Biomedical subjects

V James Raso

Publications and source records attributed to V James Raso.

8 recordsLinked to original sources

PubMed2006

A support vector machines classifier to assess the severity of idiopathic scoliosis from surface topography.

A support vector machines (SVM) classifier was used to assess the severity of idiopathic scoliosis (IS) based on surface topographic images of human backs. Scoliosis is a condition that involves abnormal lateral curvature and rotation of the spine that usually causes noticeable trunk deformities. Based on the hypothesis that combining surface topography and clinical data using a SVM would produce better assessment results, we conducted a study using a dataset of 111 IS patients. Twelve surface and clinical indicators were obtained for each patient. The result of testing on the dataset showed that the system achieved 69-85% accuracy in testing. It outperformed a linear discriminant function classifier and a decision tree classifier on the dataset.

Adolescent↗

PubMed2005

Evaluating MRI as a technique for visualizing the neurocentral junction.

STUDY DESIGN: Magnetic resonance imaging (MRI) of the neurocentral junction (NCJ) was correlated with gross anatomic and histologic sections acquired at the same position. OBJECTIVES: To determine the composition of the MRI of the NCJ and to explore the long-standing discrepancy between the ages of closure of the NCJ as determined by anatomic and imaging studies. SUMMARY OF BACKGROUND DATA: Disparate growth at the site of the NCJ has been implicated as a potential cause of adolescent idiopathic scoliosis since the early 1900s. Although anatomic studies have refuted this theory by maintaining that the NCJ closes before the age of 10 years, recent MRI studies have suggested that the NCJ remains open until adolescence. METHODS: One hundred fourteen porcine NCJs in various stages of development were visualized using MRI. Gross anatomic and histologic sections were acquired at the same position as MRI for correlation. RESULTS: The presence or absence of NCJ cartilage was represented by the presence or absence of a line on MRI. However, the NCJ image overestimated the width of the NCJ cartilage in the anteroposterior direction during development. As the NCJ underwent the process of closure, the NCJ image underestimated the extent of closure in the medial-lateral direction. CONCLUSIONS: Although MRI underestimated the extent of NCJ closure, MRI accurately showed whether cartilage was present or absent at the NCJ site. MRI determination of the age of NCJ closure appears reliable, and further exploration of the asymmetric growth hypothesis is required.

Aging↗

PubMed2005

Repetitive pointing to remembered proprioceptive targets improves 3D hand positioning accuracy.

Repetitive pointing movements to remembered proprioceptive targets were investigated to determine whether dynamic proprioception could be used to modify the initial sensorimotor conditions associated with an active definition of the target position. Twelve blindfolded subjects used proprioception to reproduce a self-selected target position as accurately as possible. Ten repetitions for each limb were completed using overhead and scapular plane pointing tasks. A 3D optical tracking system determined hand trajectory start and endpoint positions for each repetition. These positions quantified three-dimensional pointing errors relative to the target position and the initial and preceding movement repetitions, as well as changes in movement direction and extent. Target position and cumulative start position errors were significantly greater than the corresponding preceding movement (inter-repetition) errors, and increased as the trial progressed. In contrast, hand trajectory start and endpoint inter-repetition errors decreased significantly with repeated task performance, as did movement extent, although it was consistently underestimated for each repetition. Pointing direction remained constant, except for the angle of elevation for scapular plane pointing, which consistently decreased throughout the trial. The results suggest that the initial conditions prescribed by actively defining a proprioceptive target were subsequently modified by dynamic proprioception, such that movement reproduction capability improved with repeated task performance.

Biomechanical Phenomena↗

PubMed2005

A three-dimensional finite element stress analysis for tunnel placement and buttons in anterior cruciate ligament reconstructions.

This communication reports the results of a three-dimensional finite element (FE) model of stresses in a surgically altered femur and tibia. The model incorporated a novel approach in implementing orthotropic and inhomogeneous bone properties and non-uniform distributed loading. Cortical, cancellous, and subchondral bone of the femur and the tibia were modeled. Mechanical properties for the cortical and cancellous bone were mapped from published data characterizing the anisotropy and inhomogeneity of the bone properties. Mesh adequacy was determined using stress convergence and strain energy error convergence. Qualitatively, the results of the study compare well with experimental principal compressive strains from the literature. With respect to tunnel placement in anterior cruciate ligament reconstruction, the model predicted stress-shielding at the postero-lateral region of the tunnel wall, and increased stress at the postero-medial region of the tunnel wall. The stresses in the cancellous bone beneath the tunnel were, in general, lower than those above the tunnel. Prolonged stress shielding leads to bone resorption of the posterior tunnel wall leading to tunnel enlargement, and possible compromise of the ACL reconstruction. The stresses on the femoral cortex produced from a button-type fixation were noticeable for low levels of loading; the stress levels were very similar in models incorporating bone properties of patients aged 45 and 65. Repeated compression of the femoral cortex at these stress levels may cause microdamage to the cortex eventually resulting in fatigue failure.

