How I diagnose meniscal tears on knee MRI

Learning co-plane attention across MRI sequences for diagnosing twelve types of knee abnormalities

Multi-sequence magnetic resonance imaging is crucial in accurately identifying knee abnormalities but requires substantial expertise from radiologists to interpret. Here, we introduce a deep learning model incorporating co-plane attention across image sequences to classify knee abnormalities. To assess the effectiveness of our model, we collected the largest multi-sequence knee magnetic resonance imaging dataset involving the most comprehensive range of abnormalities, comprising 1748 subjects and 12 types of abnormalities. Our model achieved an overall area under the receiver operating characteristic curve score of 0.812. It achieved an average accuracy of 0.78, outperforming junior radiologists (accuracy 0.65) and remains competitive with senior radiologists (accuracy 0.80). Notably, with the assistance of model output, the diagnosis accuracy of all radiologists was improved significantly (p < 0.001), elevating from 0.73 to 0.79 on average. The interpretability analysis demonstrated that the model decision-making process is consistent with the clinical knowledge, enhancing its credibility and reliability in clinical practice.

Case Report: Dislocation of lateral menisci secondary to congenital lateral tibiofemoral cartilage thickening in both knees

A 24-year-old male patient complained of mild knee pain after jogging. The subsequent knee MRI demonstrated bilateral lateral thickened tibiofemoral cartilages, evidenced by deformities of the bilateral subchondral bone beneath the lateral femoral condyle cartilage. The corresponding dislocations of almost all the left lateral meniscus and part of the right lateral meniscus to the center of the joint were detected. After excluding diagnoses of congenital ring-shaped meniscus, bucket handle tear of the C-shaped lateral meniscus, and central tear of the discoid meniscus, the displacement of all or part of the lateral meniscus into the intercondylar notch was considered a consequence of congenital thickening of the lateral superior and inferior cartilage. This case may report a new variant of knee joint pathology.

Risk factors for false positive and false negative MRI in diagnosing medial and lateral meniscal tears with concomitant ACL injury

OBJECTIVE

To determine the diagnostic performance of MRI in evaluating meniscal abnormalities in the setting of anterior cruciate ligament (ACL) injury and recognize predictors of false positive (FP) and false negative (FN) MRI diagnosis.

MATERIAL AND METHODS

Four hundred twenty patients (mean age, 27.2 years; 326 males, 94 females) who underwent arthroscopy for ACL injury between January 2017 and August 2022, and had preoperative imaging within 4 months, were retrospectively included. Images were independently interpreted by two experienced musculoskeletal radiologists, noting the presence of medial and lateral meniscal tears including tear type and location. Results were correlated with arthroscopic findings. Multivariate logistic regression was implemented to study risk factors (RF) for FP and FN MRI diagnosis.

RESULTS

The sensitivity/specificity/positive predictive value/negative predictive value/accuracy of MRI for medial meniscus tear was 97.5%/74.46%/65.63%/98.35%/82.15%; for lateral meniscus tear, it was 83.5%/93.70%/70.8%/94.55% /87.86%, with substantial interreader agreement. Female gender (odds ratio (OR), 0.434), posterior horn and posterior root tears (OR, 3.268/22.588), horizontal tear (OR, 3.134), and ramp lesion (OR, 4.964) were found RF for FP medial meniscus, and meniscal body tears (OR, 308.011) were found RF for FP lateral meniscus. RF for FN medial meniscus were meniscal tear at the posterior horn, body, and posterior root (OR, 12.371/123.000/13.045).

CONCLUSION

MRI is an effective screening tool for meniscal tears, but less accurate in detecting all medial meniscus injuries. Gender, meniscal tear location, and type increased the risk of FP medial meniscal tear on MRI, while meniscal tear location increased the risk of FP lateral meniscus and FN medial meniscus tears.

Morphological assessment of cartilage and osteoarthritis in clinical practice and research: Intermediate-weighted fat-suppressed sequences and beyond

Magnetic resonance imaging (MRI) is widely regarded as the primary modality for the morphological assessment of cartilage and all other joint tissues involved in osteoarthritis. 2D fast spin echo fat-suppressed intermediate-weighted (FSE FS IW) sequences with a TE between 30 and 40ms have stood the test of time and are considered the cornerstone of MRI protocols for clinical practice and trials. These sequences offer a good balance between sensitivity and specificity and provide appropriate contrast and signal within the cartilage as well as between cartilage, articular fluid, and subchondral bone. Additionally, FS IW sequences enable the evaluation of menisci, ligaments, synovitis/effusion, and bone marrow edema-like signal changes. This review article provides a rationale for the use of FSE FS IW sequences in the morphological assessment of cartilage and osteoarthritis, along with a brief overview of other clinically available sequences for this indication. Additionally, the article highlights ongoing research efforts aimed at improving FSE FS IW sequences through 3D acquisitions with enhanced resolution, shortened examination times, and exploring the potential benefits of different magnetic field strengths. While most of the literature on cartilage imaging focuses on the knee, the concepts presented here are applicable to all joints. KEY POINTS: 1. MRI is currently considered the modality of reference for a "whole-joint" morphological assessment of osteoarthritis. 2. Fat-suppressed intermediate-weighted sequences remain the keystone of MRI protocols for the assessment of cartilage morphology, as well as other structures involved in osteoarthritis. 3. Trends for further development in the field of cartilage and joint imaging include 3D FSE imaging, faster acquisition including AI-based acceleration, and synthetic imaging providing multi-contrast sequences.

