in anterior cruciate ligament ( acl ) reconstruction , the use of bone patellar tendon bone graft ( bptb ) has been decreasing due to increased anterior knee pain , weakness of extensor power and difficulty of kneeling position . instead , the use of hamstring tendon has been increasing1,2 ) ; however , the disadvantages of hamstring grafts include weaker fixation strength compared to bptb grafts and 24-week period for complete bone - to - tendon healing3 ) .
adequate fixation has been considered essential for good outcomes of acl reconstruction and a variety of graft fixation methods have been introduced .
the compression method allows for early firm fixation and healing with tight bone - tendon interface and enables close fixation to the acl footprint , but it has low failure load and stability4,5 ) .
the expansion fixation mechanism can be advantageous in obtaining secure fixation because two cross pins transversely inserted through a graft provides a centrifugal pressure on the femoral tunnel , but treatment results depend on the press - fit of the graft , bone density around the femoral tunnel , and correct placement of cross pins through the graft tendon6,7,8 ) .
the suspension methods are sub - classified into cortical , cancellous and , cortio - cancellous suspension methods9 ) .
the cortical suspension method provides good fixation strength , but it has a bungee cord effect10 ) and a windshield wiper effect11 ) due to the long fixation point from the articular surface .
the cortico - cancellous suspension method has strong stability and stiffness due to the use of a metaphyseal crosspin . to et al.12 )
reported that stiffness of the graft fixation complex was more affected by fixation method than the graft type in a cadaver study .
intercondylar cortico - cancellous fixation close to the articular surface is expected to offer better results than the endobutton fixation .
speirs et al.13 ) reported that the cortico - cancellous suspensory fixation method required a short graft length due to fixation of the cross pin within the metaphysis , the lowest creep and cyclic elongation amplitude , and the highest strength and stiffness of all the tested devices .
in particular , the pinn - acl crosspin ( conmed linvatec , largo , fl , usa ) system was found to be the most rigid and strongest of all the tested reconstruction systems .
therefore , the cortico - cancellous fixation method seems to have the advantages of short graft , stability , and stiffness , and the pinn - acl crosspin implant features the proprietary self - reinforced poly - l - lactide acid polymer enabling it to be the strongest bioabsorbable implant .
the cross pin absorption begins in vivo approximately within 15 to 24 weeks after insertion , the continuous loop is composed of high strength polyethylene fiber , and the ultimate pullout tensile strength is 1700n14 ) ( fig .
, we analyzed the mid - term results of acl reconstruction using the pinn - acl crosspin system , a cortico - cancellous suspension method device .
we hypothesized that acl reconstruction using the pinn - acl crosspin system would significantly improve manual stability , anterior - posterior laxity measured by instrument , and functional score .
from june 2007 to july 2008 , 43 of 46 patients with ruptured acls were evaluated .
the patients underwent single - bundle acl reconstruction using a 4-strand semitendinosus tendon ( semi - t ) with the pinn - acl crosspin system .
three patients were excluded due to conditions that might affect the results : articular cartilage damage and osteoarthritis in 1 patient , subtotal meniscectomy in 1 patient , and total meniscectomy in 1 patient .
all included patients were male with a mean age of 28.7 years ( range , 18 to 54 years ) .
the acl reconstruction was performed on the right knee in 24 patients and on the left knee in 19 patients .
the mean follow - up period was 50 months ( range , 48 to 61 months ) .
associated lesions were meniscal tear in 15 patients , which required meniscus repair in 5 and partial meniscectomy in 10 , and medial collateral ligament injury in 2 patients , which was treated by conservative methods .
a 4-strand semi - t was used as a graft . a longer than 28 cm semi - t was harvested with an additional 2 cm of periosteum extension and was folded twice to be a 4-strand graft15 ) .
the mean length of the graft was 7.2 cm and the diameter was 8.2 cm ( fig .
depending on the diameter of the femoral tunnel , a positioning rod ( 8 mm or 9 mm ) of appropriate size was selected and assembled onto the u - guide .
when the u - guide assembly was fully inserted , the laser etch marks on the positioning rod indicated the length of the femoral tunnel .
after the u - guide was fully inserted into the tunnel , the u - guide body was rotated until the transverse cannula mounted on the u - guide body was directed toward the lateral condyle .
each cross pin had a cortical length designed to occupy the cortical side of the transverse tunnel .
a cross pin of proper length was determined as the one whose cortical length was less than , or equal to , the measured cortical tunnel length . after selecting the proper size cross pin , the hamstring graft construct ( i.e. , graft harness and graft bundle assembly ) was drawn into the knee using the graft passing guide pin .
