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. 😆

Band Heterotopia (Double Cortex Syndrome)

Clinical History: 6-year-old female child presented with first episode of seizure. Developmental history is within normal limits, excepting mild recent deterioration in an academic performance. 

Below are the MRI brain images of the Child. First image shows axial T2 image and coronal IR image. The green arrows point to the abnormal band of heterotopic gray matter situated between the layers of white matter (yellow arrows). The finding is more apparent in the coronal IR image.

This finding is called as band heterotopia or double cortex syndrome, which is a neuronal migration anomaly, affecting females and is considered a part of the Lissencephaly type I - subcortical band heterotopia spectrum. Children usually present with refractory epilepsy.

The overlying cortex (orange arrows) shows no pachygyria or polymicrogyria. 

The most common genetic abnormality is DCX gene mutation on the long arm of chromosome X, that's why mostly females are affected.  LIS1 gene, which is a gene responsible for type 1 Lissencephaly, is affected in some cases.

Straight back syndrome

The whole spine T2 sagittal image shows straightening of the normal kyphotic angulation of the dorsal spine. Reduced antero-posterior dimension of the thorax is also noted. Features are favoring Straight Back Syndrome. (The patient had come for symptoms of low backache with radiation to right leg). 

The above image shows T2 weighted MRI of the dorsal spine. Image on the left shows a yellow line drawn along the anterior surface of D4 to D12 vertebral bodies. In straight back syndrome the distance between the yellow line and anterior surface of midportion of the D8 vertebral body should be < 1.2 cm. (This is the Davies modification (1980) of the DeLeon (1956) criteria, and is actually mentioned in the lateral chest x-ray, and not in MRI). In the above image this distance measured only ~2mm. 

The right side images shows AP dimension of thorax from the posterior surface of the sternum to the anterior surface of the D8 vertebral body, which should be < 10-11 cm. Here it measured exactly 10 cm.

Straight back syndrome is considered as a benign skeletal abnormality of the thorax, narrowed AP dimension of the thoracic cavity, resulting in cardiovascular and bronchial compression, but with most of the patients being asymptomatic. If symptomatic, patients usually present with symptoms of chest pain and palpitations, mimicking a primary cardiac condition. An ejection systolic murmur may be heard in the pulmonary area on auscultation. 

Mitral Valve prolapse (MVP) may be seen as an association in up to two third of patients. Prominence of the pulmonary arteries, deviation of the heart to left and cardiomegaly are also described in association.

References: 

1. Davies, M. K., Mackintosh, P., Cayton, R. M., Page, A. J., Shiu, M. F., & Littler, W. A. (1980). The straight back syndrome. The Quarterly journal of medicine, 49(196), 443–460.

2. Gold PM, Albright B, Anani S, Toner H. Straight Back Syndrome: positive response to spinal manipulation and adjunctive therapy - A case report. J Can Chiropr Assoc. 2013;57(2):143-149.