Whole knee joint mapping using a phase modulated UTE adiabatic T1ρ (PM-UTE-AdiabT1ρ ) sequence.

PURPOSE: To develop a 3D phase modulated UTE adiabatic T1ρ (PM-UTE-AdiabT1ρ ) sequence for whole knee joint mapping on a clinical 3 T scanner. METHODS: This new sequence includes six major features: (1) a magnetization reset module, (2) a train of adiabatic full passage pulses for spin locking, (3) a phase modulation scheme (i.e., RF cycling pair), (4) a fat saturation module, (5) a variable flip angle scheme, and (6) a 3D UTE Cones sequence for data acquisition. A simple exponential fitting was used for T1ρ quantification. Phantom studies were performed to investigate PM-UTE-AdiabT1ρ 's sensitivity to compositional changes and reproducibility as well as its correlation with continuous wave-T1ρ measurement. The PM-UTE-AdiabT1ρ technique was then applied to five ex vivo and five in vivo normal knees to measure T1ρ values of femoral cartilage, meniscus, posterior cruciate ligament, anterior cruciate ligament, patellar tendon, and muscle. RESULTS: The phantom study demonstrated PM-UTE-AdiabT1ρ 's high sensitivity to compositional changes, its high reproducibility, and its strong linear correlation with continuous wave-T1ρ measurement. The ex vivo and in vivo knee studies demonstrated average T1ρ values of 105.6 ± 8.4 and 77.9 ± 3.9 ms for the femoral cartilage, 39.2 ± 5.1 and 30.1 ± 2.2 ms for the meniscus, 51.6 ± 5.3 and 29.2 ± 2.4 ms for the posterior cruciate ligament, 79.0 ± 9.3 and 52.0 ± 3.1 ms for the anterior cruciate ligament, 19.8 ± 4.5 and 17.0 ± 1.8 ms for the patellar tendon, and 91.1 ± 8.8 and 57.6 ± 2.8 ms for the muscle, respectively. CONCLUSION: The 3D PM-UTE-AdiabT1ρ sequence allows volumetric T1ρ assessment for both short and long T2 tissues in the knee joint on a clinical 3 T scanner.

Achilles tendon and enthesis assessment using ultrashort echo time magnetic resonance imaging (UTE-MRI) T1 and magnetization transfer (MT) modeling in psoriatic arthritis.

The purpose of this study is to investigate the use of ultrashort echo time (UTE) magnetic resonance imaging (MRI) techniques (T1 and magnetization transfer [MT] modeling) for imaging of the Achilles tendons and entheses in patients with psoriatic arthritis (PsA) compared with asymptomatic volunteers. The heels of twenty-six PsA patients (age 59 ± 15 years, 41% female) and twenty-seven asymptomatic volunteers (age 33 ± 11 years, 47% female) were scanned in the sagittal plane with UTE-T1 and UTE-MT modeling sequences on a 3-T clinical scanner. UTE-T1 and macromolecular proton fraction (MMF; the main outcome of MT modeling) were calculated in the tensile portions of the Achilles tendon and at the enthesis (close to the calcaneus bone). Mann-Whitney-U tests were used to examine statistically significant differences between the two cohorts. UTE-T1 in the entheses was significantly higher for the PsA group compared with the asymptomatic group (967 ± 145 vs. 872 ± 133 ms, p < 0.01). UTE-T1 in the tendons was also significantly higher for the PsA group (950 ± 145 vs. 850 ± 138 ms, p < 0.01). MMF in the entheses was significantly lower in the PsA group compared with the asymptomatic group (15% ± 3% vs. 18% ± 3%, p < 0.01). MMF in the tendons was also significantly lower in the PsA group compared with the asymptomatic group (17% ± 4% vs. 20% ± 5%, p < 0.01). Percentage differences in MMF between the asymptomatic and PsA groups (-16.6% and -15.0% for the enthesis and tendon, respectively) were higher than the T1 differences (10.8% and 11.7% for the enthesis and tendon, respectively). The results suggest higher T1 and lower MMF in the Achilles tendons and entheses in PsA patients compared with the asymptomatic group. This study highlights the potential of UTE-T1 and UTE-MT modeling for quantitative evaluation of entheses and tendons in PsA patients.

