Stuart Simpson, Stryker Orthopedics07.28.10
New designs and technologies constantly are being developed to help address the needs of higher-demand, younger and more active baby boomers. The challenge is to develop a system that works and feels as close to the patient’s natural hip as possible.
While total hip replacement is one of the most successful surgical procedures performed today, dislocation remains one of the top reported complications of this popular procedure.2 During the past decade, there has been a growing industry belief that the functional benefits of stability and mobility were related to large head sizes, and thus the use of“large-head technology” spread. These designs were believed to provide the stability surgeons were looking for, as well as the potential for reduced wear.
The Issue
To address dislocation, conventional designs use metal-on-metal large head technologies. Presentations on this topic at this year’s American Academy of Orthopaedic Surgeons annual meeting and recent New York Times articles have brought this topic to the forefront for both physicians and consumers.
Additionally, the Medicines and Healthcare products Regulatory Agency in the United Kingdom (comparable to the U.S. Food and Drug Administration) issued a device alert in April 2010, in which it identified that a small number of metal-on-metal hips may develop soft tissue reactions to wear debris, be at risk of early failure and require revision surgery.
While Stryker manufactures large-head hip technologies, it does not make or distribute a metal-on-metal bearing option for traditional primary hip replacement systems. Instead, the company’s large-head primary hip replacement systems use either ceramic bearings or its proprietary highly crosslinked polyethylene, X3 Advanced Bearing Technology. Stryker opted to develop a dual-mobility technology, its Mobile Bearing Hip System, to offer the potential benefits of a large-head bearing total hip arthroplasty (THA) system without a metal-on-metal hip articulation.
The Design
Unlike conventional fixed-bearing hip replacement systems overwhelmingly used in the United States today, dual-mobility systems have two points of articulation instead of one. Dual points of articulation help accommodate multi-directional movement, which provide greater range of motion than fixed implant designs based on laboratory testing.3While both conventional and dual-mobility systems are designed to potentially restore stability, the mobile-bearing system can use a larger diameter femoral head, which can provide improved resistance to dislocation.4
The dual-mobility concept was introduced in France in 1976 by Giles Bousquet, who created the hip to reduce wear and help increase stability and mobility. With more than 30 years of clinical history, the dual-mobility design has offered patients improved joint stability as well as the restoration of joint mechanics and function.5
Stryker’s Mobile Bearing Hip is the only dual-mobility acetabular system in the U.S. market.Its patented X3 Advanced Bearing Technology enables the hip to offer the benefits of a large diameter bearing without a metal-on-metal articulation.6 This system is called Anatomic Dual Mobility (ADM), for its anatomic cup design; cups are designed specifically for the right and left hips, in the effort to reproduce the patient’s anatomy more accurately.
Addressing Wear
Stryker’s patented X3 Advanced Bearing Technology enables surgeons to offer its Mobile Bearing Hip System to some higher demand patient groups without the risk of accelerated polyethylene wear. Studies have shown that the ADM system with X3 showed a 94 percent reduction in wear compared to metal-on-metal at 65 degrees of inclination.7 Many highly crosslinked polyethylenes on the market today involve a remelting process, which can compromise the structural strength and long-term performance of the polyethylene. The X3 Advanced Bearing Technology, however, is the first highly crosslinked polyethylene that is “annealed” to increase the wear resistance of the material while maintaining its strength. 8-17 This increased wear resistance may extend the life of the implant, making this new technology particularly important for younger patients. By combining an evolution in design with the only anatomic dual mobility acetabular system and its patented X3 Advanced Bearing Technology, the Mobile Bearing Hip System is designed to address stability and mobility in primary THA with potentially less concern over increased wear.
