Subjective assessment reported by patients shows differences between single-bundle and double-bundle anterior cruciate ligament reconstruction, systematic review and meta-analysis

To determine the functional recovery, active reincorporation, and anteroposterior and rotational stability of patients undergoing anterior cruciate ligament (ACL) reconstruction using arthroscopy techniques with simple-bundle (SB) or double-bundle (DB). The following databases were searched: PubMed, Embase (Elsevier platform), the Cochrane Central Register of Controlled Trials (Wiley platform), Web of Science, and CINAHL. Level I and II studies involving anterior cruciate ligament arthroscopy were included in the search. Records were screened by title and abstract and assessed the risk of bias of selected studies. Meta-analyses using RevMan 5.3 software were conducted on the following outcomes: knee functionality, objective measurements of knee stability, rotational knee stability and knee anterior stability, sports reincorporation, and subjective assessments. Twenty-four studies of patients undergoing ACL reconstruction were included in the qualitative and quantitative synthesis (1707 patients) for Lysholm score, Subjective International Knee Documentation Committee (IKDC) score, Tegner score, KT-1000/2000, Lachman test, Objective IKDC score, and Pivot-Shift test. A return to pre-injury level showed a significant decrease in the Lysholm score (mean difference, − 0.99; 95% CI − 1.71 to − 0.40; P = 0.007) and Tegner score (mean difference, − 0.07; 95% CI, − 0.13 to − 0.01; P = 0.02) at DB reconstruction, similar to the knee functionality outcome of the subjective IKDC score (mean difference − 1.42; 95% CI − 2.46 to − 0.38; P = 0.007). There is no clear or significant difference in clinical stability and knee function or in sports incorporation with the true difference occurring in the subjective assessment.


Results
Study selection. The search yielded 575 records (Fig. 1), which were screened by 2 investigators, including 130 records which were assessed for eligibility.
In the presented outcomes, most of the studies showed no differences; however, in 2 studies, the pivot-shift test showed better results in the double-bundle group as shown in (P < 0.001) 40 and (P = 0.003) 51 . Two studies 47,49 showed better grades of objective and subjective IKDC scores and presented high heterogeneity between the IKDC score objective studies. Koga et al. 40 showed better results in the double-bundle group (P = 0.024) in the Lachman test, and KT measurements were better in the double-bundle group (mean, 1.4 mm vs. 2.7 mm; P = 0.0023). The Tegner score was also better in the double-bundle group (P = 0.033). Zaffagnini et al. 51 showed that the double-bundle hamstring group had a significantly higher Tegner level (P = 0.0007) and a higher passive range of motion recovery (P = 0.0014). The side-to-side difference in posterior translation decreased in the double-bundle group with a significant difference between the 2 groups (P < 0.05).
Heterogeneity. We evaluated the clinical heterogeneity of 24 studies. Statistical heterogeneity was calculated for both continuous (Lysholm and Tegner score, internal rotation range, KT-1000/2000, and subjective IKDC score) and dichotomous (pivot shift, Lachman test, and objective IKDC score) variables.