Bone Biomarkers Based on Magnetic Resonance Imaging.

Magnetic resonance imaging (MRI) is increasingly used to evaluate the microstructural and compositional properties of bone. MRI-based biomarkers can characterize all major compartments of bone: organic, water, fat, and mineral components. However, with a short apparent spin-spin relaxation time (T2*), bone is invisible to conventional MRI sequences that use long echo times. To address this shortcoming, ultrashort echo time MRI sequences have been developed to provide direct imaging of bone and establish a set of MRI-based biomarkers sensitive to the structural and compositional changes of bone. This review article describes the MRI-based bone biomarkers representing total water, pore water, bound water, fat fraction, macromolecular fraction in the organic matrix, and surrogates for mineral density. MRI-based morphological bone imaging techniques are also briefly described.

T1rho MR properties of human patellar cartilage: correlation with indentation stiffness and biochemical contents.

OBJECTIVE: Cartilage degeneration involves structural, compositional, and biomechanical alterations that may be detected non-invasively using quantitative MRI. The goal of this study was to determine if topographical variation in T1rho values correlates with indentation stiffness and biochemical contents of human patellar cartilage. DESIGN: Cadaveric patellae from unilateral knees of 5 donors with moderate degeneration were imaged at 3-Telsa with spiral chopped magnetization preparation T1rho sequence. Indentation testing was performed, followed by biochemical analyses to determine water and sulfated glycosaminoglycan contents. T1rho values were compared to indentation stiffness, using semi-circular regions of interest (ROIs) of varying sizes at each indentation site. ROIs matching the resected tissues were analyzed, and univariate and multivariate regression analyses were performed to compare T1rho values to biochemical contents. RESULTS: Grossly, superficial degenerative change of the cartilage (i.e., roughened texture and erosion) corresponded with regions of high T1rho values. High T1rho values correlated with low indentation stiffness, and the strength of correlation varied slightly with the ROI size. Spatial variations in T1rho values correlated positively with that of the water content (R2 = 0.10, p < 0.05) and negatively with the variations in the GAG content (R2 = 0.13, p < 0.01). Multivariate correlation (R2 = 0.23, p < 0.01) was stronger than either of the univariate correlations. CONCLUSION: These results demonstrate the sensitivity of T1rho values to spatially varying function and composition of cartilage and that the strength of correlation depends on the method of data analysis and consideration of multiple variables.

MRI Advancements in Musculoskeletal Clinical and Research Practice.

Over the past decades, MRI has become increasingly important for diagnosing and longitudinally monitoring musculoskeletal disorders, with ongoing hardware and software improvements aiming to optimize image quality and speed. However, surging demand for musculoskeletal MRI and increased interest to provide more personalized care will necessitate a stronger emphasis on efficiency and specificity. Ongoing hardware developments include more powerful gradients, improvements in wide-bore magnet designs to maintain field homogeneity, and high-channel phased-array coils. There is also interest in low-field-strength magnets with inherently lower magnetic footprints and operational costs to accommodate global demand in middle- and low-income countries. Previous approaches to decrease acquisition times by means of conventional acceleration techniques (eg, parallel imaging or compressed sensing) are now largely overshadowed by deep learning reconstruction algorithms. It is expected that greater emphasis will be placed on improving synthetic MRI and MR fingerprinting approaches to shorten overall acquisition times while also addressing the demand of personalized care by simultaneously capturing microstructural information to provide greater detail of disease severity. Authors also anticipate increased research emphasis on metal artifact reduction techniques, bone imaging, and MR neurography to meet clinical needs.

