IJSPT
CASE REPORT
IMPROVED PRESSURE PAIN THRESHOLDS AND FUNCTION FOLLOWING NOXIOUS ELECTRICAL STIMULATION ON A RUNNER WITH CHRONIC ACHILLES TENDINOPATHY: A CASE REPORT Brian J. Eckenrode, PT, DPT, OCS1 Scott K. Stackhouse, PT, PhD1
ABSTRACT Background and Purpose: Achilles tendinopathy is a common overuse injury sustained by athletes including runners. The use of noxious electrical stimulation for the treatment of chronic tendinopathies is a novel treatment intervention, which may alter pain perception and serve as adjunct technique in the recovery of painfree function. The purpose of this case report is to demonstrate the use of noxious electrical stimulation for the treatment of chronic, bilateral Achilles tendinopathy that was resistant to conservative treatment using plantarflexor eccentric exercise. Case Description: A 27-year old male runner was referred to physical therapy with a 7-year history of bilateral Achilles tendinopathy. He scored a 73/80 on the Lower Extremity Functional Scale (LEFS) and a 64% on the Victorian Institute of Sports Assessment-Achilles (VISA-A). Pain pressure threshold testing of the Achilles tendon was performed, followed by a single session of noxious electric stimulation to bilateral Achilles tendons, and the subject was instructed to continue with eccentric gastroc-soleus complex strengthening as previously performed. Outcomes: Pain pressure threshold testing was performed to the mid-portion of the posterior Achilles tendon. The left Achilles tendon mean was 10.50kg and right Achilles tendon was 8.33kg prior to the noxious stimulation intervention. Twenty-four hours after the noxious stimulation treatment, improvements in mean pain threshold testing were found for both the left (16.31kg) and right (12.36kg) Achilles tendons. At one month after the physical therapy noxious stimulation session, the subject was able to progress his workouts to include sprints and interval training. His LEFS improved to 76/80 and his VISA-A improved to 96%. Discussion: The case illustrates the successful pain reduction and return to progressive sports activity in a runner with chronic Achilles tendinopathy. The utilization of noxious electric stimulation may have altered the pain perception of the nervous system as evidenced by the improvement in pain pressure threshold testing. Future studies on the application of noxious electric stimulation on chronic Achilles tendinopathy may help support the benefit of this intervention on pain and function. Level of Evidence: Therapy, Level 4. Keywords: Achilles tendinopathy, noxious electrical stimulation, pain, running
1
Arcadia University, Department of Physical Therapy, Glenside, PA
For a single-subject case study, institutional IRB approval was not required. The authors certify that they have no affiliations with or financial involvement in any organization or entity with a direct financial interest in the subject matter or materials discussed in the article.
CORRESPONDING AUTHOR Brian J. Eckenrode Arcadia University 450 S. Easton Road, Glenside, PA 19038 E-mail: [email protected]
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BACKGROUND AND PURPOSE Achilles tendinopathy is one of the more common overuse injuries sustained by runners,1,2 with a reported approximate 52% lifetime incidence in recreational runners.3 Pain is localized to the midportion (2-6 cm proximal to the insertion) or insertion of the Achilles tendon.4 Symptoms are often provoked during tendon loading activities, which include running, jumping, walking uphill, or ascending and descending stairs.5,6 No consensus on the etiology of Achilles tendinopathy exists. It is theorized to result from mechanical overuse with inflammation during the acute stage6-8 and degeneration in the chronic stage.4,6 Aside from the physical damage to the tendon, there may be maladaptive changes to the nociceptive system that are part of the problem associated with chronic common wrist extensor9 and patellar tendinopathies.10,11 Maladaptive changes to the nociceptive system may also contribute to the symptoms of chronic Achilles tendinopathy.12,13 Current evidence and recommendations for the treatment of chronic Achilles tendinopathy supports the use of eccentric plantarflexor exercises, which has been shown to result in a clinically meaningful pain reduction and allow for return to activity when performed 2-3 times daily over several months;14-17 however recovery can be incomplete.18 A study by de Vos et al19 demonstrated Achilles tendon pain reduction prior to evidence of morphologic changes. Evidence also exists that the central substance of the Achilles tendon exhibits a low rate of collagen turnover.20 Therefore, eccentric exercise may achieve a reduction in pain through changes in the local biochemical environment, or it may work to alter nociception through alternate pathways rather than through physical changes in tendon structure. Electrical stimulation can affect nociception through segmental inhibition,21 descending central inhibition,22,23 and several other neuromodulatory mechanisms.24-30 Transcutaneous electrical nerve stimulation (TENS), is a common modality used by rehabilitation clinicians and has been studied employing a variety of pulse frequencies, intensity-levels, and durations making it difficult to determine its effectiveness.31 The intensity level of TENS appears to mediate the analgesic response, with higher intensities resulting in greater hypoalgesia in humans.32,33 Electrical
stimulation that is delivered at high intensities (just below motor threshold through pain threshold level stimulation) can reduce central sensitization in animal models.34-36 In human studies of fibromyalgia and knee osteoarthritis, TENS can restore central inhibition and increase pressure pain thresholds at the local treatment site and sites beyond,37,38 and may thus be useful in reversing some of the adaptations that the nervous system makes when confronted with chronic pain. The purpose of this case report is to demonstrate the use of noxious electrical stimulation for the treatment of chronic, bilateral Achilles tendinopathy that was resistant to conservative treatment using plantarflexor eccentric exercise. CASE DESCRIPTION The subject of this case report is a 27-year old male runner (height 1.8m, weight 65.8kg, BMI 20.8) who was referred to outpatient physical therapy by his sports medicine physician with a diagnosis of bilateral Achilles tendinopathy. He denied any significant medical history, was not taking any medications, and reported that he was in overall good health. The subject noted that his Achilles tendon pain began in college, and he continued to experience symptoms for the seven subsequent years. The subject was a former NCAA Division 1 collegiate runner competing in both cross-country and distance track events. He reported running approximately 80 to 100 miles per week while in college, and had continued to run with bilateral Achilles tendon pain approximately 60-90 miles per week. The subject reported that the pain was consistent throughout his runs, and did not worsen unless he attempted to increase his pace faster than an 8.5 min/mile. His goal was to run pain-free and be able to increase the intensity of his training without pain symptoms. No Institutional Review Board approval was required for a single subject case report. The subject granted approval for his participation in this study. CLINICAL IMPRESSION #1 Numerous conservative approaches were attempted in the past by the subject without resolution of his symptoms, including taking a full year off from all running activity, night splints, custom orthotics, and various modalities from his college athletic trainer