Quantitative meta-analyses. A total of 24 studies with 1707 patients were included in the quantitative meta-analyses. We grouped studies for statistical analyses based on follow-up into the following categories: baseline, 6-12 months, 13 Single-bundle ACL reconstruction. The tibial tunnel was prepared using a dedicated elbow aimer in the posterior half of the native ACL footprint while maintaining the ACL stump. The femoral tunnel diameter was usually 7 to 8 mm and the tibial tunnel diameter 8 to 9 mm accordingly to the graft dimension. n = 30 Double-bundle ACL reconstruction. The semitendinosus was used for the anteromedial bundle and the gracilis for the posterolateral bundle. n = 30 Patients were evaluated preoperatively and after surgery at 6 months, 1, 3, and 6 years using the Lysholm score, IKDC form, and KT-2000 Ahlden et al. 3 I n = 103 Inclusion: patients with a unilateral ACL injury and older than 18 years Single-bundle ACL reconstruction. The femoral tunnel was first addressed. The femoral ACL insertion site was marked with a Steadman awl in the shallow aspect of the AM bundle insertion site and near the centre of the ACL footprint. n = 50 Double-bundle ACL reconstruction. The femoral tunnels were first addressed. The femoral insertion sites of the AM and PL bundles were marked with a Steadman awl. n = 53 Clinical assessments at the preoperative and follow-up times were as follows: pivot-shift test, KT-1000 arthrometer laxity measurements, manual Lachman test, range of motion, Lysholm knee-scoring scale, and Tegner activity scale, KOOS, 1-legged hop test, and square hop test Araki et al. 4 I n = 20 Inclusion: chronic ACL deficiency in one knee and had an indication for ACL reconstruction Single femoral and single tibial tunnels were created at the central position between the original insertion of the AMB and PLB. n = 10 Two femoral and two tibial tunnels to reproduce the AMB and PLB. n = 10 KT-1000 measurements, isokinetic muscle peak torque, heel-height difference, and Lysholm score at the preoperative and one-year follow-up times between these two groups Beyaz et al. 9 I n = 31 Inclusion: patients without lower limb bone fractures, who had not undergone previous lower extremity surgery, and whose other knee examination was normal In the single-bundle method, the ACL was aligned in the middle of the tibial tunnel exit. n = 16 In the dual-bundle method, a 5 cm oblique incision was made 2 cm below and medial to the tibial tuberosity to harvest gracilis and semitendinosus tendons. n = 15 Clinical evaluations were performed at 8 years postoperatively with the IKDC, Tegner, and Lysholm knee-scoring systems Bohn et al. 11 I n = 36 Inclusion: age 18-50 years, magnetic resonance imaging-verified ACL injury with symptoms of instability, no previous knee ligament surgery, no concomitant knee ligament injuries, and an uninjured contralateral knee The tibial bone tunnel was positioned in the intercondylaris anterior area in the centre of the native tibial ACL footprint using the inner aspect of the lateral meniscus anterior insertion area as a landmark. n = 13 The semitendinosus tendon (for the AM bundle) and the gracilis tendon (for the PL bundle) were looped over a 20 mm EndoButton CL femoral fixation implant. n = 23 The tibial rotation was determined during walking, running, and a pivoting task. Other outcome parameters were KT-1000 knee laxity measurements and subjective outcome scores of KOOS and IKDC Ebert et al. 20 II n = 50 Inclusion: less than 60 years old, non-cartilage lesions above grade 3 or lower than 3 cm 2 , knee joint dislocations and partial resection of the meniscus of less than 50% For the SB technique, a graft that was 7-9 mm in diameter and 7-9 cm in length was prepared by folding it. n = 31 Two grafts were prepared for the DB technique. n = 19 The VAS for pain and function, the Tegner activity score, IKDC and the Lysholm and Marshall scores were used as evaluation methods; the anterior stability (KT-1000 arthrometer measurement) and the deficits in muscle strength in extension and flexion of both knees were measured in a standardized manner one year after surgery Fujita et al. 22 I n = 55 Inclusion: the patient was diagnosed with ACL insufficiency and provided informed written consent for this study Double semitendinosus combined with double gracilis tendons for the AM bundle. n = 31 The PL bundle graft in DB reconstruction and combined quadruple semitendinosus and double gracilis tendons in the AM and PL reconstructions; 2 femoral and 2 tibial tunnels to reproduce the AM and PL bundles for DB reconstruction were created. n = 19 The