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Superior Postoperative Stability and Functional Outcomes With Anteromedial Versus Transtibial Technique of Single-Bundle Autologous Hamstring Anterior Cruciate Ligament Reconstruction: A Meta-analysis of Prospective Randomized Controlled Trials

      Purpose

      The aim of this meta-analysis was to compare the postoperative stability and functional outcomes of anteromedial (AM)– and transtibial (TT)–based single-bundle hamstring anterior cruciate ligament (ACL) reconstruction techniques.

      Methods

      A meta-analysis comparing the outcomes of single-bundle hamstring ACL reconstruction using the AM and TT techniques was performed. Prospective randomized controlled trials identified from searches of PubMed, Cochrane, and Embase were included in this review. The outcome measures analyzed included postoperative Lachman test and pivot-shift test results, side-to-side difference, International Knee Documentation Committee (IKDC) score, Lysholm score, and Tegner activity score.

      Results

      A total of 7 randomized controlled trials (654 patients) were included in this review. The AM technique, compared with the TT technique, resulted in superior postoperative stability based on the negative Lachman test rate (risk ratio [RR], 1.12; 95% confidence interval [CI], 1.01 to 1.24; P = .03; 95% prediction interval [PI], 0.32 to 3.46), negative pivot-shift test rate (RR, 1.16; 95% CI, 1.06 to 1.28; P = .002; 95% PI, 0.40 to 2.88), and side-to-side difference (weighted mean difference [WMD], –0.32 mm; 95% CI, –0.48 to –0.16; P < .0001; 95% PI, –0.55 to –0.09). Likewise, the AM technique contributed to superior postoperative functional outcomes based on the proportion of IKDC grade A findings (RR, 1.16; 95% CI, 1.02 to 1.32; P = .03; 95% PI, 0.40 to 2.83) and the Lysholm score (WMD, 0.82; 95% CI, 0.23 to 1.41; P = .007; 95% PI, –0.22 to 1.86). However, the AM and TT techniques had comparable subjective IKDC scores (WMD, 0.98; 95% CI, –0.91 to 2.88; P = .31; 95% PI, –3.18 to 5.14) and Tegner activity scores (WMD, 0.32; 95% CI, –0.23 to 0.86; P = .25; 95% PI, –3.84 to 4.48).

      Conclusions

      The AM method of single-bundle hamstring ACL reconstruction results in superior postoperative stability and functional outcomes compared with the TT method.

