Adverse condition testing with hip simulators

Abstract

Recent clinical failures and abnormal sounds observed in certain prosthetic hip designs have directed attention to adverse condition hip simulator testing. In the present study, hip simulator wear and friction tests were made with a macroscopic separation of the bearing surfaces in the swing phase, steep acetabular cup position, increased load, poor or lacking lubrication, roughened bearing surfaces including titanium third bodies, and with combinations of these. The only conditions that resulted in squeaking were dry sliding with alumina-on-alumina and metal-on-metal, and an extreme peak load of 4 kN with serum lubricated metal-on-metal. The wear rate of metal-on-metal increased by an order of magnitude when the cup position was steep, 64 degrees, compared with the optimal position of 48 degrees. The increase of the peak load from 2 kN to 3 kN with the cup position of 48 degrees increased the running-in wear of metal-on-metal, but the steady state wear rates were equally low, of the order of 1 mg per one million cycles. Crosslinked polyethylene was the superior cup material under adverse conditions, including dry sliding and roughened femoral head.

Effect of increased load on the wear of a large diameter metal-on-metal modular hip prosthesis with a high inclination angle of the acetabular cup

“…Above the limit the tribological behaviour of the device is unacceptable, i.e., wear and friction will inevitably -not only occasionally -be so high that serious damage to the patient and early failure of the arthroplasty would result. Well below the limit, the wear and its variation are low [1][2][3]. In the present study, the limit was being approached with a combination of 2 kN peak load and 70° inclination angle.…”

“…In an earlier study, high variation in wear was observed in the 52 mm diameter Metasul MoM (n = 3) with an optimal inclination of the cup, 48°, and a very high peak load of 4 kN [3]. Loud squeak was produced by the prosthesis with the highest wear rate of 116 mg/10 6 cycles.…”

“…The 12-station HUT-4 hip joint simulator, the fixation and alignment of the specimens, the test procedure and the method of MoM wear measurement have been described elsewhere [1][2][3]. Test 1 was run with three similar 52 mm diameter Metasul (Protasul-21WF, wrought- According to the definitions by Murray [18], these three angles corresponded to the anatomical inclination, operative inclination, and operative anteversion, respectively.…”

“…The wear was evaluated from the Co and Cr concentrations of the used lubricant analysed by atomic absorption spectroscopy (AAS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) as described elsewhere [1][2][3]21]. At intervals of 0.375 million cycles on the average the test was stopped, and the test chambers and the specimens were removed.…”

“…A high inclination angle of the acetabular cup (> 60°) is known to be detrimental for the wear behaviour of the MoMs [9,[11][12][13][14][15], due to the edge contact and the consequent failure of the fluid film lubrication [3,16]. In the present study, an extreme inclination angle of 70° was used.…”