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The growing number of patients undergoing arthroscopy or surgery of the knee for ligamentous injuries has led to a greater need for postoperative imaging because of poor outcome, recurrent symptoms, or a new injury. MRI is the most important imaging method when evaluating the postoperative knee. Radiologists should be familiar with the particular reconstruction technique applied to each examinee, know the spectrum of normal postoperative findings, recognize those findings that may be related to symptoms of failed reconstruction, as well as those lesions that are irrelevant to the previous surgery yet responsible for the new clinical symptoms. In view of the continually evolving surgical techniques, this review presents the current concepts of MRI evaluation of the postoperative knee ligaments based on recent literature reports., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Purpose: The anatomy of the lateral knee compartment has been recently further explored with description of the anterolateral knee ligament (ALL). The purpose of this study was to confirm the presence of ALL on cadaveric knees and to describe its normal anatomy in young healthy volunteers, utilizing a high-resolution 3-dimensional (3D) pulse sequence., Methods: Dissection was performed on 9 cadaveric knees in order to confirm the presence of ALL. Conventional 2-dimensional sequences of 10 knees at 1.5 T and 10 knees at 3 T, with a slice thickness of 2-4 mm, were reviewed for the presence of ALL. A 3D T2/T1-weighted gradient echo sequence (constructive interference in steady state [CISS]), yielding in-plane resolution of 0.4 mm × 0.4 mm × 0.4 mm, was applied in 14 healthy volunteers (26 knees). All 3D images were manipulated using multiplanar reconstruction (MPR) and the presence and width of ALL were recorded., Results: Cadaveric dissection disclosed the presence of ALL in 8 of 9 knees. Conventional knee MR imaging depicted ALL only on coronal images (18 of 20) whereas the CISS revealed ALL on 24 of 26 studied knees (92.3%). ALL has a mean thickness of 1.1 ± 0.27 mm measured on coronal MR images., Conclusions: ALL can be thoroughly assessed in young healthy individuals with the use of high-resolution 3D MR imaging with MPR at 1.5 T., (Copyright © 2016 Canadian Association of Radiologists. Published by Elsevier Inc. All rights reserved.)

Objective: Medial tibial condyle bone marrow edema (BME), associated with soft tissue edema (STe) surrounding the medial collateral ligament, was incidentally observed in MRI examinations of young and athletic individuals. The aim of the present study was to 1. Prospectively investigate the association between these findings and coexistence of localized pain, and 2. Explore the possible contribution of the tibial morphology to its pathogenesis., Methods: The medial tibial condyle crest was evaluated in 632 knee MRI examinations. The angle and depth were measured by two separate evaluators. The presence of STe and BME was recorded. A third evaluator blindly assessed the presence of pain at this site., Results: BME associated with STe was found in 24 patients (with no history of previous trauma, osteoarthritis, tumor or pes anserine bursitis). The mean crest angle was 151.3° (95%CI 147.4-155.3°) compared to 159.4° (95%CI 158.8-160°) in controls (Mann-Whitney test, P<0.0001). MRI findings were highly predictive of localized pain (sensitivity 92% specificity 99%, Fisher's exact test, P<0.0001)., Conclusion: Friction at the medial tibial condyle crest is a painful syndrome. MRI is a highly specific and sensitive imaging modality for its diagnosis., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

