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Tibial tunnel enlargement after anatomic anterior cruciate ligament reconstruction with a bone–patellar tendon–bone graft. Part 1: Morphological change in the tibial tunnel
Journal of Orthopaedic Science xxx (xxxx) xxx
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Original Article
Tibial tunnel enlargement after anatomic anterior cruciate ligament reconstruction with a boneepatellar tendonebone graft. Part 1: Morphological change in the tibial tunnel Tomoki Ohori a, Tatsuo Mae a, *, Konsei Shino b, Yuta Tachibana c, Hideki Yoshikawa a, Ken Nakata a a b c
Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2, Yamada-oka, Suita, Osaka, 565-0871, Japan Sports Orthopaedic Surgery Center, Yukioka Hospital, 2-2-3, Ukita, Kita-ku, Osaka, Osaka, 530-0021, Japan Department of Sports Orthopaedics, Osaka Rosai Hospital, 1179-3, Nagasone-cho, Kita-ku, Sakai, Osaka, 591-8025, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 26 October 2018 Received in revised form 7 January 2019 Accepted 15 January 2019 Available online xxx
Background: Three-dimensional (3D) computed tomography (CT) is reliable and accurate imaging modality for evaluating tunnel enlargement after anterior cruciate ligament (ACL) reconstruction. The purpose of this study was to evaluate the tibial tunnel enlargement including the morphological change after anatomic ACL reconstruction with a boneepatellar tendonebone (BTB) graft using 3D CT models. Methods: Eighteen patients with unilateral ACL rupture were included. The anatomic rectangular-tunnel (ART) ACL reconstruction with a BTB autograft was performed. 3D CT models of the tibia, the tibial tunnel, and the bone plug at 3 weeks and 1 year after surgery were reconstructed and superimposed using a surface registration technique. The cross-sectional area (CSA) of the tibial tunnel perpendicular to the tunnel axis was evaluated at the aperture and 5, 10, and 15-mm distal from the aperture. The CSA was measured at 3 weeks and 1 year after surgery and compared between the two time points. The locations of the center and the anterior, posterior, medial, and lateral edges of the tunnel footprint were also evaluated based on the coordinate system for the tibial plateau and compared between the two time points. Results: At the aperture, the CSA of the tibial tunnel at 1 year after surgery was significantly larger by 21.9% than that at 3 weeks (P < 0.001). In contrast, the CSA at 1 year was significantly smaller than that at 3 weeks at 10 and 15-mm distal from the aperture (P ¼ 0.041 and < 0.001, respectively). The center of the tunnel footprint significantly shifted postero-laterally with significant posterior shift of the anterior/ posterior edges and lateral shift of the lateral edge (P < 0.001). Conclusion: The tibial tunnel enlarged at the aperture by 22% 1-year after anatomic ACL reconstruction with a BTB graft, and the tunnel morphology changed in a postero-lateral direction at the aperture and into conical shape inside the tunnel. © 2019 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
1. Introduction Tibial tunnel enlargement after anterior cruciate ligament (ACL) reconstruction with a boneepatellar tendonebone (BTB) graft is a well-known phenomenon, because the proximal bone plug of a BTB graft is typically located at the femoral tunnel aperture [1e5]. The phenomenon may lead to increased knee laxity or worsen clinical outcome during the long-term follow-up, although it is
* Corresponding author. Fax: þ81 6 6879 3559. E-mail address: [email protected] (T. Mae).
insignificant in the short to mid-term [1e5]. Furthermore, tunnel enlargement often complicates revision ACL surgery as for difficulty of proper tunnel placement [6] and requirement of a two-staged procedure with bone grafting [7] due to a large bone defect at the primary tunnel location. Thus, it is important to precisely evaluate tibial tunnel enlargement after ACL reconstruction with a BTB graft. Computed tomography (CT) is more reliable for evaluating tunnel enlargement than radiography or magnetic resonance imaging (MRI) because the sclerotic tunnel margin is clearly visualized [8]. Notably, multi-planar analysis using three-dimensional (3D) CT is preferable for accurate evaluation because tunnel enlargement
https://doi.org/10.1016/j.jos.2019.01.004 0949-2658/© 2019 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
Please cite this article as: Ohori T et al., Tibial tunnel enlargement after anatomic anterior cruciate ligament reconstruction with a boneepatellar tendonebone graft. Part 1: Morphological change in the tibial tunnel, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.01.004
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occurs in multiple directions [9,10]. Tunnel morphological change after anatomic ACL reconstruction with hamstring tendon grafts was previously investigated using 3D CT, and it was demonstrated that the tunnel enlarged in the direction reflected by the ACL fiber orientation [11,12]. However, to the best of our knowledge, there has been few reports of evaluating tunnel morphological change after ACL reconstruction with a BTB graft using 3D CT. The objective of this study was to evaluate the tibial tunnel enlargement including the morphological change after anatomic ACL reconstruction with a BTB graft using 3D CT models. It was hypothesized that the tibial tunnel would enlarge in the direction reflected by the ACL fiber orientation. 2. Materials and methods From April 2010 to January 2017, 18 patients with unilateral ACL injury who underwent the anatomic rectangular-tunnel (ART) ACL reconstruction with a BTB graft in an inside-out method and consented to take CT examinations at 3 weeks and 1 year after surgery were included. We perform this procedure mainly for patients with strenuous activity, such as male athletes engaged in contact sports. The cases with revision surgery, multi-ligamentous injury, and apparent osteoarthritic change on radiographic examination (greater than grade II according to the Kellgren and Lawrence classification) were excluded. This study protocol received the approval of the institutional review board of author's institution. The participants consisted of 16 males and 2 females with a mean age of 26.6 years (range, 16e38 years) at the time of surgery. Preoperative Tegner activity level scale ranged from 7 to 9 with a mean scale of 8.1. Mean preoperative side-to-side difference (SSD) of the anterior knee laxity, as measured by a KT-2000 Knee Ligament Arthrometer (MEDmetric, San Diego, CA, USA) under a manual maximum anterior tibial load, was 7.4 mm (range, 5e15 mm). The cause of the ACL injury was trauma related to sporting activity in all the cases. All meniscal tears including five lateral, three medial, and one bilateral tears were treated by meniscal repairs, whereas no meniscectomies were performed. There were no patients with severe articular cartilage damage greater than grade II according to the Outerbridge classification system (Table 1).
