Scaphoid Overstuffing: The Effects of the Dimensions of Scaphoid Reconstruction on Scapholunate Alignment

Abstract

Osteochondral replacement of the proximal scaphoid has been reported using a vascularized flap from the medial femoral trochlea. A concern with this technique is the loss of stability of the scapholunate relationship with resection of the scaphoid proximal pole. Overexpansion of the scaphoid dimensions (overstuffing) during scaphoid reconstruction with the osteochondral flap may play a role in maintaining scapholunate alignment. Our purpose was to determine if overstuffing the scaphoid can correct rotatory carpal instability in a cadaveric model studied radiographically. The radiolunate angle and scapholunate interval were measured for 5 fresh cadaver wrists. We completely incised the scapholunate interosseous ligament and performed an osteotomy to excise the proximal third of the scaphoid to simulate a proximal pole deficiency nonunion and create a dorsal intercalated segmental instability deformity. Radiographic measurements were repeated. The proximal pole of the scaphoid was replaced with its original piece of bone; radiographic measurements were repeated without scapholunate ligament repair. The osteotomy site was overstuffed with a 4-mm sawbone spacer without scapholunate ligament repair, and radiographs were obtained. Sectioning of scapholunate ligaments and proximal pole excision successfully created carpal instability demonstrated by abnormal radiolunate angles. Without ligament repair, proximal pole replacement did not restore normal radiolunate angles. Expansion of the scaphoid dimensions corrected radiolunate angles on lateral unloaded radiographs and improved scapholunate intervals on clenched fist radiographs. These findings were statistically significant compared with the unexpanded (replaced) scaphoid. These findings suggest that scaphoid reconstruction that results in expansion of the scaphoid's normal dimensions will restore carpal alignment without scapholunate ligament reconstruction. Osteochondral reconstruction of difficult proximal pole nonunions may not require any preservation or reconstruction of scapholunate integrity if the reconstruction expands the normal dimensions of the native scaphoid. Scapholunate interval and carpal alignment may be restored by scaphoid over stuffing. The effects on increased contact pressure and range of motion require further investigation.