Please see the knee us in my previous linked publishing.
Ultrasound of the knee allows high resolution imaging of superficial knee anatomy while simultaneously allowing dynamic evaluation of some of the tendons and ligaments. Knee ultrasound is somewhat limited compared with ultrasound examinations of other joints because the cruciate ligaments and the entirety of the meniscus is usually difficult to visualize.
Anterior knee
Knee is flexed 20-30 degrees (flexion of the knee tightens the extensor tendons, decreasing the chance of anisotropy occuring in a lax tendon):
- Transverse and longitudinal images of the quadriceps tendon from its myotendinous junctions to its attachment on the superior patella (rectus femoris myotendinous junction is more cranial than the vastus junctions).
Evaluate the suprapatellar and parapatellar joint recesses.The patella is the largest sesamoid bone in the human body ( exam question). It lies within the quadriceps tendon/patella ligament and forms part of the knee joint. It can be absent,or multiple.
suprapatellar fat pad , prefemoral fat pad
- small amounts of synovial fluid may preferentially locate to the parapatellar joint recess
- Evaluate the femoral trochlea
- best examined in full knee flexion
useful for examination of the trochlear cartilage
- Evaluate the patellar retinacula
- Evaluate the medial patellar articular facet (lateral facet not visible on ltrasound).
- Evaluate the patellar tendon and patellar bursa
- prepatellar bursa normally not visible
- infrapatellar bursa
- small amount of fluid in the deep infrapatellar bursa is normal
- normally no fluid in the superficial infrapatellar bursa
- Lateral knee
Knee is flexed 20-30 degrees:
- Evaluate the distal iliotibial band in long axis (located between anterior and middle third of the lateral knee).
- Evaluate the lateral collateral ligament ( LCL) in long axis.
- may detect para-articular ganglia
- May see lateral meniscal pathology (e.g. meniscal cyst)
- extreme knee flexion may bring out a meniscal abnormality
- Medial knee
Knee is flexed 20-30 degrees, with external rotation:
- Evaluate medial collateral ligament( MCL) and pes-anserinus tendons in long axis
- valgus stress may be useful to examine the ligament
- Posterior knee
Often examined with patient prone and knee extended:
- Evaluate the medial tendons in short axis (medial to lateral):
- sartorius
- gracilis
- semitendinosis
- Moving even more medially, evaluate the semimembranosus-gastrocnemius bursa in short axis
- a popliteal cyst ( Baker’s cyst ) arises between these tendons
- Evaluate the popliteal neurovascular bundle and intercondylar fossa in short axis.
- Evaluate the posterolateral corner and biceps femoris in short and long axis.
- Evaluate the peroneal nerve
- start with the common peroneal nerve branching off the sciatic nerve above the knee
- follow it around the fibular head
Pathology
A number of knee abnormalities can be identified on ultrasound, including:
- Patellar tendinosis / patellar tendon tear.
- Quadriceps tendon tear .
- Prepatellat bursitis .
- Infrapatillar bursitis .
- Popliteal cyst. ( Baker’s cyst) .
Exam questions; Anisotropy is an artifact encountered in ultrasound, notably in muscles and tendons during MSK us exam. In musculoskeletal applications, the artifact may prompt an incorrect diagnosis of tendinosis or tendon tear.
When the ultrasound beam is incident on a fibrillar structure as a tendon or a ligament, the organized fibrils may reflect majority of the insonating sound beam in a direction away from the transducer. When this occurs, the transducer does not receive the returning echo and assumes that the insonated area should be hypoechoic.
This anisotropic effect is dependent on the angle of the insonating beam. The maximum return echo occurs when the ultrasound beam is perpendicular to the tendon. Decreasing the insonating angle on a normal tendon will cause it to change from brightly hyperechoic (the actual echo from tightly bound tendon fibers) to darkly hypoechoic. If the angle is then increased, the tendon will again appear hyperechoic.
If the artifact causes a normal tendon to appear hypoechoic, it may falsely lead to a diagnosis of tendinosis or tear.
In some situations, anisotropy may actually be useful in diagnosis. If a tendon is surrounded by other brightly hyperechoic structures (e.g. fat), then altering the angle of the transducer will cause the tendon to become hypoechoic, differentiating it from the other structures.
always use color flow to r/o hypermia .
bi patella
multi patella
posterior knee. scan the medial and lateral meniscus posterior horns, popl v and make sure there is no popl artery aneurysm, look for baker’s cyst at the gastroenteritis, and the intracondyle space for any other cysts.
Steve Ramsey, PhD- Calgary- Canada