Anatomic Design
The anatomic rim of the Mobile Bearing Hip System has been designed to address another risk of large head hip replacement technology—groin pain. Associated with psoas tendon impingement, groin pain is reported in 4 percent of patients treated with large head technologies.18The implants anatomic design is unique, featuring an iliopsoas tendon cutout, which matches the patient’s anatomy to help avoid tendon impingement. 19
The Future
As they have for decades, patient demands and expectations will continue to change. To succeed in addressing these changes, orthopaedic manufacturers must remain committed to researching and developing new ways to address people’s needs—including the introduction of new designs and new materials that make replacement joints feel and act more like the natural joint.
We can begin addressing these issues by considering solutions that already exist—some of which have been around for decades. As long as medical device makers use the lessons of the past to inform technological development of the future, the industry can continue to create effective medical solutions that meet changing patient and surgeon needs.
Stuart Simpson is vice president of Global Hip Marketing for Kalamazoo, Mich.-based Stryker Orthopaedics.
References:
1. CDC Report "Health, United States, 2009."
2. Swedish Hip Registry Annual Report 2005
3. Stryker Orthopaedics R&D Test Report: RD-06-078
4. Nevelos, J., Bhimji, S., Macintyre, J., et al. (2010). Acetabular Bearing Design Has a Greater Influence on Jump Distance than Head Size. 56th Annual ORS Meeting: Poster #2028.
5. Farizon, F., de Lavison, R., Azoulai, J.J., Bousquet, G. (1998). Results with a cementless alumina-coated cup with dual mobility. International Orthopaedics (SICOT) 22: 219-224.
6. US Patent # 6,174,934, 6,372,814, 6,664,308, 6,818,020, 7,517,919.
7. Herrera, L., Lee, R., Longaray, J., et al. (2010). Edge Loading Wear due to Inclination Angle for Three Contemporary Hip Bearings. 56th Annual ORS Meeting. Poster #2259.
8. Stryker Orthopaedics Triathlon CR Tibial Inserts made from X3 UHMWPE, 5530-G-409 show a 68% reduction in volumetric wear rate versus the same insert fabricated from N2Vac™ gamma sterilized UHMWPE, 5530-P-409. The insert tested was Size 4, 9 mm thick. Testing was conducted under multiaxial knee simulator (multi-station MTS knee joint simulator a) for five million cycles using appropriate size CoCr counterfaces, a specific type of diluted calf serum lubricant and the motion and loading conditions, representing normal walking, outlined in ISO/DIS 14243-3. Volumetric wear rates were 17.7 ± 2.2 mm3 /106 cycles for standard polyethylene inserts and 5.7 ± 1.5 mm3 /106 cycles for test samples. Test inserts were exposed to a gas plasma sterilization process. In vitro knee wear simulator tests have not been shown to quantitatively predict clinical wear performance.
9. Stryker Orthopaedics Triathlon PS Tibial Inserts made of X3 UHMWPE, 5532-G-409 show a 64% reduction in volumetric wear rate versus the same insert fabricated from N2Vac gamma sterilized UHMWPE, 5532-P-409. The insert tested was Size 4, 9 mm thick. Testing was conducted under multiaxial knee simulator (multi-station MTS knee joint simulators for five million cycles using a size 7 CoCr counterfaces, a specific type of diluted calf serum lubricant and literature or fluoroscopy based motion and loading conditions representing stair climbing.b,c Volumetric wear rates were 3.6 ± 0.61 mm3 /106 cycles for standard polyethylene inserts and were 1.3 ± 0.44 mm3 /106 cycles for test samples. Test inserts were exposed to a gas plasma sterilization process. In vitro knee wear simulator tests have not been shown to quantitatively predict clinical wear performance.
10. Stryker Orthopaedics Scorpio CR Tibial Inserts made from X3 UHMWPE, 72-22-0708, show a 79% reduction in volumetric wear rate versus the same insert fabricated from N2Vac gamma sterilized UHMWPE, 72-2-0708. The insert tested was Size 7, 8 mm thick. Testing was conducted under multiaxial knee simulator (multi-station MTS knee joint simulator a ) for five million cycles using appropriate size CoCr counterfaces, a specific type of diluted calf serum lubricant and the motion and loading conditions, representing normal walking, outlined in ISO/DIS 14243-3. Volumetric wear rates were 34.6 ± 1.5 mm3 /106 cycles for standard polyethylene inserts and 7.3 ± 0.7 mm3 /106 cycles for test samples. Test inserts were exposed to a gas plasma sterilization process. In vitro knee wear simulator tests have not been shown to quantitatively predict clinical wear performance.
