The insertion points for guide pins used in percutaneous vertebral fixation by pedicle screw are determined by establishing an approach path on a CT image, measuring on the CT image the distance from the intersection of the approach path and the skin of the patients back to the patients midline, and marking off the corresponding distance while visualizing the patient by anteroposterior fluoroscopy. An longitudinally expansible pedicle screw comprises a shaft with bone-engaging threads on a distal portion, machine screw threads on a proximal portion, and a tubular extension having wrench-engageable holes on a proximal face, and internal threads engaging the machine screw threads on the proximal portion of the shaft. An oval cannula accommodates an arthroscope and forceps simultaneously for intervertebral disc surgery.
