Effect of impact assembly on the fretting corrosion of modular hip tapers

Abstract

The goal of this study was to determine the effect of assembly load and local assembly environmental conditions on the fretting corrosion of modular femoral stem tapers. Femoral head/ taper assemblies in both similar (CoCrMo/CoCrMo) and mixed (CoCrMo/Ti-6Al-4V) alloy combinations were evaluated using an electrochemical test method. Specimens were assembled under impact loading and by hand, in both wet and dry conditions. Incremental cyclic loads ranging from 89 to 5,340 N were applied at a frequency of 3 Hz in Ringer's solution at ambient temperature. During the test, both the open circuit potential (OCP) and fretting current (i fret ) were measured using a saturated calomel electrode (SCE) and counter electrode, respectively. The results were comparable for both mixed and similar alloy couples. Decreases in OCP and increases in i fret (indicators of oxide film fracture and repassivation) were seen with increasing load magnitude, often occurring at loads well below those expected clinically. OCP at the 5,340 N cyclic load ranged from À30.4 to À103.7 mV versus SCE for similar alloy couples, and À19.1 to À181.4 mV versus SCE for mixed alloy couples. Mean peak fretting currents ranged from 0.84 to 1.42 mA and 1.06 to 3.12 mA for similar and mixed alloy couples, respectively. The larger current magnitudes and more negative shifts in OCP for mixed alloy couples indicate the difference in oxide film fracture behavior between titanium and cobalt alloys. The load at which OCP began to drop (onset of fretting) was dependent upon the assembly conditions for both material couples. Specimens assembled with impact loads in air showed the highest resistance to fretting. The results of this study indicate that the assembly load and the environment both play a role in the initial stability of modular hip taper connections.

Study of Factors Affecting Taper Joint Failures in Modular Hip Implant Using Finite Element Modelling

“…A high assembly load is desirable in producing enough taper lock to prevent the neck from having further rigid body movement during the functional loading. This finding is consistent with the experimental study by Mroczkowski et al ( 2006). An extreme case of high interference is when the conical parts are pre-assembled as a shrink fit.…”

“…This may result in considerable decrease in interfacial relative micromotion. Published experimental and retrieval data have indicated the absence of fretting damage in such pressfit situations (Brown et al, 1995;Mroczkowski et al, 2006).…”

Metal release and corrosion effects of modular neck total hip arthroplasty

“…The assembly load and environment play a major role in the initial stability of modular connections [16]. To simulate surgical conditions the modular connections were connected wet by a hammer stroke.…”

Corrosion at the Head-Neck Taper as a Cause for Adverse Local Tissue Reactions After Total Hip Arthroplasty

“…Subsequent design and manufacturing improvements minimized these concerns, allowing a nearly universal adoption of modular femoral head-neck tapers in modern total hip arthroplasty. As a result of these design improvements, corrosion at this modular taper interface has received relatively little attention over the last decade 5,11,12 . Historically, a diagnosis of corrosion at this femoral head-neck interface has been made only on the basis of retrieval analysis [2][3][4][5]8,[13][14][15][16][17][18] or, rarely, in cases of catastrophic failure 2,7 .…”