11. Stryker Orthopaedics Scorpio PS tibial inserts made from X3 UHMWPE, 72-23-0708, show a 77% reduction in volumetric wear rate versus the same tibial insert fabricated from N2Vac gamma sterilized UHMWPE, 72-3-0708. The insert tested was Size 7, 8mm thick. Testing was conducted under multiaxial knee simulator (multi-station MTS knee joint simulator) for five million cycles using appropriate size CoCr counterfaces, a specific type of diluted calf serum lubricant and literature or fluoroscopy based motion and loading conditions representing stair climbing [a,b,c]. Volumetric wear rates were 35.8 ± 1.7 mm3/106 cycles for standard polyethylene inserts and were 8.2 ± 0.7 mm3/106 cycles for test samples. Test inserts were exposed to a gas plasma sterilization process. In vitro knee wear simulator tests have not been shown to quantitatively predict clinical wear performance.
[a] A. Essner, A.Wang, C. Stark and J. H. Dumbleton. A simulator for the evaluation of total knee replacement wear, 5th World Biomaterials Congress, Toronto, Canada, May 1996, pg 580.
[b] R. Riener, M. Rabuffetti and C. Frigo. Stair ascent and descent at different inclinations, Gait and Posture 15:2002, pp. 32-44.
[c] JB.Morrison. Function of the knee joint in various activities, Bio-medical Engineering, 4:1969, pp. 573-580.
12. Stryker Orthopaedics Trident Acetabular Inserts made of X3 UHMWPE (unsterilized), 721-00-32E, show a 97% reduction in volumetric wear rate versus the same insert fabricated from N 2 Vac gamma sterilized UHMWPE, 620-00-32E. The insert tested was 7.5 mm thick with an inner diameter of 32 mm. Testing was conducted under multi-axial hip joint simulation for 5 million cycles using a 32 mm CoCr articulating counterface and calf serum lubricant. X3 UHMWPE Trident acetabular inserts showed a net weight gain due to fluid absorption phenomena but yielded a positive slope and wear rate in linear regression analysis. Volumetric wear rates were 46.39 ± 11.42 mm3 /106 cycles for N2 Vac gamma sterilized UHMWPE inserts and 1.35 ± 0.68 mm3 /106 cycles for X3 UHMWPE (unsterilized) Trident Acetabular Inserts. Although in-vitro hip wear simulation methods have not been shown to quantitatively predict clinical wear performance, the current model has been able to reproduce correct wear resistance rankings for some materials with documented clinical results.d, e, f
[d] Wang A, et al. Tribology International, Vol. 31, No. 1-3:17-33, 1998.
[e] Essner A. et al. 44th Annual Meeting, ORS, New Orleans, Mar. 16-19, 1998:774.
[f] Essner A. et al. 47th Annual Meeting, ORS, San Francisco, Feb. 25-28, 2001:1007
13. X3 UHMWPE maintains mechanical properties after accelerated oxidative aging. No statistical difference was found for Tensile Yield Strength, Ultimate Tensile Strength and Elongation as measured per ASTM D638 before and after exposure to ASTM F2003 accelerated aging (5 Atmospheres (ATM) of oxygen at 70ºC for 14 days). Tensile Yield Strength was 23.5 ± 0.3 MPa and 23.6 ± 0.2 MPa, Ultimate Tensile Strength was 56.7 ± 2.1 MPa and 56.3 ± 2.3 MPa and Elongation was 267 ± 7% and 266 ± 9% before and after accelerated oxidative aging, respectively.
