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〈 Clinical Research 〉 The Use of Low-Energy Radial Shockwave in the Treatment of Entrapment Neuropathy of the Medial Calcaneal Nerve:
Stephen L. Barrett, DPM, FACFAS, MBA, Matthew M. Reese, PhD, John Tassone, DPM, and Maria Buitrago, DPM
A Pilot Study
Abstract: Medial calcaneal nerve entrapment is a well-recognized cause of heel pain. In addition, the development of an amputation neuroma of the medial calcaneal nerve from prior heel surgery via an open incision on the medial aspect of the heel is a serious common postoperative complication and can be extremely difficult to treat. This preliminary pilot study demonstrates that the use of low-energy extracorporeal shockwave is safe and efficacious in the treatment of this disorder without the morbidity associated with denervation surgery, which would be one of the most common methods to treat this complicated situation. Four patients, 2 with bilateral affectation, for a total of 6 medial calcaneal nerves, had a series of treatments with low-energy radial shockwave with the Swiss DolorClast machine. All 4 patients had improvement in their pain scores, to the point that none elected surgical treatment, and there were no complications.
Keywords: medial calcaneal nerve; low-energy radial shockwave; heel pain; nerve entrapment
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There is, however, very little published in the medical literature directly associating plantar fasciitis (fasciosis) with pathology of the medial calcaneal nerve. Chang et al5 recently published their findings of affected sensory nerve conduction studies in 26 patients with plantar fasciitis compared with
eel pain is recognized as one of the most common causes of foot pain, and pathology of the plantar fascia is widely recognized as the most common etiology.1 The role of the plantar fascia is well documented The safety of low-energy radial in its contribution to the stability it provides the shockwave has been well documented, human foot in dynamic gait and stance.2 However, and only minor complications have been the pathomechanics is not noted. . . .” completely known and is only theorized. Even the term plantar fasciitis is a misnomer, as the condition is well 30 control patients tested. Interestingly, documented to be of a degenerative in their control group (patients withhistopathology rather than an inflammaout plantar fasciitis), 7 obese patients tory etiology.3 The exact cause of planhad slower conduction, and 12 heels tar fasciosis is unknown but is believed with “long heel loading” had significantly to be related to repeated micro or macro slower electrical findings.5 Clinically, we stress of the inferior aspect of the apohave seen a high association of entrapneurosis near its calcaneal origin.4 ment of the medial calcaneal nerve in
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DOI: 10.1177/1938640008320930. From the Midwestern University College of Health Sciences, Arizona Podiatric Medicine Program, Glendale, Arizona (SLB, JT); Barrett Foot & Ankle Clinics, Phoenix, Arizona (SLB, MMR); and Barrett Foot & Ankle Centers, Houston, Texas (MB). Address for correspondence: Stephen L. Barrett, DPM, FACFAS, MBA, Barrett Foot & Ankle Centers, 20940 N Tatum Blvd 290, Phoenix, AZ 85050; e-mail: slbarrettpod@mac.com. Copyright © 2008 Sage Publications
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Figure 1. Anatomical cadaveric dissection of the medial innervation of the human heel. Note the origin of the medial calcaneal nerve from both the tibial nerve and the lateral plantar nerve. There is an extremely high degree of variability in the neuroanatomy, which necessitates extensive dissection in the surgical technique to denervate the medial calcaneal nerve. With extracorporeal shockwave therapy, however, the patient can focus placement of the transducer on the site of pathology.
Figure 2. This is the immediate preoperative topographical marking of a painful DuVries-type incision that has resulted in a painful amputation neuroma requiring denervation surgery.
