Phillip M Reyes

Barrow Neurological Institute, Phoenix, Arizona, United States

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Publications (24)50.44 Total impact

  • Marco T Reis, Phillip M Reyes, Neil R Crawford
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    ABSTRACT: A new anchored cervical interbody PEEK spacer was devised that uses only 2 integrated variable angle screws diagonally into the adjacent vertebral bodies instead of the established device that uses 4 diagonal fixed-angle screws. To compare in vitro the stability provided by the new 2-screw interbody spacer to that of the 4-screw spacer and a 4-screw anterior plate plus independent PEEK spacer. Three groups of cadaveric specimens were tested with 2-screw anchored cage (N=8), 4-screw anchored cage (N=8), and standard plate/cage (N=16). Pure moments (1.5Nm) were applied to induce flexion, extension, lateral bending, and axial rotation while measuring 3-D motion optoelectronically. In all three groups, the mean range of motion (ROM) and lax zone (LZ) were significantly reduced relative to intact after discectomy and fixation. The 2-screw anchored cage allowed significantly greater ROM (p<0.05) than the standard plate during flexion, extension, and axial rotation and allowed significantly greater ROM than the 4-screw cage during extension and axial rotation. The 4-screw anchored cage did not allow significantly different ROM or LZ than the standard plate during any loading mode. The 2-screw variable angle anchored cage significantly reduces ROM relative to intact. Greater stability can be achieved, especially during extension and axial rotation, by using the 4-screw cage or standard plate plus cage.
    Neurosurgery 03/2014; · 2.53 Impact Factor
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    ABSTRACT: Sacroiliac (SI) joint pain has become a recognized factor in low back pain. The purpose of this study was to investigate the effect of a minimally invasive surgical SI joint fusion procedure on the in vitro biomechanics of the SI joint before and after cyclic loading.
    Medical devices (Auckland, N.Z.). 01/2014; 7:131-7.
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    ABSTRACT: The transforaminal lumbar interbody fusion (TLIF) technique supplements posterior instrumented lumbar spine fusion and has been tested with different types of screw fixation for stabilization. Transforaminal lumbar interbody fusion is usually placed through a unilateral foraminal approach after unilateral facetectomy, although extraforaminal entry allows the facet to be spared. To characterize the biomechanics of L4-L5 lumbar motion segments instrumented with bilateral transfacet pedicle screw (TFPS) fixation versus bilateral pedicle screw-rod (PSR) fixation in the setting of intact facets and native disc or after discectomy and extraforaminal placement of a TLIF technology graft. Human cadaveric lumbar spine segments were biomechanically tested in vitro to provide a nonpaired comparison of four configurations of posterior and interbody instrumentation. Fourteen human cadaveric spine specimens (T12-S1) underwent standard pure moment flexibility tests with intact L4-L5 disc and facets. Seven were studied with intact discs, after TFPS fixation, and then with TLIF and TFPS fixation. The others were studied with intact discs, after PSR fixation, and then combined with extraforaminally placed TLIF. Loads were applied about anatomic axes to induce flexion-extension, lateral bending, and axial rotation. Three-dimensional specimen motion in response to applied loads during flexibility tests was determined. A nonpaired comparison of the four configurations of posterior and interbody instrumentation was made. Transfacet pedicle screw and PSR, with or without TLIF, significantly reduced range of motion during all directions of loading. Transfacet pedicle screw provided greater stability than PSR in all directions of motion except lateral bending. In flexion, TFPS was more stable than PSR (p=.042). A TLIF device provided less stability than the intact disc in constructs with TFPS and PSR. These results suggest that fixation at L4-L5 with TFPS is a promising alternative to PSR, with or without TLIF. A TLIF device was less stable than the native disc with both methods of instrumentation presumably because of a fulcrum effect from a relatively small footplate. Additional interbody support may be considered for improved biomechanics with TLIF.
