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FRICTION SENSITIVITY OF MATERIALS IN ARTIFICIAL HIPS TO LUBRICATION SITUATION
S330
Presentation 1490 − Topic 25. Implant biomechanics
FRICTION SENSITIVITY OF MATERIALS IN ARTIFICIAL HIPS TO LUBRICATION SITUATION Arne Hothan, Nicholas Bishop, Na Fan, Michael Morlock
Institute for Biomechanics, TUHH - Hamburg University of Technology, Germany
Introduction The properties of ceramic-on-ceramic bearings in total hip replacement exhibit low friction and wear under standard conditions. However, specific challenges such as joint noises, have raised questions regarding the use of ceramics under unfavourable conditions. High joint moments, which have recently been implicated in taper-lock wear in modular head-stem systems with large metal heads, have also been related to unfavourable lubrication conditions. The aim of this study was to determine friction moments of commonly used bearing materials in lubricated and dry conditions representing standard and worst case situations in order to assess material specific advantages or risks dependent on lubrication situation.
Material and Methods The 5 most frequently used material combinations were investigated: metal-on-polyethylene (ME-PE), ceramic-on-polyethylene (CE-PE), metal-on-metal (ME-ME), ceramic-on-metal (CE-ME), ceramicon-ceramic (CE-CE) (ceramic: Biolox Delta, Ceramtec; metal: Ultamet, DePuy; poly: Marathon, DePuy). Friction moments of 28mm bearings (n=5 for each material combination) were determined in a servo-hydraulic hip simulator [1]. Gait (1Hz) was simulated by flexion-extension (+/-20°) with a cup inclination to the load vector of 33°. Stepwise varying constant axial load was applied (500N, 1500N and 2500N). Experiments were conducted under lubricated conditions (25% bovine serum) followed by dry conditions as the worst case scenario. Friction moments were measured using a six component load cell mounted between the head and the joint load actuator. The maximum friction moment of each gait cycle was determined and the friction factor μ was calculated by dividing the maximum friction moment M by the product of joint load N and bearing radius R (μ=M/(R*N)).
by a factor of 7 while ceramic-on-poly was affected the least but still significantly affected (Fig. 2; Faktoren für alle anderen Paarungen). Higher axial load decreased the friction coefficient of bearings combined with polyethylene (p<0.001) but not of hard-hard combinations (p>0.053) under lubricated as well as unlubricated condition.
Discussion The investigated dry situation is a worst case scenario, which might temporarily occur clinically due to edge load situations during activities. The high increase in friction for the hard-on-hard bearings with the loss of lubrication might explain the clinically observed phenomena such as joint noises (CE-CE and ME-ME) or excessive wear (ME-ME). Hard-on-soft articulations in contrast showed minor (CE-PE) to light (ME-PE) increase in friction in the same situation highlighting the tolerant behaviour of these bearing combinations.
Figure 1: Friction factors under lubricated condition for the different material combinations.
Results Material combination and lubrication state influenced interarticular friction greatly (p<0.001). Under lubricated conditions ceramic-on-ceramic showed the lowest friction factor (μ=0.09) and metal-on-metal the highest (μ=0.36; Fig. 1). Lack of lubricant significantly increased the friction factor for all material combinations (p<0.035). Friction of ceramic-on-ceramic bearings increased Journal of Biomechanics 45(S1)
Figure 2: Friction factors under dry condition for the different material combinations.
References [1] Hothan et al., JBiomech, 2011
ESB2012: 18th Congress of the European Society of Biomechanics
Presentation 1490 − Topic 25. Implant biomechanics
FRICTION SENSITIVITY OF MATERIALS IN ARTIFICIAL HIPS TO LUBRICATION SITUATION Arne Hothan, Nicholas Bishop, Na Fan, Michael Morlock
Institute for Biomechanics, TUHH - Hamburg University of Technology, Germany
Introduction The properties of ceramic-on-ceramic bearings in total hip replacement exhibit low friction and wear under standard conditions. However, specific challenges such as joint noises, have raised questions regarding the use of ceramics under unfavourable conditions. High joint moments, which have recently been implicated in taper-lock wear in modular head-stem systems with large metal heads, have also been related to unfavourable lubrication conditions. The aim of this study was to determine friction moments of commonly used bearing materials in lubricated and dry conditions representing standard and worst case situations in order to assess material specific advantages or risks dependent on lubrication situation.
Material and Methods The 5 most frequently used material combinations were investigated: metal-on-polyethylene (ME-PE), ceramic-on-polyethylene (CE-PE), metal-on-metal (ME-ME), ceramic-on-metal (CE-ME), ceramicon-ceramic (CE-CE) (ceramic: Biolox Delta, Ceramtec; metal: Ultamet, DePuy; poly: Marathon, DePuy). Friction moments of 28mm bearings (n=5 for each material combination) were determined in a servo-hydraulic hip simulator [1]. Gait (1Hz) was simulated by flexion-extension (+/-20°) with a cup inclination to the load vector of 33°. Stepwise varying constant axial load was applied (500N, 1500N and 2500N). Experiments were conducted under lubricated conditions (25% bovine serum) followed by dry conditions as the worst case scenario. Friction moments were measured using a six component load cell mounted between the head and the joint load actuator. The maximum friction moment of each gait cycle was determined and the friction factor μ was calculated by dividing the maximum friction moment M by the product of joint load N and bearing radius R (μ=M/(R*N)).
by a factor of 7 while ceramic-on-poly was affected the least but still significantly affected (Fig. 2; Faktoren für alle anderen Paarungen). Higher axial load decreased the friction coefficient of bearings combined with polyethylene (p<0.001) but not of hard-hard combinations (p>0.053) under lubricated as well as unlubricated condition.
Discussion The investigated dry situation is a worst case scenario, which might temporarily occur clinically due to edge load situations during activities. The high increase in friction for the hard-on-hard bearings with the loss of lubrication might explain the clinically observed phenomena such as joint noises (CE-CE and ME-ME) or excessive wear (ME-ME). Hard-on-soft articulations in contrast showed minor (CE-PE) to light (ME-PE) increase in friction in the same situation highlighting the tolerant behaviour of these bearing combinations.
Figure 1: Friction factors under lubricated condition for the different material combinations.
Results Material combination and lubrication state influenced interarticular friction greatly (p<0.001). Under lubricated conditions ceramic-on-ceramic showed the lowest friction factor (μ=0.09) and metal-on-metal the highest (μ=0.36; Fig. 1). Lack of lubricant significantly increased the friction factor for all material combinations (p<0.035). Friction of ceramic-on-ceramic bearings increased Journal of Biomechanics 45(S1)
Figure 2: Friction factors under dry condition for the different material combinations.
References [1] Hothan et al., JBiomech, 2011
ESB2012: 18th Congress of the European Society of Biomechanics