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patients with heel pain, which is primarily mechanical plantar fasciosis. This high association was also documented via neurosensory testing with the pressure-specified sensory device (PSSD; Sensory Management Services, Baltimore, Maryland) by Rose et al.6 Also important is the actual diagnosis of the true etiology of heel pain, and although many cases can be classified as multiple-etiology heel pain syndromes (MEHPS), the clinical subjectivity can be removed via the implementation of high-resolution diagnostic ultrasound, especially with power Doppler, in the initial workup for the patient with heel pain.7-12 Although the study by Chang et al5 demonstrates that there is a high association between medial calcaneal neuropathy and plantar fasciitis, nothing can be proven causally. It may be that the same factors that are documented to contribute to the development of plantar fasciosis (increased time of heel loading, high body mass index, foot mechanics, etc) also affect the medial aspect of the heel in such a manner that nerve entrapment of the medial calcaneal nerve develops (see Figures 1-3). The anatomical variability of the medial calcaneal nerve(s) is well studied and documented.13,14 In cases of amputation neuroma resulting from a painful scar from a medial DuVries-type incision from a previous heel surgery, it is also well documented that one of most successful ways to address this condition is with denervation of the medial calcaneal nerve branches with subsequent transposition into innervated skeletal muscle in the distal leg.15 We have used this surgery effectively for many years and have been satisfied with the patient outcomes. Integral to success for this type of surgery is complete exploration of the tibial nerve, as well as its branches, the medial and lateral plantar nerves, and direct visualization with loupe magnification of where and how many branches actually comprise the medial calcaneal nerve(s). It is also often necessary to perform an internal neurolysis of the tibial nerve to facilitate the fascicular separation, which is needed for proximal transposition of the medial calcaneal nerve(s) into the
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Figure 3. There is a small cutaneous indentation on the medial heel, where the extracorporeal shockwave treatment transducer was placed. This is transient and disappears several minutes after the treatment but indicates the anatomical placement, which was patient focused.
this may be a temporary clinical experience, the application of additional treatments for the patient is certainly possible with minimal sequelae. The goal of this study is to determine if low-energy extracorporeal shockwave treatment (ESWT) is an effective way to treat entrapment of the medial calcaneal nerve.
Methods
muscle of the distal leg. This subjects the patient to potential iatrogenic peripheral nerve injury while working inside the nerve, in addition to a larger incision and increased postoperative morbidity even over the morbidity associated with normal tarsal tunnel/medial ankle nerve decompression surgery. The premise for these patients was that if they were going to end up with denervation surgery to remove and transposition the medial calcaneal nerve, then there would be no real loss, except for time, to undergo low-energy shockwave treatment. The safety of low-energy radial shockwave has been well documented, and only minor complications have been noted, such as localized bruising and numbness and possible hematoma, which do not have any clinical consequence after several days.16 The use of a low-energy shockwave was introduced recently in the United States for the treatment of recalcitrant plantar fasciitis and is approved by the Food and Drug Administration (FDA) for that indication. However, this technology has
been used throughout the world for many years, and there are increasing applications ranging from treatment of ischemic cardiomyopathy to treatment of avascular necrosis of the femoral head.16 The use of low-energy radial shockwave for the treatment of human peripheral nerve has not been reported in the literature at this time, but the physics of the shockwave and its effect on the peripheral nerve has been studied in animal and rat models.17,18 It is clear that application of acoustic waves to a peripheral nerve will induce peripheral nerve injury of some type, which results in conduction block, without the development of neuroma.19 It is known that the direct application of shockwaves leads to the propagation of action potentials in intact nerves.17 It is also known that in unmyelinized nerve fibers, extracorporeal shockwave can affect the release of substance P in both the C-fibers and the A delta sensory nerve fibers.16 Depending on the type of peripheral nerve injury, regeneration of the axons would be expected with potential restoration of sensation and pain. Although
This study was prospective, and patients were enrolled in a sequential manner over a 6-month period. Each patient with the diagnosis of medial calcaneal nerve entrapment was given the option to participate in the study after being informed that the treatment was not FDA approved and that full informed consent was required. Several patients were not willing to participate in the study and opted for different treatment. In our 4 patient cases, 2 had bilateral involvement, for a total of 6 medial calcaneal nerves that were treated. Each case was thoroughly worked up by focusing on history of present illness, clinical presentation, results of neurosensory testing, and findings on high-resolution diagnostic ultrasound with power Doppler to rule out the possibility of other concomitant pathology. In addition, prior to shockwave treatment, but not at the time of treatment, 3 of 4 patients were given a diagnostic lidocaine injection just subcutaneously in the suspected area of medial calcaneal nerve distribution, also correlating to their site of pain with palpation. Subject 3 had an extreme fear of needles and was not given a diagnostic nerve block. This block was then evaluated not only for relief of this patient’s pain but also to ascertain that there was still normal sensation in both the medial and lateral plantar nerves, ensuring that the diagnostic lidocaine block was isolated to the medial calcaneal nerve only. Because this isolated nerve block relieved most if not all pain in this series of patients, it could be inferred that most of their pain was due to isolated involvement of the medial calcaneal nerve, even in those cases where other pathology was noted. Clinically, we have found this to be a very prognosticative technique
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Figure 4.