    The spine journal: official journal of the North American Spine Society 11/2013; · 2.90 Impact Factor
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    ABSTRACT: In vitro nondestructive flexibility testing of the CerviCore total disc replacement (TDR) was performed. It was hypothesized that TDR would not significantly alter biomechanics relative to intact, whereas rigid fixation would cause significant changes. To assess the ability of a cervical metal-on-metal saddle-shaped TDR to replicate normal biomechanics in vitro. Human cadaveric flexibility experiment. Nine human cadaveric C3-T1 specimens were tested intact, after TDR and after anterior plating. Flexion, extension, lateral bending, and axial rotation were induced by pure moments; flexion-extension was then repeated using a simplified muscle force model with 70-N follower load. Optical markers measured three-dimensional intervertebral motion, and eight points of laminar surface strain were recorded near the left and right C5-C6 facet joints. Biomechanical parameters studied included range of motion (ROM), lax zone (LZ), angular coupling pattern, sagittal instantaneous axis of rotation (IAR), and facet loads normal to the facet joint plane. Mean values of parameters were compared statistically using repeated measures analysis of variance and Holm-Sidak tests. Total disc replacement caused significant reduction in ROM during extension (p=.004) and significant reduction in LZ during lateral bending (p=.01). However, plating significantly reduced both ROM and LZ during flexion, extension, and lateral bending (p<.006). Sagittal IAR shifted relative to intact by 3.6 mm after TDR (p>.05) and 6.5 mm after plating (p>.05). Coupled axial rotation/degree lateral bending was 99% of intact after TDR but 76% of intact after plating (p=.15). Coupled lateral bending/degree axial rotation was 95% of intact after TDR but 85% of intact after plating (p=.43). Neither construct altered facet loads from intact. With regard to ROM, LZ, IAR, and coupling, deviations from intact biomechanics were less substantial after TDR than after plating. Facet load alterations were minimal with either construct. Our results show that this particular TDR permits ROM and maintains some measures of kinematics in a cadaver model.
    The spine journal: official journal of the North American Spine Society 10/2013; · 2.90 Impact Factor
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    ABSTRACT: BACKGROUND:: Transitioning from rigid to flexible hardware at the distal rostral or caudal lumbar or lumbosacral level hypothetically maintains motion at the transition level and protects the transition level and intact adjacent levels from stresses caused by fusion. OBJECTIVE:: To biomechanically compare transitional and rigid constructs to uninstrumented specimens in vitro. METHODS:: Human cadaveric L2-S1 segments were tested (1) intact, (2) after L5-S1 rigid pedicle screw-rod fixation, (3) after L4-S1 rigid pedicle screw-rod fixation, and (4) after hybrid fixation rigidly spanning L5-S1 and dynamically spanning L4-L5. Pure moments (maximum 7.5 Nm) induced flexion, extension, lateral bending, and axial rotation while motion was recorded optoelectronically. Additionally, specimens were studied in flexion/extension with a 400-N compressive follower load. Strain gauges on laminae were used to extract facet loads. RESULTS:: The range of motion (ROM) at the transition segment (L4-L5) for the hybrid construct was significantly less than for the intact condition and significantly greater than for the rigid 2-level construct during lateral bending and axial rotation but not during flexion or extension. Sagittal axis of rotation at L4-L5 shifted significantly after rigid 2-level or hybrid fixation (p<0.003), but shifted significantly farther posterior and rostral with rigid fixation (p<0.02). Instrumentation altered L4-L5 facet load at more than L3-L4 facet load. CONCLUSION:: The effect of the dynamic rod segment on the kinematics of the transition level was less pronounced than that of a fully rigid construct in vitro using this particular rod system. This experimental model detected no biomechanical alterations at adjacent intact levels with hybrid or rigid systems.
    Neurosurgery 06/2013; · 2.53 Impact Factor
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    ABSTRACT: STUDY DESIGN:: A new experimental protocol was applied utilizing a simplified postural control model. Multiple constructs were tested nondestructively by interconnecting segmental rods to screws. OBJECTIVE:: To investigate how posture and distribution of segmental angles under physiologic loads are affected by combined cervical arthroplasty and fusion. SUMMARY OF BACKGROUND DATA:: Previous studies of biomechanics of multilevel arthroplasty have focused on range of motion and intradiscal pressure. No previous study has investigated postural changes and segmental angle distribution. METHODS:: In seven human cadaveric C3-T1 specimens, C4-C5, C5-C6 and C6-C7 discs were replaced with ProDisc-C (Synthes). Combinations of fusion ("f") adjacent to arthroplasty ("A") were simulated at C4-C5, C5-C6 and C6-C7 respectively: fAA, AfA, AAf, ffA, fAf, Aff, fff. C3-C4 and C7-T1 remained intact. A compressive belt apparatus simulated normal muscle co-contraction and gravitational preload while C3-C4, C4-C5, C5-C6, C6-C7 and C7-T1 motions were tracked independently. Parameters studied were segmental postural compensation, neutral buckling, and shift in sagittal plane instantaneous axis of rotation (IAR). RESULTS:: With one or more levels unfused, the arthroplasty levels preferentially moved toward upright posture before the intact levels. Neutral buckling was greatest for 3-level arthroplasty, less for 2-level arthroplasty, and least for 1-level arthroplasty. Among the three 1-level arthroplasty groups (ffA, fAf, Aff), arthroplasty at the caudalmost level resulted in significantly greater buckling than with arthroplasty rostralmost or at mid-segment (P<0.04, ANOVA/Holm-Sidak). Although IAR location was related to buckling, this correlation did not reach significance (P=0.112). CONCLUSION:: Arthroplasty levels provide the "path of least resistance," through which the initial motion is more likely to occur. The tendency for specimens to buckle under vertical compression became greater with more arthroplasty levels. Buckling appeared more severe with arthroplasty more caudal. Buckling only moderately correlated to shifts in IAR, meaning slight malpositioning of the devices would not necessarily cause buckling.