      Level of Evidence

      Level I, systematic review of Level I studies.
      The anterior cruciate ligament (ACL) is the primary anterior stabilizer of the knee joint. Favorable ACL reconstruction outcomes largely depend on both anatomic and biomechanical factors. With anatomic graft positioning allowing for superior rotational stability, there has been a trend toward such anatomic ACL reconstructions. In view of the combined rotational and anteroposterior stability, failure rates of anatomically positioned ACLs have also been reported to be significantly lower than those of non–anatomically positioned grafts.
      • Marchant B.G.
      • Noyes F.R.
      • Barber-Westin S.D.
      • Fleckenstein C.
      Prevalence of nonanatomical graft placement in a series of failed anterior cruciate ligament reconstructions.
      • Diamantopoulos A.P.
      • Lorbach O.
      • Paessler H.H.
      Anterior cruciate ligament revision reconstruction: Results in 107 patients.
      • Loh J.C.
      • Fukuda Y.
      • Tsuda E.
      • Steadman R.J.
      • Fu F.H.
      • Woo S.L.
      Knee stability and graft function following anterior cruciate ligament reconstruction: Comparison between 11 o'clock and 10 o'clock femoral tunnel placement 2002 Richard O'Connor Award paper.
      • Duffee A.
      • Magnussen R.A.
      • Pedroza A.D.
      • Flanigan D.C.
      • MOON Group
      • Kaeding C.C.
      Transtibial ACL femoral tunnel preparation increases odds of repeat ipsilateral knee surgery.
      • Morgan J.A.
      • Dahm D.
      • Levy B.
      • Stuart M.J.
      MARS Study Group
      Femoral tunnel malposition in ACL revision reconstruction.
      • Hosseini A.
      • Lodhia P.
      • Van de Velde S.K.
      • et al.
      Tunnel position and graft orientation in failed anterior cruciate ligament reconstruction: A clinical and imaging analysis.
      When surgeons are performing anatomic ACL reconstructions, the landmarks for the femoral and tibial tunnels are their respective native footprints. Two main techniques have been described for graft placement: the transtibial (TT) technique and the anteromedial (AM) technique. The TT technique, however, has been described to be associated with a higher risk of vertical graft placement, which can predispose patients to rotational instability.
      • Lee M.C.
      • Seong S.C.
      • Lee S.
      • et al.
      Vertical femoral tunnel placement results in rotational knee laxity after anterior cruciate ligament reconstruction.
      This finding has been attributed to the increased technical challenge of achieving a lower femoral tunnel.
      • Arnold M.P.
      • Kooloos J.
      • van Kampen A.
      Single-incision technique misses the anatomical femoral anterior cruciate ligament insertion: A cadaver study.
      ,
      • Heming J.F.
      • Rand J.
      • Steiner M.E.
      Anatomical limitations of transtibial drilling in anterior cruciate ligament reconstruction.
      The newer AM technique, also known as the “far medial” or “transportal” drilling technique, has similarly been described for anatomic graft placement. Although it requires the creation of a separate AM portal, this technique allows surgeons greater freedom in positioning the femoral tunnel. This contributes to increased ease in establishing anatomic positioning of the ACL graft.
      • Pascual-Garrido C.
      • Swanson B.L.
      • Swanson K.E.
      Transtibial versus low anteromedial portal drilling for anterior cruciate ligament reconstruction: A radiographic study of femoral tunnel position.
      • Gavriilidis I.
      • Motsis E.K.
      • Pakos E.E.
      • Georgoulis A.D.
      • Mitsionis G.
      • Xenakis T.A.
      Transtibial versus anteromedial portal of the femoral tunnel in ACL reconstruction: A cadaveric study.
      • Garofalo R.
      • Moretti B.
      • Kombot C.
      • Moretti L.
      • Mouhsine E.
      Femoral tunnel placement in anterior cruciate ligament reconstruction: Rationale of the two incision technique.
      • Dargel J.
      • Schmidt-Wiethoff R.
      • Fischer S.
      • Mader K.
      • Koebke J.
      • Schneider T.
      Femoral bone tunnel placement using the transtibial tunnel or the anteromedial portal in ACL reconstruction: A radiographic evaluation.
      Existing systematic reviews and meta-analyses in this area have been largely based on retrospective cohorts or small sample sizes,
      • Chen Y.
      • Chua K.H.
      • Singh A.
      • et al.
      Outcome of single-bundle hamstring anterior cruciate ligament reconstruction using the anteromedial versus the transtibial technique: A systematic review and meta-analysis.
      ,
      • Riboh J.C.
      • Hasselblad V.
      • Godin J.A.
      • Mather III, R.C.
      Transtibial versus independent drilling techniques for anterior cruciate ligament reconstruction: A systematic review, meta-analysis, and meta-regression.
      making it challenging to draw meaningful conclusions to guide clinical practice. The aim of this meta-analysis was to compare the postoperative stability and functional outcomes of AM- and TT-based single-bundle hamstring ACL reconstruction techniques. We hypothesized that the AM method of single-bundle anatomic ACL reconstruction would result in superior postoperative stability and functional outcomes compared with the TT method owing to more anatomic placement of the ACL graft associated with the AM technique.

      Methods

      Search Strategy

      The PubMed, Embase, and Cochrane databases were searched from the inception of each database until October 15, 2019, without restriction on publication date or language. Our search term was as follows: (“Randomized Controlled Trials” OR trial OR placebo OR controlled OR Random∗) AND (TP OR transportal OR Transtibial OR “TT technique” OR AMP OR Anteromedial) AND (“Reconstructive Surgical Procedures” OR Arthroscopy OR Arthroscopic OR Reconstructions OR “ligament integrity”) AND (“intra-articular knee ligament” OR “Anterior Cruciate Ligament” OR ACL).

      Eligibility Criteria

      After removal of duplicates, 2 investigators (V.M. and A.A.S.) independently reviewed the abstracts and articles to determine their suitability for our study. Any discrepancy in determining an article’s eligibility for inclusion was resolved by consensus and discussion with the senior author (A.H.C.T.).
      In evaluating studies to be considered for this study, we defined the selection criteria a priori based on the study population, intervention, outcomes measured, and study design. The inclusion criteria were prospective randomized controlled trials (RCTs) directly comparing AM and TT techniques of single-bundle autologous hamstring ACL reconstruction and reporting stability and/or functional outcomes. The exclusion criteria were animal or cadaveric studies; studies not directly comparing AM and TT techniques; studies not performing single-bundle ACL reconstruction; studies using allograft, bone–patellar tendon–bone, or Achilles tendon; studies with non-RCT study designs; and studies that did not report any stability and/or functional outcomes.