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and previous physical therapists. He reported several courses of physical therapy in the past, including two months of eccentric exercise without any noticeable difference in his pain levels. The subject reported undergoing a prior Magnetic Resonance Imaging (MRI) which confirmed Achilles tendinopathy bilaterally. Given the subject’s MRI findings and failed conservative management, a thorough physical therapy evaluation was performed to confirm the diagnosis and attempt to identify potential compensatory impairments which may have contributed to this condition. EXAMINATION Objective data collected on the initial evaluation include pain at 8/10 on the numeric pain rating scale (NPRS) at worst (0/10 current) to bilateral Achilles tendons with running; right Achilles tendon pain equal to the left. He scored a 73/80 on the Lower Extremity Functional Scale (LEFS) and 64% on the Victorian Institute of Sports Assessment-Achilles (VISA-A). The NPRS has been shown to be a valid and reliable tool for assessing pain intensity,39-41 with a reported minimally clinical important difference (MCID) of between 1.7 points42 and 2 points43 for chronic musculoskeletal pain. The LEFS has been shown to have good reliability and validity with patients with lower extremity musculoskeletal problems.44 This self-report questionnaire asks patients to rate their ability to perform 20 different activities, with a score of 80 indicating maximal function. The minimum detectable change (MDC) and minimal clinically important difference (MCID) were both found to be 9 scale points for the LEFS.44 The VISA-A questionnaire has been shown to be a reliable and valid disease-specific measure of function in patients with Achilles tendinopathy.45 This selfreport measure consists of 8 questions that assess stiffness, pain, function, and sports training specific to Achilles dysfunction. The VISA-A is scored based on a percentage, with 100% indicating full pain-free function and sports. Based on reliability data published by Robinson and colleagues,45 the estimated MDC90% is 17.3 points. The subject exhibited tenderness with palpation to bilateral Achilles tendons, approximately 3cm proximal and 4cm proximal to the Achilles insertion on the calcaneus for the left and right ankles respec-
tively. A positive Arc sign was found to both Achilles tendons.46 This test is performed by having the patient actively plantarflex and dorsiflex the ankle, and the examiner looks for movement of the visible area of swelling with the ankle motion in those with tendinopathy of the Achilles tendon.46 In addition, he presented with small painful nodules laterally along the painful portion of each Achilles tendon. A 0.5cm leg length discrepancy was measured from the anterior superior illiac spine to the medial malleous, with the right lower extremity being longer. The subject reported that this was previously identified by prior practitioners and corrected for with both custom and over-the-counter orthotics. Lumbar spine range of motion was full and pain-free with no deviations or aberrant movement patterns noted. SI joint provocative tests were negative and his lower quarter screen was unremarkable for any dermatomal or myotomal impairments. Neural tension testing to the lower extremities was also unremarkable. In addition, there were no additional red flags through his medical history review. The subject presented with decreased right ankle functional dorsiflexion ROM as measured in weightbearing as described by Bennell et al47 with 14cm on the left and 11.5cm on the right. Bilateral ankle plantarflexion, inversion, and eversion ROM was within normal limits.48 Strength testing of the hips and knees was performed via hand-held dynamometry, but no major deficits were noted. Core strength was assessed through the double leg lowering test (65 degrees) and endurance with the side plank (60s right vs. 75s left). Flexibility and range of motion testing of bilateral lower extremities was with minimal to no restriction for the quadriceps, hip flexors, hamstrings, illiotibial band, and gluteal muscles. Strength testing of the ankle dorsiflexors, inverters, and everters demonstrated 5/5 manual muscle test grades and were painfree bilaterally. The subject was able to complete 20 single leg heel raises on each lower extremity, however these were accomplished with pain. He was limited to 4 single leg hops on each leg before the onset of the Achilles tendon pain symptoms (Table 1). Pain pressure threshold (PPT) testing of bilateral Achilles tendons was performed to assess deep mechanical sensitivity. The subject was supine on a
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Table 1. Improvement in Victorian Institute of Sports Assessment-Achilles (VISA-A) score over time VISA-A Total Q5 Pain immediately after doing 10 single leg heel raises from a flat surface Q6 Number of single leg hops without pain
Baseline 64%
5% (5/10) 4
1 month 96%
2 months 81%
9 months 94%
10% (0/10)
10% (0/10)
9% (1/10)
10
6
8
treatment table, and a mobilization belt was placed around the metatarsal heads to stabilize the foot and bring the ankle joint into a neutral position of dorsiflexion (approximately 0 degrees via goniometric assessment) (Figure 1). A hand-held pressure algometer (Wagner; FDIX25) with a 1-cm2 in diameter rubber tip was used to apply increasing amounts of pressure (~1kg/sec) to the most painful portion of the Achilles tendon (previously noted). The distance from the calcaneal attachment was measured so repeated testing could be performed at the same sites. Pressure was gradually applied with the algometer and the subject indicated when the pressure sensation first changed to pain, the pressure was immediately removed and the peak force recorded (done automatically by the algometer). The peak force from the trial was recorded by the clinician. The PPT test was performed two times on each Achilles tendon, with a minimum of 30-seconds of rest between bouts and the data were averaged (Table 1). Test-retest reliability for between day sessions for PPT of the Achilles is good (ICC(3,k) = 0.91) with the MDC90% CI of 2.05 kg.49 CLINICAL IMPRESSION #2 The subject presented with minimal musculoskeletal impairments aside from his reported pain symptoms,
Figure 1. Pain pressure threshold (PPT) testing set up.
