Factors Influencing Graft Impingement on the Wall of the Intercondylar Notch After Anatomic Double-Bundle Anterior Cruciate Ligament Reconstruction

Abstract

Background:

Anatomic placement of the bone tunnel reportedly reduces impingement of the graft with the intercondylar roof, but as a trade-off, the risk of impingement with the lateral wall of the intercondylar notch would increase instead in anatomic double-bundle anterior cruciate ligament (ACL) reconstruction.

Purpose:

The 2 grafts for the anteromedial bundle (AMB) and posterolateral bundle (PLB) were separately analyzed for the frequency of and risk factors for graft impingement on the wall of the intercondylar notch.

Study Design:

Case control study; Level of evidence, 3.

Methods:

A total of 51 patients (53 knees) who underwent primary anatomic double-bundle ACL reconstruction were enrolled. Based on the graft orientation plane reconstructed with 3-dimensional imaging software, graft-wall impingement was defined as overlap between the lateral wall of the notch and the line connecting each center of the intra-articular apertures of the femoral and tibial bone tunnels. The rate of wall impingement was assessed for each bundle. Parameters for bone tunnel positioning in the femur and tibia, notch width index, and knee joint rotation angle were compared between patients with and without wall impingement. The most important risk factors for wall impingement were assessed by logistic regression analysis.

Results:

Wall impingement for the AMB was observed in 22 knees (42%), whereas no patients exhibited wall impingement for the PLB. Regarding femoral bone tunnel positioning according to the quadrant method, the AMB bone tunnel was placed significantly higher in impingement-positive patients than in impingement-negative patients (P = .03). Regarding tibial tunnel positioning, the tunnel was placed significantly more anteriorly (P = .02) and laterally (P = .02) in the impingement-positive group than in the impingement-negative group. Bone tunnels positioned 48% to 50% from the medial border of the tibia demonstrated a 100% incidence of wall impingement. Based on logistic regression analysis, lateral deviation of the AMB tibial bone tunnel was significantly associated with wall impingement (odds ratio, 1.403; P = .048).

Conclusion:

The tibial bone tunnel position in the coronal orientation was most likely associated with wall impingement. Considering that tibial bone tunnels are generally created with the knee in 90° of flexion and move laterally as the knee extends because of screw-home movement, the AMB bone tunnel for the tibia should be positioned as medially as possible within its footprint to minimize the risk of wall impingement after anatomic double-bundle ACL reconstruction.

Keywords

anterior cruciate ligament wall impingement anatomic double-bundle reconstruction bone tunnel positioning

Graft impingement with the intercondylar notch is a known cause of anterior knee pain, joint effusion, limited range of motion, and failure of graft maturation after anterior cruciate ligament (ACL) reconstruction,¹³ and repeated graft-notch impingement may ultimately cause graft ruptures.¹¹ While the transtibial technique was widely used to create femoral bone tunnels in the 1990s, the nonanatomic high position (11 o’clock for right knee and 1 o’clock for left knee) was perceived as proper positioning of the femoral bone tunnel because of good isometricity, resulting in an increased incidence of notch impingement. In the context of the high position, the ACL graft is prone to impingement on the superior wall of the notch (ie, roof impingement) with the knee in extension, unless notchplasty is performed concomitantly. Anatomic placement of the femoral bone tunnel reportedly minimizes such roof impingement,^14-17 but the risk of impingement on the lateral wall of the notch (ie, wall impingement) would instead be increased in anatomic ACL reconstruction as a trade-off.

Recently, the debate about whether to position the femoral tunnel in an anatomic or isometric position has reached a consensus that subjective and objective rotational stability of the knee after anatomic tunnel positioning is superior to that after isometric reconstruction, apart from the debate regarding single- or double-bundle reconstruction.^1,5,35 Actually, anatomic double-bundle reconstruction has been growing in popularity in Japan, and issues regarding notch impingement by the ACL graft remain contentious. We hypothesized that the probability of wall impingement, but not roof impingement, with the knee in extension would increase after anatomic double-bundle ACL reconstruction because the femoral tunnel is placed at a deeper, lower position and the tibial tunnel, particularly for the anteromedial bundle (AMB), is placed more anteriorly than in traditional single-bundle reconstruction. In the present study, the incidence of wall impingement was measured using 3-dimensional (3D) planning software that was originally developed for preoperative planning of total knee arthroplasty. This is because the 2 ACL bundles, the AMB and posterolateral bundle (PLB), differ in terms of placement within the intercondylar notch, and the rate of wall impingement would differ between bundles. Wall impingement for the 2 bundles was therefore assessed separately. In addition, significant risk factors for wall impingement were analyzed by multivariate analysis.

