TY - JOUR
T1 - The effect of anterior-posterior shear on the wear of CHARITI total disc replacement
AU - Vicars, Rachel
AU - Prokopovich, Polina
AU - Brown, Thomas D.
AU - Tipper, Joanne L.
AU - Ingham, Eileen
AU - Fisher, John
AU - Hall, Richard M.
PY - 2012/4/20
Y1 - 2012/4/20
N2 - Study Design. An in vitro study of the wear rates of the CHARITI lumbar total disc replacement (TDR). Objective. To investigate the effect of anterior-posterior shear on the in vitro wear rates of the CHARITI lumbar TDR. Summary of Background Data. Current standards prescribe only 4-degrees of freedom (DOF) inputs for evaluating the in vitro wear of TDRs, despite the functional spinal unit incorporating 6 DOF. Anterior-posterior shear has been highlighted as a significant load, particularly in the lumbar spine. A previous study investigated the effect of an anterior-posterior shear on the ProDisc-L, finding that wear rates were not significantly different from 4-DOF wear tests. Methods. Six CHARITI lumbar discs were mounted in a 5 active DOF spine wear simulator and tested under 4-DOF (ISO18192) conditions. Six further CHARITI lumbar discs were tested under 5-DOF conditions, consisting of 4-DOF conditions plus an anterior-posterior shear displacement of +2/-1.5 mm. The displacement was decreased and then increased by a factor of 2 to investigate the effect of the magnitude of displacement. Micro-computed tomographic scans of the discs were taken before and after wear testing, and the height loss of the discs was calculated. These were compared with the same measurements taken from explanted CHARITI discs, micro-computed tomography scanned at another institution. Results. Wear rates for 4 DOF (12.2 ± 1.0 mg/MC) were not significantly different from 4-DOF tests on the ProDisc-L. Wear rates were significantly increased (P < 0.01) for "standard" 5-DOF conditions (22.3 ± 2.0 mg/MC), decreased 5 DOF (24.3 ± 4.9 mg/MC), and increased 5 DOF (29.1 ± 7.6 mg/MC). The height loss of the explants and in vitro tested discs were not significantly different (P > 0.05). Conclusion. The addition of anterior-posterior shear to wear testing inputs of the CHARITI lumbar TDR increases the wear rate significantly, which is in direct contrast to the previous 5-DOF testing on the ProDisc. This study highlights the importance of clinically relevant testing regimens, and that test inputs may be different for dissimilar design philosophies.
AB - Study Design. An in vitro study of the wear rates of the CHARITI lumbar total disc replacement (TDR). Objective. To investigate the effect of anterior-posterior shear on the in vitro wear rates of the CHARITI lumbar TDR. Summary of Background Data. Current standards prescribe only 4-degrees of freedom (DOF) inputs for evaluating the in vitro wear of TDRs, despite the functional spinal unit incorporating 6 DOF. Anterior-posterior shear has been highlighted as a significant load, particularly in the lumbar spine. A previous study investigated the effect of an anterior-posterior shear on the ProDisc-L, finding that wear rates were not significantly different from 4-DOF wear tests. Methods. Six CHARITI lumbar discs were mounted in a 5 active DOF spine wear simulator and tested under 4-DOF (ISO18192) conditions. Six further CHARITI lumbar discs were tested under 5-DOF conditions, consisting of 4-DOF conditions plus an anterior-posterior shear displacement of +2/-1.5 mm. The displacement was decreased and then increased by a factor of 2 to investigate the effect of the magnitude of displacement. Micro-computed tomographic scans of the discs were taken before and after wear testing, and the height loss of the discs was calculated. These were compared with the same measurements taken from explanted CHARITI discs, micro-computed tomography scanned at another institution. Results. Wear rates for 4 DOF (12.2 ± 1.0 mg/MC) were not significantly different from 4-DOF tests on the ProDisc-L. Wear rates were significantly increased (P < 0.01) for "standard" 5-DOF conditions (22.3 ± 2.0 mg/MC), decreased 5 DOF (24.3 ± 4.9 mg/MC), and increased 5 DOF (29.1 ± 7.6 mg/MC). The height loss of the explants and in vitro tested discs were not significantly different (P > 0.05). Conclusion. The addition of anterior-posterior shear to wear testing inputs of the CHARITI lumbar TDR increases the wear rate significantly, which is in direct contrast to the previous 5-DOF testing on the ProDisc. This study highlights the importance of clinically relevant testing regimens, and that test inputs may be different for dissimilar design philosophies.
KW - CHARITÉ
KW - Intervertebral disc replacement
KW - total disc replacement
KW - wear
UR - http://www.scopus.com/inward/record.url?scp=84860350519&partnerID=8YFLogxK
U2 - 10.1097/BRS.0b013e31823cbd6e
DO - 10.1097/BRS.0b013e31823cbd6e
M3 - Article
C2 - 22037530
AN - SCOPUS:84860350519
SN - 0362-2436
VL - 37
SP - E528-E534
JO - Spine
JF - Spine
IS - 9
ER -