Figure 5.
The Swiss DolorClast extracorporeal shockwave treatment (ESWT) machine.
A close-up view of the hand piece/transducer of the Swiss DolorClast machine.
for patients who have undergone surgery to denervate their medial calcaneal nerve. Although the EMS Swiss DolorClast machine (see Figures 4 and 5) is FDA approved for the treatment of plantar fasciitis, these patients were completely informed that this method of treatment was experimental and that there was no FDA approval for treatment of the medial calcaneal nerve. Informed consent was obtained, and each patient understood
that there could still be the requirement for surgical denervation of the medial calcaneal nerve with muscular transposition. Each patient was also informed that this could be only a temporary treatment, which could require additional treatments with shockwave or continue with surgical denervation of the medial calcaneal nerve. Each patient had a series of ESWT treatments that were patient focused to the area of most tenderness, without any local or regional anesthesia, where each treatment was spaced 1 to 2 weeks apart and consisted of 2000 shocks. The initial pressure was 2 bars at a frequency of 13 cycles per second. After 500 shocks, the pressure was gradually increased to 4 bars, and the frequency was increased to 15 cycles per second. All patients tolerated the treatments well and were allowed immediate return to walking and regular activity. Each patient rated his or her pain on a visual analog scale (VAS) prior to each treatment. Each patient in this study was treated by either 1 or 2 of the authors but with identical protocols. VAS scores were obtained by 1 of the nontreating authors at the time of the next office visit prior to that visit’s ESWT treatment. Because of the minimal morbidity associated with ESWT, each patient was informed that there could be a series of treatments as long as there was improvement in symptomatology and that
5 treatments would be needed to reach the optimal pain reduction based on the cumulative effect of ESWT on the peripheral nerve. Outcomes would be measured by VAS scores and clinical subjective information from the patient. Patients were followed up from 6 to 9 months from their last treatment, but results of this study would have actually improved because there has been further clinical improvement in subject 2 since the cutoff date of evaluation in this study.
Case Reports Subject 1 Subject 1, a 40-year-old man in very good health, presented with severe pinching pain in his heels and plantar forefoot bilaterally, with the right greater than the left. His right pain level started at a 7 on the right and a 5 on the left on a scale of 0 to 10 (see Figures 6 and 7). He had pain on palpation of both the medial calcaneal tubercles, as well as the medial calcaneal nerve areas bilaterally. The patient had normal palpable dorsalis pedis and posterior tibial pulses bilaterally. He had no provocation or Tinel’s signs in the tarsal tunnel, deep peroneal, or common peroneal nerve sites bilaterally. He had a history of significant varicose veins and had been dealing with his current foot pain for the past 10 years. There was no gastrocnemius equinus noted bilaterally.
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Subject 2
Figure 6. Subject 1: right medial calcaneal nerve pain levels.
Figure 7. Subject 1: left medial calcaneal nerve pain levels.
Results of a previous diagnostic ultrasound revealed normal thickness and echogenicity in all 3 bands bilaterally (see Figure 8). A .5-cc diagnostic block of plain 2% lidocaine was injected subcutaneously over the right medial calcaneal nerve. Approximately 5 minutes after the block, he related a significant reduction in his pain level. A neurosensory study was completed with a PSSD indicating no axonal degeneration bilaterally for the tibial or medial calcaneal nerves. However, the study did show elevated 2-point discrimination pressure thresholds for the medial
calcaneal and medial plantar nerve areas bilaterally. The patient received a series of 4 extracorporeal shockwave (ESW) treatments on each of his medial calcaneal nerves, starting with his right and ending with his left. No anesthesia was required. He received 2000 therapeutic shockwave impulses in total, with the first 500 impulses delivered at a frequency of 13 Hz and the final 1500 impulses at a frequency of 15 Hz. The pressure was gradually increased from 200 kPa after the first 500 impulses to 400 kPa. He experienced a reduction in pain levels bilaterally.