Lysholm score, Tegner score, anterior laxity with the KT-1000 arthrometer, rotator instability with the pivot-shift test, and muscle strength with knee extensor and flexor isokinetic peak torques at 60°/s were evaluated Hussein et al. 26 I n = 209 Inclusion: an ACL rupture in active patients with a closed growth plate The procedure of anatomic single-bundle reconstruction was similar to anatomic doublebundle reconstruction. n = 78 With the scope in the medial portal, a 3/32 Steinman pin was introduced through the accessory medial portal and placed at the centre of the PL femoral insertion site. In chronic cases, we placed it below the lateral intercondylar ridge and anterior to the bifurcate ridge. n = 138 The outcomes were the Lysholm score and subjective IKDC form. The KT-1000 arthrometer was used to evaluate anteroposterior stability, and the pivot-shift test was used to determine rotational stability Jarvela et al. 28 II n = 90 Inclusion: primary ACL reconstruction, closed growth plates, and the absence of ligament injuries to the contralateral knee The femoral tunnel was drilled through an anteromedial portal as posterior as possible without breaking the posterior wall of the femur with a freehand technique at approximately 10 o' clock in the right knee and 2 o' clock in the left knee. n = 60 Two tunnels on the femoral side were made via an anteromedial portal (not transtibial) with a free-hand technique without a guide to the anatomic position of the insertion sites of each bundle. n = 30 The evaluation methods consisted of a clinical examination, which included stability measurements using a KT-1000 arthrometer, and a manual pivotshift test. The IKDC and Lysholm knee scores were used to evaluate the knee preoperatively and at the 10 Single-bundle reconstruction with modified BPTB allograft was shaped into a column of 25 mm in length and 10 mm in diameter; n = 43 For DB ACL reconstruction, tibialis anterior allografts were prepared to make 2 doublelooped grafts for the AM and PL bundles. n = 41 Clinical outcomes including Lachman and pivot-shift tests, KT-1000 arthrometer measurements, and IKDC classification; Lysholm and Tegner activity scores were compared between the two groups at the last follow-up Karikis et al. 31 I n = 105 Inclusion: patients > 18 years old with a unilateral ACL injury The femoral tunnel was addressed first. The femoral ACL insertion site was marked with an awl in the shallow aspect of the AM bundle insertion site, which is near the centre of the ACL footprint, to place the centre of the tunnel just as deep as the bifurcate ridge approximately 8 to 10 mm from the posterior cartilage at the 3 or 9 o' clock position in the notch orientation and with the knee at 90° of flexion. n = 52 For the DB technique, both femoral and tibial remnants of AM and PL bundles were identified with the knee at 90° of flexion. The femoral tunnels were addressed first. The femoral insertion sites of the AM and PL bundles were identified and marked with an awl. n = 53 Multiple subjective and objective clinical evaluation tests and radiographic assessments of osteoarthritis (OA) were performed including the following: the Tegner score, the pivot-shift test, KT For DB reconstruction, 2 double-strand bundles for the anteromedial bundle (AMB) and posterolateral bundle (PLB) were created with the EndoButton CL devices. The open end of each graft was closed in the same fashion as the SB method. n = 28 The following evaluation methods were used: clinical examination, KT-1000 arthrometer measurement, muscle strength, Tegner activity score, Lysholm score, subjective rating scale regarding patient satisfaction and sports performance level, graft retear, contralateral ACL tear, and additional meniscus surgery Liu et al. 34 I n = 80 Inclusion: complete, isolated, chronic ACL lesions (mean injury-to-surgery interval, 23.5 months; range, 1.5-180 months) received an ACL reconstruction with a 6-to 8-stranded HG The femoral tunnel was drilled through the AAMP behind the resident's ridge as posterior as possible without breaking the posterior wall of the femur and using a 6-mm femoral guide at approximately the 10 o' clock (or 2 o' clock) position. n = 40 On the femoral side, both the AMB and PLB tunnels were drilled through the AAMP behind the resident's ridge as posterior as possible without breaking the posterior wall of the femur and using a 6-mm femoral guide. n = 40 The outcome assessment was performed by a blinded independent observer using International Knee Documentation Committee (IKDC), Tegner, and Lysholm scores as well as range of motion (ROM), Lachman test, pivot-shift