A perineural fibrosis of the medial plantar proper digital nerve (MPPDN) as it courses plantar medial to the 1st metatarsal head first described by Joplin in 1971.
The lesion, classically located on the plantar medial aspect of the 1st Metatarsophalangeal joint, is a degenerative product of irritation and inflammation involving the medial plantar proper digital nerve.
Im et al (2010) describe the neuro-anatomy of the affected structure. The medial plantar proper digital nerve is a terminal branch nerve arising from the medial plantar nerve. The medial plantar nerve, in turn, is the medial branch of the posterior tibial nerve; it divides into two terminal branches at the base of the first metatarsal bone: the medial branch, which forms the first common digital nerve, and the lateral branch, which forms the second and third common digital nerves. Before this bifurcation, the MPPDN rises from the medial plantar nerve to the medial side of the hallux (Merritt and Subotnick, 1982) and is subject to pressure as it takes this course (Still & Fowler 1998).
As the MPPDN courses distally through subcutaneous tissues, it supplies sensation to the skin on the medial plantar aspect of the first Metatarsophalangeal joint, hallux and tip of the toe (Merritt and Subotnick, 1982). Because of its superficial position, it is subject to trauma, which results in MPPD neuropathy,
The word Neuroma has been most commonly used to describe this condition however the condition is either a compressive or entrapment neuropathy.
Entrapment neuropathy is when pressure is exerted by some anatomic or patho-anatomic structure whereas compressive neuropathy refers to nerve damage as a result of pressure applied to a nerve whether internal or external. Thus all entrapment neuropathies are also compressive, but not all compressive neuropathies are due to entrapment (Still & Fowler 1998).
Causes of symptoms
Sports that involve repetitive pivoting, impact and motion of the 1st MTP joint such as running, basketball, skiing and ballet.
Tight footwear (Hetherington, Still & Fowler, Merritt and Subotnick, 1982)
The nerve either drifts laterally or in the course of the development of Hallux valgus deformity the metatarsal head drifts medially to bear weight directly on top of the nerve (Hetherington)
Plantarflexed 1st ray with forefoot valgus exposing the medial aspect of the 1st MTP joint leading to increased repetitive micro trauma during gait. Functional over pronation is probably the most common cause. Pronatory forces that concentrate body weight through the medial foot provide further compressive forces that stimulate perineural oedema and fibrosis, axon degeneration and renaut body formation (Hetherington). Abnormal pronation during the propulsive phase of gait causes hypermobility and abnormal shearing forces between the bones and subcutaneous tissues (Still & Fowler 1998).
Signs and symptoms
Symptoms reported are most commonly reported as pain, tingling, numbness and parathesias to the medial and plantar aspects of the 1st MTP joint and hallux particularly on ambulation in the propulsive phase of gait (Merritt and Subotnick 1982). The pain may be sharp and mixed with a burning sensation and some cramping proximally into the arch. (Still & Fowler 1998)
On examination palpable cordlike structure, tender on palpation of the med plantar aspect of 1st MTP jt. This can be rolled beneath the examiner’s finger (Still & Fowler 1998). Deep palpation causes symptoms to radiate distally to the tip of the toe and helps to differentially diagnose sesamoiditis (Merritt and Subotnick 1982).
- Affects women more than men, aggravated by tight footwear
- Associated with over pronation of the foot and/or
- Plantarflexed 1st Ray
- Forefoot Valgus
Still & Fowler (1998) cite the following differential diagnoses:
- Tibial Sesamoiditis
- Avascular Necrosis of Tibial Sesamoid
- Transient Neuritis
Treatment should be conservative with changes in shoe wear, protective or accommodative padding and orthoses to redistribute body weight and reduce pressure on the nerve (Hetherington 1994) should be used in the first instance. Corticosteroid injection is reported as useful (Still & Fowler 1998, Merritt and Subotnick 1982, Hetherington 1994) however Steroid injection can cause subcutaneous atrophy and increase symptoms later (Schon 1994). Often conserve measures provide only temporary relief (Hetherington 1994) or are ineffective (Merritt and Subotnick 1982).
Surgery is curative by means of surgical neurectomy (Hetherington 1994) and is the preferred method of surgical treatment (Joplin 1971, Merritt and Subotnick 1982, McGlamry et al 1992)
Im, S.; Park, J. H.; Kim, H.-W.; Yoo, S.-H.; Kim, H.-S. & Park, G.-Y. (2010), ‘New method to perform medial plantar proper digital nerve conduction studies.’, Clin Neurophysiol 121(7), 1059–1065.
Joplin, R. J. (1971), ‘The proper digital nerve, vitallium stem arthroplasty, and some thoughts about foot surgery in general.’, Clin Orthop Relat Res 76, 199–212.
McGlamry, E.; Banks, A. & Downey, M. (1992), Comprehensive Textbook of Foot Surgery, Balitmore.
Merritt, G. N. & Subotnick, S. I. (1982), ‘Medial plantar digital proper nerve syndrome (Joplin’s neuroma)–typical presentation.’, J Foot Surg 21(3), 166–169.
Hetherington, V., ed. (1994), Hallux Valgus and Forefoot Surgery, Churchill LIvingstone, New York.
Schon, L. C. (1994), ‘Nerve entrapment, neuropathy, and nerve dysfunction in athletes.’, Orthop Clin North Am 25(1), 47–59.
Still, G.P., Fowler, M.B., 91998) “Joplin’s Neuroma or compression Neuropathy of the Plantar Proper Digital Nerve to the Hallux: clinico Pathologic Study of three cases”. J Foot and Ankle Surgery. (1998) Nov-Dec: 37 (6): 524-30