Ultrasound assessment of a common cause of forefoot pain: Planter plate tear of the 2nd-5th metatarsophalangeal joints
Angela Clough, Radiology, Weston General Hospital, North Somerset.
The plantar plate is a fibrocartilaginous structure which stabilizes the plantar aspect of the metatarsophalangeal joint, preventing dorsi-extension of the toe. It is susceptible to partial or complete tears due to chronic overload, age or trauma. Tears typically present with burning, throbbing or tingling and are commonly misdiagnosed as a Morton’s neuroma, stress fracture or arthropathy.
Untreated tears can cause persistent pain and may progress to substantial deformity and dysfunction. Treatment involves strapping and NSAIDs, with surgery reserved for persistent symptoms.
A 66 year old female with metatarsalgia in the region of the 2nd toe was referred for ultrasound; a steroid injection was requested if a Morton’s neuroma was detected. A clinical examination was first performed using three specific tests for plantar plate tears, testing positive for medial toe drift, reduced plantar purchase and a positive dorsal drawer test. Ultrasound identified a hypoechoic defect on the lateral aspect of the plantar plate, consistent with a partial tear. There was also co-existing capsular disruption and osteoarthritis of the metatarsophalangeal joint.
Studies evaluating ultrasound in detecting plantar plate tears show it to be more sensitive than MRI and this, together with its low-cost and flexibility, suggest that ultrasound is suitable as the first line test. Ultrasound does however have a poorer specificity than MRI which may be too low to rely on for surgical planning, and follow-up MRI imaging may be required. Ultrasound performs well at identifying concomitant or other causes of metatarsalgia especially interspace lesions, notably Morton’s neuromas.
Accurate differentiation, particularly between a tear and a neuroma is advantageous as it indicates the correct treatment option and, in particular, it avoids the inappropriate administration of a steroid injection when the pathology is a tear.