Kinematics of the Cervical Spine After Unilateral Facet Fracture: An In Vitro Cadaver Study.
METHODS
Biomechanical study utilizing human cadaveric cervical spines.


OBJECTIVE
To quantitatively assess the effects on intervertebral motion of isolated unilateral cervical facet fracture, and after disruption of the intervertebral disc at the same level.


BACKGROUND
Clinical evidence has indirectly suggested that cervical facet fractures involving 40% of the height of the lateral mass can cause instability of the involved segment. No study to date has demonstrated the kinematic effects of such an injury in a cadaveric model of the cervical spine.


METHODS
Nine six-segment cervical spines were defrosted and fixated to a spine motion simulator capable to apply unconstrained bending moments in the three anatomical planes. The spines were subjected to a maximum torque of 2 N · m in flexion, extension, left and right lateral bending, and of 4 N · m in left and right axial rotation. Each spine was tested in the intact configuration (INTACT), and following two increasing degrees of injury at C4-C5: fracture of the facet (CF1), and CF1 with disruption of the intervertebral disc at the same level (CF2). Intervertebral kinematics was tracked via clusters of active markers fixated on each vertebra. Differences in kinematics between INTACT and the two injured configurations were assessed via one-way Analysis of Variance (P < 0.05).


RESULTS
No significant differences were detected between INTACT and CF1 across all kinematic parameters (P > 0.05) at C4-C5. CF2, however, resulted in significant increase of flexion, left axial rotation, and left lateral bending with respect to INTACT (flexion at C4-C5: INTACT = 8.7° ± 3.5°; CF2 = 14.3 ± 5.7; P < 0.05).


CONCLUSIONS
Our findings suggest that superior articular facet fractures alone involving 40% of the lateral mass may not necessarily result in intervertebral instability under physiologic loading conditions. The addition of partial injury to the intervertebral disc, however, resulted in statistically significant increase in angular displacement.


METHODS
N /A.
Movement Analysis Laboratory, Istituto Ortopedico Rizzoli, Bologna, Italy.
Paolo
P
Caravaggi
Joint Motion Laboratory, Department of Orthopedics, Rutgers University-New Jersey Medical School, Newark, NJ.
Linda
L
Chen
Joint Motion Laboratory, Department of Orthopedics, Rutgers University-New Jersey Medical School, Newark, NJ.
Linda
L
Uko
Joint Motion Laboratory, Department of Orthopedics, Rutgers University-New Jersey Medical School, Newark, NJ.
Andres
A
Zorrilla
Joint Motion Laboratory, Department of Orthopedics, Rutgers University-New Jersey Medical School, Newark, NJ.
Spencer
S
Hauser
Joint Motion Laboratory, Department of Orthopedics, Rutgers University-New Jersey Medical School, Newark, NJ.
Michael J
MJ
Vives
D001696:Biomechanical Phenomena / Q000502:physiology*; D002574:Cervical Vertebrae / Q000293:injuries / Q000502:physiology; D006801:Humans; D007403:Intervertebral Disc / Q000503:physiopathology; D016059:Range of Motion, Articular / Q000502:physiology; D016103:Spinal Fractures / Q000503:physiopathology*