Femoral and Tibial Graft Tunnel Parameters After Transtibial,Anteromedial Portal,and Outside-In Single-Bundle Anterior Cruciate Ligament Reconstruction

Abstract

Background:

Anatomic graft tunnel placement is recommended in anterior cruciate ligament (ACL) reconstruction to restore knee joint stability and function. Transtibial (TT), anteromedial portal (AMP), and outside-in (OI) retrograde drilling surgical techniques have been described for tibial and femoral bone tunnel preparation.

Purpose/Hypothesis:

The purpose of this study was to evaluate the bone tunnel parameters and compare the ability of 3 different surgical techniques to achieve placement of the ACL femoral and tibial bone tunnels at the center of the native ACL femoral and tibial attachment sites. The hypothesis was that tunnel placement using an AMP or OI technique would result in optimized tunnel parameters and more closely reconstruct the center of the native ACL femoral attachment site.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

The study population consisted of 100 patients undergoing anatomic single-bundle ACL reconstruction using multiple-stranded hamstring tendon grafts. In group 1 (n = 36), the femoral tunnel was drilled using a TT surgical technique; in group 2 (n = 32), the femoral tunnel was drilled through an AMP; and in group 3 (n = 32), the femoral tunnel was created by use of an OI technique with retrograde drilling. Computed tomography (CT) scans were obtained postoperatively, and characteristics of femoral and tibial tunnel apertures were correlated to femoral and tibial measurement grid systems. The position of the resulting tibial and femoral bone tunnels for each group was compared with the center of the native ACL attachment sites.

Results:

There were statistically significant differences (P < .05) for the ACL femoral tunnel between the 3 groups with respect to intercondylar height, total tunnel length, graft fixation length, tunnel axis, and tunnel entry angle. Statistically significant differences (P < .05) were found for the ACL tibial tunnel with respect to anteroposterior tunnel position and sagittal tunnel axis between the TT and both the OI and AMP techniques. The OI surgical technique produced more oblique and anatomically correct femoral tunnel apertures and longer femoral tunnel lengths compared with the AMP technique. Both AMP and OI techniques resulted in a more precise replication of intercondylar tunnel depth and height. There was no statistically significant difference for graft fixation length between the AMP and OI techniques.

Conclusion:

The AMP and OI surgical techniques were superior in positioning the ACL femoral tunnel at the center of the native ACL attachment site compared with the TT technique. An acceptable graft fixation length was obtained for all 3 surgical techniques.

Keywords

ACL reconstruction,transtibial technique anteromedial portal technique outside-in technique computed tomography anatomy

In recent years, biomechanical and cadaveric data have indicated a superior restoration of knee kinematics with the placement of anatomic graft tunnels in anterior cruciate ligament (ACL) reconstruction.^10,22 Nevertheless, laboratory results have not been successfully correlated to a better functional outcome.^{9,18,25,32,39} Several studies have demonstrated that drilling the ACL femoral tunnel using a transtibial (TT) surgical technique often results in a vertical femoral tunnel, which produces a vertical ACL graft orientation, resulting in inferior rotational control and inferior clinical outcomes.^24,38,39,42 In an attempt to achieve more anatomic ACL femoral tunnel placement, drilling the ACL femoral tunnel through an anteromedial portal (AMP) or an outside-in (OI) approach has been proposed.^9,26 Various methods have been suggested to measure ACL tunnel placement.^‖ Intraoperative fluoroscopy has been favored by some authors as a practical real-time method to verify correct ACL tunnel positions.^11,12,35 Most investigators have used measurement grid methods and reference values applied to plain radiographs and 3-dimensional computed tomography (3D CT) scans to document ACL tunnel placement. In vivo and in vitro comparisons of the TT and AMP techniques have found differences in insertion site coverage,²⁸ tunnel axis,^25,33 and tunnel length,³⁸ as well as a more anatomic tunnel position^2,17 and a higher incidence of a posterior femoral tunnel exit¹⁰ with AMP reconstruction. In contrast, assessments of AMP techniques have revealed diminished femoral tunnel length and possible effect on graft fixation when compared with the TT³³ and OI techniques.²² Only a few studies^10,30,31 have reported a comprehensive characterization of TT, AMP, and OI femoral and tibial tunnels in vivo and have studied whether one of the techniques might be superior with respect to accurate anatomic replacement in the center of the native attachment site. In addition, the usefulness of axial CT scans as reported in the literature is restricted by a limited applicability during surgery. The purpose of our investigation was to comparatively evaluate TT, AMP, and OI reconstruction techniques regarding femoral and tibial tunnel apertures, tunnel length, and tunnel orientation on true lateral and anteroposterior 3D CT scans and assess whether they can reliably and accurately replicate the native ACL footprints.

