HAMSTRING TENDON FIXATION USING INTERFERENCE SCREWS - A BIOMECHANICALSTUDY IN CALF TIBIAL BONE

It has recently been shown that graft fixation close to the ACL insert ion site is optimal in order to increase anterior knee stability. Hams tring tendon fixation using interference screws offers this possibilit y and a round threaded titanium interference screw has been previously developed. The use of a round threaded biodegradable interference scr ew may be equivalent. In addition, to increase initial fixation streng th, graft harvest with a distally attached bone plug may be advantageo us, but biomechanical data do not exist. This study compares the initi al pullout force, stiffness of fixation, and failure modes of three st rand semitendinosus grafts in 36 proximal calf tibiae using either bio degradable poly-(D,L-lactide) (Sysorb; Sulzer Orthopaedics Ltd, Munsin gen, Switzerland) or round threaded titanium (RCI; Smith & Nephew DonJ oy, Carlsbad, CA) interference screws, harvested either without (biode gradable: group I, titanium III) or with (biodegradable: group II, tit anium: group IV) attached tibial bone plugs. Maximum pullout force in group I (507 +/- 93 N) was significantly higher than in group III (419 +/- 77 N). Pullout force of bone plug fixation was significantly high er than that of direct tendon fixation (717 +/- 90 N in group II and 6 02 +/- 117 N in group TV). Pullout force of biodegradable fixation was significantly higher in both settings. These results indicate that in itial pullout force of hamstring-tendon graft interference screw fixat ion can be increased by using a biodegradable interference screw. In a ddition, initial pullout force of hamstring-tendon graft fixation with an interference screw can be greatly increased by harvesting the graf t with its distally attached tibial bone plug.