Biomechanical evaluation of surgical constructs for stabilization of cervical teardrop fractures.
BACKGROUND
Cervical flexion teardrop fractures (CFTF) are highly unstable injuries, and the optimal internal fixation construct is not always clearly indicated.


OBJECTIVE
The purpose of the current study was to determine whether the type of fixation construct (anterior, posterior, or combined) or number of joint levels involved in fixation (one or two) affected the relative stability of a CFTF injury at C5-C6.


METHODS
Human cadaveric cervical spine specimens were mechanically tested under displacement control in the intact state and after creation of CFTF at C5-C6 with stabilization using five different instrumentation constructs. Joint stiffness and intervertebral translation of the constructs were compared with the intact state and normalized (instrumented/intact) to assess relative differences across the five constructs.


METHODS
Spine specimens were mechanically tested in the intact state during flexion, extension, lateral bending, and axial rotation. CFTF was created at C5-C6 by creating an osteotomy at C5 and transecting the posterior ligaments and intervertebral disc. Specimens were tested with anterior, posterior, and combined single-level constructs (C5-C6). Then, a corpectomy was performed at C5, and specimens were retested with the two-level constructs (C4-C6; anterior and anterior-posterior). Joint stiffness and intervertebral translations were computed.


RESULTS
All five fixation constructs resulted in joint stability that was as good as or better than that of the intact specimens. Relative stiffness of the constructs differed depending upon the motion type considered, though the two-level anterior-posterior construct typically provided the greatest stability. Intervertebral translation along the major axis was reduced the most for both of the combined instrumentation systems, although there were few changes in total intervertebral translation across the five constructs.


CONCLUSIONS
All five constructs restored stability comparable to that of the intact specimens. The significance of the relative differences in constructs for the in vivo spine is unclear and warrants further clinical investigation.
Ianuzzi
Allyson
A
Department of Biomedical Engineering, Stony Brook University, HSC T18-030, Stony Brook, NY 11794, USA.
Zambrano
Isidoro
I
Tataria
Jigar
J
Ameerally
Azeema
A
Agulnick
Marc
M
Goodwin
Jesse S Little
JS
Stephen
Mark
M
Khalsa
Partap S
PS
D002574:Cervical Vertebrae / Q000293:injuries*; D004548:Elasticity; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D016268:Internal Fixators; D007593:Joint Instability / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular; D016103:Spinal Fractures / Q000601:surgery*; D014102:Torsion Abnormality