ESR essentials: MRI of the knee-practice recommendations by ESSR

Abstract

Many studies and systematic reviews have been published about MRI of the knee and its structures, discussing detailed anatomy, imaging findings, and correlations between imaging and clinical findings. This paper includes evidence-based recommendations for a general radiologist regarding choice of imaging sequences and reporting basic MRI examinations of the knee. We recommend using clinicians' terminology when it is applicable to the imaging findings, for example, when reporting meniscal, ligament and tendon, or cartilage pathology. The intent is to standardise reporting language and to make reports less equivocal. The aim of the paper is to improve the usefulness of the MRI report by understanding the strengths and limitations of the MRI exam with regard to clinical correlation. We hope the implementation of these recommendations into radiological practice will increase diagnostic accuracy and consistency by avoiding pitfalls and reducing overcalling of pathology on MRI of the knee. CLINICAL RELEVANCE STATEMENT: The recommendations presented here are meant to aid general radiologists in planning and assessing studies to evaluate acute and chronic knee findings by advocating the use of unequivocal terminology and discussing the strengths and limitations of MRI examination of the knee. KEY POINTS: • On MRI, the knee should be examined and assessed in three orthogonal imaging planes. • The basic general protocol must yield T2-weighted fluid-sensitive and T1-weighted images. • The radiological assessment should include evaluation of ligamentous structures, cartilage, bony structures and bone marrow, soft tissues, bursae, alignment, and incidental findings.

Keywords: Cruciate ligaments; Evidence-based practice; Knee; Magnetic resonance imaging; Menisci.

Fig. 1

A PD (fat suppressed) sagittal image shows a horizontal high-signal intensity line in keeping with a chronic meniscal lesion (arrow). Schematic drawings of the meniscal pathology in blue below. B PD sagittal image shows a vertical (radial) high-signal line in keeping with an acute tear (arrow) which occurred after valgus trauma. The arrowhead points to a subchondral impression of the lateral femoral condyle typically occurring with ACL injury. In addition, diffuse high-signal areas are seen in femur and posterior tibia indicating oedema due traumatic bone bruise. Schematic drawings of the meniscal pathology in blue below. C PD transverse image shows a high-signal line depicting a vertical (longitudinal) meniscal tear in the medial meniscus (arrows). Schematic drawings of the meniscal pathology in blue below. D. PD transverse image shows a complex rupture, where part of the posterior meniscus is flipped anteriorly (like an s-shape, blue arrow), an unstable lesion which causes a locked knee. Schematic drawings of the meniscal pathology in blue below. E PD sagittal image shows two triangles on top of each other (yellow and white arrows) in the anterior region of the meniscus, but nothing in the posterior region, the so-called double anterior horn sign. Schematic drawings of the meniscal pathology in blue below

Fig. 2

A PD sagittal image shows high signal in the ACL, and fibre discontinuity (arrow), which was proven to be a complete ACL tear. B Same knee as in A, indirect sign of anterior tibial translation in the lateral compartment, indicating ACL deficiency (yellow line). This patient also had a lateral meniscal posterior root rupture (arrowhead), where the attachment between the meniscus and the tibia is missing, i.e. a so-called ghost sign or empty meniscus sign. C PD coronal image, different case from the previous images (A–C), shows avulsion of the cortical rim, a Segond fracture (arrow), seen adjacent to a very small area of high-signal intensity in subchondral bone. Segond avulsion has a 95% association with ACL rupture (not shown); in addition, this patient also suffered a full-thickness MCL rupture at the femoral attachment (arrow head). D PD coronal image (different patient from A–C), asterisk shows ACL rupture, LCL rupture (arrow), high-signal intensity in fibular head (arrowhead). E Same patient as in D, T1 sagittal image shows pathology in the posterolateral corner (arrows) and avulsion fracture of the fibular head (arrowheads), much better appreciated on T1

Fig. 3

A PD sagittal image (with patient movement) shows high-signal intensity (arrow) in the PCL, which was also > 8 mm in thickness in the short axis. B T1 sagittal image, which shows intermediate-intensity signal in the PCL (arrow). C T1 sagittal image In the medial compartment, there is slight malalignment of the femur and tibia, where the tibia “sags” posteriorly > 10 mm, which makes the anterior medial meniscus protrude beyond the anterior rim of the tibia > 3 mm, each are by themselves an indirect sign of PCL deficiency

Fig. 4

A PD coronal image after a previous fall shows an osteochondral defect (asterisk) with a dislodged osteochondral fragment (arrowhead). Slight oedema is also seen in the femur (arrows). B PD sagittal image shows the gap (star) left by the cartilage defect and the subchondral bone marrow oedema (arrows). C PD, the fragment seen in the sagittal plane (arrowhead). D PD, transverse plane, the largest size of defect best appreciated on this view, than on the other images, highlighting how one can underestimate the size of the cartilage defect, if one does not carefully evaluate all images

Fig. 5

A PD (fat suppressed) coronal image shows extensive oedema in the medial condyle and distal femur metaphysis and diaphysis (dotted ellipse). A discrete subchondral low signal line is also seen (arrow). B PD sagittal image shows oedema in the femur (dotted circle), no certain subchondral line. C T1-weighted sagittal image shows the same oedema and a dark subchondral curved line, which represents a subchondral insufficiency fracture line

Fig. 6

A PD (fat suppressed) sagittal image shows discontinuity of the quadriceps tendons after a direct fall on the knee (arrows). B PD (fat suppressed) sagittal image shows another patient who has had non-traumatic pain for more than 6 weeks, and subtle oedema, and a low signal line is seen in the fibular head (arrow). C On the T1-weighted sagittal image, the fracture line is much better appreciated (arrow). T1-weighted images are recommended in standard MRI of the knee, as not to miss unexpected but highly relevant findings