Effect of Stress Maneuvers at the Ankle Joint on Peak Systolic Velocity and Waveforms in Popliteal and Posterior Tibial Arteries in Healthy Individuals

INTRODUCTION

Provocative maneuvers at the ankle joint are known to cause changes in the blood flow in the popliteal and the posterior tibial arteries (PTAs).^[1] These changes become relevant as aid in diagnosis, especially in cases of popliteal artery entrapment (PAE) syndrome. PAE is an anomalous anatomic relation between popliteal artery (PA) and the surrounding gastrocnemius muscle which may occur during embryonic development.^[2] Sonographic examination can show arterial compression elicited by maneuvers such as plantar flexion and dorsiflexion of the feet.^[3] During active dorsiflexion and plantar flexion, the contracted gastrocnemius muscle can cause compression and stretching of the entrapped PA with loss of pulse at the ankle which can be picked up on Doppler ultrasonography in PAE.^[4] However, it is not a specific finding and may be found in up to 53% of normal subjects.^[5] Loss of pulse is a subjective finding, and there are limited studies in healthy individuals, which measure the magnitude of change in velocity and waveform. The aim of our study was to find this change in velocity and waveform with ankle movements in healthy individuals.

MATERIALS AND METHODS

It was an observational study done over 8 months. The study was approved by the institutional review board. Informed consent was obtained from all the study participants. The study participants were selected after they were screened with a questionnaire (Table 1) and objective assessment was done using ankle brachial pressure index (ABPI) (Table 2). Subjects answering “Yes” to any of the questions or with ABPI <1 were excluded from the study.

All the Doppler ultrasounds were performed with TOSHIBA XARIO SSA 660A-V using the 7.5 MHz linear transducer probe by two radiologists. Each subject was placed in prone position with feet hanging over edge of the table. They were studied in neutral position followed by active dorsiflexion and then active plantar flexion of the ankle joint. These maneuvers were performed on each limb separately. Active plantar flexion was conducted against a wall. The angle between the plantar aspect of the foot and the surface of the slab was kept approximately 50–60°, which allowed the subject to reach maximum flexion of the foot during the provocation maneuver. Active dorsiflexion was done to the maximum angle achievable by the subject. PA was studied at knee joint level and PTA was evaluated at the level of medial malleolus. Both arteries were initially evaluated to rule out significant luminal narrowing both in gray scale and color flow. The peak systolic velocity and the waveforms at the neutral position and changes brought about in them by the above-described maneuvers were recorded and analyzed.

RESULTS

A total of 40 limbs, i.e.20 healthy volunteers were enrolled for the study. All the subjects recruited were <30 years old. Male-to-female ratio was 4:1. The youngest person in our study group was 18 years old, while oldest was 29 years old. The mean age was 23.5 years with a standard deviation of 3.7. The popliteal and PTAs were evaluated in all subjects and significant luminal narrowing was ruled out. All vessels had normal course and no anatomic variation was observed. The velocity ranges of all the 40 popliteal arteries in various maneuvers, with median and mean are shown in (Table 3). Mean PSV of the PA in the neutral position is 65.7 cm/s which increased to 69.1 cm/s on dorsiflexion and to 66.7 cm/s in plantar flexion.

In the neutral position, the 95% confidence interval was between 60.6 and 70.7 cm/s with a standard error of 2.48. On dorsiflexion, the 95% confidence interval changed to lie between 63.5 and 74.6 cm/s with a standard error of 2.74. While on plantar flexion, the 95% confidence interval was between 61.2 and 72.1cm/s with a standard error of 2.69.

Popliteal artery

Waveform

Of total 40 popliteal arteries, 39 showed triphasic waveform (Figure 1a) pattern at rest, while one was biphasic. The changes brought about by dorsiflexion and plantar flexion are shown in (Table 4).

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Figure 1

A 27-year-old male volunteer undergoing Spectral Doppler evaluation of the popliteal artery. (a) Triphasic waveform pattern of the popliteal artery with ankle at the neutral position. (b) Biphasic waveform pattern of the popliteal artery with ankle in dorsiflexion.

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Table 4 Change in waveform: Popliteal artery

Maneuvers	Triphasic (%)	Biphasic (%)	Monophasic
Dorsiflexion	21 (53.84)	18 (46.15)	0
Plantar flexion	26 (66.67)	13 (33.34)	0

On dorsiflexion, out of 39, 21 arteries (53.84%) showed no change in triphasic pattern, while 18 arteries (46.15%) showed a change from triphasic to biphasic pattern (Figure 1b). There were no changes to monophasic waveform.

On plantar flexion, a comparatively greater percentage 26 (66.67%) remained triphasic and 13 (33.34%) changed from triphasic to biphasic. There were no changes to monophasic waveform. One limb which was biphasic to start with did not show any change in its wave characteristics on performing the maneuvers.

Mean change in PA velocity from neutral to dorsiflexion

Eleven popliteal arteries (27.5%) showed decrease in velocity and 27 cases (67.5%) showed increase in velocity from the baseline neutral position velocity (Table 5). Two popliteal arteries (5%) did not show any change in velocity on performing the leg maneuvers.