14. X3 UHMWPE resists the effects of oxidation. No statistical difference was found for Tensile Yield Strength, Ultimate Tensile Strength, Elongation, Crystallinity and Density as measured per ASTM D638, D3417 and D1505 before and after ASTM F2003 accelerated aging (5 ATM of oxygen at 70°C for 14 days). Tensile Yield Strength was 23.5 ± 0.3 MPa and 23.6 ± 0.2 MPa, Ultimate Tensile Strength was 56.7 ± 2.1 MPa and 56.3 ± 2.3 MPa, Elongation was 267 ± 7% and 266 ± 9%, Crystallinity was 61.7 ± 0.6% and 61.0 ± 0.5%, and Density was 939.2 ± 0.1 kg/m3 and 939.2 ± 0.2 kg/m3 before and after accelerated oxidative aging, respectively.
15. ‘Improved Strength of Cross-linked UHMWPE Without Compromising Oxidation/Fatigue Resistance and Wear”, Yau SS; Wang A, Lovell T. 2007 Combined ORS Poster #496.
16. X3 UHMWPE virtually eliminates free radicals, as measured by Electron Spin Resonance (ESR). A very low (noise level, near instrument detection limit) concentration of residual free radicals was detected in the X3 UHMWPE. A 99% reduction of free radicals (14 ± 2 x 1014 spins/gram versus 1550 ± 32 x 1014 spins/gram) was found when compared to N2Vac gamma sterilized UHMWPE.
17.“Wear, oxidation and mechanical properties of a sequentially irradiated and annealed UHMWPE in total joint replacement”, A.Wang, H.Zeng, S-S Yau, A. Essner, M. Manley and J. Dumbleton, Journal of Physics, D:Appl:
Phys 39 (2006).
18. Nasser, A. B., Beaule, P. E., O’Neill, M., et al. (2010). Incidence of Groin Pain After Metal-on-Metal Hip Resurfacing. CORR 468: 392-399.
19. Tracol P., Vandenbussche E., Deloge N., et al. (2007). Navigation Acetabular Anatomic Study Application in the Development of a New Implant. EFORT Poster.
While total hip replacement is one of the most successful surgical procedures performed today, dislocation remains one of the top reported complications of this popular procedure.2 During the past decade, there has been a growing industry belief that the functional benefits of stability and mobility were related to large head sizes, and thus the use of“large-head technology” spread. These designs were believed to provide the stability surgeons were looking for, as well as the potential for reduced wear.
The Issue
To address dislocation, conventional designs use metal-on-metal large head technologies. Presentations on this topic at this year’s American Academy of Orthopaedic Surgeons annual meeting and recent New York Times articles have brought this topic to the forefront for both physicians and consumers.
Additionally, the Medicines and Healthcare products Regulatory Agency in the United Kingdom (comparable to the U.S. Food and Drug Administration) issued a device alert in April 2010, in which it identified that a small number of metal-on-metal hips may develop soft tissue reactions to wear debris, be at risk of early failure and require revision surgery.
While Stryker manufactures large-head hip technologies, it does not make or distribute a metal-on-metal bearing option for traditional primary hip replacement systems. Instead, the company’s large-head primary hip replacement systems use either ceramic bearings or its proprietary highly crosslinked polyethylene, X3 Advanced Bearing Technology. Stryker opted to develop a dual-mobility technology, its Mobile Bearing Hip System, to offer the potential benefits of a large-head bearing total hip arthroplasty (THA) system without a metal-on-metal hip articulation.
