Elsevier

Journal of Biomechanics

Volume 31, Issue 12, December 1998, Pages 1137-1145
Journal of Biomechanics

Material and functional properties of articular cartilage and patellofemoral contact mechanics in an experimental model of osteoarthritis

https://doi.org/10.1016/S0021-9290(98)00136-5Get rights and content

Abstract

The purposes of this study were to determine the in situ functional and material properties of articular cartilage in an experimental model of joint injury, and to quantify the corresponding in situ joint contact mechanics. Experiments were performed in the anterior cruciate ligament (ACL) transected knee of the cat and the corresponding, intact contralateral knee, 16 weeks following intervention. Cartilage thickness, stiffness, effective Young’s modulus, and permeability were measured and derived from six locations of the knee. The total contact area and peak pressures in the patellofemoral joint were obtained in situ using Fuji Pressensor film, and comparisons between experimental and contralateral joint were made for corresponding loading conditions. Total joint contact area and peak pressure were increased and decreased significantly (α=0.01), respectively, in the experimental compared to the contralateral joint. Articular cartilage thickness and stiffness were increased and decreased significantly (α=0.01), respectively, in the experimental compared to the contralateral joint in the four femoral and patellar test locations. Articular cartilage material properties (effective Young’s modulus and permeability) were the same in the ACL-transected and intact joints. These results demonstrate for the first time the effect of changes in articular cartilage properties on the load transmission across a joint. They further demonstrate a substantial change in the joint contact mechanics within 16 weeks of ACL transection. The results were corroborated by theoretical analysis of the contact mechanics in the intact and ACL-transected knee using biphasic contact analysis and direct input of cartilage properties and joint surface geometry from the experimental animals. We conclude that the joint contact mechanics in the ACL-transected cat change within 16 weeks of experimental intervention.

Introduction

It is generally accepted that tissues of the musculoskeletal system adapt to changes in the mechanical environment (Taber, 1995). These adaptations have been best quantified in bone (Carter, 1987; Cowin, 1986; Goldstein et al., 1991; Huiskes et al., 1987) and skeletal muscle (Booth, 1982; Goldberg et al., 1975; Simard et al., 1982; Tabary et al., 1972; Vandenburgh, 1982). However, the relationship between mechanical (stress–strain) state of tissue and its growth and remodelling is largely unknown.

Articular cartilage is thought to adapt to changes in its mechanical environment (Adams, 1989; Brandt et al., 1991; Jurvelin et al., 1986; Setton et al., 1994). Perturbations of the joint mechanics through surgical removal of the anterior cruciate ligament (ACL), meniscectomy, or resection of the tibial plateau in the knee of experimental models of joint injury have been shown to produce osteoarthritic changes in the articular cartilage (McDevitt et al., 1977; Moskowitz et al., 1979; Pond and Nuki, 1973). However, the changes in the in situ mechanical properties of the articular cartilage in these joint injury models are largely unknown. Furthermore, changes in the functional properties of the joint (e.g., load transmission) associated with the alterations in cartilage properties have not been determined to date.

The purposes of this study were (1) to determine the in situ functional and material properties of articular cartilage in an experimental model of joint injury; and (2) to quantify the corresponding in situ joint contact mechanics. The cat ACL-transected knee was chosen as the experimental model (Herzog et al., 1993). Measurements in the experimental knee were made 16 weeks following ACL transection; a time when biochemical and morphological changes have occurred in the articular cartilage. Reference measurements were made in the corresponding intact, contralateral knee. It is realized that the contralateral knee may have been affected by the intervention in the experimental knee, and thus, may not represent a ‘normal’ control. However, this design approximates best the injury scenario in humans in which ACL tears typically occur unilaterally.

Section snippets

Animals and surgery

All experimental measurements were performed in adult, outbred cats (mass>3.5 kg; n=5). The anterior cruciate ligament was transected in the left knee using an arthroscopic approach performed by a trained clinician while the animal was deeply anesthetized (Halothane). The right knee was left intact. Following surgery, ACL transection was functionally verified using an anterior drawer test, and was further verified following sacrifice. All experimental aspects of this study were approved by the

Gross morphology

Inspection of the experimental knees revealed that all ACLs had been cut completely except for one animal in which about 25% of the ACL had been left intact. The results of this animal did not differ from the remaining animals, thus no further distinction will be made. It should be noted though, that a partial ACL transection appeared to have similar effects on cartilage growth and remodelling, as well as on patellofemoral contact properties as a complete transection.

The experimental knees

Discussion

Anterior cruciate ligament transection has been shown to lead to complete erosion of the articular cartilage in the dog knee (Brandt et al., 1991). Our work in the ACL-transected cat shows that articular cartilage growth and remodelling is similar to that observed in the dog (Herzog et al., 1993). In the early stages of adaptation following ACL transection, canine articular cartilage has been shown to increase in thickness (Adams, 1989), and its elastic modulus and permeability (Setton et al.,

Acknowledgments

This study was supported by the Medical Research Council and The Arthritis Society of Canada.

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