The effect of soft-tissue restraints after type II odontoid fractures in the elderly: a biomechanical study.
METHODS
A biomechanical analysis of soft-tissue restraints to passive motion in odontoid fractures.


OBJECTIVE
To quantify the role of the C1-C2 facet joint capsules and anterior longitudinal ligaments (ALLs) in the setting of a type II odontoid fracture in the elderly.


BACKGROUND
The odontoid process itself is the primary stabilizer at the C1-C2 level; however, little is known about the role of the soft-tissue structures that remain intact in the setting of an odontoid fracture after a low-energy mechanism.


METHODS
Ten cadaveric C0-C2 spinal segments were studied. Specimens were tested under simulated axial rotation with an applied moment of ±1 Nm and with an application of a 10 N anteriorly directed force to the body of C2 to induce sagittal translation. Optical motion data were initially collected for the intact state and after a simulated dens fracture. The specimens were then divided into 2 groups, where 1 group underwent unilateral and then bilateral C1-C2 facet capsular injuries followed by an ALL injury. The second group underwent the ALL injury before the same capsular injuries. Changes in axial range of motion and C1-C2 translation were analyzed using 2-way repeated measures analyses of variance and post hoc Student-Newman-Keuls tests (α = 0.05).


RESULTS
In axial rotation, there was an increase in range of motion by approximately 13%, with the fracture of the dens compared with the intact state (P < 0.05). An increase was also present for each subsequent soft-tissue injury state compared with the previous (P < 0.05); however, there was no difference found between the 2 sectioning protocols. For sagittal translation testing, it was found that the odontoid fracture alone showed an increase of 3 mm of C1-C2 translation compared with intact (P < 0.05). Further soft-tissue injuries did not show an increase until the complete injury state.


CONCLUSIONS
This study identifies that type II odontoid fractures without associated soft-tissue injury may be stable under certain loading modes.
Division of Orthopaedics, Department of Surgery, The University of Western Ontario, London, Ontario, Canada.
C Maxwell J
CM
McCabe
Stewart D
SD
McLachlin
Stewart I
SI
Bailey
Kevin R
KR
Gurr
Christopher S
CS
Bailey
Cynthia E
CE
Dunning
D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D002574:Cervical Vertebrae / Q000293:injuries; D050723:Fractures, Bone / Q000150:complications*; D006801:Humans; D008022:Ligaments / Q000293:injuries; D009809:Odontoid Process / Q000293:injuries*; D012149:Restraint, Physical; D012399:Rotation; D017695:Soft Tissue Injuries / Q000209:etiology* / Q000517:prevention & control*