The Design
Unlike conventional fixed-bearing hip replacement systems overwhelmingly used in the United States today, dual-mobility systems have two points of articulation instead of one. Dual points of articulation help accommodate multi-directional movement, which provide greater range of motion than fixed implant designs based on laboratory testing.3While both conventional and dual-mobility systems are designed to potentially restore stability, the mobile-bearing system can use a larger diameter femoral head, which can provide improved resistance to dislocation.4
The dual-mobility concept was introduced in France in 1976 by Giles Bousquet, who created the hip to reduce wear and help increase stability and mobility. With more than 30 years of clinical history, the dual-mobility design has offered patients improved joint stability as well as the restoration of joint mechanics and function.5
Stryker’s Mobile Bearing Hip is the only dual-mobility acetabular system in the U.S. market.Its patented X3 Advanced Bearing Technology enables the hip to offer the benefits of a large diameter bearing without a metal-on-metal articulation.6 This system is called Anatomic Dual Mobility (ADM), for its anatomic cup design; cups are designed specifically for the right and left hips, in the effort to reproduce the patient’s anatomy more accurately.
Addressing Wear
Stryker’s patented X3 Advanced Bearing Technology enables surgeons to offer its Mobile Bearing Hip System to some higher demand patient groups without the risk of accelerated polyethylene wear. Studies have shown that the ADM system with X3 showed a 94 percent reduction in wear compared to metal-on-metal at 65 degrees of inclination.7 Many highly crosslinked polyethylenes on the market today involve a remelting process, which can compromise the structural strength and long-term performance of the polyethylene. The X3 Advanced Bearing Technology, however, is the first highly crosslinked polyethylene that is “annealed” to increase the wear resistance of the material while maintaining its strength. 8-17 This increased wear resistance may extend the life of the implant, making this new technology particularly important for younger patients. By combining an evolution in design with the only anatomic dual mobility acetabular system and its patented X3 Advanced Bearing Technology, the Mobile Bearing Hip System is designed to address stability and mobility in primary THA with potentially less concern over increased wear.
Anatomic Design
The anatomic rim of the Mobile Bearing Hip System has been designed to address another risk of large head hip replacement technology—groin pain. Associated with psoas tendon impingement, groin pain is reported in 4 percent of patients treated with large head technologies.18The implants anatomic design is unique, featuring an iliopsoas tendon cutout, which matches the patient’s anatomy to help avoid tendon impingement. 19
The Future
As they have for decades, patient demands and expectations will continue to change. To succeed in addressing these changes, orthopaedic manufacturers must remain committed to researching and developing new ways to address people’s needs—including the introduction of new designs and new materials that make replacement joints feel and act more like the natural joint.
We can begin addressing these issues by considering solutions that already exist—some of which have been around for decades. As long as medical device makers use the lessons of the past to inform technological development of the future, the industry can continue to create effective medical solutions that meet changing patient and surgeon needs.
Stuart Simpson is vice president of Global Hip Marketing for Kalamazoo, Mich.-based Stryker Orthopaedics.
References:
1. CDC Report "Health, United States, 2009."
2. Swedish Hip Registry Annual Report 2005
3. Stryker Orthopaedics R&D Test Report: RD-06-078
4. Nevelos, J., Bhimji, S., Macintyre, J., et al. (2010). Acetabular Bearing Design Has a Greater Influence on Jump Distance than Head Size. 56th Annual ORS Meeting: Poster #2028.
5. Farizon, F., de Lavison, R., Azoulai, J.J., Bousquet, G. (1998). Results with a cementless alumina-coated cup with dual mobility. International Orthopaedics (SICOT) 22: 219-224.
6. US Patent # 6,174,934, 6,372,814, 6,664,308, 6,818,020, 7,517,919.
7. Herrera, L., Lee, R., Longaray, J., et al. (2010). Edge Loading Wear due to Inclination Angle for Three Contemporary Hip Bearings. 56th Annual ORS Meeting. Poster #2259.