Ultrashort echo time magnetic resonance imaging of the osteochondral junction.

Osteoarthritis is a common chronic degenerative disease that causes pain and disability with increasing incidence worldwide. The osteochondral junction is a dynamic region of the joint that is associated with the early development and progression of osteoarthritis. Despite the substantial advances achieved in the imaging of cartilage and application to osteoarthritis in recent years, the osteochondral junction has received limited attention. This is primarily related to technical limitations encountered with conventional MR sequences that are relatively insensitive to short T2 tissues and the rapid signal decay that characterizes these tissues. MR sequences with ultrashort echo time (UTE) are of great interest because they can provide images of high resolution and contrast in this region. Here, we briefly review the anatomy and function of cartilage, focusing on the osteochondral junction. We also review basic concepts and recent applications of UTE MR sequences focusing on the osteochondral junction.

Correction of B0 and linear eddy currents: Impact on morphological and quantitative ultrashort echo time double echo steady state (UTE-DESS) imaging.

The purpose of the current study was to investigate the effects of B0 and linear eddy currents on ultrashort echo time double echo steady state (UTE-DESS) imaging and to determine whether eddy current correction (ECC) effectively resolves imaging artifacts caused by eddy currents. 3D UTE-DESS sequences based on either projection radial or spiral cones trajectories were implemented on a 3-T clinical MR scanner. An off-isocentered thin-slice excitation approach was used to measure eddy currents. The measurements were repeated four times using two sets of tested gradient waveforms with opposite polarities and two different slice locations to measure B0 and linear eddy currents simultaneously. Computer simulation was performed to investigate the eddy current effect. Finally, a phantom experiment, an ex vivo experiment with human synovium and ankle samples, and an in vivo experiment with human knee joints, were performed to demonstrate the effects of eddy currents and ECC in UTE-DESS imaging. In a computer simulation, the two echoes (S+ and S-) in UTE-DESS imaging exhibited strong distortion at different orientations in the presence of B0 and linear eddy currents, resulting in both image degradation as well as misalignment of pixel location between the two echoes. The same phenomenon was observed in the phantom, ex vivo, and in vivo experiments, where the presence of eddy currents degraded S+, S-, echo subtraction images, and T2 maps. The implementation of ECC dramatically improved both the image quality and image registration between the S+ and S- echoes. It was concluded that ECC is crucial for reliable morphological and quantitative UTE-DESS imaging.

Clinical application of ultrashort echo time (UTE) and zero echo time (ZTE) magnetic resonance (MR) imaging in the evaluation of osteoarthritis.

Novel compositional magnetic resonance (MR) imaging techniques have allowed for both the qualitative and quantitative assessments of tissue changes in osteoarthritis, many of which are difficult to characterize on conventional MR imaging. Ultrashort echo time (UTE) and zero echo time (ZTE) MR imaging have not been broadly implemented clinically but have several applications that leverage contrast mechanisms for morphologic evaluation of bone and soft tissue, as well as biochemical assessment in various stages of osteoarthritis progression. Many of the musculoskeletal tissues implicated in the initiation and progression of osteoarthritis are short T2 in nature, appearing dark as signal has already decayed to its minimum when image sampling starts. UTE and ZTE MR imaging allow for the qualitative and quantitative assessments of these short T2 tissues (bone, tendon, calcified cartilage, meniscus, and ligament) with both structural and functional reference standards described in the literature [1-3]. This review will describe applications of UTE and ZTE MR imaging in musculoskeletal tissues focusing on its role in knee osteoarthritis. While the review will address tissue-specific applications of these sequences, it is understood that osteoarthritis is a whole joint process with involvement and interdependence of all tissues. KEY POINTS: • UTE MR imaging allows for the qualitative and quantitative evaluation of short T2 tissues (bone, calcified cartilage, and meniscus), enabling identification of both early degenerative changes and subclinical injuries that may predispose to osteoarthritis. • ZTE MR imaging allows for the detection of signal from bone, which has some of the shortest T2 values, and generates tissue contrast similar to CT, potentially obviating the need for CT in the assessment of osseous features of osteoarthritis.