    Journal of spinal disorders & techniques 05/2013; · 1.21 Impact Factor
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    ABSTRACT: BACKGROUND CONTEXT: Novel dual-threaded screws are configured with overlapping (doubled) threads only in the proximal shaft to improve proximal cortical fixation. PURPOSE: Tests were run to determine whether dual-threaded pedicle screws improve pullout resistance and increase fatigue endurance compared with standard pedicle screws. STUDY DESIGN/SETTING: In vitro strength and fatigue tests were performed in human cadaveric vertebrae and in polyurethane foam test blocks. PATIENT SAMPLE: Seventeen cadaveric lumbar vertebrae (14 pedicles) and 40 test sites in foam blocks were tested. OUTCOME MEASURES: Measures for comparison between standard and dual-threaded screws were bone mineral density (BMD), screw insertion torque, ultimate pullout force, peak load at cyclic failure, and pedicular side of first cyclic failure. METHODS: For each vertebral sample, dual-threaded screws were inserted in one pedicle and single-threaded screws were inserted in the opposite pedicle while recording insertion torque. In seven vertebrae, axial pullout tests were performed. In 10 vertebrae, orthogonal loads were cycled at increasing peak values until toggle exceeded threshold for failure. Insertion torque and pullout force were also recorded for screws placed in foam blocks representing healthy or osteoporotic bone porosity. RESULTS: In bone, screw insertion torque was 183% greater with dual-threaded than with standard screws (p<.001). Standard screws pulled out at 93% of the force required to pull out dual-threaded screws (p=.42). Of 10 screws, five reached toggle failure first on the standard screw side, two screws failed first on the dual-threaded side, and three screws failed on both sides during the same round of cycling. In the high-porosity foam, screw insertion torque was 60% greater with the dual-threaded screw than with the standard screw (p=.005), but 14% less with the low-porosity foam (p=.07). Pullout force was 19% less with the dual-threaded screw than with the standard screw in the high-porosity foam (p=.115), but 6% greater with the dual-threaded screw in the low-porosity foam (p=.156). CONCLUSIONS: Although dual-threaded screws required higher insertion torque than standard screws in bone and low density foam, dual-threaded and standard pedicle screws exhibited equivalent axial pullout and cyclic fatigue endurance. Unlike single-threaded screws, the mechanical performance of dual-threaded screws in bone was relatively independent of BMD. In foam, the mechanical performance of both types of screws was highly dependent on porosity.
    The spine journal: official journal of the North American Spine Society 04/2013; · 2.90 Impact Factor
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    ABSTRACT: Object Endoscopic endonasal approaches to the craniovertebral junction (CVJ) and clivus are increasingly performed for ventral skull-base pathology, but the biomechanical implications of these approaches have not been studied. The aim of this study was to investigate the spinal biomechanics of the CVJ after an inferior-third clivectomy and anterior intradural exposure of the foramen magnum as would be performed in an endonasal endoscopic surgical strategy. Methods Seven upper-cervical human cadaveric specimens (occiput [Oc]-C2) underwent nondestructive biomechanical flexibility testing during flexion-extension, axial rotation, and lateral bending at Oc-C1 and C1-2. Each specimen was tested intact, after an inferior-third clivectomy, and after ligamentous complex dissection simulating a wide intradural exposure using an anterior approach. Angular range of motion (ROM), lax zone, and stiff zone were determined and compared with the intact state. Results Modest, but statistically significant, hypermobility was observed after inferior-third clivectomy and intradural exposure during flexion-extension and axial rotation at Oc-C1. Angular ROM increased incrementally between 6% and 12% in flexion-extension and axial rotation. These increases were primarily the result of changes in the lax zone. No significant changes were noted at C1-2. Conclusions Inferior-third clivectomy and an intradural exposure to the ventral CVJ and foramen magnum resulted in hypermobility at Oc-C1 during flexion-extension and axial rotation. Although the results were statistically significant, the modest degree of hypermobility observed compared with other well-characterized CVJ injuries suggests that occipitocervical stabilization may be unnecessary for most patients.