USA), and two leading sutures were sewn on each bone plug including the boneetendon junction. The tibial bone plug was assigned to the femoral end of the graft, and the patellar bone plug to the tibial end. The torn ACL was removed to clearly visualize the ACL footprint. Two 2.4-mm guide pins with a 5-mm distance were inserted in parallel from the center of the femoral footprint [16] to the lateral femoral cortex in an inside-out method. The proximal pin was overdrilled with a 5-mm cannulated drill bit to the lateral femoral cortex, whereas the distal pin to a 20-mm depth. The continuous round holes were dilated into a 5 10 20-mm parallelepiped socket with the 5 10-mm cannulated dilator (Smith & Nephew Endoscopy). For the tibia, a 2.4-mm guide pin was inserted from the medial tibial cortex to the anteromedial portion of the tibial footprint [17] with a tibial tip aimer set at 45 angle (Smith & Nephew Endoscopy). Another 2.4-mm guide pin was inserted behind the anterior pin with a 5-mm distance in parallel using the 10-mm offset drill guide (Smith & Nephew Endoscopy). These pins were over-drilled with a 5-mm cannulated drill bit, followed by dilation into a 5 10-mm rectangle with the 5 10-mm cannulated dilator (Smith & Nephew Endoscopy). The BTB graft was passed through the tibial tunnel into the femoral socket with the cancellous bone surface of the plug kept anteriorly by pulling the leading sutures. For femoral fixation, a 6mm interference screw with a 20e30-mm length was introduced to the proximal/posterior corner of the femoral socket, confirming that the boneetendon junction matched the aperture of the femoral socket. Then, the sutures of the tibial end were tied to a Double Spike Plate (DSP; MEIRA). The DSP was connected to the tensioner installed in a tensioning boot and manually pulled repetitively to remove the creep of the grafts. Finally, tibial fixation was achieved by anchoring the DSP to the tibia with a cancellous screw under an initial tension of 20 N at 20 of knee flexion. After immobilization with a knee brace for 1 week, range of motion exercises was started. Partial weight-bearing, full weightbearing, and jogging were permitted 2 weeks, 4 weeks, and 3 months after surgery, respectively. Return to previous sporting activity was allowed 7e9 months after surgery, depending on the recovery of the extensor and flexor power of the knee (more than 80% of the contralateral healthy side).
2.1. Surgical technique and postoperative rehabilitation 2.2. Cross-sectional area and enlargement rate of the tibial tunnel The ART ACL reconstruction with a BTB autograft was performed as previously described [13e15]. The BTB graft with a 10-mm width was harvested from the central portion of the medial half of the patellar tendon. As the graft has longer and shorter sides in its tendinous portion, the longer side was assigned to the anteromedial side of the graft, whereas the shorter side to the posterolateral side. The bone plugs at both ends were shaped into 5-mm thick 10-mm wide 15-mm long parallelepiped with the graft sizing template (Smith & Nephew Endoscopy, Andover, MA, Table 1 Patient demographic data. Sex Age, years Tegner activity level scale SSD of the anterior knee laxitya, mm Meniscal tears Articular cartilage damage greater than grade IIb
16 males/2 females 26.6 ± 6.3 (16e38) 8.1 ± 0.9 (7e9) 7.4 ± 2.5 (5e15) 5 lateral/3 medial/1 bilateral None
Mean ± standard deviation (range). a Measured by a KT-2000 Arthrometer. b According to the Outerbridge classification system. SSD, side-to-side difference.
CT scans were taken at 3 weeks and 1 year after surgery with a CT scanner (Discovery CT 750HD; General Electric, Boston, MA, USA). The volume area included 10-cm above and below the knee joint line. The beam collimation was 16 mm, the tube voltage/ current was 200 mA/120 kV, the acquisition matrix was 512 512, the field of view was 180 mm, and the slice thickness was 0.625 mm. It was considered that the bone tunnel at 3 weeks after surgery was equivalent to that created intraoperatively based on the previous report [12]. 3D CT models of the tibia, the tibial tunnel, and the bone plug at 3 weeks and 1 year after surgery were reconstructed from the Digital Imaging and Communications in Medicine (DICOM) data using a Visualization Tool Kit-based (Kitware Inc., Clifton Park, NY, USA) original program [18]. The 3D model of the tibia at 1 year after surgery was superimposed on to that at 3 weeks using a surface registration technique, and the translation/rotation matrix was obtained. This technique was performed by independently implementing the iterative closest point algorithm with the least-squared method to match the two models [19]. Then, the 3D model of the tibial tunnel at 1 year after surgery was superimposed on to that at 3 weeks by applying the obtained translation/rotation matrix (Fig. 1a).
Please cite this article as: Ohori T et al., Tibial tunnel enlargement after anatomic anterior cruciate ligament reconstruction with a boneepatellar tendonebone graft. Part 1: Morphological change in the tibial tunnel, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.01.004
T. Ohori et al. / Journal of Orthopaedic Science xxx (xxxx) xxx
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Fig. 1. (a) Superimposition of the three-dimensional models (tibial tunnel: yellow and blue, bone plug: green). (b) Measurement of the cross-sectional area of the tibial tunnel (tunnel axis: black arrow-head).
