Recurrent Neuroma: Causes And Prevention Strategies

Introduction

Our nervous system is divided into two parts: central and peripheral. The latter is concerned with innervating all of our peripheral tissues: the abdomen, lungs and limbs. Consequently, it is an important and delicate system that needs to be able to regenerate itself, as injuries to peripheral tissues are common. However, when an abnormal repair mechanism happens, a condition called neuroma can develop.¹ Neuromas mostly refer to benign tumours of the peripheral nervous tissue, although the term is frequently, yet improperly, used to refer to an overgrowth of fibrotic tissue around the nerve, compressing it.¹ 

This article will provide an overview of recurrent neuroma, also called Morton’s recurrent neuroma. This condition comprises fibrotic tissue overgrowth between the third and fourth toe and is, therefore, an implementation of the improper use of ‘neuroma’. This type of neuroma is ‘recurrent’ because, if not prevented, it can reappear even after surgical intervention¹; in fact, this type of neuroma can exhibit irregular proliferation of nervous tissue at the end of a transected nerve.² 

Understanding causes and prevention 

Immediate identification of the recurrent neuroma and proper treatment are essential to reduce the chance of facing complications. The hallmark of the condition is perineural fibrosis,^3, which is an agglomeration of inflamed tissue around the nerve in the intermetatarsal space, i.e. between the bones of the two toes. This agglomeration compresses the nerve, which leads to a sensation of tingling and numbness.⁴ While the molecular mechanism of the condition development is clear, the cause of the condition itself is less obvious: changes in gait appear to be a common cause, as well as injury.⁵ Conservative approaches to prevent and manage neuromas can be a key to reducing pain and obtaining normal and free movement. Therefore, it is key to be aware of the causes and prevention techniques of the disease.⁵ 

Causes of recurrent neuroma

Nerve compression and irritation from:

• Mechanical stress
• Trauma or injury
• Improper footwear

A common cause for Morton’s neuroma is mechanical stress on the third common digital nerve. Mechanical stress can happen as a result of excessive weight on the front part of the foot, for example, by having the habit of wearing high heels or pointy shoes. These can cause nerve compression and inflammation of the space between the third and fourth metatarsal bone heads, which are in close proximity to the nerve.⁵ 

Alternative examples of stress to the nerve can be both of mechanical or traumatic nature and can also appear after injuries. Other mechanical causes include impaired walking patterns, like foot dorsiflexion (upwards foot flexion), a movement pattern that, if repeated, compresses the nerve and causes inflammation. Traumatic injuries to the foot that lead to neuroma are those that change the gait pattern, as well as direct fourth metatarsophalangeal joint (MTPJ) injuries, which damage the third common digital nerve due to anatomical proximity.⁵ 

Inflammation and tissue changes from:

• Chronic inflammation
• Scar tissue formation
• Abnormal nerve growth

One of the proposed models to explain the cause of the condition is the ‘intermetatarsal bursa theory’, which supposes initial bursitis, which is where inflammation of the space in which the nerve sits in the intermetatarsal region of the foot leads to nerve compression and fibrotic tissue growth.¹ In fact, the peripheral nervous system is able to form scar tissue in response to nerve injury. This is a protection mechanism for the nerve, but at the same time, the process leads to inflammation, and the patients experience various sensations of physical pain, from itching to allodynia (pain from non-painful stimuli).⁶  

Abnormal nerve growth following injury can lead to a ‘pinching’ of the nerve, wherein tissue overgrowth causes nodular masses that prevent normal nerve function.⁷ Nerve overgrowth in reaction to injury also results in disruption of the correct microvascularisation of the area around the nerve, exacerbating the scar formation around the nerve and reducing the correct blood flow to the nerve itself.8  Whenever inflammation is present in a disease, injection of corticosteroids can be considered a valid treatment method: these are able to reduce inflammation by suppressing the immune system.¹² For Morton’s neuroma, corticosteroid injections are often prescribed in order to avoid surgery and appear to effectively reduce pain in around 30% of the cases.¹³ Other than surgical and pharmacological interventions, there are other conservative strategies.