Subject 2, a 54-year-old man, presented with heel pain in his left foot that had a burning nature. The patient had been dealing with and receiving treatment for his condition for the past 15 years. He previously had steroid injections, which gave him only temporary relief. A previous diagnostic ultrasound had been performed that revealed normal thickness and echogenicity in all 3 bands of the plantar fascia bilaterally. His first examination showed no pain on palpation for the medial calcaneal tubercle bilaterally. He had normal palpable pulses bilaterally. There was no gastrocnemius equinus noted bilaterally. A diagnostic ultrasound examination was performed with normal findings for his medial, central, and lateral bands. There were no hypoechoic areas noted within the plantar fascia bilaterally. The results of his neurosensory testing demonstrated an elevated 2-point discrimination pressure level for the left medial calcaneal nerve. His left medial plantar pressure level was within normal limits, indicating isolated medial calcaneal nerve involvement (see Figures 9 and 10). A diagnostic nerve block was performed on his left medial calcaneal nerve, and 1 cc of 2% lidocaine was injected subcutaneously over the left medial calcaneal nerve just proximal to the area of pain. After 10 minutes, the patient was able to wear his work boot and bear full weight with no pain. The patient received 3 ESW treatments on his left medial calcaneal nerve. No anesthesia was required. He received 2000 therapeutic shockwave impulses in total, with the first 500 impulses at a frequency of 13 Hz and the final 1500 impulses at a frequency of 15 Hz. The pressure was gradually increased from 200 kPa after the first 500 impulses to 400 kPa. The patient experienced a reduction in his pain level (see Figure 11).
Subject 3 Subject 3, a 53-year-old woman, presented with pain in the right heel. She described the pain as moving from one place to another and as “a burning tight sensation.� She is very athletic and plays professional golf on a regular basis.
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She had a 10-year history of plantar fasciitis (fasciosis), which was resolved with orthotic devices. The patient had a positive Tinel’s sign of the right posterior tibial nerve and significant positive provocation sign of the right medial
calcaneal nerve. She had a negative Tinel’s sign in regards to the left posterior tibial nerve. She had no provocation sign for the left medial calcaneal nerve. Previous diagnostic ultrasound studies revealed normal findings, with no
Figure 8. Subject 2: diagnostic ultrasound of the left medial band of the plantar fascia.
thickening or hypoechoic areas noted in the plantar fascia bilaterally. A neurosensory study was completed with a PSSD indicating no axonal degeneration bilaterally for the tibial or medial calcaneal nerves. However, the study did show elevated 2-point discrimination pressure thresholds for the right medial calcaneal and medial plantar nerve areas (see Figures 12 and 13). She was started on 50 mg Lyrica once a day in the evening. She declined a diagnostic lidocaine injection as she had a fear of needles. Her review of systems was normal, and her past medical history showed nothing significant other than the resolved plantar fasciitis (fasciosis). She had good palpable pulses bilaterally. The patient underwent 3 ESW treatments, with no anesthesia. She received 2000 therapeutic shockwave impulses in total, with the first 300 impulses at a frequency of 13 Hz and the final 1700 impulses at a frequency of 15 Hz. The pressure was gradually increased from 200 kPa after the first 300 impulses to 400 kPa. She had a significant reduction in her pain level. On her last visit, she indicated
Figure 9. Subject 2: pressure-specified sensory device (PSSD) examination results of the great toe pulp.
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Figure 10. Subject 2: pressure-specified sensory device (PSSD) examination results of the medial heel.
Figure 11. Subject 2: left medial calcaneal nerve pain levels.
that she had no pain and that she was able to walk a complete (18-hole) round of golf (see Figure 14).
