From the Journal of the American Podiatric Association, Volume 69 - Number 9 - September 1979

Evaluation of Transcutaneous Electrical Nerve Stimulation (TENS) in Podiatric Surgery

Walter A. Alm, DPM *
Mark L. Gold, DPM *
Lowell Scott Weil, DPM +

Transcutaneous Electrical Nerve Stimulation (TENS) transmits an Electrical signal through the skin to the appropriate underlying nerve to alter the message of pain traveling to the brain.  This study evaluates the usefulness of TENS in the treatment of acute postoperative pain following podiatric surgery.  Three patient catagories, 1) actual TENS, 2) placebo TENS and 3) random controls are reported.  The findings Illustrate subjective relief of pain and decreased use of analgesic medications, utilizing TENS.

It would be ideal if one could relieve a patient's pain without the use of powerful analgesics, which often have many side effects of their own.  Electrical neural stimulation may be the answer to this perplexing problem.

In 46 A.D., electricity's analgesic properties were discovered when Scribonius Largus, a Roman physician, used the electric ray of a torpedo fish to treat headache and gout.  In 1745, Galvani experimented wit the effects of direct current; Faraday discovered alternating current in the 1830's.  In 1918, a device called Electreat was introduced by a naturopath.  The medical community began to show a skeptical interest in electrical neural stimulation.  However, with new advances in biomedical engineering and pain theory, this device was later replaced with more sophisticated models.

In 1965, Melzack and Wall published the "Gate Theory of Pain".  They offered the first explanation on the theory of electrical nerve stimulation, postulating that stimulation of large non-pain impulse fibers will inhibit the smaller pain-carrying fibers in the spinal cord.  Because the large myelinated fibers have a lower threashold to stimulation, they are more readily activated electrically.  Although there is now doubt as to the accuracy of this theory, it opened a new field in medicine.

One practical utilization of this new concept was with the dorsal column stimulator.  These devices were electrical were stimulators employing electrodes implanted endodurally proximal to the dorsal column of the spinal cord.  Transcutaneous nerve stimulation was initially used as a screening procedure before dorsal column stimulators were implanted.  It was subsequently shown, however, that certain patients could obtain pain relief with TENS alone and thus avoid the risk of surgical intervention.

Much of the preliminary work with TENS has been performed by three investigators.  Dr. Norman Shealy, director of pain Rehabilitation Center at St. Francis Hospital in La Crosse, Wisconsin; Dr. Charles V. Burton, then associate professor of neurosurgery at Temple University, Pennsylvania; and Dr. Donlun M. Long, chairman of neurosurgery at Johns Hopkins Hospital, Shealy found that TENS produced excellent results in 80% of his patients suffering from acute pain.  In treating chronic pain, only 25% of his patients received complete relief and 60% were able to decrease their analgesics.  Long experimented with chronic pain and achieved a 39% relief of pain to his series.  According to Burton, TENS has its greatest application in low grade constant pain.  Hymes et al. have conducted studies using TENS for acute postoperative complications.  Results showed that 31% of the controls, who had abdominal surgery, developed postoperative atelectasis as compared to 6% of those treated with TENS.  Most of the patients reported 60 to 80% relief of postoperative pain.

In 1973, work was begun at Northlake Hospital utilizing TENS to control postoperative pain; results at that time were not published.  This paper presents our experience utilizing TENS over the last 1 ˝ years.

Materials and Methods

One hundred and twenty-five patients between the ages of 17 and 79 undergoing podiatric surgery at Northlake Hospital were selected for the study.  Bunion surgery and minor rearfoot surgery were used as minimal criteria for participation in the study.  The routine practice of interoperative use of bupivacaine hydrochloride (Marcaine) and dexamethasone phosphate (Hexedrol) was continued for all patients in the study.  The average hospital stay per patient was 4 days.  There were three categories of patient involvement.  Group 1 had 50 patients receiving TENS.  Group 2 was comprised of 25 patients receiving placebo TENS.  Group 3 consisted of 50 patients whose medication records were selected and reviewed on a random basis. 

