Several studies have established that direct MR-arthrography is better than conventional MR to find and characterize lesions at the labrum acetabular and articular capsule-level.
Contrast solution
We usually use commercially avaivalble pre-filled syringe of diluted gadolinium based chelate contrast solution.
The amount of contrast solution is about 20 ml.
Some authors prepare a contrast solution with gadolinium chelate,
saline fluid and 0,1% lidocaine in order to increas patient confort.
Other authors add to the contrast solution iodine based solution in order to perfrom also CT-arthrography.
Fig. 1: MR-arthrography of the hip is performed injecting under ultrasonography guidance about 20 ml of contrast solution into the hip joint. We usually use commercially avaivalble pre-filled syringe of diluted gadolinium based chelate contrast solution.
Joint puncture
We inject contrast solution inside the hip joint with ultrasonography guide with 20g spinal needle.
Some authors use X-ray fluroscopy guidance.
US is more safe expecially for young patients.
Fig. 2: Joint puncture is performed under Ultrasonography guidance.US iamges of the hip joint before (on the left) and after contrast solution injection.
MRA technique
MR-arthrography is performed with T1-weighted and T2-weighted images in axial,
axial oblique parallel to femoral neck,
sagitall,
coronale and radial plane.
Fig. 3: MR sequences slab positioning in axial oblique, Sagittal, Coronal and Radial plane.
MRA Anatomy
Fig. 4: MRA Anatomy in coronal plane
Fig. 5: MRA in coronal and sagittal plane with particulr attention to the fibrocartilagineous labrum (withe arrows) and chondrolabraljoint.
MRA indications and pathological essay
Fig. 6: MRA indications
Femoroacetabular Impingement syndrome (FAI).
Clinical presentation of FAI is slow onset of inguinal pain without a clear traumatic history and presents with a typical limitation of hip flexion,
adduction and internal rotation.
Femoroacteabolar impingement (FAI) is categorized in Pincer,
Cam and mixed types (when the characteristics of the first two overlap).
Fig. 7: Femoral acetabular impingement syndrome (FAI) types.
The Pincer type is characterized by an excessive,
focal or diffuse coating of the femoral head.
Fig. 8: Pincer type femoroacetabular type (yellow arrow) with a degenerative changes in the femoral head (red arrow).
Cam type by a gibbus in the femoral head-neck joint,
causing the femur head to have a flat or convex shape.
Fig. 9: Femoral acetbular impingement sydrome: cam type with anterior bump in the femoral neck.
Acetabular labrum
It is a triangular structure with a low signal intensity in all MR sequences.
In the MRA the perilabral recess can be seen too,
that is,
the space between the articular capsule and the labrum acetabular that distends itself after injecting asolution with a contrast agent.
The presence of inter-substance contrast material in continuity with the labral surface is regarded as a tear.
Fig. 10: Chondral labral separation
The displacement,
absence or truncated shape of the labrum is regarded as indirect signs of tear.
The presence of contrast in the chondro-labral junction associated with one signal alteration of the adjacent cartilage is regarded as tear/disinsertion.
The labrum thickening with intermediate signal inter-substance areas and margin irregularity is regarded as degenerative changes.
Acetabular cartilage
Cartilage lesions on the acetabular and femoral surfaces are classified according to the Outerbridge system into 5 degrees:
Degree 0,
intactarticular cartilage;
Degree I,
hypointensity in the articular cartilage
Degree II,
ulceration,
tear or fibrillation affecting less than 50% of cartilage thickness;
Degree III,
ulceration,
tear or fibrillation affecting more than 50% of cartilage thickness
Degree IV,
absence of cartilage with bone exposure.
Fig. 11: Chondral lesions of the acetabular roof (yellow arrows) and of femoral head (red arrows).
Unlike labral lesions where MRA is superior to conventional MR,
the cartilage morphological alterations are still a diagnostic challenge for both image modalities.
The acetabular cartilage lesions and those of the femur head pose the following paradox: conventional MR is excellent and superior to arthroscopy to define bone changes secondary to chondral lesions and lesions affecting the whole cartilage thickness.
The sensitivity for low-grade cartilage lesions is lower in the arthro-MR or high-field MR as opposed to the arthroscopy.
The difficulty probably lies in the fact that the hip joint cartilage thickness is really thin compared to other joints like the knee,
that the surface is curved and that the acetabular and femoral cartilage surfaces just do not fit in.
This is why applying the modified Outerbridge classification can be really difficult especially in grades 0-II.
Synovial pathology
Synovial chondromatosis is a rare,
benign (noncancerous) condition that involves the synovium and can severely damage the affected joint and,
eventually,
lead to osteoarthritis.
Early treatment is important to help relieve painful symptoms and prevent further damage to the joint.
Fig. 12: Synovial chondromatosis. MRA allws to better detect intrarticular synovial bodies whenjoint effusion is absent.
Adhesive capsulitis of the hip (ACH) is a rare clinical entity characterized by a painful decrease in active and passive range of motion as synovial inflammation in the acute stages of the disease progresses to capsular fibrosis in the chronic stages.
Fig. 13: Adhesive capsulitis. The diagnosis is eased by resistance felt by operator during intra-articular injection of contrast solution.
Synovial hyperthrophy can be even localized on the teres ligamentum and consequentely enlarge acetabular fovea.
Fig. 14: Synovial hypertrofy on teres ligamentum (red arrows) with a wide acetabular fovea (yellow arrows).
Traumatic lesions
Diagnostic traps
Sublabral sulcus is a variant of normalcy that is usually located in the posterior-inferior region without other morphological or signal alterations in the neighboring structures.
It could be confused with a labral tear or chondrolabral separation.
Fig. 15: Sublabral sulcus is a variant of normalcy that is usually located in the posterior-inferior region without other morphological or signal alterations in the neighboring structures.
A small amount of red marrow along the edge of the fovea capitis could mimic the appearance of marrow edema.
T1-weighted images are helpful in differentiating red marrow from marrow edema.
Marrow edema in the fovea capitis is often associtaed with ligamentum teres tears.
A large pulvinar and/or large ligamentum plica in the fovea can mimick the appearance of a ligamentum teres tear on fat-suppressed images.
The not-supressed images are usefull in order to differentiate tears from pulvinar or large ligamentum plica.