Deep branch of the radial nerve: effect of pronation/supination on longitudinal nerve alignment.

OBJECTIVE: To evaluate the effect of maximal pronation and supination of the forearm on the alignment and anatomic relationship of the deep branch of the radial nerve (DBRN) at the superior arcade of the supinator muscle (SASM) by using high-resolution ultrasound (HRUS). MATERIALS AND METHODS: In this cross-sectional study, HRUS in the long axis of the DBRN was performed in asymptomatic participants enrolled from March to August 2021. DBRN alignment was evaluated by measuring angles of the nerve in maximal pronation and maximal supination of the forearm independently by two musculoskeletal radiologists. Forearm range of motion and biometric measurements were recorded. Student t, Shapiro-Wilk, Pearson correlation, reliability analyses, and Kruskal-Wallis test were used. RESULTS: The study population included 110 nerves from 55 asymptomatic participants (median age, 37.0 years; age range, 16-63 years; 29 [52.7%] women). There was a statistically significant difference between the DBRN angle in maximal supination and maximal pronation (Reader 1: 95% CI: 5.74, 8.21, p < 0.001, and Reader 2: 95% CI: 5.82, 8.37, p < 0.001). The mean difference between the angles in maximal supination and maximal pronation was approximately 7° for both readers. ICC was very good for intraobserver agreement (Reader1: r ≥ 0.92, p < 0.001; Reader 2: r ≥ 0.93, p < 0.001), as well as for interobserver agreement (phase 1: r ≥ 0.87, p < 0.001; phase 2: r ≥ 0.90, p < 0.001). CONCLUSION: The extremes of the rotational movement of the forearm affect the longitudinal morphology and anatomic relationships of the DBRN, primarily demonstrating the convergence of the nerve towards the SASM in maximal pronation and divergence in maximal supination.

Ultrashort Echo Time Magnetic Resonance Imaging Techniques: Met and Unmet Needs in Musculoskeletal Imaging.

This review article summarizes recent technical developments in ultrashort echo time (UTE) magnetic resonance imaging of musculoskeletal (MSK) tissues with short-T2 relaxation times. A series of contrast mechanisms are discussed for high-contrast morphological imaging of short-T2 MSK tissues including the osteochondral junction, menisci, ligaments, tendons, and bone. Quantitative UTE mapping of T1, T2*, T1ρ, adiabatic T1ρ, magnetization transfer ratio, MT modeling of macromolecular proton fraction, quantitative susceptibility mapping, and water content is also introduced. Met and unmet needs in MSK imaging are discussed. EVIDENCE LEVEL: 1 TECHNICAL EFFICACY: Stage 3.

Time-Resolved Noncontrast Magnetic Resonance Perfusion Imaging of Paraspinal Muscles.