Objective: The purpose of this study was to evaluate the MRI characteristics of the suprapatellar fat-pad, determine the prevalence and pattern of suprapatellar fat-pad edema, and correlate the findings with the presence of anterior knee pain, patellofemoral malalignment, and patellofemoral joint osteoarthritis., Materials and Methods: We retrospectively reviewed 879 consecutive knee MRI examinations of 843 patients for the presence of a suprapatellar fat-pad mass effect on the suprapatellar joint recess. The relative signal intensity and the maximum anteroposterior, craniocaudal, and oblique diameters of the suprapatellar fat-pad on sagittal fat-suppressed intermediate-weighted turbo spin-echo images were measured. Findings of anterior knee pain, patellofemoral malalignment, and patellofemoral joint osteoarthritis were also recorded. The Fisher exact, Mann-Whitney, and independent samples Student t tests and Spearman rank correlation coefficient were used for statistical analysis., Results: The prevalence of suprapatellar fat-pad mass effect on the suprapatellar joint recess in our study population was 13.8%. The relative signal intensity (p < 0.0001) and maximum anteroposterior (p < 0.0001), craniocaudal (p = 0.0017), and oblique (p < 0.0001) diameters of the pad were significantly greater in patients with a mass effect. Significant correlation was found between the relative signal intensity and the maximum anteroposterior (ρ = 0.0986, p = 0.0053), craniocaudal (ρ = 0.0968, p = 0.0062), and oblique (ρ = 0.123, p = 0.0005) diameters. Mass effect was not significantly associated with anterior knee pain, patellofemoral malalignment, or patellofemoral joint osteoarthritis. Six patients with suprapatellar fat-pad edema had anterior knee pain., Conclusion: Suprapatellar fat-pad edema with a mass effect on the suprapatellar joint recess is a common finding at MRI examinations of the knee that is rarely associated with anterior knee pain.

Objectives: To evaluate patellofemoral congruency measurements on MRI and correlate the findings with severity of ipsilateral osteoarthritis., Methods: We retrospectively reviewed 650 consecutive knee MRI examinations from 622 patients divided into two age groups: ≤50 and >50 year-old. The femoral sulcus angle (SA) and depth (SD), lateral patellar displacement (LPD), lateral patellofemoral angle (LPFA), tibial tubercle-trochlear groove (TT-TG) distance and Insall-Salvati index as well as the grade of focal cartilage defects (ranging from I to IV) in the patellofemoral region were assessed in each subject on axial and sagittal fat-saturated intermediate-w MR images., Results: A significant difference exists between normal and knees with patellofemoral joint osteoarthritis regarding SA (p = 0.0002 and <0.0001), SD (p = 0.0004 and <0.0001), LPD (p = 0.0014 and 0.0009) and LPFA (p = 0.0002 and 0.0003) in both age groups (≤50 and >50 respectively). Significant correlation was found between grading of cartilage defects and SA (rho = 0.21, p = 0.0001 and 0.443, <0.0001), SD (rho = -0.198, p = 0.0003 and -0.418, <0.0001), LPD (rho = 0.176, p = 0.0013 and 0.251, 0.0002) and LPFA (rho = -0.204, p = 0.0002 and -0.239, 0.0005) in both age groups., Conclusions: Knee joint anterior malalignment is multivariably associated with patellofemoral osteoarthritis., Key Points: • MRI is an excellent method to evaluate knee alignment and articular cartilage damage. • Significant associations exist between alignment parameters and osteoarthritis of the patellofemoral joint. • The "sulcus angle" and "sulcus depth" were the most valuable osteoarthritic markers.

The purpose of this study was to evaluate differences in graft orientation between transtibial (TT) and anteromedial (AM) portal technique using magnetic resonance imaging (MRI) in anterior cruciate ligament (ACL) reconstruction. Fifty-six patients who were undergoing ACL reconstruction underwent MRI of their healthy and reconstructed knee. Thirty patients had ACL reconstruction using the TT (group A), while in the remaining 26 the AM (group B) was used. In the femoral part graft orientation was evaluated in the coronal plane using the femoral graft angle (FGA). The FGA was defined as the angle between the axis of the femoral tunnel and the joint line. In the tibial part graft orientation was evaluated in the sagittal plane using the tibial graft angle (TGA). The TGA was defined as the angle between the axis of the tibial tunnel and a line perpendicular to the long axis of the tibia. The ACL angle of the normal knee in the sagittal view was also calculated. The mean FGA for group A was 72 degrees, while for the group B was 53 degrees and this was statistically significant (P < 0.001). The mean TGA for group A was 64 degrees, while for the group B was 63 degrees (P = 0.256). The mean intact ACL angle for group A was 52 degrees, while for the group B was 51 degrees. The difference between TGA and intact ACL angle was statistically significant (P < 0.001) for both groups. Using the AM portal technique, the ACL graft is placed in a more oblique direction in comparison with the TT technique in the femoral part. However, there are no differences between the two techniques in graft orientation in the tibial part. Normal sagittal obliquity is not restored with both techniques.

