Computed Tomography (CT) Evaluation of Pedicle Screws Placed into Deformed Spines Over an 8-Year Period

Objective: To evaluate the incremental accuracy of pedicle screws used in spinal deformity via a free-hand-technique at a single institution over an 8-year period. Background: The in vivo accuracy of free-hand pedicle screws placed throughout the deformed spine as evaluated by CT scanning is unknown over a long time-period.

Materials/Methods: A total of 1023 pedicle screws in 60-patients (927 screws for 54-scoliosis patients and 95-screws for 6-kyphosis patients) inserted between T1-L4 during an 8-year period were investigated with postoperative CT scans. Patients were divided into 3 groups (Group-I=1998-2000,Group-II=2001-2003 and Group-III=2004-2005). All pedicle screws were inserted using the free hand technique using anatomic landmarks, specific entry sites, neurophysiologic, and radiographic confirmation. The position of the pedicle screw by CT scan was graded as an acceptable screw versus violated screw(with significant violation), defined as the axis of the screw being outside the cortex of the pedicle wall.

Results: 03/1023 pedicle screws (9.8%) demonstrated significant mediolateral pedicle wall violations (19-medial vs. 84-lateral,p=0.001). Group-I and III had significantly higher lateral wall violations than Group-II(p<0 .05) as did the kyphotic spines(vs. scoliotic spine,p<0.05). There were significantly more screws placed in periapical region over time (p<0.0001), with left-sided lateral violations (T5-8) increasing from Group-II to Group-III, while number of medial decreased (p<0.0001). Also, pedicle on right side showed a significant decrease accuracy Group-III (p="0.03)." The average transverse angle acceptable was 15.3° and different that either (23.0°,p<0.001) or lateral(10.6°,p<0.001) between Group-I Group-II. No violation demonstrated neurologic, vascular, visceral complications.

Conclusions: The overall accuracy of acceptable screws using the free-hand pedicle screw placement technique in the deformed spine was 91.2% without any neurologic, vascular, or visceral complications over an 8-year period. The rate of medial violations decreased with time, as the number of periapical region increased.