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John N Edwards

Publications and source records attributed to John N Edwards.

3 recordsLinked to original sources
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At the cords, the pinkie towards: Interpreting infraclavicular motor responses to neurostimulation.

Identification of elicited muscle twitches while performing infraclavicular block of the brachial plexus is often confusing but is critical for success of the block. An easily defined endpoint when evaluating these motor responses to neurostimulation is essential, as it is necessary to block the appropriate cord or cords. In addition to an extensive review of the motor and sensory neuroanatomy of the upper extremity, we describe an easy method to learn and remember the motor response to stimulation of each of the cords of the brachial plexus. If the arm is positioned in the anatomical position, the 5th digit (pinkie) moves laterally (pronation of the forearm) when the lateral cord is stimulated, posteriorly (extension) when the posterior cord is stimulated, and medially (flexion) when the medial cord is stimulated. The pinkie thus moves "toward" the cord that is stimulated.

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A method to estimate the depth of the sciatic nerve during subgluteal block by using thigh diameter as a guide.

BACKGROUND AND OBJECTIVE: The subgluteal approach is common for sciatic nerve block. Although the surface landmarks are clear, the depth of this nerve at this level is difficult to judge. The purpose of this study is to establish a method of estimating the sciatic nerve depth using the anteroposterior (AP) diameter of the thigh as a marker. METHODS: The study was undertaken in 2 phases. Phase 1 entailed review of 100 magnetic resonance images (MRIs) of the pelvis and proximal lower extremity of patients. Measurements were taken of the AP diameter of the thigh at the midpoint of the lesser trochanter and then compared with distances of the sciatic nerves from the skin of the posterior aspect of the thigh at the same level. Phase 2 involved enrolling 40 patients undergoing lower-extremity surgery for whom subgluteal sciatic nerve blocks were indicated. The AP diameters of the thighs were measured from the subgluteal groove to the inguinal groove with the patient in the supine position. Placing the patient in the lateral position, the subgluteal sciatic block was then performed by using a stimulating needle. The distances from the skin at which the sciatic nerves were actually found, as estimated by maximum motor response to stimulus, were noted. RESULTS: Phase 1 showed a mean AP diameter of 18.94 cm +/- 2.61 cm (mean +/- standard deviation [SD]), mean nerve depth of 6.51 cm +/- 1.46 cm (mean +/- SD), and a linear regression slope of 0.48. Phase 2 showed a mean AP diameter of 16.28 cm +/- 2.73 cm (mean +/- SD), a mean nerve depth of 6.99 cm +/- 1.39 cm (mean +/- SD), and a linear regression slope of 0.43. The thigh diameters differed (P < .001) between the groups, but there was no difference in the depth to the sciatic nerve between the 2 groups (P = .07). CONCLUSIONS: Comparing phase 1 and phase 2 datasets shows the slopes of linear regression lines are nearly parallel. The clinical data from phase 2 verify the anatomical data collected in phase 1 and show that the sciatic nerve depth to AP diameter ratio is 0.43 or the depth of the sciatic nerve is approximately 43% of thigh diameter if the patient is positioned in the lateral decubitus position.

Adult↗