This review briefly summarises some of the definitive studies of articular cartilage by microscopic MRI (µMRI) that were conducted with the highest spatial resolutions. The article has four major sections. The first section introduces the cartilage tissue, MRI and µMRI, and the concept of image contrast in MRI. The second section describes the characteristic profiles of three relaxation times (T₁, T₂ and T_1ρ) and self-diffusion in healthy articular cartilage. The third section discusses several factors that can influence the visualisation of articular cartilage and the detection of cartilage lesion by MRI and µMRI. These factors include image resolution, image analysis strategies, visualisation of the total tissue, topographical variations of the tissue properties, surface fibril ambiguity, deformation of the articular cartilage, and cartilage lesion. The final section justifies the values of multidisciplinary imaging that correlates MRI with other technical modalities, such as optical imaging. Rather than an exhaustive review to capture all activities in the literature, the studies cited in this review are merely illustrative.

Objectives. The purpose of this study was to clarify the appearance of the reparative tissue on the articular surface and to analyse the properties of the reparative tissue after hemicallotasis osteotomy (HCO) using MRI T1ρ and T2 mapping. Methods. Coronal T1ρ and T2 mapping and three-dimensional gradient-echo images were obtained from 20 subjects with medial knee osteoarthritis. We set the regions of interest (ROIs) on the full-thickness cartilage of the medial femoral condyle (MFC) and medial tibial plateau (MTP) of the knee and measured the cartilage thickness (mm) and T1ρ and T2 relaxation times (ms). Statistical analysis of time-dependent changes in the cartilage thickness and the T1ρ and T2 relaxation times was performed using one-way analysis of variance, and Scheffe’s test was employed for post hoc multiple comparison. Results. The cartilage-like repair tissue appeared on the cartilage surface of the medial compartment post-operatively, and the cartilage thickness showed a significant increase between the pre-operative and one-year post-operative time points (MFC; p = 0.003, MTP; p < 0.001). The T1ρ values of the cartilage-like repair tissue showed no difference over time, however, the T2 values showed a significant decrease between the pre-operative and one-year post-operative time points (MFC; p = 0.004, MTP; p = 0.040). Conclusion. This study clarified that the fibrocartilage-like repair tissue appeared on the articular surface of the medial compartment after HCO as evidenced by MRI T1ρ and T2 mapping. Cite this article: H. Nishioka, E. Nakamura, J. Hirose, N. Okamoto, S. Yamabe, H. Mizuta. MRI T1ρ and T2 mapping for the assessment of articular cartilage changes in patients with medial knee osteoarthritis after hemicallotasis osteotomy. Bone Joint Res 2016;5:294–300. DOI: 10.1302/2046-3758.57.BJR-2016-0057.R1

Introduction. Vertebral compression fractures are the most common type of osteoporotic fracture. Though 89% of clinical fractures occur anteriorly, it is challenging to replicate these ex vivo with the underlying intervertebral discs (IVDs) present. Furthermore, the role of disc degeneration in this mechanism is poorly understood. Understanding how disc morphology alters vertebral strain distributions may lead to the utilisation of IVD metrics in fracture prediction, or inform surgical decision-making regarding instrumentation type and placement. Aim. To determine the effect of disc degeneration on the vertebral trabecular bone strain distributions in axial compression and flexion loading. Methods. Eight cadaveric thoracolumbar segments (T11-L3) were prepared (N=4 axial compression, N=4 flexion). µCT-based digital volume correlation was used to quantify trabecular strains. A bespoke loading device fixed specimens at the resultant displacement when loaded to 50N and 800N. Flexion was achieved by adding 6° wedges. Disc degeneration was quantified with Pfirrmann grading and T2 relaxation times. Results. Anterior axial strains were 80.9±39% higher than the posterior region in flexion (p<0.01), the ratio of which was correlated with T2 relaxation time (R. 2. =0.80, p<0.05). In flexion, the central-to-peripheral axial strain ratio in the endplate region was significantly higher when the underlying IVDs were non-degenerated relative to degenerated (+38.1±12%, p<0.05). No significant differences were observed in axial compression. Conclusion. Disc degeneration is a stronger determinant of the trabecular strain distribution when flexion is applied. Load transfer through non-degenerate IVDs under flexion appears to be more centralised, suggesting that disc degeneration predisposes flexion-type compression fractures by shifting high strains anteriorly. Conflicts of interest. The authors declare none. Sources of funding. This work was funded by the Engineering & Physical Sciences Research Council (EP/V029452/1), and Back-to-Back

