Abstract
Introduction: Lesser metatarsophalangeal joint (MTPJ) instability is a common cause of forefoot pain. Instability is probably caused by tears of the plantar plate and collateral ligaments. We prospectively compared MRI and ultrasound with and without arthrography in the assessment of patients with MTPJ instability.
Materials and Methods: MTPJ instability was diagnosed by the draw test. Nineteen patients underwent imaging with consent. One musculoskeletal radiologist performed MRI arthrography and a different musculoskeletal radiologist performed ultrasonography supplemented with arthrography. Each radiologist reported his own study, blinded to the results of the other modality. Where possible, the radiological diagnosis was evaluated at surgery.
Results: MRI identified four full thickness plantar plate tears. In five studies no contrast was seen in the MTP joint and in 10 contrast was contained within the joint.
Ultrasound identified six full thickness plantar plate tears as hypoechoic zones that extended through the whole thickness of the plate. Eleven studies showed partial thickness tears. Two studies showed thinning of the plate. Ultrasound arthrography identified seven full thickness tears by extravasation of injected fluid into the flexor tendon sheath. Eleven studies showed partial thickness tears and one was normal. Ultrasound and ultrasound arthrography agreed in 14/19 patients. MRI agreed with ultrasound on 3 of 6 full thickness tears and with ultrasound arthrography in 4 of 6 full thickness tears. MRI gave additional information about the articular surfaces in four patients. Surgical comparison was available in 11/19 patients. Ultrasound with and without arthrography correctly predicted four partial thickness tears. Ultrasound arthrography correctly predicted 6/7 full thickness tears, MRI 3/7 and ultrasound 3/7.
Discussion: Ultrasound with arthrography appears the best modality to distinguish between partial and full-thickness tears. It is cheaper, simpler and can be performed in the outpatient setting. Larger studies with surgical confirmation are required to assess its value more precisely.
Correspondence should be addressed to: Mr Andrew H. N. Robinson, Editorial Secretary, Department of Trauma and Orthopaedics, BOX 37, Addenbrooke’s Hospital, Cambridge CB2 2QQ, England.