all while he continued participation in a high volume of running activity. Due to the multiple failed conservative management attempts, the chronic nature of his Achilles symptoms, and the potential maladaptive changes in the nociceptive system,12 the authors decided to incorporate a novel approach to address the pain aspect of this pathology in this runner by using noxious level electrical stimulation. On-going assessment would be performed as necessary based upon the response of the intervention and availability of the subject. Optimally, a reduction in subjective pain rating and improvement in outcome measures would be expected with a positive response to the electrical stimulation intervention. INTERVENTION Due to the chronic nature of the condition and lack of progress, a trial of noxious electrical stimulation to bilateral Achilles tendons was discussed with the subject and implemented at the initial session. Noxious electrical stimulation was applied with the subject in the test position for PPT assessment with his ankles held in neutral. Self-adhesive electrodes were cut down to 1cm by 5cm and were placed on either side of the Achilles tendon to surround the site of maximal tenderness of each Achilles tendon. An Empi 300PV electrical stimulation unit (DJO Global, Vista, CA, USA) was utilized with the following parameters: 150 pulses per second; 2-second ramp-up time; 10-seconds on time: 10-seconds off time; 400-μs phase duration; 20-minute treatment duration. The electrical current was delivered at maximum tolerable intensity with instruction to maintain a “sharp, prickly” pain rating of 5-7/10 on the NPRS. The intensity was adjusted approximately every two minutes to maintain the 5-7/10 rating. Following the single noxious stimulation treatment, the subject refrained from activity for 24 hours and he returned the next day where the pain pressure threshold testing was repeated. No additional treatment sessions were provided, due to the subject’s limited availability and travel schedule for work. The subject continued with his running program and an eccentric reloading program on his own. Current evidence supports the use of eccentric exercise in the management of chronic Achilles tendinopathy.14-16 This exercise is described as being performed off a step with the eccentric phase performed by the involved lower extremity and the
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concentric phase performed only by the uninvolved side. Given that this subject had previously completed the Achilles eccentric exercises in the past without success, he was encouraged to restart these. The author reviewed the performance of the eccentric exercises with the subject to ensure these were completed with correct form and dosage. Given the bilateral nature of these symptoms, the subject was instructed to complete this exercise bilaterally off a step. Recommended dosage was for the subject to perform 3 sets of 15 repetitions, two times per day.15 He was instructed to complete the eccentric phase over a five second time period, allow a two minute rest between sets, and to induce a pain level of no more than 2-3/10 in the Achilles tendon during the exercise. Once painfree during the bilateral eccentrics, these exercises were progressed to unilateral eccentrics then unilateral eccentrics with a weighted backpack following the same dosage progression. Follow-up testing sessions were completed at two months and nine months from the initial evaluation for a total of four sessions. Self-report outcome measures were also collected at one month, but due to the subject’s work schedule he was unable to attend an onsite session for PPT. OUTCOMES Following one treatment session of noxious electrical stimulation, the subject demonstrated Improvements in Achilles tendon PPT testing, pain levels, and function via the VISA-A, in addition to running progression gains (Tables 1-4). For PPT, the subject exhibited an increase in threshold for pain at 24-hours post noxious stimulation treatment to both Achilles tendons, with a sustained improvement seen at 9 months (Table 1). The increase in PPT at 24-hours exceeded the MDC90% CI of 2.05 kg.49 A small reduction in PPT was observed between 24 hours and two months, which may be attributed to the increase in running intensity and pace during this time period as his tissues adapted to the new forces. For the VISA-A, the subject scored a 64% at the initial evaluation, then improved to 96% at one-month post intervention (Table 2). At his two-month followup, the subject scored an 81% on the VISA-A most likely due to the recent increase in his intensity and distance with running. At his nine month follow-up
Table 2. Improved Achilles tendon mean pain pressure threshold (PPT) measurements over time Achilles
Baseline
24 hours
2 months
9 months
Right (kg)
8.33
12.36
10.91
12.78
Left (kg)
10.5
16.31
10.96
14.9
Test-Retest Reliability Between Day49: ICC(3,k) = 0.91; MDC90% CI = 2.05 kg Mean value 13.7 ± 4.9kg for PPT laboratory database mean in healthy controls49
he scored a 94% on the VISA-A, with an increased pace time with his running. His LEFS score improved from a 73/80 to 74/80 over time, which is not significant but may be due to a ceiling effect of this outcome measure (Table 3). Self-reported pain rating via the NPRS was an 8/10 to bilateral Achilles tendons at worst prior to the intervention, which decreased to a 1/10 at worst at all testing sessions thereafter. Prior to the noxious electrical stimulation intervention, the subject was able to run, but only with sustained pain of 3-5/10. Any increase in running distance or intensity would increase his symptoms bilaterally. Post intervention, there was no Achilles pain with running at one and nine month follow-ups. With running, the subject consistently ran approximately 75 miles per week before and during the course of care (Table 4). However, he noted the inability to run faster than an 8.5 min/mile and had been unable to progress his workouts without exacerbation of his symptoms. After the noxious electrical stimulation treatment, the subject reported no more than 1/10 pain to bilateral Achilles tendons
Table 3. Lower Extremity Functional Scale over time Baseline
1 month
2 months
9 months
73/80
76/80
74/80
74/80
ground Q18 Making sharp turns
3
3
2
3
while running fast
2
3
3
3
LEFS Total Score Q17 Running on uneven
Table 4. Subject progression of running Weekly Mileage
Baseline 75mi/week
1 month 75mi/week
2 months 75mi/week
9 months 75mi/week
Tempo Runs Track Work Mile Pace
No No 8.5 min/mi
No No 8.5 min/mi
Yes Yes 8 min/mile
Yes Yes 7 min/mile
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with running. He maintained this current training regimen during the first month, as he did not want to progress his running routine for fear of potentially redeveloping his pain. At two months post intervention, the subject was able to slowly increase his running pace to 8 min/mile without increased pain. He also noted the ability to add track workouts and tempo runs, which he had been unable to progress to over the past several years. The subject reported that his track workouts consisted of 6 to 12 400m runs at moderate to high intensity in track spikes. Tempo runs were approximately 20 to 30 minutes in length, designed to increase stamina through improvement of running rhythm meant to be performed at a “comfortably hard” pace. At his nine-month follow-up session, he continued to note no pain with his runs and that he was able to run a 7 min/mile pace consistently without symptoms bilaterally. He also reported the ability to run a 4:14 mile, coming close to his personal record of a 4:04 mile as a collegiate runner. He was able to achieve one of his primary goals for physical therapy, which was to run close to his best college mile time for an upcoming reunion with his college cross-country and track teammates. DISCUSSION This case illustrates the successful pain reduction and return to progressive sports activity in a runner with chronic bilateral Achilles tendinopathy. The utilization of noxious electrical stimulation may have decreased the sensitivity to mechanical stimuli as evidenced by the large increase in pain pressure thresholds at 24 hours post-treatment. The ability of noxious electrical stimulation to reduce pain sensitivity is supported by results from animal studies, which show that electrical stimulation delivered at an intensity that activated A-delta pain fibers, decreased dorsal horn neuron responsiveness.34,50,51 In humans, TENS delivered at painful intensities reduced somatosensory evoked cortical potentials and perceived pain,52 and in an osteoarthritis clinical trial, noxious intensity TENS (30% above pain threshold) produced a greater reduction in pain and stiffness after a treatment period (3x/wk for 4wks) than strong, comfortable level TENS.53 The presence of central sensitization of pain has been shown to occur in other musculoskeletal conditions with
