Factors influencing the occurrence and severity of farm accidents: comparing work-related and nonwork-related events.

Economic incentives are emerging as useful preventive approaches to motivating farmers to adopt safer farming and managerial practices. The effectiveness of these programs and incentives will be enhanced by focusing resources on factors that play a critical role in contributing to farm accidents and the injury severity. A primary objective is to identify and assess the relative impact of factors that jointly influence the probability of work-related farm accidents relative to nonwork-related accidents and the severity of farm accidents. The model uses survey data on producer characteristics, farm organization, and work routines from the Georgia Healthy Farmers Project (GHFP). A probit model describing the factors that influence the probability of a work-related accident is estimated jointly with an ordered probit model for farm accident severity. The probit model indicates that older farmers and hired farm workers have higher probabilities of experiencing work-related accidents relative to nonwork-related events. Significant variables that influence the severity of farm accidents are more difficult to identify from the ordered probit models for both work-related and nonwork-related farm accidents.

Median "pseudoneurapraxia" at the wrist: reassessment of palmar stimulation of the recurrent median nerve.

OBJECTIVE: To determine the occurrence and effect of incidental deep ulnar nerve (DUN) costimulation during palmar stimulation of the recurrent median nerve (RMN). DESIGN: Observational. SETTING: Electromyography laboratory. PARTICIPANTS: Seventeen asymptomatic adult volunteers (34 hands) and 4 fresh cadaver hands. MAIN OUTCOME MEASURES: Median nerve stimulation at the wrist and careful incremental surface and subcutaneous (needle) palmar stimulation were performed while recording thenar and first dorsal interosseous manus compound muscle action potentials. Thenar palm-to-wrist amplitude difference (P -- W Delta) and palm-to-wrist amplitude ratio (P/W) were compared with published values. Correlation of DUN costimulation with falsely elevated P -- W Delta and P/W values was assessed. Multiplanar magnetic resonance imaging (MRI) and subsequent dissection of 4 fresh cadaver hands was done to measure the distance between the RMN and DUN at the palmar stimulation site. RESULTS: Two groups emerged: Group I (63%), with DUN stimulation, and II (37%), with no DUN stimulation. When DUN costimulation occurred (Group I), there was a statistically significant increase in P -- W Delta (p =.002 percutaneous, p =.02 subcutaneous) and P/W (p =.004 percutaneous, p =.007 subcutaneous) when compared with previously published data. Combining all trials on all hands, 53% and 25% had P -- W Delta values and P/W values that exceeded previously published normative data, respectively. The mean distance between the DUN and RMN at the palmar stimulation site was determined by dissection (1.2cm) and MRI (1.5cm). CONCLUSIONS: Close proximity of the DUN to the RMN causes frequent and often unavoidable DUN activation during palmar stimulation of the RMN. This inadvertent stimulation may cause a false diagnosis of median neurapraxia at the wrist.

Electrophysiologic mapping and cadaveric dissection of the lateral foot: implications for tibial motor nerve conduction studies.

OBJECTIVE: To clarify, through electrophysiologic mapping and cadaveric dissection of the lateral foot, the previously published "proximal" and "distal" recording sites for tibial motor nerve conduction studies. DESIGN: Observational. SETTING: Electromyography laboratory; anatomy laboratory. PATIENTS OR OTHER PARTICIPANTS: Ten asymptomatic feet; eight cadaveric feet. MAIN OUTCOME MEASURES: (1) Amplitudes and onset latencies of compound muscle action potentials (CMAPs) recorded over a grid on the lateral foot that included the "proximal" and "distal" recording sites; (2) nerve supply and anatomic boundaries of the abductor digiti minimi pedis (ADMP) and nearby muscles, particularly as they relate to the above recording sites. RESULTS: (1) Relatively large CMAPs were recorded at and around the "proximal" and "distal" sites, with significantly shorter "proximal" latencies. (2) In all cadaveric feet, ADMP was innervated by only the inferior calcaneal nerve (ICN) and was located deep to the "proximal" site, with virtually no muscle fibers deep to the "distal" site. The flexor digiti minimi brevis (FDMB) was conspicuously located immediately deep to the "distal" site and was innervated by only the lateral plantar nerve (LPN). CONCLUSIONS: This study strongly suggests that the "proximal" site records predominantly from the ICN-innervated ADMP, whereas the "distal" site predominantly records from the LPN-innervated FDMB.

