Acetabular Cup Malalignment After Total Hip Resurfacing Arthroplasty: A Case for Elective Revision?

Abstract

This article describes the clinical course of a patient with a resurfacing implant in a poor cup position in combination with elevated serum metal ions prior to implant failure. Following resurfacing, the patient had substantial improvement from baseline in pain and functional status. Postoperative radiographs indicated the acetabular cup in an abducted and excessively anteverted position. The acetabular component ultimately failed after 4.5 years and a traditional total hip arthroplasty revision was performed. Serum cobalt (Co) and chromium (Cr) concentrations had been collected postoperatively of the index procedure at 6 months, 1 year, 2 years, 3 years, and pre- and postoperatively at the time of implant revision. Serum cobalt and chromium ion levels were progressively elevated to approximately 400 times more than the expected range at all time points prior to revision. Elective revision had been considered due to acetabular malalignment and elevated metal ion levels, but not performed since the patient was doing well clinically. A recent study has shown a correlation between increased cup inclination and increased serum cobalt or chromium levels and this patient's levels were >40 times greater than that typically observed with this device. Early revision should be strongly considered if component malpositioning is noted, and abnormally elevated ion concentrations should signal the need for revision regardless of the patient's clinical status. The relationship of a malpositioned cup and uncharacteristically elevated metal ion levels is related to the metal-on-metal bearing coupling and likely applies to conventional metal-on-metal total hip prostheses as well.