Which is the role of dynamic high-resolution ultrasound (D-HRUS) in the assessment of plantar plate tears?

Abstract

Purpose: Plantar plate tears are often unidentified causes of hindfoot discomfort. The purpose of our work is to describe the normal and pathologic appearance of plantar plate, assessed with dynamic high resolution ultrasound (D-HRUS). Methods and Materials: We used D-HRUS to assess 22 patients (age range 38–71) with an orthopaedic diagnosis of plantar plate tear. A Magnetic Resonance (MR) control was performed in all cases. Moreover, we performed D-HRUS on 10 healthy volunteers to understand the correct scan technique of the plantar plate and to determine the correct dynamic manoeuvres that allow to depict the normal ultrasound anatomy of this structure. Results: Normal plantar plate is a triangular structure, with homogeneous echogenic appearance; it can be easily assessed with plantar longitudinal scan on the metatarsophalangeal joint (MTPJ) and passive flexion/extension of foot fingers. The dynamic scan allows to depict the relations among the plantar plate and the flexor tendons and the articular cartilage. In our study, D-HRUS has detected a plantar plate tear in 21/22 patients (14 on MTPJ II, five on MTPJ III, two on MTPJ II and III). They appear like small hypoechoic defects of the distal insertional fibres and can be divided into partial (eight patients) and full thickness tears (13 patients). In all patients, MR confirmed the diagnosis of plantar plate rupture but in nine cases it has not been able to differentiate a partial from a full thickness tear. Conclusion: D-HRUS allows to assess the plantar plate in detail and to detect its lesions. In particular, the dynamic analysis is able to differentiate a partial from a full thickness tear.