Materials and Methods

Patients

From August 2008 to June 2012, a total of 348 anatomic double-bundle ACL reconstructions were performed in 324 consecutive patients at our institute. Of these, 53 knees from 51 patients were enrolled in this study (Table 1). The study was approved by our institutional review board, and all patients provided informed consent before enrollment. Inclusion criteria were as follows: primary ACL reconstruction with an anatomic double-bundle procedure using the semitendinosus tendon (ST), consent to undergo computed tomography (CT) of the knee postoperatively, and no evidence of radiographic osteoarthritis. Exclusion criteria comprised the following: previous ligament reconstruction or multiple ligament injuries, and reconstruction with a bone–patellar tendon–bone autograft. Patients’ mean age at the time of surgery was 30.2 years (range, 14-54 years), and the mean duration from injury to operation was 4.1 years (range, 0.1-30 years). At 2 months postoperatively, all patients had obtained knee extension equal to the contralateral knee, including hyperextension or just 0° of extension, and underwent CT with a 1-mm helical scan with the knee in 0° of extension and were subjected to analysis of graft-wall impingement.

Table 1

Patient Characteristics^a

Characteristics	Values
Patients/knees, n	51/53
Age, mean (range), y	30.2 (14-54)
Sex, male/female, n	31/20
Time from injury to operation, mean (range), y	4.1 (0.1-30)
Double-bundle ST graft/double-bundle STG graft, no. of knees	27/26
Tegner activity level, mean (range)	5.1 (2-8)
Lysholm score, mean (range)	71.6 (33-95)
Meniscal injury, no. of knees
MM	13
LM	19
Articular cartilage defect, Outerbridge classification II/III/IV, n
PF	2/0/0
MFC	2/0/2
MTP	1/0/0
LFC	1/0/0
LTP	0/0/0

LFC, lateral femoral condyle; LM, lateral meniscus; LTP, lateral tibial plateau; MFC, medial femoral condyle; MM, medial meniscus; MTP, medial tibial plateau; PF, patellofemoral; ST, semitendinosus tendon; STG, semitendinosus tendon and gracilis tendon.

Surgical Techniques

All ACL reconstructions were arthroscopically performed by a single surgeon using anatomic double-bundle procedures, as reported previously.^23,24 Briefly, all surgeries were performed under general anesthesia and with tourniquets. The ST was harvested and cut into 2 pieces, and the 2 double-looped ST grafts were prepared for AMB and PLB grafts. Arthroscopically, the ACL remnant was removed, and the bony ridge of the medial wall of the lateral femoral condyle (ie, resident ridge) was exposed. Our landmark for ideal AMB and PLB bone tunnels was the resident’s ridge, which reportedly represents the anterior border of the femoral ACL footprint and is identifiable in more than 97% of human femora.^7,8 In the sagittal plane, tunnels for the AMB and PLB were placed posterior to the resident’s ridge, and the centers of these tunnels corresponded to the center of each anatomic footprint, including the fan-like portion.^8,12 The arthroscope was moved to an anteromedial portal viewing position, and the tip of a femoral outside-in ACL aimer was placed precisely at the center of each footprint. A 3.5-mm guide pin was introduced from outside the joint through a small incision over the lateral femoral cortex. The guide pin was replaced by a flip cutter (Arthrex), which in turn cut a socket into the femur to a depth of 15 mm. Tunnel sizes varied between 5 and 6.5 mm, depending on the harvested graft, and no notchplasty was performed. In terms of tibial bone tunnel creation, two 2.4-mm guide wires were inserted into the center of the AMB and PLB footprint using a drill guide system (Smith & Nephew). After overdrilling of each bone tunnel, grafts were introduced through the tibial tunnel into the femoral tunnel. Femoral fixation for the 2 ST grafts was achieved using EndoButton CL (Smith & Nephew). Tibial graft fixation was achieved using a double spike plate (DSP, Smith & Nephew). Both grafts for the AMB and PLB were secured with 20 N tension with the knee in 20° of flexion using a ligament tensioner (Smith & Nephew).

