Final answer:
The sagittal plane is used when positioning a goniometer over the capitate bone for measuring wrist flexion and extension.
Step-by-step explanation:
The plane of wrist motion utilized when positioning the axis of a goniometer over the capitate for wrist flexion and extension is the sagittal plane. Abduction and adduction of the wrist, however, occur in the coronal plane. The sagittal plane divides the body into left and right halves and is an anterior-posterior plane of motion. Flexion and extension at the joints, including the wrist, typically happen within this plane. For the measurement of wrist flexion and extension, the goniometer's axis would be aligned over the capitate bone as part of the procedure for evaluating range of motion.