Baxter’s Nerve Entrapment: When Feet Throw a Tantrum

When it comes to ankle and foot pain, the heel is the most common complaint and you’d be right in thinking that it’s most likely related to the plantar fascia. Any one reading this who treats plantar fasciitis will know how stubborn this can be when rehabilitating. But not all heel pain is caused by this and among the many other potential foot-related maladies, one that often goes unnoticed is Baxter’s nerve entrapment. In this article we’ll look at what structures are involved, what’s happening and how we can help our athletes to recover from it.

What is Baxter’s nerve entrapment and how does it occur?

As we discovered earlier, Baxter’s nerve entrapment is an often-overlooked source of heel pain. In fact, up to 20% of chronic heel pain can be attributed to it. But before we dive in to the anatomy, let’s get to know our nemesis and what it actually is. This condition occurs when the Baxter’s nerve, also known as the inferior calcaneal nerve, gets stuck in a tight spot, usually around the heel area of the foot.

So, who’s most likely to encounter this foot fiend? While Baxter’s nerve entrapment doesn’t discriminate, it tends to target specific groups more than others. Athletes, especially those participating in sports that involve repetitive heel strikes, are often on the hit list. Runners, basketball players, and dancers, beware! Additionally, people with flat feet or a tendency to over-pronate may find themselves at greater risk of encountering Baxter’s nerve entrapment. When we are completing a subjective assessment, these are all important lines of questioning for your client or athlete. It can also be caused by the presence of anatomical variations, such as a hallux valgus/bunions, cyst or bone spur, or by wearing tight-fitting shoes. Some speculate that it can also be caused by chronic plantar fasciitis. Despite the high prevalence of foot pain in athletes and non-athletes, foot care is way behind heart, eye, teeth, skin care and nutrition among the health care of different parts of the body.

Anatomy

Now that we’ve identified the culprit, let’s look at the structures involved. Lets start with the nerve itself and zoom out from focusing on the heel for a second.

The tibial nerve derives from the sciatic nerve and is a major peripheral nerve of the lower limb. It services the leg and foot in many ways, including sensory innervation and motor function. It then splits off into various branches; the medial calcaneal branch arises within the tarsal tunnel to innervate the skin over the heel and the medial plantar nerve innervates the plantar surface of the medial three and a half digits of the foot.

The lateral plantar nerve, where Baxter’s nerve stems from, innervates the plantar surface of the lateral one and a half digits as well as the motor fibres to the abductor digiti minimi, flexor digitorum brevis and quadratus plantae. The inferior calcaneal nerve, or Baxter’s nerve, is the first branch of this lateral plantar nerve.

As we focus back in on the heel, the nerve then hooks underneath the calcaneus through the superficial fascia at the superior border of the abductor digiti minimi. The nerve travels along the medial edge of the quadratus plantae. As it reaches the border of the abductor hallucis, it turns and passes anteriorly to the medial calcaneal tuberosity until it reaches its distal target of the abductor digiti minimi.

As we said, it’s responsible for delivering sensation to the fat pad under your heel. So, if this nerve is in distress, you can expect some pretty severe discomfort in the heel area.

Clinical presentation

Baxter’s nerve is vulnerable to entrapment due to the course it takes. There are two areas where this is most likely to happen. The first is where the nerve turns laterally between the medial edge of the quadratus plantae and the thick lateral fascia of the abductor hallucis. If this becomes particularly tight, it can make contact with or compress on the nerve causing pain and/or numbness. The second point is where the nerve moves anteriorly past the calcaneal tuberosity. If the space the nerve occupies becomes narrower due to a bone spur, muscle hypertrophy, overpronation of the rearfoot/midfoot complex then impingement can, again, occur.

A key clinical finding will relate to whether the foot causes pain at night, which is suggestive of nerve pain in contrast to plantar fasciits which generally hurts in the morning when you start to weight bear or after a period of inactivity or too much time on your feet.

Now, when we start our objective assessment, the first thing we will look for is an over-pronated foot. This is a big part of the jigsaw when putting pieces together with the clues picked up during the subjective assessment.

Common symptoms and tests to complete are;

Pain is the most common symptom and presents as a nagging pain right beneath the heel, often described as a sharp, burning or aching sensation. This is most likely to flare up after an activity involving repeated heel strikes, such as walking, running or many other sports. Tenderness  often occurs above the abductor hallucis origin, which can induce laterally radiating discomfort and/or paraesthesia. It is also not uncommon for a sharp radiating pain to be reported at night after exercise.

