Biomedical subjects

J S Rovick

Publications and source records attributed to J S Rovick.

5 recordsLinked to original sources

PubMed1988

The effects of knee brace hinge design and placement on joint mechanics.

A computer model of 23 knees was obtained by embedding, slicing and digitizing the bone outlines and ligament co-ordinates. Using co-ordinate transformations, various three-dimensional motions were imposed on the knees, and calculations made of femoral-tibial contact error, contact point locations and ligament lengths. Significant deviations in these parameters were noted for abnormal motions including the elimination of internal-external rotation and a-p displacement and the misplacement of a hinge producing correct motion. The resulting mismatch could result in shear in soft tissues, cuff-to-skin slippage and inaccurate ligament length patterns.

Biomechanical Phenomena↗

PubMed1988

Pendular model of paraplegic swing-through crutch ambulation.

Kinematics of swing-through crutch ambulation for an individual with complete T11-T12 spinal cord injury was examined and quantitative aspects of the body-swing phase used to formulate and evaluate a 3-link pendular model. Model simulation parallels measured kinematics when shoulder motion is forced to follow the measured motion while hips and crutch tips are free pivots. Shoulder control contributes to increased ground clearance, influences timing and stride length, and gives flowing gait. Results indicate that mechanical work requirements during the body-swing phase are low. Metabolic energy demands exceed mechanical work requirements, due particularly to support of the body by the arms and shoulders. Exploiting low mechanical work requirements of the body-swing phase might be achieved through alternative mechanisms to assist ground clearance and to stabilize the wrists, arms, and shoulders while weight bearing.

Adult↗

PubMed1985

External knee joint design based on normal motion.

There are several advantages to accurate reproduction of knee motion in an external joint assembly such as a knee brace: reduction of pistoning forces, better ligament protection, kinematic compatability. The geometry and kinematics of the normal human knee were studied and the results applied to external joint design. Geometrically, the posterior portions of the femoral condyles were found to be spherical in shape. These spherical surfaces are projected in sagittal plane radiographs as circles with center points coincident with those of the spheres. A line connecting these centers defines an axis system and enables three-dimensional orientation of the femur on the tibia to be determined using sagittal-plane radiographs. Knee kinematics was determined as a function of flexion angle for 14 fresh cadavers and 8 volunteers. Results were in the form of eulerian rotations and displacements. The data were normalized to the size of the average knee and the results from the 22 trials were averaged. The most obvious motion was internal rotation of the tibia with flexion; however, varus rotation and posterior translation of the origin were also evident. An external joint system was then designed to mimic "average" knee motion during flexion. The joints have been incorporated into a knee brace, and clinical evaluation has begun. Other applications include cast bracing and hinge distraction.

Biomechanical Phenomena↗

PubMedDate not supplied

Three-dimensional dynamic motion analysis of the anterior cruciate ligament deficient knee joint.

Dynamic three-dimensional motion analyses of 15 fresh human knee joints subjected to combinations of flexion velocity and moment, internal and external femoral torque, and horizontal shear before and after sectioning the ACL were performed. ACL deficient specimens demonstrated marked anterior instability without rotational instability. The pivot shift phenomenon occurred with an isolated ACL deficiency and was the result of anterior instability. The pivot shift was accentuated by external femoral torque, decreased by internal femoral torque, and was present in the absence of any applied torque. The pivot shift produced a sudden directional change in the motion of both femoral condyles and may be responsible for the meniscal degeneration that accompanies chronic ACL deficiency.

Femur↗

PubMedDate not supplied

The forces in a knee brace as a function of hinge design and placement.

Customized knee braces for three normal subjects were instrumented to monitor the forces and moments across the hinges as the subjects performed various activities. The forces and moments were taken to represent a mismatch between actual knee motion and the motion the brace sought to impose. The different hinge designs studied were fixed axis, gear-on-gear, rack-and-pinion, and natural 3-D; they showed only moderate differences in forces. Much larger differences were seen if the hinges were offset 12 mm from the ideal placement. Posterior placement resulted in the least force and anterior placement the highest. The mismatch of knee motion to brace motion would probably lead to abnormal ligament lengths and tensions and other internal mechanical changes, as well as to pistoning and discomfort. The results of this study have implications on brace design, selection, and placement.

Adult↗