Methods

Between 2008 and 2013, a total of 100 patients (74 males and 26 females) with a mean age (±SD) of 32.93 ± 10.32 years (range, 15-59 years) at the time of surgery were enrolled in the study. The right knee was involved in 55 cases and the left knee in 45. All patients underwent an arthroscopic single-bundle ACL reconstruction using a 4-strand hamstring tendon autograft by 3 surgeons with 10 to 30 years of experience in ACL reconstructions. The goal of the surgery was to place the ACL bone tunnels at the center of the native ACL attachment sites. Intraoperative fluoroscopy was used in all cases to assess the radiographic appearance of the selected tunnel position. Exclusion criteria were concomitant fractures of the tibial head and femoral condyles as well as ACL avulsion fractures of the tibial spine, revision surgery, and combined procedures with posterior cruciate or multiple ligament reconstruction and corrective osteotomies. ACL rupture was diagnosed by clinical examination and magnetic resonance imaging in all cases. Patients were stratified into 3 groups: group 1 consisted of 36 patients in whom the ACL femoral tunnel was drilled by use of a TT technique, group 2 consisted of 32 patients in whom the ACL femoral tunnel was drilled through the AMP, and group 3 consisted of 32 patients in whom retrograde drilling of the ACL femoral and tibial tunnel was performed with an OI technique. As all techniques are available at our department, allocation to the study groups was exclusively based on the treating surgeon’s individual preference. The study protocol was in accordance with all legal requirements regarding ethics committee approval.

In group 1 (TT group), the ACL femoral tunnel was drilled through the tibial tunnel at a knee flexion angle of 90° and a neutral rotation of the tibia. The tibial guide pin was drilled into the part of the native ACL tibial attachment site. Drill guide inclination was 45° to the frontal plane and 45° to 55° to the sagittal plane depending on the inclination of the Blumensaat line. The external starting position for the tibial tunnel was level with the insertion of the patellar tendon and midway between the tibial tuberosity and medial margin of the proximal tibia. A 5-mm offset femoral aimer was introduced through the tibial tunnel, and an attempt was made to position the femoral guide pin at the center of the native ACL femoral attachment site, midway between the center of the anteromedial and posterolateral bundle attachment sites. The femoral tunnel was drilled to the measured diameter of the 4-strand hamstring tendon graft by use of an arthroscopic drill bit. Femoral fixation of the hamstring tendon graft was performed with a bioabsorbable cross-pin, and the tibial end of the graft was fixed at 20° of flexion with a bioabsorbable screw after manual tensioning. The screw size was dependent on graft dimension, and therefore tunnel diameter, and was usually chosen 1 mm smaller than the tunnel width.

