Bilateral Mechanically-Assisted Crevice Corrosion Resulting in Femoral Stem-Head Dissociation in Metal-on-Polyethylene Total Hip Arthroplasty

Large head metal-on-metal bearing surface with a TMZF titanium alloy femoral stem with high rates of revision and trunnion failure

Background

Mechanically assisted crevice corrosion at the head-neck interface puts implants at risk of trunnionosis, femoral head dissociation, implant failure and the development of metallosis. Metal-on-Metal bearings have very low wear rates, significantly lower than metal-on-polytethylene, but their wear results in cobalt and chromium ion systemic distribution. This is a study of the MITCH metal-on-metal bearing surface coupled with an Accolade TMZF stem.

Methods

This was a retrospective review of 24 total hip replacements 21 patients in that underwent MITCH TRH/Accolade TMZF implantation at a minimum of 12 years post operatively. The primary outcome of this study was all-cause revision with particular attention to revision due to trunnion failure and/or cobalt and chromium ion level.

Results

There was a revision rate of 66.7 % (n = 16) at a minimum of twelve years post operatively. Most notably there were six revisions for a gross trunnion failure. Two cases were revised for impending trunnion failure. There were seven cases revised for elevated serum cobalt and chromium levels and one was revised for unexplained pain.

Discussion

Patients in our study that underwent TMZF alloy cementless stems coupled with large cobalt chromium alloy heads are at high risk of catastrophic trunnion failure. The high rate of trunnnionosis in this implant combination is thought to be related to a significantly different Young's modulus due to a material mismatch coupled with galvanic corrosion.

Unusual Case of a Trunnion Fracture Following a Revision Hip Arthroplasty Surgery: A Brief Review of the Literature and Discussion About Causes of Failure

Trunnion fracture is an incredibly rare complication of total hip arthroplasty. Of the few reported cases, all involve implants with faulty designs, a small neck taper, or an extended neck length or offset. Most also report corrosion and an adverse soft-tissue reaction. We present a review of the literature and report on the first case, to our knowledge, of trunnion fracture in a well-fixed, cemented cobalt-chromium femoral component with a standard neck length and offset with no evidence of corrosion. This failure was likely related to scratching of the metal during previous procedures which led to crack propagation and catastrophic failure. The patient was treated with revision hip arthroplasty to an uncemented, distal-fit femoral component and insertion of new bearing surfaces.