    Journal of neurosurgery. Spine 02/2013; · 1.61 Impact Factor
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    ABSTRACT: Study Design: Seven different combinations of posterior screw fixation, with or without interbody support, were compared in vitro using nondestructive flexibility tests.Objective: To study the biomechanical behavior of a new cortical screw (CS) fixation construct relative to the traditional pedicle screw (PS) construct.Summary of Background Data: The CS is an alternative to the PS for posterior fixation of the lumbar spine. The CS trajectory is more sagittally and cranially oriented than the PS, being anchored in the pars interarticularis. Like PS fixation, CS fixation uses interconnecting rods fastened with top-locking connectors. Stability after bilateral CS fixation was compared to stability after bilateral PS fixation in the setting of intact disc and with direct lateral interbody fixation (DLIF) or transforaminal lateral interbody fixation (TLIF) support.Methods: Standard nondestructive flexibility tests were performed in cadaveric lumbar specimens, allowing unpaired comparisons of specific conditions from 28 specimens (4 groups of 7) within a larger experiment of multiple hardware configurations. Conditions tested and group from which results originated were (1) intact [all groups], (2) with L3-L4 bilateral PS/rods [Group 1], (3) with bilateral CS/rods [Group 2], (4) with DLIF [Group 3], (5) with DLIF+CS/rods [Group 4], (6) with DLIF+PS/rods [Group 3], (7) with TLIF+CS/rods [Group 2], and (8) with TLIF+PS/rods [Group 2]. To assess spinal stability, the mean range of motion (ROM), lax zone (LZ), and stiff zone (SZ) at L3-L4 were compared during flexion-extension, lateral bending, and axial rotation.Results: With intact disc, stability was equivalent after PS/rod and CS/rod fixation, except that PS/rod fixation was stiffer during axial rotation. With DLIF support, there was no significant difference in stability between PS/rod and CS/rod fixation. With TLIF support, PS/rod fixation was stiffer than CS/rod fixation during lateral bending.Conclusion: Bilateral CS/rod fixation provided about the same stability in cadaveric specimens as PS/rod fixation regardless of the presence of interbody, TLIF, or DLIF support.
    Spine 10/2012; · 2.16 Impact Factor
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    ABSTRACT: The Food and Drug Administration has not cleared the following medical devices for the use described in this study. The following medical devices are being discussed for an off-label use: cervical lateral mass screws. As an alternative for cases in which the anatomy and spatial relationship between C-2 and a vertebral artery precludes insertion of C-2 pedicle/pars or C1-2 transarticular screws, a technique that includes opposing laminar hooks (claw) at C-2 combined with C-1 lateral mass screws may be used. The biomechanical stability of this alternate technique was compared with that of a standard screw-rod technique in vitro. Flexibility tests were performed in 7 specimens (occiput to C-3) in the following 6 different conditions: 1) intact; 2) after creating instability and attaching a posterior cable/graft at C1-2; 3) after removing the graft and attaching a construct comprising C-1 lateral mass screws and C-2 laminar claws; 4) after reattaching the posterior cable-graft at C1-2 (posterior hardware still in place); 5) after removing the posterior cable-graft and laminar hooks and placing C-2 pedicle screws interconnected to C-1 lateral mass screws via rod; and 6) after reattaching the posterior cable-graft at C1-2 (screw-rod construct still in place). All types of stabilization significantly reduced the range of motion, lax zone, and stiff zone compared with the intact condition. There was no significant biomechanical difference in terms of range of motion or lax zone between the screw-rod construct and the screw-claw-rod construct in any direction of loading. The screw-claw-rod technique restricts motion much like the standard Harms technique, making it an acceptable alternative technique when aberrant arterial anatomy precludes the placement of C-2 pars/pedicle screws or C1-2 transarticular screws.
