***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Tunnel  enlargement after anterior cruciate ligament ( ACL ) reconstruction  may compromise revision surgery . The cause of this tunnel enlargement is not yet fully understood , but it is thought to be multifactorial , with biomechanical and biological factors playing a role . Tunnel enlargement has been described particularly in patients who underwent ACL reconstruction with hamstring tendons with extracortical fixation devices . The purpose of our study was to evaluate prospect ively with magnetic resonance imaging ( MRI ) the changes in femoral tunnel diameter  following arthroscopic anatomic ACL reconstruction with hamstring tendons .  At 3-month post-op , all tunnels had enlarged compared to the diameter of the drill and most tunnels enlarged more in the midsection than at the aperture . In the posterolateral tunnels , the entrance increased 16 % in diameter and the middle of the tunnel increased 30 % in diameter . In the anteromedial femoral tunnels , the tunnels enlarged 14 % at the aperture and 35 % in the midsection . All femoral tunnels enlarged and most of them enlarged in a fusiform manner . The biological factors explain better our findings than the mechanical theory , although mechanical factors may play a role and the cortical bone at the entrance of the tunnel may modify the way tunnels respond to mechanical stress PURPOSE To compare the incidence of tunnel widening ( TW ) in patients undergoing anterior cruciate ligament ( ACL ) reconstruction with hamstring graft using either ( group A ) transfemoral fixation implant ( Transfix ; Arthrex , Naples , FL ) and an interference screw ( Arthrex ) in the tibial tunnel or ( group B ) extracortical fixation ( EndoButton ; Smith & Nephew Endoscopy , And over , MA ) in the femur and bicortical screw and washer distal to the tibial tunnel . TYPE OF STUDY Prospect i ve r and omized study . METHODS One hundred patients were included and r and omized and 87 patients were assessed at a 1-year follow-up . The evaluation included st and ardized radiographs , KT-1000 data , International Knee Documentation Committee ( IKDC ) ratings , and Lysholm score . The diameter of the tunnel at the 1 year follow-up was , after correction for magnification , compared with the tunnel diameter of the radiograph from 2 weeks postoperatively . A more than 2-mm enlargement was considered TW . RESULTS In group A in which transfixation in the femur and interference screw in the tibia was used , 7 of 41 patients had developed femoral TW and 5 of 41 tibial TW . In group B , 20 of 46 patients had TW in the femur and 16 of 46 in the tibia ( P < .05 , chi-square test ) . No significant difference was found with respect to Lysholm score , IKDC , or arthrometric evaluation . CONCLUSIONS There was a significant reduction of TW in both the femur and the tibia using fixation points close to the joint , compared with the system where the distance between the fixation points is long . We conclude that the position of the fixation sites and type of fixation device are major factors in the development of TW after ACL surgery . LEVEL OF EVIDENCE Level I , therapeutic study in a prospect i ve r and omized clinical trial A total of 218 patients with unilateral anterior cruciate ligament deficiency were r and omly assigned to one of four groups . In group A an anatomical double bundle anterior cruciate ligament reconstruction was performed ; group B were treated by a single bundle using an Endobutton for femoral fixation ; in group C by a single bundle using RigidFix cross pins for femoral fixation ; and in group D by a single bundle using a bioabsorbable TransFix II screw for femoral fixation . For tibial fixation a bioabsorbable Intrafix interference screw was used for all the groups and the graft was fashioned from the semitendinosus and gracilis tendons in all patients . In all , 18 patients were lost to follow-up . The remaining 200 were subjected to a clinical evaluation , with assessment of the anterior drawer , Lachman 's and the pivot-shift tests , and KT-1000 arthrometer measurement . They also completed the International Knee Documentation Committee , Lysholm knee and Tegner activity scores . At a mean of 29 months ( 25 to 38 ) follow-up there were no significant differences concerning time between injury and range of movement and Lysholm knee scores among the four groups . However , the double bundle method showed significantly better results for the pivot-shift test ( p = 0.002 ) . The KT 1000 measurements showed a mean difference between the reconstructed knee and the patients ' normal knee of 1.4 mm in the double bundle group and 2.4 mm in the single bundle group ; which was statistically significant . The Lachman and anterior drawer tests also showed superior results for the double bundle method . The International Knee Documentation Committee scale showed no significant difference among the groups ( p < 0.001 ) . On clinical evaluation the double bundle group showed less laxity than the single bundle groups . However , regardless of the technique , all knees were improved by anterior cruciate ligament reconstruction compared with their pre-operative status Abstract . Changes in the femoral and tibial bone tunnel were studied prospect ively after  arthroscopic ACL reconstruction with quadruple hamstring autograft . To determine whether tunnel enlargement can be decreased by fixing the graft close to the joint line having a stiffer fixation construct we compared " anatomical " ( one absorbable interference screw femorally , and bicortical fixation with two absorbable interference screws tibially ) and extracortical fixation techniques ( Endobutton femorally , and two no. 6 Ethibond sutures over a suture washer tibially ) . Over a 2-year period we evaluated 60 patients clinical ly ( IKDC scale , Cincinnati Knee Score , KT-1000 ) and radiographically ( confirmed by MRI ) . The operated knee was radiographed immediately postoperatively and 6 and 24 months postoperatively . The femoral and tibial bone tunnel diameter was measured on anteroposterior and lateral images , and the tunnel area was calculated and compared to the initial area calculated from the perioperative drill size . In the " anatomical " group the immediately postoperative bone tunnel area was 75 % larger than the initial tunnel area , after 6 months it was increased another 31 % , and between 6 and 24 months it remained basically unchanged . In the " extracortical " group there was no significant enlargement immediately postoperatively , but after 6 months it was 65 % larger than the initial area of drill and graft size , and between 6 and 24 months it decreased to 47 % . There was no correlation between the amount of tunnel enlargement and clinical scores or KT-1000 measurement . Arthroscopic ACL reconstruction with quadruple hamstring autograft is associated with bone tunnel enlargement . Using a purely extracortical fixation technique thus significantly increased the tibial and femoral tunnel area during the first 6 postoperative months , while it decreased slightly thereafter . The insertion of large interference screws apparently not only compresses the graft in the bone tunnel but also significantly enlarges the bone tunnel itself . The immediate enlargement at the time of the operation is followed by a reduced further enlargement at 6 months and then stabilization . Tunnel widening did not influence clinical outcome over a 2-year period 
    Output:
    
No significant differences were found between the cortical button and transfemoral fixation groups .
Included studies did not report differences in clinical outcomes between the 2 groups .
Radiographic results suggest increased femoral tunnel widening in the cortical button group .
However , tunnel widening was not found to affect clinical results .
The present evidence suggests that there are no short- to medium-term differences in knee-specific outcome measures between patients treated with cortical button femoral graft fixation and those treated with suspensory transfemoral fixation when undergoing ACL reconstruction .
In addition , radiologic evidence of tunnel widening does not seem to affect short- to medium-term clinical outcomes .