Limitations of the cervical porcine spine in evaluating spinal implants in comparison with human cervical spinal segments: a biomechanical in vitro comparison of porcine and human cervical spine specimens with different instrumentation techniques.
METHODS
Porcine and human cervical spine specimens were in vitro biomechanically compared with different instrumentation techniques.


OBJECTIVE
To evaluate whether subaxial porcine cervical spines are a valid model for implant testing in a single level corpectomy.


BACKGROUND
Biomechanical in vitro tests are widely used for implant tests, mainly with human spine specimens. The availability of human cadavers is limited and the properties of the specimen regarding age, bone mineral density, and grade of degenerative changes is inhomogeneous.


METHODS
Six porcine and six human cervical specimens were loaded nondestructively with pure moments: 1) in an intact state; 2) after a corpectomy of C5 and substitution by a cage with integrated force sensor; 3) after additional instrumentation with a posterior screw and rod system with: a) lateral mass and b) pedicle screws; 4) after instrumentation with an anterior plate; and 5) with a circumferential instrumentation. The unconstrained motion and the axial loads occurring in the corpectomy gap were measured, as well as the bone mineral density of the specimen before testing.


RESULTS
The range of motion in the intact state, as well as for the different instrumentations, was comparable for flexion-extension. In lateral bending and axial rotation, marked differences in the intact state as well as for pedicle screw instrumentations occurred.


CONCLUSIONS
The subaxial porcine cervical spine is a potential model in flexion-extension because of its biomechanical similarity. For lateral bending and axial rotation, the marked differences severly restrict the comparability.
Schmidt
René
R
Department of Orthopedics and SCI, University of Ulm, Ulm, Germany. rene.schmidt@gmx.de
Richter
Marcus
M
Claes
Lutz
L
Puhl
Wolfhart
W
Wilke
Hans-Joachim
HJ
D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001696:Biomechanical Phenomena / Q000379:methods; D002574:Cervical Vertebrae / Q000502:physiology / Q000601:surgery*; D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D016268:Internal Fixators; D008297:Male; D008422:Materials Testing; D023421:Models, Animal; D019736:Prostheses and Implants; D016059:Range of Motion, Articular / Q000502:physiology; D013045:Species Specificity; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D013552:Swine