When Is Heel Pain Nerve Pain?

Although clinicians may assume plantar fasciopathy is always the cause of heel pain, the heel pain may be due to multiple etiologies. Citing the diagnostic advantages of ultrasonography, peripheral nerve blocks and neurosensory testing, this author says one can provide more tailored treatment for patients.

It is well established, and nearly universally accepted, that most heel pain is due to a problem with the plantar fascia, specifically plantar fasciopathy. An estimated 93 percent of inferior heel pain cases are caused by a degeneration of the plantar fascia.¹

This statistic could be misleading as there can be a significant percentage of patients with multiple etiologies for their heel pain. Rose and colleagues eloquently pointed this out in a 2003 study in the Journal of Foot and Ankle Surgery.¹ They found that in 84 patients with a chief complaint of plantar heel pain, more than 72 percent had a sensory disturbance of the medial calcaneal nerve and/or tarsal tunnel syndrome.

There is also an association between plantar fasciopathy and medial calcaneal neuropathy. Chang and coworkers confirmed this via sensory nerve conduction studies.² Clearly, a patient can have more than one etiology causing the heel pain and this can be problematic in establishing an accurate diagnosis. If both plantar fasciopathy and a neurogenic etiology are present, what is the best course of treatment? What is the best method to solving the puzzle of complex heel pain?

Pertinent Keys To The Initial Diagnostic Workup

The ability to listen closely to patients describe their symptoms, their onset and what patients have done to relieve their condition is vitally important in addressing all pathology. In heel pain cases, this can give the practitioner an early and tremendous amount of insight into their etiology.

Multiple Etiology Heel Pain Syndrome (MEHPS) is more likely than a patient demonstrating symptoms that are solely neurogenic. We developed a scoring system more than 15 years ago and while it has not had scientific validation, it has proven extremely accurate for multiple independent practitioners (see “A Closer Look At Multiple Etiology Heel Pain Syndrome” at left).³ As part of this scoring system, if patients say their pain worsens after they are up on their feet, the pain is of a burning nature, they have pain at night when they are not weightbearing and they have had orthotic devices that did not help, then the diagnosis should start leaning toward a neurogenic cause. If patients state that their orthotics actually made the symptoms worse, this is almost pathognomonic for neurogenic etiology. Specifically, the practitioner should examine the patient for tibial nerve entrapment at the medial ankle and entrapment of the medial and lateral plantar nerves.  

Prior to the advent of advanced technologies such as magnetic resonance imaging (MRI) and more importantly ultrasonography, the examination for heel pain usually consisted of virtually nothing more than getting a quick history from the patient and pressing one’s thumb on the bottom of the heel over the medial calcaneal tubercle and asking if it hurts. Voilà! The patient gets a diagnosis of plantar fasciitis (note I have intentionally substituted the word fasciitis here for fasciopathy, which is the more accurate nomenclature, to emphasize how blatantly the true etiology has been obfuscated).

We then used to relegate the patient to some “cookie cutter” treatment plan for a period of time, often referred to as “conservative care.” This usually consisted of orthotic devices, steroid injections, strapping, stretching exercises, night splints and other therapies. When this dogmatic and inflexible approach did not work, sadly we often cut the plantar fascia when the true etiology did not indicate cutting and the patient did no better.  

At a minimum, one ideally needs to evaluate seven things during the physical examination of the patient presenting with heel pain:

1. Vascular status
2. Presence or absence of equinus
3. Possibility of entrapment of the tibial, medial and lateral plantar nerves
4. Possibility of entrapment of the medial calcaneal nerve(s)
5. Possibility of calcaneal stress fracture
6. Status of the inferior calcaneal fat pad
7. Tenderness of the medial calcaneal tubercle

Assessment of the physical criteria listed above, combined with ultrasonography, will accurately diagnose more than 98 percent of patients presenting with plantar heel pain.³ As one can see in “A Clinical Grading System To Direct Treatment When Using Diagnostic Ultrasound To Evaluate Plantar Fascia Thickness” above at right, while there are numerous possible etiologies for plantar heel pain, clinicians can attribute most of these cases to plantar fasciopathy, tarsal tunnel syndrome and medial calcaneal neuropathy.