The axis of the tibial tunnel at 3 weeks after surgery was defined as the longitudinal axis of the principal axes of inertia (eigenvectors of the tensor of inertia). The centroids of the numerous triangular facets forming the surface of the 3D model of the tibial tunnel were used for calculating the moment arm around the axis, and the principal axes of inertia were automatically determined. Then, the cross-sectional area (CSA) of the tibial tunnel was evaluated by cutting the 3D construct along the planes perpendicular to the tunnel axis. “The aperture” was defined as the most proximal plane completely surrounded by bony area, and the CSA was evaluated at the aperture and 5, 10, and 15-mm distal from the aperture. The CSA was measured at 3 weeks and 1 year after surgery, respectively, and compared between the two time points. The tunnel enlargement rate from 3 weeks to 1 year after surgery was also calculated (Fig. 1b). In addition, the tendon length inside the tunnel was measured on the 3D models at 3 weeks after surgery as the distance between the aperture and the proximal edge of the bone plug because it has been frequently reported that tibial tunnel enlargement after ACL reconstruction with a BTB graft was related to greater tendon length inside the tunnel [20e22]. 2.3. Locations of the center and the edges of the tunnel footprint The locations of the center and the edges of the tunnel footprint were measured according to the previously reported coordinate
system for the tibial plateau surface [23]. Upper-viewed images of the tibial 3D models at the two time points on the plane parallel to the tibial plateau were obtained. The outline of the tunnel footprint was determined by connecting the manually plotted multiple points (over 30 plots) using ImageJ software (National Institutes of Health, Bethesda, MD, USA), and the center of the tunnel footprint was automatically determined. The transverse tangent line between the most posterior margins of the medial and the lateral tibial condyles was defined as the posterior border. The longitudinal lines perpendicular to the transverse line and tangential to the medial and the lateral margins of the tibial plateau were defined as the medial and the lateral border, respectively. The transverse line parallel to the posterior border and tangential to the anterior margin of the tibial plateau was defined as the anterior border. The location of the center of the tunnel footprint was measured as percentages of the anterioreposterior and the medialelateral distances on the tibial plateau from the anterior and the medial borders, respectively (Fig. 2a). The locations of the anterior and posterior edges of the tunnel footprint were measured as a percentage of the anterioreposterior distance on the tibial plateau, whereas those of the medial and lateral edges were measured as a percentage of the medialelateral distance on the plateau (Fig. 2b). By comparing the locations of the center and the edges between the two time points, the translation of the tunnel footprint was evaluated.
Please cite this article as: Ohori T et al., Tibial tunnel enlargement after anatomic anterior cruciate ligament reconstruction with a boneepatellar tendonebone graft. Part 1: Morphological change in the tibial tunnel, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.01.004
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Fig. 2. (a) Measurement of the location of the center of the tunnel footprint. (b) Measurement of the locations of the anterior, posterior, medial, and lateral edges of the tunnel footprint. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article)
3. Results
The intra- and inter-observer intra-class correlation coefficient (ICC) was 0.98e0.99 (standard deviation, 0.1e0.4) for the measurement of the CSA and 0.94e0.98 (standard deviation, 0.2e0.7) for the measurement of the locations of the center and the edges of the tunnel footprint [11].
3.1. CSA and enlargement rate of the tibial tunnel At the tunnel aperture, the CSA of the tibial tunnel at 1 year after surgery was significantly larger than that at 3 weeks (P < 0.001), and the mean tunnel enlargement rate was 21.9%. In contrast, the CSA at 1 year after surgery was significantly smaller than that at 3 weeks at 10 and 15-mm distal from the aperture (P ¼ 0.041 and < 0.001, respectively) (Table 2). The mean tendon length inside the tunnel was 8.7 mm (range, 3.3e15.5 mm). Under single linear regression analysis, the tendon length inside the tunnel had a significant positive correlation to the tibial tunnel enlargement rate at the aperture (r ¼ 0.729, P < 0.001) and 5-mm distal from the aperture (r ¼ 0.615, P ¼ 0.007), respectively (Fig. 3).
2.4. Clinical examination Range of motion, knee swelling, patellar ballottement, and knee instability involving Lachman test and pivot shift test were examined at 1 year after surgery. The pivot shift test was evaluated according to the clinical grade of the International Knee Documentation Committee guidelines [24]. In addition, SSD of the anterior knee laxity, as measured by a KT-2000 Arthrometer under a manual maximum anterior tibial load, Lysholm score, and Tegner activity level scale were also evaluated.
3.2. Locations of the center and the edges of the tunnel footprint
2.5. Statistical analysis
The center of the tunnel footprint significantly shifted posterolaterally (P < 0.001). The anterior and posterior edges of the tunnel footprint demonstrated significant posterior shifts, while the lateral edge of the tunnel footprint demonstrated significant lateral shift (P < 0.001) (Table 3).
All statistical analyses were performed with JMP software (JMP Pro version 13.1.0; SAS Institute, Cary, NC, USA). Power analysis (power: 0.8; a: 0.05; detectable difference: 8.0; standard deviation: 5.1) indicated a sample size requirement of 15 subjects for valid comparisons. The normality of the distribution of the obtained data was confirmed by the ShapiroeWilk W test. Therefore, the CSA of the tibial tunnel and the locations of the center and the edges of the tunnel footprint were compared as the change of parametric variables between the two time points with the paired t-test. The relationship between the tibial tunnel enlargement rate and the tendon length inside the tunnel was investigated by single linear regression analysis (Pearson's correlation analysis). In addition, the relationships of the tibial tunnel enlargement rate with postoperative SSD of the anterior knee laxity, Lysholm score, and Tegner activity level scale were also investigated by single linear regression analysis. Values of P < 0.05 were considered statistically significant.
3.3. Clinical examination There was no patient with loss of knee flexion/extension exceeding 5 , knee swelling, patellar ballottement, or positive Lachman test at 1 year after surgery. The pivot shift test was negative in all patients except for one graded as a glide. The mean SSD of the anterior knee laxity was 0.5 mm (range, 1e1 mm), the mean Lysholm score was 94.1 (range, 89e100), and the mean Tegner activity level scale was 7.3 (range, 5e9) at the final followup. Only 3 out of 18 patients reduced their activity level due to
Table 2 Cross-sectional area and enlargement rate of the tibial tunnel. Cross-sectional area (mm2) 3 weeks post-op.a At the aperture 5-mm distal from the aperture 10-mm distal from the aperture 15-mm distal from the aperture
51.4 50.4 43.9 37.5
± ± ± ±
2.8 3.6 8.6 7.6
Enlargement rate (%) [(b-a)/a 100]
P value (a vs. b)
21.9 ± 14.1 7.3 ± 15.7 11.5 ± 20.5 33.1 ± 20.9
<0.001a n.s. 0.041a <0.001a
1 year post-op.b 62.5 54.1 39.8 25.5
± ± ± ±
6.2 8.7 13.8 10.1
Mean ± standard deviation, a: statistically significant difference with the paired t-test (P < 0.05). Post-op., postoperatively.