In group 2 (AMP group), the ACL femoral tunnel was drilled by use of an accessory AMP. A custom-made femoral aimer was introduced through the accessory AMP and used to position a guide pin at the center of the native ACL femoral attachment site with the knee between 110° and 120° of hyperflexion depending on the circumference of the thigh. The femoral tunnel was drilled to the measured diameter of the 4-strand hamstring tendon graft by use of an arthroscopic drill bit. The ACL tibial tunnel was drilled in a similar fashion as in group 1. Femoral fixation of the hamstring tendon graft was performed with a cortical suspensory fixation button with an adjustable loop length (ACL TightRope; Arthrex) or a cross-pin. The tibial end of the hamstring tendon graft was fixed by use of a bioabsorbable screw, as in group 1.

In group 3 (OI group), femoral and tibial sockets were created with an OI technique. The sockets were drilled with a retrograde drill (RetroCutter and FlipCutter; Arthrex). Drill guide angulations were 110° for the femoral tunnel and 45° to 50° for the tibial tunnel. Femoral fixation of the hamstring tendon graft was performed by use of a cortical suspensory fixation button with an adjustable graft length loop (ACL TightRope). The tibial end of the graft was fixed with an antegrade bioabsorbable interference screw.

Axial high-resolution CT scans with frontal, sagittal, and 3D reconstructions were obtained on the second postoperative day in all patients on a GE Optima CT660 Multislice CT scanner (GE Healthcare) according to a standard knee protocol. On orthograde biplanar CT reconstructions, the centers of the intra- and extra-articular femoral and tibial tunnel apertures and the intercondylar roof (Blumensaat line) were digitally marked with crosses and dots (Figures 1 and 2). A 3D reformatting of axial scans was performed to obtain frontal and sagittal images replicating radiographic views of a knee with the tunnel markers projecting through in these images. Femoral and tibial measurements were conducted on these frontal and sagittal projections (Figure 1). A measurement grid system as suggested by Bernard et al⁵ (radiographic quadrant method) was superimposed over the lateral femoral condyle on 3D projections with lateral femoral views (Figure 1C). The measurement grid was defined by the intercondylar roof (Blumensaat line), a tangent through the lateral femoral condyle, and 2 perpendiculars through the intersection between the intercondylar roof and the anterior and posterior edges of the lateral femoral condyle. The position of the center of the femoral tunnel aperture was determined as a proportion of the intercondylar depth d (d_IC in Figure 1C) and the intercondylar height h (h_IC in Figure 1C). On frontal 3D projections, the intra-articular femoral tunnel aperture was allocated to an angle segment, α_{tunnel entry}, constructed relative to the midpoint between the femoral epicondyles and a tangent to the inferior border of the medial and lateral femoral condyles (Figure 1A). The orientation of the femoral tunnel longitudinal axis, α_{tunnel axis}, relative to this femoral condyle level was also measured on frontal 2D images (Figure 1A).

On the tibia, the position of the center of the tunnel aperture was determined as a percentage of the total mediolateral diameter of the tibial plateau (P₁) on frontal 3D projections as suggested by Amis and Jacob³ (Figure 1B) and of the total anteroposterior diameter (P₂) on sagittal 3D projections as suggested by Staubli and Rauschning³⁴ (Figure 1D). The angle between the tibial tunnel (longitudinal axis through the center of the tibial tunnel apertures) and the tibial plateau was measured on frontal (β_frontal in Figure 1B) and sagittal projections (β_sagittal in Figure 1D).

Femoral tunnel length was measured on orthograde biplanar CT reconstructions displaying the true length of the intraosseous tunnel and the true length of the femoral graft fixation (Figure 2). Because the true intraosseous tunnel length is dependent on the size of the knee, the measured length was normalized to the total mediolateral width of the tibial plateau measured according to Amis and Jacob.³ Figure 3 presents all measurements on a separate illustration. Radiographic reference values for accurate femoral and tibial tunnel placement as suggested in the literature have been used to discuss the measurement results obtained in the 3 study groups.^19,20,29

Statistical Analysis

The data were analyzed using a 1-way analysis of variance (ANOVA) with Tukey and Games-Howell post hoc tests. For nominal and ordinal data, appropriate contingency tables and Fisher exact tests were applied. Homogeneity of variance for ANOVA was tested using Levene statistics, with a significance level of P < .2. As sample sizes were larger than 30 and equal for each group, the Games-Howell post hoc test was interpreted for results in which the assumption for homogeneity of variance was violated. For isolated comparison of AMP and OI groups, 2-tailed independent-samples t tests or Welch tests were used, respectively. Significance levels were defined as P < .05 and P < .01, respectively.

