Fixation and bone remodeling around a low stiffness stem in revision surgery

Femoral stems with reduced stiffness have the potential of decreasing stress shielding and could be an alternative in revision surgery when restoration of bone stock is required. We retrospectively reviewed 38 patients (40 stems) with a central core of cobalt-chromium surrounded by a polymer and an outer titanium mesh layer containing a proximal coating of hydroxyapatite/tricalcium phosphate; 30 of the 38 patients (32 hips) had a minimum 2-year followup. We impacted morselized allograft around the stem in 28 of 32 revisions. Repeated radiostereometric examinations showed medial, distal, and posterior migration (median, 0.21 mm, 0.17 mm, and 0.96 mm, respectively) of the femoral head center for up to 6 months followed by stabilization. Measurements of bone mineral density in the seven Gruen zones at 6 months revealed either a decrease (down to a median of 3%), no change, or a slight increase (up to 5%) followed by a further increase up to 2 years in three of the regions (2, 3, and 5). Conventional radiography at 2 years demonstrated graft remodeling and incomplete radiolucent lines in 19 hips, mainly in Regions 1 and 7. Two hips were reoperated on as a result of dislocation, but none of the stems had been revised.