Not Plantar Fasciitis? Heel Pain of Neural Origin
The most common cause of heel pain is plantar fasciitis, however there are other conditions that mimic plantar fasciitis heel pain which go under the radar and are misdiagnosed as plantar fasciitis. When this occurs, patients often don't respond well to the treatment plan leading to clinician and patient frustration.
This article will focus on nerve pain as the source of heel pain. Heel pain of a neural origin can be a debilitation condition for sufferers and may play a role in both acute and chronic heel pain. It may present as an isolated entity or it may present secondary to chronic plantar fasciitis and it can often be very difficult to differentiate between plantar fascia pain and neural pain. The first report of heel pain of a neural origin was published in a Dutch language article by Roegholt in 1940. To date, although nerve entrapment in plantar heel pain is well documented (e.g. Baxter and Pfeffer, 1992; Oztuna et al., 2002), its pathophysiology, diagnosis and management are still subject to debate.
The image below demonstrates the branches of the tibial nerve which make up the nerves in heel and bottom of the foot.
Medial view of right foot demonstrating the relation of the nerves to other structures (Alshami et al 2008).
TN = tibial nerve
FR = Flexor retinaculum (connective tissue)
MCN = medical calcaneal nerve
1st B-LPN = the 1st branch of the lateral plantar nerve (also known as Baxter's nerve)
LPN = lateral plantar nerve
MPN = medial plantar nerve
PF = plantar fascia
Entrapment of Baxter's Nerve
Baxter's nerve entrapment is reported to be the most common cause of heel pain of neural origin. Baxter's nerve is the first branch of the lateral plantar nerve (1st B-LPN). Dissection studies have reported a site of possible entrapment between the abductor hallucis and the medial head of quadratus plantae muscle (Rondhuis & Huson 1986). Histological (microscopical) examination of this nerve revealed abnormal findings, suggesting chronic compression of the nerve (Baxter and Pfeffer, 1992).
Image above demonstrates entrapment of the 1st branch of the lateral plantar nerve (1st B-LPN) in between the abductor hallucis and quadratus plantae muscles.
Entrapment of the medial calcaneal nerve
The medial calcaneal nerve provides sensation to most of the heel fat pad and to the superficial tissues overlying the inferior part of the calcaneus. Entrapment of the medial calcaneal nerve is the second most commonly reported nerve that has been related to plantar heel pain of neural origin. However, entrapment of the medial calcaneal nerve may not be a very prevalent condition as only 5 out of 200 surgical cases were consistent with MCN entrapment (Schon et al 1993). Most branches of the Medial calcaneal nerve lie superficially to the abductor hallucis, flexor digitorum brevis and plantar fascia (Arenson et al 1980; Louisia & Masquelet 1999) and are therefore less likely to be compressed within these structures, but can be irritated and traumatised following atrophy (thinning) of the heel fat pad (Kopell and Thompson, 1960; Davidson and Copoloff, 1990). In cases of entrapment of the medial calcaneal nerve, pain is usually felt more towards the back of the heel.
Entrapment of the medial plantar nerve
Entrapment of the MPN is not as common as entrapment of the other nerves (Murphy and Baxter 1985), particularly as an isolated entity (Raikin and Schon, 2000). Out of 21 cases diagnosed with nerve entrapment in the ankle and foot, Murphy and Baxter (1985) concluded that only one case was consistent with MPN.
Entrapment of the posterior tibial nerve (Tarsal Tunnel Syndrome)
Tarsal tunnel syndrome is a more common condition of the foot and ankle than has been historically appreciated. It is a compression or entrapment of the tibial nerve which is a branch of the large sciatic nerve. It runs across the inside of the ankle joint, just behind the ankle bone (the tarsal tunnel). At this point the nerve splits into smaller branches which run in to the heel and the sole of the foot (see the nerve anatomy image above). Compression of this nerve may cause radiating pain into the heel and further along the foot into the toes. Currently, it is a condition that is largely under-diagnosed as a potential cause of heel pain, arch pain, and distal peripheral neuropathy (nerve pain/abnormal sensation in the toes). False-negative electrodiagnostic testing contributes to the under-diagnosis of tarsal tunnel syndrome. This is where the diagnostic test does not pick up any abnormalities in the nerve and muscle firing patterns however these tests are not 100% accurate and therefore can miss a problem with the nerve. It is also reported to be the most common chronic nerve entrapment in the lower extremity (Dellon 1996).
What causes tarsal tunnel syndrome?
It is most often believed to be caused by “space-occupying lesions,” such as soft tissue or bony lumps and bumps within the tarsal tunnel that shouldn't be there. Examples include ganglia or lipoma (fatty tissue mass), varicosities such as varicose veins which increase pressure around the nerve, fibrosis (thickening) of the tibial nerve itself which may have been triggered by injury. Other proposed causes include biomechanical issues such as collapse feet or excessively high arched feet as both these extremes narrow the space in the tarsal tunnel and may lead to compression of the nerve.
