Juay-Seng Tan

University of British Columbia - Vancouver, Vancouver, British Columbia, Canada

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Publications (6)14.24 Total impact

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    ABSTRACT: An in vitro cadaveric study comparing different implant fixation techniques using a repeated measures design. To compare the effects of cement augmentation of pedicle screws and extension of posterior fixation on (i) 3-dimensional stabilization, and (ii) adjacent level effects in the aging spine. Device loosening and adjacent level effects are concerns in implant fixation in the elderly spine. Extension of posterior fixation and cement augmentation of pedicle screws have not been previously compared with respect to stabilization and adjacent level effects. Twelve T9 to L3 cadaveric specimens were tested in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) with applied pure moments of +/-5 Nm. A T11 corpectomy was reconstructed with a vertebral body replacement device and T10 to T12 posterior instrumentation. Further stabilization was provided by posterior rod extension to L1 (flexible or rigid rods) and/or cement augmentation of T12 and L1 screws. The effects of cement augmentation and posterior rod extension on intersegmental motion were compared using the hybrid flexibility-stiffness protocol. Two-way repeated measures ANOVA and SNK post hoc tests (99% significance level) were used. Range of motion at the corpectomy T10 to T12 levels significantly decreased after cement augmentation (AR 43%, LB 71%, FE 68%), and posterior rod extension (rigid rods: AR 26%, LB 64%, FE 57%) (flexible rods: AR 16%, LB 53%, FE 39%). Posterior rod extension significantly reduced range of motion at the rod extension level. Motion at the distal noninstrumented L1 to L2 level was increased significantly by posterior rod extension and cement augmentation. There were however, smaller magnitudes of increase in motion across L1 to L2 level with flexible rod and cement augmentation (AR 12%, LB 45%, FE 31%). Cement augmentation of pedicle screws resulted in the most stable vertebral reconstruction, whereas flexible rod extension minimized changes in range of motion at both adjacent rod extension and distal noninstrumented levels.
    Spine 01/2009; 33(25):2728-40. DOI:10.1097/BRS.0b013e318188b2e4 · 2.30 Impact Factor
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    ABSTRACT: An in vitro cadaveric study comparing cage-vertebra interface strengths for 3 different screw-cement configurations. To determine the effects of cement augmentation of pedicle screws on cage-vertebra interface failure properties for 2 interbody device shapes (elliptical or cloverleaf); and to compare between pedicle and anterior vertebral body screws with cement augmentation. Pedicle or anterior screw fixation is commonly used with interbody device fixation. Cement has recently been shown to augment screw fixation in the osteoporotic spine by improving the screw-bone interface strength. The effect of cement augmentation of pedicle or anterior screws on cage-vertebra interface properties has not been previously studied or compared. An elliptical or a cloverleaf-shaped indentor covering 40% of the endplate was axially compressed against the superior endplate of 48 thoracolumbar vertebrae. Each vertebra had polymethylmethacrylate cement augmentation of 1) anterior screws, 2) pedicle screws, or 3) pedicle screws without cement. Compressive load was applied through a mechanism that allowed unconstrained rotation of the indentors. Cement augmentation of pedicle screws resulted in significantly higher failure loads (54%) and failure strength (69%) for both shaped indentors when compared with uncemented pedicle screws. There was no significant difference in failure load and failure strength between pedicle and anterior screws with cement augmentation. Indentor shape was not a significant factor on failure load or failure strength. Cage-vertebra interface properties were improved when cement was used to augment vertebral and pedicle screws. Cement augmentation of pedicle or anterior screws may reduce interbody device subsidence.
    Spine 03/2007; 32(3):334-41. DOI:10.1097/01.brs.0000253645.24141.21 · 2.30 Impact Factor
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    ABSTRACT: The wrist is a common fracture site for both young and older adults. The purpose of this study was to compare wrist kinematics in backward and forward falls with different fall protective responses. We carried out within-subject comparison of impact velocities and maximum velocities during descent of the distal radius among three different fall configurations: (a) backward falls with knees flexed, (b) backward falls with knees extended and (c) forward falls with knees flexed. We also examined the effect of fall configuration on fall durations, elbow flexion, trunk flexion and forearm angles at impact. Forward falls resulted in smaller impact velocities of the distal radius, longer fall duration, longer braking duration, greater elbow flexion and more horizontal landing position of the forearm compared to backward falls. The distal radius impact velocity during forward falls (1.33 m/s) was significantly lower than in backward falls, and among the backward falls the impact velocity of the flexed knee strategy (2.01 m/s) was significantly lower than the extended knee strategy (2.27 m/s). These impact velocities were significantly reduced from the maximum velocities observed during descent (forward falls=3.57 m/s, backward falls with knee flexed=3.16 m/s, backward falls with knees extended=3.52 m/s). We conclude that (1) smaller impact velocities of the wrists in forward falls could imply a lower fracture risk compared to backward falls, and (2) fall protective responses reduced wrist impact velocities in all fall directions.
    Journal of Biomechanics 02/2006; 39(10):1804-11. DOI:10.1016/j.jbiomech.2005.05.016 · 2.75 Impact Factor
