The use of magnetic resonance imaging to evaluate the accuracy of a handheld ultrasound machine in localizing the sciatic nerve in the popliteal fossa

The influence of age on the anatomical variability of sciatic nerve divisions in the thigh: an ultrasound study

PURPOSE

The Sciatic Nerve Division (SND) into the Common Peroneal Nerve and Tibial Nerve presents a great anatomical variability in its location in the thigh, but the influence of age on it has not been fully addressed.

METHODS

Anatomical distances from greater trochanter to SND and from SND to popliteal crease were obtained by ultrasound examination in 60 children (age 1-12 years) and 60 adult patients (age 13-80 years) who were scheduled for programmed surgery. A sciatic nerve/thigh coefficient [Greater Trochanter-SND/(Greater Trochanter-popliteal crease)*100] and its coefficient of variation (standard deviation/mean*100) were calculated. Greater Trochanter-SND and SND-Popliteal crease were also correlated with patients´ age, weight and height.

RESULTS

There were statistically significant differences between children and adult in Greater Trochanter-SND (20.5 ± 5,5 vs 33.9 ± 2.7; p < 0.0001) and in SND-Popliteal (4.9 ± 2.1 vs 6.7 ± 1.6; p < 0.0001) distances measured in cm. There were also statistically significant differences between children and adults in Sciatic nerve/thigh coefficient (80% vs 83%; p < 0.0001) and its index of variation (8.1% vs 4.8%; p < 0.0001). In children, both Greater Trochanter-SND and SND-Popliteal distances were strongly correlated with age (r2 = 0.868 and r2 = 0.261, respectively; p < 0.0001), weight (r2 = 0.778 and r2 = 0.278, respectively; p < 0.0001) and height (r2 = 0.898 and r2 = 0.225, respectively; p < 0.0001). However, in older patients, only Greater Trochanter-SND distance was statistically correlated with height (r2 = 0.372; p = 0.0001) and not with age or weight; SND-Popliteal distance did not show statistically relevant correlation, either.

CONCLUSION

Children presented even more anatomical variability than adults in sciatic nerve division due to the growth of both the proximal and distal nervous structures of the thigh before 12 years of age.

The effect of obesity on the anatomical relationship of the popliteal artery and tibial nerve in the proximal and distal popliteal fossa: relevance to popliteal sciatic nerve block and a traceback technique using the popliteal artery

STUDY OBJECTIVE

To determine the effect of body mass index (BMI) on the relationship of the popliteal artery to the sciatic and tibial nerves in the popliteal fossa.

DESIGN

Prospective, observational study.

SETTING

University medical center.

SUBJECTS

One hundred patients scheduled for magnetic resonance imaging scans of the knee.

MEASUREMENTS

BMI was recorded and magnetic resonance imaging scans were assessed at 3 different measurement points along the femur for the distance and angle between the popliteal artery and tibial nerve, or sciatic nerve if the sciatic nerve had not bifurcated at the measurement point.

MAIN RESULTS

At the distal femur, the tibial nerve was a mean of 2.9 mm from the popliteal artery. The nerve was consistently posterior to the artery; however, it was variably located medial or lateral to the artery. At the 5- and 8-cm measurement points, the nerve was 10.0 and 16.1 mm (SD, 4.1 and 5.2 mm), and 31° and 44° (SD, 15° and 16°) lateral to the popliteal artery, respectively. Zero degree was defined as directly posterior to the artery. Increasing BMI was correlated with increasing distance between the nerve and the artery at the 5- and 8-cm measurement points (r= 0.36 P> |t| .000 and .45 P> |t| .002).

CONCLUSIONS

At 5 cm proximal to the distal femoral condyles, the popliteal artery is a reliable sonographic landmark to locate the tibial nerve due to the close proximity and consistent location of the nerve 1 cm posterolateral to the artery, with only a moderate effect of BMI.