gms | German Medical Science

Objectives: Modular hip implants allow intraoperative flexibility and adaptation to patient-specific anatomy. Wear at the modular interface between stem and head taper has been acknowledged as a potential cause of total hip arthroplasty failure. It is predominately expressed in the form of mechanical fretting and chemical corrosion, and is associated with the release of metal ions, potentially causing peri-prosthetic failure. Wear might depend on variations in stem surface topography that can be split into two major groups: smooth and threaded. Here we investigate differences in surface topography and the degree of corrosion and fretting in hip implants commonly used in Germany with a threaded surface profile (profile height >10µm).

Methods: In this retrospective retrieval study, we analyzed n=49, 12/14 stem taper of four different models: Alloclassic, CLS Spotorno, Aesculap Bicontact, SL-PLUS. Age, implantation period and BMI were similar in all groups. High-resolution 3D microscopy (Olympus DSX500) was used to characterize the surface topography regarding the surface profile, profile height and width, and surface enlargement. Wear was defined as corrosion and fretting, and quantified using a scoring scheme established by Goldberg et al. (2002).

ANOVA with post hoc analysis using the Bonferroni correction was performed to show differences between implant types for normally distributed data. Otherwise, differences were analyzed by a Mann-Whitney-U test. Spearman's rank correlation was used to check for correlations between surface topography and wear.

Results and conclusion: The profile height and surface enlargement are significantly higher in the Alloclassic and CLS compared to the Bicontact and SL-PLUS stem taper. Contrarily, the profile width is significantly smaller (Tab.1 [Tab. 1], Fig.1 [Fig. 1]). Even though the surface topographies vary substantially, fretting and corrosion scores do not show inter-group differences. No correlation between surface topography and fretting and corrosion scores was found.

High resolution opto-digital microscopy revealed a much higher variability of the surface topography in commonly used implant types in Northern Germany compared to other recently investigated implants. Notably, profile heights were more than four times greater than previously published. However, not even the extraordinarily great surface variations of threaded stem tapers correlate with the degree of corrosion and fretting. The wear at the head-neck interface cannot be explained with different surface topographies. The implant geometry, corresponding stress distribution and surgical technique need to be considered to unravel the cause of wear at the interface.