To describe the protocol used in our institution to study the extensor apparatus of the knee, and its advantages over computed tomography.

The extensor mechanism of the knee is a complex biomechanical apparatus, responsible for the stabilization of the patellofemoral joint and knee extension. Abnormalities in joint congruence and stability lead to pathology and clinical symptoms. There are five main interlocking factors that affect the stability and congruence of the patellofemoral joint: patellar height; patellar tendon valgus and Q angle; lateral stabilization static mechanism; medial dynamic stabilization structures; and patellar thickness. Computed tomography (CT) has been used to measure the valgus of the patellar tendon, assess the...

In our institution we use a Siemens Magnetom Avanto 1.5 T MRI system, equipped with a dedicated knee coil. Acquisition starts with the knee placed within a quadrature standard knee coil. The foot is placed 15 degrees in external rotation. Pads are placed under the heel, to raise the foot and place the knee close to zero degrees extension (Fig. 1 and Fig. 2). Afterwards a routine MRI knee study is performed (sagittal, axial and coronal proton density, fat saturated, images and sagittal T1 and...

Although MRI takes a little more time and is more expensive compared to CT, this protocol allows a reproducible and more informative alternative, when it comes to studying the extensor apparatus and its pathology.

Aarvold A, Pope et al. MRI performed on dedicated knee coils is inaccurate for the measurement of tibial tubercle trochlear groove distance. Skeletal Radiology. 2014;43(3):345-349. 
 Biedert RM, Albrecht S. The patellotrochlear index: a new index for assessing patellar height. Knee Surg Sports Traumatol Arthrosc. 2006; 14(8):707–712. Diederichs et al. MR imaging of patellar instability: injury patterns and assessment of risk factors. Radiographics 2010; 30(4): 961-981. Seitlinger G, et al. Tibial Tubercle-Posterior Cruciate Ligament Distance: A New Measurement to Define the Position of the Tibial Tubercle...

J. Pires, R. Costa, J. Vasconcelos, R. Sampaio Hospital Lusíadas Porto Av. da Boavista 171,4050-113Porto mail to:[email protected]