Preoperative diagnosis of knee cartilage, meniscal, and ligament injuries by magnetic resonance imaging

PURPOSE

The purpose of the study was to report on the current accuracy measures specific to 1.5-Tesla MRI of the knee in the patient population prone to injuries of the anterior cruciate ligament (ACL), the menisci, and the articular cartilage.

METHODS

We accrued patients between January 2018 through August 2021 who underwent a preoperative MRI and were diagnosed with an articular cartilage injury either due to unevenness of articular cartilage in T2-weighted sequences or due to the irregularity of subchondral bone in T1-weighted sequences. All patients were treated arthroscopically. Sensitivity, specificity, and accuracy were calculated for the detection of ACL, meniscus, and cartilage injuries. A P-value of < 0.05 represented statistical significance.

RESULTS

One-hundred and forty-seven cases which included 150 knee joints were enrolled in this study. The mean age at the time of surgery was 42.9 years-old. The sensitivity in the diagnosis of ACL injuries was significantly greater than that in the diagnosis of cartilage injuries (P = 0.0083). The ratios of the equality of operative indication in 6 recipient sites were found to be between 90.0% and 96.0%. The diagnostic critical point was within a 1 cm in diameter.

CONCLUSION

The diagnostic sensitivity in cartilage injuries was significantly lower than ones of ACL and meniscal injuries. The ratios of the equality of operative indication was determined to be between 90.0% and 96.0%, if we consider the unevenness of articular cartilage or the irregularity of subchondral bone.

LEVEL OF EVIDENCE

Level III, Prospective diagnostic cohort study.

Changing primary care requesting practices for MRI knee: A quality improvement project

OBJECTIVES

The objectives of this work were first to examine referral practices from primary care for MRI knee in patients ≥45 years old and then to develop a new referral pathway to reduce the number of inappropriate MRI knee referrals. Following this, the aim was to re-assess the effect of the intervention and identify further areas for improvement.

METHODS

A baseline retrospective analysis of knee MRIs requested from primary care in symptomatic patients ≥45years over a two-month period was undertaken. A new referral pathway was implemented in consensus with orthopaedic specialists and the clinical commissioning group (CCG), via the CCG resource webpage and local education. Following implementation, a repeat data analysis was undertaken.

RESULTS

The number of MRI knees acquired from primary care referrals reduced by 42% after the new pathway was implemented. 67% (46/69) were compliant with the new guidelines. The number of patients having an MRI knee without a prior plain radiograph was 14/69 (20%) compared to 55/118 (47%) prior the pathway changes.

CONCLUSION

The new referral pathway reduced the number of knee MRI acquisitions in primary care patients ≥45 years by 42%. Changing the pathway has decreased the number of patients undergoing MRI knee without a prior radiograph from 47% to 20%. These outcomes bring our standards towards the evidence-based recommendations of the Royal College of Radiology and have reduced our outpatient waiting list for MRI knee.

IMPLICATIONS FOR PRACTICE

Implementing a new referral pathway with the local CCG can successfully reduce the number of inappropriate MRI knee acquisitions from primary care referrals in older symptomatic patients.

Can deep learning reduce the time and effort required for manual segmentation in 3D reconstruction of MRI in rotator cuff tears?

Background/Purpose

The use of MRI as a diagnostic tool has gained popularity in the field of orthopedics. Although 3-dimensional (3D) MRI offers more intuitive visualization and can better facilitate treatment planning than 2-dimensional (2D) MRI, manual segmentation for 3D visualization is time-consuming and lacks reproducibility. Recent advancements in deep learning may provide a solution to this problem through the process of automatic segmentation. The purpose of this study was to develop automated semantic segmentation on 2D MRI images of rotator cuff tears by using a convolutional neural network to visualize 3D models of related anatomic structures.

Methods

MRI scans from 56 patients with rotator cuff tears (T2 Linear Coronal MRI; 3.0T, 512 mm × 512 mm, and 2.5-mm slice thickness) were collected. Segmentation masks for the cuff tendon, muscle, bone, and cartilage were obtained by four orthopedic shoulder surgeons, and these data were revised by a shoulder surgeon with more than 20 years’ experience. We performed 2D and 3D segmentation using nnU-Net with secondary labels for reducing false positives. Final validation was performed in an external T2 MRI dataset (10 cases) acquired from other institutions. The Dice Similarity Coefficient (DSC) was used to validate segmentation quality.

Results

The use of 3D nnU-Net with secondary labels to reduce false positives achieved satisfactory results, even with a limited amount of data. The DSCs (mean ± SD) of the cuff tendon, muscle, bone, and cartilage in the internal test set were 80.7% ± 9.7%, 85.8% ± 8.6%, 97.8% ± 0.6%, and 80.8% ± 15.1%, respectively. In external validation, the DSC of the tendon segmentation was 82.74±5.2%.

Conclusion

Automated segmentation using 3D U-Net produced acceptable accuracy and reproducibility. This method could provide rapid, intuitive visualization that can significantly facilitate the diagnosis and treatment planning in patients with rotator cuff tears.

How to Report: Knee MRI

The knee is the most commonly examined joint with magnetic resonance imaging (MRI) and, as such, it is the joint that most trainee radiologists start reporting. This article addresses the main pathologies encountered on MRI examination of the knee, outlining the key features to note and report, as well as providing examples of terminology used to describe these findings.