BACKGROUND: While evaluation of blood perfusion in lumbar paraspinal muscles is of interest in low back pain, it has not been performed using noncontrast magnetic resonance (MR) techniques. PURPOSE: To introduce a novel application of a time-resolved, noncontrast MR perfusion technique for paraspinal muscles and demonstrate effect of exercise on perfusion parameters. STUDY TYPE: Longitudinal. SUBJECTS: Six healthy subjects (27-48 years old, two females) and two subjects with acute low back pain (46 and 65 years old females, one with diabetes/obesity). FIELD STRENGTH/SEQUENCE: 3-T, MR perfusion sequence. ASSESSMENT: Lumbar spines of healthy subjects were imaged axially at L3 level with a tag-on and tag-off alternating inversion recovery arterial spin labeling technique that suppresses background signal and acquires signal increase ratio (SIR) from the in-flow blood at varying inversion times (TI) from 0.12 seconds to 3.5 seconds. SIR vs. TI data were fit to determine the perfusion metrics of peak height (PH), time to peak (TTP), mean transit time, apparent muscle blood volume (MBV), and apparent muscle blood flow (MBF) in iliocostal, longissimus, and multifidus. Imaging was repeated immediately after healthy subjects performed a 20-minute walk, to determine the effect of exercise. STATISTICAL TESTS: Repeated measures analysis of variance. RESULTS: SIR vs. TI data showed well-defined leading and trailing edges, with sharply increasing SIR to TI of approximately 500 msec subsiding quickly to near zero around TI of 1500 msec. After exercise, the mean SIR at every TI increased markedly, resulting in significantly higher PH, MBV, and MBF (each P < 0.001 and F > 28.9), and a lower TTP (P < 0.05, F = 4.5), regardless of the muscle. MBF increased 2- to 2.5-fold after exercise, similar to the expected increase in cardiac output, given the intensity of the exercise. DATA CONCLUSIONS: Feasibility of an MR perfusion technique for muscle perfusion imaging was demonstrated, successfully detecting significantly increased perfusion after exercise. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY STAGE: 1.

Diversity and perception of equity and respect in the Society of Skeletal Radiology (SSR).

PURPOSE: To assess the perception of equity and respect in the workplace and within the SSR. We hypothesized that responses would differ by gender and minorities underrepresented in medicine (URiM) status. METHODS: An electronic survey was sent to 1,531 SSR members between January 2020 and March 2020 to determine perception of equity and respect. Descriptive statistics were calculated, and analysis of differences in response by gender/minority status was performed using the Fisher's exact test. The study was exempt from IRB approval. RESULTS: There were 176 responses (11.5%). Most respondents (61.9%) were between 30 and 50 years. Members identified as male (M) in 74.4%, as female (F) in 25.0%, and as "other" in 0.6%. URiM comprised 9.1% of members. Women worked more commonly in academia (p = 0.005), had the perception of unequal opportunities for leadership positions within the institution (p = 0.006), and emphasized the importance of having a mentor of the same gender (p = 0.001). URiM members were less likely to hold a leadership position (p = 0.1, trend), had a perception of unequal opportunities for leadership positions within the institution (p = 0.06, trend), and reported the importance of having a mentor of the same race (p = 0.06, trend). There were no significant differences between gender or URiM status and perception of the SSR to provide an inclusive environment and leadership opportunities (p ≥ 0.39). CONCLUSION: While survey participation was limited and potentially biased, respondents perceived that women and minorities have fewer opportunities and are treated with lower regard in the workplace compared to male, non-minority colleagues.

Detailed bone assessment of the sacroiliac joint in a prospective imaging study: comparison between computed tomography, zero echo time, and black bone magnetic resonance imaging.

OBJECTIVES: To compare the value of zero echo time (ZTE) and gradient echo "black bone" (BB) MRI sequences for bone assessment of the sacroiliac joint (SI) using computed tomography (CT) as the reference standard. MATERIALS AND METHODS: Between May 2019 and January 2021, 79 patients prospectively underwent clinically indicated 3-T MRI including ZTE and BB imaging. Additionally, all patients underwent a CT scan covering the SI joints within 12 months of the MRI examination. Two blinded readers performed bone assessment by grading each side of each SI joint qualitatively in terms of seven features (osteophytes, subchondral sclerosis, erosions, ankylosis, joint irregularity, joint widening, and gas in the SI joint) using a 4-point Likert scale (0 = no changes-3 = marked changes). Scores were compared between all three imaging modalities. RESULTS: Interreader agreement was largely good (k values: 0.5-0.83). Except for the feature "gas in SI joint" where ZTE exhibited significantly lower scores than CT (p < 0.001), ZTE and BB showed similar performance relative to CT for all other features (p > 0.52) with inter-modality agreement being substantial to almost perfect (Krippendorff's alpha coefficients: 0.724-0.983). When combining the data from all features except for gas in the SI joint and when binarizing grading scores, combined sensitivity/specificity was 76.7%/98.6% for ZTE and 80.8%/99.1% for BB, respectively, compared to CT. CONCLUSIONS: The performance of ZTE and BB sequences was comparable to CT for bone assessment of the SI joint. These sequences may potentially serve as an alternative to CT yet without involving exposure to ionizing radiation.