Results

There was no statistically significant difference between the 3 groups with respect to sex, age, or involved side (Table 1). Absolute and relative values (mean ± SD) for the position of the center of the femoral and tibial tunnel aperture on CT scans, including the results for the reference measurement of the femoral graft tunnel length in relation to the total mediolateral diameter of the tibial plateau, are demonstrated in Table 2. Intracondylar depth for the AMP and OI techniques was 72.63% ± 8.28% and 71.80% ± 14.10%, respectively, and intracondylar height for the AMP and OI techniques was 27.76% ± 10.46% and 27.29% ± 9.50%, respectively. Femoral tunnel length was 33.35 ± 6.67 mm for the AMP technique and 35.38 ± 5.29 mm for OI reconstruction. The corresponding values for graft fixation length were 24.83 ± 5.33 mm and 23.33 ± 5.16 mm, respectively. The anteroposterior tibial tunnel position was located at 45.17% ± 6.06% and at 44.80% ± 5.46% of the total anteroposterior diameter of the tibial plateau for the AMP and OI techniques, respectively, and the respective tibial tunnel axis angles were 66.90° ± 6.67° and 64.43° ± 6.06°. The femoral tunnel axis angle was 6.95° ± 13.67° for the OI technique and 27.76° ± 10.46° for the AMP technique.

Table 1

Age, Sex, and Side Distribution Between the Study Groups^a

	TT Group (n = 36)	AMP Group (n = 32)	OI Group (n = 32)
Age, mean ± SD (range), y	33.59 ± 12.17 (18-59)	31.25 ± 10.64 (15-63)	33.74 ± 7.52 (18-48)
Sex (male/female), n	28/8	27/5	19/13
Side (right/left), n	20/16	18/14	17/15

AMP, anteromedial portal; OI, outside-in; TT, transtibial.

Table 2

Relative Values for the Position of the Center of the Femoral and Tibial Tunnel Aperture on Computed Tomography Scans^a

	TT	AMP	OI	P
Center of the femoral tunnel aperture
d_T/d_IC, %	73.76 ± 9.45	72.63 ± 8.28	71.80 ± 14.10	.12
h_T/h_IC, %	18.31 ± 8.68^b	27.76 ± 10.46	27.29 ± 9.50	<.01
α_{tunnel entry}, deg	74.67 ± 4.34^b	70.13 ± 4.42^b	65.10 ± 6.01^b	<.01
α_{tunnel axis}, deg	50.40 ± 10.89^b	27.76 ± 10.46^b	6.95 ± 13.67^b	<.01
l_tunnel, mm	42.31 ± 8.49^b	33.35 ± 6.67	35.38 ± 5.29	<.01
l_{graft fixation}, mm	29.61 ± 4.30^b	24.83 ± 5.33	23.33 ± 5.16	<.01
l_tunnel/T_ML, %	—^c	0.44 ± 0.08^b	0.47 ± 0.05	.04
l_{graft fixation}/T_ML, %	—^c	0.33 ± 0.07	0.31 ± 0.09	.16
Center of the tibial tunnel aperture
P₁/T_ML, %	46.53 ± 4.31	46.24 ± 2.97	44.16 ± 4.44	.06
P₂/T_AP, %	49.58 ± 9.71^b	45.17 ± 6.06	44.80 ± 5.46	.02
β_frontal, deg	63.51 ± 8.59	66.56 ± 7.26	63.20 ± 7.61	.23
β_sagittal, deg	68.88 ± 8.41^b	66.90 ± 6.67	64.43 ± 6.06	.04

Results are reported as mean ± SD. AMP, anteromedial portal; AP, anteroposterior; d, depth; h, height; IC, intercondylar; l, length; ML, mediolateral; OI, outside-in; P₁, mediolateral tunnel position between the medial cortical border of the tibial head and the intra-articular tunnel aperture; P₂, anteroposterior tunnel position between the anterior cortical border of the tibial head and the intra-articular tunnel aperture; TT, transtibial; T, tunnel.

