Evaluation of the Accuracy of Pedicle Screw Insertion without Intraoperative Radiographic Guidance.

Abstract

Three methods of pedicle screw insertion are in common use. Each has its advantages and disad-vantages and the decision to use a particular method depends on the type of procedure, indications, the patient's age, and the preferences and experience of the operator. The accuracy of screw insertion through the vertebral arch into the vertebral body may be assessed on post-operative CT or MRI and classified according to different systems. The free-hand method was analysed according to the Gertzbein classification and was compared with the other methods in terms of accuracy and complications. The accuracy of screw insertion was evaluated with post-operative MRI of the spine. A study group of 50 patients was randomly selected from among 124 patients who had undergone surgery. The pla-cement of a total of 426 screws in the thoracic and lumbar spine was assessed. The shortest procedure was 87 minutes long and the longest surgery took 290 minutes. 93% (397) of the screws were classified as inserted in Gertzbein's "safe zone". 7% (29) of the screws were placed in the "dangerous zone"; this was seen in 14 (28%) patients. Only 2 patients had mild neurological symptoms in the form of radicular pain. 1. Free-hand pedicle screw insertion with pre-operative planning based on CT or MRI requires con-siderable experience, but if this condition is met, the percentage of successfully inserted screws is not significantly different from that seen in other techniques. 2. The highest number of screw placement errors occurs in the thoracic section of the spine, but these errors rarely prompt repeat surgery. 3. Clinically overt complications are very rare and usually have the form of radicular pain.