Please cite this article as: Ohori T et al., Tibial tunnel enlargement after anatomic anterior cruciate ligament reconstruction with a boneepatellar tendonebone graft. Part 1: Morphological change in the tibial tunnel, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.01.004
T. Ohori et al. / Journal of Orthopaedic Science xxx (xxxx) xxx
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Fig. 3. Positive correlation between the tendon length inside the tunnel and the tibial tunnel enlargement rate at the aperture (a) and 5-mm distal from the aperture (b) under single linear regression analysis.(For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article)
Table 3 Locations of the center and the edges of the tunnel footprint. Location (%)
Anterioreposterior direction Center Anterior edge Posterior edge Medialelateral direction Center Medial edge Lateral edge
Shift (%) (b-a)
P value (a vs. b)
37.9 ± 2.7 27.3 ± 2.9 48.9 ± 3.5
1.6 ± 0.8 0.8 ± 0.7 2.2 ± 1.2
<0.001a <0.001a <0.001a
47.4 ± 2.5 42.4 ± 2.9 51.9 ± 2.6
1.8 ± 0.6 0.6 ± 1.1 2.7 ± 1.2
<0.001a n.s. <0.001a
3 weeks post-op.a
1 year post-op.b
36.3 ± 2.7 26.4 ± 2.9 46.7 ± 3.8 45.6 ± 2.3 41.9 ± 2.6 49.3 ± 2.3
Mean ± standard deviation, a: statistically significant difference with the paired t-test (P < 0.05). Post-op., postoperatively.
graduation from school or fear of re-injury. There was no significant relationship between these clinical outcomes and the tibial tunnel enlargement rate under single linear regression analysis. 4. Discussion The principal finding of this study was that the tibial tunnel enlarged at the aperture by 21.9% with the morphological change in a postero-lateral direction reflected by the ACL fiber orientation 1year after the ART ACL reconstruction with a BTB graft. It has been reported that the tibial tunnel enlargement rate after ACL reconstruction with a BTB graft was 10e31% during a 9e24month follow-up period by measuring the tunnel diameter on two-dimensional radiograph or CT [5,22,25,26]. In contrast, the present study demonstrated that the tibial tunnel enlargement rate at the aperture after the ART ACL reconstruction with a BTB graft was 21.9% at 1 year after surgery under evaluation in CSA using 3D CT. It was considered that the enlargement rate after the ART procedure was relatively small compared to those in the previous reports because the estimated enlargement rate “in diameter” was almost 10%. This might be attributable to performing anatomic ACL reconstruction with a lower tension for graft fixation and conducting relatively gentle rehabilitation programs. The rectangulartunnels matched to the shape of the patellar tendon might also contribute to prevent inflammatory response due to synovial fluid propagation into the tunnel, while round tunnels must have some space around the graft inside the tunnel. The tunnel enlargement rate decreased gradually from the aperture toward the inside of the tunnel, and the tunnel morphology changed into conical shape in accordance with the
previous reports [2,3,27]. The distal bone plug usually exists inside the tibial tunnel in ACL reconstruction with a BTB graft as the proximal boneetendon junction of the graft matches the femoral tunnel aperture. The motion of the distal bone plug inside the tibial tunnel must be quite a little because the hardly-distorted bone plug snugly fits into the tunnel. Consequently, the distal bone plug is gradually incorporated with the tibial tunnel wall after surgery. Mechanical stress to the tunnel wall is generated from the tendinous portion of the graft and should be considered a rotational moment around the bone plug as a fulcrum. Thus, the mechanical stress increases gradually from the distal bone plug to the tunnel aperture. Therefore, the tibial tunnel forms from cylindrical into conical shape and the tendon length inside the tunnel positively correlates to the tibial tunnel enlargement after ACL reconstruction with a BTB graft as demonstrated in the present study. The clinical relevance of this study is that the proper tibial tunnel location in ACL reconstruction should be determined considering the tunnel enlargement in a postero-lateral direction after surgery. Although we performed anatomic ACL reconstruction with a lower initial tension and gentle postoperative rehabilitation, tibial tunnel enlargement in a postero-lateral direction occurred to some extent. Tunnel enlargement after ACL reconstruction may lead to increased knee laxity or worsen clinical outcome in the longer follow-up. Therefore, creation of the tibial tunnel within the antero-medial area in the tibial ACL footprint may be preferable. There were some limitations in the present study. First, the cohort in this study composed of mainly male patients with high activity level. The results may not be applicable to female patients or those with low activity level. Second, the tibial tunnel enlargement might already occur at 3 weeks after surgery [28], although our
Please cite this article as: Ohori T et al., Tibial tunnel enlargement after anatomic anterior cruciate ligament reconstruction with a boneepatellar tendonebone graft. Part 1: Morphological change in the tibial tunnel, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.01.004
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previous report demonstrated that the CSA of the tibial tunnel at 3 weeks was equivalent to that created intraoperatively after anatomic ACL reconstruction with hamstring tendon grafts [12]. Third, the patients were followed only for 1 year. The tibial tunnel enlargement after ACL reconstruction with a BTB graft occurs during 3e9 months after surgery and remains unchanged thereafter [2,5,27]. However, we need to continue to follow-up the patients over 1 year after surgery. Finally, the evaluation was performed on only one surgical procedure. Tibial tunnel enlargement after ACL reconstruction with hamstring tendon grafts is greater than that with a BTB graft on two-dimensional radiograph [3,25,29]. We need to compare the results of this study to those after anatomic ACL reconstruction with hamstring tendon grafts. 