Mechanism of cervical spinal cord injury during bilateral facet dislocation.
METHODS
An in vitro biomechanical study.


OBJECTIVE
The objectives were to: quantify dynamic canal pinch diameter (CPD) narrowing during simulated bilateral facet dislocation of a cervical functional spinal unit model with muscle force replication, determine if peak dynamic CPD narrowing exceeded that observed post-trauma, and evaluate dynamic cord compression.


BACKGROUND
Previous biomechanical models are limited to quasi-static loading or manual ligament transection. No studies have comprehensively analyzed dynamic CPD narrowing during simulated dislocation.


METHODS
Bilateral facet dislocation was simulated using 10 cervical functional spinal units (C3-C4: n = 4; C5-C6: n = 3; C7-T1: n = 3) with muscle force replication by frontal impact of the lower vertebra. Rigid body transformation of kinematic data recorded optically was used to compute the CPD in neutral posture (before dislocation), during dynamic impact (peak during dislocation), and post-impact (flexion rotation = 0(0) degrees ). Peak dynamic impact and post-impact CPD narrowing were statistically compared.


RESULTS
Average peak dynamic impact CPD narrowing significantly exceeded (P < 0.05) post-impact narrowing and occurred as early as 71.0 ms following impact. The greatest dynamic impact narrowing of 7.2 mm was observed at C3-C4, followed by 6.4 mm at C5-C6, and 5.1 mm at C7-T1, with average occurrence times ranging between 71.0 ms at C7-T1 and 97.0 ms at C5-C6.


CONCLUSIONS
Extrapolation of the present results indicated dynamic spinal cord compression of up to 88% in those with stenotic canals and 35% in those with normal canal diameters. These results are consistent with the wide range of neurologic injury severity observed clinically due to bilateral facet dislocation.
Ivancic
Paul C
PC
Biomechanics Research Laboratory, Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT 06520-8071, USA. paul.ivancic@yale.edu
Pearson
Adam M
AM
Tominaga
Yasuhiro
Y
Simpson
Andrew K
AK
Yue
James J
JJ
Panjabi
Manohar M
MM
D000368:Aged; D001696:Biomechanical Phenomena; D002102:Cadaver; D002574:Cervical Vertebrae / Q000293:injuries* / Q000473:pathology / Q000503:physiopathology; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D004204:Joint Dislocations / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D013117:Spinal Cord Compression / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D013119:Spinal Cord Injuries / Q000209:etiology / Q000473:pathology / Q000503:physiopathology*; D013124:Spinal Injuries / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D013130:Spinal Stenosis / Q000150:complications / Q000473:pathology / Q000503:physiopathology; D013314:Stress, Mechanical; D016474:Weight-Bearing / Q000502:physiology; D021801:Zygapophyseal Joint / Q000293:injuries* / Q000473:pathology / Q000503:physiopathology