Effect of obesity on gait symmetry following anterior cruciate ligament transection

Abstract

INTRODUCTION

High fat diet and the resulting obesity are associated with chronic inflammation, which is thought to exacerbate osteoarthritis (OA) [1]. Also, obesity has been suggested to increase gait asymmetry [2]. To our knowledge, no one has evaluated the added effect of obesity in an instability OA progression model such as anterior cruciate ligament transection (ACL-X). The purpose of this study is to assess the effect of obesity on the progression of gait asymmetry, when factors are normalized for body weight, following an ACL-X protocol. We hypothesize that High-fat diet ACL-X animals will experience greater asymmetry than low-fat ACL-X animals over time.

METHODS

Twenty-eight male Sprague-Dawley rats were randomly assigned to either a high fat diet (HFD) or a low fat diet (LFD) group. The HFD group (n=18) received high fat sucrose food (40% fat, Diet #102412, Dyets, Inc) and the LFD group (n=10) received lean chow (13.5% fat, LabDiet 5001). Twelve weeks post diet induction, baseline 2-D kinematics and 3-D kinetic measurements were collected on a runway with two embedded side-by-side 7.5 x 30 cm force plates (Bertec, Columbus, OH). A minimum of two successful kinematic and kinetic trials for each limb were included in this analysis. Then, all animals were randomly assigned to receive an ACL-X (HFD n=12, LFD n=5) or surgical sham (HFD n=6, LFD n=4). Kinematic and kinetic data were collected 1-week post surgery, and again at 8 weeks post surgery. An Asymmetry Index (AI) was used to compare differences between limbs. The AI was calculated by:

(Contralateral (BW) – Experimental (BW)) X 100%

Contralateral (BW)

All data sets were compared for AI changes due to diet, surgery, diet*surgery, and over time using non-parametric statistics.

RESULTS

Twenty animals successfully met the inclusion criteria and were analyzed. In Figure 1, the normalized AI vertical impulse result for all groups is shown. The LFD ACL-X group (n=5) normalized AI vertical impulse was 12% (±15%), 20% (±6.4%), and 17% (±5.7%) respectively. The HFD SHAM group normalized AI vertical impulse was 16% (±17.2%), 34% (±7.2%), and 44% (±13%) respectively. The HFD ACL-X normalized AI vertical impulse was 17% (±13%), 37% (±5.4%) and 44% (±1%) respectively.

Figure 1. Normalized AI vertical impulse is demonstrated over time for three time points: Pre-Surgery, 1-week post surgery and 8-week post-surgery. * Indicates p<0.05.

DISCUSSION AND CONCLUSIONS

AI impulse was increased in all groups 1-week post surgery, but the HFD ACL-X had an increased AI when compared with LFD ACL-X (p<0.05). Both HFD groups had a greater normalized AI vertical impulse when compared with the LFD ACL-X group 8-weeks post surgery (p<0.05). The rats were first introduced to the runway and force plate at baseline testing, which contributes to the large variability seen pre-surgery. In conclusion, gait asymmetry is exacerbated over time for normalized AI vertical impulse after ACL-X in HFD animals. Conversely, a trend was evident towards recovery, or decreased AI in the LFD animals. A fourth data set, 16 weeks post surgery, will be analyzed to further characterize the effect of diet and surgery on this measure in ACL-X animals over time.