Table 3

MRI evaluation protocol

MRI findingMRI sequencesDefinition
Bone marrow oedema grade 0–3Coronal STIR and T1
Axial oblique T2 FS and PD FS
Presence of high (increased) diffuse signal intensity on fluid-sensitive sequences (and decreased signal intensity on T1-weighted sequences) in pubic bone in relation to the symphyseal joint. This hyperintensity is compared with the surrounding bone marrow in the pelvic ring, allowing for variations related to physiological age-related yellow/red bone marrow distribution. Imaging artefacts should be taken into account. BMO is considered to be symphyseal-related when it is located adjacent to the symphyseal joint margins. It does not need to involve the joint margins along their entire length but can be seen as drop-shaped smaller areas of increased signal intensity. BMO should be distinguished from a parasymphyseal high-intensity line.
Measurement: The extent of BMO is measured on axial oblique sequences on PD FS or T2 FS sequences (because of more artefacts on Coronal STIR), along the long axis of the superior pubic ramus or the inferior pubic ramus. The sequence/slice with the largest visible area of higher signal intensity is selected by the observer, and the grade is determined according to this largest area. The observer draws a line parallel to the long axis of the superior or inferior pubic ramus, passing midway from the anterior and posterior margins of the pubic ramus. The extent of BMO is measured from the intersection point of this line and the symphyseal bony joint surface along the line as the longest distance where increased signal intensity is visible. The grade of BMO is determined according to this distance:
Grade 0: no BMO, Grade 1: BMO≤1 cm, grade 2: BMO ≥1 cm and ≤2 cm, grade 3: BMO ≥2 cm.
Fatty infiltration in bone marrow around the symphyseal jointCoronal T1 and STIR
Axial oblique T2 FS and PD FS
Presence of areas of high signal intensity in relation to the symphysis on T1 and low signal intensity on FatSat sequences. Fatty infiltration is only considered present if both signal intensity changes can be seen (eg, decreased signal intensity on Fatsat images alone is insufficient) and if it is immediately adjacent to the symphyseal joint. If areas of high signal intensity on T1 are seen within the BM but distant from the symphysis, they are considered islands of fat in the BM and not fatty infiltration in relation to the joint.
Symphyseal sclerosisCoronal T1
Axial oblique T1
Presence of bony sclerosis along the symphyseal joint margins. It is best visualised on T1W images (thickened articular bone). Sclerosis is seen as increased hypointense bone formation (increased thickness) along the margins of the symphyseal joint compared to a normal joint. It is often irregular in shape.
Parasymphyseal high-intensity lineAxial oblique PD FS
Coronal STIR and Coronal T1
Presence of a high-intensity line on fluid-sensitive sequences, located within the pubic bone underlying and parallel to the contour of the articular bony surface of the symphyseal joint (subchondral bone plate). There is no visible communication between this high-intensity line and the symphyseal joint space, as they are separated by a hypo-intense line visible on T1 and fluid-sensitive sequences, representing bony tissue.
Secondary cleft signCoronal STIR
Axial oblique PD FS
Verify on Sagittal STIR
Presence of a high signal intensity line extending laterally and inferiorly from the inferior part of the symphysis on fluid-sensitive sequences, in connection with the symphyseal joint space. This hyperintense line should communicate with the symphyseal joint space, meaning that the line can be tracked all the way from the joint space and out into the cleft. If a high-intensity line mimicking the above is found to be separated completely from the symphyseal joint space, it is not described as a secondary cleft sign. The secondary cleft sign is located inferior to the symphysis, and inferiorly and posteriorly from the adductor longus attachment site.
Subchondral cysts/joint surface irregularitiesCoronal STIR
Axial oblique PD FS
Presence of subchondral cysts (subchondral cystic focal elements hyperintense on T2W images), and/or presence of joint surface irregularities (areas of uneven joint surfaces/irregular cartilage on the symphyseal joint surfaces visible on T1 and PD W images. Joint surfaces should normally be smooth and linear).
Central disc protrusionCoronal T1
Axial oblique T1
Protruding central fibrous symphyseal disc. On coronal images, the central disc is bulging cranially compared to the symphyseal joint margins. On axial/oblique axial sequences, it protrudes posteriorly.
Adductor longus tendinopathyAxial oblique PD FS, T2 Fatsat and T1
Coronal T1
Presence of increased signal intensity within the adductor tendon/enthesis (intrasubstance) on fluid-sensitive and T1W sequences and/or morphological bulging of the tendon/enthesis. Normal adductor tendon is black and slender/well delineated on all sequences, and appears symmetrical and triangular on oblique axial sequences (with the base of the triangle corresponding to its insertion on the anterior aspect of the pubic bone). When it bulges (convexity) and/or has increased signal intensity on fluid-sensitive sequences, it is diagnosed as pathological.
Adductor longus musculotendinous lesionAxial oblique PD FS, T2 FS
Coronal STIR
Presence of an abnormal high intensity signal on fluid-sensitive sequences at the junction of the adductor longus tendon and muscle. The high intensity signal is not located within the adductor longus tendinous structure, but in the extratendinous space.
Superior cleft signCoronal STIR
Verify on Axial oblique PD FS
Presence of a high signal intensity line on fluid-sensitive sequences extending parallel to the inferior margin of the superior pubic ramus, in connection with the symphyseal joint space. Visible on coronal STIR (verify presence on Axial oblique Fatsat).
Rectus abdominis tendinopathySagittal STIR
Verify on Axial oblique PD FS
Presence of increased signal intensity on fluid-sensitive sequences at the junction of the muscle belly and tendon of the rectus abdominis near its attachment to the pubic symphysis, or increased thickness and increased signal intensity of the rectus abdominis tendon on fluid-sensitive sequences.
Best evaluated on Sagittal STIR, where the tendon can be followed along its long axis to its insertion anteriorly on the symphysis (verify on Axial oblique Fatsat).
  • An MRI finding is only considered present (or positive) if it is visible in at least two different imaging planes. When comparing images from two differently weighted sequences in the same plane, care should be taken to use the same TP.

  • BM, bone marrow; BMO, bone marrow oedema; PD FT, proton density fat saturation; STIR, short tau inversion recovery; T1W, T1-weighted; TP, table position.

  • If the observer is in doubt as to whether a given MRI finding is present or not, this finding is considered absent.