8. Stryker Orthopaedics Triathlon CR Tibial Inserts made from X3 UHMWPE, 5530-G-409 show a 68% reduction in volumetric wear rate versus the same insert fabricated from N2Vac™ gamma sterilized UHMWPE, 5530-P-409. The insert tested was Size 4, 9 mm thick. Testing was conducted under multiaxial knee simulator (multi-station MTS knee joint simulator a) for five million cycles using appropriate size CoCr counterfaces, a specific type of diluted calf serum lubricant and the motion and loading conditions, representing normal walking, outlined in ISO/DIS 14243-3. Volumetric wear rates were 17.7 ± 2.2 mm3 /106 cycles for standard polyethylene inserts and 5.7 ± 1.5 mm3 /106 cycles for test samples. Test inserts were exposed to a gas plasma sterilization process. In vitro knee wear simulator tests have not been shown to quantitatively predict clinical wear performance.
9. Stryker Orthopaedics Triathlon PS Tibial Inserts made of X3 UHMWPE, 5532-G-409 show a 64% reduction in volumetric wear rate versus the same insert fabricated from N2Vac gamma sterilized UHMWPE, 5532-P-409. The insert tested was Size 4, 9 mm thick. Testing was conducted under multiaxial knee simulator (multi-station MTS knee joint simulators for five million cycles using a size 7 CoCr counterfaces, a specific type of diluted calf serum lubricant and literature or fluoroscopy based motion and loading conditions representing stair climbing.b,c Volumetric wear rates were 3.6 ± 0.61 mm3 /106 cycles for standard polyethylene inserts and were 1.3 ± 0.44 mm3 /106 cycles for test samples. Test inserts were exposed to a gas plasma sterilization process. In vitro knee wear simulator tests have not been shown to quantitatively predict clinical wear performance.
10. Stryker Orthopaedics Scorpio CR Tibial Inserts made from X3 UHMWPE, 72-22-0708, show a 79% reduction in volumetric wear rate versus the same insert fabricated from N2Vac gamma sterilized UHMWPE, 72-2-0708. The insert tested was Size 7, 8 mm thick. Testing was conducted under multiaxial knee simulator (multi-station MTS knee joint simulator a ) for five million cycles using appropriate size CoCr counterfaces, a specific type of diluted calf serum lubricant and the motion and loading conditions, representing normal walking, outlined in ISO/DIS 14243-3. Volumetric wear rates were 34.6 ± 1.5 mm3 /106 cycles for standard polyethylene inserts and 7.3 ± 0.7 mm3 /106 cycles for test samples. Test inserts were exposed to a gas plasma sterilization process. In vitro knee wear simulator tests have not been shown to quantitatively predict clinical wear performance.
11. Stryker Orthopaedics Scorpio PS tibial inserts made from X3 UHMWPE, 72-23-0708, show a 77% reduction in volumetric wear rate versus the same tibial insert fabricated from N2Vac gamma sterilized UHMWPE, 72-3-0708. The insert tested was Size 7, 8mm thick. Testing was conducted under multiaxial knee simulator (multi-station MTS knee joint simulator) for five million cycles using appropriate size CoCr counterfaces, a specific type of diluted calf serum lubricant and literature or fluoroscopy based motion and loading conditions representing stair climbing [a,b,c]. Volumetric wear rates were 35.8 ± 1.7 mm3/106 cycles for standard polyethylene inserts and were 8.2 ± 0.7 mm3/106 cycles for test samples. Test inserts were exposed to a gas plasma sterilization process. In vitro knee wear simulator tests have not been shown to quantitatively predict clinical wear performance.
[a] A. Essner, A.Wang, C. Stark and J. H. Dumbleton. A simulator for the evaluation of total knee replacement wear, 5th World Biomaterials Congress, Toronto, Canada, May 1996, pg 580.
[b] R. Riener, M. Rabuffetti and C. Frigo. Stair ascent and descent at different inclinations, Gait and Posture 15:2002, pp. 32-44.
[c] JB.Morrison. Function of the knee joint in various activities, Bio-medical Engineering, 4:1969, pp. 573-580.