    Journal of neurosurgery. Spine 07/2012; 17(3):220-6. · 1.61 Impact Factor
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    ABSTRACT: In vitro assessment of rib cage biomechanics in the region of true ribs with the ribs intact then sequentially resected in 5 steps. To determine the contribution of the rib cage to thoracic spine stability and kinematics. Previous in vitro studies of rib cage biomechanics have used animal spines or human cadaveric spines with ribs left unsecured, limiting the ability of the ribs to contribute to stability. Eight upper thoracic specimens that included 4 ribs and sternum were tested in special fixtures that disallowed relative movement of the distal ribs and their vertebrae. While applying 7.5 Nm pure moments in 3 planes, angular motion at the middle motion segment was studied in intact specimens and then (1) after splitting the sternum, (2) after removing the sternum, (3) after removing 50% of ribs, (4) after removing 75% of ribs, and (5) after disarticulating and completely removing ribs. During flexion/extension, the sternum and anterior rib cage most contributed to stability. During lateral bending, the posterior rib cage most contributed to stability. During axial rotation, stability was directly related to the proportion of ribs remaining intact. On average, intact ribs accounted for 78% of thoracic stability. An intact rib cage shifted the axis of rotation unpredictably, but its position remained consistent after partial resection of the ribs. During lateral bending, coupled axial rotation was mild and unaffected by ribs. Because of testing methodology, the rib cage accounted for a greater percentage of thoracic stability than previously estimated. Different rib cage structures resisted motion in different loading planes.
    Spine 12/2011; 36(26):E1686-93. · 2.16 Impact Factor
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    ABSTRACT: Most one-level anterior cervical plates use two screws per vertebra (four screws in total). No study has addressed whether a simplified plate using one screw per vertebra is adequate for one-level fixation. To compare stability achieved by four-screw and two-screw plates after discectomy and placement of interbody spacer. Nondestructive multidirectional flexibility tests were performed in three independent groups of cadaveric spines to assess spinal stability after instrumentation. Human cadaveric C4-C7 specimens were tested intact and after discectomy followed by placement of a polyetheretherketone interbody graft and an anterior plate. Rigid two-screw (n=8), semiconstrained four-screw (n=8), and rigid four-screw (n=8) plates were compared. Nonconstraining pure moments were applied under load control (maximum 1.5 Nm) to induce flexion, extension, lateral bending, and axial rotation, whereas vertebral motion was measured optoelectronically. Mean range of motion (ROM) was compared among groups. All three plates significantly reduced ROM relative to normal in all directions of loading (p<.003). Mean ROMs±standard deviation (and corresponding intergroup p value) for rigid two-screw, semiconstrained four-screw, and rigid four-screw plates, respectively, were as follows: flexion: 2.6±2.0°, 1.8±1.1°, 1.8±0.8° (p=.46); extension: 2.5±2.6°, 2.1±1.3°, 1.4±1.3° (p=.45); lateral bending: 1.8±1.0°, 1.3±1.0°, 1.1±0.5° (p=.29); axial rotation: 2.9±1.9°, 1.6±0.9°, 1.5±0.7° (p=.08). Despite a tendency for the rigid two-screw plate to allow more motion than the four-screw plates, there was no significant difference among groups during any loading mode. In terms of immediate postoperative cervical stability after one-level discectomy and placement of an interbody spacer, the rigid two-screw plate performed comparably to conventional rigid four-screw and semiconstrained four-screw plates. Further research on relative fatigue endurance of the different plate types is also needed.
    The spine journal: official journal of the North American Spine Society 03/2011; 11(3):234-40. · 2.90 Impact Factor
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    ABSTRACT: BACKGROUND: Transoral odontoidectomy and resection of the anterior C1 arch destabilize the atlantoaxial joint and risk its stability. OBJECTIVE: To preserve stability in such cases we devised and evaluated a proof-of-concept study. The arch and dens were dissected and decompression was performed on cadavers. The dens was replaced with an odontoid screw, and the C1 arch was replaced with a rib-graft substitute using miniplates. We assessed the biomechanical strength of the C1 ring and 3D occipitoatlantoaxial flexibility before and after the repair. METHODS: Five silicon-injected fixed cadaver heads were dissected. The arch of C1 and dens were preserved and reconstructed using odontoid screws and miniplates. Once the feasibility of the technique was established, we biomechanically tested 6 cadaveric occiput-C2 specimens in 3 phases: (1) intact/normal range of motion (ROM), (2) after transection of dens and C1 arch, and (3) with odontoidoplasty using odontoid screws and C1 arch reconstruction. RESULTS: After odontoidectomy and arch removal, angular ROM increased significantly in all directions of loading. Resection increased flexion-extension at the occiput-C1 and at C1-C2 by 21% and 129%, respectively. Reconstruction slightly increased flexion-extension stability (16% and 107%, respectively) relative to normal. With 70 N applied compression, the C1 ring separation was 1145% greater than normal. After reconstruction, the separation was only 89% greater than normal (statistically significant, P = .002). CONCLUSION: C1 arch reconstruction with or without odontoidoplasty restores only partial angular stability of the atlantoaxial joint but provides restoration of the ability of the C1 lateral masses to resist splaying, often observed as postodontoidectomy cranial settling.