chronic pain,9,54-56 and the authors have since generated and presented evidence that central sensitization also occurs in people with chronic Achilles tendinopathy (> 3 months duration).57 The authors of this case report hypothesize that noxious electrical stimulation reduced the mechanical responsiveness of either the peripheral nociceptors or central neurons in the pain pathways as evidenced by the large change (> MDC90% CI) in pressure pain thresholds at 24-hours post-treatment. This is consistent with literature showing that high-frequency TENS can have both peripheral27 and central effects22,26,28 that can reduce pain sensitivity. Further research needs to address if signs of central sensitization are mitigated with treatment in people with Achilles tendinopathy. For the VISA-A scores the subject demonstrated a significant improvement in function by one month via this self-report measure. The VISA-A is designed specifically for individuals with Achilles tendon pain, and features relevant questions on the ability to perform tasks and report on activities such as minutes of Achilles stiffness in the morning, pain with heel raises, number of single leg hops without pain, and Achilles pain with sports. The subject exceeded the estimated MDC90% CI for the VISA-A at all testing time frames when compared with his initial score. He did experience a decrease from his initial posttreatment VISA-A score over the subsequent two months, which could be attributed to his increase in running activity (track workouts in spikes, tempo runs, and running pace). While the subject’s mileage remained relatively unchanged, he was able to progress the intensity of his workouts over time. The authors did recommend that the subject reduce and or cease running for a period of time to allow for recovery according to tendinopathy treatment guidelines by Davenport et al.58 However, the subject was unwilling to back off from his running due to the fact that the last break from running provided no relief of his symptoms upon return to activity. He was comfortable with the current management of his pain through the maintenance of his current running routine without any changes in intensity or distance. This approach is supported by research from Silbernagel and colleagues,18 who showed that Achilles tendon-loading
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activity can be maintained during treatment of tendinopathy using a pain-monitoring model of activity. CONCLUSIONS In summary, the application of noxious electrical stimulation in a runner with chronic history of bilateral mid-portion Achilles tendinopathy resulted in a positive effect on pain level and activity where other conservative measures failed, including eccentric plantarflexor strengthening. Although the benefit of continued eccentric exercises may have contributed to the final outcome of this case, the incorporation of noxious electrical stimulation was a novel approach to pain management of this chronic injury. The authors hypothesize that noxious electrical stimulation may work to reduce pain in chronic tendinopathies via altering central pain processing. Future directions include testing if central sensitization is present in individuals with chronic Achilles tendinopathy and testing the effects of noxious electrical stimulation and eccentric exercise on pain processing in this pathology. REFERENCES 1. Kujala UM, Sarna S, Kaprio J. Cumulative incidence of achilles tendon rupture and tendinopathy in male former elite athletes. Clin J Sport Med. 2005;15(3):133-135. 2. Knobloch K, Yoon U, Vogt PM. Acute and overuse injuries correlated to hours of training in master running athletes. Foot Ankle Int. 2008;29(7):671-676. 3. Scott A, Huisman E, Khan K. Conservative treatment of chronic Achilles tendinopathy. CMAJ : Canadian Medical Association journal = journal de l’Association medicale canadienne. 2011;183(10):1159-1165. 4. Paavola M, Kannus P, Jarvinen TA, Khan K, Jozsa L, Jarvinen M. Achilles tendinopathy. J Bone Joint Surg Am. 2002;84-A(11):2062-2076. 5. Paavola M, Kannus P, Paakkala T, Pasanen M, Jarvinen M. Long-term prognosis of patients with achilles tendinopathy. An observational 8-year follow-up study. Am J Sports Med. 2000;28(5):634-642. 6. Abate M, Silbernagel KG, Siljeholm C, et al. Pathogenesis of tendinopathies: inflammation or degeneration? Arthritis research & therapy. 2009;11(3):235. 7. Barbe MF, Gallagher S, Massicotte VS, Tytell M, Popoff SN, Barr-Gillespie AE. The interaction of force and repetition on musculoskeletal and neural tissue responses and sensorimotor behavior in a rat model of work-related musculoskeletal disorders. BMC Musculoskelet Disord. 2013;14:303.
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in the spinal cord dorsal horn. Journal of neurochemistry. 2005;95(6):1794-1801. Sluka KA, Bjordal JM, Marchand S, Rakel BA. What makes transcutaneous electrical nerve stimulation work? Making sense of the mixed results in the clinical literature. Phys Ther. 2013;93(10):1397-1402. Moran F, Leonard T, Hawthorne S, et al. Hypoalgesia in response to transcutaneous electrical nerve stimulation (TENS) depends on stimulation intensity. The journal of pain : official journal of the American Pain Society. 2011;12(8):929-935. Pantaleao MA, Laurino MF, Gallego NL, et al. Adjusting pulse amplitude during transcutaneous electrical nerve stimulation (TENS) application produces greater hypoalgesia. The journal of pain : official journal of the American Pain Society. 2011;12(5):581-590. Liu XG, Morton CR, Azkue JJ, Zimmermann M, Sandkuhler J. Long-term depression of C-fibre-evoked spinal field potentials by stimulation of primary afferent A delta-fibres in the adult rat. The European journal of neuroscience. 1998;10(10):3069-3075. Ma YT, Sluka KA. Reduction in inflammationinduced sensitization of dorsal horn neurons by transcutaneous electrical nerve stimulation in anesthetized rats. Experimental brain research. 2001;137(1):94-102. DeSantana JM, Da Silva LF, De Resende MA, Sluka KA. Transcutaneous electrical nerve stimulation at both high and low frequencies activates ventrolateral periaqueductal grey to decrease mechanical hyperalgesia in arthritic rats. Neuroscience. 2009;163(4):1233-1241. Dailey DL, Rakel BA, Vance CG, et al. Transcutaneous electrical nerve stimulation reduces pain, fatigue and hyperalgesia while restoring central inhibition in primary fibromyalgia. Pain. 2013;154(11):2554-2562. Vance CG, Rakel BA, Blodgett NP, et al. Effects of transcutaneous electrical nerve stimulation on pain, pain sensitivity, and function in people with knee osteoarthritis: a randomized controlled trial. Phys Ther. 2012;92(7):898-910. Jensen MP, Karoly P, Braver S. The measurement of clinical pain intensity: a comparison of six methods. Pain. 1986;27(1):117-126. Jensen MP, Turner JA, Romano JM. What is the maximum number of levels needed in pain intensity measurement? Pain. 1994;58(3):387-392. Price DD, Bush FM, Long S, Harkins SW. A comparison of pain measurement characteristics of mechanical visual analogue and simple numerical rating scales. Pain. 1994;56(2):217-226.