test, KT-2000 arthrometer sideto-side difference, and return-tosport data Liu et al. 35 I n = 42 Inclusion: 1. Men aged 18-40 at the time of surgery; 2. First ACL reconstruction surgery; 3. Single leg involvement; and 4. Able to attend preoperative assessment For HT-SB surgery, the semitendinosus and gracilis tendons (approximately 7-9 mm in diameter) were harvested and inserted into the femoral and tibial tunnels (both approximately 7-9 mm in diameter). n = 22 For HT-DB surgery, the semitendinosus and gracilis tendons were harvested. Two tunnels (6-7 mm in diameter for the AM tunnel and 5-7 mm in diameter for the posterolateral (PL tunnel)) were drilled over both the femur and tibia. n = 20 The KT-1000, Lysholm, IKDC, one-leg hop test and Lachman test were performed blindly at baseline and 1-year post-reconstruction Mayr et al. 37 I n = 64 Inclusion: all consecutive patients presented to the outpatient clinic with an ACL rupture For SB ACL reconstruction, both tendons were used as a 4-strand graft; for DB reconstruction, the gracilis tendon was used as a double-strand graft to replace the anteromedial bundle and the double-strand semitendinosus tendon was used for replacement of the posterolateral bundle. n = 30 In the DB technique, the femoral drill pin for the anteromedial bundle was placed into the proximal and anterior part of the femoral footprint of the ACL and for the posterolateral bundle was placed into the posterior and distal portion. n = 34 A follow-up examination 2 years after surgery consisted of IKDC 2000 assessment, Laxitester measurement of anteroposterior translation regarding rotational stability, and radiographic evaluation Mayr et al. 38 I n = 64 Inclusion: all consecutive patients presented to the outpatient clinic with an ACL rupture For SB ACL reconstruction, both tendons were used as a 4-strand graft; for DB reconstruction, the gracilis tendon was used as a double-strand graft to replace the anteromedial bundle and the double-strand semitendinosus tendon was used for replacement of the posterolateral bundle. n = 30 In the DB technique, the femoral drill pin for the anteromedial bundle was placed into the proximal and anterior part of the femoral footprint of the ACL and for the posterolateral bundle was placed into the posterior and distal portion. n = 34 A follow-up examination 5 years after surgery consisted of IKDC 2000 assessment, Laxitester measurement of anteroposterior translation regarding rotational stability, and radiographic evaluation Misonoo et al. 42 II n = 44 Inclusion: patients whose ACL was reconstructed using either a SB o rDB method For the SB reconstruction, the semitendinosus tendon was used as two double stranded grafts. First, using a tibial guide, the tibial tunnel was created at the centre of the ACL footprint. n = 22 In the technique used for DB reconstruction, two femoral and two tibial tunnels were created under controlled arthroscopic visualization to anatomically reproduce both the AM and PL bundle using the hamstring tendon graft. n = 22 Clinical assessment, including Tegner score, Lysholm score, and knee arthrometric measurement, revealed a restoration of the reconstructed knee stability Double-bundle ACL Reconstruction with Hamstring Tendon: the semitendinosus tendon was usually harvested with a tendon harvester. The distal and proximal half of the semitendinosus tendon was looped and used as the AMB and PLB graft, respectively. n = 9 Clinical outcomes (knee flexion (ROM), heel-height difference, side-to-side difference in anterior laxity, rotational laxity, and Tegner activity score) were compared between the DB and SB groups and an examination of factors affecting subjective outcomes (KOOS results) was performed Song et al. 50 II n = 130 Inclusion: patients with ACL injury, chondral lesions less than the Outerbridge grade of 3, and with or without meniscal injury For the SB ACLR, the tibialis anterior allograft was also prepared as a single-looped graft (diameter, 8-9 mm). After tibial tunnel preparation at the centre of the ACL insertion, a femoral tunnel at the centre of the footprint was created through the anteromedial portal. n = 65 For DB reconstruction, freshfrozen tibialis anterior allografts were prepared to make 2 singlelooped grafts of 6-mm diameter for PLB and of 7-mm diameter for AMB. n = 65 The stability results were evaluated using the Lachman and pivot-shift tests and stress radiography. Additionally, the functional outcomes were based on the Lysholm knee score, Tegner activity score, and IKDC subjective scale Ventura et al. 54  Patients belonging to the DB group underwent DB