Rather than being a true neuroma, which suggests a tumour or growth, Morton’s neuroma actually refers to a peri-neural fibroma. This is the correct term for a nerve that becomes abnormally thickened and surrounded with fibrous tissue. Morton's neuroma is an ‘entrapment neuropathy’ that typically occurs between the third and fourth or second and third toe metatarsals. In this condition, the nerve effectively becomes compressed against the intermetatarsal ligament.
Morton's neuroma is a common form of foot pain that is frequently seen in podiatric and orthopaedic clinics. However, there have been no formal studies to establish exactly how common it is within the general population. According to a Cochrane report (Thompson et al. 2011), "a significant proportion of patients" who attend clinics for the management of foot-related conditions suffer from Morton’s neuroma. Morton's neuroma is estimated to be responsible for 7.8 per cent of all the podiatric surgeries performed in clinical practice each year (Bennett et al 2007). Certainly, even before we offered cryosurgery at the Morton’s Neuroma Centre, we encountered the condition frequently.
The majority of patients who have a neuroma also have fluid around the "peri-neural oedema" nerve. This can build up to form a bursa – a fluid-filled sack that forms due to friction in the tissues. In some chronic cases of neuroma, the bursa can be small or absent. The bursa builds up for the same reasons as the neuroma, i.e. excessive friction and pressure between the metatarsals. Some practitioners use ultrasound to measure the neuroma and bursa as one, so "overestimating" the true size of the neuroma. Compressing the neuroma area – which will result in the bursa also partly compressing – gives a better impression of the true size of the neuroma. We prefer the term "bursa neuroma complex" to describe patients who have both issues. A bursa can reduce in size if the adverse frictional forces are overcome (i.e. change of footwear and/or orthoses). By freezing its wall and piercing with a probe, cryosurgery also disrupts the bursa. A steroid injection can be more useful for treating a bursitis than the neuroma.