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42. Farrar JT, Young JP, LaMoreaux L, Werth JL, Poole RM. Clinical importance of changes in chronic pain intensity measured on an 11-point numerical pain rating scale. Pain. 2001;94(2):149-158. 43. Salaffi F, Stancati A, Silvestri CA, Ciapetti A, Grassi W. Minimal clinically important changes in chronic musculoskeletal pain intensity measured on a numerical rating scale. European journal of pain. 2004;8(4):283-291. 44. Binkley JM, Stratford PW, Lott SA, Riddle DL. The Lower Extremity Functional Scale (LEFS): scale development, measurement properties, and clinical application. North American Orthopaedic Rehabilitation Research Network. Phys Ther. 1999;79(4):371-383. 45. Robinson JM, Cook JL, Purdam C, et al. The VISA-A questionnaire: a valid and reliable index of the clinical severity of Achilles tendinopathy. British journal of sports medicine. 2001;35(5):335-341. 46. Maffulli N, Kenward MG, Testa V, Capasso G, Regine R, King JB. Clinical diagnosis of Achilles tendinopathy with tendinosis. Clin J Sport Med. 2003;13(1):11-15. 47. Bennell KL, Talbot RC, Wajswelner H, Techovanich W, Kelly DH, Hall AJ. Intra-rater and inter-rater reliability of a weight-bearing lunge measure of ankle dorsiflexion. The Australian journal of physiotherapy. 1998;44(3):175-180. 48. Norkin C, White D. Measurement of Joint Motion: A Guide to Goniometry. Philadelphia, PA: F.A. Davis; 2003. 49. Stackhouse S, Carlin M, Fitzsimmons E, et al. Do Physical Therapy Interventions Affect Mechanical and Thermal Pain Processing Around The Healthy Achilles Tendon? J Orthop Sports Phys Ther. 2012;42(1):OPO3154. 50. Lee KH, Chung JM, Willis WD, Jr. Inhibition of primate spinothalamic tract cells by TENS. Journal of neurosurgery. 1985;62(2):276-287.
51. Sjolund BH. Peripheral nerve stimulation suppression of C-fiber-evoked flexion reflex in rats. Part 1: Parameters of continuous stimulation. Journal of neurosurgery. 1985;63(4):612-616. 52. Jung K, Rottmann S, Ellrich J. Long-term depression of spinal nociception and pain in man: influence of varying stimulation parameters. European journal of pain. 2009;13(2):161-170. 53. Defrin R, Ariel E, Peretz C. Segmental noxious versus innocuous electrical stimulation for chronic pain relief and the effect of fading sensation during treatment. Pain. 2005;115(1-2):152-160. 54. Gwilym SE, Oag HC, Tracey I, Carr AJ. Evidence that central sensitisation is present in patients with shoulder impingement syndrome and influences the outcome after surgery. J Bone Joint Surg Br. 2011;93(4):498-502. 55. Slater H, Arendt-Nielsen L, Wright A, GravenNielsen T. Sensory and motor effects of experimental muscle pain in patients with lateral epicondylalgia and controls with delayed onset muscle soreness. Pain. 2005;114(1-2):118-130. 56. Bajaj P, Bajaj P, Graven-Nielsen T, Arendt-Nielsen L. Osteoarthritis and its association with muscle hyperalgesia: an experimental controlled study. Pain. 2001;93(2):107-114. 57. Stackhouse S, Eckendrode B. Chronic Achilles tendinopathy is associated with signs of central sensitization. J Orthop Sports Phys Ther 2014;44(1):A21. 58. Davenport TE, Kulig K, Matharu Y, Blanco CE. The EdUReP model for nonsurgical management of tendinopathy. Phys Ther. 2005;85(10):1093-1103.
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CASE REPORT
IMPROVED PRESSURE PAIN THRESHOLDS AND FUNCTION FOLLOWING NOXIOUS ELECTRICAL STIMULATION ON A RUNNER WITH CHRONIC ACHILLES TENDINOPATHY: A CASE REPORT Brian J. Eckenrode, PT, DPT, OCS1 Scott K. Stackhouse, PT, PhD1
ABSTRACT Background and Purpose: Achilles tendinopathy is a common overuse injury sustained by athletes including runners. The use of noxious electrical stimulation for the treatment of chronic tendinopathies is a novel treatment intervention, which may alter pain perception and serve as adjunct technique in the recovery of painfree function. The purpose of this case report is to demonstrate the use of noxious electrical stimulation for the treatment of chronic, bilateral Achilles tendinopathy that was resistant to conservative treatment using plantarflexor eccentric exercise. Case Description: A 27-year old male runner was referred to physical therapy with a 7-year history of bilateral Achilles tendinopathy. He scored a 73/80 on the Lower Extremity Functional Scale (LEFS) and a 64% on the Victorian Institute of Sports Assessment-Achilles (VISA-A). Pain pressure threshold testing of the Achilles tendon was performed, followed by a single session of noxious electric stimulation to bilateral Achilles tendons, and the subject was instructed to continue with eccentric gastroc-soleus complex strengthening as previously performed. Outcomes: Pain pressure threshold testing was performed to the mid-portion of the posterior Achilles tendon. The left Achilles tendon mean was 10.50kg and right Achilles tendon was 8.33kg prior to the noxious stimulation intervention. Twenty-four hours after the noxious stimulation treatment, improvements in mean pain threshold testing were found for both the left (16.31kg) and right (12.36kg) Achilles tendons. At one month after the physical therapy noxious stimulation session, the subject was able to progress his workouts to include sprints and interval training. His LEFS improved to 76/80 and his VISA-A improved to 96%. Discussion: The case illustrates the successful pain reduction and return to progressive sports activity in a runner with chronic Achilles tendinopathy. The utilization of noxious electric stimulation may have altered the pain perception of the nervous system as evidenced by the improvement in pain pressure threshold testing. Future studies on the application of noxious electric stimulation on chronic Achilles tendinopathy may help support the benefit of this intervention on pain and function. Level of Evidence: Therapy, Level 4. Keywords: Achilles tendinopathy, noxious electrical stimulation, pain, running
1
Arcadia University, Department of Physical Therapy, Glenside, PA
For a single-subject case study, institutional IRB approval was not required. The authors certify that they have no affiliations with or financial involvement in any organization or entity with a direct financial interest in the subject matter or materials discussed in the article.
