Mr imaging of the postoperative knee a pictorial essay

In the femur and tibia the attachments spread out like fans or ducks foot [ 123 ]. Anatomically it is two bundled but there is an ongoing debate whether the ACL is functionally two bundled or not [ 4 ]. Injury to the ACL usually occurs due to extreme hyper-extension or a twisting trauma.

Mr imaging of the postoperative knee a pictorial essay

Chang, MD, and Ambrose J. Chang is a Radiology Resident and Dr. The contrast between the high T2 signal intensity joint fluid and the intermediate T2 signal intensity cartilage helps to assess for surface irregularities and defects of the cartilage.

MR of articular cartilage lesions of the knee

However, 3-dimensional SPGR is not typically included in imaging protocols because of decreased contrast between the cartilage and the adjacent joint fluid, long imaging times, increased metallic artifact in the case of a post-surgical kneeand uneven fat suppression, even though it is considered standard for morphologic imaging of cartilage.

Table 1 lists several MR cartilage imaging pitfalls and troubleshooting techniques. MR arthrography MRA of the knee also helps to increase sensitivity for cartilage lesions and for detection of intra-articular bodies and their donor sites, but it is also not routinely performed.

Indications for MRA include evaluation of osteochondral defects for stability and evaluation of postoperative menisci for retear. The collagen leaves extend perpendicularly from the bony surface and curve 90 degrees until they are approximately horizontal or parallel to the bone at the articular surface.

The different angles and orientations of the proteoglycans likely affect the water mobility within and the dipole-dipole interactions of the collagen fibrils, which result in the MR appearance of cartilage on a T2-weighted sequence as three poorly demarcated layers: The orientation of the cartilage relative to the orientation of the static magnetic field B0 also affects the thickness, signal intensity, and distinctness of these layers.

Mr imaging of the postoperative knee a pictorial essay

Therefore, since much of the cartilage surfaces of the knee are curved eg, the femoral condylesappearance of the articular cartilage varies. The uniformity of the collagen fiber orientation at the articular and the bony surfaces helps to elucidate the reason magic angle phenomenon affects cartilage Figure 2and the curvature of the collagen fibers also helps to explain the curved appearance of many cartilage lesions.

This finding is nonspecific, as it is often seen in asymptomatic patients; concurrent underlying marrow signal abnormality increases its specificity. The lesion can be described as a superficial defect or surface irregularity Figure 4partial-thickness defect Figure 5or full-thickness defect Figure 6.

Partial and full-thickness lesions may be associated with flap formation Figure 7. The ICRS has developed one such system, in which lesions are graded 0 to 4 based on depth of the lesion Table 2. Grade 1 and 2 lesions have excellent prognosis.

Grade 2 and 3 lesions may benefit from cartilage debridement or other more conservative surgical measures. Grade 4 lesions extend into the subchondral bone and may require bone grafting if bony cavitation is extensive. Subchondral marrow edema is more likely to be associated with higher-grade lesions30 and, in the setting of acute trauma, indicates that the lesion may be full thickness.

Since the grading of cartilage lesions is largely a matter of local practice preference and no one classification scheme is overwhelmingly used over all others, our practice reports the size, depth, and location of the cartilage lesion to allow the referring physicians to fit the lesion into their own grading system.


MRI has been shown to be an accurate method for detection of cartilage lesions. Ninety percent of lesions were within one grade between MRI and arthroscopy, and the majority of the lesions undergraded on MR imaging. In general, MRI underestimates the true dimensions of a cartilage defect due to volume averaging and challenges of imaging a curved surface.

There are some distinguishing characteristics of each category.

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An acute lesion has sharp margins oriented perpendicular to the bone surface, occurs on weight-bearing surfaces, and has subjacent bone marrow edema Figure 8. In osteoarthritis, early proteoglycan loss leads to expansion of the residual proteoglycans and increased cartilage water content, which may appear as increased cartilage thickness on MRI.

This edematous cartilage deforms more easily and is therefore more susceptible to mechanical stress and cartilage damage. Eventually, the cartilage matrix fragments. Cartilage lesions in osteoarthritis tend to be shallower and have wide, horizontal, or obtuse margins with respect to the bone surface Figure 9.

Because synovial fluid is toxic to bone marrow, subchondral cysts form if the defect extends to the subchondral bone surface.Osteochondral defect is a broad term that describes the morphological change of a localised gap in the articular cartilage and subchondral bone 5.

It is often used synonymously with osteochondral injury/defect in the paediatric population. MR Imaging of the Postoperative Knee: A Pictorial Essay1 The most common procedures include partial meniscectomy and meniscal repair, anterior cruciate ligament (ACL) .

Magnetic resonance (MR) imaging of the postoperative knee has become more common because more arthroscopic repair procedures are being performed.

The most common procedures include partial meniscectomy and meniscal repair, anterior cruciate ligament (ACL) . Introduction Magnetic resonance (MR) imaging of the knee after surgical repair is becoming more common because of the increasing number of therapeutic. Symptomatic patients might present with complications related to the graft itself such as graft failure, roof impingement, post operative stiffness, tunnel widening due to cyst formation, iliotibial band friction syndrome, hardware failure and infection.

Introduction Magnetic resonance (MR) imaging of the knee after surgical repair is becoming more common because of the increasing number of therapeutic.

Osteochondral defect | Radiology Reference Article |