Kinematic analysis of engagement and bending capabilities of a point-of-care, incremental skeletal fixation plate bending system

Abstract

The current standard of care for skeletal reconstruction surgery is to join skeletal disunions with fixation plates and these plates are most commonly fit to bones through manual bending. The bending procedure is often performed in the surgical operating theatre with specialized pliers or, if available, lengthy pre-operative bending to fit a 3D printed skeletal model prepared on computer as part of a virtual surgical plan. Manual bending of fixation plates by eye or to a model can take considerable time. Repetitive bending at a single location can result in work hardening that increases the subsequent risk of fatigue failure. However, incremental forming systems may provide a solution to automatically bend fixation plates accurately, rapidly, and as little at any one location as possible. This paper is an investigation of the kinematics and manipulability of two versions of an incremental fixture plate bending system for Point of Care Manufacturing (POCM) of craniomaxillofacial (CMF) skeletal fixation hardware. The Automatic Plate Bender (APB) v1 is a minimal POCM system that is designed for simple straight plates with a constant incremental pitch. The APB v2 is a more complex POCM that is designed to accommodate a larger variety of standard plates. Kinematic and manipulability analysis demonstrate the engagement and bend classes that each system can accomplish, and identifies a critical singularity in the APB v2 mechanism. The paper concludes with two case studies in which a path planning algorithm uses a manipulability analysis to avoid singularities during incremental bending.