The Relationship Between Cobalt/Chromium Ratios and the High Prevalence of Head-Stem Junction Corrosion in Metal-on-Metal Total Hip Arthroplasty.

BACKGROUND: The size of the clinical impact of corrosion of the taper junction of metal-on-metal total hip arthroplasties (MOM-THAs) is unclear. Examination of a large number of retrieved MOM resurfacings and total hip arthroplasties can help us understand the role of taper corrosion in metal ion release.

METHODS: We graded the severity of corrosion at the taper junction of 395 MOM-THAs and compared the prerevision whole blood metal ion levels of these hips with 529 failed MOM hip resurfacings.

RESULTS: Virtually all MOM-THA hips (n = 388) had evidence of corrosion of the head-stem taper junction and graded as severe in 31% (n = 124). The median cobalt/chromium (Co/Cr) ratio was 1.58 (0.01-13.82) and 1.08 (0-4.86) for MOM-THA and MOM hip resurfacing, respectively; this difference was significant (P < .001). THA hips with severely corroded tapers had the highest median Co/Cr ratio of 1.86 (0.01-10).

CONCLUSIONS: This study demonstrates the high prevalence of severe taper corrosion, which may be related to an elevated Co/Cr ratio before revision.