Introduction. Successful joint preservation surgery requires the ability to accurately assess the health of the articular cartilage pre-operatively. Traditional radiological methods allow morphological assessment of the cartilage and therefore only identify those with established degeneration. Biophysical properties of cartilage are now being used to identify these changes occurring earlier in the disease processes. Prior literature states that healthy cartilage has a transverse relaxation time of between 15–60 ms (16). Our study aims to establish the correlation and accuracy of MRI with T2 cartilage mapping with observed intra-operative chondral defects. Methods. We routinely request MRI with T2 mapping on all patients with suspected or confirmed femoroacetabular impingement (FAI). A review was performed on all patients who underwent both pre-operative imaging and subsequent hip arthroscopy for FAI over a 24-month period. Using linear regression we correlated intra-operatively observed chondral defects of the femoral head and acetabulum (Outerbridge classification scores) with the pre-operative transverse relaxation times. Statistical analysis of 66 chondral points was undertaken. Results. Results show that there is a significant association between an increase in transverse relaxation time and higher acetabular Outerbridge classification (p = 0.0141). Discussion. This study has identified that MRI with T2 cartilage mapping is an accurate predictor of acetabular cartilage health. Our findings suggest that 3T MRI with T2 cartilage mapping is a useful tool in joint preservation surgery and provides accurate information allowing hip arthroscopists to identify patients who may benefit most from conservative operative intervention

Summary. The quantification of T1Rho relaxation times is not related with internal loading. Improvements in modeling and imaging techniques might lead to better understanding of the pathomechanics of the knee. Introduction. The onset and progression of knee osteoarthritis has been associated with an increased external knee adduction moment (EKAM). However, this external measure has no direct relationship with internal loading of the knee. For a better understanding of the pathomechanics of the knee musculoskeletal models could be used to relate external and internal knee loading. Consequently, high internal loading might cause cartilage degeneration in patients with OA. T1RhoMRI can detect changes in proteoglycan content and is therefore a non-invasive measure of cartilage degeneration in knee OA. The purpose of this study was to relate internal loading of the knee simulated by musculoskeletal models with cartilage health using T1rhoMRI. Patients & Methods. Preliminary results showed data of seven women (50–65yrs), four healthy and three OA. Subjects underwent 3D gait analysis (VICON Nexus) at comfortable walking speed, EKAM was calculated. Simulations of multi-body musculoskeletal models were driven based on the motion capture data, in order to calculate internal medial-lateral knee forces (MLforce). Besides a T1RhoMRI scan of the knee (Phillips 3T) provided cartilage health of the midsection of the medial condyle according to Pedersen et al, 2011 [4]. Differences between healthy and OA were tested with a one sided T-test, correlations between EKAM and MLforce were calculated. Results. Anthropometrics and walking speed showed no significantly different between OA patients and healthy controls. OA patients had significant larger EKAM and MLforce (p<0.05). T1Rho values were not significantly different between the groups. EKAM was positively correlated with MLforce (R. 2. =0.91, p<0.05) in healthy subjects, no association was found in knee OA patients (R. 2. < 0.01). Discussion / Conclusion. The current study demonstrates that external loading of the knee does not predict internal loading in knee OA patients. We did not find a significant effect of knee OA on cartilage quality assessed by T1Rho MRI. However a non-significant increase was visible at the posterior region of the femoral condyle in OA patients. This elevated T1Rho relaxation is in line with expectations and could be related to an increased cartilage degeneration