    Neurosurgery 02/2011; 68:ons103-ons113. · 2.53 Impact Factor
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    ABSTRACT: Unstable fractures at the thoracolumbar junction often require extended, posterior, segmental pedicular fixation. Some surgeons have reported good clinical outcomes with short-segment constructs if additional pedicle screws are inserted at the fractured level. The goal of this study was to quantify the biomechanical advantage of the index-level screw in a fracture model. Six human cadaveric T10-L4 specimens were tested. A 3-column injury at L-1 was simulated, and 4 posterior constructs were tested as follows: one-above-one-below (short construct) with/without index-level screws, and two-above-two-below (long construct) with/without index-level screws. Pure moments were applied quasistatically while 3D motion was measured optoelectronically. The range of motion (ROM) and lax zone across T12-L2 were measured during flexion, extension, left and right lateral bending, and left and right axial rotation. All constructs significantly reduced the ROM and lax zone in the fractured specimens. With or without index-level screws, the long-segment constructs provided better immobilization than the short-segment constructs during all loading modes. Adding an index-level screw to the short-segment construct significantly improved stability during flexion and lateral bending; there was no significant improvement in stability when an index-level screw was added to the long-segment construct. Overall, bilateral index-level screws decreased the ROM of the 1-level construct by 25% but decreased the ROM of the 2-level construct by only 3%. In a fracture model, adding index-level pedicle screws to short-segment constructs improves stability, although stability remains less than that provided by long-segment constructs with or without index-level pedicle screws. Therefore, highly unstable fractures likely require extended, long-segment constructs for optimum stability.
    Journal of neurosurgery. Spine 02/2011; 14(2):192-7. · 1.61 Impact Factor
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    ABSTRACT: Posterior screw-rod fixation for thoracic spine trauma usually involves fusion across long segments. Biomechanical data on screw-based short-segment fixation for thoracic fusion are lacking. The authors compared the effects of spanning short and long segments in the thoracic spine. Seven human spine segments (5 segments from T-2 to T-8; 2 segments from T-3 to T-9) were prepared. Pure-moment loading of 6 Nm was applied to induce flexion, extension, lateral bending, and axial rotation while 3D motion was measured optoelectronically. Normal specimens were tested, and then a wedge fracture was created on the middle vertebra after cutting the posterior ligaments. Five conditions of instrumentation were tested, as follows: Step A, 4-level fixation plus cross-link; Step B, 2-level fixation; Step C, 2-level fixation plus cross-link; Step D, 2-level fixation plus screws at fracture site (index); and Step E, 2-level fixation plus index screws plus cross-link. Long-segment fixation restricted 2-level range of motion (ROM) during extension and lateral bending significantly better than the most rigid short-segment construct. Adding index screws in short-segment constructs significantly reduced ROM during flexion, lateral bending, and axial rotation (p < 0.03). A cross-link reduced axial rotation ROM (p = 0.001), not affecting other loading directions (p > 0.4). Thoracic short-segment fixation provides significantly less stability than long-segment fixation for the injury studied. Adding a cross-link to short fixation improved stability only during axial rotation. Adding a screw at the fracture site improved short-segment stability by an average of 25%.
