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Popliteal artery is used for auscultation while measuring blood pressure in the lower limb.
(The patient lies prone, knee flexed, and stethoscope placed deep in the fossa.)
Arrangement of structures (from superficial to deep):
Tibial nerve → Popliteal vein → Popliteal artery.
Order in upper, middle, and lower parts:
Upper part (medial → lateral): A V N
Middle part (posterior → anterior): N V A
Lower part (medial → lateral): N V A
Short (small) saphenous vein begins at the lateral end of the dorsal venous arch and drains into the popliteal vein within the fossa.
Popliteus muscle unlocks the locked knee joint by laterally rotating the femur on the tibia to initiate flexion.
Tibial nerve gives:
Genicular branches (upper part)
Cutaneous branch (middle part)
Muscular branches (lower part)
Common peroneal (fibular) nerve winds around the neck of the fibula — the most frequently injured nerve in the lower limb.
Injury results in foot drop (loss of dorsiflexion and eversion).
Popliteal artery gives five genicular branches (2 superior, 2 inferior, 1 middle) that form the genicular anastomosis around the knee.
Popliteal lymph nodes (6–7 in number) lie along the small saphenous vein and popliteal vessels, draining the lateral foot and posterior leg into deep inguinal nodes.
The popliteal artery is prone to aneurysm formation because of its fixed position between strong fibrous structures (femur and fascia).
Case:
A 45-year-old male complains of weakness and coldness in both lower limbs. His blood pressure measured at the ankles is much lower than that in the upper limbs.
Questions:
How is blood pressure in the lower limb taken?
The patient lies prone.
A wider cuff is wrapped around the thigh.
The popliteal artery is auscultated in the fossa while the cuff is slowly deflated.
What could be the reason for low blood pressure in the lower limbs?
Coarctation of the aorta — a congenital narrowing of the aortic arch just distal to the origin of the left subclavian artery.
This reduces blood flow to the descending aorta and hence to the lower limbs, resulting in diminished popliteal and posterior tibial pulses.
What clinical findings support this diagnosis?
Higher pressure in upper limbs, weak femoral and popliteal pulses, and radio-femoral delay.
Collateral circulation develops through the intercostal, internal thoracic, and scapular arteries to bypass the narrowed segment.
Treatment:
Surgical correction or stent placement to restore aortic continuity and improve lower limb perfusion.
Case: A middle-aged man presents with weakness in both lower limbs and diminished pulses in the popliteal region.
Explanation: The blood pressure in lower limbs is taken by auscultating the popliteal artery with the patient prone.
Finding: A lower popliteal pressure compared to brachial indicates coarctation of the aorta — narrowing of the aorta below the origin of subclavian artery, leading to reduced lower limb blood flow.
Management: Surgical repair or stenting of the narrowed segment.
Case: A patient has a pulsatile swelling behind the knee with pain radiating down the leg.
Explanation: The popliteal artery, being fixed between the femur and popliteal fascia, is prone to aneurysm formation.
Symptoms: Localized swelling, pressure over tibial nerve (causing calf pain), or common peroneal nerve (causing paresthesia).
Treatment: Ligation or graft repair; collateral circulation through genicular anastomosis maintains blood supply.
Case: Elderly patient with intermittent claudication (pain on walking).
Explanation: Atherosclerosis or thrombosis of the popliteal artery causes ischemic pain; collateral circulation via the profunda femoris artery often prevents gangrene.
Case: A bedridden patient develops pain, warmth, and swelling of the calf.
Explanation: Thrombosis of the popliteal vein due to stasis of blood or post-surgical immobility.
Complication: May lead to pulmonary embolism if the thrombus dislodges.
Diagnosis: Doppler ultrasound; treated with anticoagulants.
Case: A plaster cast compresses the neck of fibula; patient cannot dorsiflex the foot.
Explanation: The common peroneal nerve winds around the fibular neck; injury leads to foot drop (loss of dorsiflexion and eversion) but normal plantar flexion and inversion.
Sign: Toes drag while walking (“steppage gait”).
Case: A child with an infected wound on the lateral sole presents with tender swelling behind the knee.
Explanation: Infection drains via small saphenous vein to popliteal lymph nodes, causing inflammation.
Note: Popliteal nodes enlarge in infections on the posterolateral foot and leg.
Case: An athlete complains of calf pain and numbness in sole after vigorous exercise.
Explanation: Tibial nerve or popliteal artery compressed by abnormal muscle slip of gastrocnemius or fibrous bands → causes intermittent ischemia or paresthesia.
Management: Surgical decompression of entrapped structures.
Case: A runner experiences difficulty unlocking the knee during flexion.
Explanation: The popliteus muscle initiates flexion by laterally rotating the femur on tibia; strain or injury can cause painful locking of the joint.
Case: A patient with chronic arthritis presents with soft swelling in the popliteal fossa that enlarges during knee extension.
Explanation: A synovial outpouching from the posterior capsule of the knee, between semimembranosus and medial gastrocnemius.
Clinical Test: Swelling reduces on flexion and reappears on extension.
Treatment: Aspiration or excision of cyst after managing underlying joint pathology.
Case: Student unable to locate popliteal pulse in a patient.
Explanation: Pulse is palpated with the knee flexed to relax the fascia; pressing deeply in the midline between hamstring tendons.
Clinical Significance: Absence of popliteal pulse indicates blockage proximal to knee or femoral artery occlusion.
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