Research articleThe “second ulnar groove”, a MRI sign suggesting a previous palmar luxation of the ulna at the distal radioulnar joint

IntroductionA cortical lined impaction on the radiodorsal side of the ulnar head may be at the origin of a “second ulnar groove” (SUG). The goal of this article is to illustrate this MRI sign, prompting for further investigation of the distal radioulnar joint (DRUJ). Hence associated soft tissue pathology may be detected, which may lead to instability.Material and methodsFollowing an anterior luxation of the ulna at the DRUJ a second cortical lined groove in a previously normal distal ulna was discovered. A data base review from January 2008 to August 2016 of the axial FS PD-TSE WI 1.5 T MRI views of 1.716 patients was accomplished in search of similar bone defects.ResultsEight patients with previous severe wrist trauma presented with a similar posttraumatic ulnar bone defect. The preceding anterior luxation at the DRUJ was only clearly demonstrated in five patients. However, two more patients had a residual anterior subluxation. Different imaging techniques are discussed and the differential diagnosis is well illustrated.ConclusionsThe type of trauma, the specific location and the morphology of a second ulnar groove, all compatible with a sequel of an anterior luxation of the ulna at the DRUJ, should lead to a further specific clinical and MRI revaluation of the DRUJ.