5. Conclusion The tibial tunnel enlarged at the aperture by 22% 1-year after anatomic ACL reconstruction with a BTB graft, and the tunnel morphology changed in a postero-lateral direction at the aperture and into conical shape inside the tunnel. Conflict of interest The authors declare that they have no conflict of interest. Acknowledgements The authors would like to thank Dr. Tsuyoshi Murase and Mr. Ryoji Nakao for developing the software. References [1] Fahey M, Indelicato PA. Bone tunnel enlargement after anterior cruciate ligament replacement. Am J Sports Med 1994 MayeJun;22(3):410e4. [2] Peyrache MD, Djian P, Christel P, Witvoet J. Tibial tunnel enlargement after anterior cruciate ligament reconstruction by autogenous boneepatellar tendonebone graft. Knee Surg Sports Traumatol Arthrosc 1996;4(1):2e8. [3] Clatworthy MG, Annear P, Bulow JU, Bartlett RJ. Tunnel widening in anterior cruciate ligament reconstruction: a prospective evaluation of hamstring and patella tendon grafts. Knee Surg Sports Traumatol Arthrosc 1999;7(3):138e45. [4] Zijl JA, Kleipool AE, Willems WJ. Comparison of tibial tunnel enlargement after anterior cruciate ligament reconstruction using patellar tendon autograft of allograft. Am J Sports Med 2000 JuleAug;28(4):547e51. [5] Fink C, Zapp M, Benedetto KP, Hackl W, Hoser C, Rieger M. Tibial tunnel enlargement following anterior cruciate ligament reconstruction with patellar tendon autograft. Arthroscopy 2001 Feb;17(2):138e43. [6] Wilson TC, Kantaras A, Atay A, Johnson DL. Tunnel enlargement after anterior cruciate ligament surgery. Am J Sports Med 2004 Mar;32(2):543e9. [7] Thomas NP, Kankate R, Wandless F, Pandit H. Revision anterior cruciate ligament reconstruction using a 2-staged technique with bone grafting of the tibial tunnel. Am J Sports Med 2005 Nov;33(11):1701e9. [8] Marchant Jr MH, Willimon SC, Vinson E, Pietrobon R, Garrett WE, Higgins LD. Comparison of plain radiography, computed tomography, and magnetic resonance imaging in the evaluation of bone tunnel widening after anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 2010 Aug;18(8):1059e64. [9] Robbrecht C, Claes S, Cromheecke M, Mahieu P, Kakavelakis K, Victor J, Bellemans J, Verdonk P. Reliability of a semi-automated 3D-CT measuring method for tunnel diameters after anterior cruciate ligament reconstruction: a comparison between soft-tissue single-bundle allograft vs. autograft. Knee 2014 Oct;21(5):926e31. [10] de Beus A, Koch JE, Hirschmann A, Hirschmann MT. How to evaluate bone tunnel widening after ACL reconstruction - a critical review. Muscles Ligaments Tendons J 2017 Sep 18;7(2):230e9.
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Please cite this article as: Ohori T et al., Tibial tunnel enlargement after anatomic anterior cruciate ligament reconstruction with a boneepatellar tendonebone graft. Part 1: Morphological change in the tibial tunnel, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.01.004
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Original Article
Tibial tunnel enlargement after anatomic anterior cruciate ligament reconstruction with a boneepatellar tendonebone graft. Part 1: Morphological change in the tibial tunnel Tomoki Ohori a, Tatsuo Mae a, *, Konsei Shino b, Yuta Tachibana c, Hideki Yoshikawa a, Ken Nakata a a b c
Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2, Yamada-oka, Suita, Osaka, 565-0871, Japan Sports Orthopaedic Surgery Center, Yukioka Hospital, 2-2-3, Ukita, Kita-ku, Osaka, Osaka, 530-0021, Japan Department of Sports Orthopaedics, Osaka Rosai Hospital, 1179-3, Nagasone-cho, Kita-ku, Sakai, Osaka, 591-8025, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 26 October 2018 Received in revised form 7 January 2019 Accepted 15 January 2019 Available online xxx
Background: Three-dimensional (3D) computed tomography (CT) is reliable and accurate imaging modality for evaluating tunnel enlargement after anterior cruciate ligament (ACL) reconstruction. The purpose of this study was to evaluate the tibial tunnel enlargement including the morphological change after anatomic ACL reconstruction with a boneepatellar tendonebone (BTB) graft using 3D CT models. Methods: Eighteen patients with unilateral ACL rupture were included. The anatomic rectangular-tunnel (ART) ACL reconstruction with a BTB autograft was performed. 3D CT models of the tibia, the tibial tunnel, and the bone plug at 3 weeks and 1 year after surgery were reconstructed and superimposed using a surface registration technique. The cross-sectional area (CSA) of the tibial tunnel perpendicular to the tunnel axis was evaluated at the aperture and 5, 10, and 15-mm distal from the aperture. The CSA was measured at 3 weeks and 1 year after surgery and compared between the two time points. The locations of the center and the anterior, posterior, medial, and lateral edges of the tunnel footprint were also evaluated based on the coordinate system for the tibial plateau and compared between the two time points. Results: At the aperture, the CSA of the tibial tunnel at 1 year after surgery was significantly larger by 21.9% than that at 3 weeks (P < 0.001). In contrast, the CSA at 1 year was significantly smaller than that at 3 weeks at 10 and 15-mm distal from the aperture (P ¼ 0.041 and < 0.001, respectively). The center of the tunnel footprint significantly shifted postero-laterally with significant posterior shift of the anterior/ posterior edges and lateral shift of the lateral edge (P < 0.001). Conclusion: The tibial tunnel enlarged at the aperture by 22% 1-year after anatomic ACL reconstruction with a BTB graft, and the tunnel morphology changed in a postero-lateral direction at the aperture and into conical shape inside the tunnel. © 2019 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
1. Introduction Tibial tunnel enlargement after anterior cruciate ligament (ACL) reconstruction with a boneepatellar tendonebone (BTB) graft is a well-known phenomenon, because the proximal bone plug of a BTB graft is typically located at the femoral tunnel aperture [1e5]. The phenomenon may lead to increased knee laxity or worsen clinical outcome during the long-term follow-up, although it is
* Corresponding author. Fax: þ81 6 6879 3559. E-mail address: [email protected] (T. Mae).
