In healthy dogs, the forelimbs bear approximately 60% of the body weight and the hind limbs bear approximately 40% of the body weight, independent of gait (eg, walking1–4 or trotting5–9). Differences among breeds attributable to the relative distribution of body mass and body conformation have been described.10,11 For example, Greyhounds apply 55% of their body weight to the forelimbs and 45% to the hind limbs.6,12 However, the symmetry or asymmetry between the proportion of body weight supported by both forelimbs or both hind limbs is used to identify whether a dog is clinically sound or lame.13–20
In an attempt to unload an injured limb, an animal will alter the load distribution among the limbs. Most studies have focused on the limb contralateral to the affected limb, and it has been established that the load is shifted to the contralateral limb.21–23 Although a substantial unloading of a limb likely affects the entire body, only 2 studies12,24 have been conducted to investigate forelimb lameness in dogs by including all 4 limbs in the data collection. In one of those studies,12 a compensatory shift of load to both the contralateral forelimb and hind limb was detected, whereas in the other study,24 there was an increase in PFz of only the contralateral hind limb. The lack of more detailed information on the kinetic changes in all 4 limbs hinders understanding of the load redistribution and thus the specific load shifting mechanisms used by lame dogs.
The purpose of the study reported here was to determine specific kinetic changes in all 4 limbs that are associated with forelimb lameness. To directly compare data for the sound and lame conditions, we obtained data before and after inducing lameness in dogs. The method used to induce lameness allowed for the systematic study of compensatory mechanisms in relatively controlled conditions, thereby reducing the number of factors (eg, severity, duration, or cause of lameness) that could introduce variation into the results. Because walking and trotting are mechanically fundamentally different25 and lameness may be visible during trotting but not walking,19,26,27 which implies that the load redistribution depends on gait, we evaluated dogs while walking and trotting. In addition to the commonly analyzed PFz,24 we also analyzed MFz and IFz. Furthermore, footfall patterns were evaluated because an increase in ground contact time is 1 means of decreasing PFz while maintaining IFz.28 Because naturally occurring and induced lameness may differ with regard to the manner in which limb loading changes, we compared the results for the study reported here with published results for orthopedic patients with clinically relevant lameness.
Ground reaction force
Mean vertical force
Peak vertical force
Model 4060–08, Bertec Corp, Columbus, Ohio.
Vicon Nexus, Vicon Motion Systems Ltd, Oxford, England.
MyoResearch XP master edition, Noraxon, Scottsdale, Ariz.
Excel, Microsoft Corp, Redmond, Wash.
GraphPad Prism, version 4, GraphPad Software Inc, La Jolla, Calif.
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