Elsevier

Journal of Biomechanics

Volume 31, Issue 6, 1 June 1998, Pages 511-517
Journal of Biomechanics

One-year changes in hind limb kinematics, ground reaction forces and knee stability in an experimental model of osteoarthritis

https://doi.org/10.1016/S0021-9290(98)00041-4Get rights and content

Abstract

Long-term changes in the three-dimensional external loading, hind limb kinematics and knee stability were assessed in an anterior cruciate ligament (ACL)-transected cat model of osteoarthritis (OA). Seven skeletally mature cats (mean mass 4.6±1.4 kg) were studied before ACL transection (ACLT) and at 1 and 3 weeks, and at 3, 6, 9 and 12 months following ACLT.

One week following ACLT, significant changes from the normal locomotion pattern were observed: peak vertical and anterior–posterior ground reaction forces were decreased, particularly the peak posterior forces in the early phase of stance. Furthermore, knee angles were reduced by about 15° throughout the whole gait cycle, while ankle and hip angles were reduced at paw off in the experimental compared to the contralateral hind limbs. Ground reaction forces and hind limb kinematics recovered to near pre-surgical patterns over the one year period assessed.

ACLT was also associated with an increased knee instability which improved over time. X-rays suggested that there was a continued degeneration in the experimental knee over the one year period; there was osteophyte formation at the joint margins and an increase in cartilage thickness throughout the joint.

It was speculated that the more flexed knee angles and the reduced anterior–posterior ground reaction forces in the ACL-transected compared to the intact hind limb represent an adaptive strategy aimed at avoiding excessive anterior displacement of the tibia in the early phase of stance. The recovery of the locomotion pattern with time might be related to the corresponding improvement of knee stability.

Introduction

Acute joint injuries often produce long-term problems and have been found to result in an increased incidence of osteoarthritis (OA, Noyes et al., 1983). Various animal models have been used to simulate the pathological events associated with OA and to study the mechanisms underlying the onset and progression of the joint degeneration. Mechanical factors such as joint instabilities and changes in loading characteristics following injury or experimental intervention (e.g. anterior cruciate ligament transection, ACLT) have been attributed a key function in the onset and pathogenesis of OA in the joint and the articular cartilage (Herzog et al., 1993; Moskowitz, 1977). Following ACLT, unloading of the transected hind limb in dogs and cats was observed. The altered loading pattern was reflected by changes in the kinematics and the vertical ground reaction forces (Hasler, 1996; Herzog et al., 1993; Korvick et al., 1994; O’Connor et al., 1989; Threlkeld et al., 1993; Vilensky et al., 1994; Visco et al., 1990), which did not recover to pre-intervention values within three to six months post ACLT (O’Connor et al., 1989; Threlkeld et al., 1993; Visco et al., 1990). The changes in hind limb kinematics and kinetics were associated with histological and biochemical adaptations in the articular cartilage, which approximate the human condition (Adams and Brandt, 1991; Brandt et al., 1991a, Brandt et al., 1991b; Dedrick et al., 1993; Herzog et al., 1993).

Little information is available on the long-term effects of ACLT in experimental models of OA. There is only a single study in which the full time course of OA was investigated in three dogs (Brandt et al., 1991a, Brandt et al., 1991b). At 36 months post ACLT, MRI demonstrated thickening of the cartilage in the transected limb, indicating a stage of hypertrophic cartilage repair. Nine months later, focal loss of the cartilage was observed, which resulted in a full-thickness loss of the cartilage on the medial femoral condyles at 54 months post ACLT. Vertical ground reaction forces of the transected hind limbs measured at 24, 36 and 45 months post ACLT were about 50% of body weight compared to 65% of body weight in the contralateral hind limbs. The small number of animals, the limited number of experimental observations, and the restriction to a uni-directional (vertical) ground reaction force analysis give only limited insight into the time history of the mechanical events associated with OA.

The present study was aimed at describing long-term changes in the three-dimensional external loading, hind limb kinematics and knee joint stability in a ACL-transected cat model of OA. It was hypothesized that ACLT causes instability and unloading of the injured joint which would be associated with degenerative, osteoarthritic changes in the knee. It was further speculated that, in contrast to the dog, the loading characteristics would return to normal, pre-transection values over time. The present data represent a one-year follow-up for seven cats, which will be monitored until a full thickness loss of the cartilage occurs.

Section snippets

Methods

Seven skeletally mature male cats (mean mass 4.6± 1.4 kg) were studied. The study was approved by the Committee on Animal Ethics at The University of Calgary. ACLTs were performed on the left hind limbs of each animal using an established protocol (Herzog et al., 1993).

External loading was measured using two force platforms (Herzog et al., 1993). Vertical (Fz), anterior–posterior (Fy) and medial–lateral (Fx) ground reaction forces were recorded at 200 Hz per channel. During each experimental

Ground reaction forces pre and immediately (1–3 weeks) following ACLT

Typical examples of a single step of the same cat before ACLT and one week after ACLT are shown in Fig. 1aFig. 1b, respectively. Following ACLT, the magnitude of Fzmax was decreased in the experimental hind limbs, and increased in the contralateral hind limbs (Fig. 2a), and the typical bimodal shape of the Fz force–time curve (Fig. 1a) was changed to a unimodal shape (Fig. 1b). The magnitudes of the anterior–posterior ground reaction forces were also decreased immediately following ACLT;

Discussion

It is generally accepted that changes in joint mechanics following injury trigger adaptive responses which may lead to joint degeneration and OA (Moskowitz, 1977; Radin et al., 1972). The relationship between joint mechanics and the time history of OA has not been studied systematically. Except for pilot work on a limited number of animals, few time points, and restricted kinematic and kinetic descriptors (Korvick et al., 1994; O’Connor et al., 1989; Threlkeld et al., 1993; Visco et al., 1990),

Acknowledgements

This study was supported by grants from the Medical Research Council Canada, The Arthritis Society of Canada and the Foundation for Biomedical Research, Switzerland.

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