reconstruction using a 2-stranded semitendinosus tendon for the AM bundle and a 2-stranded gracilis tendon for the PL bundle. n = 40 Patients were assessed preoperatively with functional assessment including the International Knee Documentation Committee 2000 knee subjective form and visual analogue scale as well as physical examination (including the pivot-shift test and instrumented knee laxity measurement). Vertical jump assessment with the Optojump system has been introduced as a method comparing functional ability between the 2 surgical techniques. The same protocol was repeated at 6 months, 12 months, and 2 years after surgery Volpi et al. 55 II n = 40 Inclusion: specific sports activities age 18-45, no additional ligamentous lesions, absence of rheumatic pathologies, type IV Outerbridge chondral lesions, axial deviation of the knee, and any previous surgery to the examined knee Single-bundle ACL reconstructions with the patellar tendon were performed using two re-absorbable cross pins for the femoral fixation and both tibial rigid fix and re-absorbable pins for the tibial fixation. n = 20 Double-bundle ACL reconstruction with semitendinosus and gracilis tendons were performed using the transtibial technique with a dedicated guide. The femoral fixation of both PL and AM bundles was achieved with pins, while for the tibial side, both bundles were fixed with a metal staple or bioscrew at 108° and 45-50° of flexion, respectively. n = 20 Clinical assessment, including Tegner score, Lysholm score, IKDC and KT-1000 Xu et al. 58 I n = 80 Inclusion: primary ACL rupture in adult patients The procedure was similar to the anatomic double-bundle reconstruction. The femoral tunnel was also created through the accessory medial portal, but the centre of the tunnel was placed in the middle of the insertion site. n = 40 The AM and PL tunnels on the femur were drilled based on the identified insertion sites through the accessory medial portal. n = 40 Pre-and post-operatively, all patients received a preoperative examination, including Lachman, anterior drawer, and pivot shift testing, and were also tested with KT-1000 arthrometer with a knee flexion of 30 and 90° and a manual maximum force. All patients were also evaluated with the IKDC subjective score, Lysholm score and Tegner score Zaffagnini et al. 60  In single-bundle reconstruction, a tibial tunnel was first made by inserting a 2.0 Kirschner wire into the centre of ACL insertion to the tibia and then drilling with a cannulated drill and a dilatar to create a bone tunnel with the same diameter as the tendon graft. n = 49 In double-bundle reconstruction, a 2.0 Kirschner wire was inserted posterior to the footprint of ACL insertion into the tibia via the Pro-trae ACL guide system; then, a dilatar and a cannulated drill were used to create a bone tunnel with the same diameter as the PL bundle of the graft. n = 45 The rotational stability, as evaluated by the pivot-shift test, was significantly superior in Group DB compared to that in Group SB. No significant difference regarding ACL revisions, total flexion work, mean peak flexion torque and extension work between the groups was detected using the Tegner activity score, the knee injury and osteoarthritis outcome score, the Lysholm functional score, anterior knee pain or mobility, and subjective knee function. In addition, the Lachman test or the KT-1000 maximum manual force test was investigated Table 1 Table 2). Regarding dichotomous variables, the Lachman test percentage no was higher in the double-bundle group than in the single-bundle group (RD, 0.01; 95% CI − 0.01 to 0.04; P = 0.13) 30,31,33,38,39,43,47,52 (Fig. 6 A) (Table 3).
Data on the re-rupture rate in both techniques were not evaluated in the included studies.

Discussion
In this meta-analysis, we attempted to show whether there were significant differences between SB and DB interventions in the recovery of functionality after ACL tears, since previous studies did not demonstrate this result strongly enough. We found significant differences favourable to DB reconstruction in the return to the preinjury level according to the Lysholm score (P = 0.007) and the functionality of the knee according to the IKDC subjective score (P = 0.007). Residual instability in reconstructive ACL surgery is the main cause of mechanical failure. Techniques that reduce this instability, mainly in the rotational plane, have been previously described and highlight those that involve the performance of a DB to reproduce the original anatomy of the ACL in the anteromedial (AM) and posterolateral (PL) bundles by arthroscopic surgery.
