A revisitation of distractive-extension injuries of the subaxial cervical spine: a cadaveric and radiographic soft tissue analysis.
METHODS
A biomechanical cadaveric and radiographic analyses.


OBJECTIVE
To identify and elaborate on specific anatomic soft tissue structures that are injured during various stages of a distractive-extension (DE) injury of the lower cervical spine and their role in angulation and posterior translation.


BACKGROUND
Two DE stages (DES) of injury to the cervical spine have been described as follows: DES-1 and DES-2. However, the role of the soft tissue structures involved in such injuries has not been clearly defined. Furthermore, the importance of the facet capsules in DES injuries has not been well-addressed.


METHODS
A total of 15 adult cadaveric motion segments of the lower cervical spine were isolated and tested. Motion segments were mounted, with the cervical spine in extension, such that a distractive load was applied through the cephalad body. Anatomic supporting structures were serially sectioned from anterior to posterior to simulate varying degrees of soft-tissue disruption as occurring with the DE mechanism. Specimens were loaded at each stage of injury and measurements of angulation and posterior translation were recorded from fluoroscopic images by 2 independent observers.


RESULTS
A strong correlation was noted between the 2 sets of independent measurements. A statistical significant difference was noted between the degree of soft-tissue injury to the change in angulation and posterior translation (P < 0.001). The mean change in angulation and posterior translation was significantly greatest following sectioning of the anterior aspect of the facet capsules and to a lesser extent following sectioning of the posterior longitudinal ligament (PLL) (P < 0.001). A greater mean percent change between sequential sectioning of soft tissue structures was largely associated with posterior translation rather than angulation.


CONCLUSIONS
Sequentially greater angulation and posterior translation was seen after serial sectioning of the anterior facet capsule and to a lesser degree the PLL. This suggests that there are in fact 2 main "tethers" to angulation and posterior translation in the DE injury model, with the anterior facet capsule being the major stabilizer and to a lesser degree the PLL. Thus, based on our findings, it would appear that an expansion of the DE injury classification may be warranted, based on angulation and posterior translation, and regarded as DES-1, DES-2A, DES-2B, and DES-3. Such categorization based on the degree of angulation and posterior translation may prove advantageous in designing appropriate treatment strategies to address DE injuries of the lower cervical spine; however, further studies are needed to validate the clinical applications of such categorization.
Samartzis
Dino
D
Department of Orthopaedics and Traumatology, University of Hong Kong, Hong Kong, SAR China.
Wein
Scott M
SM
Shen
Francis H
FH
Beazell
James
J
Francke
Erick I
EI
Anderson
David G
DG
D000328:Adult; D001696:Biomechanical Phenomena; D002102:Cadaver; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging* / Q000293:injuries / Q000503:physiopathology; D006801:Humans; D007403:Intervertebral Disc / Q000000981:diagnostic imaging / Q000293:injuries; D004204:Joint Dislocations / Q000150:complications / Q000000981:diagnostic imaging* / Q000503:physiopathology; D007593:Joint Instability / Q000000981:diagnostic imaging / Q000209:etiology* / Q000503:physiopathology; D017846:Longitudinal Ligaments / Q000000981:diagnostic imaging / Q000293:injuries; D011859:Radiography; D016059:Range of Motion, Articular; D017695:Soft Tissue Injuries / Q000000981:diagnostic imaging* / Q000503:physiopathology; D013314:Stress, Mechanical; D016474:Weight-Bearing