    Journal of neurosurgery. Spine 02/2011; 14(2):226-34. · 1.61 Impact Factor
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    ABSTRACT: Anatomically and biomechanically, the atlantoaxial joint is unique compared with the remainder of the cervical spine. To assess the in vitro stability provided by 2 C2 screw sparing techniques in a destabilized model of the atlantoaxial joint and compare with the gold standard system. The 3-dimensional intervertebral motion of 7 human cadaveric cervical spine specimens was recorded stereophotogrammetrically while applying nonconstraining, nondestructive pure moments during flexion-extension, left and right axial rotation, and left and right lateral bending. Each specimen was tested in the intact state, followed by destabilization (odontoidectomy) and fixation as follows: (1) C1 and C3 lateral mass screws rods with sublaminar wiring of C2 (LC1-C3 + SW), (2) C1 and C3 lateral mass screws rods with a cross-link in the C1-2 interlaminar space (LC1-C3 + CL), (3) C1 and C3 lateral mass screw rods alone (negative control), and (4) C1 lateral mass and C2 pedicle screws rods augmented with C1-2 interspinous wire and graft (LC1-PC2, control group). Compared with the intact spine, each instrumented state significantly stabilized range of motion and lax zone at C1-2 (P < .001, 1-way repeated-measures analysis of variance). LC1-C3 + SW was equivalent to LC1-PC2 during flexion and lateral bending and superior to LC1-C3 + CL during lateral bending, while LC1-C3 + CL was equivalent to LC1-PC2 only during flexion. In all other comparisons, LC1-PC2 was superior to both techniques. From a biomechanical perspective, both C2 screw sparing techniques provided sufficient stability to be regarded as an alternative for C1-2 fixation. However, because normal motion across C2-3 is sacrificed, these constructs should be used in patients with unfavorable anatomy for standard fixations.
    Neurosurgery 12/2010; 67(2 Suppl Operative):422-8. · 2.53 Impact Factor
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    ABSTRACT: Transoral odontoidectomy and resection of the anterior C1 arch destabilize the atlantoaxial joint and risk its stability. To preserve stability in such cases we devised and evaluated a proof-of-concept study. The arch and dens were dissected and decompression was performed on cadavers. The dens was replaced with an odontoid screw, and the C1 arch was replaced with a rib-graft substitute using miniplates. We assessed the biomechanical strength of the C1 ring and 3D occipitoatlantoaxial flexibility before and after the repair. Five silicon-injected fixed cadaver heads were dissected. The arch of C1 and dens were preserved and reconstructed using odontoid screws and miniplates. Once the feasibility of the technique was established, we biomechanically tested 6 cadaveric occiput-C2 specimens in 3 phases: (1) intact/normal range of motion (ROM), (2) after transection of dens and C1 arch, and (3) with odontoidoplasty using odontoid screws and C1 arch reconstruction. After odontoidectomy and arch removal, angular ROM increased significantly in all directions of loading. Resection increased flexion-extension at the occiput-C1 and at C1-C2 by 21% and 129%, respectively. Reconstruction slightly increased flexion-extension stability (16% and 107%, respectively) relative to normal.With 70 N applied compression, the C1 ring separation was 1145% greater than normal. After reconstruction, the separation was only 89% greater than normal (statistically significant, P = .002). C1 arch reconstruction with or without odontoidoplasty restores only partial angular stability of the atlantoaxial joint but provides restoration of the ability of the C1 lateral masses to resist splaying, often observed as postodontoidectomy cranial settling.
    Neurosurgery 12/2010; 68(1 Suppl Operative):103-113; discussion 113. · 2.53 Impact Factor
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    ABSTRACT: The authors investigated the biomechanical properties of transpedicular discectomy in the thoracic spine and compared the effects on spinal stability of a partial and total facetectomy. Human thoracic specimens were tested while intact, after a transpedicular discectomy with partial facetectomy, and after an additional total facetectomy was incorporated. Nonconstraining pure moments were applied under load control (maximum 7.5 Nm) to induce flexion, extension, lateral bending, and axial rotation while spinal motion was measured at T8-9 optoelectronically. The range of motion (ROM) and lax zone were determined in each specimen and compared among conditions. Transpedicular discectomy with and without a total facetectomy significantly increased the ROM and lax zone in all directions of loading compared with the intact spine (p < 0.008). The segmental increase in ROM observed with the transpedicular discectomy was 25%. The additional total facetectomy created an insignificant 3% further increase in ROM compared with medial facetectomy (p > 0.2). Transpedicular discectomy can be performed in the thoracic spine with a modest decrease in stability expected. Because the biomechanical behavior of a total facetectomy is equivalent to that of a medial facetectomy, the additional facet removal may be incorporated without further biomechanical consequences.
