Purpose
To compare the long-term clinical and radiological outcomes of modified transtibial and anteromedial portal techniques in single-bundle anterior cruciate ligament (ACL) reconstruction to provide more comprehensive guidance for treatment.
Methods
This study included patients who underwent arthroscopic single-bundle ACL reconstruction with adequate follow-up between January 2010 and December 2014. Patients were grouped according to the surgical techniques used: those who underwent the modified transtibial technique (group 1) and those who underwent the anteromedial portal technique (group 2). Clinical assessments included the 2000 International Knee Documentation Committee subjective knee score, Lysholm knee score, Tegner activity scale, Hospital for Special Surgery Knee score, Lachman test, and pivot-shift test. Radiological evaluations assessed the femoral tunnel’s location and length, as well as the inclination angles in the coronal, sagittal, and axial planes through computed tomography scans, while the graft bending angle and ligament maturity were evaluated via magnetic resonance imaging.
Results
A total of 73 patients were included: 36 in group 1 and 37 in group 2. No clinically significant differences were observed between the 2 techniques in the International Knee Documentation Committee score (mean difference [MD], 2.7; 95% confidence interval [CI],–1.5 to 6.9; minimal clinically important difference [MCID], 13.8), Lysholm score (MD,–0.1; 95% CI,–5.0 to 4.8; MCID, 8.9), Tegner score (MD, 0.6; 95% CI,–0.3 to 1.5; MCID, 1), and Hospital for Special Surgery Knee score (MD, 3.0; 95% CI, 0.3 to 5.7; MCID, 5.4). However, significant differences were noted in the mean distances from the femoral tunnel center to the posterior condylar surface (36.77% ± 4.60% in group 1 vs 32.14% ± 5.21% in group 2; P <.001) and to the Blumensaat line (24.34% ± 4.36% vs 30.02% ± 6.44%; P <.001). The inclination angles of the femoral tunnel differed significantly between the 2 groups in the coronal plane (55.21° ± 6.10° vs 35.79° ± 8.79°; P <.001), sagittal plane (27.80° ± 8.26° vs 40.06° ± 9.29°; P <.001), and axial plane (43.21° ± 7.21° vs 31.21° ± 8.36°; P <.001). Compared with group 2, group 1 presented a significantly greater femoral tunnel length (38.63 ± 4.33 vs 33.97 ± 2.65; P <.001). Furthermore, the graft bending angle in group 1 was significantly smaller than that in group 2 (26.62° ± 7.49° vs 36.92° ± 5.92°; P <.001). There was no statistically significant difference in graft maturity between the 2 groups (5.32 ± 3.52 vs 4.82 ± 2.91; P =.544).
Conclusions
The modified transtibial and anteromedial portal techniques for ACL reconstruction achieved comparable clinical outcomes. Despite some differences in femoral tunnel placement, there are no significant differences in long-term clinical results.
Level of Evidence
III, Retrospective cohort study.
Over the past few decades, anterior cruciate ligament (ACL) reconstruction techniques have undergone substantial advancements aimed at restoring the anatomic structure and function of the knee joint. The technique used for femoral tunnel drilling plays a critical role in the postoperative outcomes of ACL reconstruction. Currently, 3 different femoral drilling techniques are available: transtibial (TT) technique, anteromedial portal (AMP) technique, and outside-in technique. The TT technique for femoral tunnel positioning is widely used because of its simplicity, safety, and reproducibility. However, as the understanding of ACL anatomy and biomechanics has deepened, the limitations of this technique have become more apparent. , Compared with the AMP technique, the TT technique tends to result in a more anterior and superior femoral tunnel location, which fails to achieve the anatomic center of the ACL footprint. Furthermore, this malpositioning can limit the ability of the ACL to prevent rotational instability and anterior tibial translation. Studies have found that the TT technique was more likely to create more oblique femoral tunnels than the AMP technique. Although some studies have shown no difference in the revision rates between TT and AMP techniques for ACL reconstruction, the AMP technique consistently performs better in terms of knee stability and functional recovery. ,,
Compared with the TT technique, anatomic single-bundle ACL reconstruction has been shown to improve rotational stability, leading to better clinical outcomes. However, a major issue is how to define “anatomic” reconstruction of the ACL. As Borque et al. pointed out, although all tunnel positions that fall within the large footprint of the native ACL could be considered anatomic, it is impossible to truly re-create a ligament that is 3.5 times larger at its tibial and femoral insertions than at its midpoint with a single cylindrical graft. Compared with the TT technique, the AMP technique allows independent drilling of the femoral tunnel, enabling a more accurate and anatomic horizontal placement of the ACL femoral insertion. ,, However, the AMP technique also has limitations, such as requiring deep knee flexion to create the femoral tunnel, which can restrict the arthroscopic view and increase the risk of short femoral tunnels and posterior wall breakage. ,, Additionally, the AMP technique may pose a risk of condylar cartilage damage. ,
To overcome these limitations, the modified transtibial technique (MTT) was developed. This technique alters the starting point of the tibial tunnel to a more proximal position, which allows for a more oblique trajectory of the femoral tunnel. The MTT aims to combine the operational convenience of the TT technique with the anatomic accuracy of the AMP technique. , A simple modification involving tibial varus and external rotation during femoral tunnel creation can result in a more anatomic position between the anteromedial and posterolateral bundles of the ACL. Previous studies have shown that both MTT and AMP techniques produce good femoral tunnel positions and clinical outcomes in short-term follow-up, including manual laxity tests, arthrometric analysis, and clinical scores, with no significant differences. ,,, However, data on the long-term clinical performance and ligament graft maturity of these techniques are limited. ,, Our research included a follow-up period of at least 10 years, during which we evaluated clinical functional scores, femoral tunnel positioning, and ligament maturity.
