A preliminary biomechanical evaluation in a simulated spinal fusion model. Laboratory investigation.
OBJECTIVE
A preliminary in vitro biomechanical study was conducted to determine if the pressure at a bone graft-mortise interface and the load transmitted along a ventral cervical plate could be used as parameters to assess fusion status.


METHODS
An interbody bone graft and a ventral plate were placed at the C3-4 motion segment in six fresh cadaveric goat spines. Polymethylmethacrylate (PMMA) was used to simulate early bone fusion at the bone graft site. The loads along the plate and the simultaneous pressures induced at the graft-endplate interfaces were monitored during simulated stages of bone healing. Each specimen was nondestructively tested in compression loading while the pressures and loads at the graft site were recorded continuously. Each specimen was tested under five conditions (Disc, Graft, Plate, PMMA, and Removal).


RESULTS
The pressure at the interface of the bone graft and vertebral endplate did not change significantly with the addition of the ventral plate. The interface pressure and segmental stiffness did increase following PMMA augmentation of the bone graft (simulating an intermediate phase of bone fusion). The load transmitted along the ventral plate in compression increased after the addition of the bone graft, but decreased after PMMA augmentation. Thus, there was an increase in pressure at the graft-endplate interface and a decrease in load transferred along the ventral plate after the simulation of bone fusion. Upon removal of the ventral plate, the simulated fusion bore most of the axial load, thus explaining a further increase in graft site pressure.


CONCLUSIONS
These observations support the notions of load sharing and the redistribution of loads occurring during and after bone graft incorporation. In the clinical setting, these parameters may be useful in the assessment of fusion after spine surgery. Although feasibility has been demonstrated in this preliminary study, further research is needed.
Ferrara
Lisa A
LA
Spine Research Laboratory, Cleveland Clinic Spine Institute Ohio, USA. lisa@orthokinetic.com
Gordon
Illya
I
Coquillette
Madeline
M
Milks
Ryan
R
Fleischman
Aaron J
AJ
Roy
Shuvo
S
Goel
Vijay K
VK
Benzel
Edward C
EC
D000818:Animals; D001860:Bone Plates; D002102:Cadaver; D002574:Cervical Vertebrae; D006041:Goats; D023421:Models, Animal; D019904:Polymethyl Methacrylate; D011312:Pressure; D013123:Spinal Fusion / Q000379:methods*; D013314:Stress, Mechanical; D016474:Weight-Bearing / Q000502:physiology
D019904:Polymethyl Methacrylate