Subject 4 Subject 4, a 45-year-old woman, presented with exquisite pain on palpation of the medial calcaneal nerve distribution bilaterally. She had no tenderness
on palpation of the plantar fascia at the medial calcaneal tubercle bilaterally. She had normal palpable pulses bilaterally. She had a previous bunionectomy on the right foot in 1994. A diagnostic ultrasound revealed some thickening of the medial and central bands of the left plantar fascia (see Figure 15). The power Doppler function of the ultrasound revealed a loss of vascularity in
the left medial band of the plantar fascia (see Figure 16). She was given 2 diagnostic injections subcutaneously over the distribution of the medial calcaneal nerve bilaterally and was then allowed to walk around for 3 hours. When she returned, her pain had been eliminated. An initial neurosensory study (PSSD) done in 2006 indicated limited axonal degeneration in the right medial plantar nerve with elevated pressure thresholds for 2-point discrimination in the medial calcaneal nerve bilaterally. A second study conducted in 2007 indicated increased pressure thresholds for 2-point discrimination in both the medial calcaneal nerve and medial plantar nerve bilaterally with no axonal degeneration. The patient was given a series of 4 ESW treatments at the medial calcaneal nerve area bilaterally. She received 2000 therapeutic shockwave impulses in total, with the first 500 impulses at a frequency of 13 Hz and the final 1500 impulses at a frequency of 15 Hz. The pressure was gradually increased from 200 kPa after the first 300 impulses to 400 kPa. She experienced a significant reduction in her pain levels bilaterally. (see Figures 17 and 18).
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Figure 12. Subject 3: pressure-specified sensory device (PSSD) examination results for the great toe pulp.
Figure 13. Subject 3: pressure-specified sensory device (PSSD) examination results for the medial heel.
Results There was reduction of pain for every patient treated in this pilot study. All patients tolerated the extracorporeal shockwave treatments well, and there were no complications.
None of these patients had an amputation neuroma of the medial calcaneal nerve. As can be seen in Figure 19, dramatic improvement was made, without any change in lifestyle activity or cessation of normal activity for these patients resulting from their series of
treatments. No pain medication was required for any patient after ESWT treatment, nor was there any ecchymosis noted. Local indentation and temporary erythema were noted, as seen in Figure 3, after treatment in all patients.
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Figure 14. Subject 3: medial calcaneal nerve pain levels.
Figure 15. Subject 4: diagnostic ultrasound of the left medial band.
Discussion Multiple-etiology heel pain syndrome can be complex and difficult to diagnose. Rose et al6 reported that there was a 23% incidence of isolated medial calcaneal nerve entrapment and a 49% occurrence
of entrapment of both the medial calcaneal nerve and the medial plantar nerve in patients diagnosed with plantar fasciitis. The use of high-resolution diagnostic ultrasound in addition to neurosensory testing with the PSSD removes much of the subjective input, which goes into the
overall diagnosis of heel pain. Although the PSSD has not been embraced to the level of electrodiagnostic testing universally at this time, the technology is used in large medical university hospitals and medical schools such as Johns Hopkins and the Cleveland Clinic. More than 80 peer-reviewed journal articles also have been published validating its sensitivity and specificity compared with nerve conduction velocity studies, or its use has been integrated into accepted clinical research.20-32 Substantiation of the neurosensory testing findings in patients with medial calcaneal nerve entrapment is that they can be correlated clinically when the patient demonstrates a positive provocation sign with pressure in the distribution of that nerve and when the patients have all or nearly all of their pain relieved with only a small amount of lidocaine infiltrated subcutaneously around the medial calcaneal nerve, without nerve block of the tibial, medial, and lateral nerves. Some patients are able to differentiate their symptoms and that they had overlay when 1 etiological factor is removed, but some type of heel pain is still present. We have had many patients who have had successful treatment for their plantar fasciosis, either conservative or interventional, but who still had heel pain. Sometimes, close attention to the history of present illness will delineate this for the clinician, but there are those patients who cannot differentiate their subtle pain and believe that their prior treatment was not effective—only to find out with a more sophisticated and closer look that they also suffered from entrapment of the medial calcaneal nerve, and then their fasciosis was successfully treated. Once this is discovered, the practitioner is faced with few options for successful treatment except denervation of the medial calcaneal nerve. Unfortunately, this type of surgery is demanding and requires complete exploration of the medial ankle neural complex via large incision and surgical exposure, with subsequent microsurgery to denervate the nerve(s) and transposition them into innervated skeletal muscle of the lower leg.
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Figure 16. Subject 4: diagnostic ultrasound of the left medial band with power Doppler.