The TENS units used were NEUROMOD PULSE GENERATORS (Medtronic, Inc.).  The Model 3701 system (single channel) was used for unilateral cased and the Model 3702 system (dual channel) was used for bilateral cases (Fig. 1). Specifications of the stimulators can be found in Table 1.  The electrical stimulators perceived by the patient is altered by the following controls: A (amplitude), PW (pulse width) and R (rate).  The individual settings range from 0 to 10.  A placebo TENS effect was obtained by reversing the batteries for our group 2 patients.

Group 1 and 2 were randomly selected and participation within the study was voluntary.  Informed consent was obtained after briefly discussing the theory of TENS and the operation of the unit.

Table 1. Generator Specifications

Rubber carbon electrodes were then placed proximal to the bandage and patients were instructed not to remove the electrodes during their hospital stay.  Patients were permitted to utilize any combination of settings to achieve minimal pain relief and were advised to use TENS as often as needed with no time limit per stimulation.  Group 1 patient were told to expect a tingling sensation at the electrode sites.  Group0 2 patients were told not to expect to feel any sensation; the unit would work by means of a deep nerve interference.

Patients were assured that the pain medications prescribed by their podiatrist would be available if TENS did not relieve their pain, and also that they could withdraw from the study at any time.  All study participants were supplied with daily log sheets to document time and duration of each stimulation, setting used and percentage relief of pain.  Patients were consulted daily to evaluate their progress.

Application

Subsequent to informed consent TENS was applied to patients in groups 1 and 2 in the following manner.  Skin surfaces and rubber electrode pads were cleansed with alcohol prior to application.  After experimentation with various electrode sites, the pretibial area was selected for electrode placement (Fig. 2).   The pretibial area provides greater electrode contact than more distal locations on the feet.  This placement site also seemed to be more comfortable to the patient.  Electrode gel was applied to the rubber carbon electrodes to provide optimal contact.  Standard adhesive tape was utilized to affix the electrodes to the skin.  Patients with either a history of tape allergies or use of  cardiac pacemakers were eliminated from this study since they are contraindicated.

In our group of 75 patients receiving TENS, we observed no significant skin reactions.  Patients were instructed to walk freely, within the limits of their podiatrists' orders, during the period of TENS application.  In those patients requiring below the knee case application, the placement off the electrodes was above the knee.  This electrode site appeared to yield satisfactory results.

Stimulation, Dosage and Duration

Patients were advised to use any combination of TENS control settings for a duration as long as necessary, and at intervals as frequent as needed for pain control.  We found the average duration of stimulation to be approximately 20 to 40 minutes.  The interval between stimulation was too variable to correlate.  TENS control settings in group 1 were unique to each patient and were dependent on each patient's perception and tolerance of the tingling sensation.  Average settings fell into the realm of 3 to 4 amplitude, 3 pulse width, and 3 to 4 rate.  It was found in group 2 patients receiving placebo TENS that average settings were much higher.  It was not uncommon to have a patient utilize a setting of 10 on all controls to achieve a psychologic relief of pain.

Results

To evaluate the patient response to TENS we chose to use the following parameters: 1) percentage of incidence of meperidine hydrochloride (Demerol) and codeine preparations usage at four levels: none, light, moderate and heavy for each group; 2) subjective assessment by the patient of TENS relief; 3) average milligrams of Demerol and codeine preparations taken per individual for each group.  The subjective assessment was accomplished by categorizing the patient response as excellent (75 to 100& relief of pain) and poor (under 50% relief of pain).

Analysis of the three groups revealed significant difference3s in the incidence of Demerol (P < .025) and codeine preparations (P < 0.005) usage among the three groups.  Upon examination of our random group of 50 patients (Fig. 3) utilized Demerol at some time during their postoperative hospital stay and that 80% (Fig. 4) needed codeine preparations during the same time period.  Average Demerol usage was computed at 45 mg. per hospital stay, while average intake for codeine preparations was 102 mg. (Table 2).

