This new series of blogs comprises 50 stories that emerge from neuroanatomy and its relationship to what we do in life. With the current focus on the brain, it seems that the rest of the nervous system has been forgotten. This, plus a chance to share clinical anecdotes from decades of neurodynamics work was an inspiration for the series. This first blog will be on Morton’s Neuroma.
Forgotten neural links in the foot
Morton neuroma, usually referred to Morton’s metatarsalgia is probably the most common nerve compression/irritation syndrome in the lower limb. The aetiology is a neuroma (growth, swelling of nerve, rarely carcinoma) in one of the common plantar digital nerves, usually the one to the third and fourth toes. This nerve arises from an anastomosis of the lateral branch of the medial plantar and a branch of the lateral plantar nerves. You won’t see this nerve connection on most anatomical drawings but it is present in most individuals (Jones & Klenerman 1984) and relevant to this story.
Betts in my home town of Adelaide was the first to report the aetiology (Betts 1940) of the syndrome – the symptoms of which were initially reported by Morton in Philadelphia in 1876. Sort of nice as I have lots of friends in Philly!
The problem is much more common in women and probably related to repetitive high heel trauma linked to forefoot hyperextension and stretch of the nerves and other tissues over the transverse metatarsal ligament, plus pinching due to tight shoes.
Treatment via neurectomy has often been reported as failproof after Betts had 19/19 patients with complete relief of pain (that’s odd as neurectomy elsewhere in the body is often a disaster). A recent (and the only) prospective study (Bucknall et al. 2016) noted that only 63% of their cohort were painfree and they warned of the dangers of second surgery.
Most treatments suggested are invasive though a recent case study reports benefits from forefoot joint mobilisation (Sault et al. 2016).
A variant on the story
Why the nerve to the third and four toes? Well, if you go up and down on your tippytoes, the neural complex in the sole of your foot slides within neighbouring tissues but the tethering effect of the lateral/ medial plantar nerve connection may well minimise the movement and over time with pressure on the transverse metatarsal ligament, a neuropathy capable of mid axon discharge emerges. The tethering effect has been mentioned years ago by others (Graham & Graham 1984) but it makes more sense if you have an understanding of neurodynamics.
I have had repeated clinical findings of reproduction of metatarsalgia symptoms and/or limitations of movement when the forefoot and ankle are dorsiflexed and the leg straight leg raised. If the forefoot is pinched as in a tight shoe, adding SLR will often aggravate symptoms as you would expect. High heel shoes offer a give and take to the plantar/tibial nerve complex – the ankle dorsiflexion forced by a high heeled shoe actually unloads the nerve at the ankle while loading it at the forefoot. You may hear someone say that it is actually easier in high heels, which may hint at contributing issues higher up in the nerve.
Overall – leave surgery to the most recalcitrant states. Women should be off the heels for a time and men out of their pointy toed brothel creepers, to be graded back over time. Get a nice pair of wide forefoot shoes like Campers. Wriggle and loosen up any stiff bits in the foot. Guide the nervous system so it moves and slides like the other side. And tell the nerve story to make sense of it for patients, remembering too that the term ’Morton neuroma’ is scary – nerve swelling, bursa around the nerve is less threatening.
Comments welcome. Keep an eye out for the second blog in this series – dural ligaments in the lumbar spine.
– David Butler
- Jones JR & Klenerman L (1984) A study of the communicating branches between the medial and lateral plantar nerves. Foot Ankle 4:313-315.
- Betts L (1940) Morton’s metatarsalgia: Neuritis of the fourth digital nerve. Med J Aust 1:514.
- Bucknall V et al. (2016) Outcomes following excision of Morton’s interdigital neuroma: a prospective study. The Bone & Joint Journal. 98B: 1376-1381.
- Sault J et al. (2016) Manual therapy in the management of a patient with a symptomatic Morton’s Neuroma: A case report. Musculoskelet Sci Prac 21: 307-310.
- Graham CE & Graham DM (1984) Morton’s neuroma: A microscopic evaluation. Foot Ankle 5:150-153.
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