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Assessment of Proximal Junctional Kyphosis and Shoulder Balance with Proximal Screws vs. Hooks in Posterior Spinal Fusion for Adolescent Idiopathic Scoliosis: PAPER #7

Pahys, Joshua M. MD; Samdani, Amer F. MD; Betz, Randal R. MD; Trobisch, Per D. MD; Garg, Hitesh MD; Newton, Peter O. MD; Marks, Michelle C. PT, MA; Bastrom, Tracey MA; Harms Study Group; Cahill, Patrick J. MD

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Spine Journal Meeting Abstracts: 2011 - Volume - Issue - p 58
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Summary: A large multicenter database review was performed (n=364) to evaluate the effect on proximal junctional kyphosis (PJK) and shoulder balance with the use of proximal hooks vs. screws in an otherwise all pedicle screw posterior spinal fusion (PSF) for adolescent idiopathic scoliosis (AIS). Proximal implant type did significantly affect shoulder asymmetry at 2 years. However, cases with proximal screws demonstrated a significant increase in PJK and decrease in thoracic kyphosis at 2 years compared to hooks.

Introduction: Less rigid forms of fixation at the top of constructs in degenerative lumbar PSF have been postulated to decrease the risk of PJK. This study evaluates a large series of patients to discern the effect of proximal hooks vs. screws on PJK as well as shoulder balance in otherwise all pedicle screw (>80%) PSF constructs in patients with AIS.

Methods: A multicenter AIS surgical database was reviewed to identify all patients who underwent instrumented PSF with all pedicle screw (>80%) constructs and minimum two‐year follow‐up. The “hook” group of patients had at least one or more hooks used at the top of the construct, compared to the “screw” group in which only pedicle screws were used.

Results: A total of 364 patients were identified, 274 (75%) in the screw group, and 90 (25%) in the hook group. There were no significant preoperative differences with regards to curve type, coronal/sagittal Cobb, and curve flexibility for either group. At two years post‐op, the coronal Cobb correction was similar for both groups (60%). There was no difference in correction of shoulder asymmetry when the groups were matched for pre‐op shoulder balance. However, in the sagittal plane, T5‐T12 Cobb was significantly larger in the hook group (p<0.001), while T2‐T12 (p=0.024) and T2‐T5 (p=0.055) were larger in the screw group. PJK, defined as the sagittal Cobb between the uppermost instrumented and uninstrumented vertebrae, was significantly higher in the screw group (p=0.027). The screw group demonstrated a greater decrease in kyphosis from preop to 2 years postop at T2‐T12 (p<0.001) and T5‐T12 (p<0.001). Table 1

Conclusion: This is the largest study to date to evaluate the impact of the type of implant used at the top of an all pedicle screw construct for PSF in AIS. Pedicle screws at the top of a PSF construct lead to a decrease in thoracic kyphosis and an increase in PJK. Hook fixation at the top of a scoliosis construct may protect against PJK. Proximal implant type did not have any bearing on correction of shoulder asymmetry.

© 2011 Lippincott Williams & Wilkins, Inc.