CORRESPONDING AUTHOR Brian J. Eckenrode Arcadia University 450 S. Easton Road, Glenside, PA 19038 E-mail: [email protected]
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BACKGROUND AND PURPOSE Achilles tendinopathy is one of the more common overuse injuries sustained by runners,1,2 with a reported approximate 52% lifetime incidence in recreational runners.3 Pain is localized to the midportion (2-6 cm proximal to the insertion) or insertion of the Achilles tendon.4 Symptoms are often provoked during tendon loading activities, which include running, jumping, walking uphill, or ascending and descending stairs.5,6 No consensus on the etiology of Achilles tendinopathy exists. It is theorized to result from mechanical overuse with inflammation during the acute stage6-8 and degeneration in the chronic stage.4,6 Aside from the physical damage to the tendon, there may be maladaptive changes to the nociceptive system that are part of the problem associated with chronic common wrist extensor9 and patellar tendinopathies.10,11 Maladaptive changes to the nociceptive system may also contribute to the symptoms of chronic Achilles tendinopathy.12,13 Current evidence and recommendations for the treatment of chronic Achilles tendinopathy supports the use of eccentric plantarflexor exercises, which has been shown to result in a clinically meaningful pain reduction and allow for return to activity when performed 2-3 times daily over several months;14-17 however recovery can be incomplete.18 A study by de Vos et al19 demonstrated Achilles tendon pain reduction prior to evidence of morphologic changes. Evidence also exists that the central substance of the Achilles tendon exhibits a low rate of collagen turnover.20 Therefore, eccentric exercise may achieve a reduction in pain through changes in the local biochemical environment, or it may work to alter nociception through alternate pathways rather than through physical changes in tendon structure. Electrical stimulation can affect nociception through segmental inhibition,21 descending central inhibition,22,23 and several other neuromodulatory mechanisms.24-30 Transcutaneous electrical nerve stimulation (TENS), is a common modality used by rehabilitation clinicians and has been studied employing a variety of pulse frequencies, intensity-levels, and durations making it difficult to determine its effectiveness.31 The intensity level of TENS appears to mediate the analgesic response, with higher intensities resulting in greater hypoalgesia in humans.32,33 Electrical
stimulation that is delivered at high intensities (just below motor threshold through pain threshold level stimulation) can reduce central sensitization in animal models.34-36 In human studies of fibromyalgia and knee osteoarthritis, TENS can restore central inhibition and increase pressure pain thresholds at the local treatment site and sites beyond,37,38 and may thus be useful in reversing some of the adaptations that the nervous system makes when confronted with chronic pain. The purpose of this case report is to demonstrate the use of noxious electrical stimulation for the treatment of chronic, bilateral Achilles tendinopathy that was resistant to conservative treatment using plantarflexor eccentric exercise. CASE DESCRIPTION The subject of this case report is a 27-year old male runner (height 1.8m, weight 65.8kg, BMI 20.8) who was referred to outpatient physical therapy by his sports medicine physician with a diagnosis of bilateral Achilles tendinopathy. He denied any significant medical history, was not taking any medications, and reported that he was in overall good health. The subject noted that his Achilles tendon pain began in college, and he continued to experience symptoms for the seven subsequent years. The subject was a former NCAA Division 1 collegiate runner competing in both cross-country and distance track events. He reported running approximately 80 to 100 miles per week while in college, and had continued to run with bilateral Achilles tendon pain approximately 60-90 miles per week. The subject reported that the pain was consistent throughout his runs, and did not worsen unless he attempted to increase his pace faster than an 8.5 min/mile. His goal was to run pain-free and be able to increase the intensity of his training without pain symptoms. No Institutional Review Board approval was required for a single subject case report. The subject granted approval for his participation in this study. CLINICAL IMPRESSION #1 Numerous conservative approaches were attempted in the past by the subject without resolution of his symptoms, including taking a full year off from all running activity, night splints, custom orthotics, and various modalities from his college athletic trainer
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and previous physical therapists. He reported several courses of physical therapy in the past, including two months of eccentric exercise without any noticeable difference in his pain levels. The subject reported undergoing a prior Magnetic Resonance Imaging (MRI) which confirmed Achilles tendinopathy bilaterally. Given the subject’s MRI findings and failed conservative management, a thorough physical therapy evaluation was performed to confirm the diagnosis and attempt to identify potential compensatory impairments which may have contributed to this condition. EXAMINATION Objective data collected on the initial evaluation include pain at 8/10 on the numeric pain rating scale (NPRS) at worst (0/10 current) to bilateral Achilles tendons with running; right Achilles tendon pain equal to the left. He scored a 73/80 on the Lower Extremity Functional Scale (LEFS) and 64% on the Victorian Institute of Sports Assessment-Achilles (VISA-A). The NPRS has been shown to be a valid and reliable tool for assessing pain intensity,39-41 with a reported minimally clinical important difference (MCID) of between 1.7 points42 and 2 points43 for chronic musculoskeletal pain. The LEFS has been shown to have good reliability and validity with patients with lower extremity musculoskeletal problems.44 This self-report questionnaire asks patients to rate their ability to perform 20 different activities, with a score of 80 indicating maximal function. The minimum detectable change (MDC) and minimal clinically important difference (MCID) were both found to be 9 scale points for the LEFS.44 The VISA-A questionnaire has been shown to be a reliable and valid disease-specific measure of function in patients with Achilles tendinopathy.45 This selfreport measure consists of 8 questions that assess stiffness, pain, function, and sports training specific to Achilles dysfunction. The VISA-A is scored based on a percentage, with 100% indicating full pain-free function and sports. Based on reliability data published by Robinson and colleagues,45 the estimated MDC90% is 17.3 points. The subject exhibited tenderness with palpation to bilateral Achilles tendons, approximately 3cm proximal and 4cm proximal to the Achilles insertion on the calcaneus for the left and right ankles respec-
tively. A positive Arc sign was found to both Achilles tendons.46 This test is performed by having the patient actively plantarflex and dorsiflex the ankle, and the examiner looks for movement of the visible area of swelling with the ankle motion in those with tendinopathy of the Achilles tendon.46 In addition, he presented with small painful nodules laterally along the painful portion of each Achilles tendon. A 0.5cm leg length discrepancy was measured from the anterior superior illiac spine to the medial malleous, with the right lower extremity being longer. The subject reported that this was previously identified by prior practitioners and corrected for with both custom and over-the-counter orthotics. Lumbar spine range of motion was full and pain-free with no deviations or aberrant movement patterns noted. SI joint provocative tests were negative and his lower quarter screen was unremarkable for any dermatomal or myotomal impairments. Neural tension testing to the lower extremities was also unremarkable. In addition, there were no additional red flags through his medical history review. The subject presented with decreased right ankle functional dorsiflexion ROM as measured in weightbearing as described by Bennell et al47 with 14cm on the left and 11.5cm on the right. Bilateral ankle plantarflexion, inversion, and eversion ROM was within normal limits.48 Strength testing of the hips and knees was performed via hand-held dynamometry, but no major deficits were noted. Core strength was assessed through the double leg lowering test (65 degrees) and endurance with the side plank (60s right vs. 75s left). Flexibility and range of motion testing of bilateral lower extremities was with minimal to no restriction for the quadriceps, hip flexors, hamstrings, illiotibial band, and gluteal muscles. Strength testing of the ankle dorsiflexors, inverters, and everters demonstrated 5/5 manual muscle test grades and were painfree bilaterally. The subject was able to complete 20 single leg heel raises on each lower extremity, however these were accomplished with pain. He was limited to 4 single leg hops on each leg before the onset of the Achilles tendon pain symptoms (Table 1). Pain pressure threshold (PPT) testing of bilateral Achilles tendons was performed to assess deep mechanical sensitivity. The subject was supine on a
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Table 1. Improvement in Victorian Institute of Sports Assessment-Achilles (VISA-A) score over time VISA-A Total Q5 Pain immediately after doing 10 single leg heel raises from a flat surface Q6 Number of single leg hops without pain
Baseline 64%
5% (5/10) 4
1 month 96%
2 months 81%
9 months 94%
10% (0/10)
10% (0/10)
9% (1/10)
10
6
8
treatment table, and a mobilization belt was placed around the metatarsal heads to stabilize the foot and bring the ankle joint into a neutral position of dorsiflexion (approximately 0 degrees via goniometric assessment) (Figure 1). A hand-held pressure algometer (Wagner; FDIX25) with a 1-cm2 in diameter rubber tip was used to apply increasing amounts of pressure (~1kg/sec) to the most painful portion of the Achilles tendon (previously noted). The distance from the calcaneal attachment was measured so repeated testing could be performed at the same sites. Pressure was gradually applied with the algometer and the subject indicated when the pressure sensation first changed to pain, the pressure was immediately removed and the peak force recorded (done automatically by the algometer). The peak force from the trial was recorded by the clinician. The PPT test was performed two times on each Achilles tendon, with a minimum of 30-seconds of rest between bouts and the data were averaged (Table 1). Test-retest reliability for between day sessions for PPT of the Achilles is good (ICC(3,k) = 0.91) with the MDC90% CI of 2.05 kg.49 CLINICAL IMPRESSION #2 The subject presented with minimal musculoskeletal impairments aside from his reported pain symptoms,
Figure 1. Pain pressure threshold (PPT) testing set up.