Bone Marrow Aspirate Concentrate Augmentation May Accelerate Allograft Ligamentization in Anterior Cruciate Ligament Reconstruction: A Double-Blinded Randomized Controlled Trial.

PURPOSE: To assess the effect of bone marrow aspiration concentrate (BMAC) augmentation on clinical outcomes and magnetic resonance imaging (MRI) findings in anterior cruciate ligament (ACL) reconstruction (ACLR) with bone-patellar tendon-bone (BTB) allografts. METHODS: A double-blinded, randomized controlled trial was conducted on 80 patients undergoing ACL reconstruction using BTB allografts. Patients were randomized to 2 groups: (1) bone marrow aspirate was collected from the iliac crest, concentrated, and approximately 2.5 mL was injected into the BTB allograft, or (2) a small sham incision was made at the iliac crest (control). MRI was performed at 3 months and 9 months postoperatively to determine the signal intensity ratio of the ACL graft. RESULTS: Seventy-three patients were available for follow-up at 1-year postoperatively (36 BMAC, 37 control). International Knee Documentation Committee (IKDC) scores were significantly greater in the BMAC group versus the control at the 9-month postoperative period (81.6 ± 10.5 vs 74.6 ± 14.2, P = .048). There was no significant difference in the proportion of patients who met the minimal clinically important difference for IKDC between the BMAC and control groups at 9 months (89% vs 85%; P = .7). Three months postoperatively, signal intensity ratio of the inferior third of the ACL graft was significantly greater in the BMAC group versus the control group (3.2 ± 2.2 vs 2.1 ± 1.5; P = .02). CONCLUSIONS: Patients who received BMAC augmentation of the BTB allograft during ACL reconstruction demonstrated greater signal intensity scores on MRI at 3 months, suggesting increased metabolic activity and remodeling, and potentially accelerated ligamentization. Additionally, patients in the BMAC group had greater patient-reported outcomes (IKDC) at 9 months postoperatively when compared with those who underwent a standard surgical procedure. There was no significant difference in the proportion of patients who met the minimal clinically important difference for IKDC between the BMAC and control groups at 9 months, suggesting limited clinical significance at this time point. LEVEL OF EVIDENCE: I, randomized control trial.

Quantitative magnetic resonance imaging of meniscal pathology ex vivo.

OBJECTIVE: To determine the ability of conventional spin echo (SE) T2 and ultrashort echo time (UTE) T2* relaxation times to characterize pathology in cadaveric meniscus samples. MATERIALS AND METHODS: From 10 human donors, 54 triangular (radially cut) meniscus samples were harvested. Meniscal pathology was classified as normal (n = 17), intrasubstance degenerated (n = 33), or torn (n = 4) using a modified arthroscopic grading system. Using a 3-T MR system, SE T2 and UTE T2* values of the menisci were determined, followed by histopathology. Effect of meniscal pathology on relaxation times and histology scores were determined, along with correlation between relaxation times and histology scores. RESULTS: Mean ± standard deviation UTE T2* values for normal, degenerated, and torn menisci were 3.6 ± 1.3 ms, 7.4 ± 2.5 ms, and 9.8 ± 5.7 ms, respectively, being significantly higher in degenerated (p < 0.0001) and torn (p = 0.0002) menisci compared to that in normal. In contrast, the respective mean SE T2 values were 27.7 ± 9.5 ms, 25.9 ± 7.0 ms, and 35.7 ± 10.4 ms, without significant differences between groups (all p > 0.14). In terms of histology, we found significant group-wise differences (each p < 0.05) in fiber organization and inner-tip surface integrity sub-scores, as well as the total score. Finally, we found a significant weak correlation between UTE T2* and histology total score (p = 0.007, Rs2 = 0.19), unlike the correlation between SE T2 and histology (p = 0.09, Rs2 = 0.05). CONCLUSION: UTE T2* values were found to distinguish normal from both degenerated and torn menisci and correlated significantly with histopathology.

