Comparison of Loading Behavior of Femoral Stems of Ti-6Al-4V and Cobalt-Chromium Alloys: A Three-Dimensional Finite Element Analysis

Abstract

Large stiff, small moderately stiff, and small flexible femoral total hip components cemented in the proximal femur have been investigated using a three-dimensional finite element model and validated using experimental strain gage techniques. A physiological load of three times body weight (2000 N), 18 deg from vertical was utilized to compute stresses in the bone, cement, and metal construct. For a well-fixed total hip replacement, the results show stem stresses to be between 5 and 20 percent of the reported fatigue limits for the metals analyzed. Cement stresses in the proximal-lateral region were negligible for all stems tested. In looking at the failure stress for cement, the proximal-medial cement stresses were seen to be only 4 to 6 percent of the reported compression failure criteria and the distal stresses only 5 to 10 percent of tensile failure criteria. The proximal-medial bone stress was 30 percent of normal for a titanium alloy small stem, 21 percent of normal for a moderately stiff small stem, and only 6 percent of normal for a large stiff stem. Distal bone stress on the medial cortex was 39 percent higher for the stiff stem than for the flexible stem and 20 percent higher laterally. In viewing these results in light of the stem design or femoral component failure criteria, the cement does not appear to be the weak link for the well-fixed total hip replacement, regardless of the stem design. If failure initiation does not begin within the cement in a well-fixed hip, physiological changes in the bone may be responsible for loosening at the cement-bone interface, and the cement may then be prejudiced. Some advantages of load transfer to bone are gained with the use of flexible stems, but the significance of these changes can only be confirmed or disputed with detailed clinical and radiographic follow-up.

Osseointegration of Ti6Al4V alloy implants coated with titanium nitride by a new method

“…22,26 Theoretically, less stiff implants reduce stress within the stem and transfer load over a greater area of the cortical bone. 43,44 In our study, comparison of similar titanium and chromium-cobalt implants showed that the stiffness of the implant had no significant effect on micromovement at the cement-bone interface. Furthermore, the two stems presented comparable lower peak values for shear stress at this site.…”

“…Therefore cobalt-chromium seems to be the best material for THA. Previous numerical models 43,44 have shown, however, that a cobalt-chromium stem unloads the proximal femur to a higher degree than a titanium stem and that this may enhance stress-shielding. 22,26 Theoretically, less stiff implants reduce stress within the stem and transfer load over a greater area of the cortical bone.…”

A review on the recent advances concerning the fatigue performance of titanium alloys for orthopedic applications

“…In the work by Semlitsch et al [36] published in the ASTM STP796, a rotating bending fatigue strength of 400 MPa was reported to be the minimum requirement of hot-forged Ti-6Al-4V for hip implants. Tarr et al [37] reported in the same ASTM publication the fatigue stress value of 550 MPa as a failure criterion for a Ti-6Al-4V alloy to be employed in femoral stems. These values are nearly within the same range pointed out by Potomati et al [34] when Fig.…”

Verankerungsprobleme bei der zementierten Hüfttotalendoprothese — Eine Literaturstudie - Comented Total Hip Endoprosthesis-Problems of Anchorage - A Review of the Literature

“…Obwohl die Zementiertechniken und die Prothesen inzwischen erheblich verbessert werden konnten, zählt noch immer die frühzeitige aseptische Lockerung des Schaftes zu den Hauptproblemen. Die Ursachen für diesen massiven Knochenabbau werden sowohl in der toxischen Wirkung von nicht auspolymerisierten Monomeren des Knochenzementes [92] als auch in der Störung der Blutversorgung durch den Zementköcher [7,9] vermutet, vor allem der unphysiologischen Belastung des Knochens unterhalb der Re-sektionsebene nach dem Prinzip der funktionellen Anpassung zugeschrieben [4,18,22,45,51,49,69,72,71,81,84,94,95,9,41,21]. Einerseits wird die Schwachstelle des zementierten künstlichen Hüftgelenks im Knochenzement gesehen und daraus gefolgert, daß alle Maßnahmen, die den Knochenzement proximal medial entlasten, die Lebenserwartung des Gelenkersatzes erhöhen [12,13,15].…”

“…Die Ursachen für diesen massiven Knochenabbau werden sowohl in der toxischen Wirkung von nicht auspolymerisierten Monomeren des Knochenzementes [92] als auch in der Störung der Blutversorgung durch den Zementköcher [7, 9] vermutet, vor allem der unphysiologischen Belastung des Knochens unterhalb der Re-sektionsebene nach dem Prinzip der funktionellen Anpassung zugeschrieben [4,18,22,45,51,49,69,72,71,81,84,94,95,9, 41,21].Dieser Beitrag befaßt sich mit den wichtigsten aktuellen Fragen im Zusammenhang mit der Zementprothese. Aufgrund des unterschiedlichen -Moduls von Ti-und CoCr-Legierungen kommt es zu verschiedenen Krafteinleitungscharakteristiken in das proximale Femur.…”