Extensor Carpi Ulnaris (ECU) tendinosis with interstitial tear

Extensor carpi ulnaris tendinosis is one of the common causes of ulnar sided wrist pain. Extensor carpi ulnaris passes through a fibro-osseous tunnel (the sixth extensor compartment), lying within a bony groove on the dorsal surface of ulna. ECU is maintained in this groove by the extensor retinaculum and the ECU subsheath. The ECU subsheath is not attached to the tendon.

The ECU originates from two heads, one from lateral epicondyle and other from the posterior middle third of ulna and distally it inserts into the posterior aspect of the base of fifth metacarpal.  

Racquet Sports and golf athletes are at an increased risk of ECU tendon pathology. In non-athletes rheumatoid arthritis is also to be excluded. The pathologies which can affect the ECU tendon includes tenosynovitis, tendinosis, tendon instability and rupture.

The PDFS axial and coronal image above shows mild thickening and intermediate signal intensity of the ECU tendon favoring tendinosis, with thickening and hyperintense signal intensity of the tendon sheath with associated mild soft tissue edema (suggesting tenosynovitis).

Serial axial sections of the wrist (clockwise) shows thickened ECU tendon with irregular shaped hyperintense intrinsic linear signal intensity favoring and interstitial tear.

No subluxation or dislocation of the ECU tendon is noted from the ulnar groove. The ECU subsheath and the extensor retinaculum appears intact. The orange thick arrow corresponds to the retinaculum and the thin green narrow corresponds to the ECU subsheath.

The above T2 axial image of the wrist is also showing the intact ECU subsheath (green narrow).

References: 

1. https://radiopaedia.org/articles/extensor-carpi-ulnaris-tendinopathy
2. https://radsource.us/extensor-carpi-ulnaris-subsheath-injury/

Patellar Dislocation and Relocation (PDR)

20Y old male presented with history of fall and direct injury to anterior knee.

The above axial PDFS images demonstrate the torn medial patello-femoral ligament (MPFL, blue arrow) and the medial patellar retinaculum (orange arrow) more distally. Marrow edema is noted in the medial portion of the patella (green arrow). Lateral patellar tilt, mild to moderate joint effusion and shallow trochlear sulcus angle (145°) ( suggesting trochlear dysplasia) were also noted. The lateral trochlear inclination angle measured approximately 10°.

The two axial and last coronal PDFS images shows the contusion in the lateral femoral condyle, caused due to the impaction by the dislocated patella.

Here the first image is showing the PDFS coronal image in the anterior aspect of the knee, with the arrow pointing to edema in the inferomedial anterior aspect of patella with small a avulsion fragment. Axial and coronal CT bone window images shows multiple small chip/avulsion fractures of the medial patella. In the CT sections of patella appear slightly laterally subluxed. (Note: The small fragment like appearance of the femoral condyles in CT axial section is actually due to the physeal plate, and not fractures).

The above PDFS sagittal image shows injury to the Hoffa's fat pad represented by the yellow arrow heads. The image on the right (T2 sagittal) shows increased Insall-Salvati Index, measuring 1.55, suggestive of Patella Alta. 

The risk factors of patellar dislocation include shallow patellar depth, shallow trochlear sulcus, dysplasia of the femoral condyle or patella, lateral position of the tibial tuberosity, patella alta, patellar dysplasia (nail patella syndrome) , ligamentous laxity (Marfan syndrome, Ehlers Danlos, Down's syndrome and polio) and tight lateral retinaculum.

The most common finding in the patellar dislocation is hemarthrosis or lipohemarthrosis. 

The contusion in the lateral femoral condyle which may be seen up to 80-100% of patients and is considered most specific MR imaging finding of a patellar dislocation. The contusion of the lateral femoral condyle seen in the patellar dislocation/relocation is located more anteriorly, laterally and superiorly when compared to the ACL injury contusion pattern.

Patellar contusion is seen in approximately 40% of the patients and is located in the medial and inferior aspect of the patella, in relation to the attachment of the medial retinacular complex.

The injury pattern characteristic of 'patellar dislocation/relocation' is the so called 'kissing contusions' because of the patella compressing on the lateral femoral condyle during dislocation.

Reference:

Thomas Lee Pope, MR imaging of patellar dislocation and relocation, Seminars in Ultrasound, CT and MRI, Volume 22, Issue 4, 2001,Pages 371-382, ISSN 0887-2171,
https://doi.org/10.1016/S0887-2171(01)90027-7.

Special Thanks to Prasad George, Senior MRI Technologist. 😆

Ring shaped lateral meniscus

Ring shaped lateral meniscus is a very rare anatomical variant which can easily mimic and make it difficult to distinguish from a bucket handle tear. Unlike the normal C-shape, this variant forms a complete ring.

Usually the lateral portion appears as in normal cases, with angular margins or sometimes can appear deficient anteriorly. The additional medial component appear like displaced torn fragment and easily gets mistaken for a bucket handle tear (where the body of meniscus will be truncated c.f. ring meniscus).

In differentiation from central perforation of a discoid lateral meniscus, the inner margins in central perforation will be irregular with degenerative changes. Associated osteophytes and chondral lesions may also be seen unlike a case of ring shaped lateral meniscus.