Effects of a new shape-memory alloy interspinous process device on pressure distribution of the intervertebral disc and zygapophyseal joints in vitro.
OBJECTIVE
To quantify the pressure distribution of lumbar intervertebral discs and zygapophyseal joints with different degrees of distraction of the interspinous processes by using a new shape-memory interspinous process stabilization device, and to research the relationship between changing disc and zygapophyseal joint loads and the degree of distraction of interspinous processes, and thus optimize usage of the implant.


METHODS
Six cadaver lumbar specimens (L(2)-L(5)) were loaded. The loads in disc and zygapophyseal joints were recorded at each L(3-4) disc level. Implants with different spacer heights were then placed by turn and the pressure measurements repeated.


RESULTS
An implant with 10 mm spacer height does not significantly share the load. A 12 mm implant reduces the posterior annulus load, and meanwhile decreases the zygapophyseal joints pressure, but only in extension. A 14 mm implant shares the loads of posterior annulus, nucleus, and zygapophyseal joints in extension and the neutral position, but slightly increases the anterior annulus' load. Though 16-20 mm implants do decrease the loads in the posterior annulus and zygapophyseal joints, the anterior annulus' load was apparently increased.


CONCLUSIONS
Different degrees of distraction of the interspinous processes lead to different load distribution on the intervertebral disc. The implant tested is not appropriate in cases of serious spinal stenosis because of the contradiction that, while over-distraction of the interspinous processes decreases the posterior annulus and the zygapophyseal joints load and distracts the intervertebral foramina, it leads to a marked increase in the load of the anterior annulus, which is recognized to accelerate disc degeneration.
Department of Orthopaedic Surgery, Nanjing First Hospital Affiliated to Nanjing Medical University, Nanjing Medical University, Nanjing, China.
Qing-qiang
QQ
Yao
Sheng-nai
SN
Zheng
Li
L
Cheng
Peng
P
Yuan
Dong-sheng
DS
Zhang
Xiang-wen
XW
Liao
Yan
Y
Xu
Li-ming
LM
Wang
D000497:Alloys; D001696:Biomechanical Phenomena; D006801:Humans; D066298:In Vitro Techniques; D007403:Intervertebral Disc / Q000502:physiology*; D055959:Intervertebral Disc Degeneration / Q000150:complications / Q000601:surgery; D008159:Lumbar Vertebrae / Q000502:physiology*; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000295:instrumentation*; D011312:Pressure; D019736:Prostheses and Implants; D011474:Prosthesis Design; D013130:Spinal Stenosis / Q000209:etiology / Q000601:surgery; D016474:Weight-Bearing; D021801:Zygapophyseal Joint / Q000502:physiology*
D000497:Alloys