Purpose: The aim of the study was to present the MRI findings of non-traumatic edema-like lesions presented acutely in the adult knee and to correlate them with the 3-year outcome and the bone mineral density (BMD) in the spine., Materials and Methods: Ninety-eight patients (40 men, 58 women, mean age 60.1+/-11 years, age range 27-82 years), were followed up clinically as well as with MR imaging, when indicated, for at least 3 years. Patients were classified according to presentation in 3 groups (A: bone marrow edema (BME), B: BME and subchondral fracture, C: BME and articular collapse) and according to outcome in 2 groups (A: reversible BME, B: articular collapse). BMD measurements of the spine were carried out in males over 70 and females over 60 years old using DEXA., Results: The isolated BME pattern was observed in 64.3% (Group A), subchondral fractures without articular collapse in 11.2% (Group B) and articular collapse in 24.5% (Group C). Significant differences were found among the 3 groups at presentation, regarding the age, sex, BMD, affected area and duration of symptoms prior to imaging (p<0.05). Localization of the lesions in the weight-bearing areas of the knee was shown in 100% of C, in 90.9% of B and in 50.8% of A. The duration of symptoms prior to imaging was longer in C (7.6+/-2.8m) than in A (2.5+/-1.7m) and B (4.0+/-3.2m) (p<0.05). Group B progressed to articular collapse in 45.5%, the rest demonstrating a favourable outcome. Group C showed clinical improvement in 75% and persistent symptoms that required knee arthroplasty in 25% of cases. Articular collapse was the final outcome in 29.6% and transient BME in 70.4% of patients. These two groups showed significant differences regarding the age (p approximately 0), sex (p=0.002), low BMD (p=0.004), affected area (p approximately 0), presence of subchondral sparing (p approximately 0), duration of symptoms prior to imaging (p approximately 0), time from onset of symptoms to the final outcome (p approximately 0) and need for arthroplasty (p=0.001). None of the patients with transient BME syndrome eventually progressed to articular collapse., Conclusion: In the context of acute non-traumatic knee BME, the age and sex of the patient, the duration of symptoms before imaging, the pattern of BME, and the BMD appear to correlate with the final outcome.

Objective: Acute non-traumatic bone marrow edema (BME) in the knee is a common clinical problem. The aim of the present study is to present the MR imaging findings of the uncommon transient migratory pattern of this syndrome., Materials and Methods: Twenty-two patients (21 men, 1 woman, age range 35-73 years, mean 49.4+/-7.6) who presented with pain in the knee joint (ranging from 2 weeks to 6 months) and BME in the MR imaging examination, were included in the study. In all cases, the knee joint BME was either preceded or followed by another site of BME in the same or another joint. All patients were studied with plain X-rays and MR imaging at presentation and with MR imaging after resolution of symptoms., Results: The eight patients with initial involvement in the knee showed migration either intra-articularly (5), or/and in the contralateral knee (2) and only 1 case showed migration to the ipsilateral hip joint. In two patients the BME shifted from the hip first to the foot and then to the knee. The median migration period was 4 months for the second involvement in all patients and 3 months for the third involvement (10 patients)., Conclusions: The present study reports the largest series of patients with regional migratory osteoporosis involving the knee. In most of the cases, shifting of BME remains in the joint or moves to the contralateral knee. In only one case the BME shifted from the knee elsewhere. All lesions were transient.

Localized pigmented villonodular synovitis (PVNS) of the knee is an uncommon entity, presenting with different clinical signs and symptoms. We report on a case of a 42-year-old woman who presented with a 3-year history of knee pain and mechanical problems such as locking. On examination she was found to have a palpable and painful mass over the anteromedial joint line. Magnetic resonance imaging (MRI) revealed a soft tissue mass in the anteromedial compartment of the knee joint. The lesion was completely resected arthroscopically, and histologic examination confirmed the diagnosis of localized PVNS. The patient was free of symptoms, and MRI examination showed no evidence of recurrence at 1-year follow-up.