Introduction. Osteochondral lesions of the talus are common injuries following acute and chronic ankle sprains and fractures, the treatment strategies of which include both reparative and restorative techniques. Recently, restorative techniques (i.e., autologous osteochondral transplantation) have been become increasingly popular as a primary treatment strategy, in part due to the potential advantages of replacing “like with like” in terms of hyaline cartilage at the site of cartilage repair. The current study examines the functional results of autologous osteochondral transplantation of the talus in 72 patients. Methods. Between 2005 and 2009, 72 patients underwent autologous osteochondral transplantation under the care of the care of the senior author. The mean patient age at the time of surgery was 34.19 years (range, 16–85 years). The mean follow-up time was 28.02 months (range, 12–64 months). Patient-reported outcome measures were taken pre-operatively and at final-follow-up using the Foot and Ankle Outcome Score and Short-Form 12 general health questionnaire. Quantitative T2-mapping MRI was also performed on select patients at 1-year post-operatively. Results. The mean FAOS scores improved from 52.67 points pre-operatively to 86.19 points post-operatively (range, 71–100 points). The mean SF-12 scores also improved from 59.40 points pre-operatively to 88.63 points post-operatively (range, 52–98 points). Three patients reported donor site knee pain after surgery. Quantitative T2-mapping MRI demonstrated relaxation times that were not significantly different to those of native cartilage in both the superficial and deep halves of the repair tissue. Discussion and Conclusion. Autologous osteochondral transplantation is a reproducible and primary treatment strategy for large osteochondral lesions of the talus and provides repair tissue that is biochemically similar to that of native cartilage on quantitative T2-mapping MRI. This may ultimately allow the ankle joint to function adequately over time

Purpose: Quantitative MRI is currently being tested as an early and non-invasive diagnostic tool of disc problems prior to the appearance of symptoms. The aim of the present study was to determine the effects of cyclic loading and enzymatic digestion on quantitative MRI, biochemical composition, and mechanical properties of intervertebral disc tissue. Methods: Bovine tail segments consisting of three discs were subjected to 16h of cyclic compression loading (50N–300N–50N at 1Hz) or left unloaded for 16h while in saline solution at 37°C. Prior to loading, the nucleus pulposus were injected with either a trypsin or buffer solution. MR examinations were carried out in a 1.5T Siemens` Avanto system to measure T1 and T2 relaxation times, magnetization transfer ratio (MTR), and trace of the apparent diffusion coefficient (TrD). The nucleus pulposus and annulus fibrosus were dissected and analyzed for contents of water, glycosaminoglycan, total collagen, and denatured collagen. Cylindrical nucleus pulposus and annulus fibrosus tissue plugs were harvested, prepared, and tested under confined compression to measure compressive modulus (HA) and hydraulic permeability (k). ANOVA and linear regression analyses were performed (p< 0.05). Results: Loading decreased the T1, T2, and TrD of NP while it increased MTR. Only water content in the nucleus pulposus was significantly influenced by loading. T1, water content, and k of the annulus fibrosus tissue were significantly reduced with loading.|Enzymatic treatment of the nucleus pulposus had no effect on its MR properties, but increased the percent of denatured collagen and thus decreased HA. None of the biochemical, mechanical, and MR parameters of the annulus fibrosus changed with trypsin treatment. Conclusions: Dynamic loading of the disc segments for 16h decreased the permeability of both disc tissues. This was consistent with the measured drop in tissue hydration and was observed as a decrease in T1. Targeted trypsin digestion of the nucleus pulposus was confirmed with no detectable changes in the biochemical, biomechanical, or MR properties of the annulus fibrosus. Future studies will address additional quantitative MR parameters such as T1-rho, a higher strength magnet, and different enzymatic treatments. Funding: Other Education Grant Funding Parties: Canadian Institutes of Health Research, McGill William Dawson Scholar Award, and Whitaker Foundation