      Data Collection

      Data were extracted from the included studies by the same 2 researchers independently, and any discrepancy was resolved by consensus subsequently. Basic study characteristics extracted from the included articles were first author, year of publication, study design, level of evidence, average age of patients, sample size, follow-up duration, graft tendon used, and fixation method.
      The postoperative outcomes of stability and function extracted from the articles were as follows: proportion of negative Lachman test results, proportion of negative pivot-shift test results, side-to-side difference (SSD) using KT-1000 arthrometer (MEDmetric, San Diego, CA) measurements, International Knee Documentation Committee (IKDC) subjective score and objective score, Lysholm score, and Tegner activity score. When we had any questions about an article, we tried to reach the corresponding author of the article.
      Working independently, the same 2 researchers assessed the risk of bias of the included studies using The Cochrane Collaboration’s risk-of-bias tool for RCTs.
      • Higgins J.P.
      • Thompson S.G.
      Quantifying heterogeneity in a meta-analysis.
      ,
      • Higgins J.P.
      • Thompson S.G.
      • Deeks J.J.
      • Altman D.G.
      Measuring inconsistency in meta-analyses.
      Seven domains of bias were assessed: random sequence generation and allocation of concealment (both under “selection bias”), performance bias, detection bias, attrition bias, reporting bias, and other bias. For each domain, the risk of bias was assessed as high, low, or unclear.

      Statistical Analysis

      RevMan (Review Manager, version 5.3 [2014]; The Cochrane Collaboration–The Nordic Cochrane Centre, Copenhagen, Denmark) was used for all statistical analyses in this study. Binary outcomes were analyzed by determining the risk ratio (RR) and 95% confidence interval (CI) when comparing surgical techniques. For continuous variables, the weighted mean difference (WMD) and 95% CI were determined. Statistical heterogeneity of outcomes of comparison was determined using the χ2 test and I2 statistic. The I2 statistic describes the proportion of total variation in study estimates that is due to heterogeneity; it is a widely used measure of heterogeneity in meta-analyses.
      • Higgins J.P.
      • Thompson S.G.
      Quantifying heterogeneity in a meta-analysis.
      Random-effects models were used for analyses, assuming that the included studies represented a random sample from the larger population of such studies. The random-effects model takes into account interstudy heterogeneity and provides a more conservative evaluation of the significance of the association than an evaluation based on fixed effects. For each analysis, 95% prediction intervals (PIs) were also determined, as described by IntHout et al.
      • IntHout J.
      • Ioannidis J.P.
      • Rovers M.M.
      • Goeman J.J.
      Plea for routinely presenting prediction intervals in meta-analysis.
      In addition, the degree of agreement between the researchers for each domain of the risk-of-bias assessment was quantified with the κ statistic.
      • Landis J.R.
      • Koch G.G.
      The measurement of observer agreement for categorical data.

      Results

      Search Results

      We identified 432 studies via our search strategy; 224 duplicates were subsequently removed. After all titles and abstracts were reviewed, 197 studies were excluded based on our selection criteria. Thereafter, 4 studies were excluded after their full texts were reviewed because 3 did not have a prospective RCT study design and 1 did not directly compare AM and TT techniques of ACL reconstruction. Seven articles were eventually selected for meta-analysis.
      • Bohn M.B.
      • Sorensen H.
      • Petersen M.K.
      • Soballe K.
      • Lind M.
      Rotational laxity after anatomical ACL reconstruction measured by 3-D motion analysis: A prospective randomized clinical trial comparing anatomic and nonanatomic ACL reconstruction techniques.
      • Geng Y.
      • Gai P.
      Comparison of 2 femoral tunnel drilling techniques in anterior cruciate ligament reconstruction. A prospective randomized comparative study.
      • Guglielmetti L.G.
      • Cury Rde P.
      • de Oliveira V.M.
      • de Camargo O.P.
      • Severino N.R.
      • Fucs P.M.
      Anterior cruciate ligament reconstruction: a new cortical suspension device for femoral fixation with transtibial and transportal techniques.
      • Hussein M.
      • van Eck C.F.
      • Cretnik A.
      • Dinevski D.
      • Fu F.H.
      Prospective randomized clinical evaluation of conventional single-bundle, anatomic single-bundle, and anatomic double-bundle anterior cruciate ligament reconstruction: 281 cases with 3- to 5-year follow-up.
      • MacDonald P.
      • Kim C.
      • McRae S.
      • Leiter J.
      • Khan R.
      • Whelan D.
      No clinical differences between anteromedial portal and transtibial technique for femoral tunnel positioning in anterior cruciate ligament reconstruction: A prospective randomized, controlled trial.
      • Mirzatolooei F.
      Comparison of short term clinical outcomes between transtibial and transportal TransFix(R) femoral fixation in hamstring ACL reconstruction.
      • Zhang Q.
      • Zhang S.
      • Li R.
      • Liu Y.
      • Cao X.
      Comparison of two methods of femoral tunnel preparation in single-bundle anterior cruciate ligament reconstruction: A prospective randomized study.
      A summary of the selection process can be found in Figure 1.
      Figure thumbnail gr1
      Fig 1PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) flowchart summarizing article selection. (ACL, anterior cruciate ligament; AM, anteromedial; RCT, randomized controlled trial; TT, transtibial.)