After ruling out plantar fasciopathy or determining that plantar fasciopathy is only partially contributing to the patient’s heel pain, a focused neurological examination is necessary. Assessment of the medial ankle over the tibial, medial, lateral plantar and the medial calcaneal nerves should begin with basic provocation testing and whether or not the practitioner can elicit a Tinel’s sign. Note that while a Tinel’s sign may be absent, the provocation sign is almost always present when there is a nerve entrapment. While it is rare to note a Tinel’s sign with the medial calcaneal nerve, the nerve will almost always be tender upon palpation. Since the medial calcaneal nerve(s) is usually a very small nerve and the site of entrapment is very distal, elicitation of a Tinel’s sign is not usually possible, but simple provocation can prove useful in the diagnosis.

Can Diagnostic Ultrasonography Have An Impact?

Perhaps nothing is more important in the accurate diagnosis of heel pain than ultrasonography. It is the gold standard for determining and quantifying plantar fasciopathy.^3-5 Ultrasonography is inexpensive and one can perform it repeatedly to assess treatment success objectively. Ultrasonography does not have any radiation exposure, has a minimal learning curve for the practitioner and is quick and easy to use in the clinic setting. More importantly, it allows for an extremely fast and accurate diagnosis that allows definitive and tailored treatment for each individual.

The left photo above reveals no pathology of the plantar fascia and one can eliminate the differential diagnosis of plantar fasciopathy. The skilled physician would have a difficult time erroneously diagnosing the patient with plantar fasciopathy when using diagnostic ultrasonography. In the right photo below, significant pathology of the plantar fascia is present. For this patient, one can make a likely diagnosis of either isolated plantar fasciopathy or, less likely, a case for MEHPS. Then further diagnostic workup is needed to elucidate potential pain generators and their substantive contribution to the patient’s overall pain.

Since the advent of routine use of ultrasonography in podiatric medicine and surgery, the treatment paradigm has drastically shifted and improved. The practice that does not employ ultrasound technology today is severely handicapped in its ability to render an accurate diagnosis and ultimately expedient and effective patient care.

Leong and colleagues demonstrated this in 125 consecutive patients with recalcitrant plantar fasciopathy.⁶ The researchers’ use of ultrasonography enabled them to delineate insertional, distal and mixed fasciopathies that would go undifferentiated without sophisticated imaging. The authors found that 66 percent of patients had classic “insertional disease,” 22 percent had “mixed” insertional and distal disease, and 12 percent had a “pure distal disease.” Clearly, without having an accurate determination of the target and its severity, as one can determine easily with sonography, a practitioner is severely hampered in rendering ultimate and definitive care for the patient with heel pain.

Researchers have well established normative values for thickness of the plantar fascia. When one combines these normative values with signal intensity, ultrasonography is highly sensitive and specific for the determination of plantar fasciopathy.^7-11 Additionally, there are varying degrees of plantar fasciopathy and when one combines this with a neurogenic pain generator, knowing the severity of the degeneration of the plantar fascia provides critical insight into optimizing treatment. When a patient presents with plantar heel pain and does not have any signs of degeneration and thickening of the plantar fascia, there is a higher index of suspicion for isolated nerve entrapment.

As per “A Clinical Grading System To Direct Treatment When Using Diagnostic Ultrasound To Evaluate Plantar Fascia Thickness” above, we can effectively grade plantar fasciopathy by determining the plantar fascia’s thickness and signal intensity. A severely degenerative plantar fascia will manifest more intrasubstance mucoid material, thus increasing the hypoechoic signal intensity.

What You Can Learn From The Use Of Diagnostic Peripheral Nerve Blocks

The infiltration of a small amount (0.5 cc) of lidocaine in the distribution of the medial calcaneal nerve can allow for a very quick diagnosis of medial calcaneal nerve entrapment as the generator of the patient’s heel pain. With careful location of the infiltration, making sure to keep away from the lateral and medial plantar nerves, this is a very powerful, simple and fast tool to diagnose this condition.