The purpose of this study was to compare the long-term clinical and radiological outcomes of MTT and AMP techniques in single-bundle ACL reconstruction to provide more comprehensive guidance for treatment. We hypothesized that the long-term clinical outcomes of the MTT and the AMP technique would be similar and that both procedures would exhibit favorable clinical results.
Methods
Study Design and Population
The study population consisted of patients who underwent ACL reconstruction surgery from January 1, 2010, to December 31, 2014. The inclusion criteria were as follows: (1) aged between 18 and 50 years; (2) diagnosed with ACL injury, who may also have concurrent meniscal or cartilage injuries, but no other ligament injuries in the affected knee; (3) underwent first-time ACL reconstruction with a single-bundle technique using autologous hamstring grafts; (4) underwent surgery between January 1, 2010, and December 31, 2014; (5) were able to complete a full postoperative rehabilitation program; and (6) had a minimum 120-month follow-up period. The exclusion criteria were as follows: (1) severe knee osteoarthritis or previous knee surgeries, (2) concurrent ligament injuries or fractures, and (3) incomplete follow-up data or inability to be contacted. Subjects were divided into 2 groups: those who underwent the MTT procedure (group 1) and those who underwent the AMP procedure (group 2).
The study was approved by the institutional review board of the participating hospital, and informed consent was obtained from all participating patients.
Surgical Procedure
The surgeries were performed by senior chief physician (C.J.) with the patient in the supine position and under either epidural or general anesthesia. Standard arthroscopic examinations were conducted using anteromedial and anterolateral portals to assess ACL status and related injuries. Hemostasis was achieved with a pressure of 300 mm Hg. The surgical procedure included the following steps: preparing the tibial tunnel, marking, and creating the femoral tunnel via either the modified transtibial or anteromedial portal method. Both techniques employed autologous hamstring tendon grafts. Femoral fixation was achieved via the use of the Endo-Button CL (Smith & Nephew) suspension device, whereas tibial fixation involved the use of bioabsorbable screws or other similar devices, such as the Intrafix (Johnson & Johnson).
Modified Transtibial Technique
In the MTT, the femoral tunnel was created through the tibial tunnel under an anteromedial arthroscopic view. A guide pin was positioned and marked at the ACL’s original attachment site. The entry point of the tibial tunnel was set 4 to 5 cm distal to the joint line and 2 to 3 cm posterior to the tibial tubercle, 1 cm above the pes anserinus attachment and anterior to the medial collateral ligament. The tibial guide was inserted (Acufex), positioned at a 43° angle to the tibial plateau and 30° to 40° to the sagittal plane, and then drilled to create the tibial tunnel. During the creation of the femoral tunnel, the knee was flexed to 80° to 90°, and a varus and external rotational force was applied to the proximal tibia. This external rotational force directed the guide pin toward the anatomic center between the anteromedial and posterolateral bundles of the ACL. The guide pin was adjusted as needed to ensure anatomic accuracy, and the prepared tendon graft was passed through the tibial tunnel into the femoral tunnel. Throughout the surgical procedure, adjustment of the positional relationship between the tibia and femur was emphasized in the modified transtibial technique to achieve improvements over the traditional transtibial technique, with the aim of more closely reconstructing the natural anatomic position of the ACL. A surgical schematic is shown in Figure 1 .