      Characteristics of Included Studies

      All 7 articles were prospective RCTs directly comparing single-bundle hamstring ACL reconstruction using AM and TT techniques. The follow-up duration ranged from 6 to 52 months among the included studies. There were a total of 331 and 323 patients in the AM and TT groups, respectively, across the different studies. The basic characteristics of all the included studies are displayed in Table 1. Relevant outcomes of the AM and TT techniques that were extracted from each article are presented in Table 2.
      Table 1Basic Characteristics of Included Studies
      Authors (Year)Study Design/LOEAge, yr, mean or mean ± standard deviationFollow-up, monGraft TendonFixation MethodOutcome Measured
      AMTTAMTTOutcome ScoreStability Testing
      Geng and Gai
      • Geng Y.
      • Gai P.
      Comparison of 2 femoral tunnel drilling techniques in anterior cruciate ligament reconstruction. A prospective randomized comparative study.
      (2018)
      Prospective RCT/I29.6 ± 11.731.8 ± 11.012-375648HamstringEB + IntrafixLKS, IKDC score, TASLT, PST, SSD
      MacDonald et al.
      • MacDonald P.
      • Kim C.
      • McRae S.
      • Leiter J.
      • Khan R.
      • Whelan D.
      No clinical differences between anteromedial portal and transtibial technique for femoral tunnel positioning in anterior cruciate ligament reconstruction: A prospective randomized, controlled trial.
      (2018)
      Prospective RCT/I30.7± 9.332.4 ± 8.9243635HamstringEB + BSRange of motion, IKDC scoreLT, PST, SSD
      Bohn et al.
      • Bohn M.B.
      • Sorensen H.
      • Petersen M.K.
      • Soballe K.
      • Lind M.
      Rotational laxity after anatomical ACL reconstruction measured by 3-D motion analysis: A prospective randomized clinical trial comparing anatomic and nonanatomic ACL reconstruction techniques.
      (2015)
      Prospective RCT/I24.3 ± 4.927.5 ± 7.212-181211HamstringEB + BSIKDC grade, IKDC score, KOOS, TAS, LKS, 3D motion analysisLT, PST, SSD
      Guglielmetti et al.
      • Guglielmetti L.G.
      • Cury Rde P.
      • de Oliveira V.M.
      • de Camargo O.P.
      • Severino N.R.
      • Fucs P.M.
      Anterior cruciate ligament reconstruction: a new cortical suspension device for femoral fixation with transtibial and transportal techniques.
      (2014)
      Prospective RCT/I<4063835HamstringETD + MISIKDC grade, femoral tunnel lengthLT, PST, SSD, anterior drawer test
      Hussein et al.
      • Hussein M.
      • van Eck C.F.
      • Cretnik A.
      • Dinevski D.
      • Fu F.H.
      Prospective randomized clinical evaluation of conventional single-bundle, anatomic single-bundle, and anatomic double-bundle anterior cruciate ligament reconstruction: 281 cases with 3- to 5-year follow-up.
      (2012)
      Prospective RCT/I34.232.6AM: 50.5

