Wear and Corrosion of Modular Interfaces in Total Hip Replacements

Abstract

Modular components allow for the customization of hip replacements to the individual patient. Modular head-neck components allow for mixed material systems to minimize polyethylene wear as well as provide the ability to vary neck length and head size independent of the stem. Modular interfaces, however, result in an increased susceptibility to interface corrosion and wear debris generation. One hundred eight uncemented femoral stems with modular heads retrieved for reasons other than loosening with modular heads were examined for interface corrosion. In addition, in an effort to quantify the amount of wear debris generated at modular interfaces due to cyclic loading, mechanical testing and electrozone particle analysis was used to study various surface, material, and design size range less than 5 gm. As many as 2.5 million particles were generated the first million cycles loading, with as many as eight million particles generated a t ten million cycles. The results indicate that surface preparation and material affect particle generation. Head-neck tolerance mismatch appears to be significantly variable in the number of particles generated.Modular stems are widely used in total hip replacement. Modular head-neck components provide the ability to vary neck length and head size independent of the stem while also reducing inventory. In addition, modular heads allow for mixed alloy systems such --combinations. Detectable degrees of corrosion were observed in ten of 29 (34.5%) mixed alloy systems and seven of 79 (9%) single alloy components at an averageof25 months insit,,. l h e r e was no correlation between presence or extent of corroas the combination of a titanium alloy stem with a cobalt-chrome head. Mears" predicted that cobalt-chrome and titanium alloy could be combined in a modular configusion or surface damage with time in siru, initial diagnosis, reason for removal, age, or weight. Stems with corrosion were less likely to have bone ingrowth histologically. The results of mechanical testing showed a significant number of wear particles were generated by all head-neck combinations. The wear debris was almost totally in the ration without significantly enhancing the potential for corrosion. Likewise, studies by Lucas rt a/.14 and Kummer and Rose" predicted no exaggerated in vivo corrosion with such a mixed alloy system. Collier rl u / . ,~,~ however, have reported galvanic corrosion at this interface in human retrieved specimens and concluded that the process is time dependent and may be due to a form ofgalvanically accelerated crevice Corrosion.

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

“…Since that time, there have been numerous reports of corrosion at this taper interface, documented primarily in retrieval studies [2][3][4][5]8,[13][14][15][16][17][18] or, in rare cases, in association with catastrophic failure 2,7 . Although there have been concerns 9 that fretting corrosion at the modular taper may produce soluble and particulate debris that can migrate locally or systemically 19 , to the best of our knowledge there have been only two prior case reports of corrosion at the head-neck taper as a cause of occult, ongoing hip pain or as a cause of adverse local tissue reactions 21,22 .…”

“…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 . Although there have been sporadic reports of elevated serum metal levels 1 and particle deposition within local tissues 19 and isolated case reports of soft-tissue reactions [20][21][22] associated with corrosion of modular implants, symptomatic adverse tissue reactions have not been described in a cohort of patients, to our knowledge.…”

Modern Trunnions Are More Flexible: A Mechanical Analysis of THA Taper Designs

“…Corrosion at this modular junction was first described in the early 1980s [30] and has since been well documented in numerous retrieval analyses [10,12,13,18,28]. The underlying etiology for corrosion at this interface is multifactorial, but one of the strongest predictors of corrosion found at retrieval was the flexural rigidity of the femoral trunnion [23].…”

“…Should revision arthroplasty be required, it also allows for easier surgical exposure and more potential options [8,14]. Shortly after the introduction of modularity in THA, issues of fretting and corrosion at the modular head-neck junction were identified [30], and have since been well documented [10,12,13,18,28]. Early retrieval analyses of femoral components attempted to identify the cause of corrosion, and although initially thought to be galvanic [7], an increasing body of literature points toward a mechanical etiology secondary to fretting and crevice-associated mechanisms of corrosion at the head-neck junction [4,22].…”

CORR Insights®: Does Surface Topography Play a Role in Taper Damage in Head-neck Modular Junctions?

“…Conversely, contact area, surface topography, and roughness, together with the type of constitutive materials of the head-neck couple, are all factors in the electrochemical stability of the interface [2,10]. The use of different metal combinations in the head-neck couple, highlighted further by modular necks that add a new interface between neck and stem and promote the use of dissimilar metals in the construct headneck stem, remains unresolved.…”