High resolution imaging of the knee on 3‐Tesla MRI: A pictorial review

Normal anatomical variants of the menisci and cruciate ligaments that may mimic disease

There are many normal anatomical variants of the knee joint. Some are common and others are rare. With continuing improvements in the spatial resolution of MRI, smaller variants are more clearly demonstrated and can be mistaken for disease. They can all be differentiated from pathological conditions by understanding their anatomy and key differentiating features. This review compares normal variants of the menisci and cruciate ligaments with the pathological disorders that can mimic them.

Prevalence and incidence of new meniscus and cartilage injuries after a nonoperative treatment algorithm for ACL tears in skeletally immature children: a prospective MRI study

BACKGROUND

The increased risk of long-term osteoarthritis from concomitant injuries to the menisci or cartilage after an anterior cruciate ligament (ACL) injury in adults is well established. In skeletally immature children, ACL reconstruction is often recommended to reduce the risk of new intra-articular injuries. However, the prevalence and incidence of new injuries after nonoperative treatment of ACL injuries in children are unknown.

PURPOSE

To prospectively investigate the incidence of new injuries to the menisci and joint cartilage in nonoperatively treated, skeletally immature children with a known ACL injury by use of bilateral 3.0-T MRI.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Forty skeletally immature children with a ruptured ACL (41 knees) followed a nonoperative treatment algorithm and were evaluated with bilateral 3.0-T MRI on 2 occasions (MRI1 and MRI2). The intra-articular structures were analyzed by 2 independent MRI radiologists. Monitoring of participation in physical activities was accomplished through a monthly online activity survey. Descriptive statistics and frequencies were extracted from the scoring forms and compared using the Fisher exact test.

RESULTS

Fourteen girls (35%) and 26 boys (65%) with a mean age of 11.0 ± 1.4 years at the time of injury were included. Time from injury to the final follow-up was 3.8 ± 1.4 years. Eighty-eight percent of the ACL-deficient children confirmed monthly participation in pivoting sports and/or in physical education classes in school. The prevalence of meniscus injuries in the 28 nonreconstructed knees was 28.5% at MRI1 and MRI2, and the incidence of new meniscus and cartilage injuries in the nonreconstructed knees from MRI1 to MRI2 was 3.6%. Thirteen children underwent ACL reconstruction, with a prevalence of meniscus procedures of 46.2%. The incidence of new meniscus injuries from diagnostic MRI to final follow-up was 19.5%. Surgical treatments for meniscus injuries were performed in 8 of the 41 knees.

CONCLUSION

The incidence of new injuries to menisci and joint cartilage was low between MRI1 and MRI2 in the 28 nonreconstructed knees. Thirty-two percent of the knees required ACL reconstruction, and 19.5% required meniscus surgeries during the 3.8 ± 1.4 years of follow-up from injury. Further follow-up is needed to evaluate the long-term knee health in these children.

Phase-sensitive X-ray imaging of synovial joints

OBJECTIVE

To test the efficacy of phase-sensitive X-ray imaging for intact synovial joints, whereby refraction effects, along with the attenuation of conventional radiography, can be exploited.

DESIGN

Intact cadaveric human knee joints were imaged, in the computed tomographic mode, using an analyzer-based X-ray system at the National Synchrotron Light Source, Brookhaven National Laboratory. A collimated fan beam of 51 keV X-rays was prepared by a silicon [1,1,1 reflection] double-crystal monochromator. The X-ray beam transmitted through the specimen was imaged after diffraction in the vertical plane by means of the analyzer crystal with the analyzer crystal tuned to its half-reflectivity point (6.5 microrad). A two-dimensional filtered backprojection (FBP) algorithm was used for reconstructing transverse slices of images.

RESULTS

The resulting images demonstrate simultaneous soft tissue and bone contrast at a level that has not been achieved previously. Identifiable structures include articular cartilage, cruciate ligaments, loose connective tissue, menisci, and chondrocalcinosis.

CONCLUSION

Phase-sensitive X-ray imaging using an analyzer-based system renders exceptionally high quality images of soft and hard tissues within synovial joints, with high contrast and resolution, and thus holds promise for the eventual clinical utility.

Overview of imaging in inflammatory arthritis

Whether magnetic resonance imaging (MRI) or ultrasound (US) are chosen for the purposes of musculoskeletal interrogation depends upon a variety of factors ranging from the anatomy targeted to cost considerations and the time of acquisition. Newer technologies such as higher-strength MRI or 3D-US promise to help overcome some of the disadvantages of each option. Improving technical proficiency is the thrust of efforts to support more widespread application of sonographic assessment in various clinical arenas. Finally, these technologies offer the opportunity to diagnose inflammatory conditions at early stages of their disease progression.

Assessment of cartilage-dedicated sequences at ultra-high-field MRI: comparison of imaging performance and diagnostic confidence between 3.0 and 7.0 T with respect to osteoarthritis-induced changes at the knee joint

OBJECTIVE

The objectives of the study were to optimize three cartilage-dedicated sequences for in vivo knee imaging at 7.0 T ultra-high-field (UHF) magnetic resonance imaging (MRI) and to compare imaging performance and diagnostic confidence concerning osteoarthritis (OA)-induced changes at 7.0 and 3.0 T MRI.

MATERIALS AND METHODS

Optimized MRI sequences for cartilage imaging at 3.0 T were tailored for 7.0 T: an intermediate-weighted fast spin-echo (IM-w FSE), a fast imaging employing steady-state acquisition (FIESTA) and a T1-weighted 3D high-spatial-resolution volumetric fat-suppressed spoiled gradient-echo (SPGR) sequence. Three healthy subjects and seven patients with mild OA were examined. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), diagnostic confidence in assessing cartilage abnormalities, and image quality were determined. Abnormalities were assessed with the whole organ magnetic resonance imaging score (WORMS). Focal cartilage lesions and bone marrow edema pattern (BMEP) were also quantified.

RESULTS

At 7.0 T, SNR was increased (p < 0.05) for all sequences. For the IM-w FSE sequence, limitations with the specific absorption rate (SAR) required modifications of the scan parameters yielding an incomplete coverage of the knee joint, extensive artifacts, and a less effective fat saturation. CNR and image quality were increased (p < 0.05) for SPGR and FIESTA and decreased for IM-w FSE. Diagnostic confidence for cartilage lesions was highest (p < 0.05) for FIESTA at 7.0 T. Evaluation of BMEP was decreased (p < 0.05) at 7.0 T due to limited performance of IM-w FSE.

CONCLUSION

Gradient echo-based pulse sequences like SPGR and FIESTA are well suited for imaging at UHF which may improve early detection of cartilage lesions. However, UHF IM-w FSE sequences are less feasible for clinical use.