[Computed tomography and magnetic resonance in the follow-up to interventions for the prosthetic replacement of the carpal bones].

The authors examined with CT and MRI 12 patients submitted to prosthetic replacement of necrotic carpal bones--7 of them because of scaphoid proximal pole posttraumatic osteonecrosis and 5 because of lunate Kienböck's disease. The prosthetic implants were autologous in all patients: they were taken from palmaris gracilis tendon and modified to give them a rounded shape, to adapt them to the new anatomic site. All patients exhibited postoperative limitation in flexion-extension movements; 5 of them reported associated wrist pain. The authors investigated the anatomic reasons of the postoperative symptoms and tried to assess CT and MR diagnostic capabilities in depicting these conditions. CT was performed with thin sections (1.5 mm) and multiplanar reconstructions, with a Philips Tomoscan LX unit. MRI was performed with a GE MR Max Plus unit at 0.5 T and a Medical Advances transmit-receiving extremity coil, on the axial, coronal and sagittal planes, with T1- and T2-weighted sequences. All patients had been submitted to conventional radiography of the wrist. In 6 patients CT and MRI showed severe synovial reaction in the surgical site, with new ligament absorption in 5 of them. In 5 of these patients CT identified some nodular calcifications, while MRI better depicted the fibrotic portion, if present. MRI demonstrated the carpal dorsal intercalated instability which was present in all the patients submitted to scaphoid proximal pole resection; in the patients operated on for Kienböck's disease, volar tilt of the scaphoid was increased. Both kinds of carpal instability were correlated with scaphoid-lunate surgical dissociation. These instabilities were greatly correlated with the postoperative symptoms. Currently, MRI is the gold standard in studying carpal instability and it is therefore fundamental in investigating the complex anatomic and biomechanical features of these patients postoperatively.