Figure 17. Subject 4: right medial calcaneal nerve pain levels.
morbidity, easily can be repeated over time. Subjects 1 and 2 did not take Lyrica, whereas both subjects 3 and 4 took 50 mg once per day. This may have contributed to the overall improved subjective outcome and had a type of cumulative effect. This does not diminish the contribution of reducing peripheral nerve symptomatology by the ESWT treatments because of the very low dose taken and because subject 3 discontinued use of the drug very early in the course of treatment with ESWT. Complications from a medial DuVries-type incision are well known and usually include pathology, which can be attributed to an amputation neuroma of the medial calcaneal nerve(s). These complications may present with more painful symptomatology than the original condition, necessitating extensive surgical intervention. Low-energy ESWT could be studied in the future in patients who have symptomatic amputation neuromas of the medial calcaneal nerve, to determine if there is any efficacy in the treatment with ESWT prior to surgical denervation and transposition.
Conclusions
The use of a low-energy shockwave (ESWT) may provide an interim noninvasive treatment for patients who suffer from documented medial calcaneal nerve entrapment, which allows
immediate return to normal activity and, at the very least, does not harm the patient. This type of treatment may even be temporary but, because of the low risk and virtually no postprocedure
Complex, recalcitrant heel pain has been well established to be caused by multiple factors. As demonstrated by the results in our initial small study of 4 patients, the implementation of lowenergy extracorporeal shockwave treatment for isolated medial calcaneal nerve entrapment or amputation neuroma may become a valuable instrument in the treatment of these difficult cases before intervention with surgical peripheral denervation. There were no complications in this series of patients, and they generally tolerated the procedure well without local anesthesia. This type of treatment allows immediate return to regular activity and shoe gear. Although it is possible that treatment with the Swiss DolorClast
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Figure 18. Subject 4: left medial calcaneal nerve pain levels.
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low-energy radial shockwave may have had only a placebo effect, we believe that, based on the individual patient profiles included in this small study, there was a true peripheral nerve physiological response that could be attributed to the ESWT treatments. The positive outcomes from this initial study warrant future study of extracorporeal shockwave treatment for pathology of the medial calcaneal nerve amputation neuroma and entrapment. This type of intervention appears to be safe, and there was no postprocedure morbidity in any of these initial subjects.
Figure 19. Hand piece transducer for the Swiss DolorClast extracorporeal shockwave treatment (ESWT) machine. The end of the transducer is placed into the area of most sensitivity, as directed by the patient. It is calibrated at the end to ensure proper pressure application to the musculoskeletal site prior to administration of the shockwaves.
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in patients with peripheral neuropathy. Ann Plast Surg. 2006;56:145-150. 24. Fels KW, Cunha MS, Sturtz GP, Gemperli R, Ferreira MC. Evaluation of cutaneous abdominal wall sensibility after abdominoplasty. Aesthetic Plast Surg. 2005;29:78-82. 25. Ferreira MC, Costa MP, Cunha MS, Sakae E, Fels KW. Sensibility of the breast after reduction mammaplasty. Ann Plast Surg. 2003;51:1-5. 26. Ferreira MC, Rodrigues L, Fels K. New method for evaluation of cutaneous sensibility in diabetic feet: preliminary report. Rev Hosp Clin Fac Med São Paulo. 2004;59:286-290. 27. Howard M, Lee C, Dellon AL. Documentation of brachial plexus compression (in the thoracic inlet) utilizing provocative neurosensory and muscular testing. J Reconstr Microsurg. 2003;19:303-312. 28. Radoiu H, Rosson GD, Andonian E, Senatore J, Dellon AL. Comparison of measures of large-fiber nerve function in patients with chronic nerve compression and neuropathy. J Am Podiatr Med Assoc. 2005;95:438-445. 29. Siemionow M, Zielinski M, Sari A. Comparison of clinical evaluation and neurosensory testing in the early diagnosis of superimposed entrapment neuropathy in diabetic patients. Ann Plast Surg. 2006;57:41-49. 30. Soomekh D. Quantitative sensory testing. Clin Podiatr Med Surg. 2006;23: 545-557. 31. Tassler PL, Dellon AL. Pressure perception in the normal lower extremity and in the tarsal tunnel syndrome. Muscle Nerve. 1996;19:285-289. 32. Tassler PL, Schwartz BS, Coresh J, Stewart WF, Todd AC. Associations of tibia lead, DMSA-chelatable lead, and blood lead with measures of peripheral nervous system function in former organolead manufacturing workers. Am J Ind Med. 2001;39: 254-261.