Influence of graft size on spinal instability with anterior cervical plate fixation following in vitro flexion-distraction injuries.
BACKGROUND
Anterior cervical discectomy and fusion with plating (ACDFP) is commonly used for the treatment of distractive-flexion cervical spine injuries. Despite the prevalence of ACDFP, there is little biomechanical evidence for graft height selection in the unstable trauma scenario.


OBJECTIVE
This study aimed to investigate whether changes in graft height affect the kinematics of instrumented ACDFP C5-C6 motion segments in the context of varying degrees of simulated facet injuries.


METHODS
In vitro cadaveric biomechanical study was used as study design.


METHODS
Seven C5-C6 motion segments were mounted in a custom spine simulator and taken through flexibility testing in axial rotation, lateral flexion, and flexion-extension. Specimens were first tested intact, followed by a standardized injury model (SIM) for a unilateral facet perch at C5-C6. The stability of the ACDFP approach was then examined with three graft heights (computed tomography-measured disc space height, disc space height undersized by 2.5 mm, and disc space height oversized by 2.5 mm) within three increasing unstable injuries (SIM, an added unilateral facet fracture, and a simulated bilateral facet dislocation injury).


RESULTS
In all motions, regardless of graft size, ACDFP reduced range of motion (ROM) from the SIM state. For flexion-extension, the oversized graft had a larger decrease in ROM compared with the other graft sizes (p<.05). Between graft sizes and injury states, there were a number of interactions in axial rotation and lateral flexion, where specifically in the most severe injury, the undersized graft had a larger decrease in ROM than the other two sizes (p<.05).


CONCLUSIONS
This study found that graft size did affect the kinematic stability of ACDFP in a series of distractive-flexion injuries; the undersized graft resulted in both facet overlap and locking of the uncovertebral joints leading to decreased ROM in lateral bending and axial rotation, whereas an oversized graft provided larger ROM decreases in flexion-extension. As such, a graft that engages the uncovertebral joint may be more advantageous in providing a rigid environment for fusion with ACDFP.
Division of Orthopaedics, Department of Surgery, Western University, London, ON, Canada.
Reina
R
Yao
Jack McBain Biomechanical Testing Laboratory, Thompson Engineering Building, Western University, London, ON, Canada; Department of Mechanical and Materials Engineering, Western University, London, ON, Canada.
Stewart D
SD
McLachlin
Division of Orthopaedics, Department of Surgery, Western University, London, ON, Canada.
Parham
P
Rasoulinejad
Division of Orthopaedics, Department of Surgery, Western University, London, ON, Canada; London Spine Centre, London Health Sciences Centre, London, ON, Canada.
Kevin R
KR
Gurr
Division of Orthopaedics, Department of Surgery, Western University, London, ON, Canada; London Spine Centre, London Health Sciences Centre, London, ON, Canada.
Fawaz
F
Siddiqi
Division of Orthopaedics, Department of Surgery, Western University, London, ON, Canada; Jack McBain Biomechanical Testing Laboratory, Thompson Engineering Building, Western University, London, ON, Canada; Department of Mechanical and Materials Engineering, Western University, London, ON, Canada.
Cynthia E
CE
Dunning
Division of Orthopaedics, Department of Surgery, Western University, London, ON, Canada; London Spine Centre, London Health Sciences Centre, London, ON, Canada. Electronic address: chris.bailey@lhsc.on.ca.
Christopher S
CS
Bailey
D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001860:Bone Plates / Q000009:adverse effects; D002102:Cadaver; D002574:Cervical Vertebrae / Q000601:surgery*; D017586:Diskectomy / Q000009:adverse effects / Q000379:methods*; D006801:Humans; D007593:Joint Instability / Q000209:etiology*; D008875:Middle Aged; D011183:Postoperative Complications; D016059:Range of Motion, Articular; D012399:Rotation; D013124:Spinal Injuries / Q000601:surgery*
Anterior instrumentation; Cervical spine biomechanics; Facet injury; Graft height