Standing Versus Supine Radiographs to Evaluate Femoral Head Penetration in the Polyethylene Liner After Total Hip Arthroplasty

The linear penetration rates for ceramic femoral heads on conventional and highly cross-linked polyethylene were measured and compared with radiographs taken in the standing and supine position taken three weeks postoperatively and at final follow-up. Seventy-five patients (83 hips) with conventional polyethylene (group-1) and two hundred and seventy five patients (300 hips) with highly cross-linked polyethylene (group-2) were studied. Follow-up periods were 14.5 years in group-1 and 8.6 years in group-2. The average penetration rates in group-1 were 0.17 mm/year in supine position and 0.18 mm/year in standing position (P < 0.05). On the other hand, the rates in group-2 were 0.03 mm/year and 0.04 mm/year respectively (P < 0.05). Although there were statistical differences between groups, 0.01 mm differences are probably not clinically relevant.