Statistically significant (P < .05).

These calculations for the TT group were not performed because only a difference between the AMP and OI groups with respect to knee size needed to be demonstrated.

The TT technique resulted in higher tunnel positions compared with AMP and OI, with the difference being statistically significant. The femoral intracondylar tunnel depth was distributed equally between all groups. A statistically significant difference was found for femoral tunnel axis and tunnel entry angle between the 3 study groups, proving the most oblique graft tunnel position for the OI technique. Total intraosseous femoral tunnel lengths as well as the length of the femoral graft fixation were distributed in favor of the TT technique, with statistical significance. Because the total diameter of the tibial plateau can be considered a constant reference factor and its mean values did not yield a statistically significant difference between study groups, a comparison of the total femoral tunnel length in relation to the total mediolateral diameter of the tibial plateau was performed, and it demonstrated a statistically significant shorter tunnel length with the AMP technique but no difference for the ratio of the total graft fixation length between study groups. Accordingly, a strong correlation was found between the total diameter of the tibial plateau and the total femoral tunnel length in both AMP and OI groups (AMP, r = 0.46; 95% CI, 0.2-0.7; P < .01; OI, r = 0.66; 95% CI, 0.4-0.8; P < .01) (Figure 4). In the AMP group, 6% of femoral tunnels yielded a total length less than 25 mm and 10% had a graft fixation length less than 20 mm. The corresponding values for the OI group were 0% and 7%, respectively, without statistically significant differences.

On the tibia, TT tunnels were located more posterior compared with both AMP and OI tunnels and were higher angled compared with OI tunnels. The TT sagittal tunnel axis angles on the tibia were highest, with statistically significant differences compared with both the AMP and OI tunnels. The OI technique resulted in the flattest tunnel entry angles and most posterior tunnel apertures, but this did not reach statistical significance when compared with AMP reconstruction. Isolated comparison between the AMP and OI tunnels revealed no statistically significant differences in the position of the femoral and tibial tunnel apertures. Mean values for femoral and tibial tunnel parameters for the 3 study groups are plotted on a representative frontal and sagittal 3D CT image in Figure 5.

Discussion

The main findings of our investigation indicate an adequate replication of anatomic femoral and tibial ACL footprints and sufficient tunnel and graft fixation length for AMP and OI techniques in vivo. The study provides a dataset of radiographic reference values deducted from a comprehensive CT-based measurement grid system that is easily transferrable to intraoperative fluoroscopic and postoperative plain radiographic confirmation of correct femoral and tibial graft tunnel placement.

Only a few studies have compared tunnel positions after use of TT, AMP, and OI techniques.^10,30,31 Gadikota et al¹⁰ observed a larger posterolateral bundle coverage and a closer replication of the native ACL footprint center by AMP and OI techniques but also a higher incidence of a posterior femoral tunnel exit relative to the lateral epicondyle with the AMP reconstruction in a cadaveric study. Shin et al³⁰ noted a higher femoral tunnel position with TT techniques but no differences in the deep-to-shallow direction in vivo when using a measurement grid based on anatomic axis coordinates. Shin et al³¹ found a femoral tunnel length of more than 30 mm in all 3 groups. None of these authors included tibial tunnel properties or graft fixation length, however.