MRI of the Meniscus

The menisci of the knee are accurately evaluated by MRI. Knowledge of normal anatomy, imaging parameters, imaging appearance of the normal and torn meniscus, and common anatomic variants and pitfalls are essential in obtaining the correct imaging diagnosis. There are multiple imaging signs of meniscal tear, including linear signal intensity extending to an articular surface on at least 2 images, altered meniscal shape, displaced meniscal flap, ghost meniscus, meniscal extrusion, and parameniscal cyst. After surgery, granulation tissue may mimic tear. Diagnosis is improved by comparison to preoperative images, operative note, and intra-articular contrast administration.

A review of strategies for development of tissue engineered meniscal implants

The meniscus is a key stabilizing tissue of the knee that facilitates proper tracking and movement of the knee joint and absorbs stresses related to physical activity. This review article describes the biology, structure, and functions of the human knee meniscus, common tears and repair approaches, and current research and development approaches using modern methods to fabricate a scaffold or tissue engineered meniscal replacement. Meniscal tears are quite common, often resulting from sports or physical training, though injury can result without specific contact during normal physical activity such as bending or squatting. Meniscal injuries often require surgical intervention to repair, restore basic functionality and relieve pain, and severe damage may warrant reconstruction using allograft transplants or commercial implant devices. Ongoing research is attempting to develop alternative scaffold and tissue engineered devices using modern fabrication techniques including three-dimensional (3D) printing which can fabricate a patient-specific meniscus replacement. An ideal meniscal substitute should have mechanical properties that are close to that of natural human meniscus, and also be easily adapted for surgical procedures and fixation. A better understanding of the organization and structure of the meniscus as well as its potential points of failure will lead to improved design approaches to generate a suitable and functional replacement.

Five Overlooked Injuries on Knee MRI

This article highlights five knee injuries that, in the author's experience, are commonly overlooked by readers inexperienced in knee MRI: ramp lesions, meniscocapsular tears, meniscal root ligament tears, posterior capsular ligament tears, and partial anterior cruciate ligament tear. While these injuries are readily apparent when the images are assessed for the given abnormality, the author's belief is that these may be overlooked because either the injury is not considered, or the affected area is not closely inspected. While these injuries may not alter immediate clinical management or require surgical intervention, they may, nevertheless, result in patient symptoms and may potentially increase the risk of further knee injury. Further, these injuries are difficult to recognize clinically and arthroscopically. In this review, we present these five injuries, emphasising relevant anatomy, normal MRI appearances, common injury patterns, and tips to avoid their being overlooked. Routine review of these areas when interpreting knee MRI, with additional imaging as necessary, will allow these injuries to be recognized more regularly.

Intra-substance meniscal changes and their clinical significance: a meta-analysis

The degeneration of radial tie fibres of the central meniscal layer, and thinning of its lamellar layer results in increased intensity signals on magnetic resonance imaging, making it difficult to differentiate from true meniscal tear. This study aimed to assess the rate of encountered MRI grades 1 and 2 intrasubstance meniscal changes, and to set guidelines to report these changes based on predicted clinical outcome. A systematic review approach was employed using search engines, libraries, and databases (Google Scholar, ERIC, PubMed, and Medline) to search for scholarly sources on meniscal lesions and their significance in MRI published between 1 January 2000 and 30 June 2019. It retrieved 2750 abstracts, out of which 2738 were excluded and 13 studies meeting inclusion criteria were meta-analysed. It found an association between intrasubstances meniscal changes and outcomes. It resulted that intrasubstance meniscal changes were preservable through the protective functioning of the meniscus. Other than weight gain, no other significant risk factor of developing true meniscal tears later in life was found. It is important to examine intrasubstance meniscal change when patients suffer from mechanical meniscal symptoms especially in old age.

Accuracy measures of 1.5-tesla MRI for the diagnosis of ACL, meniscus and articular knee cartilage damage and characteristics of false negative lesions: a level III prognostic study

BACKGROUND

MRI is the most accurate imaging modality for diagnosing knee pathologies. However, there is uncertainty concerning factors predicting false negative MRI, such as meniscal tear patterns as well as patient factors. The aims of this study were to report 1.5-Tesla MRI accuracy of ACL, meniscus and articular cartilage damage and characterize false negative lesions.

METHODS

Two hundred eighteen consecutive knee arthroscopies performed in our institution between 2013 and 2016 and their respective prospectively-collected MRI reports were reviewed. Inclusion criteria were age > 15 years-old, primary arthroscopy, 1.5-Tesla MRI performed at the same institution, and time interval MRI-surgery < 6 months. Exclusion criteria were revision arthroscopy and arthroscopic-assisted fracture fixation or multiligament surgery. Accuracy measures and Kappa coefficients were calculated comparing the MRI diagnosis to the arthroscopic findings. Moreover, the arthroscopic findings of false negative MRI were compared to the findings of true positive MRI using the Fisher-exact test. Pearson correlation was used for testing the correlation between MRI accuracy and patient age.

RESULTS

The highest accuracy was observed in medial meniscus and in ACL findings. For the medial meniscus sensitivity, specificity, agreement, and Kappa coefficient were 77, 92, 86%, and 0.7, and for the ACL these measures were 82, 97, 87%, and 0.73. MRI accuracy was lower in the lateral meniscus and articular cartilage with Kappa coefficient 0.42 and 0.3, respectively. More specifically, short peripheral tears in the posterior horn of the medial meniscus were characteristic of false negative findings compared to true positive findings of the MRI (p <  0.01). MRI accuracy correlated negatively compared to arthroscopic findings with patient age for the medial meniscus (r = - 0.21, p = 0.002) and for articular cartilage damage (r = - 0.45, p <  0.001).

