A fluoroscopy-based surgical navigation system for high tibial osteotomy.

High tibial osteotomy is a widely accepted treatment for unicompartmental osteoarthritis of the knee and other lower extremity deformities, particularly in young and active patients. However, it is generally recognized as a technically demanding procedure. The lack of intraoperative control of the mechanical axis of the affected limb often results in postoperative malalignments, which is one of the main reasons for poor long-term results. Moreover, inaccurate osteotomies, such as insufficient or excessive bone cut, or incorrect orientation of the chisel or saw blade, have been observed. A computer assisted intraoperative planning and navigation system is therefore proposed in order to address these technical problems. During operation, fluoroscopic images are acquired and anatomical landmarks are digitized; a patient-specific coordinate system is established accordingly. After the three-dimensional measurement of the deformity and interactive planning of the osteotomy plane, the deformity is corrected under navigational guidance. The proposed system has been successfully introduced into the clinical practice of surgery after encouraging laboratory evaluations, with results affirming that it is safe and accurate.     

Statistical model based shape prediction from a combination of direct observations and various surrogates: Application to orthopaedic research

In computer-assisted orthopaedic surgery, recovering three-dimensional patient-specific anatomy from incomplete information has been focus of interest due to several factors such as less invasive surgical procedures, reduced radiation doses, and rapid intra-operative updates of the anatomy. The aim of this paper is to report results obtained combining statistical shape modeling and multivariate regression techniques for predicting bone shape from clinically and surgically relevant predictors, including sparse observations of the bone surface but also morphometric and anthropometric information. Different state of the art methods such as partial least square regression, principal component regression, canonical correlation analysis, and non-parametric kernel-based regression are compared. Clinically relevant surrogate variables and combinations are investigated on a database of 142 femur and 154 tibia shapes obtained from CT images. The results are evaluated using cross validation to quantify the prediction error. The proposed approach enables to characterize the added value of different predictors in a quantitative and localized fashion. Results indicate that complementary sources of information can be efficiently exploited to improve the accuracy of shape prediction.     

Implementation, accuracy evaluation, and preliminary clinical trial of a CT-free navigation system for high tibial opening wedge osteotomy.

OBJECTIVE: The objectives of this study are to design and evaluate a CT-free intra-operative planning and navigation system for high tibial opening wedge osteotomy. This is a widely accepted treatment for medial compartment osteoarthritis and other lower extremity deformities, particularly in young and active patients for whom total knee replacement is not advised. However, it is a technically demanding procedure. Conventional preoperative planning and surgical techniques have so far been inaccurate, and often resulting in postoperative malalignment representing either under- or over-correction, which is the main reason for poor long-term results. In addition, conventional techniques have the potential to damage the lateral hinge cortex and tibial neurovascular structures, which may cause fixation failure, loss of correction, or peroneal nerve paralysis. All these common problems can be addressed by the use of a surgical navigation system. MATERIALS AND METHODS: Surgical instruments are tracked optically with the SurgiGATE((R)) navigation system (PRAXIM MediVision, La Tronche, France). Following exposure, dynamical reference bases are attached to the femur, tibia, and proximal fragment of the tibia. A patient-specific coordinate system is then established, on the basis of registered anatomical landmarks. After intra-operative deformity measurement and correction planning, the osteotomy is performed under navigational guidance. The deformities are corrected by realigning the mechanical axis of the affected limb from the diseased medial compartment to the healthy lateral side. The wedge size, joint line orientation, and tibial plateau slope are monitored during correction. Besides correcting uni-planar varus deformities, the system provides the functionality to correct complex multi-planar deformities with a single cut. Furthermore, with on-the-fly visualization of surgical instruments on multiple fluoroscopic images, penetration of the hinge cortex and damage to the neurovascular structures due to an inappropriate osteotomy can be avoided. RESULTS: The laboratory evaluation with a plastic bone model (Synbone AG, Davos, Switzerland) shows that the error of deformity correction is <1.7 degrees (95% confidence interval) in the frontal plane and <2.3 degrees (95% confidence interval) in the sagittal plane. The preliminary clinical trial confirms these results. CONCLUSION: A novel CT-free navigation system for high tibial osteotomy has been developed and evaluated, which holds the promise of improved accuracy, reliability, and safety of this procedure.     

A transcutaneous bone digitizer for minimally invasive registration in orthopedics: a real-time focused ultrasound beam approach.