Assessment of Wall Impingement

In this study, 3D imaging software (ATHENA, Soft Cube) that had originally been developed for preoperative planning of total knee arthroplasty was used to reconstruct an arbitrarily oriented imaging plane and radiographs from the CT data. This software allows for digitally reconstructed radiographs to be made from CT data, simulating different X-ray source positions and angles. The graft orientation plane passing through the centers of the extra- and intra-articular apertures of the femoral tunnel and the center of the intra-articular aperture of the tibial tunnel³⁴ was made using ATHENA (see Appendix Figure A1, available in the online version of this article at http://ajsm.sagepub.com/supplemental). This plane exhibited the smallest graft-bending angle at the intra-articular aperture of the femoral tunnel and might most accurately demonstrate putative graft-wall impingement. Graft-wall impingement was defined as overlap between the lateral wall of the notch and the line connecting each center of the intra-articular apertures of the femoral and tibial bone tunnels (Figure 1). As variables potentially affecting the rate of graft-wall impingement, 3D positioning of the bone tunnels (see Appendix Figure A2, available online), notch width index (NWI) (see Appendix Figure A3, available online), and knee joint rotation angle (see Appendix Figure A4, available online) were analyzed using CT data. Femoral tunnel apertures for the AMB and PLB were evaluated according to the quadrant technique, as described by Bernard et al.⁴ Tibial tunnel positions for the AMB and PLB were evaluated in the sagittal orientation, according to the method of Amis and Jakob.² Tibial tunnel positions in the coronal orientation were also assessed by dividing the distance from the medial border of the tibia to the bone tunnel center by the bicondylar width of the tibia. A Holmblad 70° view was simulated to create a notch-view radiograph, and the NWI was obtained according to the method described by Souryal and Freeman.²⁸ The notch width at the level of the popliteal groove was measured and divided by the bicondylar width at the same level (Appendix Figure A3). The tibiofemoral rotation angle was expressed as the knee joint rotation angle, as reported by Liodakis et al,²¹ defined as the angle between the posterior condylar axis of the femur and the tibia (Appendix Figure A4).

Clinical Assessment

Follow-up examinations were performed more than 2 years after ACL reconstruction. The data were compared between impingement-positive and impingement-negative groups, in terms of anteroposterior knee laxity measured using a KT-2000 arthrometer (MEDmetric Corp), pivot shift test, and Lysholm score.

Statistical Analysis

Statistical analysis was performed using SPSS version 17.0 software (SPSS Inc). The χ² and Fisher exact tests were used to compare the probability of wall impingement between the AMB and PLB. The Student t test was used to compare the NWI, knee joint rotation angle, and several parameters for bone tunnel positioning between patients with and without graft-wall impingement. Multivariate analyses were performed using logistic regression. Factors found to be associated with graft-wall impingement at the P < .05 level according to either the Student t test or the χ² test were included in the logistic regression analysis. Statistical significance for the multivariate model was accepted at the P < .05 level. The κ statistic was used to assess interobserver and intraobserver agreement for the interpretations of wall impingement. κ values for intraobserver agreement of 2 assessors were 0.92 (P < .001) and 0.81 (P < .001) (see Appendix Table A1, available online), and the value for interobserver agreement was 0.85 (P < .001) (see Appendix Table A2, available online).

Results

Among the 53 knees, wall impingement was observed in 22 knees for the AMB (42%), whereas no patients exhibited wall impingement for the PLB (Figure 2). We therefore analyzed risk factors predisposing to AMB graft-wall impingement. After patients were divided into either an impingement-positive or an impingement-negative group, multiple variables considered likely to influence the rate of graft-wall impingement were compared. In terms of femoral bone tunnel positioning assessed by the quadrant method of Bernard et al⁴ (Figure 3), quadrant B was significantly smaller in the impingement-positive group than in the impingement-negative group (P = .03), while no significant difference was seen in quadrant A between groups (Table 2). Regarding tibial tunnel positioning in the sagittal plane (Figure 4), tunnels were placed significantly more anteriorly (P = .02) in the impingement-positive group than in the impingement-negative group (Table 2). For coronal positioning of tibial tunnels, patients in the impingement-positive group demonstrated significantly more lateral positioning than those in the impingement-negative group (P = .02) (Table 2). In terms of knee joint rotation angle, defined as the angle between the posterior condylar axes of the femur and tibia with the knee in extension, no significant difference was seen between impingement-positive and impingement-negative groups. Analysis of the NWI in the Holmblad 70° view³³ revealed that the NWI was comparable between the 2 groups.