insignificant in the short to mid-term [1e5]. Furthermore, tunnel enlargement often complicates revision ACL surgery as for difficulty of proper tunnel placement [6] and requirement of a two-staged procedure with bone grafting [7] due to a large bone defect at the primary tunnel location. Thus, it is important to precisely evaluate tibial tunnel enlargement after ACL reconstruction with a BTB graft. Computed tomography (CT) is more reliable for evaluating tunnel enlargement than radiography or magnetic resonance imaging (MRI) because the sclerotic tunnel margin is clearly visualized [8]. Notably, multi-planar analysis using three-dimensional (3D) CT is preferable for accurate evaluation because tunnel enlargement
https://doi.org/10.1016/j.jos.2019.01.004 0949-2658/© 2019 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
Please cite this article as: Ohori T et al., Tibial tunnel enlargement after anatomic anterior cruciate ligament reconstruction with a boneepatellar tendonebone graft. Part 1: Morphological change in the tibial tunnel, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.01.004
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occurs in multiple directions [9,10]. Tunnel morphological change after anatomic ACL reconstruction with hamstring tendon grafts was previously investigated using 3D CT, and it was demonstrated that the tunnel enlarged in the direction reflected by the ACL fiber orientation [11,12]. However, to the best of our knowledge, there has been few reports of evaluating tunnel morphological change after ACL reconstruction with a BTB graft using 3D CT. The objective of this study was to evaluate the tibial tunnel enlargement including the morphological change after anatomic ACL reconstruction with a BTB graft using 3D CT models. It was hypothesized that the tibial tunnel would enlarge in the direction reflected by the ACL fiber orientation. 2. Materials and methods From April 2010 to January 2017, 18 patients with unilateral ACL injury who underwent the anatomic rectangular-tunnel (ART) ACL reconstruction with a BTB graft in an inside-out method and consented to take CT examinations at 3 weeks and 1 year after surgery were included. We perform this procedure mainly for patients with strenuous activity, such as male athletes engaged in contact sports. The cases with revision surgery, multi-ligamentous injury, and apparent osteoarthritic change on radiographic examination (greater than grade II according to the Kellgren and Lawrence classification) were excluded. This study protocol received the approval of the institutional review board of author's institution. The participants consisted of 16 males and 2 females with a mean age of 26.6 years (range, 16e38 years) at the time of surgery. Preoperative Tegner activity level scale ranged from 7 to 9 with a mean scale of 8.1. Mean preoperative side-to-side difference (SSD) of the anterior knee laxity, as measured by a KT-2000 Knee Ligament Arthrometer (MEDmetric, San Diego, CA, USA) under a manual maximum anterior tibial load, was 7.4 mm (range, 5e15 mm). The cause of the ACL injury was trauma related to sporting activity in all the cases. All meniscal tears including five lateral, three medial, and one bilateral tears were treated by meniscal repairs, whereas no meniscectomies were performed. There were no patients with severe articular cartilage damage greater than grade II according to the Outerbridge classification system (Table 1).
USA), and two leading sutures were sewn on each bone plug including the boneetendon junction. The tibial bone plug was assigned to the femoral end of the graft, and the patellar bone plug to the tibial end. The torn ACL was removed to clearly visualize the ACL footprint. Two 2.4-mm guide pins with a 5-mm distance were inserted in parallel from the center of the femoral footprint [16] to the lateral femoral cortex in an inside-out method. The proximal pin was overdrilled with a 5-mm cannulated drill bit to the lateral femoral cortex, whereas the distal pin to a 20-mm depth. The continuous round holes were dilated into a 5 10 20-mm parallelepiped socket with the 5 10-mm cannulated dilator (Smith & Nephew Endoscopy). For the tibia, a 2.4-mm guide pin was inserted from the medial tibial cortex to the anteromedial portion of the tibial footprint [17] with a tibial tip aimer set at 45 angle (Smith & Nephew Endoscopy). Another 2.4-mm guide pin was inserted behind the anterior pin with a 5-mm distance in parallel using the 10-mm offset drill guide (Smith & Nephew Endoscopy). These pins were over-drilled with a 5-mm cannulated drill bit, followed by dilation into a 5 10-mm rectangle with the 5 10-mm cannulated dilator (Smith & Nephew Endoscopy). The BTB graft was passed through the tibial tunnel into the femoral socket with the cancellous bone surface of the plug kept anteriorly by pulling the leading sutures. For femoral fixation, a 6mm interference screw with a 20e30-mm length was introduced to the proximal/posterior corner of the femoral socket, confirming that the boneetendon junction matched the aperture of the femoral socket. Then, the sutures of the tibial end were tied to a Double Spike Plate (DSP; MEIRA). The DSP was connected to the tensioner installed in a tensioning boot and manually pulled repetitively to remove the creep of the grafts. Finally, tibial fixation was achieved by anchoring the DSP to the tibia with a cancellous screw under an initial tension of 20 N at 20 of knee flexion. After immobilization with a knee brace for 1 week, range of motion exercises was started. Partial weight-bearing, full weightbearing, and jogging were permitted 2 weeks, 4 weeks, and 3 months after surgery, respectively. Return to previous sporting activity was allowed 7e9 months after surgery, depending on the recovery of the extensor and flexor power of the knee (more than 80% of the contralateral healthy side).
2.1. Surgical technique and postoperative rehabilitation 2.2. Cross-sectional area and enlargement rate of the tibial tunnel The ART ACL reconstruction with a BTB autograft was performed as previously described [13e15]. The BTB graft with a 10-mm width was harvested from the central portion of the medial half of the patellar tendon. As the graft has longer and shorter sides in its tendinous portion, the longer side was assigned to the anteromedial side of the graft, whereas the shorter side to the posterolateral side. The bone plugs at both ends were shaped into 5-mm thick 10-mm wide 15-mm long parallelepiped with the graft sizing template (Smith & Nephew Endoscopy, Andover, MA, Table 1 Patient demographic data. Sex Age, years Tegner activity level scale SSD of the anterior knee laxitya, mm Meniscal tears Articular cartilage damage greater than grade IIb
16 males/2 females 26.6 ± 6.3 (16e38) 8.1 ± 0.9 (7e9) 7.4 ± 2.5 (5e15) 5 lateral/3 medial/1 bilateral None
Mean ± standard deviation (range). a Measured by a KT-2000 Arthrometer. b According to the Outerbridge classification system. SSD, side-to-side difference.
