***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 
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    ***EXAMPLES*** 
    Input: Background There are different techniques for drilling the femoral tunnel in the anterior cruciate ligament reconstruction ( ACLR ) , but their influence in the bone tunnel enlargement in unknown . The purpose of this study was to compare two different surgical techniques for evaluating femoral tunnel enlargement in ACLR . The hypothesis was that tunnel placement using the outside-in technique leads to less tunnel enlargement compared to the transtibial technique . Methods Forty-four patients treated for ACLR between March 2013 and March 2014 were prospect ively enrolled in this study . According to the surgical technique , subjects were assigned to Group A ( Out-in ) or Group B ( Transtibial ) . All patients underwent CT examination  in order to evaluate the  femoral tunnel enlargement at four different levels . Moreover , all patients were evaluated with the  Lachman test and pivot shift test , and the KT1000 arthrometer was used to measure the anterior laxity of the knee . A subjective evaluation was performed using the 2000 International Knee Documentation Committee Subjective Knee score , Lysholm knee score and Tegner activity scale . All patients were assessed after 24 months of follow-up . Results At the final follow-up , there were statistically significant differences ( p < 0.05 ) in femoral tunnel enlargement between the two groups at all four femoral levels in favor of the out-in group . No statistical significant differences were found in the objective and subjective clinical outcomes between the two groups ( p > 0.05 ) . Conclusions In ACLR with a suspension system , the outside-in technique leads to less enlargement of the femoral tunnel lower than the transtibial technique BACKGROUND Bone tunnel enlargement after anterior cruciate ligament ( ACL ) reconstruction is well documented in the literature . The cause of this tunnel enlargement is unclear , but is thought to be multifactorial , with mechanical and biological factors playing a role . AIM The aim of this prospect i ve study was to evaluate how the different techniques may affect the bone tunnel enlargement and clinical outcome . PATIENTS AND METHODS Forty-five consecutive patients undergoing ACL reconstruction with autologous doubled semitendinosus and gracilis tendons  entered this study . They were r and omly assigned to enter group A ( In-Out technique , with cortical fixation and Interference screw ) and group B ( Out-In technique , metal cortical fixation on the femour and tibia ) . At a mean follow-up of 10 months , all the patients underwent CT scan exam to evaluate the post-operative diameters of both femoral and they underwent tibial tunnels clinical examination after 24 months . RESULTS The mean femoral tunnel diameter increased significantly from 9.05±0.3 mm to 10.01±2.3 mm in group A and from 9.04±0.8 mm to 9.3±1.12 mm in group B. The mean increase in femoral tunnel diameters observed in group A was significantly higher than that observed in group B ( p < 0.05 ) The mean tibial tunnel diameter increased significantly from 9.03±0.04 mm to 10.68±2.5 mm in group A and from 9.04±0.03 mm to 10.±0.78 mm in group B. The mean increase in tibial tunnel diameters observed in group A was significantly higher than that observed in group B ( p < 0.05 ) . No clinical differences were found between two groups and no correlations between clinical and radiological results were found in any patients of both groups . CONCLUSIONS Results of the study suggest that different mechanical fixation devices could influence tunnel widening . The lower stiffness of the fixation devices is probably responsible of the tunnel widening through the fixation devices 's micromotions in the femoral and tibial tunnels The purpose of this study was to evaluate the effect of the AperFix device ( Cayenne Medical , Inc , Scottsdale , Arizona ) , composed of polyetheretherketone ( PEEK ) polymer , on tunnel widening after hamstring anterior cruciate ligament ( ACL ) reconstruction as compared with 2 other fixation devices : the TransFix ( Arthrex , Inc , Naples , Florida ) and the EndoButton ( Smith & Nephew Endoscopy , Mansfield , Massachusetts ) . Sixty-seven patients with isolated total ACL ruptures who underwent arthroscopically assisted reconstruction using hamstring autografts at the authors ' institution were included in the study . Patients were assigned into 1 of 3 groups in a nonr and omized fashion : AperFix ( n=18 ) , TransFix ( n=29 ) , and EndoButton ( n=20 ) . Mean follow-up was 30 months . Tunnel widening measurements