Computer-guided navigation of surgical tool position in computer-assisted orthopedic systems requires the registration of computer tomographic (CT) images with underlying bone. This process is presently performed by manually digitizing points on bone with a pointer and aligning them to a preoperative CT scan. We propose the use of ultrasound to obtain points on bone transcutaneously. A custom-made A-mode probe features a modular lens focusing system and a one-step calibration method. A stable and precise echo detection algorithm is also implemented. The accuracies of three signal detection algorithms--standard deviation, cross-correlation (XCORR) and short-time Fourier transform--were compared using a known reflected signal. XCORR showed the most accurate and stable operation. To test our method of obtaining bone surface points, a plastic model of the fourth human lumbar vertebra was CT scanned and then immersed in a water bath. Six surface registrations of the vertebra using an accurate pointing device were compared to ten registrations obtained using the US probe (using the XCORR algorithm). Student's T-test showed no significant difference in error between the two methods, proving that ultrasound registration, using our method, is equivalent to the more conventional pointer method.     

The effect of glatiramer acetate treatment on pre-existing headaches in patients with MS

During the first 6 months of glatiramer acetate therapy in 82 consecutive patients with multiple sclerosis, in only 6% frequency of pre-existing headaches increased by more than 50%. This is less than the headache aggravation reported in an earlier study in up to 35% of patients during the first 6 months on interferon beta.     

Computer aided high tibial open wedge osteotomy

High tibial osteotomy is a widely accepted treatment of medial compartment osteoarthritis as well as other lower extremity deformities. However, it is a technically demanding procedure. The lack of exact intraoperative real time control of the mechanical axis often results in postoperative malalignments, which is one reason for poor long term results. These problems can be addressed with the use of a surgical navigation system. Following exposure, dynamic reference bases (DRBs) are attached to the femur, and the proximal and the distal part of the tibia. After intraoperative measurement of the deformities and correction planning, the osteotomy is performed under navigational guidance. The wedge size, joint line orientation, and tibial plateau slope are monitored during correction. The in vitro evaluation with a plastic bone model suggests that the error of deformity correction is less than 1.7 degrees (95% confidence limits) in the frontal, and less than 2.3 degrees (95% confidence limits) in the sagittal plane, respectively. On a cadaver study of 13 legs, the mechanical axis intersected the Fujisawa line in 80.7% (range 77.5-85.8%). The preliminary clinical experience confirms these results. A novel computer tomography free navigation system for high tibial osteotomy has been developed that holds the promise of improving the accuracy, reliability, and safety of this kind of approach.     

Multisensory integration after traumatic brain injury: a reaction time study between pairings of vision,touch and audition

Traumatic brain injury (TBI) frequently results in deficits in attention and speed of information processing. In order to disentangle the influence of sensory-specific factors and the role of cross-modal integration from the supra-modal aspects of cognitive slowing, the present reaction time (RT) study was designed. Simple and choice RT to pairings of visual, auditory and tactile stimuli were measured in 35 TBI patients and 35 matched controls. Results proved a strong influence of sensory-specific and cross-modal factors in the RTs. The tactile modality was more difficult to integrate with the visual and the auditory modality, rather than the visual and the auditory modalities between them. TBI patients showed prolonged simple and choice RTs throughout all tasks, but their difficulty with integrating the tactile modality was disproportionately higher in comparison to controls.     

Allograft selection for transepiphyseal tumor resection around the knee using three-dimensional surface registration

Transepiphyseal tumor resection is a common surgical procedure in patients with malignant bone tumors. The aim of this study is to develop and validate a computer-assisted method for selecting the most appropriate allograft from a cadaver bone bank. Fifty tibiae and femora were 3D reconstructed from computed tomography (CT) images. A transepiphyseal resection was applied to all of them in a virtual environment. A tool was developed and evaluated that compares each metaphyseal piece against all other bones in the data bank. This is done through a template matching process, where the template is extracted from the contralateral healthy bone of the same patient. The method was validated using surface distance metrics and statistical tests comparing it against manual methods. The developed algorithm was able to accurately detect the bone segment that best matches the patient’s anatomy. The automatic method showed improvement over the manual counterpart. The proposed method also substantially reduced computation time when compared to state-of-the-art methods as well as the manual selection. Our findings suggest that the accuracy, robustness, and speed of the developed method are suitable for clinical trials and that it can be readily applied for preoperative allograft selection.