Follow-up results of 10-12 years after total hip arthroplasty using cementless tapered stem -- frequency of severe stress shielding with synergy stem in Japanese patients.

Synergy stems are tapered stems featuring a proximal porous coating, grid blasting below the proximal third to the distal end. This study included 41 patients (50 hips) who underwent total hip arthroplasty with follow-ups for 10 years or more. No stem reimplantations were performed. Spot welds were observed in the distal stem in Gruen zones 3 and 5 in 35 and 32 hips, respectively. First-degree stress shielding occurred in 8 hips; 2nd-degree, 20 hips; 3rd-degree, 13 hips; and 4th-degree, 9 hips. Because of bone fixation to the distal grit-blasted section of the stem, severe stress shielding was observed in nearly half of the cases. Multiple regression analysis of stress shielding determinants revealed a correlation between stem size and short patient height, showing the cause of stress shielding to be a mismatch in size between the stem and the femoral bone.