Calculation of dynamic spinal ligament deformation.
OBJECTIVE
Previous methods to determine spinal ligament deformation have included either custom-designed transducers or computational methods using rigid body transformation of kinematic data. Goals of the present study were to describe a computational methodology to determine dynamic deformations of an arbitrarily oriented ligament in a spine specimen and its associated errors.


METHODS
Calculation of ligament deformation in a spinal segment with vertebral motion tracking flags utilized digital stereophotography, lateral neutral posture radiograph, and detailed quantitative anatomy to develop geometrical relationships between flag markers and ligament attachment points. A custom jig, consisting of two flags each with four markers, was constructed to quantify errors associated with computed ligament deformation, flag marker translation, and flag rotation.


RESULTS
Average error in ligament deformation was dependent upon motion direction and ranged between 0.03 mm (SD 0.45 mm) and 0.28 mm (SD 0.18 mm). Average error for flag marker translation ranged between 0.02 mm (SD 0.14 mm) and 0.11 mm (SD 0.39 mm), and for flag rotation ranged between -0.06 degrees (SD 0.17 degrees ) and 0.07 degrees (SD 0.12 degrees ).


CONCLUSIONS
Accuracy of the present technique was equivalent to or greater than that of previous methods. The present technique utilized relatively cost-effective digital stereophotography, and may be used to calculate strain in ligaments not readily accessible for transducer application. The methodology has wide-spread applicability for analyses of dynamic or static spinal or other ligament strains, and may be used to determine spinal canal and intervertebral foramen narrowing and area reduction.
Ivancic
Paul C
PC
Biomechanics Research Laboratory, Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
Wang
Jaw-Lin
JL
Panjabi
Manohar M
MM
D001696:Biomechanical Phenomena; D005471:Fluoroscopy; D006801:Humans; D017846:Longitudinal Ligaments / Q000033:anatomy & histology / Q000293:injuries / Q000502:physiology; D008962:Models, Theoretical; D010781:Photography / Q000379:methods; D013124:Spinal Injuries / Q000175:diagnosis* / Q000503:physiopathology; D014159:Transducers