Richard W. Sellens

Validation of a new surgical procedure for percutaneous scaphoid fixation using intra-operative ultrasound

A new technique for percutaneous fixation of non-displaced scaphoid fractures is described. The technique used pre-operative planning from computed tomography images, registration to intra-operatively acquired three-dimensional ultrasound images, and intra-operative guidance using an optical tracking system. Two stand-alone software applications were developed. The first one was used to determine the surgical plan pre-operatively and the second one was used to guide the surgeon during screw insertion. Laboratory validation of the technique included measurements of the inter-operator and intra-operator variability in the outcome of scaphoid fixation using the proposed procedure, and also included comparison of the performance of this procedure with the conventional percutaneous fixation technique using fluoroscopy. The results showed that the tight accuracy requirements of percutaneous scaphoid fixation were met and that the consistency was superior to the conventional technique.

An Augmented Reality Haptic Training Simulator for Spinal Needle Procedures

This paper presents the prototype for an augmented reality haptic simulation system with potential for spinal needle insertion training. The proposed system is composed of a torso mannequin, a MicronTracker2 optical tracking system, a PHANToM haptic device, and a graphical user interface to provide visual feedback. The system allows users to perform simulated needle insertions on a physical mannequin overlaid with an augmented reality cutaway of patient anatomy. A tissue model based on a finite-element model provides force during the insertion. The system allows for training without the need for the presence of a trained clinician or access to live patients or cadavers. A pilot user study demonstrates the potential and functionality of the system.

Simulation of extension, radial and ulnar deviation of the wrist with a rigid body spring model

A novel computational model of the wrist that predicts carpal bone motion was developed in order to investigate the complex kinematics of the human wrist. This rigid body spring model (RBSM) of the wrist was built using surface models of the eight carpal bones, the bases of the five metacarpal bones, and the distal parts of the ulna and radius, all obtained from computed tomography (CT) scans of a cadaver upper limb. Elastic contact conditions between the rigid bodies modeled the influence of the cartilage layers, and ligamentous structures were constructed using nonlinear, tension-only spring elements. Motion of the wrist was simulated by applying forces to the tendons of the five main wrist muscles modeled. Three wrist motions were simulated: extension, ulnar deviation and radial deviation. The model was tested and tuned by comparing the simulated displacement and orientation of the carpal bones with previously obtained CT-scans of the same cadaver arm in deviated (45 degrees ulnar and 15 degrees radial), and extended (57 degrees ) wrist positions. Simulation results for the scaphoid, lunate, capitate, hamate and triquetrum are presented here and provide credible prediction of carpal bone movement. These are the first reported results of such a model. They indicate promise that this model will assist in future wrist kinematics investigations. However, further optimization and validation are required to define and guarantee the validity of results.

Ultrasound-Guided percutaneous scaphoid pinning: operator variability and comparison with traditional fluoroscopic procedure

This paper reports on pilot laboratory experiments with a recently proposed surgical procedure for percutaneous screw insertion into fractured scaphoid bones using ultrasound guidance. The experiments were intended to determine the operator variability of the procedure and its performance in comparison with a traditional pinning procedure using fluoroscopy. In the proposed procedure, a three-dimensional surface model is created from pre-operative computed tomography images and intra-operatively registered to the patient using ultrasound images. A graphical interface that communicates with an optical camera tracking the surgical tools, guides the surgeon during the procedure in real time. The results of the experiments revealed non-significant differences between operators for the error in the entry location of the drill hole (p=0.90); however, significant differences for the exit location (p<0.05). Comparison with the traditional pinning procedure shows that the outcome of the recently proposed procedure appears to be more consistent.

Percutaneous scaphoid pinning using ultrasound guidance

A new procedure for percutaneous screw insertion in the scaphoid is proposed. The procedure involves pre-surgery planning using computed tomography imaging and intra-operative guidance using three-dimensional ultrasound. Preoperatively, the desired screw location and orientation is chosen on a three-dimensional surface model generated from computed tomography images. During the surgery, ultrasound images are captured from the targeted anatomy of the patient using an ultrasound probe that is tracked with a Certus optical camera. The tracked probe enables the registration of the surface model and the surgical plan to the patient in the operating room. The surgical drill, used by the surgeon for screw insertion, is also tracked with the optical camera. A graphical user interface has been developed to display the surface model, the surgical plan and the drill in real-time. By means of this interface, the surgeon is guided during the screw insertion procedure. Our experiments on scaphoid phantoms demonstrate that the accuracy of the proposed procedure is potentially of the same order as an open reduction and screw fixation surgery. The advantages of this new procedure are a reduced risk of infections and minimal soft tissue damage due to its percutaneous nature. The procedure also reduces the exposure to ionizing radiation for patients and operating room staff due to the employment of ultrasound imaging instead of fluoroscopy.

Wrist Kinematics from Computed Tomography Data

Three-dimensional (3-d) surface models of human carpal bones obtained from Computed Tomography (CT) were used to investigate their kinematic behavior throughout the entire physiological range of motion of the human wrist joint. The 3-d motion of the bones was visualized graphically by the finite helical axis (FHA) and smooth animations. It was found that extension mainly occurs in the radial-carpal joint and flexion is shared between the radial-carpal and midcarpal joints. During radial and ulnar deviation, the relative motion between the scaphoid and lunate was larger than in flexion-extension. This study will improve our understanding of carpal bone motion in a range of wrist poses, and will provide morphological data for the design of a functional wrist replacement arthroplasty.