The oblique cord of the forearm (chorda obliqua) is a flat, inconstant fibrous band running from the lateral side of the ulnar tuberosity obliquely downward and laterally to the radius just below the bicipital tuberosity. Its fibres run in the opposite direction to the upper part of the interosseous membrane. It is present in approximately 75% of individuals and is distinct from both the annular ligament and the interosseous membrane.
Supplements the proximal radioulnar joint capsule and provides additional restraint against distraction at the proximal radioulnar joint, resisting distal forces transmitted from the radius to the ulna through the interosseous membrane.
The oblique cord is identified during surgical approaches to the proximal radius and during interosseous membrane reconstruction procedures for Essex-Lopresti injury (axial forearm dissociation). Its fibres run perpendicular to the main interosseous membrane fibres, providing resistance in a different axis. Absence of the oblique cord in some individuals may increase vulnerability to proximal radioulnar joint instability. It is a landmark in posterior interosseous nerve decompression at the arcade of Frohse level.
In axial forearm dissociation with disruption of both the interosseous membrane and radial head, the oblique cord and central band of the interosseous membrane must be reconstructed using tendon graft to restore the longitudinal forearm stability preventing proximal radial migration.
