Hinged External Fixators for Knee Rehabilitation Kinematic Concept of a Two Degree-of-Freedom System Gianluca Gatti 1 , Shadi Shweiki 1 , Giorgia Lupinacci 1 , Gionata Fragomeni 2 and Guido Danieli 1 1 Dept. of Mechanical, Energy and Management Engineering, University of Calabria, V. Bucci, 87036 Rende (CS), Italy 2 Dept. of Medical and Surgical Sciences, University of Magna Graecia, V. Europa, 88100 Catanzaro (CZ), Italy Keywords: Knee Kinematics, Passive Knee, Hinged External Fixator, Knee Dislocation. Abstract: Hinged external fixators are used in knee dislocation treatment, where they have shown their effectiveness. They are proposed as a technique to protect ligament reconstructions while allowing early postoperative rehabilitation. A hinged external fixator usually consists of two rigid links connected to each other by a revolute joint. Each link is then fixed to the femur and tibia, via direct pin fixation. A single-axis hinged external fixator thus well accommodates the main knee movement, i.e. the flexion and extension. This paper presents an investigation on the conceptual idea of a double-axis hinged external fixator for the human knee, which accommodates for both flexion-extension and longitudinal internal-external rotation of the tibia respect to the femur. The potential advantage of such a design is foreseen in the increasing range of motion in postoperative knee rehabilitation and a better accommodation of natural knee motion. 1 INTRODUCTION Injuries and trauma that may occur in the human knee often lead to difficulties in having a fast and complete rehabilitation. Among these trauma, dislocation is one of the most severe injuries. Clinical outcomes after knee dislocations are frequently unsatisfactory, and pain, instability and arthrofibrosis are the most frequent complications (Stannard et al., 2003; Stayner and Coen, 2000). The instability basically lies in the injury of ligaments, and in some cases, even after repair, there is insufficient stability for early rehabilitation. This is the reason why preliminary reports on such treatment focused on achieving stability of the ligaments by means prolonged immobilisation during the postoperative period, although this would lead to stiffness of the joint (Noyes and Barber- Westin, 1997; Shapiro and Freedman, 1995). In more recent studies, authors intensely advocate early and aggressive mobility despite the risk of ligament repair or reconstruction failing (Cole and Harner, 1999; Yeh et al., 1999), and this led to the concept of the fixator with motion capabilities (Deszczynski et al., 2000; Fitzpatrick et al., 2005). A hinged external fixator usually consists of two rigid links connected to each other by a revolute joint. Each link is fixed to the femur and tibia through direct pin fixation. Previous biomechanical studies showed that a single-axis hinged external fixator is able to reproduce and accommodate the normal knee kinematics in a limited portion of the range of motion without harmfully loading the structures (Sommers et al., 2004; Wroble et al., 1997). Such external hinge, set to an approximate rotational axis of the articular joint, neutralises the displacing forces during the movement, and control the natural repair mechanism of the ligament apparatus. The fixator will thus allow patient mobility without the risk of loading the injured area during treatment and rehabilitation. The main difficulty in the application of hinged external fixators is the implantation and, in particular, the location of the articular joint axis of rotation. Commonly, this axis is manually identified by means of radiographs on the base of bony landmarks (Fragomeni et al., 2006; Richter and Lobenhoffer, 1998) and then the mechanical hinge of the fixator is aligned through screw adjustments. This technique may be prone to errors and the approximation in enforcing an articular joint to an unnatural mechanical behaviour may lead to unwanted outcomes in post-traumatic knee kinematics. This latter is, in fact, a result of a 224 Gatti G., Shweiki S., Lupinacci G., Fragomeni G. and Danieli G.. Hinged External Fixators for Knee Rehabilitation - Kinematic Concept of a Two Degree-of-Freedom System. DOI: 10.5220/0004904002240229 In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2014), pages 224-229 ISBN: 978-989-758-013-0 Copyright c  2014 SCITEPRESS (Science and Technology Publications, Lda.)