Interference screws should be shorter than the hamstring tendon graft in the bone tunnel for best fixation

Abstract

Purpose Interference screw fixation of hamstring tendon grafts in bone has to overcome the challenges that tendons have a slippery surface and viscoelastically adapt under pressure. As the typical failure mode of the graft is to slip past the interference screw, it was hypothesized that the position and configuration of the graft end may be of influence on the fixation strength. Methods Different configurations of the graft ending and its effect to primary fixation with interference screws after viscoelastic adaptation were tested in six groups: I: graft and the screw inserted at the same depth, II/III: the graft overlaps the tip of the screw (interference screw of 28 and 19 mm in length, respectively), IV: strengthening of the graft ending with additional suture knots, V: Endopearl, respectively, and VI: effect of partial retraction of the screw after excessive insertion. In vitro tests were performed with fresh calf tendon grafts and interference screws in bone tunnels (fresh porcine distal femur) all of 8 mm in diameter. Results The relative position of the graft ending to the tip of the interference screw thereby was recognized as a significant factor on pullout forces. Further strengthening at the graft endings with additional suture knots or an Endopearl device could improve primary hold as well. Conclusions Better fixation strength is achieved if the tip of interference screw does not extend past the end of a tendon graft. Enforcement of the tendon end with sutures or an implant can further improve fixation.

Effect of the positional relationship between the interference screw and the tendon graft in the bone tunnel in ligament reconstruction

“…Even at the 0° traction angle, the maximum pullout load of the long-graft group was higher than that of short-graft group. Stalder et al 4 showed that better fixation strength is achieved if the tip of the IS does not extend past the end of the tendon graft, and they theorized that if the end of the tendon graft is caught at the tip of the IS, the fixation strength is affected. We believe that the pullout load difference for the 0° traction angle observed in the present study reflects this idea, although the difference in the contact area as described earlier is considerable.…”

“…[8][9][10][11] Regarding the length of the screw, it has been reported that the use of a longer screw resulted in higher maximum pullout loads. 8,9 On the other hand, Stalder et al 4 showed that the pullout strength is increased with a short IS because a short IS can be caught on the tendon graft edge when a tendon graft longer than the IS is used.…”

“…2 The primary fixation strength of the tendon graft is recognized as an important factor in enabling the early rehabilitation of patients who have undergone ligament reconstruction. 3,4 Several authors have reported research pertaining to the primary fixation strength of the tendon grafts. [5][6][7] It was reported that the initial fixation strength of the tendon graft depended on the contact area of the IS and the tendon graft and the diameter of IS.…”

“…[5][6][7] It was reported that the initial fixation strength of the tendon graft depended on the contact area of the IS and the tendon graft and the diameter of IS. [8][9][10][11] Stalder et al 4 showed that the pullout force was increased with a short IS, because better graft fixation was achieved when the tip of the IS did not extend past the end of the tendon graft. However, to the best of our knowledge, there have been no reports focusing on the positional relationship between the IS and the tendon graft and the effect of the pullout direction of the tendon graft.…”

Estudo biomecânico de diferentes dispositivos de fixação femoral na reconstrução do ligamento patelofemoral medial em joelhos de suínos

“…6,17 A 7-mm cannulated drill was passed over the wire up to 30 mm in depth to accommodate the free ends of the tendon and preventing the 25 mm screw of going beyond the free end of the tendon in the tunnel to ensure better fixation. 19 Using a 2-mm Beath pin, the ends of the tendon were passed through the femoral tunnel, with the stems coming out through the lateral condyle. Applying traction to the stem, the graft was fixed with a 7 Â 25-mm titanium interference screw and, as in the preconized technique, the screw head was buried subcortically.…”