PubMed Health⌕ Search

Biomedical subjects

M S Hefzy

Publications and source records attributed to M S Hefzy.

23 records · Page 2Linked to original sources
PubMed1983

Error analysis of a system for measuring three-dimensional joint motion.

In the past ten years there has been increased use of six-degree-of-freedom instrumented spatial linkages for the measurement of biological joint motions. In spite of the increased popularity, little information has been reported on the accuracy of these devices. In this paper, we present a two-part investigation of the accuracy of the instrumented spatial linkage when used to measure knee joint kinematics. In the first part, we present the results of a theoretical analysis and an experimental determination of the errors associated with spatial linkage systems. In the second part, we describe the errors associated with a bi-planar X-ray system used to obtain the coordinate transformation between the linkage ends and coordinate systems located in the bones comprising the joint. We found that the theoretical error analysis consistently overestimated the actual measurement error, thus providing an unreliable estimate of errors. The experimental study of both the linkage system and the bi-planar X-ray system demonstrated that the accuracy of displacement measurement is insensitive to large systematic errors in position measurement.

Biomechanical Phenomena↗
PubMed1983

An analytical technique for modeling knee joint stiffness--Part II: Ligamentous geometric nonlinearities.

An analytical technique previously developed to evaluate the contribution of the ligaments to the nonlinear, coupled stiffness characteristics of the human knee joint [1] is extended here to include geometric nonlinearities. In [1], we assumed that the ligaments act as tensile bands running in a straight line between tibial and femoral insertion sites. Here, two forms of geometric nonlinearities are introduced and analyzed: ligaments wrapping around bone surfaces, such as occurs with the medial collateral ligament, the posterior capsule, and the anterior cruciate in hyperextension, and wrapping of ligaments around each other, such as occurs with the cruciate ligaments as the knee is flexed and internally rotated.

Biomechanical Phenomena↗
PubMedDate not supplied

Factors affecting the region of most isometric femoral attachments. Part I: The posterior cruciate ligament.

We measured how the distance between selected tibial and femoral attachments of the PCL changes with knee flexion in six intact cadaver knee. The femoral location was the primary determinant of whether the distance increased, decreased, or remained nearly constant. The proximal-distal location of a fiber's femoral attachment had a stronger effect than had the anterior-posterior location. The tibial location had only a small statistically significant effect. These results suggest that the function of fibers within the PCL is determined primarily by their femoral attachment location. We determined all femoral attachments whose tibio-femoral distance changed 0, 2, 4, 6, 8, and 10 mm during flexion from 0 degrees to 90 degrees. No absolutely isometric point existed. Attachments whose separation distance changed less than 2 mm formed a bullet-shaped region whose base was against the roof of the intercondylar notch and whose nose pointed posteriorly and slightly distally. The axis of the "bullet" was near the proximal edge of the femoral insertion of the PCL. Along the axis, anterior attachments, located near the roof of the intercondylar notch, were more isometric than were posterior attachments, located near the cartilage. Attachments located distal to the axis moved away from the tibial insertion of the PCL when the knee was flexed. The more distal the femoral attachment, the larger the increase in tibiofemoral distance that occurred with flexion. The opposite was true of attachments proximal to the 2 mm region.

Adult↗
PubMedDate not supplied

Factors affecting the region of most isometric femoral attachments. Part II: The anterior cruciate ligament.

During flexion of the intact knee, we measured the changes in distance between possible tibial and femoral attachments of an intraarticular ACL substitute. The change in distance during motion was described by the difference between the longest and shortest distances measured. Using knees from eight cadaver donors, we studied the effects of varying tibial and femoral attachment locations, applying anterior and posterior forces, and altering the range of flexion. We found that altering the femoral attachment had a much larger effect than had altering the tibial attachment. No femoral attachments were completely isometric. Femoral attachments that produced the smallest change in tibiofemoral distance, 2 mm and less, formed a band whose greatest width ranged from 3 to 5 mm. The axis of the 2 mm region was nearly proximal-distal in orientation and located near the center of the ACL's femoral insertion. Attachments located anterior to the axis moved away from the tibial attachment with flexion, whereas attachments located posterior to the axis moved toward the tibia. The AP position of the tibial attachment affected the orientation of the 2 mm region. Moving the tibial attachment posteriorly caused the proximal part of the region to move anterior, with little change in the location of the distal part of the region. Changing the applied joint force from anterior to posterior was similar to moving the tibial attachment posteriorly, but the effect was less pronounced. Increasing the range of flexion from 90 degrees to 120 degrees caused the 2 mm region to become narrower and changed its orientation.

Adult↗