Robotically assisted nerve and facet blocks: a cadaveric study

RATIONALE AND OBJECTIVES: This study was performed to evaluate the feasibility of using a joystick-controlled robotic needle driver to place a 22-gauge needle for nerve and facet blocks. MATERIALS AND METHODS: Biplane fluoroscopy and a robotic needle driver were used to place 12 needles into the lumbar paraspinal region of an embalmed female cadaver (age at death, 98 years). Small metal BB nipple markers (1 mm in diameter) were inserted percutaneously to serve as targets. Six needles were then placed near the nerve root, and six were placed near the facet root. Anteroposterior and lateral radiographs were obtained after each needle placement to assess its accuracy. RESULTS: All needles were placed within 3 mm of the target BB. The average distance was 1.44 mm +/- 0.66 (standard deviation). DISCUSSION: A robotic needle driver can be used to place needles accurately in the nerve and facet regions. Clinical studies are required to investigate the advantages and disadvantages of this system for interventional procedures involving needles.     

Physiologic basis of potentials recorded in electromyography

The extracellularly recorded configuration of a single muscle fiber discharge is generally appreciated to be triphasic with an initially positive deflection. However, careful attention to waveform appearance during the electrodiagnostic medicine examination reveals that both innervated and denervated muscle waveforms may display a pantheon of configurations. Further, despite the fact that innervated and denervated single muscle fiber discharges arise from distinctly different intracellular action potential (IAP) configurations, their extracellularly recorded waveforms can appear quite similar, leading to potential misidentification and, hence, the possibility of an erroneous diagnostic conclusion. The least appreciated, but nevertheless critical, aspect of explanations for muscle waveform configurations is the relationship between the muscle fiber and recording electrode. Additionally, it is important to appreciate both the near-field and far-field aspects of single fiber and compound muscle action potentials. In this review, the leading/trailing dipole model is used to explain muscle waveform configurations in both innervated and denervated tissues.     

Morbid obesity: a surgical perspective

Morbid obesity is a chronic illness of multifactorial aetiology which is defined as Body Mass Index (BMI) greater than 40 kg/sq.m. Non-surgical treatments for this condition have been shown to be ineffective. Surgery is the only effective treatment and obtains the best long-term outcomes. Surgery is indicated when BMI is greater than 40, or BMI is greater than 35 with significant associated co-morbidities. Four types of operations are currently performed: restrictive, malabsorptive, combined procedures (malabsorptive-restrictive) and motility-reducing pro-cedures. With restrictive procedures (adjustable gastric banding and vertical banded gastroplasty), patients can expect a long-term excess weight loss of 44-68%; for combined procedures (Roux-en-Y gastric by-pass) this is 60-70%, whereas for malabsorptive procedures (bilio-pancreatic diversion with or without duodenal switch), this is 75-80%. Intra-gastric stimulation is the least invasive treatment, but induces the lowest excess weight loss (32%) in the first two years after the operation. Gastric banding offers the best results when balancing risks and benefits. All procedures are now performed laparoscopically with comparable results to open surgery. The overall mortality rate in specialized centers is less than 0.3%. Different techniques are indicated according to BMI and the patient's eating habits. Surgery for morbid obesity has proved to improve quality of life and significantly reduce associated co-morbidities.     

AAEM Minimonograph #10: volume conduction

A volume conductor is any medium with the capability of passively conducting a current between regions of potential difference. The monophasic positive intracellular action potential produces a monophasic negative extracellular waveform and a triphasic extracellular waveform in a poor and good volume conductor, respectively. The observed waveform characteristics are dependent upon both the recording electrode montage and the type of volume conductor surrounding the excitable tissue. The extracellular current flow associated with an action potential can be divided into two current sources flanking a central current sink. If a recording electrode is located over the negative current sink, a negative potential is observed. When the two current sources approach a recording electrode, a positive potential is recorded. If a positive deflection of the baseline is observed, one may conclude that the wave of depolarization under investigation did not originate under, but traveled toward, the recording location. Electric currents from external sources are free to propagate extraneurally as the body is a good volume conductor. Care must be taken to not activate nearby nerves and, subsequently, obtain a waveform contaminated with potentials from undesired sources. Additionally, electrical activity from neighboring muscles and nerves can summate in the volume conductor and yield responses capable of masking pathology. An understanding of the principles of volume conduction theory can help the electrodiagnostician avoid artifactual errors and erroneous conclusions.     

Needle and surface electrode somatosensory evoked potential normative data: a comparison

Subdermal needle electrodes are now used routinely to record cortical somatosensory evoked potentials (SEPs). Investigators may make assumptions that: (1) SEP normative data obtained with surface electrodes can be used to interpret needle recordings, and (2) there is an increased potential for local dermal infection with needle electrodes. This investigation compared the waveform parameters obtained with surface and needle electrodes after stimulation of the tibial nerve, sural nerve, and L5 dermatome in 20 subjects. No statistically significant difference was found in the P latency, N latency, or P/N amplitude of the needle recordings as compared to the surface recordings. Additionally, 20 subjects studied for one week after four hours of needle insertion did not show any evidence of dermal infection. This study objectively documents no statistically significant difference between needle and surface SEP recordings and substantiates the use of surface normative data for needle SEP investigations.     

Electrophysiologic investigation of thallium poisoning

Electrophysiologic findings in thallium intoxication are usually untimely, limited in extent, and often uninformative. This report documents serial conduction and electromyographic findings in a case of thallium poisoning, beginning 10 days after symptom onset and ending 24 months later. Initially, the plantar nerves in the foot demonstrated profound axonal loss while the sural and peroneal nerves were essentially normal. The latter two nerves subsequently underwent axonal loss. Two years were required for the sural and peroneal nerves to display recovery. At 24 months, the plantar nerves continue to remain absent. A primarily distal axonopathy, significantly worse in the lower than upper extremities and requiring more than 2 years for recovery, now documents what was previously speculated: the electrophysiologic course of thallium intoxication. Additionally, this case emphasizes the need to examine the plantar nerves of the foot to avoid missing distal axonopathies during the early course of the disease process. The clinical course and pathophysiology of thallium poisoning are also reviewed.     

Digit distribution of proper digital nerve action potential.

Antidromic sensory nerve action potential testing is well characterized and commonly used to assess the sensory component of the upper limb median and ulnar nerves. The final terminal segments of these nerves are the proper digital nerves. Ring recording electrodes are commonly used to detect the proper digital nerves' antidromic responses. Attempts to record the separate contributions of individual digital nerves along the lateral aspects of each finger, using small surface electrodes, is shown to be unreliable for determining the integrity of a single terminal digital branch. We found between 50% to 77% of the stimulated terminal branch's response amplitude when recorded at electrodes positioned over the nonstimulated branch located 180 degrees from the activated terminal branch. Detecting a single terminal nerve response was achieved by using the fourth digit and the second digit with one of the second digit's branches neurophysiologically blocked by local anesthetic. The volume-conducted response from the opposite side of the finger resulted in this relatively large recorded response, which remains within the range of reference values precluding the simple use of antidromic techniques to assess injury to a single proper digital nerve. Techniques are proposed to avoid such pitfalls and to assess most accurately the desired response.