Surface Analysis of Ti-Alloy Micro-Grooved 12/14 Tapers Assembled to Non-Sleeved and Sleeved Ceramic Heads: A Comparative Study of Retrieved Hip Prostheses

Abstract

Ti6Al4V titanium alloy (Ti-alloy) sleeved ceramic heads have become widely used in revision surgery when the hip stem is left in situ. This solution guarantees a new junction between the bore of the ceramic head and the Ti-alloy sleeve, regardless of any possible, slight surface damage to the Ti-alloy taper of the stem. However, this solution introduces an additional Ti-alloy/Ti-alloy interface pairing, which is potentially susceptible to mechanically assisted crevice corrosion. This study evaluated both qualitatively and quantitatively the damage that occurred in vivo on Ti-alloy micro-grooved 12/14 tapers of (i) primary implants with non-sleeved ceramic heads (Group 1), (ii) secondary implants with non-sleeved ceramic heads (Group 2), and (iii) secondary implants with sleeved ceramic heads (Group 3). A total of 45 explants—15 for each group, including short-, medium- and long-neck heads—underwent optical evaluation for surface damage (Goldberg scoring), surface roughness analysis, and SEM/EDX analysis. The Goldberg scores did not reveal different patterns in the tapers’ surface damage; surface damage was classified as absent or mild (surface damage score ≤2) in 94%, another 94%, and 92% of the analysed regions for Group 1, Group 2, and Group 3, respectively. Small but significant differences in morphological changes occurred in the tapers of the three groups: reductions no greater than a few percentage points in median values of roughness parameters were found in Group 1 and Group 2, while negligible changes were found in Group 3. SEM/EDX analysis revealed little (i.e., a slight increase in the oxygen content) to undetectable changes in the chemical composition on the Ti-alloy surface independently of the group. These results suggest that the Ti-alloy/Ti-alloy sleeve/taper junction is only mildly susceptible to mechanically assisted crevice corrosion. Assembling a sleeved ceramic head, with variable neck lengths up to a “long-neck”, to a Ti-alloy micro-grooved 12/14 taper of a stem left in situ does not seem to increase the risk of revision due to trunnionosis, as long as junction stability (i.e., the proper seating of the sleeved ceramic head on the 12/14 taper) is achieved intraoperatively.

Characterization of Micro-Threaded Stem Taper Surfaces of Cementless Hip Endoprostheses

“…The retrieved stems were manufactured by SL-Plus, Smith & Nephew (London, UK), and Endoplus (London, UK). After revision surgery, the implants were sent for sonication and microbiological analysis in Ringer’s solution, followed by cleaning and sterilization [ 4 , 5 , 6 , 7 ].…”

“…All these values are not standardized and vary between manufacturers. Every modular connection of metal alloys in contact with body fluids and exposed to micromotion is subject to corrosion [ 6 , 7 , 8 ]. The taper’s interface is influenced by several factors, such as (i) design and material, (ii) assembly (surgical factors), and (iii) loading (patient factors) [ 4 , 7 ].…”

“…Every modular connection of metal alloys in contact with body fluids and exposed to micromotion is subject to corrosion [ 6 , 7 , 8 ]. The taper’s interface is influenced by several factors, such as (i) design and material, (ii) assembly (surgical factors), and (iii) loading (patient factors) [ 4 , 7 ]. Urish et al thoroughly described the fundamental principles of various types of corrosion that can affect the surface of an orthopedic implant, including pitting, crevice corrosion, fretting, and mechanically assisted crevice corrosion [ 6 ].…”