      TT: 52.0
      7872HamstringSF + BSLKS, IKDC score, IKDC gradeSSD, PST
      Mirzatolooei
      • Mirzatolooei F.
      Comparison of short term clinical outcomes between transtibial and transportal TransFix(R) femoral fixation in hamstring ACL reconstruction.
      (2012)
      Prospective RCT/I26.626.8188088HamstringTransFixIKDC grade, LKSLT, PST, SSD
      Zhang et al.
      • Zhang Q.
      • Zhang S.
      • Li R.
      • Liu Y.
      • Cao X.
      Comparison of two methods of femoral tunnel preparation in single-bundle anterior cruciate ligament reconstruction: A prospective randomized study.
      (2012)
      Prospective RCT/I28123134HamstringRigidfix + IntrafixLKSSSD
      AM, anteromedial; BS, Bio-Interference Screw; EB, EndoButton; ETD, Endo Tunnel Device; IKDC, International Knee Documentation Committee; KOOS, Knee Injury and Osteoarthritis Outcome Score; LKS, Lysholm knee score; LOE, level of evidence; LT, Lachman test; MIS, metal interference screw; PST, pivot-shift test; RCT, randomized controlled trial; SF, suspensory fixation; SSD, side-to-side difference; TAS, Tegner activity score; TT, transtibial; 3D, 3-dimensional.
      Table 2Postoperative Stability and Functional Recovery Outcomes of AM Group Versus TT Group
      StudyNStability OutcomesFunctional Recovery Outcomes
      Lachman Test Result (N/P)Pivot-Shift Test Result (N/P)SSD (KT-1000), mmIKDC Grade A Finding (Yes/No)IKDC ScoreLysholm ScoreTegner Activity Score
      AMTTAMTTAMTTAMTTAMTTAMTTAMTT
      Geng and Gai
      • Geng Y.
      • Gai P.
      Comparison of 2 femoral tunnel drilling techniques in anterior cruciate ligament reconstruction. A prospective randomized comparative study.
      (2018)
      10444/1236/1244/1232/161.5 ± 0.91.6 ± 0.889.5 ± 8.887.4 ± 10.093.3 ± 5.091.6 ± 6.56.8 ± 1.46.3 ± 1.4
      MacDonald et al.
      • MacDonald P.
      • Kim C.
      • McRae S.
      • Leiter J.
      • Khan R.
      • Whelan D.
      No clinical differences between anteromedial portal and transtibial technique for femoral tunnel positioning in anterior cruciate ligament reconstruction: A prospective randomized, controlled trial.
      (2018)
      8829/530/918/1814/21
      Bohn et al.
      • Bohn M.B.
      • Sorensen H.
      • Petersen M.K.
      • Soballe K.
      • Lind M.
      Rotational laxity after anatomical ACL reconstruction measured by 3-D motion analysis: A prospective randomized clinical trial comparing anatomic and nonanatomic ACL reconstruction techniques.
      (2015)
      239/38/310/28/32.0 ± 1.72.3 ± 1.93/93/876 ± 1371 ± 1586 ± 1281 ± 145.5 ± 1.05.6 ± 1.2
      Guglielmetti et al.
      • Guglielmetti L.G.
      • Cury Rde P.
      • de Oliveira V.M.
      • de Camargo O.P.
      • Severino N.R.
      • Fucs P.M.
      Anterior cruciate ligament reconstruction: a new cortical suspension device for femoral fixation with transtibial and transportal techniques.
      (2014)
      7333/525/1033/526/928/1018/17
      Hussein et al.
      • Hussein M.
      • van Eck C.F.
      • Cretnik A.
      • Dinevski D.
      • Fu F.H.
      Prospective randomized clinical evaluation of conventional single-bundle, anatomic single-bundle, and anatomic double-bundle anterior cruciate ligament reconstruction: 281 cases with 3- to 5-year follow-up.
      (2012)
      15052/2630/421.6 ± 0.82.0 ± 0.969/957/1590.6 ± 6.490.2 ± 7.691.8 ± 4.390.9 ± 7.0
      Mirzatolooei
      • Mirzatolooei F.
      Comparison of short term clinical outcomes between transtibial and transportal TransFix(R) femoral fixation in hamstring ACL reconstruction.
      (2012)
      16870/1068/2070/1070/181.73 ± 0.852.2 ± 1.1381.41 ± 8.278.32 ± 10.7
      Zhang et al.
      • Zhang Q.
      • Zhang S.
      • Li R.
      • Liu Y.
      • Cao X.
      Comparison of two methods of femoral tunnel preparation in single-bundle anterior cruciate ligament reconstruction: A prospective randomized study.
      (2012)
      651.96 ± 1.022.14 ± 0.9195.1 ± 1.094.5 ± 1.1
      NOTE. Continuous variables are presented as mean ± standard deviation; the remaining data are presented as number of patients.
      AM, anteromedial; N, negative; P, positive; SSD, side-to-side difference; TT, transtibial.
      The quality of included studies was assessed. All the included trials were at a low or unclear risk of bias when assessed using The Cochrane Collaboration’s risk-of-bias tool for RCTs
      • Higgins J.P.
      • Thompson S.G.
      Quantifying heterogeneity in a meta-analysis.
      ,
      • Higgins J.P.
      • Thompson S.G.
      • Deeks J.J.
      • Altman D.G.
      Measuring inconsistency in meta-analyses.
      (Fig 2). The agreement between the 2 researchers for each domain ranged from moderate to excellent (weighted κ, 0.59 to 1.00).
      Figure thumbnail gr2
      Fig 2Summary of quality assessment of included trials.