Pelvic floor function/dysfunction and electrodiagnostic evaluation.

The pelvic floor provides support for the bladder, rectum, and genital systems, as well as proper positioning and orientation of the urethral and anal sphincters. Impairment may result in prolapse, urinary and fecal incontinence, and sexual dysfunction. The impact is enormous in terms of personal, social, and financial burden. Pertinent anatomy is presented, followed by an overview of available electrodiagnostic techniques and a description of pudendal nerve conduction studies, sacral reflex testing and selected electromyographic techniques. Clinical applications are discussed throughout the text and the need for further research is addressed.

Electrodiagnostic evaluation of the foot.

Focal entrapment neuropathies in the foot, as compared to those of the hand, represent a daunting diagnostic challenge to many electromyographers. This article emphasizes an understanding of the anatomy of the foot as a fundamental key to its electrodiagnostic evaluation. The anatomic course of specific nerves will be described in terms of entrapment sites, and the clinical and electrophysiologic manifestations of each nerve entrapment will be discussed.

Abductor hallucis false motor points: electrophysiologic mapping and cadaveric dissection.

False motor points (FMPs) can occur in intrinsic foot or hand muscles, causing spuriously prolonged distal motor latencies by misrepresenting the compound muscle action potential (CMAP) onset. We investigated the motor point (MP) and possible FMPs in abductor hallucis (AH) by three methods: (1) electrophysiologic mapping of the CMAP with a grid of approximately 29 G1 sites over AH (n = 20), including commonly used MPs just anterior to (Ant-MP) and posterior to (Post-MP) the navicular tuberosity; (2) electrophysiologic mapping with direct percutaneous threshold stimulation of AH (same grid as above); and (3) cadaveric dissection (n = 4). We found AH FMPs in 19 of 20 feet (2.7 FMPs/foot) which resulted in prolongation of the CMAP onset latency by 0.5-2.3 ms. Post-MP had a significantly lower mean threshold stimulus intensity than all other grid sites, including the FMPs. The anatomic MP of AH was consistently found just inferior and posterior to the navicular tuberosity. This study demonstrates that AH FMPs: (1) can be identified in virtually all feet; (2) do not correspond to the true MP (i.e., Post-MP); and (3) are likely due to superimposed compound action potentials from nearby muscles or nerves.

Generator sources for the early and late ulnar hypothenar premotor potentials: short segment electrophysiologic studies and cadaveric dissection.

OBJECTIVE: Determine the generator sources for the ulnar hypothenar premotor potentials (PMPs). DESIGN: Observational. SETTING: EMG laboratory. SUBJECTS: Ten asymptomatic adult volunteers, three cadaver hands. MAIN OUTCOME MEASURE: Far-field versus near-field characteristics of recorded PMPs as determined by bipolar and referential recording electrode montages. A possible anatomic basis for any observed differences between ulnar PMPs and previously studied median PMPs were explored through cadaveric dissection. RESULTS: An early PMP (E-PMP) had a latency that varied with changes in the position of G1 only. A late PMP (L-PMP was seen only when G1 and G2 were on different volumes (palm vs fifth digit, or second digit vs fifth digit); its latency did not vary significantly with changes in the position of G1 and G2. CONCLUSIONS: (1) E-PMP is a near-field potential generated by the ulnar nerve passing near the G1 electrode. (2) L-PMP represents a far-field potential generated by the ulnar digital nerves as they traverse from the hand volume containing G1 to the finger volume containing G2. (3) Greater L-PMP-to-CMAP separation in the median than in the ulnar nerve was explained by cadaveric dissection, which revealed that the motor branch (responsible for the trailing CMAP) is longer in the median nerve than in the ulnar nerve relative to each nerve's corresponding digital sensory branch (responsible for the preceding L-PMP). (4) The PMP that is typically recorded with G1 at the hypothenar motor point and G2 on the fifth digit most likely represents E-PMP. (5) Any proposed diagnostic use of the ulnar PMPs must take into consideration these generator sources.

"Guided" intramuscular fine wire electrode placement. A new technique.