There are some differences between the technical aspects and tips but the real difference between the whole DB reconstruction surgery is the realization of an only tibial tunnel or double tibial tunnel as well, since all the DB Mostly of the studies included in our systematic review showed highlight an improvement in rotational stability (based on exploratory manoeuvres) throughout the follow-up according to functional reincorporation by using DB reconstruction surgery. This study was conducted to compare the early-, mid-, and long-term follow-up of patient operations using DB and SB techniques. The results show that there is no clear or significant difference in the clinical stability and knee function or in sports incorporation with the true difference being the subjective assessment by the patient. These results are consistent with those presented by another recent systematic review and adds subjective assessment data to previous datasets 55 . The non-differences in the previous laxity do not confirm previous findings. Björnsson et al. 56 shows results with DB improvement, but this systematic review presents RCT, prospective and retrospectives studies with less evidence regarding this meta-analysis and in the context of rotational stability. Our findings stand out with a non-significant improvement (internal rotation and pivot shift), which seems to be in contrast with the technical gesture of adding a PL fascicle to the conventional technique. Perhaps the classic concept of injury of "the other" peripheral structures, such as the collateral ligaments and the muscles that cross the joint and play an important role in the concept of rotational stability 55,57 .
In Kongtharvonskul et al. study, clinical function showed a significant statistical difference between the DB and SB techniques in autologous ACL reconstruction 58 , results similar to those found in our meta-analysis.
The strengths of results present in this works are: 1. Although there do not seem to be any functional differences from the immediate postoperative period, in the return to physical and sports activity differences are shown at 18 months after the DB, which are also evident after 3 years for the Lysholm and Tegner score (Fig. 4). For sports, this is of the utmost importance and often not shown during these mid-term and long-term follow-ups, according to results shown by Xu et al. 10 . 2. Subjective assessment through the IKDC shows a higher score with a better feeling of stability from the subjective viewpoint in the mean score of the total in the DB vs. SB technique, which is the most statistically significant for the outcomes of the study. This analysis of the subjective feeling of the patient in favour of the DB technique allows the patient greater confidence in their return to physical activities in patients undergoing the DB technique. Furthermore, this disagrees with previous studies that found no differences in subjective outcome measures between DB and SB reconstruction 10 . These results were not seen in the objective IKDC score, but there was a significant and favourable trend toward the DB technique observed (P = 0.10) (Fig. 3), which agrees with Xu et al.'s meta-analysis 10 and concludes that DB anterior cruciate ligament reconstruction resulted in significantly better anterior and rotational stability and higher IKDC objective scores than SB reconstruction. Therefore, the evaluation of the patient and activity levels could be the strength of choice when choosing the DB technique. 3. Lachman anteroposterior instability shows similar results in both techniques, which indicates that there is no advantage for any technique from the medical anteroposterior point  (Fig. 6) showed statistically significant differences with less anterior laxity in 45% of studies that included the DB technique 56,59 . Based on current evidence, DB reconstruction appears to have fewer re-ruptures and less antero-posterior and rotatory laxity. 4. Rotational stability (internal rotation and pivot shift) is slightly better but not significant in DB reconstruction. This benefit is especially important regarding the concept of reinjury since the persistence of rotational instability has become evident as a cause of rupture. Therefore, although both patients needed to maintain "anti-rotational" muscle enhancement, this should be more demanding in patients with the SB technique. These results present controversy from previous systematic reviews showing that DB provided significantly better knee stability than the SB technique 10,56,58,59 . According to results presented by our work, DB was better in the long-term follow-up than the SB technique, but not in all follow-ups of the included studies. Similar to a previous systematic review 58 , heterogeneity was present in some outcomes, but there was no evidence of publication bias for any outcome. The double-bundle technique may be better than the single-bundle ACL reconstruction technique for rotational stability but not for function, translation, and complications. As previously shown in studies and meta-analysis, there is a biomechanical improvement in postoperative knee stability by using DB reconstruction technique [59][60][61] . However, in the rotational stability, only 2 studies have shown statistical results in favour of the DB 40,51 , compared to several studies that present better objective scores 46,49 .