      Clinical Outcomes of Knee Stability

      Postoperative Lachman test findings were reported in 4 studies with a total of 368 patients. The results suggested that the AM group had a significantly higher rate of negative postoperative Lachman test results than the TT group (RR, 1.12; 95% CI, 1.01 to 1.24; P = .03; 95% PI, 0.32 to 3.46) (Fig 3A ).
      Figure thumbnail gr3
      Fig 3Meta-analysis of postoperative clinical outcomes of knee stability. (A) Negative Lachman test findings. (B) Negative pivot-shift test findings. (C) Side-to-side differences (in millimeters). (AM, anteromedial; CI, confidence interval; TT, transtibial.)
      Six studies with a total of 591 patients reported postoperative pivot-shift test findings. The overall pooled results suggested that the AM group had a significantly higher rate of negative pivot-shift test results than the TT group (RR, 1.16; 95% CI, 1.06 to 1.28; P = .002; 95% PI, 0.40 to 2.88) (Fig 3B).
      Five studies with a total of 510 patients reported postoperative SSD data. The overall pooled results suggested that the TT group had significantly higher SSDs than the AM group (WMD, –0.32 mm; 95% CI, –0.48 to –0.16; P < .0001; 95% PI, –0.55 to –0.09) (Fig 3C). There was no significant heterogeneity between the trials when results were pooled for the postoperative Lachman test (P = .81, I2 = 0%), pivot-shift test (P = .35, I2 = 11%), or SSD (P = .50, I2 = 0%).

      Clinical Outcomes of Functional Recovery

      Four studies with a total of 317 patients reported IKDC grades. The pooled results revealed a higher proportion of IKDC grade A (normal) findings in the AM group (RR, 1.16; 95% CI, 1.02 to 1.32; P = .03; 95% PI, 0.40 to 2.83) (Fig 4A ).
      Figure thumbnail gr4
      Fig 4Meta-analysis of postoperative clinical outcomes of functional recovery of knee. (A) International Knee Documentation Committee (IKDC) grade A (normal) findings. (B) IKDC subjective scores. (C) Lysholm scores. (D) Tegner activity scores.
      Three studies with a total of 277 patients reported postoperative IKDC scores. However, the postoperative IKDC scores were not significantly different between the AM and TT groups based on the overall pooled results (WMD, 0.98; 95% CI, –0.91 to 2.88; P = .31; 95% PI, –3.18 to 5.14) (Fig 4B). Five studies with a total of 510 patients reported postoperative Lysholm scores. The pooled results suggested that postoperatively, the AM group had higher Lysholm scores than the TT group (WMD, 0.82; 95% CI, 0.23 to 1.41; P = .007; 95% PI, –0.22 to 1.86) (Fig 4C).
      Two studies with a total of 127 patients reported postoperative Tegner activity scores. However, the postoperative Tegner activity scores were not significantly different between the AM and TT groups (WMD, 0.32; 95% CI, –0.23 to 0.86; P = .25; 95% PI, –3.84 to 4.48), as identified from the overall pooled results (Fig 4D). Finally, there was no significant heterogeneity between the trials when the results were pooled for IKDC grades (P = .60, I2 = 0%), IKDC scores (P = .58, I2 = 0%), Lysholm scores (P = .38, I2 = 5%), or Tegner activity scores (P = .27, I2 = 19%).

