Residual dysfunction after a fracture of the distal radius is most often mild but may give rise to significant impairment especially in the younger active population. The symptoms often manifest around the distal ulna when loading the hand or rotating the forearm. In this region are found articular and soft tissue connections running from the distal ulna to the distal radius as well as to the ulnar side of the carpus. The aims of this thesis were to investigate the effects of distal radius fractures on the structures about the distal ulna and to what extent malunion and ulnar soft tissue lesions affect function. Both patients and cadaver specimens were used in the five different studies. In a retrospective study of 17 malunited distal radius fractures supination impairment improved significantly by correction of the skeletal malunion. This highlights the importance of distal radioulnar joint congruity for forearm rotation in a subset of cases. The pathomechanisms of injury to the triangular fibrocartilage complex (TFCC) were studied. In a cadaveric distal radius fracture model different restraining properties and injury patterns were investigated. Similar patterns of injury were then observed in 20 patients with a displaced distal radius fracture. It was found that a TFCC injury can be expected with dorsal displacement of the distal radius fragment of 32o or more from the anatomically correct position. The distribution of a TFCC injury apparently differs depending on the size of an associated ulnar styloid fracture. In cases of an intact ulnar styloid or a concomitant tip fracture (Type 1) the first stage of injury seems to be extensor carpi ulnaris subsheath separation from the distal ulna and the dorsal radioulnar ligament. Thereafter follows a disruption of the deep insertions into the fovea of the ulna starting from the palmar and extending dorsally and radially. An extensive injury can be detected with a novel non-invasive test called the ‘bald ulnar head test’, which is performed under anaesthesia. Diagnosis of an acute TFCC injury is difficult using non-invasive methods. In a prospective study of 48 patients, CT scanning to detect pathologic subluxation was found to be of little use in both acute and chronic cases, and is therefore not endorsed on this indication. A radioulnar stress test, which in previous studies has correlated well to a deep TFCC injury, was found to be highly reliable but not to correspond with significant disability in self-administered questionnaires of functional outcome two years or more after injury. This indicates that the subset of patients possibly benefiting from acute repair must be identified by other means.