Three-dimensional reconstructed CT image showing the medial view of the lateral femoral condyle, with use of the quadrant method to evaluate the position of the femoral tunnel aperture. The sagittal image of the knee, with the patella and tibia removed, leaving only the femur. (A) A = total length of the lateral condyle; a = distance from the center of the femoral tunnel aperture to the posterior cortical surface along line A; B = total depth of the intercondylar notch; b = distance from the center of the femoral tunnel aperture to the intercondylar notch; h = line perpendicular to the Blumensaat line; t = line parallel to the Blumensaat line. (B) The range of femoral tunnel center points for the 2 groups (95% confidence interval), with the yellow ellipse representing the modified transtibial technique group, the blue ellipse representing the anteromedial portal group, and the red area indicating the overlap.
Anteromedial Portal Technique
For the AMP technique, the knee was flexed to 110° to 120° or more to prevent posterior wall blowout and ensure an adequate femoral tunnel length. Under arthroscopy, the posterior edge of the femoral condyle cartilage was exposed. The femoral attachment site of the ACL was located approximately 2 mm above the posterior edge of the femoral condyle cartilage. The guide pin was positioned through the anteromedial portal, and a 4.5-mm hollow drill was used to penetrate the lateral femoral cortex. A femoral tunnel was then created. Next, the integrity of the tunnel wall was verified before graft insertion, and the length of the tunnel was measured to confirm its suitability for graft placement.
Postoperative Rehabilitation
All patients followed the same postoperative rehabilitation protocol. Ankle pump exercises begin on the day of surgery to prevent thrombosis. Partial weightbearing begins on postoperative day 1, gradually transitioning to full weightbearing walking by week 3. Passive knee extension starts on day 1, and passive knee flexion exercises begin on day 4, with flexion gradually increasing from 90° to match the healthy side. From week 3, the brace range of motion is adjusted starting at 30°, and the brace is removed at 6 months, allowing for full activity.
Clinical and Radiological Assessments
Patient-Reported Outcome Measures and Knee Joint Tests
At the final follow-up, subjective and objective clinical assessments were performed on the patient, along with computed tomography (CT) and magnetic resonance imaging (MRI) scans. The subjective clinical assessment included the 2000 International Knee Documentation Committee (IKDC) subjective knee score, Lysholm knee score, Tegner activity scale, and Hospital for Special Surgery Knee (HSS) score. Evaluations were conducted by an attending physician (G.D.) through a telephone follow-up, during which the patients completed questionnaires detailing their knee function. Objective evaluations were conducted via the Lachman test and pivot-shift test. Upon the patient’s return to the hospital for imaging examinations, an attending physician (H.L. or F.C.) conducted the Lachman test and the pivot-shift test. The attending physician does not know the specific surgical technique used for patients.
Radiological Analysis
Three-Dimensional CT Scans
The position of the femoral tunnel aperture was evaluated using 3-dimensional CT (3D-CT) based on the quadrant method described by Bernard et al. The medial view of the lateral femoral condyle was selected, and the image was sectioned to obtain a clear lateral condylar view ( Fig 2 ). The quadrant system was used to locate the center of the femoral tunnel on the image, and its position was expressed as a percentage.
The bone tunnel angles in 3 planes were measured via Cobb’s method (left knee). (A) Axial plane: the angle between the bone tunnel and the posterior condylar axis (FAA). (B) Coronal plane: the angle between the bone tunnel and the tibial plateau (FAC). (C) Sagittal plane: the angle between the bone tunnel and the longitudinal axis of the femoral shaft (FAS). The red lines indicate the measured angles.
Two-Dimensional CT Scans
The inclination angles of the femoral tunnel were measured on 2-dimensional CT images via Cobb’s method, assessing angles in the axial (the angle between femoral tunnel and posterior condylar axis; Fig 3 A ), coronal (the angle between femoral tunnel and tibial plateau; Fig 3 B), and sagittal (the angle between femoral tunnel and femoral shaft axis; Fig 3 C) planes.
Knee magnetic resonance imaging (left knee). (A) Evaluation of the signal-to-noise quotient: a 5-mm 2 circular region of interest (ROI1, anterior cruciate ligament) was selected at the femoral end of the graft to measure the anterior cruciate ligament signal intensity, with the patellar tendon region (ROI2, patellar tendon) used as a reference. The magnetic resonance imaging view is from the sagittal plane. (B) Measurement of the graft bending angle (GBA): the GBA was defined as the angle between the femoral tunnel and the intra-articular portion of the graft. The range of GBA angles for the 2 groups (95% confidence intervals) is shown, with yellow representing the modified transtibial technique group and blue representing the anteromedial portal group. The red dotted line indicates the line used for the angle measurement. The magnetic resonance imaging view is from the coronal plane.
