.004). CONCLUSIONS: In vivo Na-MRI is a robust and reproducible method that allows to differentiate between low-grade, focal cartilage lesions and normal-appearing articular cartilage, which supports the concept that compositional cartilage changes can be found early, before the development of advanced morphological changes visible at clinical 3-T MRI.