Comparison of Radiographic, Ultrasound, and Magnetic Resonance Imaging for the Detection of Retained Stingray Barb: A Cadaveric Study.

INTRODUCTION: Stingray envenomations are a common marine animal injury for which it is important to identify and remove retained barbs to prevent secondary infection. The optimal imaging modality in stingray foreign body detection is not well characterized in the existing literature. In this study, we compared the accuracy of plain radiography, ultrasound, and magnetic resonance imaging (MRI) in detecting stingray barbs in the human foot and ankle. METHODS: This cadaveric study included a 1:1 randomization to the presence or absence of barbs in 24 sample injuries of human cadaveric foot and ankle specimens. Physicians trained in emergency medicine and radiology performed ultrasound examinations on each specimen and interpreted the presence or absence of a barb. Participants also interpreted x-ray images in the same manner. MRI scans were separately interpreted by a musculoskeletal radiology attending. Data were analyzed using McNemar's test. RESULTS: The 19 participants included 14 (74%) trained in emergency medicine and 5 (26%) trained in radiology. Forty-seven percent were residents, 42% faculty, and 11% fellows. X-ray was associated with the highest sensitivity of 94% for the identification of a retained barb, followed by MRI (83%) and ultrasound (70%). MRI was associated with the highest specificity of 100%, followed by x-ray (98%) and ultrasound (73%). CONCLUSIONS: Retained stingray barbs can lead to secondary infection after envenomation. In human cadaveric specimens, x-ray demonstrated the highest sensitivity, MRI demonstrated the highest specificity, and ultrasound demonstrated lower sensitivity and specificity.

High-Resolution MRI of the First Metatarsophalangeal Joint: Gross Anatomy and Injury Characterization.

The first metatarsophalangeal joint (MTPJ) is vital to the biomechanics of the foot and supports a weight up to eight times heavier than the body during athletic activities. The first MTPJ comprises osseous and cartilaginous surfaces along with a complex of supporting structures, including the dorsal extensor tendons, collateral ligaments, and a plantar plate complex. In contradistinction to the lesser MTPJ plantar plates, a single dominant fibrocartilaginous capsular thickening does not exist at the first MTPJ. Instead, the plantar plate complex comprises a fibrocartilaginous pad that invests the hallux sesamoids and is inseparable from the plantar capsule, the intersesamoid ligament, paired metatarsosesamoid and sesamoid phalangeal ligaments (SPLs), and the musculotendinous structures. Acute injury at the first MTPJ is typically secondary to forced hyperextension-turf toe-and can involve multiple structures. During hyperextension, the resulting forces primarily load the distal SPLs, making these structures more susceptible to injury. SPL injuries are best seen in the sagittal plane at MRI. Radiography can also aid in diagnosis of full-thickness SPL tears, demonstrating reduced sesamoid excursion at lateral dorsiflexed (stress) views. Hallux valgus is another common condition, resulting in progressive disabling deformity at the first MTPJ. Without appropriate treatment, first MTPJ injuries may progress to degenerative hallux rigidus. The authors detail the anatomy of the first MTPJ in cadaveric forefeet by using high-resolution 3-T and 11.7-T MRI and anatomic-pathologic correlation. Injuries to the plantar plate complex, collateral ligaments, and extensor mechanism are discussed using clinical case examples. Online supplemental material is available for this article. ©RSNA, 2020.

Is There a Role for Cartilage Imaging in Athletes?

