Supplemental bio-tenodesis improves tibialis anterior allograft yield load in extremely low density tibiae

Abstract

Improved soft tissue tendon graft mechanical properties have led to their increased use for anterior cruciate ligament (ACL) reconstruction. Because they do not have an osseous component; however, there are greater concerns regarding tibial graft slippage during early postoperative rehabilitation and activities of daily living, particularly in patients with poor bone mineral density (BMD), such as older patients, women, smokers, and patients undergoing revision ACL reconstruction surgery. This in vitro biomechanical study attempted to determine the effectiveness of supplemental ACL graft fixation in low BMD tibiae. Eight paired knees (16 specimens) were harvested from female cadavers (mean age=76, range=60-88years). Tibiae were assigned to either a combination bioabsorbable interference screw, bio-tenodesis screw group (Group 1, n=8, apparent BMD=0.44±0.13g/cm(2)) or a bioabsorbable interference screw group (Group 2, n=8, apparent BMD=0.44±0.14g/cm(2)). Double-strand (single loop) tibialis anterior tendon allografts were fixed in matched diameter tibial tunnels. Using a custom 6° of freedom jig, potted constructs were mounted on to a servo hydraulic device with the axial loading force aligned directly with the tibial tunnel. Constructs underwent progressive cyclic tensile loading from 10 to 150N with a 25N load increase every 20 cycles. This was followed by yield load to failure testing (20mm/min). Groups did not display displacement differences during progressive cyclic loading. Group 1 (312.7±67.5N) displayed 25% greater yield load at failure than Group 2 (235.0±47.6N), P=0.045. Both groups displayed fixation levels well below the previously reported minimal safe threshold estimate for early unrestricted weight bearing, accelerated rehabilitation and activities of daily living. Supplemental bio-tenodesis fixation may improve early tibial-soft tissue tendon graft fixation in patients that have poor tibial BMD, but study results suggest that both methods may require weightbearing, rehabilitation, and activity of daily living restrictions during the early postoperative period to prevent graft slippage.