Comparison of survival and cost-effectiveness between unicondylar arthroplasty and total knee arthroplasty in patients with primary osteoarthritis: a follow-up study of 50,493 knee replacements from the Finnish Arthroplasty Register - Koskinen, E; Eskelinen, A; Paavolainen, P; Pulkkinen, P; Remes, V (Acta Orthop, 2008)