INTRODUCTION

There is a growing interest in surgical variables that are controlled by the orthopaedic surgeon, including lower leg alignment and soft tissue balancing. Since more tight control over these factors is associated with improved outcomes of total knee arthroplasty (TKA), several computer navigation systems have been developed. Many meta-analyses showed that mechanical axis accuracy and component positioning are improved using computer navigation and one may therefore expect better outcomes with computer navigation but studies showing this are lacking. Therefore, a systematic review with meta-analysis was performed on studies comparing functional outcomes of computer-navigated and conventional TKA. Goals of this study were to (I) assess outcomes of computer-navigated versus conventional TKA and (II) to stratify these results by the surgical variables the systems aim to control.

Trauma surgeries in the pelvic area are often difficult and prolonged processes that require comprehensive preoperative planning based on a CT scan. Preoperative planning is essential for the appreciation and spatial visualisation of the bone fragments, for planning the reduction strategy, and for determining the optimal type, size, and location of the fixation hardware.

We have developed a novel haptic-based patient specific preoperative planning system for pelvic bone fractures surgery planning. The system provides a virtual environment in which 3D bone fragments and fixation hardware models are interactively manipulated with full spatial depth and tactile perception. It supports the choice of the surgical approach and the planning of the two mains steps of bone fracture surgery: reduction and fixation. The purpose of the tool is to provide an intuitive haptic spatial interface for the manipulation of bone fracture 3D models extracted from CT images, to support the selection of bone fragments, the annotation of the fracture surface, the selection and placement of fixation screws, and the creation and placement of fixation plates with an anatomically fit shape.

The system incorporates ligament models that constrain the bone fragments motions and provides a realistic interactive fracture reduction support feeling to the surgeon. It allows the surgeon to view the fracture from various directions, thereby allowing fast and accurate fracture reduction planning. Two haptic devices, one for each hand, provide tactile feedback when objects touch without interpenetrating. To facilitate the reduction, the system provides an interactive, haptic fracture surface annotation tool and a fracture reduction algorithm that automatically minimises the pairwise distance between the fracture surfaces. For fracture fixation, the system provides a screw creation and placement capability as well as custom anatomical-fit fixation plate creation and placement. The screw placement is facilitated by the transparent viewing mode that allows the surgeon to navigate the screws inside the bone fragments while constraining them to remain within the bone fragments with haptic forces.

Our experimental results with five surgeons show that the method allows highly accurate reduction planning to within 1 mm or less. To evaluate the alignment in terms of quantity, we created a model of an artificial fracture in a healthy pelvis bone. The created model is placed in its anatomic location thus allowing us to measure the error in relation to its initial position. We calculate the anatomic alignment error by measuring the Hausdorff distance in mm between the fragment positioned in the desired location and the fragment placed by the surgeon. The new haptic-based system also supports patient-specific training of pelvic fracture surgeries.

Supra-condylar humerus fractures (SCHF) are amongst the most common fractures requiring surgical stabilisation in the pediatric age group (1). Closed reduction and percutaneous fixation with Kirschner wires (KW) is currently the standard of care (2). The number of KW used and their configuration has been the subject of much research (3, 4). The failure modes leading to loss of fracture reduction are not clear and have not been quantified. The aim of this study is to compare the mechanical stability of the opt-used configurations for various loading modes and contact interactions at the KW/bone interface.

A Gartland type-III SCHF was introduced to a fourth generation composite saw bone (Sawbones®, Vashon, Washington, USA). The model was CT scanned with a slice spacing of 0.5mm and pixel size 0.3×0.3mm. The CT data set was imported into AmiraDev (AmiraDev 5.2 Visage Imaging, Inc). A uniaxial mechanical test was conducted in order to measure the KW pullout forces from the distal humerus.

A model of the fractured humerus was constructed with the following steps: 1) manual segmentation; 2) surface generation of each fragment, and; 3) automatic volumetric grid generation for each fragment. The fracture was then virtually reduced and KWs were placed at the desired configurations (Fig 1a-b). For each configuration, a separate model was generated. Material properties were assigned to the bone-model elements according to the manufacturer's data sheet; Young's modulus E = 16GPa and E = 150MPa for the cortical and cancellous bone respectively. The KW were assigned a Young's modulus of 200GPa. Each of the models created in Amira was imported to a finite element application (Abaqus 6.9, DS-Simula) for structural analysis. For each of KW configuration four different torque forces load types were simulated (Fig 1c left): 1) a clockwise and counterclockwise torque with a magnitude of 1.5 NM (Newton/Meters); 2) a translational force with a magnitude of 30 N (Newtons) in the direction of the humerus shaft, and; 3) a shear force with a magnitude of 30 N in the direction parallel to the fracture plane. The results were normalised such that the maximum displacement for the crossed pin configuration with a coefficient of friction equal to zero (μ = 0) was used as unity for each load configuration. Similarly, for each of KW configuration four different translational forces load types were simulated (Fig 1c right): 1) a clockwise and counter clock-wise torque with a magnitude of 1.5 NM (Newton/Meters); 2) a translational force with a magnitude of 30N in the direction of the humerus shaft, and; 3) a shear force with a magnitude of 30N in the direction parallel to the fracture plane. The results were normalised as described above.