MR Imaging Provides Practical Information for Preoperative Assessment of Radial Polydactyly with Bifurcation at the Metacarpophalangeal Joint Level

PURPOSE: We aimed to evaluate the use of magnetic resonance imaging (MRI) to visualize unossified bone sites that are often not visible with radiography in pediatric radial polydactyly patients with bifurcation at the metacarpophalangeal (MP) joint level. The MRI validation could help in planning for surgical procedures. PATIENTS AND METHODS: A total of 141 thumbs in 139 pediatric patients with bifurcation at the MP joint on radiography were included in this study. All the patients had undergone MRI with proton density-weighted fat-suppressed fast spin-echo (FS PDWI) sequence and fast fat-suppressed 3D spoiled gradient-recalled echo (FS 3D SPGR) sequence. The MR images of the cartilaginous structure and joint characteristics at the MP joint were evaluated and categorized by two experienced radiologists. RESULTS: Our analysis demonstrated that MR imaging, especially the FS 3D SPGR sequence, yields better visibility of the cartilaginous structure and shows clearer joint characteristics that could not be detected by radiography. The abnormalities included a cartilaginous connection on the base of duplicated proximal phalanx, cartilaginous joint connection and the shape of articular cartilage on the head of metacarpal and soft tissue band. Radiologically encountered duplications at the MP joint level were successfully classified into six types based on the MRI-detected structural changes. The distribution of the six types was 17.7% (25/141) in type 1, 53.9% (76/141) in type 2, 2.8% (4/141) in type 3, 9.9% (14/141) in type 4, and 13.5% (19/141) in type 5. CONCLUSION: This data showed that MR imaging provides practical information on the anatomic characteristics in radial polydactyly with bifurcation at the MP joint level that could aid surgical decision-making processes. Thus, the FS 3D SPGR sequence could be used as a MR imaging technique in radial polydactyly.