Calcium phosphate particulates increase friction in the rat knee joint M.L. Roemhildt, M.G. Gardner-Morse, C.F. Morgan, B.D. Beynnon, G.J. Badger  Osteoarthritis and Cartilage  Volume 22, Issue 5, Pages 706-709 (May 2014) DOI: 10.1016/j.joca.2014.02.938 Copyright © 2014 Osteoarthritis Research Society International Terms and Conditions

Fig. 1 A) Pendulum apparatus for measuring the coefficients of friction of rat knee joints showing the rat knee joint in the mounting block, a weighted pendulum with infrared reflectors and a trigger bar to start the pendulum oscillations. B) Close up view of the rat femur in the mounting block and the tibia fitted to the pendulum. Osteoarthritis and Cartilage 2014 22, 706-709DOI: (10.1016/j.joca.2014.02.938) Copyright © 2014 Osteoarthritis Research Society International Terms and Conditions

Fig. 2 A) Representative data from individual trials illustrating the decrease (decay) in anterior-posterior (AP) amplitude of the pendulum oscillations in a rat knee joint. The three test conditions were: (1) naïve (solid light gray line), (2) after injection of 100 μL of phosphate buffered saline (sham) (dotted medium gray line) and (3) after injection of 100 μL of 1 mg/mL basic calcium phosphate (BCP) solution (dashed black line). Data illustrate decreased amplitude and number of oscillations with BCP injection as compared to naïve and saline conditions (See Supplemental Fig. 2 for this plot in color). B) Mean coefficients of friction (dimensionless) ±95% confidence interval for the one (●) and two (■) parameter model fits to the pendulum oscillation data showing a significant increase in the friction with the injection of 100 μL of 1 mg/mL basic calcium phosphate (BCP) suspension into the rat knee joint (n = 8). The coefficient of friction with the BCP injection was significantly higher than the naïve joint (*, P < 0.003) and the sham injection of 100 μL of phosphate buffered saline into the joint (**, P < 0.012). There was no significant difference between the coefficients of friction for the naïve and saline injected joints. Osteoarthritis and Cartilage 2014 22, 706-709DOI: (10.1016/j.joca.2014.02.938) Copyright © 2014 Osteoarthritis Research Society International Terms and Conditions

Fig. S1. Preliminary study demonstrating increasing coefficient of friction (COF) with increasing concentration of basic calcium phosphate (BCP) suspension as compared to phosphate buffered saline injection (sham) and the naïve conditions in the rat knee (2 specimens; 100 μL injections; n = 6 trials per data point). Results from the one parameter Stanton linear model. Note that BCP concentrations increase by factors of 10. Means ±95% confidence interval. Only in this preliminary study did the right hind leg and left hind leg of one separate Sprague–Dawley rat have injections with increasing BCP concentrations. Osteoarthritis and Cartilage 2014 22, 706-709DOI: (10.1016/j.joca.2014.02.938) Copyright © 2014 Osteoarthritis Research Society International Terms and Conditions

Fig. S2. Representative data from individual trials illustrating the decrease (decay) in anterior-posterior (AP) amplitude of the pendulum oscillations in a rat knee joint. The three test conditions were: (1) naïve (solid green line), (2) after injection of 100 μL of phosphate buffered saline (sham) (dashed blue line) and (3) after injection of 100 μL of 1 mg/mL basic calcium phosphate (BCP) solution (solid red line). Data illustrates decreased amplitude and number of oscillations with BCP injection as compared to naïve and saline conditions. Osteoarthritis and Cartilage 2014 22, 706-709DOI: (10.1016/j.joca.2014.02.938) Copyright © 2014 Osteoarthritis Research Society International Terms and Conditions