Abstract
Background
There are numerous concerns associated with femoral stems that feature a modular neck design, including the potential for corrosion, modular neck fracture, and adverse local tissue reactions. These stems have a higher-than-anticipated rate of failure in registry results, but large single-center cohort studies are lacking.
Methods
This is a retrospective, single-surgeon cohort of 133 hips in 119 patients implanted with a single dual-tapered titanium alloy stem with a modular titanium alloy neck (Profemur® Z; Wright Medical Technology, Arlington, TN). Several bearing surface combinations were used, including metal-on-polyethylene, ceramic-on-polyethylene, metal-on-metal, and ceramic-on-ceramic couples. Patients were evaluated at a mean of 4.5 years (range 2.0–9.0 years) with Harris Hip scores (HHS), radiographic analysis, and metal ion testing.
Results
Mean HHS were 84.8 points at latest follow-up (range, 30 to 100 points). Five hips were revised during the study period, for an overall Kaplan-Meier survival of 0.881 at 8 years. There was only one modular neck fracture (0.75%), but others demonstrated ALTR or corrosion at the neck-body interface. Mean serum titanium levels were 4.3 ng/dL (range, < 1 to 46 ng/dL), mean serum cobalt levels were 2.5 ng/dL (range, < 0.1 to 30 ng/dL), and mean serum chromium levels were 1.8 ng/dL (range, < 0.1 to 28.4 ng/dL). Overall 9% of hips had serum titanium levels greater than 7 ng/dL, 10% had serum cobalt levels greater than 7 ng/dL, and 4% had serum chromium levels greater than 7 ng/dL. There was substantial variation in serum metal levels among different bearing surface combinations.
Conclusions
The Profemur® Z stem offers good clinical results in the majority of patients with a low rate of modular neck fracture, however there is an increased rate of femoral revision at mid-term follow-up consistent with registry results. We urge caution in the use of stem designs with a modular neck as this additional interface creates a site for unique failure mechanisms that do not occur with monolithic stem designs.