CONCLUSION

1.5-Tesla MRI will accurately diagnose ACL and medial meniscal tears and can reliably complete the diagnostic workup following physical examination, particularly in young adults. This modality however is not reliable for diagnosing short peripheral tears at the posterior horn of the medial meniscus and partial thickness articular cartilage lesion of the femoral condyles. For these lesions, definitive diagnosis may require cartilage-specific MRI sequences or direct arthroscopic evaluation.

LEVEL OF EVIDENCE

Prognostic study, Level III.

The prevalence and characteristics of osseous erosions associated with parameniscal cysts on knee MRI

OBJECTIVES

To determine the prevalence and characteristics of erosions associated with parameniscal cysts (PMCs) and to evaluate the profile of the associated meniscal tears MATERIALS AND METHODS: PACS database was reviewed for knee MRI scans performed over a 5-year period identifying those with PMCs in patients aged 18 years and above. The scans with PMCs were evaluated for the presence of associated osseous erosions. These erosions and PMCs were then analyzed.

RESULTS

The search revealed 6773 knee MRI examinations, of which 555 had confirmed PMCs. There were 7 PMC-associated erosions for a prevalence of 1.3% (95% CI 0.6, 2.6). All erosions involved the proximal tibia. Three of 7 erosions had underlying marrow edema, and 4 out of 7 had an overhanging margin. The mean dimension of all PMCs was 13 mm (SD = 11). The mean dimension of PMCs associated with erosions was 38 mm (SD = 22), while that of PMCs without erosions was 12 mm (SD = 10) (P < 0.001, Wilcoxon rank sum test). Ninety-three percent (95% CI 90.5, 94.8) of PMCs had associated meniscal tears, most commonly of the horizontal type (57%). All PMCs with underlying erosions were associated with meniscal tears, most commonly complex type tears (5/7).

CONCLUSION

Erosions can rarely be associated with contiguous parameniscal cysts (PMCs). These cysts are significantly larger compared with those without underlying erosions.

Magnetic resonance imaging of the knee

Knee pain is frequently seen in patients of all ages, with a wide range of possible aetiologies. Magnetic resonance imaging (MRI) of the knee is a common diagnostic examination performed for detecting and characterising acute and chronic internal derangement injuries of the knee and helps guide patient management. This article reviews the current clinical practice of MRI evaluation and interpretation of meniscal, ligamentous, cartilaginous, and synovial disorders within the knee that are commonly encountered.

Illustrative review of knee meniscal tear patterns, repair and replacement options, and imaging evaluation

This review article aims to reinforce anatomical concepts about meniscal tears while linking associated treatment options. The main teaching points start with the basic meniscal anatomy and key differences between the medial and lateral menisci. Subsequently, various meniscal tear patterns along with their associated history and physical exam findings will be discussed with corresponding illustrations and MR images. Additional discussion will involve the different surgical repair techniques (with arthroscopic correlates), their indications with pertinent imaging findings, imaging related to previous meniscal tear repairs, and novel surgical techniques. Lastly, keys to evaluating for retear with an emphasis on MRI arthrogram findings will be reviewed. While each of these topics is not discussed in totality, the key points of the review article will enforce key concepts and help radiologists evaluate the menisci on imaging.

Magnetic resonance imaging of the meniscal roots

The meniscal roots and supporting structures anchor the menisci to the tibial plateau and resist hoop stress, thereby preventing radial displacement of the menisci and secondary degenerative tibiofemoral compartment changes that may occur if this is compromised. The anatomy of the four meniscal roots and their supporting structures on magnetic resonance imaging (MRI) will be outlined in this review article, as well as the imaging appearances of meniscal root-related pathology, namely meniscal root degeneration and tears, meniscal extrusion and tibial plateau cystic lesions.

Reliability of meniscus tear description: a study using MRI from the Osteoarthritis Initiative

Despite being one of the most common indications for surgery, data on the types of meniscus tear that should be treated surgically are limited. Improving patient selection requires agreement on meniscus tear description. This study evaluates a simple MRI tear classification system for inter-observer agreement. Knee MRI examinations from 57 subjects from the Osteoarthritis Initiative cohort were reviewed by two sub-specialty trained, musculoskeletal radiologists. Based on two pulse sequences, each meniscus was classified by: tear or no tear; location of tear in anterior, middle or posterior third or multiple thirds; and displaced or non-displaced radial, horizontal, longitudinal or complex tear pattern. A tear was defined as signal abnormality extending to the surface on at least two images and displacement as more than 2 mm of extrusion or separation measured orthogonal to the tear plane. Kappa, weighted Kappa and percentage agreement were calculated. For the medial meniscus, Kappa and percentage agreement estimates were, respectively: the presence of tear, 0.79 and 89.5%; tear with displacement, 0.70 (weighted Kappa) and 66.0%; tear description, 0.47 and 61.4%; tear location, 0.64 and 79.0%. For the lateral meniscus, estimates were: the presence of tear, 0.75 and 89.5%; tear with displacement, 0.81 (weighted Kappa) and 86.0%; tear description, 0.56 and 78.9%; tear location, 0.74 and 87.7%. The strength of agreement between readers was moderate to substantial underscoring the challenge of meniscus tear classification.

The accuracy of magnetic resonance imaging diagnosis of non-osseous knee injury at Steve Biko Academic Hospital

Background

Preoperative magnetic resonance imaging (MRI) has internationally been proven to reduce unnecessary knee arthroscopies and assist with surgical planning. This has the advantage of avoiding unnecessary surgery and the associated anaesthetic risk, as well as reducing costs. No data were found in the recently published literature assessing the accuracy of MRI interpretation of knee ligament injury in the public sector locally.