This report describes a new technique for placing intramuscular fine wire electrodes into muscles for kinesiologic electromyographic (EMG) studies. Currently, a pair of fine wire electrodes (one active, one reference) within a hypodermic needle is inserted into the selected muscle. The needle is then withdrawn, leaving the two fine wires positioned within the muscle. Electrical stimulation of the muscle through these fine wire electrodes confirms their correct placement. However, if positioning is incorrect, additional pairs of wires are inserted within needles until correct placement is achieved. Our "guided" method combines this "blind" technique with diagnostic needle EMG techniques. Using a conventional EMG machine and selective activation of the desired muscle, the electromyographer inserts the hypodermic needle while monitoring the muscle's electrical signal through the advancing fine wire electrodes. This signal is used to "guide" the needle into the proper muscle. Once correct positioning of the wires is confirmed by the EMG signal, the needle is removed. With this techniques additional needle insertions are avoided, electrical stimulation is seldom needed, and rarely studied muscles are accessed as easily as commonly studied ones. We have used this technique with pediatric and adult patients as well as in kinesiologic EMG research and have found it to be well tolerated and reliable.

Generators of the early and late median thenar premotor potentials.

The generator sources of the median thenar premotor potentials (PMPs) have remained elusive despite debate in the literature. By studying the median nerve in the hand with a variety of bipolar and referential recording montages, we systematically examined the possible near-field and far-field sources that may determine these potentials. The results suggest that the early PMP is a near-field potential recorded by G1 and generated by the median nerve traversing the distal carpal tunnel. The late PMP represents a far-field potential generated by the median digital nerve fibers as they pass from the palm volume into the thumb volume. Characteristics of the late PMP are explained using the leading/trailing dipole (L/TD) model of far-field potential generation. The diagnostic utility of these PMPs is questionable, since they are recorded from "regions" along the nerve rather than from more clearly defined sites.

The medial calcaneal nerve: anatomy and nerve conduction technique.

We report a new technique for studying conduction in the medial calcaneal nerve (MCN). Dissection of 14 cadaver feet revealed the optimal G1 site to be one third of the way from the apex of the heel to a point midway between the navicular tuberosity and the prominence of the medial malleolus. Seventy-two feet (36 healthy volunteers) were studied using surface stimulation of the tibial nerve 10 cm proximal to the G1 surface electrode. Averaging technique was not required. Reference values (mean +/- 2 SD) were determined for MCN onset latency (2.0 +/- 0.3 ms), peak latency (2.5 +/- 0.3 ms), onset conduction velocity (61 +/- 11 m/s), peak conduction velocity (40 +/- 5 m/s), baseline-to-peak amplitude (18 +/- 6 microV), and maximum intrasubject side-to-side differences in these values (0.3 ms, 0.3 ms, 15 m/s, 5 m/s, and 17 microV, respectively). This study provides an easily performed, reproducible method for electrophysiologic evaluation of the MCN.

Development of a model of the premotor potential.

This study explored the sensory nature of the small negative premotor potential (PMP) that is often seen preceding the compound muscle action potential. We developed a model of the PMP, using the ulnar and superficial radial sensory (SRS) nerves. Standard conduction studies of the deep ulnar motor nerve recording over the first dorsal interosseous manus (FDIM) and of the SRS nerve recording over the same site were done separately, then simultaneously, on 20 normal hands. In all subjects, there was no FDIM PMP, but with simultaneous stimulation of both nerves, there was a potential in all subjects that appeared similar to their median thenar and ulnar hypothenar PMPs. Reference data for the median thenar, ulnar hypothenar, and model PMP were generated. Findings from this study are discussed and appear to support the concept of the PMP being either a sensory potential or a junctional potential.

Electrodiagnostic medicine.

Electrodiagnostic testing examines the physiologic integrity of the peripheral nervous system. However, such testing should represent only one part of an electrodiagnostic consultation in which the entire clinical context, including the history, physical examination, laboratory studies, and electrodiagnostic testing, is considered as a whole. Although each electrodiagnostic laboratory establishes its own normal values for nerve conduction studies and needle EMG, these values should not be used in isolation. The electrodiagnostic consultation can help narrow an otherwise broad differential diagnosis, confirm a suspected diagnosis, or help define a confusing clinical picture.