Does the DISI matter after distal scaphoidectomy with tendon interposition for STT osteoarthritis?

Progression to dorsal extension of the lunate after distal scaphoidectomy was described more than a decade ago. Still, this technique remains a popular choice for surgical treatment of isolated scaphotrapeziotrapezoid osteoarthritis (STT OA). This study aimed to investigate short-term postoperative function, patient satisfaction and radiographic outcomes of distal scaphoidectomy with tendon interposition for isolated STT OA in the wrist. Scaphoid resection width, amount of DISI and postoperative complications were also assessed. We evaluated all distal scaphoidectomies done at our hospital from 2012 to 2018. Postoperative clinical analysis consisted of grip and key pinch strength, joint amplitude, pain on visual analog scale (VAS), hand usability (VAS) and functional scores (QuickDASH and PRWHE scores). On follow-up radiographs, we measured the amount of DISI, resection height and scaphoid working length and compared them to functional scores. Eighteen patients with 21 operated wrists were eligible. Average time to postoperative evaluation was 36 (5-78) months. We observed DISI in 95% of the cases (n=19). A mean increase of 13° (±6) in radiolunate angle was noted when comparing pre- and postoperative radiographs. Neither the amount of DISI nor the resection height was significantly correlated with the functional scores. No revision surgery for advanced wrist collapse was reported. Four concomitant surgeries were needed. Distal scaphoid excision with tendon interposition yields good short-term results in isolated STT OA. While 95% of cases developed a DISI deformity, there were no cases of functional impairment. Longitudinal studies with long-term follow-up are required to further evaluate lunate extension and possible clinical implications.