Characterization of Femoral Head Taper Corrosion Features Using a 22-Year Retrieval Database

Abstract

Background: Modularity in total hip arthroplasty has been used for decades with great success, but new findings regarding corrosion artifacts have caused a resurgence in tapered junction research. Mechanically assisted crevice corrosion (MACC) is thought to be the mechanism by which corrosive attack occurs. Myriad multi-factorial variables are known to influence the susceptibility of a modular taper junction to MACC. Some of these variables are design and manufacture related and others can be controlled by the surgeon. Questions/Purposes: This study was performed to assess a 22-year retrieval database to determine if correlations exist between severity of corrosion artifacts and head size, time in vivo, head offset, or head material. Secondarily, the agreement of visual and semi-quantitative scoring methods was assessed using the retrieved components. Methods: A total of 210 femoral head tapers were scored and heads receiving high scores were measured to quantify material loss due to MACC. Results: Increased head size and increased time in vivo did not correlate to higher corrosion scores. Contrarily, there were differences in corrosion scores based on femoral head offset and material. Deviations away from a neutral offset (where neutral is defined as the alignment of femoral head center and stem taper gage point) resulted in higher scores. Cobalt-chromium-molybdenum heads were associated with higher corrosion scores and higher material loss as compared to oxidized zirconium heads. Conclusion: Reducing the moment arm at the head-neck junction and choosing a more inert material appears to provide greater resistance to corrosion.

Trunnion corrosion

“…Retrieval analysis has demonstrated lower mean corrosion scores with Oxidised Zirconium (Oxinium, Smith & Nephew, Memphis, Tennessee) heads compared with cobalt-chrome (1.9, sd 0.7 versus 2.5, sd 1.0; p < 0.001); 19 corroborating the findings of other studies. 20 Comparison of non-oxidised zirconia/cobalt-chrome and cobalt-chrome/cobalt-chrome couples also identified lower fretting corrosion; 21 similar to a comparative retrieval study of alumina compared with cobalt-chromium heads, 22 and a matched study comparing corrosion of retrieved stems associated with either a ceramic or cobalt-chromium head. 23 Oxinium heads conferred no advantage over cobalt-chromium in a retrieval analysis of 16 matched stems (eight Oxinium heads, eight cobalt chrome heads).…”

Do SiNx coatings bear the potential to reduce the risk of micromotion in modular taper junctions?

“…1 Nevertheless, retrieval studies have highlighted increasing fretting and crevice corrosion within the taper junction of modular THA for almost every taper design. [2][3][4] Observed material loss patterns demonstrate the specific contact conditions of the mating surfaces, providing insights in the various mechanical and geometrical facets that affect this kind of failure. 5 Mostly the material loss at the taper interface is negligible and does not result in mechanical implant failure.…”

“…3,[9][10][11] Therefore, the reduction of metal debris is of great importance for the patient outcome. 4,[11][12][13][14] Although the process of taper corrosion is still not entirely understood, recent studies indicate a combination of mechanical and electrochemical factors described as mechanically assisted crevice corrosion (MACC) as the driving force. [15][16][17][18] Micromotion between the mating surfaces of the modular components causes the continuous disruption of the passivation layer on the metal surface.…”

What the Surgeon Can Do to Reduce the Risk of Trunnionosis in Hip Arthroplasty: Recommendations from the Literature

“…This force becomes nil when the coefficient of friction approaches 0.05 (Figure 4). Symptomatic trunnionosis appears to be associated with increased head offsets and longer neck lever arms [21,22,56,57]. Micro-grooved tapers, designed to improve stress distributions in ceramic heads, may increase the likelihood of corrosion when combined with metal heads [21,58,59].…”

“…In addition, and perhaps somewhat counterintuitively, the length of the trunnion does not appear to have a significant impact on micromotion or fixation force [47,64]. Increased trunnionosis has also been linked with low flexural rigidity necks (i.e., those with increased elasticity) [65] and small taper Symptomatic trunnionosis appears to be associated with increased head offsets and longer neck lever arms [21,22,56,57]. Micro-grooved tapers, designed to improve stress distributions in ceramic heads, may increase the likelihood of corrosion when combined with metal heads [21,58,59].…”