Aged↗

PubMed2005

Investigation of a hybrid method of soft tissue graft fixation for anterior cruciate ligament reconstruction.

To increase knee stability following anterior cruciate ligament (ACL) reconstruction, development of increasingly stronger and stiffer fixation is required. This study assessed the initial pullout force, stiffness of fixation, and failure modes for a novel hybrid fixation method combining periosteal and direct fixation using porcine femoral bone. A soft tissue graft was secured by combining both an interference screw and an EndoButton (Smith and Nephew Endoscopy, Andover, MA). The results were compared with the traditional direct fixation method using a titanium interference screw. Twenty porcine hindlimbs were divided into two groups. Specimens were loaded in line with the bone tunnel on a materials testing machine. Maximum pullout force of the hybrid fixation (588+/-37 N) was significantly greater than with an interference screw alone (516+/-37 N). The stiffness of the hybrid fixation (52.1+/-12.8 N/mm) was similar to that of screw fixation (56.5+/-10.2 N/mm). Graft pullout was predominant for screw fixation, whereas a combination of graft pullout and graft failure was seen for hybrid fixation. These results indicate that initial pullout force of soft tissue grafts can be increased by using the suggested novel hybrid fixation method.

Animals↗

PubMed2005

A parametric analysis of fixation post shape in tibial knee prostheses.

A primary concern of total knee replacement (TKR) is aseptic loosening of the tibial component, which may be caused by shielding of mechanical stresses in the bone and may require subsequent revision surgery. A three-dimensional (3D) finite element (FE) model has been developed to study bone and interface stresses for four different tibial prosthesis designs. The model described here incorporates orthotropic and heterogeneous bone properties with physiologically representative loading conditions. Results from this model indicate that stress distribution is affected by the incorporation of anisotropy and spatial variation of bone properties. All bone properties were mapped from published data to characterize their anisotropy and heterogeneity. Physiological loading was incorporated by mapping experimentally determined contact patterns. Convergence testing was performed to ensure model accuracy. In terms of interface forces, a tapered post decreased post shear while slightly increasing post compression compared to a cylindrical post; a post of elliptical cross-section increased post shear and decreased post compression. In terms of cancellous bone stress, tapered and elliptical posts both relieved compression compared to a cylindrical post, while a tapered post also produced increased peripheral stress. The inclusion of medial and lateral pegs in addition to a central fixation post caused localized stress shielding in the periphery of the pegs. In general, all implant models caused a reduction of cancellous bone stress plus high compression beneath the central fixation posts.

Arthroplasty, Replacement, Knee↗

PubMed2005

A support vectors classifier approach to predicting the risk of progression of adolescent idiopathic scoliosis.

A support vector classifier (SVC) approach was employed in predicting the risk of progression of adolescent idiopathic scoliosis (AIS), a condition that causes visible trunk asymmetries. As the aetiology of AIS is unknown, its risk of progression can only be predicted from measured indicators. Previous studies suggest that individual indicators of AIS do not reliably predict its risk of progression. Complex indicators with better predictive values have been developed but are unsuitable for clinical use as obtaining their values is often onerous, involving much skill and repeated measurements taken over time. Based on the hypothesis that combining common indicators of AIS using an SVC approach would produce better prediction results more quickly, we conducted a study using three datasets comprising a total of 44 moderate AIS patients (30 observed, 14 treated with brace). Of the 44 patients, 13 progressed less than 5 degrees and 31 progressed more than 5 degrees. One dataset comprised all the patients. A second dataset comprised all the observed patients and a third comprised all the brace-treated patients. Twenty-one radiographic and clinical indicators were obtained for each patient. The result of testing on the three datasets showed that the system achieved 100% accuracy in training and 65%-80% accuracy in testing. It outperformed a "statistically equivalent" logistic regression model and a stepwise linear regression model on the said datasets. It took less than 20 min per patient to measure the indicators, input their values into the system, and produce the needed results, making the system viable for use in a clinical environment.

Adolescent↗

PubMed2004

Dynamic upper limb proprioception in multidirectional shoulder instability.

The ability of subjects with multidirectional shoulder instability to use proprioception to complete a series of upper limb repositioning tasks was investigated. Twelve subjects with multidirectional instability and 12 control subjects were blindfolded and instructed to use proprioception to reproduce a self-selected target position as accurately as possible. Subjects completed 10 repetitions for each limb using three distinct upper limb movements: overhead reaching, scapular plane pointing, and humeral external rotation with abduction. A three-dimensional video motion analysis system tracked limb position and determined spatial hand position error. Subjects with multidirectional shoulder instability showed significantly greater hand position error than control subjects. No hand position error differences were found between the symptomatic and the asymptomatic limbs of subjects in the instability group. Inter-repetition error for subjects in both groups improved significantly during the first three movement cycles. These results suggest that after movement initiation, dynamic proprioception was a factor in improving hand position accuracy in both groups, but to a lesser degree in subjects with multidirectional instability. Consequently, subjects with multidirectional instability may have a reduced capacity to use proprioception to refine and control the motor output of the upper limb.

Adult↗