Testing of Total Hip Replacements: Endurance Tests and Stress Measurements: Part 1: Endurance Tests

Abstract

This is a paper in two parts. Part 1 gives details of fatigue tests carried out on Howse II hip prostheses. Three types of tests were carried out in accordance with three different draft test standards. Standard (I) was BSI DD91: 1984 in which the load range is 0.3-4.1 kN and the antero-posterior offset angle is 15 degrees. Standard (II) was BSI DD91: 1986 where the load range is 0.3-2.3 kN and the offset angle is 9 degrees. Standard (III) was ISO/DP 7206/3 in which the load range is 0.3-4.1 kN and the offset angle is 0 degrees. Four specimens were tested according to each standard. It was found that all the specimens tested according to standard (I) failed by fatigue after less than 6 x 10(5) cycles. All the specimens tested according to standards (II) and (III) withstood 5 x 10(6) cycles without failure. It is clear that the offset angle has an important influence on the fatigue life of the prosthesis. It is concluded that tests according to standard (I) are too severe, while tests according to standards (II) and (III) are either adequate or lax. This led to Part 2 of the investigation where the stresses in the prostheses were measured and calculated.

Hip stem fatigue: : The implications of increasing patient mass

“…For fatigue testing, an Instron Electropulse e3000 (Instron, High Wycombe, UK) fatigue testing machine was used to apply an axial sinusoidal force to the femoral stems at a frequency of 7.5 Hz for a duration of 10 million cycles ( Figure 2); this was greater than the recommended test duration from ISO. Wroblewski et al 2,13 reported that 10 million cycles were more realistic compared to the 5 million cycles the ISO standard requires. Note that the size 11 component required a much greater force to cause fracture and an Instron 5985 with a triangular load waveform was used for this stem to create fatigue failure.…”

“…These studies have found that the maximum stress and crack initiation have been reported to be located in the anterior lateral aspect of the stem at the fixation surface where the bending moment is the greatest. [9][10][11][12][13] However, studies like this are very implant specific as the individual material and geometry of the stem dictate the specific location and magnitude of the maximum tensile stress/strain where cracks initiate. Ploeg et al 14 compared the accuracy of different empirical models for predicting fatigue in titanium stems and concluded that the classic S-N curve proposed by Basquin was accurate at low stress levels.…”

Ultra-high molecular weight polyethylene wear particle effects on bioactivity

“…To simulate the wear of total joint replacement in the human body, wear studies of UHMWPE have been performed in bovine serum at ranges of contact pressure and sliding speed encountered in real situations [58][59][60][61][62][63][64][65][66]. Scanning electron microscopy results have demonstrated that surface damages of UHMWPE include adhesion wear, abrasion, and delamination wear.…”

Fatigue testing of a proximal femoral hip component

“…Subsequent observations of the contribution of torsion and bending to failure led to a further test procedure with similar support conditions but more rigorous loadings to mimic the out-of-plane bending of normal gait inducing increased stress in curved intramedullary stems [12,15]. Endurance limits were set to model ten years' clinical service under normal gait, or 5 million cycles under 3 kN sinusoidal load [16], but when laboratory failures of clinically successful implants occurred at these loads under the conditions of ISO 7206-4 [17], an alternative endurance limit of 2 kN was proposed for the torsional set-up [12,[18][19][20].…”