Our results confirm a more anatomic replication of the intercondylar tunnel height with the AMP and OI techniques as well as a total femoral tunnel length between 33 and 35 mm; additionally, they indicate a femoral graft fixation length of 23 and 25 mm for the AMP and OI techniques, respectively. This contradicts the result reported by Kim et al,¹⁵ who found significantly shorter fixed graft lengths—between 16 and 18 mm—for both techniques after a double-bundle reconstruction. In contrast to the findings of Kim et al, we found no statistically significant difference for the absolute femoral tunnel and graft fixation lengths but we did find a significant variance of the femoral tunnel length in relation to the constant total mediolateral diameter of the tibial plateau indicating shorter tunnels with smaller knees.

The AMP technique has been described as a technically challenging procedure.²¹ Reported pitfalls include socket blowout, impingement by the lateral wall of the intercondylar notch, difficulties in achieving an adequate hyperflexion position and avoiding iatrogenic damage to the cartilage of the medial femoral condyle, guide pin bending, and so on, with some of them potentially resulting in short or bicortical tunnels.²¹ However, controversies regarding the amount of knee flexion during AMP tunnel drilling have been reported since increased flexion results in more horizontal tunnel orientation, acute graft bending angle, and contact pressure on the graft.¹⁶ Recommendations range between 110° and full flexion.¹⁶ The in vivo results of our study confirm these shortcomings by verifying a higher percentage of shorter femoral tunnels less than 25 mm and reduced graft fixation length less than 20 mm in the AMP group, even though the difference did not reach statistical significance. Mean tunnel lengths did not differ between AMP and OI techniques, however. Using an even lower critical value than that used by Chang et al,⁶ our data indicate a substantial risk of femoral tunnel length inappropriate for sound graft healing. However, a consensus regarding adequate tunnel length for biologic fixation is not available in the literature. This emphasizes the necessity of safety measures and careful patient selection for AMP procedures.

Regarding reliable parameters for anatomic footprint replication, the radiographic correlation of femoral and tibial attachment sites was recently and extensively studied and discussed by Lee et al.¹⁹ The authors found an intercondylar depth and height of the femoral ACL footprint at 37.3% and 41.0% of the total intercondylar depth and height, respectively. Lee et al also noted a growing mismatch between and within the specifications for the anatomic and radiographic ACL footprint and the corresponding landmarks, and they noted that the femoral footprint mean values from several of these studies were between 23% and 30% in relation to the intercondylar depth and between 26% and 35% in relation to the intercondylar height, respectively.^{1,7,8,13,26,27,37,41} Despite providing valuable data on anatomic ACL footprint location and verifying reliable correlation of radiographic and CT-based measurements, the study by Lee et al¹⁹ failed to use a clinically extractable tibial imaging modality by assessing axial CT scans. Compared with these reference values, we noted a nonanatomic intercondylar height of the femoral tunnel position in the TT group. Both AMP and OI techniques resulted in anatomic tunnel position from the radiomorphometric point of view.

From the biomechanical perspective, Kato et al¹⁴ reported the closest restoration of native ACL in situ forces with a midposition footprint replication and the highest in situ forces and least anterior tibial translation with an anteromedial bundle reconstruction of the ACL. According to the radiographic analysis by Lee et al,¹⁹ the femoral insertion of the anteromedial bundle is located at 66.5% of the intercondylar depth and at 27.6% of the intercondylar height. This indicates that the location of the femoral tunnel in this series was marginally too deep, whereas most previous anatomic studies^{1,5,7,8,13,27,36,37,42} identified the femoral ACL footprint center at an average intercondylar depth of 71% and the anteromedial bundle center at an average intercondylar depth of 75.5%.^¶ These parameters were most closely restored with the OI technique in our investigation.