Prevention strategies:

• Choosing proper footwear 
• Use footwear with wide-toe boxes and good arch support
• Avoiding high heels and narrow shoes

Conservative methods of treating recurrent neuroma, which refers to non-surgical or pharmacological methods, seem to be effective in 48% of patients.⁹ One of these methods includes changing the amount of stress on the toes by avoiding footwear that either compresses or leads to putting one’s weight on the toes, such as narrow and pointy shoes or high heels.⁵ t is also essential to improve the arch support with proper footwear, as this has several benefits for the feet:

1. Aids to avoid over-pronation, which is displaced weight towards the midline of both feet while standing, and other balance issues that can lead to gait defects
2. Is effective in the prevention of connective tissue overstretching
3. Arch pads have cushioning effects on the feet and toes, which reduces pain and fatigue while moving.¹¹ 

Modifying activities and reducing stress on the feet: 

• Avoiding repetitive high-impact activities
• Using orthotic devices or padding

Conservative treatments are designed to reduce the mechanical weight on the metatarsal bones and to avoid gait patterns that can increase the pain: it is often suggested that the patients rest or implement metatarsal pads.¹⁰ A strategy designed to reduce the stress and pressure on the foot during movement is the use of orthotic implants, which can be directly inserted in the shoes and benefit movement.¹⁴ In addition, well-padded shoes can also be helpful in pain reduction.¹ 

Studies analysing the movement parameters relevant to movement, in particular during running and during repetitive high-impact activities, highlight the relevance of using orthotics to reduce mechanical stress and pressure on the foot.14 It is important to note that running with improper footwear is one of the causes of neuroma development in the first place¹⁵, and after the neuroma has developed, it is important to seek medical advice before starting to run again, even with orthotic implants.

Maintaining a healthy weight: 

• Reducing pressure on the feet
• Achieving a healthy BMI

Conservative treatments aim to reduce the weight that is put on the metatarsal space, which exacerbates the painful symptoms of Morton’s neuroma. Therefore, another important aspect is to aim to maintain a healthy weight since obesity and associated complications increase the weight and pressure that is put on the feet. This consequently increases foot-related conditions and inflammation.¹ 

Other studies do not report a significant correlation between the incidence of neuromas and BMI (Body Mass Index), but find a correlation between Morton’s neuroma and ankle dorsiflexion (ankle mobility).¹⁹ Excessive BMI does increase the odds of problems with ankle dorsiflexion; therefore, it can be considered an indirect cause of neuromas rather than a direct impacting factor.19 It is reasonable, however, to assume that, though not a direct cause of neuroma, the increased weight, which in cases of elevated BMI is put onto an improperly supporting foot, will increase the painful nerve compression already present.

Stretching and strengthening exercises: 

• Promoting flexibility and foot strength
• Specific exercises for toes and arches

Stretching is important in case of foot pain, as peripheral nerves benefit from stretching and are able to stretch in a plastic way.¹⁶ While stretching is able to alleviate pain by reducing fluid accumulation - and therefore nerve pressure - the stretch should not be too extensive because it can also cause small ischemic (block of oxygen and nutrient supply to the tissue) areas around the nerve.¹⁶ Therefore, it is important to follow specific exercises that can promote foot strength and stretching without increasing the pain. For example, following physical therapy can help strengthen and increase the flexibility of the soft tissues around the nerve, which benefits pain relief from Morton’s neuroma.¹⁷ In addition, massages and the use of tapes on the foot have also been shown to be effective.¹⁷ 

Seeking appropriate medical care:

• Early diagnosis and treatment
• Consulting with healthcare professionals

It is essential to seek medical attention to avoid complications after the onset of foot pain: if Morton’s recurrent neuroma is left untreated, it can develop into chronic pain syndromes (which involve constant dull pain arising from the central nervous system even in the absence of peripheral stimuli) and neuromas (actual tumours).¹ To avoid these complications, podiatrists, orthopaedic surgeons, and sports physicians play a key role in the treatment of the syndrome, as well as the fundamental change of footwear.¹  In addition, proper medical attention is essential to assess whether the condition is Morton’s neuroma or if the pain arises from other nerve entrapment conditions, and therefore, the treatment has to be adjusted taking with respect to the different foot pain causes.¹⁸ 

Summary 

Recurrent neuroma is a painful condition affecting the nerves of the foot, which impairs normal movement. It is a condition which arises because of fibrotic tissue overgrowth and inflammation of the nerve between the third and fourth metatarsal bones of the feet. This leads to compression of the nerve, which results in the perceived pain. The condition can be treated surgically, as well as through corticosteroid injections, which are able to reduce the inflammation and the pain, both after previous surgical approaches or conservative treatments. These latter alternatives to surgery, if avoidable, mainly focus on reducing the pressure on the nerve and its compression. Therefore, appropriate footwear with pads and orthotic implants are recommended, combined with arch strengthening and stretching exercises, which can be suggested by physiotherapists. Medical attention is essential to undertake the best treatment to alleviate the pain and to obtain pain-free recovery, as well as reduce the incidence of the recurrence of the neuroma after surgery or the development of chronic pain. In fact, Morton’s recurrent neuroma is treatable if the right professional attention is given, combined with lifestyle improvements that benefit foot health in general and improve gait patterns.