      Discussion

      The key finding of our meta-analysis was that single-bundle hamstring ACL reconstruction using the AM technique results in both superior postoperative stability and superior postoperative functional outcomes. Optimal femoral and tibial tunnel positioning is important to prevent anteroposterior and rotational instability and, hence, reduce the risk of graft stretching, loosening, and failure. The most common techniques for graft placement in ACL reconstruction are the TT and AM techniques.
      Several factors may account for the increased biomechanical stability and consequent functional outcomes observed with the AM technique. In a biomechanical study, Bedi et al.
      • Bedi A.
      • Musahl V.
      • Steuber V.
      • et al.
      Transtibial versus anteromedial portal reaming in anterior cruciate ligament reconstruction: An anatomic and biomechanical evaluation of surgical technique.
      found that the center of the native femoral ACL footprint could not be captured by use of a TT technique because the tibial tunnel was anatomically restricted. In contrast, the AM technique allowed guidewire positioning at the center of the femoral footprint in all cases, resulting in significantly greater time-zero control of tibial translation with Lachman and pivot-shift testing. Previous studies have also shown the technical impossibility of restoring both the anatomic tibial and femoral origins of the ACL using a TT technique despite any modifications, with tunnels being located in an anterior and vertical position relative to the native footprint.
      • Dargel J.
      • Schmidt-Wiethoff R.
      • Fischer S.
      • Mader K.
      • Koebke J.
      • Schneider T.
      Femoral bone tunnel placement using the transtibial tunnel or the anteromedial portal in ACL reconstruction: A radiographic evaluation.
      ,
      • Giron F.
      • Cuomo P.
      • Edwards A.
      • Bull A.M.
      • Amis A.A.
      • Aglietti P.
      Double-bundle "anatomic" anterior cruciate ligament reconstruction: A cadaveric study of tunnel positioning with a transtibial technique.
      Moreover, studies have revealed that the AM technique better locates the femoral tunnel within the anatomic footprint.
      • Riboh J.C.
      • Hasselblad V.
      • Godin J.A.
      • Mather III, R.C.
      Transtibial versus independent drilling techniques for anterior cruciate ligament reconstruction: A systematic review, meta-analysis, and meta-regression.
      ,
      • Sukur E.
      • Akman Y.E.
      • Senel A.
      • Unkar E.A.
      • Topcu H.N.
      • Ozturkmen A.Y.
      Comparing transtibial and anteromedial drilling techniques for single-bundle anterior cruciate ligament reconstruction.
      ,
      • Azboy I.
      • Demirtas A.
      • Gem M.
      • Kiran S.
      • Alemdar C.
      • Bulut M.
      A comparison of the anteromedial and transtibial drilling technique in ACL reconstruction after a short-term follow-up.
      This occurs partly because in the AM technique, femoral tunnel positioning is not restrained by the tibial tunnel. In contrast, in the TT technique, with the knee flexed at a right angle, it is unlikely for the endpoint of the femoral tunnel, via the tibial tunnel, to entirely correspond with the anatomic endpoint.
      • Zhang Q.
      • Zhang S.
      • Li R.
      • Liu Y.
      • Cao X.
      Comparison of two methods of femoral tunnel preparation in single-bundle anterior cruciate ligament reconstruction: A prospective randomized study.
      In the literature, it has been established that the positioning of the femoral tunnel contributes to the ACL graft having similar biomechanical properties to the natural ACL in terms of both rotational stability and anteroposterior stability.
      • Chechik O.
      • Amar E.
      • Khashan M.
      • Lador R.
      • Eyal G.
      • Gold A.
      An international survey on anterior cruciate ligament reconstruction practices.
      • Lee J.K.
      • Lee S.
      • Seong S.C.
      • Lee M.C.
      Anatomic single-bundle ACL reconstruction is possible with use of the modified transtibial technique: A comparison with the anteromedial transportal technique.
      • Tasdemir Z.
      • Gulabi D.
      • Saglam F.
      • Tokgoz Ozal S.
      • Elmali N.
      Does the anteromedial portal provide clinical superiority compared to the transtibial portal in anterior cruciate ligament reconstruction in nonprofessional athletes in short-term follow-up?.
      Numerous studies have also concluded that minor differences in femoral tunnel positioning will significantly affect graft isometry and consequent knee stability postoperatively.
      • Brophy R.H.
      • Voos J.E.
      • Shannon F.J.
      • et al.
      Changes in the length of virtual anterior cruciate ligament fibers during stability testing: A comparison of conventional single-bundle reconstruction and native anterior cruciate ligament.
      • Musahl V.
      • Plakseychuk A.
      • VanScyoc A.
      • et al.
      Varying femoral tunnels between the anatomical footprint and isometric positions: Effect on kinematics of the anterior cruciate ligament-reconstructed knee.

      McPherson GK, Mendenhall HV, Gibbons DF, et al. Experimental mechanical and histologic evaluation of the Kennedy ligament augmentation device. Clin Orthop Relat Res 1985;(196):186-195.