all while he continued participation in a high volume of running activity. Due to the multiple failed conservative management attempts, the chronic nature of his Achilles symptoms, and the potential maladaptive changes in the nociceptive system,12 the authors decided to incorporate a novel approach to address the pain aspect of this pathology in this runner by using noxious level electrical stimulation. On-going assessment would be performed as necessary based upon the response of the intervention and availability of the subject. Optimally, a reduction in subjective pain rating and improvement in outcome measures would be expected with a positive response to the electrical stimulation intervention. INTERVENTION Due to the chronic nature of the condition and lack of progress, a trial of noxious electrical stimulation to bilateral Achilles tendons was discussed with the subject and implemented at the initial session. Noxious electrical stimulation was applied with the subject in the test position for PPT assessment with his ankles held in neutral. Self-adhesive electrodes were cut down to 1cm by 5cm and were placed on either side of the Achilles tendon to surround the site of maximal tenderness of each Achilles tendon. An Empi 300PV electrical stimulation unit (DJO Global, Vista, CA, USA) was utilized with the following parameters: 150 pulses per second; 2-second ramp-up time; 10-seconds on time: 10-seconds off time; 400-μs phase duration; 20-minute treatment duration. The electrical current was delivered at maximum tolerable intensity with instruction to maintain a “sharp, prickly” pain rating of 5-7/10 on the NPRS. The intensity was adjusted approximately every two minutes to maintain the 5-7/10 rating. Following the single noxious stimulation treatment, the subject refrained from activity for 24 hours and he returned the next day where the pain pressure threshold testing was repeated. No additional treatment sessions were provided, due to the subject’s limited availability and travel schedule for work. The subject continued with his running program and an eccentric reloading program on his own. Current evidence supports the use of eccentric exercise in the management of chronic Achilles tendinopathy.14-16 This exercise is described as being performed off a step with the eccentric phase performed by the involved lower extremity and the
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concentric phase performed only by the uninvolved side. Given that this subject had previously completed the Achilles eccentric exercises in the past without success, he was encouraged to restart these. The author reviewed the performance of the eccentric exercises with the subject to ensure these were completed with correct form and dosage. Given the bilateral nature of these symptoms, the subject was instructed to complete this exercise bilaterally off a step. Recommended dosage was for the subject to perform 3 sets of 15 repetitions, two times per day.15 He was instructed to complete the eccentric phase over a five second time period, allow a two minute rest between sets, and to induce a pain level of no more than 2-3/10 in the Achilles tendon during the exercise. Once painfree during the bilateral eccentrics, these exercises were progressed to unilateral eccentrics then unilateral eccentrics with a weighted backpack following the same dosage progression. Follow-up testing sessions were completed at two months and nine months from the initial evaluation for a total of four sessions. Self-report outcome measures were also collected at one month, but due to the subject’s work schedule he was unable to attend an onsite session for PPT. OUTCOMES Following one treatment session of noxious electrical stimulation, the subject demonstrated Improvements in Achilles tendon PPT testing, pain levels, and function via the VISA-A, in addition to running progression gains (Tables 1-4). For PPT, the subject exhibited an increase in threshold for pain at 24-hours post noxious stimulation treatment to both Achilles tendons, with a sustained improvement seen at 9 months (Table 1). The increase in PPT at 24-hours exceeded the MDC90% CI of 2.05 kg.49 A small reduction in PPT was observed between 24 hours and two months, which may be attributed to the increase in running intensity and pace during this time period as his tissues adapted to the new forces. For the VISA-A, the subject scored a 64% at the initial evaluation, then improved to 96% at one-month post intervention (Table 2). At his two-month followup, the subject scored an 81% on the VISA-A most likely due to the recent increase in his intensity and distance with running. At his nine month follow-up
Table 2. Improved Achilles tendon mean pain pressure threshold (PPT) measurements over time Achilles
Baseline
24 hours
2 months
9 months
Right (kg)
8.33
12.36
10.91
12.78
Left (kg)
10.5
16.31
10.96
14.9
Test-Retest Reliability Between Day49: ICC(3,k) = 0.91; MDC90% CI = 2.05 kg Mean value 13.7 ± 4.9kg for PPT laboratory database mean in healthy controls49
he scored a 94% on the VISA-A, with an increased pace time with his running. His LEFS score improved from a 73/80 to 74/80 over time, which is not significant but may be due to a ceiling effect of this outcome measure (Table 3). Self-reported pain rating via the NPRS was an 8/10 to bilateral Achilles tendons at worst prior to the intervention, which decreased to a 1/10 at worst at all testing sessions thereafter. Prior to the noxious electrical stimulation intervention, the subject was able to run, but only with sustained pain of 3-5/10. Any increase in running distance or intensity would increase his symptoms bilaterally. Post intervention, there was no Achilles pain with running at one and nine month follow-ups. With running, the subject consistently ran approximately 75 miles per week before and during the course of care (Table 4). However, he noted the inability to run faster than an 8.5 min/mile and had been unable to progress his workouts without exacerbation of his symptoms. After the noxious electrical stimulation treatment, the subject reported no more than 1/10 pain to bilateral Achilles tendons
Table 3. Lower Extremity Functional Scale over time Baseline
1 month
2 months
9 months
73/80
76/80
74/80
74/80
ground Q18 Making sharp turns
3
3
2
3
while running fast
2
3
3
3
LEFS Total Score Q17 Running on uneven
Table 4. Subject progression of running Weekly Mileage
Baseline 75mi/week
1 month 75mi/week
2 months 75mi/week
9 months 75mi/week
Tempo Runs Track Work Mile Pace
No No 8.5 min/mi
No No 8.5 min/mi
Yes Yes 8 min/mile
Yes Yes 7 min/mile