the lead suture was passed on the graft harness through the eyelet of the graft passing guide pin and , while maintaining lateral to medial alignment of the axis of the eyelet in the graft harness , the graft construct was passed into the tibial tunnel .
it was firmly pulled on the graft construct until fullly seated in the femoral socket .
a sheathed scope could be placed into the transverse cannula to visualize the alignment of the axis of the graft harness eyelet with the axis of the transverse tunnel .
the crosspin driver was inserted into the proximal end of the implant and tapped with a mallet to move the implant through the transverse cannula and into the transverse tunnels .
the corsspin implant , pressed into the lateral transverse tunnel , was advanced with the driver and a mallet until it stops while pulling out the transverse cannula .
the position of the femoral tunnel was at the center of the footprint , directed 10:30 ( or 1:30 ) o'clock position .
3 ) . we tried to preserve the remnants of acl as much as possible .
tibial side fixation was done using a bioabsorbable screw and then post - tied with a washer and screw .
range of motion exercises were allowed at 2 weeks after surgery with extension locking braces applied .
up to 90 of active range of motion was permitted for 4 weeks and full range of motion exercise was performed thereafter . from 6 weeks after surgery
, patients followed a usual rehabilitation program17 ) . in patients who had undergone concomitant meniscal repair ,
anterior instability was evaluated on the day of admission using the lachman test and the kneelax3 arthrometer ( monitored rehab systems , haarlem , netherlands)18 ) .
rotational instability was evaluated using the pivot - shift test with the patient under anesthesia immediately before surgery .
functional knee score was evaluated using the international knee documentation committee ( ikdc ) subjective score and objective grade .
student 's t - test was used to analyze parametric continuous data and chi - square test was used for non - parametric data .
statistical significance was accepted for p - values of < 0.05 , and spss ver . 21.0 ( ibm corp .
the range of motion was improved to normal without limitation at final follow - up .
the lachman test results were improved form grade ii ( n=40 ) or iii ( n=3 ) to grade i ( n=3 ) or grade 0 ( n=40 ) at final follow - up ( p=0.001 ) .
the pivot - shift test results were improved from grade i ( n=20 ) or ii ( n=10 ) to grade i ( n=8 ) or grade 0 ( n=22 ) at final follow - up ( p=0.001 ) .
the ikdc subjective score was improved to 88.7 and the objective grades a and b were noted in 93% of the patients at final follow - up ( p=0.039 , 0.001 ) . anterior laxity measured by the kneelax3 arthrometer was improved from 6.74.5 mm preoperatively to 2.11.0 mm at final follow - up ( p=0.021 ) ( table 1 ) .
three cases of complications occurred : a graft re - rupture was treated with revision reconstruction at 2 years after surgery ; a superficial infection on the tibial side was improved after debridement ; and a deep knee infection on the tibial side found at 2 weeks after surgery was identified as methicillin resistance staphylococcus aureus and treated with thorough arthroscopic debridement , massive irrigation , and 4 weeks of antibiotic injection .
in this study , anterior instability evaluated using the lachman test and kneelax3 arthrometer , and rotational instability evaluated by the pivot - shift test were significantly improved after surgery .
the functional knee score evaluated using the ikdc score & grade was also remarkably improved after surgery .
seo et al.19 ) reported on 56 cases of acl reconstruction using the pinn - acl crosspin system . in the study , the side - to - side difference measured by the kt-1000 arthrometer was 2.4 mm at a mean of 14.5-month follow - up and the mean ikdc score was 87.3 .
kong et al.20 ) reported on 56 cases of acl reconstruction using rigidfix , another crosspin system . in their study , the mean side - to - side difference was 2.1 mm and 98.2% of the cases had ikdc grades a or b. streich et al.21 ) reported about 25 cases of single bundle acl reconstruction with a single semi - t : the mean side - to - side difference was 0.94 mm , the pivot - shift test was grade 0 in 19 cases , more than grade 1 in 6 cases , and the mean ikdc score was 88.6 .
seo et al.19 ) reported that the incidence of crosspin - femoral tunnel mismatch was high . to prevent this problem
, they tried to firmly fix the drill guide sheath to the femur or create a short femoral tunnel to perform drilling at almost perpendicular direction to the cortical bone , but this technique requires further improvement of tools for minimization of complications . in our study , we encountered a mismatch between the harness hole within the femoral tunnel and the crosspin tunnel caused by rotation of the harness in bone tunnel .
we solved this problem by firmly fixing the guide assembly and switching from a small sized stick to a larger one of the same size of the harness hole to make 90% of the harness hole coincide with the crosspin tunnel .
yamazaki et al.22 ) and zantop et al.23 ) reported on the optimal length of the soft - tissue graft within a bone tunnel .
they concluded that a graft length of over 15 mm does not influence the kinematic or structural properties of the knee joint .
although lipscomb et al.24 ) indicated that slight or no deficits were observed in the knee flexor strength , most reports suggested that deficits of 10% to 20% in the knee flexor strength are common after acl reconstruction using both semi - t and gracilis tendon autograft25,26 ) .
the single 4-strand semi - t tendon acl graft was shorter but could be made thicker , had biomechanical benefits , and decreased donor site morbidity by not harvesting the gracilis tendon27 ) . for a four - strand hamstring graft , at least a graft length of 7 cm is recommended15 ) ( fig .