CT scans were taken at 3 weeks and 1 year after surgery with a CT scanner (Discovery CT 750HD; General Electric, Boston, MA, USA). The volume area included 10-cm above and below the knee joint line. The beam collimation was 16 mm, the tube voltage/ current was 200 mA/120 kV, the acquisition matrix was 512 512, the field of view was 180 mm, and the slice thickness was 0.625 mm. It was considered that the bone tunnel at 3 weeks after surgery was equivalent to that created intraoperatively based on the previous report [12]. 3D CT models of the tibia, the tibial tunnel, and the bone plug at 3 weeks and 1 year after surgery were reconstructed from the Digital Imaging and Communications in Medicine (DICOM) data using a Visualization Tool Kit-based (Kitware Inc., Clifton Park, NY, USA) original program [18]. The 3D model of the tibia at 1 year after surgery was superimposed on to that at 3 weeks using a surface registration technique, and the translation/rotation matrix was obtained. This technique was performed by independently implementing the iterative closest point algorithm with the least-squared method to match the two models [19]. Then, the 3D model of the tibial tunnel at 1 year after surgery was superimposed on to that at 3 weeks by applying the obtained translation/rotation matrix (Fig. 1a).
Please cite this article as: Ohori T et al., Tibial tunnel enlargement after anatomic anterior cruciate ligament reconstruction with a boneepatellar tendonebone graft. Part 1: Morphological change in the tibial tunnel, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.01.004
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Fig. 1. (a) Superimposition of the three-dimensional models (tibial tunnel: yellow and blue, bone plug: green). (b) Measurement of the cross-sectional area of the tibial tunnel (tunnel axis: black arrow-head).
The axis of the tibial tunnel at 3 weeks after surgery was defined as the longitudinal axis of the principal axes of inertia (eigenvectors of the tensor of inertia). The centroids of the numerous triangular facets forming the surface of the 3D model of the tibial tunnel were used for calculating the moment arm around the axis, and the principal axes of inertia were automatically determined. Then, the cross-sectional area (CSA) of the tibial tunnel was evaluated by cutting the 3D construct along the planes perpendicular to the tunnel axis. “The aperture” was defined as the most proximal plane completely surrounded by bony area, and the CSA was evaluated at the aperture and 5, 10, and 15-mm distal from the aperture. The CSA was measured at 3 weeks and 1 year after surgery, respectively, and compared between the two time points. The tunnel enlargement rate from 3 weeks to 1 year after surgery was also calculated (Fig. 1b). In addition, the tendon length inside the tunnel was measured on the 3D models at 3 weeks after surgery as the distance between the aperture and the proximal edge of the bone plug because it has been frequently reported that tibial tunnel enlargement after ACL reconstruction with a BTB graft was related to greater tendon length inside the tunnel [20e22]. 2.3. Locations of the center and the edges of the tunnel footprint The locations of the center and the edges of the tunnel footprint were measured according to the previously reported coordinate
system for the tibial plateau surface [23]. Upper-viewed images of the tibial 3D models at the two time points on the plane parallel to the tibial plateau were obtained. The outline of the tunnel footprint was determined by connecting the manually plotted multiple points (over 30 plots) using ImageJ software (National Institutes of Health, Bethesda, MD, USA), and the center of the tunnel footprint was automatically determined. The transverse tangent line between the most posterior margins of the medial and the lateral tibial condyles was defined as the posterior border. The longitudinal lines perpendicular to the transverse line and tangential to the medial and the lateral margins of the tibial plateau were defined as the medial and the lateral border, respectively. The transverse line parallel to the posterior border and tangential to the anterior margin of the tibial plateau was defined as the anterior border. The location of the center of the tunnel footprint was measured as percentages of the anterioreposterior and the medialelateral distances on the tibial plateau from the anterior and the medial borders, respectively (Fig. 2a). The locations of the anterior and posterior edges of the tunnel footprint were measured as a percentage of the anterioreposterior distance on the tibial plateau, whereas those of the medial and lateral edges were measured as a percentage of the medialelateral distance on the plateau (Fig. 2b). By comparing the locations of the center and the edges between the two time points, the translation of the tunnel footprint was evaluated.
Please cite this article as: Ohori T et al., Tibial tunnel enlargement after anatomic anterior cruciate ligament reconstruction with a boneepatellar tendonebone graft. Part 1: Morphological change in the tibial tunnel, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.01.004
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Fig. 2. (a) Measurement of the location of the center of the tunnel footprint. (b) Measurement of the locations of the anterior, posterior, medial, and lateral edges of the tunnel footprint. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article)
3. Results
The intra- and inter-observer intra-class correlation coefficient (ICC) was 0.98e0.99 (standard deviation, 0.1e0.4) for the measurement of the CSA and 0.94e0.98 (standard deviation, 0.2e0.7) for the measurement of the locations of the center and the edges of the tunnel footprint [11].
3.1. CSA and enlargement rate of the tibial tunnel At the tunnel aperture, the CSA of the tibial tunnel at 1 year after surgery was significantly larger than that at 3 weeks (P < 0.001), and the mean tunnel enlargement rate was 21.9%. In contrast, the CSA at 1 year after surgery was significantly smaller than that at 3 weeks at 10 and 15-mm distal from the aperture (P ¼ 0.041 and < 0.001, respectively) (Table 2). The mean tendon length inside the tunnel was 8.7 mm (range, 3.3e15.5 mm). Under single linear regression analysis, the tendon length inside the tunnel had a significant positive correlation to the tibial tunnel enlargement rate at the aperture (r ¼ 0.729, P < 0.001) and 5-mm distal from the aperture (r ¼ 0.615, P ¼ 0.007), respectively (Fig. 3).