Objectives

This pilot study aimed to determine the accuracy of MRI in detecting non-osseous knee injury in a resource-limited tertiary-level academic hospital in Pretoria, South Africa, compared to the gold standard arthroscopy findings.

Method

This was an exploratory retrospective analysis of 39 patients who had MRI and arthroscopy at Steve Biko Academic Hospital (SBAH). True positive, true negative, false positive and false negative results were extrapolated from findings in both modalities and translated into sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for each structure.

Results

Negative predictive values were recorded as 97%, 81%, 90% and 100% (anterior cruciate ligament [ACL], medial meniscus [MM], lateral meniscus [LM] and posterior cruciate ligament [PCL], respectively), which were comparative to recently published international literature. The PPV results were lower than those previously evaluated at 55%, 58%, 55% and not applicable. The sensitivities and specificities of the ligaments were 83%, 58%, 83% and not applicable; and 87%, 81%, 70% and not applicable, respectively.

Conclusion

Magnetic resonance imaging was found to be sensitive and specific, with a high NPV noted in all structures evaluated. Negative results can therefore be used to avoid unnecessary surgery to the benefit of the patient and state. The study reiterates that high accuracy can be obtained from MRI on a 1.5-tesla non-dedicated scanner, with interpretation by generalist radiologists.

Medial meniscal extrusion and spontaneous osteonecrosis of the knee

PURPOSE

Causes of spontaneous osteonecrosis of the knee (SONK) have not been clearly elucidated. This study investigated the relationship between medial meniscal extrusion and SONK.

METHODS

We reviewed 108 SONK knees and determined their Aglietti stage. Meniscal extrusion is defined when it extends beyond the medial margin of tibial plateau and osteophytes are excluded for determining the margin. Both absolute extrusion (AE) and relative percentage of extrusion (RPE) were measured, and meniscal tear patterns were evaluated in the early stages of SONK (I and II).

RESULTS

All knees had meniscal extrusion. Stage I was detected in 39 knees; II, in 23; III, in 16; IV, in 18; and V, in 12. The mean AE and RPE were 4.2 mm and 42% in stage I, 5.0 mm and 52% in stage II, 6.8 mm and 71% in stage III, 7.0 mm and 69% in stage IV, and 7.8 mm and 80% in stage V, respectively. The knees in the early stages showed less AE and RPE than those in late stages IV (p < 0.05) and V (p < 0.01). Additionally, the level of AE (ρ = 0.63, p < 0.0001) and RPE (ρ = 0.58, p < 0.0001) correlated with the SONK stage. Of knees with early-stage SONK, 12 knees had no tear, 26 had horizontal tears, 1 had longitudinal tear, 6 had degenerative tears, 2 had radial tears, 1 had complex tear, and 14 had root tears. Neither AE nor RPE differed significantly among tear patterns.

CONCLUSIONS

Meniscal extrusion was recognized even in early stages, with a significant correlation between the SONK stage and extrusion. Although the most frequent tear pattern in early-stage SONK was horizontal tear, 12 knees had meniscal extrusion with no tears. Therefore, meniscal extrusion, which indicates meniscal dysfunction, may be a cause of SONK and be related with the developmental stage of SONK.

MRI comparison of injury mechanism and anatomical factors between sexes in non-contact anterior cruciate ligament injuries

Non-contact anterior cruciate ligament (ACL) rupture is mostly caused by a pivot shift mechanism including valgus collapse and internal tibial rotation. In female athletes, the incidence of ACL rupture has been reported to be significantly higher than in their male counterparts. However, to date, there have been limited reports and controversy regarding sex differences underlying injury mechanisms of ACL and severity of injury. In this study, we hypothesized that 1) in patients with non-contact ACL rupture, the incidence and severity of pivot shift injury, which are determined by injury pattern on MRI, would be significantly higher in females, and 2) anatomical factors associated with pivot shift injury would be significantly associated with female sex. A total of 148 primary ACL ruptures (145 patients) caused by non-contact injury mechanisms were included in this study. Among them, 41 knees (41 patients) were female and 107 knees (104 patients) were male. The status of the osseous lesions, lateral and medial tibial slope, depth of the medial tibial plateau, collateral ligaments, and menisci were assessed by MRI and compared between sexes. The severity of osseous lesions at the lateral tibial plateau, lateral femoral condyle, medial tibial plateau, and medial femoral condyle were comparable between sexes. There were no significant differences between sexes in the location of tibial contusions (p = 0.21), femoral contusions (p = 0.23), or meniscus tears (p = 0.189). Lateral tibial slope was found to be significantly larger in females (8.95° vs. 6.82°; p<0.0001; odds ratio = 1.464), and medial tibial depth was significantly shallower in females (1.80mm vs. 2.41mm; p<0.0001; odds ratio = 0.145). In conclusion, females showed greater lateral tibial slope and shallower medial tibial depth compared to males, however it did not affect the sex differences in injury pattern.

Clinics in diagnostic imaging (177). Medical meniscus bucket-handle tear with medial oblique meniscomeniscal ligament

A 29-year-old man with a previous football injury to his left knee presented with pain of the same knee. The patient twisted it as he was turning a corner quickly while going up the stairs, leading to internal rotation of his femur on his tibia with his knee in flexion. MR imaging revealed a bucket-handle tear of the medial meniscus, as well as a complete tear of the anterior cruciate ligament. However, image interpretation was complicated by the presence of a medial oblique meniscomeniscal ligament, a rare normal variant among intermeniscal ligaments of the knee. All four recognised variants of intermeniscal ligaments are discussed, with emphasis on their prevalence, imaging and anatomical features, and the way in which they may mimic meniscal tears.

