Abstract
Modular tapered stems have become increasingly popular in femoral revisions and stem subsidence remains a reported clinical problem. Computer modeling and biomechanical testing demonstrated a minimum initial line-to-line fit of 25 mm was required to reduce the risk of subsidence. We examined XR imaging of 110 consecutive femoral revisions by a single surgeon using two different modular tapered stems to determine if this biomechanical threshold was of clinical relevance. 72% of the revisions were done for aseptic loosening and 28% for periprosthetic fracture or infection. Stem subsidence of any degree was observed in 24 (21.8%), while 12 (10.9%) demonstrated substantial subsidence of > 10 mm. We matched this cohort to 12 patients who had no stem subsidence. The average age of patients with subsidence was 59 years (43 to 79 years). The average of patients without subsidence was 66 years (41 to 77 years). Each group had 7 men and 5 women. Stem subsidence was observed in the first 3 months post-surgery. The demographics, bone deficiency, stem design, and stem diameter were similar between groups.
83% of patients with substantial stem subsidence had less than 25 mm of line-to-line fit compared to 17% of patients without subsidence. The 12 cases of no stem subsidence had a mean line-to-line fit of 48 mm (25 to 55 mm). 75% of patients with substantial stem subsidence had also undergone an extended trochanteric osteotomy (ETO) compared to 33% of patients without subsidence.
We conclude that there is a positive correlation with the biomechanical testing parameters and substantial stem subsidence. ETO was found to be associated with higher stem subsidence.