      • Liu-Barba D.
      • Howell S.M.
      • Hull M.L.
      High-stiffness distal fixation restores anterior laxity and stiffness as well as joint line fixation with an interference screw.
      • Maletis G.B.
      • Cameron S.L.
      • Tengan J.J.
      • Burchette R.J.
      A prospective randomized study of anterior cruciate ligament reconstruction: A comparison of patellar tendon and quadruple-strand semitendinosus/gracilis tendons fixed with bioabsorbable interference screws.
      However, the AM technique has certain limitations. Surgeons have to be careful not to drill cortically short femoral tunnels
      • Chang C.B.
      • Choi J.Y.
      • Koh I.J.
      • Lee K.J.
      • Lee K.H.
      • Kim T.K.
      Comparisons of femoral tunnel position and length in anterior cruciate ligament reconstruction: Modified transtibial versus anteromedial portal techniques.
      or compromise the integrity of the posterior wall of the lateral femoral intercondylar notch.
      • Chechik O.
      • Amar E.
      • Khashan M.
      • Lador R.
      • Eyal G.
      • Gold A.
      An international survey on anterior cruciate ligament reconstruction practices.
      ,
      • Bedi A.
      • Raphael B.
      • Maderazo A.
      • Pavlov H.
      • Williams III, R.J.
      Transtibial versus anteromedial portal drilling for anterior cruciate ligament reconstruction: A cadaveric study of femoral tunnel length and obliquity.
      Moreover, in a large registry-based study, Rahr-Wagner et al.
      • Rahr-Wagner L.
      • Thillemann T.M.
      • Pedersen A.B.
      • Lind M.C.
      Increased risk of revision after anteromedial compared with transtibial drilling of the femoral tunnel during primary anterior cruciate ligament reconstruction: Results from the Danish Knee Ligament Reconstruction Register.
      revealed that after ACL reconstruction, higher revision rates were found when using the AM technique than when using the TT technique, potentially a result of the presence of a learning curve and surgeons being less familiar with the AM technique. Additionally, prior studies have shown that a greater force is carried by an anatomic ACL reconstruction than by a nonanatomic graft placement. Xu et al.
      • Xu Y.
      • Liu J.
      • Kramer S.
      • et al.
      Comparison of in situ forces and knee kinematics in anteromedial and high anteromedial bundle augmentation for partially ruptured anterior cruciate ligament.
      showed significantly greater force in AM bundles that were reconstructed anatomically than in grafts placed non-anatomically. This greater load, carried by an anatomically reconstructed graft, transfers more load to other structures in the knee, making it more susceptible to graft failure.
      Previous systematic reviews and meta-analyses on this topic have been performed, with varying conclusions. In 2013, a meta-analysis by Riboh et al.
      • Riboh J.C.
      • Hasselblad V.
      • Godin J.A.
      • Mather III, R.C.
      Transtibial versus independent drilling techniques for anterior cruciate ligament reconstruction: A systematic review, meta-analysis, and meta-regression.
      revealed no significant clinical differences between the AM and TT techniques. In 2015, in another meta-analysis, Chen et al.
      • Chen Y.
      • Chua K.H.
      • Singh A.
      • et al.
      Outcome of single-bundle hamstring anterior cruciate ligament reconstruction using the anteromedial versus the transtibial technique: A systematic review and meta-analysis.
      concluded that the AM technique resulted in superior knee stability but had similar postoperative functional outcomes when compared with the TT technique. Nevertheless, our results were concordant with the findings of a more recent meta-analysis by Chen et al.
      • Chen H.
      • Tie K.
      • Qi Y.
      • Li B.
      • Chen B.
      • Chen L.
      Anteromedial versus transtibial technique in single-bundle autologous hamstring ACL reconstruction: A meta-analysis of prospective randomized controlled trials.
      in 2017, which also concluded that in the context of single-bundle hamstring ACL reconstruction, better postoperative knee stability and functional outcomes could be achieved using the AM technique instead of the TT technique. However, the meta-analysis by Chen et al.
      • Chen H.
      • Tie K.
      • Qi Y.
      • Li B.
      • Chen B.
      • Chen L.
      Anteromedial versus transtibial technique in single-bundle autologous hamstring ACL reconstruction: A meta-analysis of prospective randomized controlled trials.
      included only 5 studies, with limited study sample sizes and outcome data. Only 1 of the 5 studies included by Chen et al. had a follow-up duration greater than 24 months. In contrast, 3 of the 7 studies included in our meta-analysis had follow-up durations greater than 24 months, suggesting that superior stability and functional outcomes of the AM technique exist at least up to 24 months after surgery and not just in the early postoperative period. Furthermore, Chen et al.
      • Chen H.
      • Tie K.
      • Qi Y.
      • Li B.
      • Chen B.
      • Chen L.
      Anteromedial versus transtibial technique in single-bundle autologous hamstring ACL reconstruction: A meta-analysis of prospective randomized controlled trials.
      did not consider certain key functional outcome scores, such as the Tegner activity score, owing to limited data from only 5 trials. In contrast, our study has provided a more comprehensive and updated analysis of the topic, taking into account 7 prospective RCTs and additional validated functional outcome instruments.

      Limitations

      Nevertheless, there were still several limitations to our meta-analysis: (1) The lengths of follow-up of the 7 studies varied, potentially contributing to some heterogeneity in the outcomes when comparing the AM and TT techniques. (2) Some of the subjective outcome testing, such as the Lachman test and anterior drawer test, may have significant variability in reporting between clinical testers administering the examination across the studies, further contributing to heterogeneity in the outcomes when comparing the 2 techniques. (3) All included studies experienced performance bias as a result of not being able to blind the surgeons within these studies. (4) Only published data were included in this review, resulting in the potential for reporting bias because negative results were less likely to be reported.

      Conclusions

      The AM method of single-bundle hamstring ACL reconstruction results in superior postoperative stability and functional outcomes compared with the TT method.

      Supplementary Data

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