This article reviews implications for cartilage imaging in athletes in the setting of (1) acute chondral injury diagnosis, (2) evaluation and follow-up of conservative and surgical therapy, and (3) evaluation of cartilage as a surrogate for meniscal function and joint stability. Focal knee cartilage defects are common in athletic populations. Athletes with articular cartilage injury may initially be able to return to sport with conservative therapy; however, a reduction of athletic ability and progression to osteoarthritis is expected in athletes with untreated severe chondral injury. For diagnostic and pre- and postsurgical evaluation purposes, morphological magnetic resonance (MR) assessment of the articular cartilage with high-resolution protocols is crucial. Although not widely implemented for clinical use, compositional MR techniques have great potential for monitoring the development and progression of biochemical and microstructural changes in cartilage extracellular matrix before gross morphological changes occur.

MR imaging pattern of tibial subchondral bone structure: considerations of meniscal coverage and integrity.

OBJECTIVES: To compare regional differences in subchondral trabecular structure using high-resolution MRI in meniscus-covered/meniscus-uncovered tibia in cadaveric knees with intact/torn menisci. MATERIALS AND METHODS: 3D proton density CUBE MRI of 6 cadaveric knees without significant osteoarthritis (OA) was acquired, 0.25-mm resolution. Menisci were evaluated and classified intact or torn. MR data were transferred to ImageJ program to segment tibial 3D volume of interest (VOI). Data was subdivided into meniscus-covered/meniscus-uncovered regions. Segmented VOI was classified into binary data, trabeculae/bone marrow. The trabecular bone data was used to measure MR biomarkers (apparent subchondral plate-connected bone density (adapted from spine MR), apparent trabecular bone volume fraction, apparent mean trabecular thickness, apparent connectivity density, and structure model index (SMI)). Mean value of parameters was analyzed for the effects of meniscal tear/tibial coverage. RESULTS: Nine torn menisci and 3 intact menisci were present. MR measures of bone varied significantly due to meniscal coverage/tear. Subchondral plate-connected bone density under covered meniscus regions increased from 10.9 to 23.5% with meniscal tear. Values increased in uncovered regions, 19.3% (intact) and 32.4% (torn). This reflects higher density when uncovered (p = 0.048) with meniscal tear (p = 0.007). Similar patterns were found for trabecular bone fraction (coverage p < 0.001, tear p = 0.047), trabecular thickness (coverage p = 0.03), connectivity density (coverage p = 0.002), and SMI (coverage p = 0.015). CONCLUSION: Quantitative trabecular bone evaluation emphasizes intrinsic structural differences between meniscus-covered/meniscus-uncovered tibias. Results offer insight into bone adaptation with meniscal tear and support the hypothesis that subchondral bone plate-connected bone density could be important in early subchondral bone adaptation.

Standard and Advanced Imaging of Hip Osteoarthritis. What the Radiologist Should Know.

Osteoarthritis (OA) of the hip is caused by degeneration of articular cartilage and the underlying bone and can be divided into two types: primary (associated with advancing age) and secondary (subsequent to fractures, avascular necrosis, infection, developmental dysplasia, and femoroacetabular impingement). Radiography remains the first-line imaging modality for diagnosing and monitoring OA, due to its accessibility, low cost, and ease of interpretation. Kellgren-Lawrence and Tönnis classification systems are radiographic OA grading systems used primarily in research, and they reflect the degree of joint space narrowing, sclerosis, cysts, deformity of the femoral head and acetabulum, and osteophytes. Unenhanced computed tomography (CT) provides detailed visualization of the hip joint segments that may be difficult to appreciate on radiographs, such as the inferoposterior and posterolateral hip joint. CT arthrography, magnetic resonance imaging (MRI), and magnetic resonance arthrography with two-dimensional reconstructions can delineate labral abnormalities, cartilage lesions, and other intra-articular hip pathology. T2 and T2* mapping, delayed gadolinium-enhanced MRI of cartilage, T1rho, ultra-short echo time, and zero echo time are investigative MR techniques with promising evaluation of hip OA.