Regarding tunnel entry angles and graft orientation, biomechanical data suggest an influence of femoral tunnel angles on postoperative knee joint flexion moment and posterior shear force during walking in favor of more oblique tunnel orientation with AMP and OI techniques.³⁹ The femoral tunnel axis was found to be lowest after use of the OI technique and more than half of the value reported by Shin et al.³¹ Robert et al²⁸ used the anatomic longitudinal axis of the femur to determine the angle of the femoral tunnel axis but also found statistically significant differences between all groups in a cadaveric setting, indicating the most oblique femoral graft entry with OI drilling. Even though gentler graft bending angles were found with AMP technique,¹⁵ the OI retrograde drilling offers substantial variability in adjusting the femoral drill guide. Lubowitz et al²³ published reference values for the angulation of the femoral guide pin entrance that most anatomically restores the femoral ACL footprint regarding length, width, area, and angular orientation using the OI technique.

In our study, the tibial insertion was found to be most posterior in the TT group, indicating an improved anteroposterior tibial tunnel position with tunnel-independent techniques in accordance with the suggestion by Bedi et al⁴ that anterior tibial tunnel positions better control Lachman and pivot shift. Based on the reference data reported by Lee et al,¹⁹ Scheffel et al,²⁹ and Lorenz et al,²⁰ replication within the center of the native ligament insertion site was accomplished with AMP and OI techniques. The tibial insertion area is located on average between 41% and 45% of the anteroposterior diameter of the tibial plateau on axial images.^{7,19,26,27,37} The mediolateral tibial tunnel position did not yield statistically significant differences and was sufficient for all study groups. Van der Bracht et al³⁸ reported an increased amount of tibial footprint coverage with larger tibial tunnel diameters and smaller drill guide angles. In accordance with this recommendation, the tibial tunnel axis angles were smallest with OI technique in both the coronal and sagittal planes.

The anteroposterior femoral and tibial tunnel position was reported to be the most variable measure between orthopaedic surgeons,⁴⁰ and graft orientation in the coronal and sagittal plane was nonanatomic and too vertical in 88% of revision surgeries after primary ACL reconstruction with subsequent failure.²⁴ Intraoperative fluoroscopy and postoperative CT scans have therefore been recommended to improve the accuracy of tunnel placement^11,35 and to allow for positive feedback loops and a process of individual improvement.¹² In contrast to the measurement grid system used by Gadikota et al¹⁰ and Shin et al,³⁰ our reference system is based on more direct and easily accessible landmarks in 2-dimensional imaging, which might facilitate a transfer of our in vivo results of ACL tunnel placement to intraoperative quality validation via fluoroscopy.³⁵

There are several limitations to this study. A rather small sample size might impair the statistical significance, and a correlation to functional results is not available. Moreover, some authors have suggested the use of internal tibial rotation and varus stress during femoral tunnel drilling in TT ACL reconstruction to better adjust femoral tunnel placement to the native ligament footprint.⁴¹ This modification was not performed in our TT group.

Intercondylar depth and height were anatomic for AMP and OI techniques. The femoral graft bending angle was highest for the OI technique, indicating a potential effect on graft strain. Tibial tunnel characteristics were most appropriate after OI reconstructions. Femoral tunnel and graft fixation length tended to be smaller after AMP reconstruction. These shortcomings are inherent to AMP reconstructions but certainly also depend on the quality of surgical performance. AMP and OI surgical techniques were superior in positioning the ACL femoral tunnel at the center of the native ACL attachment site compared with the TT technique. An average graft fixation length above 30 mm was obtained for all 3 surgical techniques. However, the comparison of functional results after different reconstruction techniques seems to be mandatory to determine the potential clinical relevance of these findings. A cautious interpretation of our data might clarify remaining questions of tunnel characteristics and graft position after use of the TT, AMP, and OI techniques.

Footnotes

The authors declared that they have no conflicts of interest in the authorship and publication of this contribution.

‖

References 1 -5, 7, 8, 12, 13, 19, 20, 29, 34, .

¶

References 1, 5, 7, 8, 13, 19, 27, 36, 37, .

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