Corrosion at the Stem-Sleeve Interface of a Modular Titanium Alloy Femoral Component as a Reason for Impaired Disengagement Christian R. Fraitzl, MD,* Luis E. Moya, MD,* Lorenzo Castellani, MD,* Timothy M. Wright, PhD, y and Robert L. Buly, MD* Abstract: Modularity in sleeved femoral components allows the exchange of the stem without disruption of the fixation between the sleeve and the surrounding bone at revision surgery. Failure to disengage the stem from the sleeve would represent an unnecessary compromise from the intended usefulness of the modular design. We report the results of an examination of 22 modular titanium alloy femoral components retrieved after 0.0 to 8.8 years in vivo. In 7 implants, the stem-sleeve interface could not be disengaged without cutting through the components or using mechanical force. Moderate to severe corrosion was detected in all 7 of these cases. Corrosive surface changes were observed in an additional 6 interfaces. There was no correlation with the length of time that the devices had been implanted. When only the stem is to be revised, orthopedic surgeons should be aware of difficulties in disengagement and anticipate alternative surgical procedures. Keywords: total hip replacement, modular femoral component, titanium-alloy, corrosion. © 2011 Elsevier Inc. All rights reserved. The S-ROM modular hip system (DePuy, Warsaw, Ind) has a cementless modular femoral component made of titanium alloy with a distally fluted and slotted stem. The stem mates with a sleeve that is implanted in the proximal femur. The system's versatility was initially appreciated in revision hip arthroplasty, but the system has also become a valued tool in primary hip arthro- plasty, especially in complex cases such as dysplastic hips for which the ability to adjust anteversion is an advantage [1,2]. Good mid-term and long-term results have been reported for both primary and revision arthroplasty [3-8]. Few revisions or re-revisions were reported, in which the stem was temporarily removed or replaced, leaving the sleeve in place in the femoral metaphysis. In only 1 case was “obvious fretting without obvious titanium debris” noted [4], whereas in 3 other cases, “no radiographic or histologic evidence of fretting” was found [6]. Furthermore, no reports exist in the literature of intraoperative difficulties in disengaging the stem-sleeve interface. In vitro biomechanical testing has established the fatigue behavior, torsional fixation strength, and the wear debris generated at the stem-sleeve interface [9-12]. Little attention has been paid, however, to the occurrence of fretting-assisted crevice corrosion as in modular head-neck components [13]. Incidental sur- face analysis of stems and sleeves, however, revealed incomplete, frequently small localized fretting damage at the interface between sleeve and stem [9,11,12]. Only one study has been published on retrieved S-ROM stem-sleeve interfaces, in which small fretting areas measuring only a few square millimeters were reported with no evidence of corrosion after a mean follow-up of 2.3 years [14]. Of 17 specimens, 6 were retrieved with the sleeve still intact on the stem, showing dried biological deposits on most of the taper surfaces once disassembled. However, corrosion was not described in these specimens. Induced by the impossibility of intraoperatively dis- connecting the stem-sleeve interface in a patient with the consequence of an unintended revision of a well- fixed sleeve from the metaphysis of the femur, we asked whether in vivo evidence for fretting-assisted crevice corrosion of the mating surfaces could be found in additional retrieved components, and whether its appearance is influenced by factors such as length of From the *Hip and Knee Service, Hospital for Special Surgery, New York, New York; and yDepartment of Biomechanics, Hospital for Special Surgery, New York, New York. Supplementary material available online at www.arthroplastyjour- nal.org. Submitted January 11, 2009; accepted October 25, 2009. No benefits or funds were received in support of the study. Reprint requests: Christian R. Fraitzl, MD, Department of Orthopae- dics, University of Ulm, Oberer Eselsberg 45, D-89081 Ulm, Germany. © 2011 Elsevier Inc. All rights reserved. 0883-5403/2601-0019$36.00/0 doi:10.1016/j.arth.2009.10.018 113 The Journal of Arthroplasty Vol. 26 No. 1 2011