Foot & Ankle Specialist 231

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

⟨ Clinical Research ⟩

The Use of Low-Energy Radial Shockwave in the Treatment of Entrapment Neuropathy of the Medial Calcaneal Nerve:A Pilot Study

Stephen L. Barrett, DPM, FACFAS, MBA, Matthew M. Reese, PhD, John Tassone, DPM, and Maria Buitrago, DPM

vol. 1 / no. 4

Abstract: Medial calcaneal nerve entrapment is a well-recognized cause of heel pain. In addition, the development of an amputation neu-roma of the medial calcaneal nerve from prior heel surgery via an open incision on the medial aspect of the heel is a serious common post-operative complication and can be extremely difficult to treat. This pre-liminary pilot study demonstrates that the use of low-energy extracor-poreal shockwave is safe and effica-cious 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 affecta-tion, 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

Heel pain is recognized as one of the most common causes of foot pain, and pathology of the plan-

tar fascia is widely recognized as the most common etiology.1 The role of the plantar fas-cia is well documented in its contribution to the stability it provides the human foot in dynamic gait and stance.2 However, the pathomechanics is not completely known and is only theorized. Even the term plantar fasciitis is a misnomer, as the condition is well documented to be of a degenerative histopathology rather than an inflamma-tory etiology.3 The exact cause of plan-tar fasciosis is unknown but is believed to be related to repeated micro or macro stress of the inferior aspect of the apo-neurosis near its calcaneal origin.4

There is, however, very little published in the medical literature directly asso-ciating 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

30 control patients tested. Interestingly, in their control group (patients with-out plantar fasciitis), 7 obese patients had slower conduction, and 12 heels with “long heel loading” had significantly slower electrical findings.5 Clinically, we have seen a high association of entrap-ment of the medial calcaneal nerve in

The safety of low-energy radial

shockwave has been well documented,

and only minor complications have been

noted. . . .”

“

August 2008Foot & Ankle Specialist232

patients with heel pain, which is primarily mechanical plantar fasciosis. This high association was also docu-mented 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 clin-ical subjectivity can be removed via the implementation of high-resolution diag-nostic 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 asso-ciation between medial calcaneal neu-ropathy and plantar fasciitis, nothing can be proven causally. It may be that the same factors that are documented to contribute to the development of plan-tar 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 calca-neal 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 amputa-tion 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 suc-cessful ways to address this condition is with denervation of the medial calcaneal nerve branches with subsequent trans-position into innervated skeletal muscle in the distal leg.15 We have used this sur-gery effectively for many years and have been satisfied with the patient outcomes. Integral to success for this type of sur-gery 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

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.

Foot & Ankle Specialistvol. 1 / no. 4 233

muscle of the distal leg. This subjects the patient to potential iatrogenic periph-eral 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 cal-caneal 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 plan-tar 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 applica-tions 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 treat-ment 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 devel-opment 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 sub-stance 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 resto-ration of sensation and pain. Although

this may be a temporary clinical experi-ence, the application of additional treat-ments for the patient is certainly possible with minimal sequelae.

The goal of this study is to determine if low-energy extracorporeal shockwave treat-ment (ESWT) is an effective way to treat entrapment of the medial calcaneal nerve.

MethodsThis study was prospective, and

patients were enrolled in a sequential manner over a 6-month period. Each patient with the diagnosis of medial cal-caneal 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 calca-neal nerves that were treated. Each case was thoroughly worked up by focusing on history of present illness, clinical pre-sentation, results of neurosensory testing, and findings on high-resolution diagnos-tic ultrasound with power Doppler to rule out the possibility of other concomitant pathology. In addition, prior to shock-wave treatment, but not at the time of treatment, 3 of 4 patients were given a diagnostic lidocaine injection just subcu-taneously in the suspected area of medial calcaneal nerve distribution, also cor-relating to their site of pain with palpa-tion. Subject 3 had an extreme fear of needles and was not given a diagnos-tic nerve block. This block was then eval-uated 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 iso-lated 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 involve-ment 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

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.

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for patients who have undergone sur-gery 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 fas-ciitis, 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 cal-caneal nerve with muscular transposi-tion. Each patient was also informed that this could be only a temporary treatment, which could require additional treat-ments with shockwave or continue with surgical denervation of the medial cal-caneal nerve. Each patient had a series of ESWT treatments that were patient focused to the area of most tenderness, without any local or regional anesthe-sia, 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 vis-it’s ESWT treatment. Because of the mini-mal 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 periph-eral 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 ReportsSubject 1Subject 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 palpa-tion of both the medial calcaneal tubercles, as well as the medial calcaneal nerve areas bilaterally. The patient had normal palpa-ble 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.

Figure 4.

The Swiss DolorClast extracorporeal shockwave treatment (ESWT) machine.

Figure 5.