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    ABSTRACT: A biomechanical investigation using a human cadaver, multisegmental lumbosacral spine model. To determine if 2 small, posterolaterally positioned titanium mesh interbody cages would provide superior construct strength and stiffness in compression compared to central cage placement. In addition, determine construct stiffness with interbody cages as opposed to an intact spine and assess the effect of bone mineral density (BMD). Previous work has shown that the posterolateral corners of the lumbosacral endplates are stronger than the anterior and central regions. Information to suggest appropriate interbody cage positioning to avoid subsidence into adjacent vertebrae would be valuable for spine surgeons and implant designers. A total of 27 functional spinal units from L3 to S1 were dual x-ray absorptiometry scanned for BMD, instrumented with pedicle screw systems, and tested to failure in compression with titanium mesh interbody cages placed in 1 of 3 positions: 2 small posterolateral, 2 small central, or 1 large central. Analysis of covariance was conducted to compare failure load and stiffness across the different cage configurations. Repeated measures analysis of variance was used to analyze stiffness between functional spinal units with intact disc, discectomy, or interbody cages. Failure load was correlated against BMD. Of the 3 placement patterns, 2 small titanium mesh cages in the posterolateral corners had 20% higher failure loads, although the difference was not significant (P = 0.20). Stiffness in compression for the 3 cage positions was not significantly different (P = 0.82). All intact discs with posterior instrumentation were significantly stiffer than any of the cage patterns (P = 0.0001). BMD of the vertebrae significantly correlated with failure loads (P = 0.007). The placement of 2 small interbody cages posterolaterally tended to result in higher failure loads than central cage placement, although the results were not statistically significant. It is noteworthy that cage placement in any position resulted in a less stiff construct in compression than with an intact disc.
    Spine 11/2005; 30(19):E556-61. DOI:10.1097/01.brs.0000181053.38677.c2 · 2.30 Impact Factor
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    ABSTRACT: An in vitro cadaveric study to compare compressive failure load, strength, and stiffness of the implant-vertebra interface. To determine the effect of cage shape (kidney, cloverleaf, or oval) and cage surface area on endplate failure strength and secondly to determine the extent and pattern of trabecular failure adjacent to an interbody device. Recent studies indicate that the posterolateral and peripheral regions of the endplate are stronger than the central. Current implants are not designed to take advantage of these stronger regions of the endplate. The zone of trabecular failure that results from interbody device subsidence has not been reported extensively in the literature. Uniaxial compression testing with unrestricted rotation was carried out on the superior endplates of 48 thoracolumbar (T9-L2) vertebrae with 1 of 3 shaped indentors covering 20% or 40% of the endplate area. Failure load, failure strength, and stiffness were compared. Quantitative computed tomography scans were carried out before and following indentation tests to identify areas of trabecular densification that indicate localized failure. The cloverleaf-shaped indentors resulted in significantly higher (P < 0.001) failure loads (by >45%), strength (>49%), and construct stiffness (>35%) for both the 20% and 40% cross-sectional area sizes. Trabecular bone failure occurred in a semielliptical zone underlying the interbody devices, leaving the endplate and underlying cancellous bone intact. The cloverleaf-shaped indentor displayed an improved strength and stiffness profile when compared to oval or kidney-shaped indentors of similar surface areas.
    Spine 04/2005; 30(6):638-44. DOI:10.1097/01.brs.0000155419.24198.35 · 2.30 Impact Factor
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    ABSTRACT: A biomechanical study addressing the motion of pedicle screws in a human cadaveric, osteoporotic spine model. To compare the fixation of pedicle screws in an osteoporotic spine model after augmentation with laminar hooks, sublaminar wires, or calcium phosphate cement and to determine the kinematic patterns of these screws. Numerous techniques exist for improving the quality of fixation within the osteoporotic spine, including supplementing the construct with laminar hooks, sublaminar wires, or calcium phosphate cement. Direct comparisons of these practices, however, are lacking. METHODS.: Twenty-four cadaveric lumbar vertebrae were instrumented with a pedicle screw and rod construct augmented with laminar hooks, sublaminar wires, or calcium phosphate cement. The screws were tested cyclically with physiologic loads. Rigid body motions of the screws were measured using an optoelectronic camera system, and the motion at the screw tip and at the screw head were calculated. Screw motions were compared using nonparametric paired statistical analysis. Between augmentation groups, there were no significant differences in the magnitude of motion at the screw head and at the screw tip. After calcium phosphate cement supplementation, screw motion was predominantly rotational in nature, whereas rigid body translation of the screw was more common with sublaminar wires or laminar hooks. The three augmentation techniques were similar in their ability to enhance the rigidity of fixation of the pedicle screws. Differences did exist, however, in the patterns of pedicle screw motion, with the calcium phosphate cement augmentation resulting in less rigid body translation than the other two techniques.
    Spine 09/2004; 29(16):1723-30. DOI:10.1097/01.BRS.0000134569.63542.49 · 2.30 Impact Factor

Publication Stats

139 Citations
14.24 Total Impact Points

Top Journals


  • 2005-2009
    • University of British Columbia - Vancouver
      • • Department of Mechanical Engineering
      • • Department of Orthopaedics
      Vancouver, British Columbia, Canada