Methodology of ultrasound of the knee joint

When performing an ultrasound examination (US) of the knee joint, a certain sequence should be followed and standard positions (sections) should be sought. Four standard approaches are used to display all elements of the joint during an ultrasound examination: anterior, medial, lateral and posterior.

Anterior approach

This approach provides visualization of the quadriceps tendon, anterior recess, patella, suprapatellar bursa, patellar ligament, infrapatellar bursa, and fat pad of the knee joint. The patient is in a supine position with the limb straightened. The examination begins with an assessment of the condition of the quadriceps tendon, for which a longitudinal section is obtained. The quadriceps tendon does not have a synovial membrane and is surrounded by a hyperechoic strip at the edges. To reduce the effect of anisotropy, the limb can be bent by 30-45 degrees or a bolster can be placed under the knee.

In the distal part behind the tendon of the quadriceps muscle of the thigh there is a suprapatellar bursa. Normally it may contain a small amount of fluid.

Proximally upward, the structure of the muscle tissue is studied, transverse and longitudinal sections of the quadriceps muscle of the thigh are obtained. The panoramic scanning mode provides visualization of all four muscle bundles that make up the quadriceps muscle of the thigh.

Next, an image of the patella and the patellar ligament is obtained. At the same time, the condition of the fat pad of the knee and the infrapatellar bursa is assessed.

Medial approach

This approach provides visualization of the medial collateral ligament, the body of the medial meniscus, and the medial part of the articular space.

The patient is in a supine position, the limb is straightened. The sensor is installed on the medial surface of the joint, in a longitudinal position, along the midline in relation to the joint space.

When the sensor is installed correctly, the joint space should be clearly visible on the monitor screen. Improved visualization of the meniscus can be achieved by bending the leg at the knee joint to 45-60 degrees. The condition of the joint space, the contours of the femur and tibia, the thickness and condition of the hyaline cartilage, and the presence of effusion in the joint cavity are assessed.

The fibers of the medial collateral ligament are visible above the joint space, originating from the proximal part of the medial condyle of the femur and inserting on the proximal part of the metaphysis of the tibia. To improve visualization of the body of the medial meniscus, the limb should be rotated outward, which causes the joint space to diverge and the meniscus to be located posterior to the medial collateral ligament.

The anterior cruciate ligament can sometimes be visualized from the medial approach. To do this, the patient is asked to bend the leg at the knee joint as much as possible. The sensor is positioned below the patella and the scanning plane is directed into the joint cavity. The bone landmarks are the femoral condyle and the tibial epicondyle. The fibers of the anterior cruciate ligament are partially visualized. Due to the anisotropy effect, the ligament may be hypoechoic, and only some of the fibers located perpendicular to the ultrasound beam will be hyperechoic.

Lateral approach

This approach provides visualization of the distal part of the broad fascia of the thigh, the popliteal tendon, the lateral collateral ligament, the distal part of the biceps femoris tendon, the body of the lateral meniscus, and the lateral part of the joint space.

The patient is in a supine position, the leg is bent at the knee joint at an angle of 30-45 degrees, rotated inwards. The sensor is installed on the lateral surface of the joint, in a longitudinal position, along the midline in relation to the joint space. The bone landmarks are the head of the fibula, Gerdiy tubercle of the tibia, and the lateral condyle of the femur. Scanning in the cranial direction allows examining the fibers of the broad fascia of the thigh. The bone landmark for the attachment of the tendon fibers is Gerdiy tubercle on the anterolateral surface of the tibia. Between Gerdiy tubercle of the tibia and the lateral condyle of the femur, in the notch, is the tendon of the popliteal muscle, attached to the posterior surface of the tibia.

Part of this tendon can be visualized by scanning the lateral collateral ligament. The fibers of the lateral collateral ligament pass over the joint space.

The lateral collateral ligament originates from the lateral condyle of the femur, passes over the tendon of the popliteal muscle and attaches to the head of the fibula, merging with the fibers of the tendon of the lateral head of the biceps femoris.

With the sensor fixed in the fibular head area and the proximal end of the sensor rotated downwards, the tendon of the lateral head of the biceps femoris is determined. To assess the body of the lateral meniscus or to determine the integrity of the fibers of the lateral collateral ligament, the limb must be rotated inwards, with the meniscus located posterior to the lateral collateral ligament and separated from its fibers by the tendon of the popliteal muscle. With three-dimensional reconstruction of the meniscus, it is possible to obtain a frontal section of the articular surface of the tibia and femur, as well as to assess the extent of meniscus tears.

Rear access

With this approach, the vascular-nerve bundle of the popliteal fossa, the medial and lateral heads of the gastrocnemius muscle, the distal part of the fibers of the tendon of the semimembranosus muscle, the posterior horn of the medial meniscus and the posterior horn of the lateral meniscus, and the posterior cruciate ligament are visualized.

The patient is in the prone position. The transducer is positioned transversely to the long axis of the limb in the popliteal fossa. The neurovascular bundle is displaced laterally in the popliteal fossa. The popliteal artery is located behind the vein, with the muscle bundles of the popliteal muscle visualized below. Panoramic scanning using power mapping can trace the course of the popliteal artery. The tendons of the medial and lateral heads of the gastrocnemius muscle originate from the corresponding condylar surfaces of the femur. The tendon of the semimembranosus muscle inserts on the posteromedial surface of the proximal tibia. Between the tendon of the semimembranosus muscle and the medial head of the gastrocnemius muscle there is a small bursa, which usually contains the neck of a Baker's cyst. The landmarks for visualizing this bursa during transverse scanning are: the posterior surface of the medial condyle of the femur, covered with hyaline cartilage, the tendon of the semimembranosus muscle, and the fibers of the gastrocnemius muscle.

During longitudinal scanning of the popliteal fossa, the sensor is displaced laterally and rotated according to the plane of the joint cavity. In this case, the posterior horn of the lateral meniscus is visualized. From this position, the posterior cruciate ligament is also visualized, with the sensor rotated counterclockwise by 30 degrees when examining the right limb and by 30 degrees clockwise when examining the left limb. The posterior cruciate ligament, as well as the anterior one, is partially visualized. Its fibers are hypoechoic due to the anisotropy effect.

To evaluate the posterior horn of the medial meniscus, the transducer must be moved medially in the popliteal fossa to image the fibers of the tendon of the medial head of the biceps femoris that attach to the medial epicondyle of the tibia. From this position, the body of the medial meniscus is visualized.

From the posterior approach, the peroneal nerve can also be assessed, which, leaving the lateral part of the sciatic nerve in the distal thigh, follows laterally and downward along the posterior surface of the distal biceps femoris tendon to the popliteal region, then around the head of the fibula to the anterior surface of the leg. In this area, nerve injuries often occur between the fibers of the fibrous tunnel.