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Pedicle Screw Instrumentation Does Not Cause Hypokyphosis Following the Surgical Correction of AIS

Saturday, October 20, 2012: 3:06 PM
Melrose (Hilton Riverside)
Adam Wollowick1, Vishal Sarwahi1, Elliot Harmon1, Preethi M. Kulkarni1, Jonathan J. Horn1, Meredith Steinman1, Dan Wang2 and Terry Amaral1, (1)Orthopaedic Surgery, Albert Einstein College of Medicine, Bronx, NY, (2)Epidemiology, Albert Einstein College of Medicine, Bronx, NY

Purpose: Pedicle screw instrumentation in AIS has been shown to produce hypokyphosis. Contributing factors may include rod size, rod material, and correction maneuvers. This study seeks to evaluate the ability of pedicle screws to maintain normal kyphosis or restore normal kyphosis in patients with preoperative hypokyphosis.

Methods: 110 AIS patients who underwent posterior spinal fusion utilizing pedicle screws between 2004 and 2009 were evaluated for kyphosis (T3-12), sagittal balance and proximal junction kyphosis (> 10°). Preoperative, immediate post-op, one- and two-year post-op x-rays were reviewed. Charts were reviewed for patients and curve characteristics and intra-operative maneuvers, including DVR. 

Results: 43 patients had a complete set of data at two year follow up. 63 patients (57%) had normal pre-op kyphosis. Immediately post-op, 72% of patients had normal kyphosis. This increased to 74% at one year and 69% at two years. The change was not statistically significant. Rod translation, rod derotation and DVR were not found to have a hypokyphosing effect. Patient and curve characteristics, length of fusion, LIV, and number of screws were not found to have a significant effect on kyphosis. Of the patients with 2 year follow-up, 67% had normal preoperative kyphosis. Of patients who started with normal pre op kyphosis, 83% maintained normal kyphosis at 2 years, while 17% had hypokyphosis post op and remained unchanged at two years. 57% of patients with preoperative hypokyphosis were restored to normal thoracic kyphosis which was maintained at two year follow up. Patients did not significantly change their sagittal balance over a two year follow up. High strength rods were utilized in 51% of patients. The use of high strength rods did not improve the ability to maintain or restore thoracic kyphosis. There was no significant incidence of PJK. 

Conclusion: In this study, pedicle screws did not produce hypokyphosis as previously reported . No specific curve characteristics or surgical maneuver was found to reduce kyphosis in AIS patients. Pedicle screws allow the surgeon to maintain kyphosis in patients with normal kyphosis at baseline. Further attention needs to be paid to patients with pre-op hypokyphosis as only 53% were normalized.