DOS 2020

DOS Kongressen 2020 · 7 Press-fit fixation of a conical shaped trapezium cup is superior in cortical compared to cancellous bone: A radiostereometric analysis in a pig bone model Janni Kjærgaard Thillemann , Lene Dremstrup , Torben Bæk Hansen , Maiken Stilling Department of Orthopaedics, Hospital Unit West; Department of Clinical Medicine, Aarhus University Background: Cup failure is a major problem in trapeziometacarpal (TMC) ar- throplasties. Primary press-fit bone fixation is important for achievement of lat- er osseointegration of cementless implants. The articulating trapezium surface is usually cut, leaving a level cancellous surface for cup insertion. The cortical bone is stronger, but cup insertion in a saddle shaped surface may be challeng- ing. Purpose / Aim of Study: We aimed to compare primary cancellous and corti- cal press-fit fixation of a new conical shaped TMC cup design, and to investigate the effect of cup diameter. Materials and Methods: Thirty-two hydroxyapatite-coated conical cup de- signs of 9mm and 10mm were randomly allocated to cancellous or cortical bone fixation in a 1:1:1:1 ratio. The saddle- shaped bone from the forefeet of two- month old pigs were dissected and rigidly fixed in epoxy glue. Before press-fit fixation of the cups, six tantalum beads of 1mm were inserted in the bone. Cup migration was evaluated with static radiostereometric (RSA) radiographs, re- corded at baseline and repeated after cyclic-load tests (Mark10), performed from 150N to 1050N with 100N intervals. RSA precision was evaluated by double- examinations. The total translation (TT) was calculated and an >0.5mm increase, between two pressure load tests, was defined as cup-failure. Findings / Results: The precision of TT was 0.09 mm and the random error was 0.12 mm. From 0N to 750N load , all cups had a TT of less than 0.5mm migration between each load cycle, but the TT of cups with cancellous bone fixation was higher (up to 0.25mm (CI95 0.12-0.37)) compared to cups with cortical bone fixation (p<0.04). In 9mm cups, a 250N pressure load resulted in a higher TT of cancellous fixated cups compared to cups with cortical bone fixation (p=0.001), whereas the 10 mm cups required to 550N to detect a dif- ference (p=0.008). The Kaplan-Meier cumulative survival estimate (at 1050N) was best for 10 mm cortical fixated cups (88%; CI95 39-98) and least for 9mm cancellous bone fixated cups (13%; CI95 0-42). Conclusions: Based on this experimental study, we advise clinical use of the largest possible size conical shaped cup in addition to cortical bone fixation, when treating TMC joint osteoarthritis with total TMC joint arthroplasty. 2.