Sciatic nerve function following hindlimb thermal injury

Thermal Dynamics of a Novel Radio-Frequency Device for Endoscopic Spine Surgery: An Experimental Model

STUDY DESIGN

Experimental study.

OBJECTIVE

In this study, the ambient temperature of a radiofrequency (RF) electrode tip was compared and analyzed in terms of products, mode, flow quantity, and flow rate.

SUMMARY OF BACKGROUND DATA

Endoscopic spine surgery is a widely used operation for degenerative lumbar stenosis and herniated lumbar disc. To perform endoscopic spine surgery, dedicated instruments like a RF generator and electrode are essential.

METHODS

An evaluation system capable of measuring temperature under equal conditions at a certain distance from the electrode tip was manufactured. The distance between the electrode tip and the temperature sensor was set to 1, 5, and 10 mm. The flow quantities of 0, 50, 100, and 150 mL/min and the flow rates of 0, 0.20, 0.53, and 0.80 m/s were compared and statistically analyzed.

RESULTS

The temperatures measured in the experiments conducted on the four combinations of RF device showed similar values, and showed differences according to the characteristics of each mode of the RF. As the distance between the electrode tip and the temperature sensor increased, the temperature decreased, and as flow quantity or flow rate increased, the temperature decreased. The maximum temperatures differed significantly according to flow quantity, between flow quantities of 0 and 100 mL/min (P  = 0.03) and between 0 and 150 mL/min (P ≤ 0.01). The maximum temperatures also differed significantly between the flow rate of 0 m/s, and the flow rates of 0.20, 0.53, and 0.80 m/s, with P ≤ 0.01 in all three comparisons.

CONCLUSION

This is the first study in which we made a customized RF temperature evaluation system and verified the temperature changes in various environments. When irrigation was performed, we could confirm that the maximum temperature was less than 60°C. Irrigation is considered essential in endoscopic spine surgery.

LEVEL OF EVIDENCE

3.

Is carpal tunnel release safe in electrical burn decompressive therapy: Six-years experience

Objective: Upper extremity electrical burn can create severe sequela and debilitation if not treated properly. Immediate decompression with fasci- otomy and carpal tunnel release seem to be the most promising choice of treatment. Neurologic functional loss can be avoided if median nerve is liberated.

Material and Methods: During 6-year time interval, 50 out of 1158 burn patients underwent upper extremity decompressive fasciotomy with carpal tunnel release. Their hand motor function based on nerve innervation and daily usage questionnaire were followed in 12-month intervals.

Results: Average score rose markedly after 18th month and reached nearly normal at the end of 66th month. Median, ulnar and radial nerve function tests were all positive, and no irreversible nerve function loss observed.

Conclusion: All compartments of the forearm should be explored and carpal tunnel release should be added into upper extremity decompressive fasciotomy after electrical burns.

Histological evaluation of thermal damage to Osteocytes: A comparative study of conventional and ultrasonic-assisted bone grinding

This paper addresses an important issue faced by neurosurgeons during surgical skull bone grinding, a common process used to remove bone in skull base tumour removal surgery to enable the neurosurgeon to reach the target region. The heat generated during bone grinding could harm the soft tissues and can lead to osteonecrosis and cell death. In the present study, a novel process of rotary ultrasonic bone grinding (RUBG) was proposed for osteotomy to limit the temperature to a safe level. A systematic investigation was conducted to determine the effect of varying process parameters on osteonecrosis at the cut surface. Three input parameters - rotational speed, feed rate and frequency - were investigated (at three levels) in terms of change in temperature and thermal biological damage. A sterile solution was used as a coolant to irrigate the grinding zone. Viable lacunae (filled osteocytes), non-viable lacunae (empty lacunae), necrosed tissues, and Haversian canal were found during the histological examination. Statistical analysis revealed that feed rate (45.43%) had the highest contribution towards temperature rise during grinding, followed by ultrasonic frequency (23.87%), and rotational speed (12.85%). The optimal machining parameters to avoid osteonecrosis and thermal trauma were rotational speed 35,000 rpm, feed rate 20 mm/min and ultrasonic frequency 20 kHz. Furthermore, histograms revealed that ultrasonic skull bone grinding was associated with greater cell viability and reduced temperature compared with conventional bone grinding.

