Summary
A novel tibial fixation device for a bone plug of bone-patellar tendon-bone (BTB) graft : the Bone plug Tensioning and Fixation (BTF) system showed superb performance in tension adjustability and mechanical strength.
Abstract
Purpose
To evaluate mechanical properties on fixation of a bone plug of bone-tendon-bone (BTB) graft to the tibia using with a novel device, the Bone plug Tensioning and Fixation (BTF) system (Smith & Nephew Endoscopy, Inc., Andover, MA, USA) for tibial fixation in ACL reconstruction, and to compare them with those with an interference screw (IFS).
Methods
Forty patellae and tibiae taken from porcine knees were used.
Ten of the 40 BTB specimens were served for graft tension adjustability test. After the bone plug from the whole patella was fixed to the force gauge on the tensile testing apparatus, the bone plug of 10-mm width from the tibia/ tibial bone plug was introduced into the tibial tunnel created in the tibia fixed on base of the apparatus. Then an initial tension of 9.8 or 19.6 N was applied to the tibial bone plug using a weight and maintained for 5 minutes. The bone plug fixation to the tibial tunnel was achieved with the BTF system or with an IFS under either 9.8 or 19.6 N tension. After the fixation is completed, the weight was removed, and the residual graft tension was recorded for 5 minutes.
Cyclic loading test followed by tension-to-failure test was performed on all of the 40 specimens.
Results
The residual tension after fixation at the initial tension of 9.8N was 10.6 ± 2.2 N in the BTF group and 23.4 ± 7.4 N in the IFS group, while that for 19.6N group was 18.9 ± 2.1 N in the BTF group and 28.9 ± 11.5N in the IFS group. Thus, in either 9.8N or 19.6N initial tension group, the differences between the predetermined initial tension and the residual tension were significantly smaller in the BTF group than those in the IFS group (9.8N, p < 0.001; 19.6N, p=0.009).
The mean displacement of the bone plug after cyclic loading test was significantly less in the BTF group (1.2 ± 0.6 mm) than in the IFS group (2.2 ± 1.0 mm; p < 0.01). Stiffness was significantly greater in the BTF group (504.6 ± 148.8 N/mm) than that in the IFS group (294.7 ± 96.7 N/mm; p < 0.01), whereas the maximum failure loads in the two groups did not differ significantly (724.2 ± 180.3 N in the BTF group and 634.8 ± 159.4 N in the IFS group; p = 0.2).
Conclusions
BTF system achieved graft fixation at the tension closer to the predetermined tension than did IFS fixation. BTF fixation also resulted in less displacement of the bone plug during cyclic loading test and in higher stiffness than did IFS fixation, whereas maximum failure loads between the two fixations did not differ significantly.