were performed on anteroposterior and lateral digital plain radiographs taken in postoperative week 1 and at final follow-up . Laxity testing , Lysholm scoring , and arthrometric evaluation were performed . All 3 graft fixation devices result ed in significant tunnel widening in both tibial and femoral tunnels at final follow-up when compared with the immediate postoperative period . Tunnel widening between groups was not significantly different in terms of coronal and sagittal femoral tunnel diameters . Tibial tunnel diameter increase in the sagittal plane in the EndoButton group was significantly smaller than that in the TransFix and AperFix groups . No correlation was found between the amount of tunnel enlargement and clinical outcomes of ACL surgery . This study 's findings suggest that tunnel enlargement after ACL reconstruction is influenced by the type of graft fixation on the tibial side irrespective of clinical outcome , and PEEK polymer does not have an effect on tunnel widening after hamstring ACL reconstruction The use of platelet-rich plasma ( PRP ) as an adjuvant to tissue repair is gaining favour in orthopaedic surgery . Tunnel widening after anterior cruciate ligament ( ACL ) reconstruction is a recognised phenomenon that could compromise revision surgery . The purpose of this study was to determine whether PRP might prevent tunnel widening in ACL reconstruction . Patients undergoing ACL reconstruction using a hamstring graft were r and omly allocated either to have PRP introduced into the tunnels peri-operatively or not . CT scanning of the knees was carried out on the day after surgery and at three months post-operatively and the width of the tunnels was measured . Patients were also evaluated clinical ly at three months , when laxity was also measured . Each group comprised 25 patients , and at three months post-operatively all were pain-free with stable knees , a negative Lachman test and a good range of movement . Arthrometric results had improved significantly in both groups ( p < 0.001 ) . Despite slightly less tunnel widening in the PRP group , there was no significant difference between the groups at the femoral opening or the mid-tunnel ( p = 0.370 and p = 0.363 , respectively ) nor at the tibial opening or mid-tunnel ( p = 0.333 and p = 0.177 , respectively).We conclude that PRP has no significant effect in preventing tunnel widening after ACL reconstruction PURPOSE This study aim ed to undertake a retrospective analysis of prospect ively collected data comparing , at a minimum follow-up of 5 years ( 78.1 ± 5.3 months v 75.6 ± 4.8 months ) , the clinical , functional , and radiographic outcomes of 2 homogeneous groups of athletes who had undergone arthroscopic single-bundle autologous hamstring reconstruction of the anterior cruciate ligament ( ACL ) using a transtibial ( TT ) or an anteromedial portal ( AMP ) approach to drill the femoral tunnel . METHODS Ninety-four patients were operated on in 2005 and 2006 , and 88 ( 93.6 % ) ( 73 men , 15 women ) were evaluated subjectively and objective ly , using the Lysholm and International Knee Documentation Committee ( IKDC ) scores , manual maximum displacement test with a KT-1000 arthrometer ( MEDmetric , San Diego , CA ) and the Lachman test , and rotational instability with the pivot shift test . Degenerative changes were assessed on radiographs according to the Fairbank classification . RESULTS The median age at operation was 29 years ( 20 to 43 years ; SD , 5.4 ) in the TT group 1 and 28 years ( 19 to 45 years ; SD , 6.1 ) in the AMP group 2 . At the last appointment , the 2 groups had similar results for the Lysholm and IKDC scores ( primary outcome ) . Patients who underwent the AMP approach had less glide pivot shift ( P = .42 ) and Lachman ( P = .47 ) phenomena , with no statistically significant intergroup difference . Radiography showed fewer , but not significantly different , degenerative changes in the AMP ACL reconstruction group at final follow-up ( P = .47 ) . CONCLUSIONS In our series , ACL reconstruction using a femoral tunnel drilled through an AMP provided better rotational stability and anterior translation than drilling the femoral tunnel using the TT technique . This difference likely is not relevant from a clinical and functional viewpoint . The 2 groups of patients were not significantly different in terms of development of degenerative changes seen radiographically at a minimum follow-up of 5 years . LEVEL OF EVIDENCE Level III , retrospective comparative study PURPOSE The purpose of this study was to compare the amount of postoperative bone tunnel enlargement after anatomic double-bundle ( DB ) and single-bundle ( SB ) anterior cruciate ligament ( ACL ) reconstruction 6 to 8 months after surgery . METHODS Twenty-one consecutive patients undergoing anatomic 4-tunnel DB ACL reconstruction and 24 patients undergoing anatomic 2-tunnel SB ACL reconstruction  were included in this study . In both groups a hybrid fixation technique with interference screw and extracortical fixation at the tibia and an extracortical fixation technique at the femur were used . Magnetic resonance imaging was performed on the second postoperative day and at a mean of 8 months ' follow-up ( range , 6.8 to 8.3 months ) to assess intraoperative and postoperative bone tunnel enlargement . Tunnel widening was determined in different planes by digitally measuring the diameters of the bone tunnels . Tunnel position was measured and classified according to Harner et al. ( femoral ) and Stäubli et al. and Petersen et al. ( tibial ) . RESULTS Magnetic resonance imaging showed that all bone tunnels were anatomically placed within the area of the original ACL insertion zone . Compared with the intraoperative drill diameter , we observed only a slight increase in tunnel diameter in both groups on the second postoperative day . At 8 months postoperatively , significant bone tunnel widening occurred in all bone tunnels ( P < .001 ) . However , no significant differences were found between tunnel enlargement in the DB group and tunnel enlargement in the SB group ( P > .05 ) , either on the tibial side or on the femoral side . In 2 cases tibial tunnel communication was noted at follow-up . CONCLUSIONS With the use of anatomic SB and DB ACL reconstruction techniques , the results of bone tunnel enlargement were comparable ; no significant difference was observed between the tibial and femoral tunnels . LEVEL OF EVIDENCE Level III , prospect i ve comparative study Purpose To determine graft bending angle ( GBA ) during knee motion after anatomic anterior cruciate ligament ( ACL ) reconstruction and to clarify whether surgical techniques affect GBA . Our hypotheses were that the graft bending angle would be highest at knee extension and the difference of surgical techniques would affect the bending steepness . Methods Eight healthy volunteers with a mean age of 29.3 ± 3.0 years were recruited and 3D MRI knee models were created at three flexion angles ( 0 ° , 90 ° and 130 ° ) . Surgical simulation of the tunnel drilling was performed with anatomic tunnel position using each outside-in ( OI ) , trans-portal ( TP ) and trans-tibial ( TT ) techniques on the identical cases . The models were matched to other knee positions and the GBA in 3D was measured using computational software . Double-bundle ACL reconstruction was analysed first , and single-bundle reconstruction was also analysed to evaluate its effect to reduce GBA . A repeated- measures ANOVA was used to compare GBA difference at three flexion angles , by three techniques or of three bundles . Results GBA changed substantially with knee motion , and it was highest at full extension ( p < 0.001 ) in each surgical technique . OI technique exhibited highest GBA for anteromedial bundle ( 94.3 ° ± 5.2 ° ) at extension , followed by TP ( 83.1 ° ± 6.5 ° ) and TT ( 70.0 ° ± 5.2 ° ) techniques ( p < 0.01 ) . GBA for posterolateral bundle at extension were also high in OI ( 84.6 ° ± 7.4 ° ) , TP ( 83.0 ° ± 6.3 ° ) and TT ( 77.2 ° ± 7.0 ° ) techniques ( n.s . ) . Single-bundle grafts did not decrease GBA compared with double-bundle grafts . In OI technique , a more proximal location of the femoral exit reduced GBA of each bundle at extension and 90 ° flexion . Conclusion A significant GBA change with knee motion and considerably steep bending at full extension , especially with OI and TP techniques , were simulated . Although single-bundle technique did not reduce GBA as seen in double-bundle technique , proximal location of femoral exits by OI technique , with tunnels kept in anatomic position , was effective in decreasing GBA at knee extension and flexion . For clinical relevance , high stress on graft and bone interface has been suggested by steep GBA at full extension after anatomic ACL reconstruction . Level of evidence Therapeutic study ( prospect i ve comparative study ) , Level II Tunnel  enlargement after anterior cruciate ligament 
    Output:
    
Conclusion No significant difference in femoral tunnel widening was observed between the AMP and TT techniques , both in absolute millimeter and relative percentage , in patients who underwent single-bundle ACL reconstruction .
This finding could alleviate the potential concerns associated with femoral tunnels being wider for the AMP than for the TT technique .