Table 5 Mean change in popliteal artery velocity from neutral to dorsiflexion

Observed	Mean	Standard error	95% Confidence interval
Decreased (n=11)	13.90	1.89	9.69-18.11
Increased (n=27)	15.04	2.16	10.60-19.49

The mean percentage decrease in velocity was 13.90 with the 95% confidence interval ranging between 9.69 and 18.11. The mean percentage increase in velocity observed was 15.04 with the 95% confidence interval ranging between 10.6 and 19.49.

Mean change in PA velocity from neutral to plantar flexion

Eighteen popliteal arteries (45%) showed decrease in velocity of the PA and 20 (50%) showed increase in the velocity. The remaining 2 arteries (5%) did not show any change in velocity on performing the maneuvers (Table 6).

Table 6 Mean change in popliteal artery velocity from neutral to plantar flexion

Observed	Mean	Standard error	95% Confidence interval
Decreased (n=18)	15.68	2.66	10.06-21.30
Increased (n=20)	22.00	5.74	9.98-34.01

The mean percentage decrease in velocity was 15.68 with the 95% confidence interval ranging between 21.30 and 10.06. The mean percentage increase in velocity was 22 with the 95% confidence interval ranging between 9.98 and 34.01.

DISCUSSION

Sonographic examination can show arterial compression elicited by maneuvers such as plantar flexion and dorsiflexion of the feet.^[3] Even though arterial compression can be shown on sonography, stress maneuvers such as active plantar flexion and passive dorsiflexion of the ankle increase the diagnostic accuracy. Active plantar flexion may cause compression of the entrapped PA by the contracted gastrocnemius muscle, and the entrapped PA may be stretched with passive dorsiflexion.^[4,6]

There is limited data currently available in the literature regarding the variations in the velocity and Doppler wave characteristics of popliteal and PTAs, brought about by doing various stress maneuvers at the ankle joint in healthy individuals. We studied this change in velocity and waveforms in popliteal and PTA in 20 healthy volunteers. As PA entrapment is common in young age group,^[7] we have selected all of our subjects with age <30 years. In addition to PA, PTA has also been assessed so as to evaluate the distal changes brought about by compression of the PA on performing the maneuvers.

Our study shows that plantar flexion of the foot causes relatively more increase in the mean velocity of PA as compared to dorsiflexion (mean increase of 22 vs. 15 cm/s). None of our subjects demonstrated any loss of blood flow in the artery with plantar flexion. These findings are in contrast to a study conducted by Akkersdijk et al.,^[8] in which disappearance of blood flow was seen in up to 59% during active plantar flexion.

Of 38 PTAs, 30 (75%) showed increase in velocity on plantar flexion with mean increase of 36.7 cm/s. On dorsiflexion, 22 arteries (up to 58%) showed increase with a mean increase of 33.3 cm/s.

Typically, in the absence of consensus on ultrasound criteria on a significant increase in velocity, most radiologists use doubling of velocity as the criteria. In our study, none of the volunteers showed doubling of velocity on performing of the maneuvers.

The normal Doppler waveform seen in lower limb arteries is triphasic in appearance.^[9] However, we saw significant variations in the triphasic pattern while performing the dorsi- and plantar flexion maneuvers. The changes in waveforms were seen more on dorsiflexion than on plantar flexion in the case of PA and the reverse pattern was seen in PTA.

The most notable change in PA was the change into biphasic form from the originally triphasic wave pattern in 46% of arteries on dorsiflexion. Comparatively on plantar flexion, 33% changed into biphasic from original triphasic and none changed into monophasic. The waveform change to biphasic could likely be attributed to temporary narrowing of the vessel owing to compression by the contracting muscles on performing the stress maneuvers.

In PTA, on dorsiflexion, 25% changed to biphasic and 7% to monophasic, whereas on plantar flexion the change to biphasic was same at 25% with monophasic being at 14%.

In contradiction to the above findings, Miles et al.^[10] described normal Doppler waveforms and ankle pressures after active plantar flexion; however, in their study, the subjects had their knee flexed at 60° which reduces muscle tension in the popliteal fossa during exercise. In our study, the knees were kept in full extension throughout the maneuvers.

There are some limitations of our study. Anatomical entrapment of the blood vessel cannot be ruled out completely with Doppler examination and requires cross-sectional imaging like MRI for definite exclusion. Accuracy of the Doppler examination depends on the machine as well as the expertise of the person performing the Doppler. As this is a pilot study, the small sample size may not be representative of the entire population; a large sample data would be needed to validate these results.

Knowledge of the normal range of variation brought about by stress maneuvers on the waveform patterns and blood flow velocities in the popliteal and PTAs helps in preventing overdiagnosis of PAE or occlusion.

CONCLUSION

The change in blood flow velocity is more with plantar flexion on performing different stress maneuvers in the popliteal and PTAs in healthy individuals. Predominantly, a pattern of increase is seen in the mean velocity on plantar flexion and dorsiflexion in both the arteries. The most common change in the Doppler waveforms was the absence of diastolic flow (biphasic pattern). None of the arteries show complete absence of blood flow on these maneuvers.

Our study confirms that waveforms in the popliteal and PTA can even be monophasic depending on the position of the foot in normal healthy individuals; therefore, when biphasic/ monophasic in appearance, they should not be interpreted as abnormal or diseased.