Fluid Lubrication and Cooling Effects in Diamond Grinding of Human Iliac Bone

Background and Objectives: Although there have been research on bone cutting, there have been few research on bone grinding. This study reports the measurement results of the experimental system that simulated partial laminectomy in microscopic spine surgery. The purpose of this study was to examine the fluid lubrication and cooling in bone grinding, histological characteristics of workpieces, and differences in grinding between manual and milling machines. Materials and Methods: Thiel-fixed human iliac bones were used as workpieces. A neurosurgical microdrill was used as a drill system. The workpieces were fixed to a 4-component piezo-electric dynamometer and fixtures, which was used to measure the triaxial power during bone grinding. Grinding tasks were performed by manual activity and a small milling machine with or without water. Results: In bone grinding with 4-mm diameter diamond burs and water, reduction in the number of sudden increases in grinding resistance and cooling effect of over 100 °C were confirmed. Conclusion: Manual grinding may enable the control of the grinding speed and cutting depth while giving top priority to uniform torque on the work piece applied by tools. Observing the drill tip using a triaxial dynamometer in the quantification of surgery may provide useful data for the development of safety mechanisms to prevent a sudden deviation of the drill tip.

Electrocautery in arthroscopic surgery: intra-articular fluid temperatures above 43 °C cause potential tissue damage

PURPOSE

The use of electrocautery during arthroscopy may heat intra-articular saline and subsequently damage intra- and extra-articular tissue. Newer electrocautery devices have the ability to measure the outflow fluid temperature and switch off before reaching a certain threshold; however, the scientific evidence establishing these temperature thresholds' potential for inadvertent damage is lacking. The aim of this study was to analyse current available literature on temperature thresholds for tissue damage after exposure to heated fluid and provide a recommendation for the maximum temperature of intra-articular fluid to prevent tissue damage.

METHODS

In February 2018, a systematic literature review was performed using the MEDLINE/PubMed and Embase databases. Inclusion was limited to studies investigating temperature thresholds for thermal damage to at least one of the tissues of interest: skin, bone, cartilage, soft tissues, and nerves. Studies not reporting specific temperature thresholds for thermal damage were excluded.

RESULTS

Twenty articles were selected for the final evaluation and data extraction. Varying temperature thresholds, based on the lowest reported temperature causing tissue damage, were found for the different tissues of interest: 44 °C for dermal tissues, between 47 and 50 °C for bony tissues, 50 °C for cartilage, between 43 and 55 °C for soft tissues, and 43 °C for nerves.

CONCLUSION

Based on the current literature, a temperature threshold for intra-articular fluid of 43 °C during an arthroscopic procedure is recommended to prevent tissue damage. Higher temperatures may cause damage to surrounding intra- and extra-articular tissues. The threshold for irreversible damage is likely to be higher. In clinical practise, one should be aware of possible heating of intra-articular fluid when using electrocautery and related risk of tissue damage.

LEVEL OF EVIDENCE

III.

Peripheral Neuropathy and Nerve Compression Syndromes in Burns

Peripheral neuropathy and nerve compression syndromes lead to substantial morbidity following burn injury. Patients present with pain, paresthesias, or weakness along a specific nerve distribution or experience generalized peripheral neuropathy. The symptoms manifest at various times from within one week of hospitalization to many months after wound closure. Peripheral neuropathy may be caused by vascular occlusion of vasa nervorum, inflammation, neurotoxin production leading to apoptosis, and direct destruction of nerves from the burn injury. This article discusses the natural history, diagnosis, current treatments, and future directions for potential interventions for peripheral neuropathy and nerve compression syndromes related to burn injury.

Burn injury and long-term nervous system morbidity: a population-based cohort study

OBJECTIVE

To investigate if children and adults who are hospitalised for a burn injury have increased long-term hospital use for nervous system diseases.

DESIGN

A population-based retrospective cohort study using linked administrative health data from the Western Australian Data Linkage System.

PARTICIPANTS

Records of 30 997 persons hospitalised for a first burn injury in Western Australia during the period 1980-2012, and 123 399 persons who were age and gender frequency matched with no injury admissions randomly selected from Western Australia's birth registrations and electoral roll.

