Hooks Versus Pedicle Screws at the Upper Instrumented Level: An In Vitro Biomechanical Comparison. Issue 7 (1st April 2023)

• Record Type: Journal Article
• Authors: Colantonio, Donald F.; Le, Anthony H.; Pisano, Alfred J.; Chung, Joon M.; Wagner, Scott C.; Fredericks, Donald R.; Roach, William B.; Schlaff, Cody; Dill, Andrew; Mauntel, Timothy C.; Hendershot, Brad D.; Helgeson, Melvin D.
• Is Part Of: Spine. Volume 48:Issue 7(2023)
• Page Start: E94
• Page End: E100
• Publication Date: 2023-04-01
• Subjects: proximal junctional kyphosis -- biomechanical -- posterior spinal fusion -- thoracolumbar -- PJK -- pedicle screws -- transverse process hooks; Spine -- Abnormalities -- Periodicals; Spine -- Diseases -- Periodicals; Spine -- Surgery -- Periodicals; 616.73005
• DOI: 10.1097/BRS.0000000000004547
• Languages: English
• ISSNs: 0362-2436

Abstract

Abstract : Study Design: Controlled laboratory study. Objective: The aim was to compare motions at the upper instrumented vertebra (UIV) and supra-adjacent level (UIV+1) between two fixation techniques in thoracic posterior spinal fusion constructs. We hypothesized there would be greater motion at UIV+1 after cyclic loading across all constructs and bilateral pedicle screws (BPSs) with posterior ligamentous compromise would demonstrate the greatest UIV+1 range of motion. Summary of Background Data: Proximal junctional kyphosis is a well-recognized complication following long thoracolumbar posterior spinal fusion, however, its mechanism is poorly understood. Materials and Methods: Twenty-seven thoracic functional spine units were randomly divided into three UIV fixation groups (n=9): (1) BPS, (2) bilateral transverse process hooks (TPHs), and (3) BPS with compromise of the posterior elements between UIV and UIV+1 (BPS-C). Specimens were tested on a servohydraulic materials testing system in native state, following instrumentation, and after cyclic loading. functional spine units were loaded in flexion-extension (FE), lateral bending, and axial rotation. Results: After cyclic testing, the TPH group had a mean 29.4% increase in FE range of motion at UIV+1 versus 76.6% in the BPS group ( P <0.05). The BPS-C group showed an increased FE of 49.9% and 62.19% with sectioning of the facet joints and interspinous ligament respectively prior to cyclic testing. Conclusion: BPSs at the UIV led to greater motion at UIV+1 compared to bilateral TPH after cyclic loading. This is likely due to the increased rigidity of BPS compared to TPH leading to a "softer" transition between the TPH construct and native anatomy at the supra-adjacent level. Facet capsule compromise led to a 49.9% increase in UIV+1 motion, underscoring the importance of preserving the posterior ligamentous complex. Clinical studies that account for fusion rates are warranted to determine if constructs with a "soft transition" result in less proximal junctional kyphosis in vivo .