Perform the initial infiltration over the medial aspect of the heel, where the patient demonstrates pain with palpation. It is important for the practitioner to remember there usually is more than one branch of the medial calcaneal nerve.¹² Accordingly, if a patient relates only partial or no reduction in pain with the initial block, the practitioner would need to infiltrate more lidocaine posteriorly or anteriorly, depending on the location of the initial block.

After completing the block, verify that the block did not cross over to the medial or lateral plantar nerves. One can do this with light scratching on the plantar surface of the first and fifth digits. If the patient cannot feel this light stimulus on the bottom of the toe, then the practitioner cannot make a valid diagnosis with specificity to which nerve branch is the pain generator. By using ultrasonography, one can easily and accurately map out the neural anatomy of the medial ankle, which will allow for the precise placement of the local anesthetic infiltration. This thereby gives a powerful differentiation of what nerve is or is not acting as a true pain generator.

Practical Insights On Conducting Neurosensory Testing

Clinicians cannot conduct nerve conduction velocity testing for the medial calcaneal nerve and I have found traditional electrodiagnostic testing can be falsely negative greater than 50 percent of the time in lower extremity nerve entrapments. One can evaluate peripheral nerve entrapment effectively with neurosensory testing through modalities such as AcroVal (AxoGen), formerly known as the Pressure Specified Sensory Device (PSSD).

A reduction in two-point discrimination is a function of A-beta fiber pathology, which is usually due to focal entrapment, and can be a very early marker of pathology such as diabetes. It is important to note that use of a 5.07 Semmes Weinstein monofilament only gives a positive result in very late stage nerve entrapment and severe neuropathy, and the monofilament’s use in this application is essentially worthless. I can proffer that the false sense of security provided by the use of the 5.07 monofilament can also be dangerous for patients. By the time patients are unable to feel the monofilament, their nerves are severely damaged and we can do little for restoration from nerve decompression.

There is a significantly elevated threshold for both one- and two-point static discrimination. This would be indicative of a medial calcaneal nerve entrapment. If one used the Semmes-Weinstein 5.07 monofilament in this case, the clinician would likely declare the patient has no pathology or significant sensory deficit. It is necessary to test for tarsal tunnel entrapment as well and there is an elevated two-point threshold for the medial plantar nerve as well. Neurosensory testing does not make the diagnosis. It only determines the ability of a patient to discern one- and two-point discrimination within anatomically defined areas. It is incumbent upon the physician to put all of the parts of the puzzle together. This testing modality is also highly useful in postoperative assessment of nerve function.

Current Concepts With The Algorithm For Multifunctional Heel Pain

Not only can multifactorial heel pain be difficult to diagnose, it also confronts the provider with sometimes very challenging decision-making. What is the ideal course of treatment? There are so many variables to consider with these patients. Accordingly, when one looks at “cookie cutter” approaches, we quickly realize that these “ideal” protocols are really nothing more than a guide for thought. However, providers can benefit from algorithms if they use algorithms with the understanding that they can serve as frameworks that can help effectively guide individualized treatment regimens.

The table “A Closer Look At Multiple Etiology Heel Pain Syndrome” above shows that MEHPS usually is comprised of two pain generators: plantar fasciopathy and some type of neurogenic component. One can then grade the fasciopathy to be mild to moderate (grade IA-IIIB) or severe (grade IIIC-IVC).

The neurogenic component usually breaks down into three subsets: isolated medial calcaneal nerve entrapment, tarsal tunnel syndrome without medial calcaneal nerve entrapment, and tarsal tunnel syndrome with medial calcaneal nerve entrapment.

In addition to these considerations, the problem of decision-making is compounded by the documented severity of the neurogenic etiology. For example, in a case with mild disturbances in two-point discrimination as one might find on an AcroVal neurosensory test, in which there is no evidence of axonal degeneration, then any treatment of the neurogenic component is subordinate to treatment of severe plantar fasciopathy. It has been my clinical experience that primary treatment of severe plantar fasciopathy, in the presence of nerve pathology, many times resolves both issues with no treatment oriented specifically to nerve. In the table “A Clinical Grading System To Direct Treatment When Using Diagnostic Ultrasound To Evaluate Plantar Fascia Thickness” above, this concept is further delineated for the surgeon but with the caution that every case of heel pain is individual and has its own nuances.

