A mechanism for rotation restraints in the knee joint

Ligament function in restraining axial rotation of the tibia relative to the femur cannot be revealed by analysis of ligament forces alone. The action of the articular surfaces should be taken into account as well. In this study: three-dimensional mathematical models of four human knee joints were used to determine the limits of axial rotation between 0 and 90 degrees of flexion, whereby the forces in the ligaments and articular contact were calculated, together with their contribution to the restraint moment that was required to counterbalance the applied axial moment of 3 Nm. In external rotation, the direct axial restraint was provided by the collateral ligaments. In internal rotation, when the cruciate ligaments and medial collateral ligament were predominantly loaded, the direct restraint moment resulting from the ligament forces was not sufficient to counterbalance the applied moment. The articular contact forces, which resulted from balancing the axial components of the ligament forces? contributed considerably to the restraint of internal rotation. Depending on the flexion angle, the contact forces provided approximately 50-85% of the internal restraint, whereas 95-100% of the external rotation restraint was accounted for by the ligament force

Clock drawing performance in cognitively normal elderly

The Clock Drawing Test (CDT) is a common neuropsychological measure sensitive to cognitive changes and functional skills (e.g., driving test performance) among older adults. However, normative data have not been adequately developed. We report the distribution of CDT scores using three common scoring systems [Mendez, M. F., Ala, T., & Underwood, K. L. (1992). Development of scoring criteria for the Clock Drawing Task in Alzheimer's Disease. Journal of the American Geriatrics Society, 40, 1095-1099; Cahn, D. A., Salmon, D. P., Monsch, A. U., Butters, N., Wiederholt, W. C., & Corey-Bloom, J. (1996). Screening for dementia of the Alzheimer type in the community: The utility of the Clock Drawing Test. Archives of Clinical Neuropsychology, 11(6), 529-539], among 207 cognitively normal elderly. The systems were well correlated, took little time to use, and had high inter-rater reliability. We found statistically significant differences in CDT scores based on age and WRAT-3 Reading score, a marker of education quality. We present means, standard deviations, and t- and z-scores based on these subgroups. We found that "normal" CDT performance includes a wider distribution of scores than previously reported. Our results may serve as useful comparisons for clinicians wishing to know whether their patients perform in the general range of cognitively normal elderly. © 2007 National Academy of Neuropsychology

Validation of a three-dimensional model of the knee

Three-dimensional mathematical models of the tibio-femoral joint require input of the geometry of articulating surfaces and ligament insertions, and the mechanical properties of cartilage and ligaments. This paper describes a validation of a knee model through a direct specimen-related comparison between the knee model and the kinematics of four knee joint specimens from which the geometry data were used as input of the model. The knee model is quasi-static and is based on equilibrium of forces and moments. The stiffness properties of the ligaments and articular cartilage were estimated on the basis of data reported in the literature. The so-called reference strains in the ligament bundles for the joint in extension, were determined by using an optimization procedure, minimizing the difference between the kinematics of the model and the kinematics of experimentally obtained flexion motions with an internally or an externally rotated tibia (+or-3 Nm load). A reasonable to good agreement between the model and the experimental kinematics could be obtained for internal-external rotation laxity and the coupled translations and varus-valgus rotation. The disparity between model and experiment varied from knee to knee, average deviations ranging from close to zero to 8 degrees internal rotation deviation and from 5 mm posterior to 3 mm anterior position deviation. The average anterior-posterior laxities at both 20 degrees and 90 degrees flexion were within the variations reported in the literature, although for each individual joint with some underestimation or overestimation. It was concluded that the optimization procedure compensated for the lack of menisci and capsular structures by higher prestrains, thereby overestimating the ligament forces. Despite the gross simplifications relative to the complex anatomy of the knee, the present knee model can realistically simulate the passive motion characteristics of the human knee join