Circumferential dynamic stabilization of the lumbar spine: a biomechanical analysis.
OBJECTIVE
To assess segmental angulation and mobility following implantation of the Charité artificial disc in combination with the posterior dynamic fixation device dynamic stabilization system (DSS) and the interspinous spacer Coflex at the L4-L5 segment, respectively.


METHODS
Six human L4-L5 specimens were loaded with pure moments of ±7.5 Nm in flexion/extension, lateral bending, and axial rotation in a custom-made spine tester. The testing protocol was as follows: (a) intact condition, (b) destabilization by resection of the anterior longitudinal ligament (ALL), (c) implantation of the Charité with retained posterior longitudinal ligament (PLL), (d) supplemental DSS implantation, (e) removal of DSS rods and PLL resection, (f) DSS rod re-implantation, (g) enlargement of rod length, and (h) removal of DSS and implantation of Coflex. Range of motion (ROM), neutral zone, and segmental angulation were determined.


RESULTS
ALL resection did not influence significantly ROM. TDR increased lateral bending and axial rotation only after resection of the PLL, whereas flexion/extension remained unchanged. DSS limited all degrees of freedom prior to and after PLL resection. Rod length enlargement had no significant effect. Coflex limited significantly flexion/extension compared to the intact state and TDR, whereas lateral bending and axial rotation remained unchanged. TDR increased lordosis, whereas Coflex had a substantial kyphosing effect.


CONCLUSIONS
This study demonstrates that posterior dynamic stabilization in combination with TDR reduces flexion/extension ROM and segmental lordosis in a monosegmental biomechanical model.
Department of Orthopaedic Surgery, University of Ulm Medical School, Oberer Eselsberg 45, 89081, Ulm, Germany, wkaefer@westpfalz-klinikum.de.
Wolfram
W
Käfer
Balkan
B
Cakir
Stefan
S
Midderhoff
Heiko
H
Reichel
Hans-Joachim
HJ
Wilke
D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D019299:Decompression, Surgical / Q000295:instrumentation; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000601:surgery; D055959:Intervertebral Disc Degeneration / Q000601:surgery; D007593:Joint Instability / Q000601:surgery; D007738:Kyphosis / Q000209:etiology; D008141:Lordosis / Q000209:etiology; D008159:Lumbar Vertebrae / Q000502:physiology / Q000601:surgery*; D008297:Male; D008422:Materials Testing; D008875:Middle Aged; D008954:Models, Biological; D019736:Prostheses and Implants; D016059:Range of Motion, Articular; D012399:Rotation; D059145:Total Disc Replacement / Q000295:instrumentation