BACKGROUND: A versatile image acquisition method called echo surgetics has been developed for minimally invasive computer-assisted orthopaedic procedures. The principle of echo surgetics is to use freehand three-dimensional (3D) ultrasound to acquire relevant 3D bone surface and point data transcutaneously, eliminating access problems associated with conventional digitizers. The concept has been implemented in three technologies: Echo Point, Echo Matching and Echo Morphing. METHODS: Cadaver experiments were carried out to evaluate the accuracy of (a) Echo Point for digitization of the anterior pelvic plane (APP) in total hip arthroplasty, and (b) Echo Morphing for reconstructing the distal femur in minimally invasive knee surgery. RESULTS AND CONCLUSIONS: Echo Point provided significantly improved results (p < 0.001) over conventional digitization where mean tilt errors exceeded 20 degrees. The Echo Morphing experiments demonstrated that with a reasonable number of points (ca. 1000) and initial attitude (IA) error (ca. 5-10 mm and 5-10 degrees ) we can obtain an average accuracy of approximately 1 mm that is sufficient for most of clinical applications.

Abstract

BACKGROUND: Clinical examination remains empirical and may be confusing in the setting of rotatory knee instabilities. Computerized navigation systems provide the ability to visualize and quantify coupled knee motions during knee stability examination. HYPOTHESIS: An image-free navigation system can reliably register and collect multiplanar knee kinematics during knee stability examination. STUDY DESIGN: Controlled laboratory study. METHODS: Coupled knee motions were determined by a robotic/UFS testing system and by an image-free navigation system in 6 cadaveric knees that were subjected to (1) isolated varus stress and (2) combined varus and external rotation force at 0 degrees, 30 degrees, and 60 degrees. This protocol was performed in intact knees and after complete sectioning of the posterolateral corner (lateral collateral ligament, popliteus tendon, and popliteofibular ligament). The correlation between data from the surgical navigation system and the robotic positional sensor was assessed using the intraclass correlation coefficient. The 3-dimensional motion paths of the intact and sectioned knees were assessed qualitatively using the navigation display system. RESULTS: Intraclass correlation coefficients between the robotic sensor and the navigation system for varus and external rotation at 0 degrees, 30 degrees, and 60 degrees were all statistically significant at P < .01. The overall intraclass correlation coefficient for all tests was 0.9976 (P < .0001). Real-time visualization of the coupled motions was possible with the navigation system. Post hoc analysis of the knee motion paths during loading distinguished distinct rotatory patterns. CONCLUSION: Surgical navigation is a precise intraoperative tool to quantify knee stability examination and may help delineate pathologic multiplanar or coupled knee motions, particularly in the setting of complex rotatory instability patterns. Repeatability of load application during clinical stability testing remains problematic. CLINICAL RELEVANCE: Surgical navigation may refine the diagnostic evaluation of knee instability.

Abstract

In this paper we focus on the design of Computer Assisted Surgery (CAS) systems and more generally Augmented Reality (AR) systems that assist a user in performing a task on a physical object. Digital information or new actions are defined by the AR system to facilitate or to enrich the natural way the user would interact with the real environment. We focus on the outputs of such systems, so that additional digital information is smoothly integrated with the real environment of the user, by considering an innovative device for displaying guidance information: the mini-screen. We first motivate the choice of the mini-screen based on the ergonomic property of perceptual continuity and then present a design space useful to create interaction techniques based on a mini-screen. Two versions of a Computer ASsisted PERicardial (CASPER) puncture application, as well as a computer assisted renal puncture application, developed in our teams, are used to illustrate the discussion.