Traumatic Meniscus and Cruciate Ligament Tears in Young Patients: A Comparison of 3T Versus 1.5T MRI

Objective:

To compare diagnosis value of 1.5T and 3T MRI in the detection of traumatic knee injuries in young patients by reference to arthroscopy.

Materials and Methods:

One hundred patients were prospectively included. All patients randomly underwent standardized knee 1.5T or 3T MRI with subsequent knee arthroscopy. Meniscus and cruciate ligaments tears were blindly assessed by two independent musculoskeletal radiologists.

Results:

Comparison of 1.5T and 3T MRI groups in the diagnosis of medial and lateral meniscal tears showed significantly higher sensitivity (p = 0.015) of 1.5T MRI in the diagnosis of lateral meniscal tears. Sensitivity and specificity for complete ACL tears were 100 percent [35/35] and 100 percent [23/23] at 1.5T MRI (p = < 0.0001) versus 95.5 percent [21/22] and 100 percent [16/16] at 3T MRI (p = < 0.0001).

Only three complete PCL tears were observed in this study. Sensitivity and specificity for all complete CL tears were 100 percent [37/37]; 100 percent [77/77] for 1.5T MRI (p < 0.0001); and 95.7 percent [22/23] and 100 percent [59/59] for 3-T MRI (p < 0.0001). Diagnosis value of 1.5T and 3T MRI was equal for ACL and PCL complete tears.

Conclusion:

Diagnosis value of 1.5T was similar to 3T MRI for medial meniscal and cruciate ligament tears of the knee in symptomatic patients and higher for lateral meniscal tears.

Magnetic resonance imaging of the knee: An overview and update of conventional and state of the art imaging

Magnetic resonance imaging (MRI) has become the preferred modality for imaging the knee to show pathology and guide patient management and treatment. The knee is one of the most frequently injured joints, and knee pain is a pervasive difficulty that can affect all age groups. Due to the diverse pathology, complex anatomy, and a myriad of injury mechanisms of the knee, the MRI knee protocol and sequences should ensure detection of both soft tissue and osseous structures in detail and with accuracy. The knowledge of knee anatomy and the normal or injured MRI appearance of these key structures are critical for precise diagnosis. Advances in MRI technology provide the imaging necessary to obtain high-resolution images to evaluate menisci, ligaments, and tendons. Furthermore, recent advances in MRI techniques allow for improved imaging in the postoperative knee and metal artifact reduction, tumor imaging, cartilage evaluation, and visualization of nerves. As treatment and operative management techniques evolve, understanding the correct application of these advancements in MRI of the knee will prove to be valuable to clinical practice.

LEVEL OF EVIDENCE

5 J. MAGN. RESON. IMAGING 2017;45:1257-1275.

A systematic review and meta-analysis of the diagnostic accuracy of MRI for suspected ACL and meniscal tears of the knee

PURPOSE

To determine the diagnostic accuracy of magnetic resonance imaging (MRI) and ultrasound (US) in the diagnosis of anterior cruciate ligament (ACL), medial meniscus and lateral meniscus tears in people with suspected ACL and/or meniscal tears.

METHODS

MEDLINE, Web of Science and the Cochrane library were searched from inception to March 2014. All prospective studies of the diagnostic accuracy of MRI or US against arthroscopy as the reference standard were included in the systematic review. Studies with a retrospective design and those with evidence of verification bias were excluded. Methodological quality of included studies was assessed using the QUADAS-2 tool. A meta-analysis of studies evaluating MRI to calculate the pooled sensitivity and specificity for each target condition was performed using a bivariate model with random effects. Sub-group and sensitivity analysis were used to examine the effect of methodological and other study variables.

RESULTS

There were 14 studies included in the meta-analysis of the accuracy of MRI for ACL tears, 19 studies included for medial meniscal tears and 19 studies for lateral meniscal tears. The summary estimates of sensitivity and specificity of MRI were 87 % (95 % CI 77-94 %) and 93 % (95 % CI 91-96 %), respectively, for ACL tears; 89 % (95 % CI 83-94 %) and 88 % (95 % CI 82-93 %), respectively, for medial meniscal tears; and 78 % (95 % CI 66-87 %) and 95 % (95 % CI 91-97 %), respectively, for lateral meniscal tears. Magnetic field strength had no significant effect on accuracy. Most studies had a high or unclear risk of bias. There were an insufficient number of studies that evaluated US to perform a meta-analysis.

CONCLUSION

This study provides a systematic review and meta-analysis of diagnostic accuracy studies of MRI and applies strict exclusion criteria in relation to the risk of verification bias. The risk of bias in most studies is high or unclear in relation to the reference standard. Concerns regarding the applicability of patient selection are also present in most studies.

LEVEL OF EVIDENCE

III.

MR T1ρ and T2 of meniscus after acute anterior cruciate ligament injuries

OBJECTIVE

To evaluate differences in meniscal T1ρ and T2 quantification in patients with acute anterior cruciate ligament (ACL) injuries and to determine correlations of these differences with MR morphological grading and patient-reported outcomes.