MAIN OUTCOME MEASURES

Admission rates and summed length of stay for nervous system diseases. Negative binomial and Cox proportional hazards regression modelling were used to generate incidence rate ratios (IRRs) and HRs with 95% CIs, respectively.

RESULTS

After adjustment for demographic factors and pre-existing health status, the burn injury cohort had 2.20 times (95% CI 1.86 to 2.61) as many nervous system admissions and 3.25 times the number of days in hospital (95% CI: 2.28 to 4.64) than the uninjured cohort. This increase was found for those who had sustained burns during childhood (<15 years: IRR, 95% CI: 1.97, 1.49 to 2.61) and early to mid-adulthood (15-45 years: IRR, 95% CI: 2.70, 2.06 to 3.55) and older adults (≥45 years: IRR, 95% CI: 1.62, 1.33 to 1.97). Significantly elevated first-time postburn admissions were observed for children for 15 years postburn discharge (0-5 years: HR, 95% CI: 1.97, 1.75 to 2.22; 5-15 years: HR, 95% CI: 1.44, 1.28 to 1.63) and for adults 45 years and older at index burn for 5 years postburn only (HR, 95% CI: 1.72, 1.42 to 2.09).

CONCLUSIONS

Burn injury appears to be associated with increased nervous system-related morbidity for many years after burn injury. Further work into the mechanisms and possible treatments to reduce this morbidity are warranted in light of these findings.

Thermal effects of 2450 MHz microwave exposure near a titanium alloy plate implanted in rabbit limbs

This study aimed to examine the safety profile of microwave therapy on limbs with metal implants. New Zealand white rabbits were implanted with titanium alloy internal fixation plates. Femurs were exposed to 20, 40, 60, or 80 W of microwave radiation for 30 min (microwave applicator at 2450 MHz), and temperatures of the implants and muscles adjacent to implants were recorded. To evaluate thermal damage, nerves were electrodiagnostically assessed immediately after radiation, and histologic studies performed on nerve and muscle sections. As expected, implant temperature was highest in the exposure field. Temperatures of limbs with titanium alloy implants increased significantly at 60 and 80 W, with a significant decline in the nerve conduction velocity and acute thermal injuries in nerves and muscles adjacent to implants. However, temperature remained unchanged and no adverse effects were observed in nerves and muscles at 20 and 40 W. These findings are inconsistent with the current notion that surgical metal implants in the treatment field are contraindications for microwave therapy. Hence, we believe that a lower dose of continuous wave microwave irradiation is safe for limbs with titanium alloy implants.

Monopolar radiofrequency use in deep gluteal space endoscopy: sciatic nerve safety and fluid temperature

PURPOSE

The purpose of this study was to evaluate the temperature at the sciatic nerve when using a monopolar radiofrequency (RF) probe to control bleeding in deep gluteal space endoscopy, as well as assess the fluid temperature profile.

METHODS

Ten hips in 5 fresh-frozen human cadaveric specimens from the abdomen to the toes were used for this experiment. Temperatures were measured at the sciatic nerve after 2, 5, and 10 seconds of continuous RF probe activation over an adjacent vessel, a branch of the inferior gluteal artery. Fluid temperatures were then measured at different distances from the probe (3, 5, and 10 mm) after 2, 5, and 10 seconds of continuous probe activation. All tests were performed with irrigation fluid flow at 60 mm Hg allowing outflow.

RESULTS

After 2, 5, or 10 seconds of activation over the crossing branch of the inferior gluteal artery, the mean temperature increased by less than 1°C on the surface and in the perineurium of the sciatic nerve. Considering the fluid temperature profile in the deep gluteal space, the distance and duration of activation influenced temperature (P < .05). Continuous delivery of RF energy for 10 seconds caused fluid temperature increases of 1.2°C, 2°C, and 3.1°C on average at 10 mm, 5 mm, and 3 mm of distance, respectively.

CONCLUSIONS

This study found the tested monopolar RF device to be safe during use in vessels around the sciatic nerve after 2, 5, and 10 seconds of continuous activation. The maximum fluid temperature (28°C) after 10 seconds of activation at 3 mm of distance is lower than the minimal reported temperature necessary to cause nerve changes (40°C to 45°C).