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with running. He maintained this current training regimen during the first month, as he did not want to progress his running routine for fear of potentially redeveloping his pain. At two months post intervention, the subject was able to slowly increase his running pace to 8 min/mile without increased pain. He also noted the ability to add track workouts and tempo runs, which he had been unable to progress to over the past several years. The subject reported that his track workouts consisted of 6 to 12 400m runs at moderate to high intensity in track spikes. Tempo runs were approximately 20 to 30 minutes in length, designed to increase stamina through improvement of running rhythm meant to be performed at a “comfortably hard” pace. At his nine-month follow-up session, he continued to note no pain with his runs and that he was able to run a 7 min/mile pace consistently without symptoms bilaterally. He also reported the ability to run a 4:14 mile, coming close to his personal record of a 4:04 mile as a collegiate runner. He was able to achieve one of his primary goals for physical therapy, which was to run close to his best college mile time for an upcoming reunion with his college cross-country and track teammates. DISCUSSION This case illustrates the successful pain reduction and return to progressive sports activity in a runner with chronic bilateral Achilles tendinopathy. The utilization of noxious electrical stimulation may have decreased the sensitivity to mechanical stimuli as evidenced by the large increase in pain pressure thresholds at 24 hours post-treatment. The ability of noxious electrical stimulation to reduce pain sensitivity is supported by results from animal studies, which show that electrical stimulation delivered at an intensity that activated A-delta pain fibers, decreased dorsal horn neuron responsiveness.34,50,51 In humans, TENS delivered at painful intensities reduced somatosensory evoked cortical potentials and perceived pain,52 and in an osteoarthritis clinical trial, noxious intensity TENS (30% above pain threshold) produced a greater reduction in pain and stiffness after a treatment period (3x/wk for 4wks) than strong, comfortable level TENS.53 The presence of central sensitization of pain has been shown to occur in other musculoskeletal conditions with
chronic pain,9,54-56 and the authors have since generated and presented evidence that central sensitization also occurs in people with chronic Achilles tendinopathy (> 3 months duration).57 The authors of this case report hypothesize that noxious electrical stimulation reduced the mechanical responsiveness of either the peripheral nociceptors or central neurons in the pain pathways as evidenced by the large change (> MDC90% CI) in pressure pain thresholds at 24-hours post-treatment. This is consistent with literature showing that high-frequency TENS can have both peripheral27 and central effects22,26,28 that can reduce pain sensitivity. Further research needs to address if signs of central sensitization are mitigated with treatment in people with Achilles tendinopathy. For the VISA-A scores the subject demonstrated a significant improvement in function by one month via this self-report measure. The VISA-A is designed specifically for individuals with Achilles tendon pain, and features relevant questions on the ability to perform tasks and report on activities such as minutes of Achilles stiffness in the morning, pain with heel raises, number of single leg hops without pain, and Achilles pain with sports. The subject exceeded the estimated MDC90% CI for the VISA-A at all testing time frames when compared with his initial score. He did experience a decrease from his initial posttreatment VISA-A score over the subsequent two months, which could be attributed to his increase in running activity (track workouts in spikes, tempo runs, and running pace). While the subject’s mileage remained relatively unchanged, he was able to progress the intensity of his workouts over time. The authors did recommend that the subject reduce and or cease running for a period of time to allow for recovery according to tendinopathy treatment guidelines by Davenport et al.58 However, the subject was unwilling to back off from his running due to the fact that the last break from running provided no relief of his symptoms upon return to activity. He was comfortable with the current management of his pain through the maintenance of his current running routine without any changes in intensity or distance. This approach is supported by research from Silbernagel and colleagues,18 who showed that Achilles tendon-loading
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activity can be maintained during treatment of tendinopathy using a pain-monitoring model of activity. CONCLUSIONS In summary, the application of noxious electrical stimulation in a runner with chronic history of bilateral mid-portion Achilles tendinopathy resulted in a positive effect on pain level and activity where other conservative measures failed, including eccentric plantarflexor strengthening. Although the benefit of continued eccentric exercises may have contributed to the final outcome of this case, the incorporation of noxious electrical stimulation was a novel approach to pain management of this chronic injury. The authors hypothesize that noxious electrical stimulation may work to reduce pain in chronic tendinopathies via altering central pain processing. Future directions include testing if central sensitization is present in individuals with chronic Achilles tendinopathy and testing the effects of noxious electrical stimulation and eccentric exercise on pain processing in this pathology. REFERENCES 1. Kujala UM, Sarna S, Kaprio J. Cumulative incidence of achilles tendon rupture and tendinopathy in male former elite athletes. Clin J Sport Med. 2005;15(3):133-135. 2. Knobloch K, Yoon U, Vogt PM. Acute and overuse injuries correlated to hours of training in master running athletes. Foot Ankle Int. 2008;29(7):671-676. 3. Scott A, Huisman E, Khan K. Conservative treatment of chronic Achilles tendinopathy. CMAJ : Canadian Medical Association journal = journal de l’Association medicale canadienne. 2011;183(10):1159-1165. 4. Paavola M, Kannus P, Jarvinen TA, Khan K, Jozsa L, Jarvinen M. Achilles tendinopathy. J Bone Joint Surg Am. 2002;84-A(11):2062-2076. 5. Paavola M, Kannus P, Paakkala T, Pasanen M, Jarvinen M. Long-term prognosis of patients with achilles tendinopathy. An observational 8-year follow-up study. Am J Sports Med. 2000;28(5):634-642. 6. Abate M, Silbernagel KG, Siljeholm C, et al. Pathogenesis of tendinopathies: inflammation or degeneration? Arthritis research & therapy. 2009;11(3):235. 7. Barbe MF, Gallagher S, Massicotte VS, Tytell M, Popoff SN, Barr-Gillespie AE. The interaction of force and repetition on musculoskeletal and neural tissue responses and sensorimotor behavior in a rat model of work-related musculoskeletal disorders. BMC Musculoskelet Disord. 2013;14:303.
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