The borders of the lozenge-shaped popliteal fossa are formed by the gastrocnemii, the biceps femoris and the semitendinosus and semimembranosus muscles. The bottom is formed by the posterior capsule and the popliteus muscle .The popliteal fossa is covered by a fascia. The lozenge is vertically crossed (from lateral to medial) by: the tibial nerve, popliteal vein and popliteal artery. The common peroneal nerve descends along the inner border of the biceps.
Palpation is performed with the subject in the prone-lying position. The knee is slightly bent to release the posterior fascia. A slight resisted flexion of the knee brings the upper borders of the popliteal fossa into prominence.Medially the tendon of the semitendinosus is easily identified as a round cord. The semimembranosus is situated deeper and has a flatter consistency on palpation.
At the lateral side the biceps tendon can also be recognized easily. Its insertion is on the superior and posterior aspect of the fibular head.
The junction between the semimembranosus and the biceps forms the superior angle of the fossa.The inferior borders, which are shorter than the superior ones, are formed by both gastrocnemii . Their junction constitutes the inferior angle of the lozenge. The palpation is facilitated by a resisted plantiflexion of the foot. The posterior aspects of medial and lateral femoral condyles can be palpated just under the gastrocnemii, the insertion of which is more proximally on the condyles. The tibial nerve is located in the centre of the lozenge and divides it in two. The tibial vein and the tibial artery are located medial to it.
Nerve and artery can be palpated as follows. The patient is in the supine position, the knee bent to a right angle and the foot flat on the couch. The examiner sits on the couch, next to the knee, and palpates the fossa from the medial aspect with the ipsilateral hand. The nerve is felt as a hard and round structure in the centre of the lozenge, near the upper angle. To palpate the pulsations of the artery, the fingers must be plunged deeper and more medially.
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