In comparison to our random group, it was found that fewer patients in group 1 (utilizing actual TENS) required analgesics.  Incidence of usage of Demerol and codeine preparations in group 1 during the postoperative hospital stay was 12% (Fig. 3) and 32% (Fig.4) respectively.  These patients took an average of 12 mg. of Demerol and 20-4 mg. of codeine preparations (Table 2).

In evaluating the 25 patients in group 2 (those receiving placebo TENS treatment), the percentage need for analgesics within this group was 32% requiring Demerol (Fig. 3) and 48% needing codeine preparations (Fig. 4).  The average usage of Demerol was 26.0 mg. and 27.6 mg. of codeine preparations (Table 2).

Significant differences were also seen among the three groups in the subjective patient response to pain relief (P < 0.0005) (Fig. 5); 32 or 74% of the group 1 patients, relating symptoms of pain, had excellent pain relief as compared to 4 or 17% of the group 2 patients.  Fair pain relief was achieved by 9 or 20% of the patients in group 2.  Two patients or 4% in group 1 were judged to have poor relief of pain using TENS as compared to 14 patients or 60% claiming poor response in group 2.  Seven patients in group 1 and 2 patients in group 2 related no subjective complaint of pain during their postoperative course significant enough to require a TENS treatment or analgesic medication.  Nine of our 50 random group patients also related no complaint of pain significant enough to warrant postoperative analgesic medications. Incidence levels of patients reporting no subjective level of pain for the three groups did not vary significantly (P < 0.5) (Fig. 6).

Table 2. Comparison of Demerol and Codeine Usage

Discussion

Patient Response.  We have successfully demonstrated a significant analgesic effect with the use of TENS.  We have also shown a significant placebo effect.  Thornsteinsson et al. demonstrated a 48% analgesic effect with actual TENS, and a 32% analgesic effect with placebo TENS.  Their study, however, was conducted in patients with chronic pain.  Our study has shown a higher success rate with the actual TENS and a lower success rate with the placebo device.

In a number of studies dealing with the relief of chronic pain the placebo effect of TENS lasted up to 2 weeks.  In our study, the placebo effect was most effective during the first postoperative day and decreased with subsequent trials.

Theory.  Since 1965, Melzack and Walls Gate Control hypothesis has been used to explain the mechanism of such pain relief.  The effectiveness for TENS to relieve pain has been demonstrated in clinical trials by Wall and Sweet.  Their basic premise was that pain relief was from central spinal cord suppression.  In recent years, however, several authors have disputed this theory.  Ignelzi and Nyquist have conducted experiments with isolated peripheral nerves and have found that peripheral changes in the nerve occur before the first spinal cord synapse.  Their results have shown that repetitive stimulations of the isolated peripheral nerve cause changes in both the A-alpha and beta and the A-delta waves of the compound action potential.  Their experiments successfully correlated A-delta wave pain suppression and pain relief.

Similar findings have been reported by Taub and Campbell.  There have also been varying studies relating the analgesic effects of electrical stimulation to the release of endogenous morphine-like substances, termed endorphins.  Reversal of electrically induced analgesia has been achieved with naloxone hydrochloride (a narcotic antagonist).  This adds credence to the fact that an endogenous, morphine-like substance is secreted centrally.

Other Uses.  We have also utilized TENS successfully in treating athletes' pain conditions associated with overuse syndromes.  The scope of TENS is unlimited and we are just now beginning to utilize it to its fullest capacity.  TENS should especially be considered in the patient allergic to analgesic medication and in the patient with respiratory disease, where respiratory depression from narcotic analgesics may be a factor.

