The friction coefficient of XXXX remains remarkably low over 24h of loading.

@entity1 @entity227 @entity291 @entity2720
UNASSIGNED: The frictional response of whole @entity1 joints over durations spanning activities of daily living has not been reported previously. This study measured the friction of @entity1 @entity2720 during 24h of reciprocal loading in a pendulum testing device, at moderate (0.2mm/s, 4320 cycles) and low (0.02mm/s, 432 cycles) sliding speeds, under a 200N load. The effect of joint congruence was also investigated by testing @entity1 humeral heads against significantly larger mature @entity291 glenoids. Eight @entity1 joints and six @entity291 joints were tested in four combinations: @entity1 joints tested at moderate (hHCMS, n=6) and low speed (hHCLS, n=3), @entity1 humeral heads tested against @entity291 glenoids at moderate speed (LCMS, n=3), and @entity291 joints tested at moderate speed (bHCMS, n=3). In the first half hour the mean  standard deviation of the friction coefficient was hHCMS: 0.0016  0.0011, hHCLS: 0.0012  0.0002, LCMS: 0.0008  0.0002 and bHCMS: 0.0024  0.0008; in the last four hours it was hHCMS: 0.0057  0.0025, hHCLS: 0.0047  0.0017, LCMS: 0.0012  0.0003 and bHCMS: 0.0056  0.0016. The initial value was lower than the final value (p<0.0001). The value in LCMS was significantly lower than in hHCMS and bHCMS (p<0.01). No @entity227 was observed in any of the specimens. These are the first results to demonstrate that the friction coefficient of natural @entity1 shoulders remains remarkably low (averaging as little as 0.0015 and no greater than 0.006) for up to 24h of continuous loading. The sustained low friction coefficients observed in @entity2720 rolling rather than sliding friction.