Recognizing The Advantages Of Tailored Treatment For Plantar Fasciopathy

We can now tailor the treatment of plantar fasciopathy to the patient based on his or her disease severity. With regenerative medicine primarily centered on minimally invasive techniques using amniotic tissue allografts, we can now effectively treat severe cases of plantar fasciopathy.

There are several advantages with these techniques. First, the treatment is regenerative and does not disturb the biomechanical function of the plantar fascia. One can treat severe cases from the initial patient presentation as there is no need to waste time and resources with non-efficacious conservative care. There is minimal disruption of the patient’s lifestyle. Finally, many times in my clinical experience, nerve pathology resolves with restoration of normal gait, obviating any invasive nerve surgery.  

In Summary

We can facilitate the effective management of complex heel pain by accurate initial diagnosis and implementation of patient-tailored custom treatment. By shifting the paradigm from “conservative management for six months until this fails and then surgery” to “what is really the patient’s condition and how one can treat it effectively now,” patient outcomes will improve.

Dr. Barrett is an Adjunct Professor within the Arizona Podiatric Medicine Program at the Midwestern University College of Health Sciences. He is a Fellow of the American College of Foot and Ankle Surgeons.

References

1.     Rose JD, Malay DS, Sorrento DL. Neurosensory testing of the medial calcaneal and medial plantar nerves in patients with plantar heel pain. J Foot Ankle Surg. 2003; 42(4):173-177.
2.     Chang CW, Wang YC, Hou WH, Lee XX, Chang KF. Medial calcaneal neuropathy is associated with plantar fasciitis. Clin Neurophysiol. 2007; 118(1):119-123.
3.     Tassone J, Barrett DL. Diagnostic Ultrasound of the Foot and Ankle. Data Trace, Baltimore, 2013.
4.     Cheng JW, Tsai WC, Yu TY, Huang KY. Reproducibility of sonographic measurement of thickness and echogenicity of the plantar fascia. J Clin Ultrasound. 2012; 40(1):14-19.
5.     Uzel M, Cetinus E, Bilgic E, Ekerbicer H, Karaoguz A. Comparison of ultrasonography and radiography in assessment of the heel pad compressibility index of patients with plantar heel pain syndrome. Measurement of the fat pad in plantar heel pain syndrome. Joint Bone Spine. 2006; 73(2):196-199.
6.     Ieong E, Afolayan J, Carne A, Solan M. Ultrasound scanning for recalcitrant plantar fasciopathy. Basis of a new classification. Skel Radiol. 2013; 42(3):393-398.
7.     Gibbon WW, Long G. Ultrasound of the plantar aponeurosis (fascia). Skeletal Radiol. 1999; 28(1):21-26.
8.     Kane D, Greaney T, Shanahan M, Duffy G, Bresnihan B, Gibney R, FitzGerald O. The role of ultrasonography in the diagnosis and management of idiopathic plantar fasciitis. Rheumatol. 2001; 40(9):1002-1008.
9.     Ozdemir H, Yilmaz E, Murat A, Karakurt L, Poyraz AK, Ogur E. Sonographic evaluation of plantar fasciitis and relation to body mass index. Eur J Radiol. 2005; 54(3):443-447.
10.     Tsai WC, Chiu MF, Wang CL, Tang FT, Wong MK. Ultrasound evaluation of plantar fasciitis. Scand J Rheumatol. 2000; 29(4):255-259.
11.     Wall JR, Harkness MA, Crawford A. Ultrasound diagnosis of plantar fasciitis. Foot Ankle. 1993; 14(8):465-470.
12.     Dellon AL, Kim J, Spaulding CM. Variations in the origin of the medial calcaneal nerve. J Am Podiatr Med Assoc. 2002; 92(2):97-101.

For further reading, see “Neurogenic Heel Pain And The Use Of Diagnostic Ultrasound” in the February 2016 issue of Podiatry Today or “Point-Counterpoint: EPF: Is It Necessary For Recalcitrant Plantar Fasciitis?” in the January 2016 issue.

To access the archives, visit www.podiatrytoday.com.