Numbness can occur if the nerve becomes compress, rather than just irritated. As a result some may experience tingling or numbness in the heel area of the affected foot

Swelling is another common symptoms found with a nerve entrapment. Due to the irritation going on around the nerve, your heel might swell. This can range from being very mild to quite severe

Atrophy of the muscles innervated by the nerve may also occur. It may be more difficult for you, or your patient, to spot, but muscle wastage of the abductor digiti minimi muscle is often found in these cases and is important to look out for.

Tinel Sign is a common neurological test used around the body, but here specifically we would use it to rule out tarsal tunnel syndrome where the anterior tibial branch of the deep peroneal nerve s affected as well. To be clear, we are talking about the same nerve here as with a Baxters nerve entrapment, just a little higher up.

Phalens Test is another common test used elsewhere, but here we are looking at bringing on the symptoms by passively inverting and plantar flexing the foot.

The Windlass test helps us to rule out plantarfascitis, a common cause of foot and heel pain and should be considered as a differential cause of pain.

All of these tests and symptoms, together with a good subjective history, will direct us towards a diagnosis, but in some cases imaging such as ultrasound or MRI may be used to get a closer look at the nerve and surrounding tissues.

Differential diagnosis:

As with all conditions, when assessing it is vital we consider alternatives. Without this, there is high probability we get the diagnosis wrong, and then wonder why our treatments aren’t working. Some of these might include;

• Plantar fasciitis
• Tarsal tunnel syndrome
• Seronegative arthritis-induced inflammation
• Tarsal tunnel syndrome
• Medial calcaneal neuritis
• Heel spurs
• Trauma
• Fat pad atrophy
• Calcaneal stress fractures
• Periosteal inflammation

Treatment:

Now we’ve nailed down a diagnosis, you and your patient will be looking for a solution. There are a multitude of avenues we can go down to help and what we decide to use ultimately depends on how and why it became a problem in the first place.

Consequently, we must understand the various modalities to address the pathology. As we know, there’s no single right answer as research has shown us that there is no optimal treatment strategy. Rest, non-steroidal anti-inflammatories and open distal tarsal tunnel release have been employed for the treatment of Baxter’s neuropathy.

Rest is often recommended as part of the management of a Baxters Nerve Entrapment, but, as with so many injuries, is rarely the sole answer. Other passive modalities will include massage, non-steroidal anti-inflammatory medications and even Shockwave therapy. Yes, it’s likely to feel better, which is great, but if we aren’t working on the underlying cause it will only come back.

Plantar fasciitis: Common pitfalls in mistreating plantar fasciitis relate to under loading the foot: to counter this, make sure to include some heavy slow resistance isometric exercises. These help to prep the foot for  the demands it faces later down the line. According to a paper by Lee et al (2020), they looked at the relative weakness of the hamstring and quadriceps muscles as a potential contributing factors to Plantar Fasciitis. The main takeaway for us was the introduction of fast reactive style calf strengthening, especially for the gastrocnemius muscle. In our experience, we see a lot of rehab programs exclude any hopping/low level plyometric drills which hinder the rehab for foot pain and plantar fascia. So if your rehab program, did not include hamstring/quadriceps strengthening or some form of isometrics and hopping, the likelihood is the rehab could be improved.    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7646081/  

Consider over-pronation as a cause!

Is there a weakness further up the chain which is causing a knee valgus moment resulting in this over-pronation at the foot? What are their glutes doing? Is there a weakness in their obliques? Identifying this and prescribing effective strengthening work will offer a more long term solution than just to rest. As a more short term solution, we may consider orthotics to help offload the heel and distribute weight more evenly around the foot.

Has training volume dramatically increased recently? We know that this is often a cause of heel pain in runners and other athletes so it’s another aspect we need to think about. We may need ti recommend a period of active recovery where the athlete reduces the amount they are running, but their time in the gym actually increases.

Remember, it’s essential to work closely with your patient to create a personalised treatment plan that suits there specific needs and lifestyle.

Conclusion:

Baxter’s nerve entrapment might be a sneaky little troublemaker, but with the right guidance you can help your patients, clients and athletes to send this foot gremlin packing. Plantarfascitis is notoriously difficult to get to the bottom of, so if you have a client who is struggling, make sure you consider this!

For more information on foot and ankle pain, or to help get rid of any stubborn plantar fascia pain, or nerve irritation, book in to see one of the team at Pro health Physio NE. We also offer virtual appointments if you are not based in the North East of England.

Author, James Nowosielski