Presentation of neural pain
Heel pain of neural origin typically presents as a burning, sharp, shooting, electrical pain with pins and needles, numbness. Pain is worse during weight bearing and relieved by rest. However pain may also be present during non-weight bearing. It has been suggested that Pain at night may be due to nerve compression as a result of venostasis (slowing of venous outflow) and venous engorgement which results in increased compression of the soft tissues of the foot and ankle (Kopell and Thompson, 1960; Doxey, 1987). Like plantar fasciitis it is very common to experience pain first thing in the morning and after long periods of rest.
So how do I know if it's plantar fasciitis or neural heel pain?
This is not an easy question to answer even for competent, experienced clinicians. This is why it is a very challenging problem for both patients and clinicians. The fact that the conservative management of plantar heel pain is still challenging can be attributed to the difficulties in establishing the correct differential diagnosis and cause.
There are various diagnostic tests to help confirm neurogenic pain whether it be from compression of one of the small plantar nerves of the heel or the tibial nerve. It is important to point out that diagnostic testing should complement the physical examination and should not be relied upon in isolation to make an accurate diagnosis.
An MRI can be ordered to help confirm diagnosis. MRI may also be useful in establishing the presence of a space-occupying lesion beneath the flexor retinaculum at the ankle joint resulting in tarsal tunnel syndrome, which can mimic symptoms of plantar fasciitis. However, the incidence of such lesions is rare. Some studies have reported MRI to be highly accurate (82%–83%) in the diagnosis of tarsal tunnel syndrome (Reade et al 2001).
Diagnostic ultrasound is less frequently ordered when suspicious of nerve entrapment and currently there is no evidence to support its accuracy. But it can be used to check for synovitis of peripheral tendon sheaths such as the posterior tibial and flexor tendons about the ankle. Ganglia and space-occupying lesions can also be identified in the region of the tarsal tunnel or surrounding structures. The tibial nerve and its branches can also be traced to evaluate the potential presence of a high division; this can result in overfill of the tarsal canal by the medial and lateral plantar nerve branches.
Electrodiagnostic studies have traditionally been the gold standard for confirming and evaluating the clinical diagnosis of tarsal tunnel syndrome. Motor and sensory nerve conduction studies (NCS) and electromyography (EMG) should be evaluated. EMG may show motor latencies in the abductor hallucis (muscle connected to the big toe) or abductor digiti minimi (muscle connected to the little toe). It has been suggested that sensory action potentials is a more sensitive test. False negative NCS and EMG are not uncommon, and so unfortunately, do not rule out tarsal tunnel syndrome (Franson & Baravarian 2006).
Quantitative Sensory Testing
A more recent diagnostic tool is computer-assisted quantitative sensory testing, also known as a pressure-specified sensory device or PSSD (Dellon 1996). This neurosensory testing device has been shown to provide a more sensitive appreciation of peripheral nerve compromise, which can confirm a clinical diagnosis earlier in the progression of tarsal tunnel syndrome. The PSSD machine is designed to address the subtle changes that occur in peripheral nerves as nerve damage increases.
If you have seen a podiatrist or suitably qualified specialist who suspects neural heel pain then you have probably been advised on the general non-surgical treatments used to treat plantar fasciitis including rest, anti-inflammatories, night splint, foot orthoses (insoles) to correct any biomechanical abnormalities, soft soled shoes, foot supports, massage roller, stretching exercises for the achilles tendon and plantar fascia, extra-corporeal shockwave therapy, cast immobilisation. Surprisingly, the treatment plan for heel pain whether it is plantar fasciitis or neural heel pain is almost identical.
Additional non-surgical treatment one should try if neural heel pain is suspected is neural mobilisation techniques. These are often provided by physiotherapists. I have posted a few techniques to stretch the nervous system which you can find on my YouTube channel here.
Surgery is considered if conservative treatment has failed usually at least after 6-12 months. There are many surgical procedures for treating heel pain and often a combination of procedures are performed during the surgery. With regards to isolated procedures involving surgical release of the offending nerve previous studies have reported excellent outcomes with 83% of patients reporting complete resolution of pain involving 69 heels (Baxter & Pfeffer 1992). A study by Hendrix and colleagues (1998) reported 90% complete resolution in symptoms following surgical decompression of tarsal tunnel which relieves the pressure on the tibial nerve.
Generally, surgical release of nerve entrapment has a good post-op recovery as it involves minimal damage to the surrounding soft tissue of the foot and ankle and usually no damage to bone unless there is a bony problem causing the entrapment. If neurogenic heel pain has not responded to non-surgical treatment, then surgical release should be considered as a suitable treatment option.
Heel pain of neural origin is often overlooked. Proper patient education about this condition is of paramount importance in order to help patients self manage and improve their pain. Clinicians should suspect a neural component to a patients pain if symptoms aren't improving as expected and consider diagnostic tests to help get to the route of the problem. Once this is achieved then the most appropriate management plan can be put in place.
Thanks for reading. Comments welcome.