Double whip stitch for free graft femoral fixation in ACL reconstruction: experimental study on porcine model

Using free quadriceps tendon graft for anterior cruciate ligament (ACL) reconstruction has become more popular in the last years due to the low morbidity at the harvest site and biomechanical and structural properties similar to other types of graft (hamstring and patellar tendons). As long as the tibial tunnel fixation with interference screws is considered the standard fixation, femoral fixation is still an open subject. Even though the most common type of femoral tunnel fixation are the cortical suspension devices, the type of suture used for tying the graft to the loop is still evaluated and discussed. We aimed to evaluate the resistance and elongation of a double whip stitch used for tying a tendon to the loop of a cortical suspension device. We used 10 porcine flexor digitorum profundus as free graft for a graft-suture-cortical suspension device construct using the double whip stitch. The total length of the construct and tendon length were recorded before and after the test was performed. Tensioning curves, total construct elongation and maximum tension at breaking point were electronically recorded on the testing device's software. The mean values and coefficient of variance were assessed. We noted the breaking of the suture wire where the wires passed through the loop of the cortical suspension device as final point for all tests. The mean of maximum load was 505.68N (Max=639.38 N; min=358.93 N; SD=82.88078 N) and the mean of total construct elongation was 39.54784mm (Max= 48.60466 mm; min=31.74853 mm; SD=4.85371 mm). With some minor improvement in technique and graft preconditioning and pretensioning, the double whip stitch can be used in connecting a free tendon to a cortical suspension device.