Migration of press-fit cups fixed with poly-L-lactic acid or titanium screws: A randomized study using radiostereometry

The early migration of porous acetabular cups was studied in 43 patients with osteoarthrosis. The patients were randomly allocated to additional fixation of the cup with either biodegradable poly-L-lactic acid screws or titanium screws. Radiostereometric evaluation was done during the first 2 years after the procedure in 43 hips (23 with poly-L-lactic acid screws and 20 with titanium screws). At the 2-year follow-up, cups fixed with poly-L-lactic acid screws had migrated significantly more in the proximal-distal (p < 0.05) and medial-lateral (p < 0.05) directions. Cups with titanium screws displayed more pronounced rotations around the longitudinal axis (p < 0.05). Postoperatively, on the lateral view, there was an increased occurrence of radiolucencies at the dome of the cups fixed with poly-L-lactic acid screws (p < 0.05). The clinical result did not differ between the two groups. Inferior implant-bone contact in the poly-L-lactic acid group, local changes of the bone quality, and diminishing support of the poly-L-lactic acid screws caused by their degradation with time could be reasons for the different pattern of migration observed.