Purpose: To carry out a modern diagnostic survey among patients with a clinical and radiological diagnosis of early osteoarthritis of the knee., Materials and Methods: A magnetic resonance imaging survey was performed on 70 patients (82 knees) with a mean age of 59 years. (range, 40-71 years) who had chronic knee pain, clinical diagnosis of early osteoarthritis of the knee and conventional knee radiographs classified as 1 and 2 on the Kellgren-Lawrence scale., Results: A variety of different disorders was found; degenerative meniscal lesions with or without ruptures of the anterior cruciate ligament in 70.7% of the knees, osteonecrosis of the femoral and tibial condyles in 9.75%, osteophytes and degenerative articular cartilage lesions in 8.54%, transient osteoporosis in 2.44% and benign neoplasms and cysts in 6.1%., Conclusions: The existence of such a heterogenous group of disorders in these "early osteoarthritic knees" may explain failures in treatment and it may justify a modern MRI imaging approach to proper diagnosis.

This study was conducted to compare a three-dimensional (3D) multi-shot echo-planar imaging (EPI) sequence with fat-suppression (FS) with the 3D-fat-suppressed gradient echo (GRE-FS) sequence in imaging the cartilage of the knee. One hundred sixty-nine patients were studied prospectively. The cartilage was imaged in the sagittal plane with: (a) 3D-T1-EPI-FS and (b) 3D-T1-GRE-FS sequences using a 1T MR scanner. The signal-to-noise ratio (SNR) of bone (b) and cartilage (c), and relative contrast (ReCon) between bone and cartilage and meniscus and cartilage were measured in 60 patients with arthroscopically normal cartilage. The imaging accuracy was assessed by comparing with linear regression analysis (length and depth) 32 defects in the cartilage of cadaveric (human and bovine) knees. The 3D-T1-EPI-FS provided better bone marrow signal suppression, better SNRc and better ReCon(bc) and ReCon(cm) (p<0.01). The 3D-T1-EPI-FS showed better accuracy concerning the depth of the defects and the 3D-T1-GRE-FS better accuracy concerning the length of the defects. In conclusion, the 3D-T1-EPI-FS pulse sequence could be included in the routine protocol in imaging the cartilage of the knee because it achieves high SNR of the cartilage and high ReCon compared to the surrounding structures, at a reduced scan time.

Objective: To assess the frequency of increased signal intensity in the patellar tendon using three-dimensional T1-weighted MRI pulse sequences., Design and Patients: Sixty patients were examined with a 1.0 T scanner (15 mT/m gradient strength) using a quadrature coil. Three pulse sequences were applied in the sagittal plane: PD turbo spin echo (PD-TSE), 3D T1-weighted gradient echo with fat suppression (3D-T1-FFE-FS) and 3D T1-weighted echo planar imaging with fat suppression (3D-T1-EPI-FS). The high signal intensity areas were measured in their maximum length. The angle of the patellar tendon relative to the main field position was measured in the same slice. In eight patients with anterior knee pain, and in 11 with no anterior knee pain, a fourth T2-weighted TSE pulse sequence (T2-TSE) was obtained to rule out patellar tendinitis., Results: The correlation of the high signal intensity areas with the relative position of the tendon was found to be significant with the 3D sequences (P = 0.03 for 3D-T1-FFE-FS and P = 0.003 for 3D-T1-EPI-FS). The length of the high signal intensity area in the tendon was 5.4 mm with 3D-T1-FFE-FS, 4.9 mm with 3D-T1-EPI-FS and 3.1 mm with PD-TSE images. No patellar tendinitis was demonstrated on the T2-TSE images., Conclusion: The magic angle effect is commonly observed in the 3D based T1-weighted pulse sequences with fat suppression. The presence of the above sign must be recognized by radiologists, so that misdiagnosis of patellar tendinitis is avoided.