A close-up view of the hand piece/transducer of the Swiss DolorClast machine.

Foot & Ankle Specialistvol. 1 / no. 4 235

Results of a previous diagnostic ultra-sound revealed normal thickness and echogenicity in all 3 bands bilaterally (see Figure 8). A .5-cc diagnostic block of plain 2% lidocaine was injected subcuta-neously 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 degen-eration bilaterally for the tibial or medial calcaneal nerves. However, the study did show elevated 2-point discrimina-tion pressure thresholds for the medial

calcaneal and medial plantar nerve areas bilaterally.

The patient received a series of 4 extra-corporeal shockwave (ESW) treatments on each of his medial calcaneal nerves, start-ing 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 2Subject 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 pal-pation for the medial calcaneal tuber-cle bilaterally. He had normal palpable pulses bilaterally. There was no gastroc-nemius 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 discrim-ination 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 min-utes, 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 3Subject 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.

Figure 7.

Subject 1: left medial calcaneal nerve pain levels.

Figure 6.

Subject 1: right medial calcaneal nerve pain levels.

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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 poste-rior tibial nerve. She had no provocation sign for the left medial calcaneal nerve. Previous diagnostic ultrasound studies revealed normal findings, with no

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 his-tory showed nothing significant other than the resolved plantar fasciitis (fas-ciosis). She had good palpable pulses bilaterally.

The patient underwent 3 ESW treat-ments, 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.

Figure 8.

Subject 2: diagnostic ultrasound of the left medial band of the plantar fascia.

Foot & Ankle Specialistvol. 1 / no. 4 237

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, pre-sented with exquisite pain on palpation of the medial calcaneal nerve distribu-tion bilaterally. She had no tenderness

Figure 11.

Subject 2: left medial calcaneal nerve pain levels.

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 cen-tral 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 plan-tar nerve with elevated pressure thresh-olds for 2-point discrimination in the medial calcaneal nerve bilaterally. A second study conducted in 2007 indi-cated increased pressure thresholds for 2-point discrimination in both the medial calcaneal nerve and medial plan-tar 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).

Figure 10.

Subject 2: pressure-specified sensory device (PSSD) examination results of the medial heel.

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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 extra-corporeal shockwave treatments well, and there were no complications.

None of these patients had an ampu-tation neuroma of the medial calca-neal 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 ecchymo-sis noted. Local indentation and temporary erythema were noted, as seen in Figure 3, after treatment in all patients.

Figure 12.

Subject 3: pressure-specified sensory device (PSSD) examination results for the great toe pulp.

Foot & Ankle Specialistvol. 1 / no. 4 239

Figure 15.

Subject 4: diagnostic ultrasound of the left medial band.

Figure 14.

Subject 3: medial calcaneal nerve pain levels.

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 calca-neal nerve and the medial plantar nerve in patients diagnosed with plantar fasci-itis. 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 univer-sally 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 sen-sitivity 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 entrap-ment is that they can be correlated clin-ically when the patient demonstrates a positive provocation sign with pres-sure 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 subcu-taneously 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 etio-logical factor is removed, but some type of heel pain is still present. We have had many patients who have had suc-cessful treatment for their plantar fascio-sis, either conservative or interventional, but who still had heel pain. Sometimes, close attention to the history of pres-ent illness will delineate this for the cli-nician, 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 success-ful 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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The use of a low-energy shockwave (ESWT) may provide an interim nonin-vasive treatment for patients who suf-fer 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

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 symptomatol-ogy 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 neu-roma of the medial calcaneal nerve(s). These complications may present with more painful symptomatology than the original condition, necessitating exten-sive surgical intervention. Low-energy ESWT could be studied in the future in patients who have symptomatic ampu-tation neuromas of the medial cal-caneal nerve, to determine if there is any efficacy in the treatment with ESWT prior to surgical denervation and transposition.

ConclusionsComplex, 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 low-energy extracorporeal shockwave treat-ment for isolated medial calcaneal nerve entrapment or amputation neu-roma may become a valuable instru-ment 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 anes-thesia. This type of treatment allows immediate return to regular activity and shoe gear. Although it is possible that treatment with the Swiss DolorClast

Figure 17.

Subject 4: right medial calcaneal nerve pain levels.

Figure 16.

Subject 4: diagnostic ultrasound of the left medial band with power Doppler.

Foot & Ankle Specialistvol. 1 / no. 4 241

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.

Figure 18.

Subject 4: left medial calcaneal nerve pain levels.

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 phys-iological response that could be attrib-uted to the ESWT treatments. The positive outcomes from this initial study warrant future study of extracor-poreal shockwave treatment for pathol-ogy of the medial calcaneal nerve amputation neuroma and entrapment. This type of intervention appears to be safe, and there was no postproce-dure morbidity in any of these initial subjects.

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