Table 2

Univariate Analysis^a

	Positive Impingement	Negative Impingement	P Value
Femoral position, %
Quadrant A	20.0 ± 5.5	20.6 ± 5.9	.34
Quadrant B	18.4 ± 8.7	22.5 ± 6.4	.03
Tibial position, %
Sagittal	32.1 ± 4.0	34.4 ± 4.4	.02
Coronal	44.2 ± 2.0	43.0 ± 1.9	.02
Knee joint rotation angle, deg	2.3 ± 4.6	3.0 ± 3.9	.27
Notch width index	0.29 ± 0.024	0.29 ± 0.027	.46

Values are expressed as mean ± standard deviation.

Multivariate logistic regression analysis that included femoral bone tunnel positions (quadrant B) and tibial bone tunnel positions in both the sagittal and coronal planes as covariates was performed to assess predisposing factors for wall impingement (Table 3). The results demonstrated that lateral deviation of the AMB bone tunnel was significantly associated with graft-wall impingement (odds ratio, 1.403; P = .048). When the rate of wall impingement was analyzed every 2% according to coronal positioning of the AMB bone tunnel, the rate of wall impingement increased with increasing lateral deviation of the AMB (Figure 5). Of note was the finding that a coronal position of 48% to 50% yielded a 100% incidence of wall impingement.

Table 3

Multivariate Logistic Regression Analysis

	P Value	Odds Ratio	95% CI
Tibial position, %
Coronal	.048	1.403	1.002-1.963
Sagittal	.1	0.871	0.738-1.027
Femoral position, quadrant B, %	.1	0.933	0.857-1.015

To assess the clinical significance of wall impingement, clinical outcomes of the enrolled patients were compared between impingement-positive and impingement-negative groups. The Lysholm score, rate of positive results for the pivot-shift test, and KT-2000 arthrometer values demonstrated no significant difference between groups, although patients in the impingement-positive group tended to exhibit a higher rate of positive results for the pivot-shift test (P = .19) and larger KT-2000 arthrometer values (P = .68) compared with those in the impingement-negative group (Table 4).

Table 4

Clinical Results

	Positive Impingement	Negative Impingement	P Value
No. of knees	22	31	—
Mean follow-up period, mo	2.2	2.4	—
Anterior cruciate ligament reinjury, no. of knees	0	1	—
KT-2000 arthrometer value, mean ± SD, mm	0.75 ± 2.1	0.5 ± 2.2	.68
KT-2000 arthrometer value ≥4 mm, no. of knees	2	3	.94
Positive pivot shift, no. of knees	5	3	.19
Lysholm score, mean ± SD	95.2 ± 5.6	95.8 ± 5.2	.58

Discussion

During the past decade, advances in knowledge of the anatomy of the ACL have led to the development of modern reconstruction techniques mimicking the original double bundles of the ACL. To date, several double-bundle ACL reconstructive procedures have been developed to restore optimal rotational and anterior knee stability.^1,5,22,36 According to previous biomechanical cadaveric studies,³⁵ the advantage of the anatomic double-bundle procedure is favorable control of anterior knee stability and rotational stability as compared with a conventional single-bundle procedure. From the surgeon’s perspective, the anatomic double-bundle procedure is a relatively complicated technique accompanied by a steep learning curve.²⁷ However, the technique is increasingly being improved and becoming more sophisticated, and satisfactory clinical outcomes of this technique have been accumulating in the literature.¹⁹