DESIGN

Bilateral knees of 52 patients with acute ACL injury and 20 healthy controls were scanned using 3 T magnetic resonance imaging (MRI) T1ρ and T2 mapping in this prospective study. Quantitative analysis of the meniscus was performed in anterior and posterior horns of the lateral and medial menisci. Morphological meniscal damage was assessed using modified whole-organ MRI scores (WORMS). Measurements were compared between injured, uninjured contralateral, and control knees using a mixed-effects regression model. Correlations between meniscal T1ρ/T2, WORMS and Knee Injury and Osteoarthritis Outcome Scores (KOOS) were examined using partial correlation analysis.

RESULTS

Mean meniscal T1ρ and T2 values were significantly higher in ACL-injured knees compared to control and contralateral knees. Menisci of ACL-injured knees without tears, including those limited to modified meniscal WORMS grade 0, also had significantly higher T1ρ and T2 values compared to menisci of uninjured knees. Within ACL-injured knees, T1ρ and T2 values showed significant positive associations with meniscal WORMS and significant negative associations with KOOS.

CONCLUSION

Acute ACL injuries are associated with significantly increased meniscal T1ρ and T2 values in both patients with and without meniscal lesions or tears, suggesting quantitative MRI provides more sensitive measures of meniscal differences compared to traditional morphological MRI sequences. Correlation between meniscal T1ρ/T2 and KOOS suggest that quantitative MRI is reflective of the extent of patients' clinical symptoms.

Reporting knee meniscal tears: technical aspects, typical pitfalls and how to avoid them

Magnetic resonance imaging (MRI) is the most accurate imaging technique in the diagnosis of meniscal lesions and represents a standard tool in knee evaluation. MRI plays a critical role in influencing the treatment decision and enables information that would obviate unnecessary surgery including diagnostic arthroscopy. An accurate interpretation of the knee depends on several factors, starting with technical aspects including radiofrequency coils, imaging protocol and magnetic field strength. The use of dedicated high-resolution orthopaedic coils with a different number of integrated elements is mandatory in order to ensure high homogeneity of the signal and high-resolution images. The clinical imaging protocol of the knee includes different MRI sequences with high-spatial resolution in all orientations: sagittal, coronal, and axial. Usually, the slice thickness is 3 mm or less, even with standard two-dimensional fast spin echo sequences. A common potential reason for pitfalls and errors of interpretation is the unawareness of the normal tibial attachments and capsular attachment of the menisci. Complete description of meniscal tears implies that the radiologist should be aware of the patterns and the complex classification of the lesions.

TEACHING POINTS

• Technical factors may influence MRI interpretation. • Unawareness of the normal meniscal anatomy may lead to errors of interpretation. • Description of meniscal tears implies the knowledge of meniscal tear classification.

Rotator cuff tear shape characterization: a comparison of two-dimensional imaging and three-dimensional magnetic resonance reconstructions

BACKGROUND

The purpose of this study was to see if 3-dimensional (3D) magnetic resonance imaging (MRI) could improve our understanding of rotator cuff tendon tear shapes. We believed that 3D MRI would be more accurate than two-dimensional (2D) MRI for classifying tear shapes.

METHODS

We performed a retrospective review of MRI studies of patients with arthroscopically proven full-thickness rotator cuff tears. Two orthopedic surgeons reviewed the information for each case, including scope images, and characterized the shape of the cuff tear into crescent, longitudinal, U- or L-shaped longitudinal, and massive type. Two musculoskeletal radiologists reviewed the corresponding MRI studies independently and blind to the arthroscopic findings and characterized the shape on the basis of the tear's retraction and size using 2D MRI. The 3D reconstructions of each cuff tear were reviewed by each radiologist to characterize the shape. Statistical analysis included 95% confidence intervals and intraclass correlation coefficients.

RESULTS

The study reviewed 34 patients. The accuracy for differentiating between crescent-shaped, longitudinal, and massive tears using measurements on 2D MRI was 70.6% for reader 1 and 67.6% for reader 2. The accuracy for tear shape characterization into crescent and longitudinal U- or L-shaped using 3D MRI was 97.1% for reader 1 and 82.4% for reader 2. When further characterizing the longitudinal tears as massive or not using 3D MRI, both readers had an accuracy of 76.9% (10 of 13). The overall accuracy of 3D MRI was 82.4% (56 of 68), significantly different (P = .021) from 2D MRI accuracy (64.7%).

CONCLUSION

Our study has demonstrated that 3D MR reconstructions of the rotator cuff improve the accuracy of characterizing rotator cuff tear shapes compared with current 2D MRI-based techniques.

Ring-shaped lateral meniscus with hypoplasic anterior cruciate ligament

Knee joint lesions can be solitary or occur concomitantly with other lower limb abnormalities. Ring-shaped lateral meniscus (RSM) and hypoplasic anterior cruciate ligament (ACL) are two rare malformations. The therapeutic management of such abnormalities is not consensual, and highly depends on clinical symptomatology. We report a case of a 25-year-old girl with progressive knee pain whose MRI demonstrated a continuous segment of lateral meniscus situated along the medial aspect of the lateral compartment, continuous with the otherwise normal-appearing lateral meniscus, compatible with an RSM. This anatomic variant can be mistaken by a displaced meniscal fragment, like a bucket-handle tear, a central tear of a discoid meniscus, or incomplete discoid meniscus, as previously reported. Her MRI examination also showed a thinned ACL with anomalous lateral course. This abnormality may be mistaken for an ACL rupture and/or a meniscofemoral ligament with agenesis of ACL. Multiple images in different planes as well as following the course of meniscal and ligaments are critical clues to avoid misdiagnosis. As a result, the diagnosis of an RSM along with hypoplasic ACL with abnormal attachment was assumed based on MRI and confirmed during arthroscopy. The patient was treated conservatively with clinical outcome improvement.

