US and MRI of the Forefoot: Intermetatarsal Bursitis or Morton's Neuroma

The Danish Rheumatism Association, Hvidovre University Hospital, Bispebjerg Hospital, Gentofte Hospital

The aim of this study is to investigate the incidence of intermetatarsal bursitis and Morton's neuroma in patients with metatarsalgia (i.e. pain in the forefoot) and control subjects by diagnostic imaging with ultrasound and MRI.

In a group of patients with intermetatarsal pain found by an orthopedic surgeon, the investigators want to assess the incidences of intermetatarsal bursitis and Morton's neuroma, using diagnostic imaging; ultrasound and MRI. The hypothesis is, that intermetatarsal bursitis is an overlooked diagnosis in patients with metatarsalgia. As a result of sparse literature and lack of knowledge about this condition with symptoms mimicking Morton's neuroma, a part of patients diagnosed with Morton's neuroma, suffers from intermetatarsal bursitis instead. Additionally, the investigators want to evaluate the clinical sign opening toes. Based on clinical photos of the feet, the investigators want to document the presence of opening toes and investigate if there is a correlation with either intermetatarsal bursitis and/or Morton's neuroma.

High intensity on T2 weighted images, low signal on T1. Thin peripheral enhancement on T1 contrast enhanced pictures.

Hypoechoic mass between metatarsal heads closest to dorsal surface of foot. Compressible. Activity on power/color doppler.

Hypoechoic mass between metatarsal heads closest to plantar surface of foot. Non-compressible. The interdigital nerve can be seen entering the mass. Close relation to the interdigital artery.

Inclusion Criteria: Age > 18 years Pain in an intermetatarsal space (patient group) Exclusion Criteria: Age <18 years Open wounds or ongoing infection in the forefoot at the time of examination Persons with contraindications to participate in MRI scan Persons with a history of significant trauma in the forefoot, e.g. any fracture or previous surgeries in the forefoot Persons who have previously received treatment for Morton's neuroma in the same foot, e.g. injection (within 6 months) or operation (anytime) Persons with severely impaired renal function (GFR <30 ml/min) Persons with a systemic inflammatory condition like rheumatoid arthritis, due to clinically silent intermetatarsal bursitis in this group (control group)