CLINICAL RELEVANCE

Monopolar RF seems to be safe to the neural structures when used at more than 3 mm of distance and with less than 10 seconds of continuous activation in deep gluteal space endoscopy with fluid inflow and outflow.

Thresholds for thermal damage to normal tissues: an update

The purpose of this review is to summarise a literature survey on thermal thresholds for tissue damage. This review covers published literature for the consecutive years from 2002-2009. The first review on this subject was published in 2003. It included an extensive discussion of how to use thermal dosimetric principles to normalise all time-temperature data histories to a common format. This review utilises those same principles to address sensitivity of a variety of tissues, but with particular emphasis on brain and testis. The review includes new data on tissues that were not included in the original review. Several important observations have come from this review. First, a large proportion of the papers examined for this review were discarded because time-temperature history at the site of thermal damage assessment was not recorded. It is strongly recommended that future research on this subject include such data. Second, very little data is available examining chronic consequences of thermal exposure. On a related point, the time of assessment of damage after exposure is critically important for assessing whether damage is transient or permanent. Additionally, virtually no data are available for repeated thermal exposures which may occur in certain recreational or occupational activities. For purposes of regulatory guidelines, both acute and lasting effects of thermal damage should be considered.

Prostate thermal therapy with high intensity transurethral ultrasound: the impact of pelvic bone heating on treatment delivery

PURPOSE

This study was designed to assess pelvic bone temperature during typical treatment regimens of transurethral ultrasound thermal ablation of the prostate to establish guidelines for limiting bone heating.

METHODS

Treatment with transurethral planar, curvilinear, and sectored tubular applicators was simulated using an acoustic and biothermal pelvic model that accommodates applicator sweeping, boundary temperature control, and changes in perfusion and attenuation with thermal dose to more accurately model ultrasound energy penetration. The effects of various parameters including power and frequency (5-10 MHz) on bone heating were assessed for a range of prostate cross-sections (3-5 cm) and bone distances (1-3 cm).

RESULTS

All devices can produce significant bone heating (temperatures >50 degrees C, thermal dose >240 EM(43 degrees C)) without optimization of applied frequency or power for bone <3 cm from the prostate boundary. In small glands ( approximately 3 cm) increasing operating frequency of curvilinear and planar devices can increase bone temperatures, whereas the tubular applicator can be used at 10 MHz to avoid likely bone damage. In larger prostates (4-5 cm wide) increasing frequency reduces bone heating but can substantially increase treatment time. Lowering power can reduce bone temperature but may increase thermal dose by increasing treatment duration. All applicators can be used to treat glands 4-5 cm with limited bone heating by selecting appropriate power and frequency.

CONCLUSIONS

Pubic bone heating during ultrasound thermal therapy of the prostate can be substantial in certain situations. Successful realization of this therapy will require patient-specific treatment planning to optimally determine power and frequency in order to minimize bone heating.

Thermal tissue damage caused by ultrasonic cement removal from the humerus

BACKGROUND

Ultrasound devices can selectively remove cement during revision arthroplasty. These instruments initially were designed for the hip and knee but also have been applied to the upper extremity. We describe a patient in whom a radial nerve palsy and a pathologic humeral fracture developed after ultrasonic cement removal was performed because of an infection at the site of a total elbow arthroplasty. Biopsies of the humerus, the triceps muscle, and the radial nerve showed widespread necrosis consistent with thermal injury.

METHODS

A study involving six human cadaveric specimens was conducted to measure temperature elevations in bone and adjacent soft tissue during cement removal with use of an ultrasound device with and without irrigation.

RESULTS

While temperature increased only minimally during cement polymerization, ultrasonic melting and removal of cement with use of constant energy delivery led to markedly elevated temperatures in the humeral cortex, the triceps muscle, and the radial nerve. These temperatures were above the known thresholds for thermal injury and necrosis. Subsequently, strategies designed to allow for safe ultrasonic cement removal from the humerus were applied, including intermittent delivery of energy and the use of cold irrigation between probe passes. These strategies resulted in markedly lower maximum temperatures in all tissues tested.

CONCLUSIONS

Temperatures in the humerus, triceps, and, most importantly, the radial nerve can reach potentially dangerous levels when ultrasound technology is used to remove cement from the humerus. We suggest intermittent cold irrigation of the humeral canal, no tourniquet use, education of surgeons with regard to proper techniques designed to limit heat generation, and consideration of exposure and protection of the radial nerve when ultrasound devices are used.