MRI Evaluation
Ligament graft maturity was assessed using high-resolution MRI to calculate the signal-to-noise quotient (SNQ). A 1.5 Tesla MRI scanner was used, with imaging parameters set for T1-weighted, T2-weighted, and proton density–weighted sequences. A 5-mm 2 circular region of interest was manually selected at the femoral end of the graft on sagittal images, using the patellar tendon region as a reference ( Fig 4 A ). The average signal intensity within the region of interest (SI_graft) and the noise region (SI_noise) was measured, and the SNQ was calculated with the following formula:
Flowchart of the included and excluded patients.
Additionally, the graft bending angle (GBA), defined as the angle between the femoral tunnel and the intra-articular graft, was measured on coronal images ( Fig 4 B).
Statistical Analysis
Data analysis was performed via SPSS version 27.0.1. Normality was assessed via the Shapiro-Wilk test, and homogeneity of variance was evaluated via Levene’s test. For normally distributed and homoscedastic data, parametric tests were employed; otherwise, nonparametric methods were used. For normally distributed continuous variables with equal variance, independent samples t tests were used to compare differences between the MTT and AMP groups. The Mann-Whitney U test was used for ordinal categorical variables and nonnormally distributed continuous variables. The χ 2 test was employed to compare the distributions of unordered categorical variables between groups. The clinical evaluation metrics included IKDC subjective knee scores, Lysholm knee scores, Tegner activity scale scores, HSS scores, Lachman tests, and pivot-shift tests. Group comparisons of these metrics were made via independent samples t tests or Mann-Whitney U tests. Radiological evaluation metrics, including the femoral tunnel position, tunnel inclination angle (coronal and sagittal), and graft maturity (SNQ), were also compared through similar statistical tests. The minimal clinically important difference value was obtained based on data from previous studies. ,, We calculated the mean differences and their confidence intervals for the 4 knee scores between groups and performed a 1-sided t test to test whether the mean difference is lower than the minimal clinically important difference. Statistical significance was set at P <.05, and significant differences were reported with the specific P values.
Results
In this study, a total of 73 patients (73 knees) underwent ACL reconstruction, with 36 patients receiving the MTT and 37 receiving the AMP technique ( Fig 5 ). There were no significant differences in the baseline characteristics of the patients, including age, sex, or body mass index, at the last follow-up, between the 2 groups ( Table 1 ). In addition, there was no difference in the incidence of meniscal tears and cartilage lesions observed under the arthroscope during the surgery between the 2 groups of patients.
Intraoperative photograph of the left knee. (A) The tibial locator angle is set to 40° to 43°. (B) The tibial locator maintains a 30° to 40° angle with the sagittal plane. (C) Knee flexion is 80° to 90° degrees when the femur stops being located. (D) A femoral tunnel is drilled through the tibia. The red lines in the image indicate the measured angles.
Table 1
Patient Characteristics
| Parameter | MTT Group (n = 36) | AMP Group (n = 37) | P Value |
|---|---|---|---|
| Age, mean ± SD, y | 41.51 ± 10.17 | 38.39 ± 9.87 | .200 |
| Sex, male/female, n | 31/5 | 29/8 | .388 |
| Side of the knee, left/right, n | 16/20 | 16/21 | .918 |
| BMI, mean ± SD | 25.23 ± 2.79 | 24.47 ± 3.51 | .309 |
| Meniscal tears, % | 66.7 | 64.9 | .871 |
| Cartilage lesions, % | 25.0 | 27.0 | .844 |
AMP, anteromedial portal; MTT, modified transtibial technique.
Clinical Assessment
The postoperative clinical evaluations showed no significant clinical differences in the assessments, including IKDC, Lysholm, Tegner, and HSS score ( Table 2 and Appendix Table 1 , available at www.arthroscopyjournal.org ).
Table 2
Clinical Results
| Parameter | MTT Group (n = 36) | AMP Group (n = 37) | P Value | MCID |
|---|---|---|---|---|
| IKDC, mean ± SD | 89.3 ± 9.9 | 86.6 ± 8.1 | .111 | 13.8 |
| Lysholm, mean ± SD | 90.4 ± 9.0 | 90.5 ± 11.8 | .521 | 8.9 |
| Tegner, mean ± SD | 5.6 ± 1.7 | 5.0 ± 2.3 | .129 | 1 |
| HSS, mean ± SD | 97.2 ± 3.6 | 94.2 ± 7.2 | .084 | 5.41 |
| Lachman (grade 0/1/2/3), n | 27/6/2/1 | 24/8/3/2 | .783 | NA |
| Pivot shift (grade 0/1/2/3), n | 28/6/1/1 | 26/7/2/2 | .897 | NA |
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