Summary

1. TENS has been shown to be an effective modality for the control of acute postoperative pain,  In                                    our study, 74% of the patients demonstrated 75 to 100% relief of pain utilizing TENS and 20% of the patients achieved a 50 to 75% relief of pain.
2. A definitive placebo effect has been illustrated in this study.  Utilizing placebo TENS, 17% of the patients received a 75 to 100% relief of pain , 21% received a 50 to 75% relief of pain, and 60% of the patients utilizing placebo TENS stated less than 50% relief of pain.
3. The frequency of patients requiring postoperative analgesics was less for patients using TENS than those receiving placebo TENS and a random group of patients using no TENS.
4. The computed average Demerol and codeine preparations intake levels were less for patients using TENS than those with placebo TENS and a group of 50 random patients without TENS.

Acknowledgment.  The authors wish to thank Medtronic, Incorporated for its cooperation with this project.

References

1.  A new approach to pain.  Emergency Med., 6: 241, 1974.
2.  Melzack, R. and Wall, P.D.: Pain mechanism: a new theory. Science, 150: 971, 1965.
3. Hymes, A. C., Yonehiro, E. G., Raab, D. E., et al:  Electrical surface stimulation for treatment and prevention of ileus and atelactasis. Surg. Forum, 25: 222, 1974
4.  Thornsteinson, G., Stonnington, H., Stillwell, G., et al:  Transcutaneous electrical stimulation: a double-blinded trial of its efficiency for pain..  Arch. Phys. Med. Rehabil., 58: 8, 1977.
5.  Wall, P. D. and Sweet, W. H.: Temporary abolition of pain in man. Science, 155: 108, 1967.
6.  Ignelzi, R. and Nyquist, J.: Direct effect of electrical stimulation on the peripheral nerve evoked activity:  Implications in pain relief. J. Neurosurg., 45: 159, 1976.
7.  Ignelzi, R. and Nyquist, J.: Peripheral nerve stimulation for pain relief.  Effect on cutaneous peripheral nerve evoked activity.  Surg. Forum, 26: 474, 1975.
8.  Taub, A. and Campbell, J.: Percutaneous local electrical analgesia; peripheral mechanisms. International Symposium on Pain ("Advances in Neurology", Vol. 4). Edited by John J. Bonica, Raven Press, New York, 1973.
9.  Electricity and morphine may act similarly on brain. Med Trib., 17: 22, 1976.
10. Endorphin: brains own 'morphine'.  Electrostimulation appears to induce secretion of pain killer.  Med. World News, 17: 59, 1976.
11. Adams, J: Naloxone reversal of analgesia produced by brain stimulation in the human. Pain, 2:161, 1976.

Additional References

Burton, C.: Trancutaneous electrical nerve stimulation to relieve pain.  Postgrad. Med., 59: 105, 1976.
Burton, C. and Mauer, D.: Pain suppression by transcutaneous electronic stimulation. IEEE Trans. Biomed. Eng., BME-21: 81, 1974.
Burton, C. and Mauer, D.:  Solvent-activated current passing tape electrode for transcutaneous electrical stimulation of the peripheral nervous system. IEEE Trans. Biomed. Eng., BME-23: 346, 1976.
Cooperman, A., Hall, B., Sadar, E., et al: Use of transcutaneous electrical stimulation in control of postoprtive pain. Surg. Forum, 26: 77-78, 1975.
Long, D.M.: Electrical stimulation for the control of pain. Arch. Surg., 112: 884, 1977.
Melzack, R.: Prolonged relief of pain by bried, intense, transcutaneous somatic stimulation. Pain, 1: 357, 1975.
Roeser, W., Meeks, L., Venis, R., et al: The use of transcutaneous stimulation for pain control in athletic medicine. A preliminary report. Am. J. sports Med., 4:210, 1976.
Shealy, C.N.: Transcutaneous electrical stimulation for control of pain. Clin. Neurosurgerg. 21: 269, 1974.
Vanderack, G.D. and McGrath, K.A.: Transcutaneous electrical stimulation in treatment of postoperative pain. Am. J. Surg., 130: 338, 1975.
Woods, W.: Relief of localized pain by transcutaneous electro-stimulation. Am. J. Acupuncture, 3: 133, 1975.

*Submitted during residence, Northlake Community Hospital, Northlake, Illinois
+Fellow, American College of Foot Surgeons.