Design and Biomechanical Analysis of Dynamic External Skeletal Fixator with Arthrodiatasis for Upper Extremity
Date Issued
2009
Date
2009
Author(s)
Shih, Kao-Shang
Abstract
Abstract The external fixators have been used for the treatments of the fractures in the elbow joint and wrist joint of the upper extremity. The clinical practices using the commercial external fixators were performed and the positive results were reported in this thesis. Other than the commercial fixators of which we reviewed the function, we also proposed our conceptual design of the fixator with the arthrodiatasis. Several biomechanical analyses were performed based on the fixator of our design. Firstly we analysis the effect of the pin placement and the elbow angle on the hinge-alignment of the elbow fixator. From the kinematic viewpoint, the bone-fixator construct forms a closed linkage system. For the traditional static fixator, previous study demonstrated numerically that the placement of the fixing pins and the initial condition at the fracture site significantly restrained the fracture reduction and fixator adjustability. For the hinged dynamic fixator, the functions of joint distraction and hinge alignment might be closely related to some devices (e.g. fixator design), surgery (e.g. pin placement), and joint factors (e.g. elbow angle). In our parametric analysis of the bridged elbow-fixator linkage system under various initial configurations, there are multiple solutions to achieve hinge alignment which prevent the concerns that when only a unique solution exists for the hinge alignment, the arthrodiatasis inevitably becomes a highly technique-demanding surgery for setting the initial configuration of the bone-pin-fixator construct. Secondly we evaluated the effects of elbow angle and pin deflection on the concentric distraction and distraction loss of the elbow-fixator-pin construct since it is of clinical importance to clarify the loss between distracted distance of the articular surfaces and fixator’s distractor(s) for surgery planning. We deployed four finite-element elbow models with the unilaterally hinged fixator and stiffened periarticular tissues. The distraction values from the fixator distractor and fixing pins to the stiffened elbow, along the specified load-transferring path, were calculated and compared on both humeral and ulnar sides and thus improved the use of the elbow hinged fixator with arthrodiatasis. Thirdly we performed the kinemtic analysis to evaluate the influence of the pin locations and insertion angle to the hinge alignment of the bridging wrist joint fixator via the principle of homogeneous transformation matrix. The pin placement variables were parametrically changed to analyze their kinematic limitations. The numerical results were validated by the trigonometric model and computerized simulation. The influences of the pin placements were also evaluated with Taguchi method. The bone pin locations and orientations under different scenarios obtained from HTM analysis can be a good reference for the surgical application in the practical surgery. The current study demonstrated that the adequate pin placement and optimal fixator design which provided the hinge alignment function were critical for the postoperative bridged wrist motion.
Subjects
arthrodiatasis
external fixators
hinge alignment
distraction loss
Type
thesis
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