Three-dimensional MRI analysis of elbow anatomy and kinematics in children with ulnar dimelia.

Ulnar dimelia often presents with restricted elbow movement. To develop a treatment strategy to improve elbow mobility, a detailed understanding of the skeletal deformity is needed. We created 3-D models of the cartilage and bone in the elbows of four children with ulnar dimelia by segmentation of MRI scans. We analysed the anatomy and performed a kinematic analysis. In all four children, the distal humerus was triangular in shape and consisted of a medial epicondyle, an enlarged lateral epicondyle and an anterior epicondyle. By comparing the 3-D images with conventional radiographs, we found that the projection of the enlarged lateral epicondyle created two longitudinal lines, which is a radiographic hallmark feature of the triangular-shaped distal humerus. In addition, during elbow flexion, the radial forearm bone slides along the lateral trochlea rather than rotates. This knowledge can aid surgeons to plan treatment for improving elbow mobility in ulnar dimelia.Level of evidence: IV.