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In the present study, the adaptability of the distal radioulnar joint (DRUJ) was evaluated using conventional computed tomography (CT) evaluation methods. In addition, we investigated/compared a new method to evaluate dorsal displacement of the ulnar head. Our subjects consisted of 32 healthy volunteers (64 wrists) and 11 patients (13 wrists) with extensor tendon injuries related to dorsal displacement of the ulnar head. To diagnose instability in the DRUJ based on CT scans, the radioulnar line method and the modified radioulnar line method were measured. Instability was evaluated by the new method that the ulnar head was located on the dorsal side from a line involving the peak of Lister's tubercle in parallel to this baseline was regarded as showing abnormal dorsal displacement of the ulnar head. The diagnostic accuracy of each method was calculated. The sensitivities, specificities, false-positive rates, positive predictive values and the negative predictive value of new methods were better than other two methods. The new method that we recommend is simple. Based on the results of this study, an evaluation of normal/abnormal dorsal displacement of the ulnar head in the DRUJ using the new method may be useful for determining the timing of surgery.

Dislocation of the thumb interphalangeal (IP) joint is uncommon because of the inherent stability of the joint. Cases in which reduction was blocked by the volar plate, the flexor pollicis longus (FPL) tendon, the sesamoid bone, and an osteochondral fragment have been described in the literature. This article reports a case of closed thumb IP joint dislocation caused by the displacement of the FPL tendon. A new percutaneous reduction technique for this injury will also be presented. A 63-year-old woman presented to the emergency room with an obvious thumb deformity. Radiographs confirmed dorsal dislocation of the thumb IP joint without associated fracture. Closed reduction was not successful. Percutaneous reduction was performed under locoregional anesthesia, because the dislocation was due to an FPL tendon that had displaced dorsally and radially to the proximal phalanx. After reduction, Kirschner wire fixation was not needed, but IP joint immobilization with a splint was required for 3 weeks. Postoperatively, there were no complications in soft tissues and the operative scar was almost unrecognizable. This technique enables a mini-invasive reduction by operating percutaneously on the FPL. In addition, unlike with a volar zigzag approach, it is possible to suppress the occurrence of postoperative adhesion of the flexor tendon. This new minimally invasive reduction technique is useful for irreducible dislocation of the thumb IP joint due to a displaced FPL tendon.

Rupture of the triceps tendon is a rare condition. We report a case of triceps tendon rupture with avulsion fracture of the olecranon with discussion about pathogenesis from the viewpoint of healing of the olecranon ossification nucleus. An 18-year-old man presented with avulsion fracture of the olecranon and triceps tendon rupture. Operative treatment was conducted with good results. Rupture of the triceps tendon is a rare injury comprising approximately 2% of all tendon injuries, and avulsion at insertion into the olecranon is the most common site of rupture. This injury is most likely to happen in young people as sports-related trauma. Among young people who have insufficient healing of the olecranon ossification nucleus, avulsion fracture of the olecranon may occur due to strong contraction force of the triceps tendon. Our clinical evidence may suggest that avulsion fracture of the olecranon is related in olecranon ossification center healing. Most triceps tendon ruptures are accompanied by avulsion fracture of the olecranon, and it is important to suspect this injury when radiographs show a small fleck of bone avulsed from the olecranon.