Abstract
Bone-patellar tendon-bone autografts, hamstring autografts or allografts are widely used grafts for ACL revision surgeries. Also use of quadriceps autograft for both primary and revision ACL surgeries is in an increasing popularity due to its biomechanical superior properties and less donor site morbidity. However, although several fixation techniques and devices for quadriceps tendon graft fixation on femoral side have been reported, literature lacks about biomechanical studies comparing properties of these different fixation techniques and devices. We aimed to investigate whether there is a difference between the fixation techniques of quadriceps tendon graft by using different fixation techniques and devices on the femoral side in terms of stiffness and amount of slippage in the tunnel.
Full-thickness central parts of quadriceps tendons from paired knees of twenty five calf knees were fixed through a 10mm x 25mm tunnel in twenty five paired sheep femurs. Quadriceps tendon patellar side with soft tissue ending fixed with four different fixation devices (adjustable suspensory system (group 1), absorbable interference screw (group 2), titanium interference screw (group 3) and adjustable suspensory system + absorbable interference screw (group 4)) and quadriceps tendon with a patellar bone plug fixed with a titanium interference screw (group 5) were tested in a servohydraulic materials testing machine. 10 samples were included in each group. After applying a preload of 10 N, a cyclic force was applied for 20 cycles from 10N to 110N at a 1 hertz frequency. Amount of slippage in the tunnel was calculated as the difference measured in millimeters between length at 10 N after 20 cycles and starting length at 10 N (Graph 1). To determine the stiffness, a single load-to-failure cycle was performed at a strain rate of 20 mm/min as the last step (Figure 1).
Rupture of the graft was not seen in any of the samples. Median values of amount of slippage in the tunnel were 6,41mm, 5,99mm, 3,01mm, 4,83mm, and 3,94mm respectively. Median values of maximum load at failure were 464N, 160N, 350N, 350N and 389N respectively. Amount of slippage in the tunnel was highest in the group 1 and was lowest in the group 3 (p<0.001). Group 1 was found to be most resistant group against load-to-failure test and group 2 was the weakest (p<0.001). However inter-group analyses between group 3 and 5 revealed that, although group 3 had the least slippage in the tunnel, group 5 was better in terms of stiffness, but there was no statistically significant difference (p=0,124 and 0,119 respectively). There was a significant difference between group 2 and 3 in both amount of slippage in the tunnel and stiffness (p=0,001 and 0.028 respectively)(Table 1).
Our study revealed that, although quadriceps graft with a bone plug fixed with metal interference screws is widely presumed to be a stable fixation technique, there was no significant difference in terms of stiffness when compared with quadriceps graft with soft tissue ending fixed with a metal interference screw. Although adjustable suspensory device group was the best in the terms of resistance against load-to-failure, it was the worst in terms of amount of slippage from the tunnel. Thus, if a suspensory device is to be used, it must be kept in mind that a strong 20 cycles of intra-operative tension force must be applied to prevent further slippage of the graft in the tunnel which can result in failure of reconstruction.
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