12. Stryker Orthopaedics Trident Acetabular Inserts made of X3 UHMWPE (unsterilized), 721-00-32E, show a 97% reduction in volumetric wear rate versus the same insert fabricated from N 2 Vac gamma sterilized UHMWPE, 620-00-32E. The insert tested was 7.5 mm thick with an inner diameter of 32 mm. Testing was conducted under multi-axial hip joint simulation for 5 million cycles using a 32 mm CoCr articulating counterface and calf serum lubricant. X3 UHMWPE Trident acetabular inserts showed a net weight gain due to fluid absorption phenomena but yielded a positive slope and wear rate in linear regression analysis. Volumetric wear rates were 46.39 ± 11.42 mm3 /106 cycles for N2 Vac gamma sterilized UHMWPE inserts and 1.35 ± 0.68 mm3 /106 cycles for X3 UHMWPE (unsterilized) Trident Acetabular Inserts. Although in-vitro hip wear simulation methods have not been shown to quantitatively predict clinical wear performance, the current model has been able to reproduce correct wear resistance rankings for some materials with documented clinical results.d, e, f
[d] Wang A, et al. Tribology International, Vol. 31, No. 1-3:17-33, 1998.
[e] Essner A. et al. 44th Annual Meeting, ORS, New Orleans, Mar. 16-19, 1998:774.
[f] Essner A. et al. 47th Annual Meeting, ORS, San Francisco, Feb. 25-28, 2001:1007
13. X3 UHMWPE maintains mechanical properties after accelerated oxidative aging. No statistical difference was found for Tensile Yield Strength, Ultimate Tensile Strength and Elongation as measured per ASTM D638 before and after exposure to ASTM F2003 accelerated aging (5 Atmospheres (ATM) of oxygen at 70ºC for 14 days). Tensile Yield Strength was 23.5 ± 0.3 MPa and 23.6 ± 0.2 MPa, Ultimate Tensile Strength was 56.7 ± 2.1 MPa and 56.3 ± 2.3 MPa and Elongation was 267 ± 7% and 266 ± 9% before and after accelerated oxidative aging, respectively.
14. X3 UHMWPE resists the effects of oxidation. No statistical difference was found for Tensile Yield Strength, Ultimate Tensile Strength, Elongation, Crystallinity and Density as measured per ASTM D638, D3417 and D1505 before and after ASTM F2003 accelerated aging (5 ATM of oxygen at 70°C for 14 days). Tensile Yield Strength was 23.5 ± 0.3 MPa and 23.6 ± 0.2 MPa, Ultimate Tensile Strength was 56.7 ± 2.1 MPa and 56.3 ± 2.3 MPa, Elongation was 267 ± 7% and 266 ± 9%, Crystallinity was 61.7 ± 0.6% and 61.0 ± 0.5%, and Density was 939.2 ± 0.1 kg/m3 and 939.2 ± 0.2 kg/m3 before and after accelerated oxidative aging, respectively.
15. ‘Improved Strength of Cross-linked UHMWPE Without Compromising Oxidation/Fatigue Resistance and Wear”, Yau SS; Wang A, Lovell T. 2007 Combined ORS Poster #496.
16. X3 UHMWPE virtually eliminates free radicals, as measured by Electron Spin Resonance (ESR). A very low (noise level, near instrument detection limit) concentration of residual free radicals was detected in the X3 UHMWPE. A 99% reduction of free radicals (14 ± 2 x 1014 spins/gram versus 1550 ± 32 x 1014 spins/gram) was found when compared to N2Vac gamma sterilized UHMWPE.
17.“Wear, oxidation and mechanical properties of a sequentially irradiated and annealed UHMWPE in total joint replacement”, A.Wang, H.Zeng, S-S Yau, A. Essner, M. Manley and J. Dumbleton, Journal of Physics, D:Appl:
Phys 39 (2006).
18. Nasser, A. B., Beaule, P. E., O’Neill, M., et al. (2010). Incidence of Groin Pain After Metal-on-Metal Hip Resurfacing. CORR 468: 392-399.
19. Tracol P., Vandenbussche E., Deloge N., et al. (2007). Navigation Acetabular Anatomic Study Application in the Development of a New Implant. EFORT Poster.