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.
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.


METHODS
Prospective, observational study.


METHODS
University medical center.


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


METHODS
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.


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.
Department of Anesthesiology and Perioperative Medicine, Oregon Health and Science University, Portland, OR 97239, USA. Electronic address: woodworg@ohsu.edu.
Glenn E
GE
Woodworth
Department of Anesthesiology and Perioperative Medicine, Oregon Health and Science University, Portland, OR 97239, USA.
Jason
J
Trujillo
Department of Radiology, Oregon Health and Science University, Portland, OR 97239, USA.
Erik
E
Foss
Department of Anesthesiology and Perioperative Medicine, Oregon Health and Science University, Portland, OR 97239, USA.
Michael
M
Semenza
D000328:Adult; D015992:Body Mass Index; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000098:blood supply* / Q000000981:diagnostic imaging / Q000294:innervation*; D008279:Magnetic Resonance Imaging; D008297:Male; D009407:Nerve Block / Q000379:methods*; D009765:Obesity / Q000473:pathology*; D011150:Popliteal Artery / Q000000981:diagnostic imaging / Q000473:pathology*; D011446:Prospective Studies; D012584:Sciatic Nerve / Q000187:drug effects* / Q000473:pathology; D013979:Tibial Nerve / Q000473:pathology*; D018084:Ultrasonography, Interventional
Popliteal artery; Sciatic nerve