Response of the popliteal artery to treadmill exercise and stress positioning in patients with and without exertional lower extremity symptoms

Objective: Functionally limiting exertional lower extremity pain and neurologic symptoms are commonly encountered in military and civilian settings. Exertional muscle compression of the popliteal artery (PA) and tibial nerve in the proximal calf (the "popliteal outlet") can be associated with these symptoms but is rarely investigated as a cause. Exertional ankle-brachial index (EABI) and dynamic PA ultrasound imaging may be suitable to screen for this syndrome of "functional" popliteal entrapment, but neither has been rigorously studied. Our objective was to characterize the response of the PA to lower extremity exertion and dynamic ankle positioning in symptomatic and asymptomatic limbs. Methods: Limbs characterized as symptomatic (n = 29) or asymptomatic (n = 61) had duplex ultrasound PA diameter and peak systolic velocity measurements with the ankle neutral and maximally plantar flexed. EABIs were obtained at rest and 1 minute and 5 minutes after walking (5 minutes, 3 mph, 10-degree incline) and running (5 minutes, 6 mph, 0-degree incline). Significance was set at P <= .05. Data are expressed as mean +/- standard error of the mean. Results: Plantar flexion resulted in PA occlusion and changes in diameter and peak systolic velocity in symptomatic (three occluded, -2.4 +/- 0.34 mm, +49 cm/s) and asymptomatic (six occluded, -1.6 +/- 0.21 mm, +65 cm/s) limbs. The difference in percentage change was significant between groups only for diameter change. EABIs in both groups were similar at rest, decreased with running and walking at 1 minute, and were not fully recovered by 5 minutes. Symptomatic limbs had a greater decrease in ABI than did asymptomatic limbs with both running and walking. The decrease was greatest at 1 minute after running and significantly more pronounced in symptomatic (-0.18) than in asymptomatic (-0.02) limbs. Conclusions: EABI decrease at 1 minute after running and PA diameter decrease with dynamic ankle plantar flexion are significantly greater in limbs with than without exertional lower extremity symptoms. These noninvasive measurements may be valuable in the workup of such symptoms. PA and tibial nerve compression at the popliteal outlet may be a more frequent cause of functionally limiting exertional lower extremity pain and neurologic symptoms than previously recognized.