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Objective To test the following hypotheses: (i) anterior cervical discetomy and fusion ( ACDF) using stand-alone interbody spacers will significantly reduce the range of motion from intact spine; and (ii) the use of a static or a rotational-dynamic plate will significantly augment the stability of stand-alone interbody spacers, with similar beneficial effect when compared to each other. Methods Eleven human cadaveric subaxial cervical spines (age: 48.2 ± 5.4 years) were tested under the following sequence: (i) intact spine; (ii) ACDF at C4- C5 using a stand-alone interbody spacer; (iii) ACDF at C5- C6 and insertion of an interbody spacer (two-level construct); and (iv) randomized placement of either a two-level locking static plate or a rotational-dynamic plate. Results Insertion of stand-alone cage at C4- C5 and C5- C6 caused a significant decrease in the range of motion compared to intact spine ( P < 0.05). Placement of both the locking and the rotational dynamic plate further reduced the range of motion at C4- C5 and C5- C6 compared to stand-alone cage ( P < 0.01). No significant differences in range of motion restriction at either C4- C5 or C5- C6 were found when the two plating systems were compared ( P > 0.05). Conclusions Cervical stand-alone interbody spacers caused significant restriction in the range of motion. Both plates significantly augmented the stability of stand-alone interbody spacers, with similar stabilizing effect. [ABSTRACT FROM AUTHOR]

ABSTRACT MRI allows non-invasive assessment of intervertebral disc degeneration with the added clinical benefit of using non-ionizing radiation. What has remained unclear is the relationship between assessed disc degeneration and lumbar spine kinematics. Kinematic outcomes of 54 multi-segment (L1-Sacrum) lumbar spine specimens were calculated to discover if such an underlying relationship exists with degeneration assessed using the Pfirrmann grading system. Further analyses were also conducted to determine if kinematic outcomes were affected by motion segment level, gender or applied compressive preload. Range of motion, hysteresis, high flexibility zone size and rotational stiffness in flexion-extension, lateral bending and axial rotation were the kinematic outcomes. Caudal intervertebral discs in our study sample were more degenerative than cranial discs. L5-S1 discs had the largest flexion-extension range of motion ( p < 0.005) and L1-L2 discs the lowest flexion high flexibility zone size ( p < 0.013). No other strict cranial-caudal differences in kinematic outcomes were found. Low flexibility zone rotational stiffness increased with disc degeneration grade in extension, lateral bending and axial rotation ( p < 0.001). Trends towards higher hysteresis and lower range of motion with increased degeneration were observed in flexion-extension and lateral bending. Applied compressive preload increased flexion-extension hysteresis and augmented the effect of degeneration on hysteresis ( p < 0.0005). Female specimens had about one degree larger range of motion in all rotational modes, and higher flexion extension hysteresis ( p = 0.016). These results suggest that gender differences exist in lumbar spine kinematics. Additionally high disc loads, applied compressive preload or applied moment, are needed to kinematically distinguish discs with different levels of degeneration. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1389-1398, 2016. [ABSTRACT FROM AUTHOR]

The article presents an evidence-based medicine approach in determining the factors that may affect the result of lumbar artificial disc replacement. Questions were asked about patient selection issues, surgical placement accuracy, and evidence that motion preservation affects degeneration history and the answers were ranked according to level of evidence. Results suggest that the existing evidence does not offer definite answers in questions about factors that may affect the outcome.