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The effect of soft-tissue restraints after type II odontoid fractures in the elderly: a biomechanical study
C Maxwell J McCabe1, Stewart D McLachlin, Stewart I Bailey
1Division of Orthopaedics, Department of Surgery, The University of Western Ontario, London, Ontario, Canada.
Study Design:
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.
Summary Of Background Data:
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.
Conclusion:
This study identifies that type II odontoid fractures without associated soft-tissue injury may be stable under certain loading modes.