No abstract

Experimental evidence suggests that the tensile behavior of tendons and ligaments is in part a function of tissue hydration. The models currently available do not offer a means by which the hydration effects might be explicitly explored. To study these effects, a finite element model of a collagen sub-fascicle, a substructure of tendon and ligament, was formulated. The model was microstructurally based, and simulated oriented collagen fibrils with elastic-orthotropic continuum elements. Poroelastic elements were used to model the interfibrillar matrix. The collagen fiber morphology reflected in the model interacted with the interfibrillar matrix to produce behaviors similar to those seen in tendon and ligament during tensile, cyclic, and relaxation experiments conducted by others. Various states of hydration and permeability were parametrically investigated, demonstrating their influence on the tensile response of the model.

Several candidate predictors for the occurrence of surface fissures in cartilage, including impact force, shear stress, and tensile strain have been previously proposed without an analytic basis. In this study a controlled impact experiment was performed where a dropped mass and three impact interfaces were used to identify loads associated with the initiation of fissuring. A Finite Element Model of each experiment was used to obtain stresses and strains associated with each impact event. The resulting experimental and analytical data were analyzed using logistic regression in order to determine the strongest predictor of a fissure, and thus to propose a failure criterion for articular cartilage during a blunt insult. The logistic regression indicated that shear stress, rather than impact force or drop height (an indicator of impact energy), was the strongest predictor for the occurrence of a fissure.

Load on the navicular bone and associated joints was highest during dorsiflexion. This increased load may be responsible for microscopic changes of tidemark advancement and proteoglycan depletion in the articular cartilage and of proteoglycan production in the DSIL and DDFT Such microscopic changes may represent adaptive responses to stresses that may progress and contribute to lameness.

Meniscal repair is common and recommended in young patients. Suture techniques and fixation devices were developed for stronger, more facile repairs. Three devices (T-Fix, Meniscal Staple, Meniscus Arrow) were biomechanically compared to horizontal PDS suture. Peripheral tears were created in porcine menisci and repaired using the manufacturer's technique. An Instron was used to distract the menisci at 50 mm/min in axial-pullout and longitudinal shear loads. Load to failure curves and peak failure loads were noted. Load to failure in axially loaded pull-out mode was: Staple, 4.195+/-3.70 N; Arrow, 39.755+/-11.37 N; T-Fix, 45.892+/-13.99 N; Suture, 107.65+/-22.37 N. Analysis of variance with post hoc testing revealed Staple failure at lower load than all devices and Suture failure at higher loads than all devices; Arrow and T-Fix were similar. The data varied significantly from that obtained in shear. Shear loads to failure were: Staple, 8.39+/-8.62 N; Arrow, 27.67+/-14.33 N; T-Fix, 57.47+/-17.05 N; Suture, 64.15+/-17.05 N. Analysis of variance, power analysis, and pair-wise multiple comparisons revealed significant differences between: Suture and Staple, Suture and Arrow, and T-Fix and Staple. No differences were noted between Suture and T-Fix, T-Fix and Arrow, or Arrow and Staple. In pullout, Suture and T-Fix maintained better apposition at low loads. As load increased, the menisci separated until device failure. Arrows allowed low load separation but held tissue until failure. Staples failed at low load. For shear, the menisci attempted to reorient parallel to the force. The devices failed in a pull-slide pattern. Suture failed by pull-through. Meniscal repair devices are easy to use and may provide resistance to shear and pull out. The resistance to pullout loads was very different than the resistance to longitudinal shear loads.