Temperature along the axillary nerve during radiofrequency-induced thermal capsular shrinkage

BACKGROUND

There have been reports of axillary nerve palsy after thermal capsular shrinkage with radiofrequency energy-generating devices. The exact cause of this is unknown.

HYPOTHESIS

The temperature of the axillary nerve increases during shoulder capsular shrinkage at various degrees of shoulder abduction.

STUDY DESIGN

Laboratory study.

METHODS

Fifteen cadaveric shoulders had fiberoptic thermometer probes placed at various points along the axillary nerve and major branches under the capsule. The shoulders underwent thermal capsular shrinkage with a radiofrequency energy-inducing device at various positions of abduction.

RESULTS

With the arm at the side, temperatures above 50 degrees C (56 degrees -61 degrees C) were evident along the teres minor branch of the axillary nerve in 4 of 6 specimens. The increase in temperature was noted in the middle to posterior aspect of the inferior capsule. At 45 degrees of abduction, 4 of 5 shoulders demonstrated increases in temperature greater or equal to 50 degrees. Three of 4 shoulders tested at 90 degrees of abduction revealed similar temperature increases.

CONCLUSIONS

The arthroscopic technique of thermal capsular shrinkage causes an increase in the temperature of the axillary nerve and its branches in 11 of 15 cadaveric specimens tested at various arm positions-particularly affected is the teres minor branch.

CLINICAL RELEVANCE

Orthopaedic surgeons using the radiofrequency device for thermal capsular shrinkage need to be aware of the possible increase in temperature along the axillary nerve and its branches during this procedure. The clinical effect of this type of increase on the nerve is unknown.

Axillary nerve temperatures during radiofrequency capsulorrhaphy of the shoulder

PURPOSE

The purpose of this study was to determine the temperatures along the course of the axillary nerve during radiofrequency (RF) capsulorrhaphy of the shoulder in a cadaver model. The hypothesis of this project was that temperatures capable of damaging neural tissue would be recorded during simulated RF capsulorrhaphy.

TYPE OF STUDY

Basic science evaluation.

METHODS

This study used 9 fresh-frozen cadaver shoulder capsules removed en bloc along with the underlying axillary nerve and soft tissue. The axillary nerve was instrumented with 4 thermocouples placed along the course of the nerve (2 thermocouples anterior and 2 posterior to the 6 o'clock position, spaced 7 mm apart). Each of the specimens underwent RF thermal capsulorrhaphy during which the temperature at each of the thermocouple positions was continuously recorded.

RESULTS

The average of the maximum temperature at each of the 4 positions measured along the course of the axillary nerve were 52.2 +/- 18.0 degrees C at the most anterior place probed, 45.8 +/- 5.44 degrees C (mid anterior), 44.5 +/- 8.7 degrees C (mid posterior), and 42.8 +/- 10.1 degrees C at the most posteriorly positioned probe. Two specimens had a maximum temperature greater than the 67 degrees C set point of the device, and 7 specimens had a maximum temperature greater than 45 degrees C in at least 1 thermocouple position.

CONCLUSIONS

This study shows that heating of the axillary nerve can occur during RF capsular shrinkage of the shoulder and may potentially reach levels that can damage neural tissue.

Axillary nerve injury after thermal capsular shrinkage of the shoulder

The purpose of this study was to evaluate 4 cases in which axillary nerve injury was observed after radiofrequency capsular shrinkage of the shoulder. These cases were used to evaluate the clinical circumstances under which axillary nerve injury occurred, the time frame over which these injuries recovered, and the ultimate outcome observed in these patients. The case histories of each of these 4 patients were carefully evaluated. In 2 of the 4 cases, purely sensory findings were found, and in 2 cases both sensory and motor injuries occurred. In each case the inferior axillary recess was treated using the Oratech Interventions Tac-S probe. The authors conclude that injury to the axillary nerve during this procedure is possible and postulate that heat penetration through the capsule to the nerve is the most likely cause of injury.

Noncontusive segmental spinal cord injury using radiofrequency current

OBJECTIVE

To develop a nondisruptive model for the study of spinal cord injury.

