Popliteus

The flexor muscles of the knee are located in the posterior compartment of the thigh. They are the hamstrings, the gracilis, the sartorius, the popliteus, and the gastrocnemius muscles. AU of these muscles are biarticular, with the exception of the popliteus and the short head of the biceps. Their action on knee flexion is related to the position of the hip. Rotation of the knee is also a function of these knee flexors. 

The popliteus and the short head of the biceps are the only two knee flexors that are one joint muscles. All the others are two joint muscles. 

With the patient supine, the examiner grasps one lower extremity under the heel. With his other hand he supports the calf. The knee is allowed to move from 10 degrees of flexion to full extension (Fig. 94-4). If the knee becomes hyperextended with external rotation of the tibia and tibial varus, the test is positive. This indicates injury to the arcuate ligament, popliteus, and fibular collateral ligament. 

The lateral aspect of the knee joint is examined by asking the patient to rotate the leg internally. From anterior to posterior, the structures to be evaluated are the distal aspect of the iliotibial band, the external femorotibial joint space with the lateral meniscus, the lateral collateral ligament, the popliteus tendon and the superior tibiofibular joint. 

Just deep to the proximal part of the lateral collateral ligament, the popliteus tendon can be imaged on coronal US planes as an oval structure located in its bony groove (Fig. 14.34). Depending on the incidence of the US beam, substantial anisotropy may be evident in the popliteus tendon (De Maeseneer et al. 2002). The US examination of the lateral aspect of the knee should be completed with an evaluation of the superior tibiofibular joint. Transverse and coronal US scans obtained over the anterior aspect of the fibular head are adequate for this purpose. 

The posterior tibial artery is the direct continuation of the popliteal artery down to the distal margin of the popliteus muscle. During its course, this artery is accompanied by the tibial nerve and two or more posterior tibial veins. This posterior neurovascular bundle passes deep to the tendinous arch of the soleus and, after giving off the peroneal artery, courses superficial to the tibialis posterior muscle to reach the tarsal tunnel (Fig. 15.12a,b). The posterior tibial artery is a useful landmark to separate the deep from the superficial group of calf... 

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