Abstract
Introduction:
The addition of neck-stem modularity of femoral components allowed for increased versatility in controlling stability, head center, and limb length in total hip arthroplasty (THA). Recent reports of neck-stem corrosion, complicated by adverse local tissue reaction, have raised concern and prompted further patient evaluation for revision arthroplasty.
Methods:
This was a single center, retrospective case series of thirteen hips in twelve patients. The cohort included eight women and four men, with an average age of 69.5 years (range 50–82), who underwent primary THA with a dual-taper femoral component with a titanium alloy stem, cobalt-chromium (CoCr) alloy modular neck and CoCr alloy head. Patients were followed an average of 34.3 months postsurgical (range 24–38.5 months). Each patient underwent serologic studies including metal ion levels, and Metal Artifact Reduction Sequence (MARS) magnetic resonance imaging (MRI) or Ultrasound. All patients were then referred for fluoro-assisted hip aspiration. Four patients underwent revision surgery.
Results:
Ten of thirteen hips were symptomatic at the time of evaluation. ESR and CRP were normal in all patients. Serum Cobalt was elevated in 10/12 patients, with an average serum Cobalt level 4.16 mcg/L (range 1.7–9.4). Serum Chromium levels were normal in all patients. MRI was completed in eleven of twelve patients, with abnormal findings consistent with adverse local tissue reaction in nine hips. Three hips were normal by MRI. One patient had an abnormal ultrasound. Hip aspirations were positive in nine hips, negative in three, and indeterminate in one.
Asymptomatic hips (3/13) all had elevated cobalt levels, and 2/3 had positive MRI and aspirates. One patient had a normal MRI and a negative aspirate. Of ten symptomatic hips, eight had elevated cobalt. 7/10 had an abnormal MRI, 2/10 a normal MRI, and 1 abnormal Ultrasound. 5/10 had aspirates that were consistent with the MRI. One aspirate was indeterminate. Four symptomatic patients had discrepancies between MRI findings and aspiration (negative MRI with positive aspirate, or vice versa); one patient had normal labs and MRI, but a positive aspirate, and was noted to have extensive adverse local tissue reaction at revision.
Discussion:
Patients with dual-taper femoral stems are at risk of neck-stem corrosion and adverse local tissue reactions. The workup of these patients should include serologic studies as well as advanced imaging with MRI or Ultrasound. Hip aspiration may be a useful adjunct in identifying underlying soft tissue destruction in patients with normal or indeterminate labs or advanced imaging.