Recent randomized clinical trials comparing single-bundle versus double-bundle ACL reconstructions and meta-analyses of results from those trials have demonstrated that the anatomic double-bundle procedure guarantees superior stabilization and a lower rate of postoperative graft failure compared with single-bundle reconstruction.^20,29 However, a substantial rate of graft failure occurs after anatomic double-bundle ACL reconstruction, and Fu et al⁹ reported a graft failure rate of 8%. One potential explanation may be that, despite reproducing the native ACL anatomy, graft-notch impingement still exists. Reportedly, wall impingement but not roof impingement is responsible for disruption of the anatomically reconstructed ACL as well as the native ACL,^10,25 as corroborated by a biomechanical study showing that wall impingement of the graft occurs with the knee in 10° of valgus and 29° of external rotation.²⁵ Indeed, 42% of patients in the present study exhibited graft-wall impingement for the AMB in knee extension, regardless of the mean NWI, and NWI values were confirmed as comparable with those in previous reports.^3,6,33 In fact, concerns have been raised regarding how much stress is loaded between the ACL graft and the wall of the intercondylar notch and the frequency of wall impingement causing graft failure in clinical settings. Clinical outcomes in the present ACL reconstruction series demonstrated a tendency toward inferior anterior-posterior and rotational stability in the impingement-positive group at 2 years postoperatively, but statistical significance was lacking possibly because of the small sample size. Further investigation with a larger sample size is warranted to elucidate the real effect of wall impingement on clinical results of ACL reconstruction.

Unlike the AMB, PLB graft-wall impingement with the knee in extension was not observed in our ACL reconstruction series. Likewise, Fung et al¹⁰ reported that only the AMB exhibited wall impingement based on a magnetic resonance imaging study. Considering screw-home movement at terminal knee extension, the anatomically reconstructed AMB graft comes into contact with the lateral wall of the notch because tibial external rotation is maximized with the knee in extension. In the context of the PLB, its anatomic position might be approximated to the rotational axis of the knee joint so that the PLB graft might be protected from wall impingement, irrespective of tibiofemoral rotation. Surgeons should be aware that AMB graft-wall impingement may occur with the knee in extension.

According to multivariate logistic regression analysis, the lateral deviation of the tibial tunnel position in the coronal orientation was significantly associated with AMB graft-wall impingement (odds ratio, 1.403; P = .048; 95% confidence interval, 1.002-1.963). If the tibial tunnel position moves laterally by 1%, the risk for graft-wall impingement increases 1.4-fold. As the medial-lateral width of the tibia averaged 74 mm in our case series, the risk of wall impingement increased 1.4-fold for every additional 0.74 mm of lateral deviation of the bone tunnel. As the mean diameter of the tibial footprint for the ACL reportedly ranges from 7 to 10 mm,^18,26,30 even a small lateral deviation of the bone tunnel may dramatically increase the risk of wall impingement. Furthermore, AMB bone tunnel positioning at 48% to 50% from the medial border of the tibia demonstrated a 100% incidence of wall impingement. Because tibial bone tunnels are generally created with 90° to 110° of knee flexion intraoperatively, and the tibia undergoes more than 10° of external rotation as the knee extends, wall impingement would occur even if a sufficient interval seems to exist between the graft and the lateral wall of the notch. Particularly in a dynamic situation such as running, ACL-reconstructed knees are reportedly more externally rotated than normal contralateral knees,^31,32 suggesting that the risk of wall impingement after ACL reconstruction is much higher than expected.

Three potential limitations must be taken into consideration in this study. First, we must acknowledge that the small sample size in this series might have obscured precise statistically analyses. Second, no load was applied to the knee during CT, and the graft orientation plane reconstructed with 3D imaging software might ensure only static, not dynamic, positions of the graft and intercondylar wall. Third, this study did not measure actual impingement pressure, so the clinical relevance of wall impingement and its effect on the graft remain unclear. The clinical significance of wall impingement might depend on the magnitude of actual contact pressure between the graft and intercondylar wall.

In conclusion, femoral bone tunnel positions (quadrant B) and tibial bone tunnel positions in both the sagittal and coronal orientations were associated with the probability of graft-wall impingement after anatomic double-bundle ACL reconstruction. In particular, the tibial bone tunnel position in the coronal orientation was most likely associated with graft-wall impingement. Given that tibial bone tunnels are generally created with the knee in 90° of flexion and move laterally with the knee extending because of screw-home movement, it is our recommendation that the tibial bone tunnel for the AMB should be positioned as medially as possible within its footprint. Improvement of the coronal tunnel position of the AMB may minimize the risk of graft-wall impingement and subsequent graft ruptures after anatomic double-bundle ACL reconstruction.

Footnotes

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

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