Plantar plate imaging - correlating ultrasound arthrography and surgical findings

J. Viner, R. Jugdey, S. Khan, A. Zubairy, J. Barrie

Introduction: Instability and synovitis of the lesser metatarsalphalangeal (MTP) joints is a significant cause of forefoot pain. Plantar plate imaging traditionally has been through MRI and fluoroscopic arthrography. We have described ultrasound arthrography as a less resource-intensive technique without radiation exposure. We report the correlation between ultrasound arthographic and surgical findings.

Methods: Patients with lesser MTP joint instability and pain underwent ultrasound arthrography by a consultant musculoskeletal radiologist. The main finding was the presence of a full or partial tear of the plantar plate. In some patients the location of the tear along with its size in the long and short axis was also reported. Authors who were not involved in the imaging or surgery reviewed the operation notes of patients who underwent surgery to identify: Whether a partial or full thickness tear was identified and size and location of the tear. The accuracy of ultrasound arthrography was calculated using surgical findings as the standard.

Results: 53 patients with 55 joints underwent ultrasound arthrography, and of these 34 went on to have surgery. 23 patients had adequate documentation of surgical and ultrasound findings. Surgery confirmed plantar plate tears in 21 patients (91.3%) with 9 full thickness tears and 7 partial thickness tears confirmed both operatively and with ultrasound (in 5 patients the operation note did not specify completeness of tear). In 2 patients, in whom ultrasound demonstrated a partial thickness tear, no tear was found at surgery. The sensitivity of ultrasound arthrography for plantar plate tears is 100%, specificity is 0% (although based on few patients), and positive predictive value of 91.3%.

Conclusion: Ultrasound arthrography has a high sensitivity, but low specificity for plantar plate tears, comparable with ultrasound in previous studies. It allows differentiation of partial and full thickness tears which may be important for treatment.