EFFECT OF PEGS AND SCREWS ON BONE INGROWTH IN CEMENTLESS TOTAL KNEE ARTHROPLASTY

The purpose of the present study was to assess the effects of pegs and screws on bone ingrowth into the tibial component in cementless total knee replacement. Left total knee replacements were performed in 21 m ature male dogs with 3 cementless porous-coated tibial tray configurat ions (7 animals per group): (1) 4-peg design implanted with cortical s crews passing through the pegs; (2) 4-peg design implanted without scr ews; and (3) pegless design secured by 4 cortical screws. The animals were allowed unrestricted activity and were euthanized 6 months postop eratively. The pegless components (Group 3) had the highest extent of bone ingrowth into the tray (90.3% +/- 9.4%), followed by the componen ts with 4 pegs only (Group 2, 82.8% +/- 9.2%), and the components with 4 pegs and 4 screws (Group 1, 75.9% +/- 11.8%). The difference betwee n Groups 1 and 3 was statistically significant (p < 0.05). The volume fraction of bone ingrowth in the tray did not differ among the 3 group s, with an overall mean of 22.5% (+/-4.6%). At the posterolateral quad rant, Group 1 had significantly less bone ingrowth than Group 3 within the tray whether measured as the extent (63.6% +/- 20.5% versus 91.0% +/- 10.6%, p < 0.05) or volume fraction (19.1% +/- 8.8% versus 32.9% +/- 10.5%, p < 0.05). There were no between-group differences at the o ther quadrants. This study indicated that pegs provided no added benef it in a circumstance where sufficient initial fixation was obtained wi th screws.