Can A Novel Rectangular Footplate Provide Higher Resistance to Subsidence Than Circular Footplates? An Ex Vivo Biomechanical Study
ABSTRACT Ex vivo biomechanical evaluation using cadaveric vertebral bodies.
To compare the subsidence characteristics of a novel rectangular footplate design with a conventional circular footplate design.
Cage subsidence is a postoperative complication after reconstruction of corpectomy defects in the thoracolumbar spine and depends on factors, such as bone quality, adjunctive fixation, and the relationship between the footplate on the cage and the vertebral body endplate.
Twenty-four cadaveric vertebrae (T12-L5) were disarticulated, potted in a commercial resin, loaded with either a circular or a rectangular footplate, and tested in a servo hydraulic testing machine. Twelve vertebral bodies were loaded with a circular footplate, and after subsidence the same vertebral bodies were loaded with a rectangular footplate. The second set of 12 vertebral bodies was loaded with a rectangular footplate only. Force-displacement curves were developed for the 3 groups, and the ultimate load to failure and stiffness values were calculated.
The ultimate load to failure with the circular footplate was 1310 N (SD, 482). The ultimate load to failure with a rectangular footplate with a central defect and without a central defect was 1636 N (SD, 513) and 2481 N (SD, 1191), respectively. The stiffness of the constructs with circular footplate was 473 N/mm (SD, 205). The stiffness of the constructs with a rectangular footplate with a central defect and without a central defect was 754 N/mm (SD, 217) and 1054 N/mm (SD, 329), respectively.
A rectangular footplate design is more resistant to subsidence than a circular footplate design in an ex vivo biomechanical model. The new design had higher load to failure even in the presence of a central defect. These findings suggest that rectangular footplates may provide better subsidence resistance when used to reconstruct defects after thoracolumbar corpectomy.
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ABSTRACT: Corpectomy cages with rectangular endcaps utilize the stronger peripheral part of the endplate, potentially decreasing subsidence risk. The authors evaluated cage subsidence during cyclic biomechanical testing, comparing rectangular versus round endcaps. Fourteen cadaveric spinal segments (T12-L2) were dissected and potted at T12 and L2, then assigned to a rectangular (n=7) or round (n=7) endcap group. An L1 corpectomy was performed and under uniform conditions a cage/plate construct was cyclically tested in a servo-hydraulic frame with increasing load magnitude. Testing was terminated if the test machine actuator displacement exceeded 6mm, or the specimen completed cyclic loading at 2400N. Number of cycles, compressive force and force-cycles product at test completion were all greater in the rectangular endcap group compared with the round endcap group (cycles: 3027 versus 2092 cycles; force: 1943N versus 1533N; force-cycles product: 6162kN·cycles versus 3973kN·cycles), however these differences were not statistically significant (p⩾0.076). After normalizing for individual specimen bone mineral density, the same measures increased to a greater extent with the rectangular endcaps (cycles: 3014 versus 1855 cycles; force: 1944N versus 1444N; force-cycles product: 6040kN·cycles versus 2980kN·cycles), and all differences were significant (p⩽0.030). The rectangular endcap expandable corpectomy cage displayed increased resistance to subsidence over the round endcap cage under cyclic loading as demonstrated by the larger number of cycles, maximum load and force-cycles product at test completion. This suggests rectangular endcaps will be less susceptible to subsidence than the round endcap design.Journal of Clinical Neuroscience 05/2014; 21(9). DOI:10.1016/j.jocn.2013.12.028 · 1.32 Impact Factor
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ABSTRACT: Over the past decade, the minimally disruptive lateral transpsoas approach for lumbar interbody fusion (MI-LIF) is increasingly being used as an alternative to conventional surgical approaches. The purpose of this review was to evaluate four primary questions as they relate to MI-LIF: (1) Is there an anatomical justification for MI-LIF at L4-5? (2) What are the complication and outcome profiles of MI-LIF and are they acceptable with respect to conventional approaches? (3) Given technical and neuromonitoring differences between various MI-LIF procedures, are there any published clinical differences? And, (4) are modern minimally disruptive procedures (e.g., MI-LIF) economically viable? Through a MEDLINE and Google Scholar search, a total of 237 articles that discussed MI-LIF were identified. Of those, topical areas included anatomy (22), biomechanics/testing (17), technical descriptions (11), case reports (40), complications (30), clinical and radiographic outcomes (43), deformity (23), trauma or thoracic applications (10), and review articles (41). In answer to the questions posed, (1) there is a high strength of evidence showing MI-LIF to be anatomically justified at all levels of the lumbar spine from L1-2 to L4-5. The evidence also supports the use of advanced neuromonitoring modalities. (2) There is moderate strength evidence in support of reproducible and reasonable complication, side effect, and outcome profiles following MI-LIF which may be technique dependent. (3) There is low-strength evidence that shows elevated neural complication rates in non-traditional (e.g., shallow-docking approaches and/or those without specialized neuromonitoring) MI-LIF, and (4) there is low- to moderate-strength evidence that modern minimally disruptive surgical approaches are cost-effective. There is considerable published evidence to support MI-LIF in spinal fusion and advanced applications, though the results of some reports, especially concerning complications, vary greatly depending on technique and instrumentation used. Additional cost-effectiveness analyses would assist in fully understanding the long-term implications of MI-LIF.European Spine Journal 04/2015; 24(S3). DOI:10.1007/s00586-015-3886-1 · 2.47 Impact Factor