Browsing by Author "Transfeldt E.E."

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    Biomechanical comparison of a two-level Maverick disc replacement with a hybrid one-level disc replacement and one-level anterior lumbar interbody fusion
    (2009) Erkan S.; Rivera Y.; Wu C.; Mehbod A.A.; Transfeldt E.E.
    Background context: Multilevel lumbar disc disease (MLDD) is a common finding in many patients. Surgical solutions for MLDD include fusion or disc replacement. The hybrid model, combining fusion and disc replacement, is a potential alternative for patients who require surgical intervention at both L5-S1 and L4-L5. The indications for this hybrid model could be posterior element insufficiency, severe facet pathology, calcified ligamentum flavum, and subarticular disease confirming spinal stenosis at L5-S1 level, or previous fusion surgery at L5-S1 and new symptomatic pathology at L4-L5. Biomechanical data of the hybrid model with the Maverick disc and anterior fusion are not available in the literature. Purpose: To compare the biomechanical properties of a two-level Maverick disc replacement at L4-L5, L5-S1, and a hybrid model consisting of an L4-L5 Maverick disc replacement with an L5-S1 anterior lumbar interbody fusion using multidirectional flexibility test. Study design: An in vitro human cadaveric biomechanical study. Methods: Six fresh human cadaveric lumbar specimens (L4-S1) were subjected to unconstrained load in axial torsion (AT), lateral bending (LB), flexion (F), extension (E), and flexion-extension (FE) using multidirectional flexibility test. Four surgical treatments-intact, one-level Maverick at L5-S1, two-level Maverick between L4 and S1, and the hybrid model (anterior fusion at L5-S1 and Maverick at L4-L5) were tested in sequential order. The range of motion of each treatment was calculated. Results: The Maverick disc replacement slightly reduced intact motion in AT and LB at both levels. The total FE motion was similar to the intact motion. However, the E motion is significantly increased (approximately 50% higher) and F motion is significantly decreased (30%-50% lower). The anterior fusion using a cage and anterior plate significantly reduced spinal motion compared with the condition (p<.05). No significant differences were found between two-level Maverick disc prosthesis and the hybrid model in terms of all motion types at L4-L5 level (p>.05). Conclusion: The Maverick disc preserved total motion but altered the motion pattern of the intact condition. This result is similar to unconstrained devices such as Charité. The motion at L4-L5 of the hybrid model is similar to that of two-level Maverick disc replacement. The fusion procedure using an anterior plate significantly reduced intact motion. Clinical studies are recommended to validate the efficacy of the hybrid model. © 2009 Elsevier Inc. All rights reserved.
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    Alignment of pedicle screws with pilot holes: Can tapping improve screw trajectory in thoracic spines?
    (2010) Erkan S.; Hsu B.; Wu C.; Mehbod A.A.; Perl J.; Transfeldt E.E.
    Pedicle screws are placed using pilot holes. The trajectory of pilot holes can be verified by pedicle sounding or radiographs. However, a pilot hole alone does not insure that the screw will follow the pilot hole. No studies have characterized the risk of misalignment of a pedicle screw with respect to its pilot hole trajectory. The objective of this study was to measure the misalignment angles between pedicle screws and pilot holes with or without tapping. Six human cadaveric thoracic spines were used. One hundred and forty pilot holes were created with a straight probe. Steel wires were temporarily inserted and their positions were recorded with CT scans. The left pedicles were tapped with 4.5 mm fluted tap and the right pedicles remained untapped. Pedicle screws (5.5 mm) were inserted into the tapped and untapped pedicles followed by CT scans. The trajectories of pilot holes and screws were calculated using three-dimensional vector analysis. A total of 133 pilot holes (95%) were inside pedicles. For the untapped side, 14 out of 68 (20%) screws did not follow the pilot holes and were outside the pedicles. For the tapped side, 2 out of 65 (3%) did not follow and breached the pedicles. The average misalignment angles between the screw and pilot hole trajectory were 7.7° ± 6.5° and 5.6° ± 3.2° for the untapped side and tapped side, respectively (P < 0.05). Most pedicle screws had lateral screw breach (13 out of 16) whereas most pilot holes had medial pedicle breach (6 out of 7). Tapping of pilot holes (1 mm undertap) helps align pedicle screws and reduces the risk of screw malposition. Although most pedicle screws had lateral breach, the risk of medial pedicle breach of the pilot holes must be recognized. © 2009 Springer-Verlag.
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    Biomechanical comparison of transpedicular versus extrapedicular vertebroplasty using polymethylmethacrylate
    (2010) Erkan S.; Wu C.; Mehbod A.A.; Cho W.; Transfeldt E.E.
    Study Design: An in vitro biomechanical study using osteoporotic cadaveric vertebrae. Objective: To compare the biomechanics of transpedicular and extrapedicular approaches in polymethylmethacrylate vertebroplasty in terms of height restoration, strength, and stiffness. Summary Background Data: Cement is typically injected through a transpedicular approach in both vertebroplasty and kyphoplasty procedures. Previous biomechanical studies were primarily focused on the transpedicular approach. Extrapedicular approach has been recently developed to provide more symmetric cement filling and has good clinical results. However, no biomechanical data are available to compare these 2 techniques. Methods: Twenty-four osteoporotic vertebral bodies were randomly divided into 2 groups for either transpedicular or extrapedicular vertebroplasty. Six lumbar and 6 thoracic vertebrae were used for each group. Each vertebral body was compressed by 25% of its original height and its strength and stiffness were measured. The vertebral bodies were treated with polymethylmethacrylate using either transpedicular or extrapedicular approach. The height restoration was measured before the treated vertebrae were recompressed to determine posttreatment strength and stiffness. Results: Both techniques increased vertebral strength by approximately 50% of the intact strength. There was no statistical difference in posttreatment strength between these 2 techniques. However, the transpedicular technique had higher stiffness recovery (70% to 80%) from the intact stiffness than the extrapedicular technique (60%). The extrapedicular approach achieved greater height restoration in thoracic vertebrae. Conclusions: Both extrapedicular and transpedicular techniques increased strength but reduced stiffness compared with the intact condition. The extrapedicular technique achieved greater height restoration possibly attributed to its easier access to the fracture site. These biomechanical data provide useful information when selecting an approach for cement injection in vertebroplasty procedures. Copyright © 2010 by Lippincott Williams & Wilkins.