METHODS

A 2-MHz radiofrequency heating chamber was mounted over the rat T13-L1 vertebral column via a short dorsal incision. Epidural temperature at chamber level was monitored via a small proximal laminotomy. Forty-three rats were studied using time-temperature heating regimens from 45 to 48.5 degrees C and 4 to 15 minutes. A blinded numerical hind limb impairment score (Neurologic Impairment Score) was determined at intervals up to 2 weeks after injury. Segmental spinal cord blood flow was measured using [14C]butanol tissue uptake in injured and control rats.

RESULTS

Above the injury threshold, increasing the time-temperature regimens was associated with a progressively worse Neurologic Impairment Score (r = 0.73-0.87 up to 24 hours after injury). Cord blood flow was unchanged at 2 hours but was 44% depressed at the injury level 6 hours after injury (p < 0.01). Histologically, injury extended minimally beyond the injured segment. Vascular thrombosis was not seen.

CONCLUSION

This comparatively noninvasive model does not mechanically disrupt cord components and results in progressive neurologic impairment that correlates with the time-temperature regimen used for injury. It should be useful in identifying secondary phenomena that worsen functional status after cord trauma.

Selective decrease of small sensory neurons in lumbar dorsal root ganglia labeled with horseradish peroxidase after ND:YAG laser irradiation of the tibial nerve in the rat

Recent electrophysiological evidence indicates that Q-switched Nd:YAG laser irradiation might have selective effects on neural impulse transmission in small slow conducting sensory nerve fibers as compared to large diameter afferents. In an attempt to clarify the ultimate fate of sensory neurons after laser application to their peripheral axons, we have used horseradish peroxidase (HRP) as a cell marker to retrogradely label sensory neurons innervating the distal hindlimb in the rat. Pulsed Nd:YAG laser light was applied to the tibial nerve at pulse energies of 70 or 80 mJ/pulse for 5 min in experimental rats. Seven days later HRP was applied to the left (laser-treated) and to the contralateral (untreated) tibial nerve proximal to the site of laser irradiation. In control animals the numbers of HRP-labeled dorsal root ganglion cells were not significantly different between the right and the left side. In contrast, after previous laser irradiation labeling was always less on the laser-treated side (2183 +/- 513 cells, mean +/- SEM) as compared to the untreated side (3937 +/- 225). Analysis of the dimensions of labeled cells suggested that the reduction of labeled cells on the laser-treated side was mainly due to a deficit in small sensory neurons. Since the conduction velocity of nerve fibers is related to the size of their somata, our histological data imply that laser light selectively affects retrograde transport mechanisms for HRP in slow conducting sensory nerve fibers.

Regional blood flow in resting and stimulated sciatic nerve of diabetic rats

The role of ischemia in the pathogenesis of diabetic peripheral neuropathy remains uncertain. We used the distribution of [14C]butanol to measure resting regional sciatic nerve blood flow in normal, anesthetized rats and in rats with acute experimental diabetes from streptozotocin administration. Regional flows in hind limb biceps femoris muscle and skin were simultaneously measured. In additional diabetic rats, these blood flows were compared in both limbs after proximal electrical stimulation of one sciatic trunk (10 shocks/s) for 15 min. One month after streptozotocin administration, 8 of 11 test rats were hyperglycemic. Resting nerve blood flow in the hyperglycemic rats--5.6 +/- 3.07 ml.min-1.100 g-1--was significantly less than that in the controls (9.4 +/- 3.9 ml.min-1.100 g-1, P = 0.002). Muscle blood flow was normal and skin blood flow decreased in these rats. Calculated tissue vascular resistances were elevated in all three tissues. Stimulation of one sciatic trunk in five other diabetic rats resulted in a stimulated nerve blood flow of 15.7 +/- 7.7 ml.min-1.100 g-1, and nerve blood flow in the resting control limb was 7.7 +/- 4.3 ml.min-1.100 g-1 (P = 0.009). Muscle blood flow increased approximately fourfold on the stimulated side but skin blood flow did not increase. Resting sciatic nerve blood flow is modestly decreased in acute streptozotocin-induced diabetes, but the neural blood vessels are still responsive to the increase in nerve metabolic activity associated with nerve stimulation.