Background In humans, evaluation of tissue structure changes in OA is performed indirectly by use of surrogate markers, e.g. imaging and/or biochemical markers. In contrast, pain/disability can be validated directly, with questionnaires.

A direct evaluation of tissue changes can be performed in detail in animal models of OA, however, evaluation of OA pain/disability is challenging. For dogs, force plate analysis (FPA) is a widely used method which provides detailed information of joint loading (3 degrees of freedom; brake (Fy max), stance (Fz) and propulsion (Fy min) force). Unfortunately, this technique is time consuming and needs prolonged training. Therefore, a simplified method of studying joint loading was developed: a mobile weighing platform with 4 individual scales. The loading of the hind stifle joints was evaluated during progression of experimentally induced OA and, primarily, compared to FPA-Fz.

Objectives Can the 4-plates balance be used as an intermittent analysis, and partially replenish FPA, in measurement of joint unloading in an canine OA model?

Methods In twelve mixed breed (mongrel) dogs experimental OA was induced in the right stifle joint according to the Groove model¹. Twice at baseline and at every 5 weeks FPA was performed, as well as the 4-plates balance measurements. Five measurements of 10 seconds were performed and analysed. The average of these 5*10 sec measurements were compared to the FPA-Fz. In this first analyses baseline values (before surgery) and 10 weeks values (after surgery) were analysed, because the 5 week condition might still include pain/disability due to surgery.

Results By use of the 4-plates balance a decrease in loading of the OA right hind leg was found from 2.8±0.2kg at baseline to 2.5±0.2kg at 10 weeks follow-up (p<0.05). A similar pattern was seen for the FPA-Fz from 4.5±0.1N to 4.3±0.1N (p<0.01). A positive linear correlation was found between the delta as well as percentage decrease in loading of the right OA hind leg (10 weeks compared to pre-treatment) for both methods (R=+0.27 and R=+0.33, respectively; both p<0.03).

The change in loading between the left control and the right OA leg at baseline was -0.6±0.3kg (ns) and increased to -1.0±0.3kg at 10 weeks follow-up (p<0.003). The same was found for FPA-Fz, from +0.1±0.1N at baseline (ns) to -0.3±0.1N at 10 weeks (p<0.01). Also for this difference between the control and OA hind joints a positive linear correlation existed between the 4-plates balance and the FPA-Fz (R=+0.46, p<0.007).

Similar, statistically significant relations were found for the 4-plates balance and FPA-Fy max, but not for FPA-Fy min.

Conclusions Pain/disability due to OA is difficult to determine in animal models. The present study clearly demonstrates that the 4-plates balance is a useful method to measure pain/disability due to OA in dogs. The technique is less expensive, less time-consuming and can be performed at any location. Although, FPA is clearly a more elaborated technique and provides more information about gait and different forces and the 4-plates balance is a more static measurement, the latter may be of added value in evaluating pain/disability in canine models of OA.

1. Mastbergen et al. Osteoarthritis and Cartilage 2006.

Disclosure of Interest None Declared