Investigating the performance of a wrist stabilization device for image-guided percutaneous scaphoid fixation.

PURPOSE: Conventional navigated surgery relies on placement of a reference marker on the anatomy of interest. However, placement of such a marker is not readily feasible in small anatomic regions such as the scaphoid bone of the wrist. This study aimed to develop an alternative mechanism for patient tracking that could be used to perform navigated percutaneous scaphoid fixation.

METHODS: A prototype wrist stabilization device was developed to immobilize the scaphoid relative to a reference marker attached to the device. A position measurement system and 3D fluoroscopy were used to study the accuracy and limitations of wrist stabilization during simulated clinical usage with a cadaver specimen. Reference markers mounted on the device were used to measure intra-device motion. Radiometallic beads implanted in the scaphoid were used to measure patient-device motion. Navigated planning and guidance of scaphoid fixation were performed in five cadaver and eight "ideally immobilized" plastic specimens. Postoperative 3D fluoroscopy was used to assess the accuracy of navigated drilling.

RESULTS: The average intra-device motion was 1.9 mm during load application, which was elastically recovered upon release of the load. Scaphoid motion relative to the reference marker was predominately rotational with an average displacement of 1.25 mm and 2.0°. There was no significant difference in the accuracy of navigated drilling between the cadaver specimens and the ideally immobilized group.

CONCLUSIONS: The prototype wrist stabilization device meets the criteria for effective wrist stabilization. This study provides insight concerning proper use of the device to minimize scaphoid displacement and design recommendations to improve immobilization.