    Journal of neurosurgery. Spine 08/2010; 13(2):253-9. · 1.61 Impact Factor
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    ABSTRACT: To study the stability offered by a clamping lumbar interspinous anchor (ISA) for transforaminal lumbar interbody fusion (TLIF). Seven human cadaveric lumbosacral specimens were tested: 1) intact; 2) after placing ISA; 3) after TLIF with ISA; 4) with TLIF, ISA, and unilateral pedicle screws-rod; 5) with TLIF and unilateral pedicle screws-rod (ISA removed); and 6) with TLIF and bilateral pedicle screws-rods. Pure moments (7.5 Nm maximum) were applied in each plane to induce flexion-extension, axial rotation, and lateral bending while recording angular motion optoelectronically. Compression (400 N) was applied while upright foraminal height was measured. All instrumentation reduced angular range of motion (ROM) significantly from normal. The loading modes in which the ISA limited ROM most effectively were flexion and extension, where the ROM allowed was equivalent to that of pedicle screws-rods (P > .08). The ISA was least effective in reducing lateral bending, with this mode reduced to 81% of normal. TLIF with unilateral pedicle screws-rod was the least stable configuration. Addition of the ISA to this construct significantly improved stability during flexion, extension, lateral bending, and axial rotation (P < .008). Constructs that included the ISA increased the foraminal height an average of 0.7 mm more than the other constructs (P < .05). In cadaveric testing, the ISA limits flexion and extension equivalently to pedicle screws-rods. It also increases foraminal height. When used with TLIF, a construct of ISA or ISA plus unilateral pedicle screws-rod may offer an alternative to bilateral pedicle screws-rods for supplemental posterior fixation.
    World Neurosurgery 05/2010; 73(5):572-7. · 1.77 Impact Factor
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    ABSTRACT: An interspinous anchor (ISA) provides fixation to the lumbar spine to facilitate fusion. The biomechanical stability provided by the Aspen ISA was studied in applications utilizing an anterior lumbar interbody fusion (ALIF) construct. Seven human cadaveric L3-S1 specimens were tested in the following states: 1) intact; 2) after placing an ISA at L4-5; 3) after ALIF with an ISA; 4) after ALIF with an ISA and anterior screw/plate fixation system; 5) after removing the ISA (ALIF with plate only); 6) after removing the plate (ALIF only); and 7) after applying bilateral pedicle screws and rods. Pure moments (7.5 Nm maximum) were applied in flexion and extension, lateral bending, and axial rotation while recording angular motion optoelectronically. Changes in angulation as well as foraminal height were also measured. All instrumentation variances except ALIF alone reduced angular range of motion (ROM) significantly from normal in all directions of loading. The ISA was most effective in limiting flexion and extension (25% of normal) and less effective in reducing lateral bending (71% of normal) and axial rotation (71% of normal). Overall, ALIF with an ISA provided stability that was statistically equivalent to ALIF with bilateral pedicle screws and rods. An ISA-augmented ALIF allowed less ROM than plate-augmented ALIF during flexion, extension, and lateral bending. Use of the ISA resulted in flexion at the index level, with a resultant increase in foraminal height. Compensatory extension at the adjacent levels prevented any significant change in overall sagittal balance. When used with ALIF at L4-5, the ISA provides immediate rigid immobilization of the lumbar spine, allowing equivalent ROM to that of a pedicle screw/rod system, and smaller ROM than an anterior plate. When used with ALIF, the ISA may offer an alternative to anterior plate fixation or bilateral pedicle screw/rod constructs.
    Journal of neurosurgery. Spine 04/2010; 12(4):372-80. · 1.61 Impact Factor

Publication Stats

58 Citations
50.44 Total Impact Points

Institutions

  • 2010–2014
    • Barrow Neurological Institute
      • Department of Neurosurgery
      Phoenix, Arizona, United States
    • NorthShore University HealthSystem
      Chicago, Illinois, United States
    • Gaziosmanpasa University
      • Faculty of Medicine
      Dazimon, Tokat, Turkey
  • 2013
    • Florida Atlantic University
      Boca Raton, Florida, United States
  • 2011
    • University of South Florida
      • Morsani College of Medicine
      Tampa, FL, United States
  • 2009
    • Indiana University-Purdue University Indianapolis
      • Department of Neurological Surgery
      Indianapolis, IN, United States
    • Berufsgenossenschaftliche Unfallklinik Frankfurt am Main
      Frankfurt, Hesse, Germany