Navigated scaphoid screw placement using customized scaphoid splint: an anatomical study.

INTRODUCTION

Accuracy in navigated surgery depends on placement and registration of stable reference markers close to the anatomic region of interest. Navigation in small and complex anatomic regions, such as the scaphoid, is challenging due to difficulties in placing a stable reference marker. In the current paper, we describe the use of a customized wrist-positioning device "Scaph-splint" with a built-in reference marker that facilitates navigated scaphoid screw insertion in combination with a 3D imaging device.

MATERIALS AND

METHODS

Initial cadaveric feasibility study Five fresh-frozen cadaveric upper extremity specimens were utilized. Each specimen was secured onto the "Scaph-splint" with the wrist in about 90 degrees of extension. Using a 3D fluoroscope, a series of images were taken of the carpal bones and reconstructed in axial, sagittal, and coronal planes. Navigated planning and guidance of scaphoid drilling and screw placement was performed. Next, a repeat 3D scan was taken to analyze the drill canal. The accuracy of navigated scaphoid drilling, drilling trials, and any penetration of the scaphoid outside of the planned drill trajectory were evaluated. A grading scheme was used to assess the drilling accuracy: Grade 1 <1 mm deviation, Grade 2 <2 mm deviation, Grade 3 <3 mm.

RESULTS

Scaphoid drilling was confirmed to be completely accurate (Grade 1) in two specimens, highly accurate (Grade 2) in two specimens, and accurate (Grade 3) in one specimen. No specimen required a repeat drilling of the scaphoid. In one specimen, the proximal scaphoid pole was perforated by the drill. No registration failures or loosening of the reference marker occurred.

CONCLUSION

The use of the "Scaph-splint" enabled stabilization of the hand and wrist, thus adequately fixing the reference marker in relation to scaphoid for optimal navigation and screw placement without the need to directly penetrate the scaphoid with a reference marker. The use of 3D fluoroscopy further increased the accuracy and precision of scaphoid screw placement.