, the minimum required semi - t tendon length is 28 cm for a four - strand semi - t graft .
it is possible to obtain an additional 2 cm of semi - t tendon by including the periosteum15 ) . in this
study the mean graft length was 7.2 cm , the mean diameter was 8.2 mm , which was thicker than the semi - t / gracilis 4-strand graft .
so , we could expect less decrease of the knee flexor strength without harvesting of the gracilis tendon , enhanced tendon healing to the bone tunnel due to inclusion of the periosteum in the graft and a thicker graft28 ) .
the pinn - acl crosspin instrument could be one of the useful cortio - cancellous suspensory devices for femoral fixation , allowing for easy fixation with a shorter graft ( single semi - t 4-strand ) and reducing donor site morbidity .
the other crosspin , rigidfix system , requires a 3-cm long graft in the femoral bone tunnel for adequate fixation .
however , the pinn - acl crosspin needs a 1.5 - 2 cm graft for adequate fixation .
one case of graft re - rupture occurred , but it was not related to the fixation method . regarding the one case of deep infection and another case of superficial infection , these two infections were improved after debridement .
we suspect that the cause of infection might have been contamination of the guide assembly because the pinn - acl crosspin instrument was complex and composed of several small parts and guide assembly .
so , we believe there is a need for thorough cleansing and sterilization including foreign body particle removal from the guide assembly before surgery .
maletis et al.29 ) evaluated the incidence of postoperative acl reconstruction infections in the total 10,626 cases and concluded that graft choice would make a difference .
the overall incidence of surgical site infection ( ssi ) was 0.48% ( n=51 ) , with 17 ( 0.16% ) superficial infections and 34 ( 0.32% ) deep infections .
hamstring tendon autografts ( 0.61% ) had the highest incidence of deep ssis of the total graft types ( bptb autograft 0.07% vs. allograft 0.27% ) .
after adjusting for age , sex , and body mass index , the likelihood of a patient with a hamstring autograft having a deep ssi was 8.24 times higher than someone receiving a bptb autograft .
van tongel et al.30 ) reported the incidence of septic arthritis after acl reconstruction using semi - t / gracilis autograft was 0.51% .
the limitations of this study are no inclusion of a control group , retrospective study design , and no performance of radiologic evaluation .
this study demonstrated that good results can be obtained after single - bundle acl reconstruction using 4-strand semi - t tendon with the pinn - acl crosspin system at a minimum follow - up of 48 months .
we believe the pinn - acl crosspin system is a useful instrument for shorter graft fixation .
 purposethis study evaluated mid - term results of anterior cruciate ligament ( acl ) reconstruction using the pinn - acl crosspin system that allowed for short graft fixation.materials and methodsforty - three patients underwent single - bundle acl reconstruction with a 4-strand semitendinosus tendon graft using the pinn - acl crosspin system . 
 femoral fixation was done using the pinn - acl crosspin system , and the tibial side was fixed with post - tie and a bioabsorbable interference screw . 
 the mean follow - up period was 50 months . 
 evaluation was done using the lachman test , pivot - shift test , international knee documentation committee ( ikdc ) score and grade . 
 anterior displacement was assessed.resultsthere was improvement in the lachman test and pivot - shift test at final follow - up , form grade ii ( n=40 ) or iii ( n=3 ) to grade i ( n=3 ) or 0 ( n=40 ) and from grade i ( n=20 ) or ii ( n=10 ) to grade i ( n=8 ) or 0 ( n=22 ) , respectively . 
 the mean ikdc score was 88.7 , and grade a and b were 93.0% at final follow - up . 
 side - to - side difference was improved from 6.7 mm to 2.1 mm at final follow - up . 
 complications occurred in 3 patients , a re - ruptured due to trauma at 2 years after surgery and a deep infection and a superficial infection.conclusionsthe mid - term follow - up results of acl reconstruction with the pinn - acl crosspin system were satisfactory . the pinn - acl crosspin can be considered as a useful instrument for short graft fixation . 
Introduction
Materials and Methods
Results
Discussion
Conclusions