Date of Award

12-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Program

Biomedical Engineering and Imaging

Research Advisor

Denis J. Diangelo, Ph.D.

Committee

Richard John Kasser, Ph.D. Brian P. Kelly, Ph.D. Gladius Lewis, Ph.D. John Williams, Ph.D.

Keywords

Arthrodesis, Biomechanics, Bone plate, Bone screws, Coordinate frame Talonavicular

Abstract

Introduction: Talonavicular fusion is a surgery used for treating many hind foot pathologies. A problem associated with the procedure is non-union which may be due to inadequate stabilization. The objective of our study was to compare the effect of two surgical fixation techniques on the motion and biomechanics of the talonavicular joint in a human cadaveric foot model.

Materials and Methods: Thirteen human cadaveric foot specimens were prepared, mounted in a multi-axis programmable robot, and loaded using four loading scenarios. Each of the four loading scenarios consisted of a constant Achilles tendon load of 350N followed by either internal or external rotation (moment limit 10Nm) and a compressive load (load limit 850N) applied to the specimens either sequentially after rotation or simultaneously with the rotation. Each specimen was thus subjected to four tests - internal rotation sequential test, internal rotation simultaneous test, external rotation sequential test and external rotation simultaneous test. Each foot specimen was tested in intact state and retested after fixation using either a locked compression plate plus one screw or two screws. Six specimens (plate screw group) received the plate plus a lag screw, where the screw was inserted in a retrograde manner. Seven specimens (two screw group) received two lag screws, both inserted in retrograde manner. Three dimensional targets were fixed to the talus and navicular bones and the motion of the targets was tracked using an optoelectrical camera. The motion was analyzed at a point located in the talonavicular joint space. The relative translational and rotational motions between the two bones were analyzed in two different coordinate frames: one aligned with the anatomical planes (sagittal, coronal and transverse planes) of the body (camera frame) and another aligned with the talonavicular joint (joint frame). The relative translations were compared statistically using three factor ANOVA with a mixed model.

Results: In the joint frame, talonavicular motion for the plate screw group relative to intact state showed significantly reduced translation along the long axis of the talus during internal rotation sequential test (0.9mm versus 1.8mm), internal rotation simultaneous test (1.4mm versus 2.0mm), and external rotation simultaneous test (0.9mm versus 1.9mm). When the translations were analyzed in the camera frame, no statistically significant differences were observed. When the relative rotations were analyzed in the joint frame, the plate screw group showed significantly reduced flexion-extension motion as compared to the two screws group during the external rotation sequential test (0.6degrees versus 2.5degrees) and the external rotation simultaneous test (1.0degrees versus 3.0degrees). When the same rotations were analyzed in the camera frame, the plate screw group showed highly significant restriction of flexion extension the external rotation sequential test (0.4degrees versus 2.5degrees) and the external rotation simultaneous test (0.7degrees versus 3.0degrees).

Conclusion: A human cadaveric foot model was developed to study talonavicular joint biomechanics. The study provided insight into the motion and mechanics of the talonavicular joint and investigated the capability of different surgical fixation techniques to immobilize the talonavicular joint. Compared to two screws, a plate and screw was more effective at preventing separation between the bones along the long axis of the talus, as well as preventing flexion-extension at the talonavicular joint, which should lead to a higher rate of talonavicular joint fusion and reduce the incidence of non-union. The method of transforming the talonavicular motion into its joint coordinate frame (as opposed to an anatomical coordinate frame) highlighted the ability of the plate and screw to prevent joint motion. The method developed in the study provided a better understanding of the local joint biomechanics and can be used to study other joints as well as joint fixation or instrumentation techniques.

DOI

10.21007/etd.cghs.2010.0109

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