ISAKOS classification of meniscal tears-illustration on 2D and 3D isotropic spin echo MR imaging

Magnetic Resonance Imaging is modality of choice for the non-invasive evaluation of meniscal tears. Accurate and uniform documentation of meniscal pathology is necessary for optimal multi-disciplinary communication, to guide treatment options and for validation of patient outcomes studies. The increasingly used ISAKOS arthroscopic meniscus tear classification system has been shown to provide sufficient interobserver reliability among the surgeons. However, the terminology is not in common use in the radiology world. In this article, the authors discuss the MR imaging appearances of meniscal tears based on ISAKOS classification on 2D and multiplanar 3D isotropic spin echo imaging techniques and illustrate the correlations of various meniscal pathologies with relevant arthroscopic images.

A biomechanical approach to interpreting magnetic resonance imaging of knee injuries

This article discusses common injury mechanisms and the subsequent constellation of magnetic resonance (MR) imaging findings in the knee following trauma in the context of instability, as distinguished by the degree of knee flexion and tibial rotation at the time of initial injury, in addition to the direction and magnitude of the responsible force vectors. Using 3-dimensional imaging, common injury mechanisms are illustrated and correlated with MR imaging findings of the resulting osteochondral, ligamentous, meniscal, and musculotendinous lesions. The most common classification and grading systems for these individual lesions and their subsequent treatment implications are discussed.

The shiny corner of the knee: a sign of meniscal osteochondral unit dysfunction

OBJECTIVE

The purpose of this retrospective study is to describe the MRI findings of the "shiny corner" of the knee (bone marrow lesions at the meniscal-covered portions of the tibial plateau) and to determine its association with compromise of the medial meniscal-osteochondral unit.

MATERIALS AND METHODS

A retrospective review of 200 knee MRI exams was performed and images were evaluated in consensus by two musculoskeletal radiologists. Presence and location of a shiny-corner lesion was recorded, which was defined as a focal, peripheral hyperintense lesion on fluid-sensitive images at the superior portion of the medial tibial plateau. Meniscal and root ligament abnormalities were recorded, including tearing, degeneration, and extrusion.

RESULTS

Sixty exams demonstrated a shiny-corner lesion. Shiny corners involved the medial rim of the medial tibial plateau in 50 cases, only involved the posterior rim in seven cases, and only involved the anterior rim in two cases. Patients with shiny corners were older than patients without shiny corners (mean, 53 years vs. 44 years, p = 0.01). The shiny-corner sign was associated with tears of the medial meniscus, root ligament, and meniscal extrusion (p < 0.001). The presence of a shiny-corner lesion could detect a tear of the medial meniscus or root ligaments with a sensitivity, specificity, positive predictive value, and negative predictive value of 62, 97, 95, and 75%, respectively.

CONCLUSIONS

Shiny-corner lesions of the knee are associated with tears of the menisci and root ligaments. This observation supports the concept that the menisci protect the underlying covered portions of the tibial plateau.

Development of a Comprehensive Osteochondral Allograft MRI Scoring System (OCAMRISS) with Histopathologic, Micro-Computed Tomography, and Biomechanical Validation

OBJECTIVE

To describe and apply a semi-quantitative MRI scoring system for multi-feature analysis of cartilage defect repair in the knee by osteochondral allografts, and to correlate this scoring system with histopathologic, micro-computed tomography (μCT), and biomechanical reference standards using a goat repair model.

DESIGN

Fourteen adult goats had two osteochondral allografts implanted into each knee: one in the medial femoral condyle (MFC) and one in the lateral trochlea (LT). At 12 months, goats were euthanized and MRI was performed. Two blinded radiologists independently rated nine primary features for each graft, including cartilage signal, fill, edge integration, surface congruity, calcified cartilage integrity, subchondral bone plate congruity, subchondral bone marrow signal, osseous integration, and presence of cystic changes. Four ancillary features of the joint were also evaluated, including opposing cartilage, meniscal tears, synovitis, and fat-pad scarring. Comparison was made with histological and μCT reference standards as well as biomechanical measures. Interobserver agreement and agreement with reference standards was assessed. Cohen's kappa, Spearman's correlation, and Kruskal-Wallis tests were used as appropriate.

RESULTS

There was substantial agreement (κ>0.6, p<0.001) for each MRI feature and with comparison against reference standards, except for cartilage edge integration (κ=0.6). There was a strong positive correlation between MRI and reference standard scores (ρ=0.86, p<0.01). OCAMRISS was sensitive to differences in outcomes between the types of allografts.

CONCLUSIONS

We have described a comprehensive MRI scoring system for osteochondral allografts and have validated this scoring system with histopathologic and μCT reference standards as well as biomechanical indentation testing.

Magnetic resonance imaging and arthroscopic appearance of the menisci of the knee

The menisci are critical for normal function of the knee, providing shock absorption and load transmission that reduce stress on the articular cartilage. When torn, a meniscus may require surgery to restore function, reduce pain, and eliminate mechanical symptoms. Patterns of meniscal tears include longitudinal and bucket-handle, which are often reparable; and horizontal, radial, vertical flap, horizontal flap, and complex. Root tears are usually radial and occur in the posterior roots. When reviewing magnetic resonance images, one must be aware of normal variants and imaging pitfalls that may simulate pathology.