A Pedicle Screw Construct Gives an Enhanced Posterior Correction of Adolescent Idiopathic Scoliosis When Compared to Other Constructs – Myth or Reality?

Summary: We compared the initial and 2yr follow up of posterior correction of Lenke 1 AIS achieved by the hook and wire, hook - screw - wire, and pedicle screw constructs in 72 patients, after accounting for the preoperative flexibility of the curves. The postoperative correction of the thoracic curve was expressed as a ratio of the preoperative flexibility and was termed postoperative correction index. The corrective index for the hook and wire group was better than the other 2 groups.

Purpose: We compared the initial and 2yr F/U of posterior correction of Lenke 1 AIS achieved by 3 different constructs, after accounting for the preoperative flexibility of the curves.

Methods: A tri-center retrospective cohort study of 72 patients with Lenke 1 AIS who underwent a PSF with a 2 year F/U was performed. Each center represented a single surgeon using only one type of construct. Group 1 (proximal and distal hooks and segmental collar button intraspinous wires) consisted of 24 patients, group 2 (proximal hooks, distal screws and apical sublaminar wires) consisted of 23 patients and group 3 (pedicle screws only) consisted of 25 patients. The postoperative correction of the thoracic curve was expressed as a ratio of the preoperative flexibility (Suk et al) with the following formula and was termed postoperative correction index. Postop Correction Index equals (postop correction / preop erect Cobb angle) divided by (supine bending preop correction / preop erect Cobb angle). The postoperative saggital correction was also measured.

Results: Postoperative correction index for group1 (1.95) was significantly better than group 2 (1.48) and group 3 (1.34). Group 3 and group 1 constructs actually lordosed the patients by as much as 12 degrees whereas patients in group 2 retained their preoperative kyphosis. Also, the postoperative correction (without considering the preoperative flexibility) was similar for group 1 (73 %) and group 3 (71%) and greater than that achieved by group 2 (63%).

Discussion: The hook and wire construct (group 1) afforded a better correction of the scoliosis, when the preoperative flexibility of the curve was considered, probably due to increased levels of segmental fixation. Also, the pedicle screw construct has a lordosing effect on the thoracic spine, contrary to prior reports. Therefore, we feel that there is no significant advantage in using a pedicle screw construct which is, reportedly, more expensive.