Functional Dart-Throwing Motion: A Clinical Comparison of Four-Corner Fusion to Radioscapholunate Fusion Using Inertial Motion Capture

Background Dart-throwing motion (DTM) is an important functional arc of the wrist from radial extension to ulna flexion. An aim of partial fusion surgery of the wrist is to maintain maximal functional motion while addressing the pathology. The radioscapholunate (RSL) fusion, accompanied with partial resection of the distal scaphoid, is thought to allow better DTM than other partial wrist fusions such as the four-corner fusion (4CF). Question Does an RSL fusion allow better functional DTM than 4CF, and how does this range compare with healthy wrists and the patient's contralateral wrist? Patients and Methods Patients who have undergone an RSL fusion or 4CF at our tertiary center were identified and invited to present to have their DTM arc measured. To accurately measure DTM, a previously validated inertial measurement device was used. Patient's functional DTM arc was measured in both unrestrained (elbow and shoulder free to move) and restrained (elbow and shoulder immobilized) fashions. This was compared with their contralateral wrist and a group of healthy control volunteers. Results Overall five RSL fusions, 10 4CF and 24 control patients were enrolled in the study. There was no significant difference between functional DTM when 4CF and RSL fusion were compared. Both had significantly reduced functional DTM arc than control patients. There was no significant difference between the operated wrist compared with the patient's contralateral unoperated wrist. Conclusion RSL fusion is not significantly better at maintaining functional DTM when compared with 4CF. Both surgeries result in decreased functional DTM arc when compared with control patients. This is a cohort study and reflects a level of evidence IV.