The need for this systematic review and meta-analysis is based on the joint interpretation of mid-and longterm clinical outcomes of knee functionality, objective measurements of knee stability, rotational knee stability and knee anterior stability, sports reincorporation and subjective assessments to confirm the current discordant results in SB and DB ACL reconstruction.
Limitations. Only studies published in English were included, and therefore, some relevant studies may have been missed. The "anatomical technique" that uses the anteromedial portal to perform femoral tunnels has not been included as a study variable as it is a relatively new technique and still without relevant RCTs to complete the meta-analysis proposed by the research team; there is a proposal for a future meta-analysis of the interventions with this new procedure. Associated complications that may influence the failure of the plasty and the assessment of future osteoarthritis were not assessed. The risk of bias was unclear, and heterogeneity was moderate to high in several outcomes.

Conclusion
Currently, there are no clear or significant differences in clinical stability and knee function or in sports incorporation for the recommendation of DB in the primary ACL. The true difference between both techniques is shown in the subjective assessment by the IKDC score reported by patients.

Methods
Systematic search. We used the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) to conduct this systematic review and meta-analysis 62 in conformity with updated guidance of The Cochrane Collaboration Principles for Systematic Reviews 63 . Inclusion criteria were (1) participants older than 14 years with a ruptured ACL isolated or combined with other soft tissue injuries requiring ACL reconstruction; (2) randomized clinical trial design; (3) comparison of a single-bundle with a double-bundle (3 t or 4 t); and (4) main outcome measures such as measurements of knee functionality as measured by the patient or by the    and a return to pre-injury activity levels (Tegner activity score and Lysholm score). Secondary outcome measures: objective measurements of knee stability (rotational knee stability (pivot-shift test and range of mobility of internal rotational)) and knee anterior stability was measured using the Lachman test and KT-1000/2000; and (5) publication between database inception and July 2019. We developed comprehensive search strategies with the assistance of a health sciences documentalist with background in searching for systematic reviews including both index and keyword methods for PubMed, Embase (Elsevier platform), the Cochrane Central Register of Controlled Trials (Wiley platform), Web of Science, and CINAHL (Cumulative Index to Nursing and Allied Health Literature; EBSCO platform). To maximize sensitivity, no pre-set limits for the database were used. The PubMed search strategy was adapted for use with the other electronic databases. Complete search strategies are shown in Table 4.
The search was conducted in July 2019. In addition to the databases, we searched the reference lists of relevant studies and proceedings of orthopaedic conferences. The search results were exported to Excel (Microsoft Office 365 ProPlus) and duplicates were electronically removed.
Two investigators and one experienced senior orthopaedic surgeon independently screened records by title and abstract. In addition, records included by the first screening were assessed through a full-text review. Any discrepancies between the reviewers were resolved through discussion, and when necessary, a third reviewer was consulted.
Data extraction. Two investigators individually extracted data from eligible studies using a data collection form. Discrepancies were resolved through discussion with a third reviewer. The following data elements were extracted: the name of the first author, publication year, design, patient characteristics, interventions (singlebundle and double bundle), outcomes (Lysholm score, Pivot shift, Range of mobility (degrees), Internal rotational range (mm), KT-1000/2000, Tegner score, Lachman test, Subjective and Objective IKDC score, statistical analyses, and results.
Risk of bias assessment. The Cochrane Collaboration's tool for assessing risk of bias (RoB) was used to evaluate the study risk of bias within the included randomized controlled trials 63 . Three investigators indepen- Table 4. Search strategy.