2.4. Clinical examination Range of motion, knee swelling, patellar ballottement, and knee instability involving Lachman test and pivot shift test were examined at 1 year after surgery. The pivot shift test was evaluated according to the clinical grade of the International Knee Documentation Committee guidelines [24]. In addition, SSD of the anterior knee laxity, as measured by a KT-2000 Arthrometer under a manual maximum anterior tibial load, Lysholm score, and Tegner activity level scale were also evaluated.
3.2. Locations of the center and the edges of the tunnel footprint
2.5. Statistical analysis
The center of the tunnel footprint significantly shifted posterolaterally (P < 0.001). The anterior and posterior edges of the tunnel footprint demonstrated significant posterior shifts, while the lateral edge of the tunnel footprint demonstrated significant lateral shift (P < 0.001) (Table 3).
All statistical analyses were performed with JMP software (JMP Pro version 13.1.0; SAS Institute, Cary, NC, USA). Power analysis (power: 0.8; a: 0.05; detectable difference: 8.0; standard deviation: 5.1) indicated a sample size requirement of 15 subjects for valid comparisons. The normality of the distribution of the obtained data was confirmed by the ShapiroeWilk W test. Therefore, the CSA of the tibial tunnel and the locations of the center and the edges of the tunnel footprint were compared as the change of parametric variables between the two time points with the paired t-test. The relationship between the tibial tunnel enlargement rate and the tendon length inside the tunnel was investigated by single linear regression analysis (Pearson's correlation analysis). In addition, the relationships of the tibial tunnel enlargement rate with postoperative SSD of the anterior knee laxity, Lysholm score, and Tegner activity level scale were also investigated by single linear regression analysis. Values of P < 0.05 were considered statistically significant.
3.3. Clinical examination There was no patient with loss of knee flexion/extension exceeding 5 , knee swelling, patellar ballottement, or positive Lachman test at 1 year after surgery. The pivot shift test was negative in all patients except for one graded as a glide. The mean SSD of the anterior knee laxity was 0.5 mm (range, 1e1 mm), the mean Lysholm score was 94.1 (range, 89e100), and the mean Tegner activity level scale was 7.3 (range, 5e9) at the final followup. Only 3 out of 18 patients reduced their activity level due to
Table 2 Cross-sectional area and enlargement rate of the tibial tunnel. Cross-sectional area (mm2) 3 weeks post-op.a At the aperture 5-mm distal from the aperture 10-mm distal from the aperture 15-mm distal from the aperture
51.4 50.4 43.9 37.5
± ± ± ±
2.8 3.6 8.6 7.6
Enlargement rate (%) [(b-a)/a 100]
P value (a vs. b)
21.9 ± 14.1 7.3 ± 15.7 11.5 ± 20.5 33.1 ± 20.9
<0.001a n.s. 0.041a <0.001a
1 year post-op.b 62.5 54.1 39.8 25.5
± ± ± ±
6.2 8.7 13.8 10.1
Mean ± standard deviation, a: statistically significant difference with the paired t-test (P < 0.05). Post-op., postoperatively.
Please cite this article as: Ohori T et al., Tibial tunnel enlargement after anatomic anterior cruciate ligament reconstruction with a boneepatellar tendonebone graft. Part 1: Morphological change in the tibial tunnel, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.01.004
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Fig. 3. Positive correlation between the tendon length inside the tunnel and the tibial tunnel enlargement rate at the aperture (a) and 5-mm distal from the aperture (b) under single linear regression analysis.(For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article)
Table 3 Locations of the center and the edges of the tunnel footprint. Location (%)
Anterioreposterior direction Center Anterior edge Posterior edge Medialelateral direction Center Medial edge Lateral edge
Shift (%) (b-a)
P value (a vs. b)
37.9 ± 2.7 27.3 ± 2.9 48.9 ± 3.5
1.6 ± 0.8 0.8 ± 0.7 2.2 ± 1.2
<0.001a <0.001a <0.001a
47.4 ± 2.5 42.4 ± 2.9 51.9 ± 2.6
1.8 ± 0.6 0.6 ± 1.1 2.7 ± 1.2
<0.001a n.s. <0.001a
3 weeks post-op.a
1 year post-op.b
36.3 ± 2.7 26.4 ± 2.9 46.7 ± 3.8 45.6 ± 2.3 41.9 ± 2.6 49.3 ± 2.3
Mean ± standard deviation, a: statistically significant difference with the paired t-test (P < 0.05). Post-op., postoperatively.
graduation from school or fear of re-injury. There was no significant relationship between these clinical outcomes and the tibial tunnel enlargement rate under single linear regression analysis. 4. Discussion The principal finding of this study was that the tibial tunnel enlarged at the aperture by 21.9% with the morphological change in a postero-lateral direction reflected by the ACL fiber orientation 1year after the ART ACL reconstruction with a BTB graft. It has been reported that the tibial tunnel enlargement rate after ACL reconstruction with a BTB graft was 10e31% during a 9e24month follow-up period by measuring the tunnel diameter on two-dimensional radiograph or CT [5,22,25,26]. In contrast, the present study demonstrated that the tibial tunnel enlargement rate at the aperture after the ART ACL reconstruction with a BTB graft was 21.9% at 1 year after surgery under evaluation in CSA using 3D CT. It was considered that the enlargement rate after the ART procedure was relatively small compared to those in the previous reports because the estimated enlargement rate “in diameter” was almost 10%. This might be attributable to performing anatomic ACL reconstruction with a lower tension for graft fixation and conducting relatively gentle rehabilitation programs. The rectangulartunnels matched to the shape of the patellar tendon might also contribute to prevent inflammatory response due to synovial fluid propagation into the tunnel, while round tunnels must have some space around the graft inside the tunnel. The tunnel enlargement rate decreased gradually from the aperture toward the inside of the tunnel, and the tunnel morphology changed into conical shape in accordance with the
previous reports [2,3,27]. The distal bone plug usually exists inside the tibial tunnel in ACL reconstruction with a BTB graft as the proximal boneetendon junction of the graft matches the femoral tunnel aperture. The motion of the distal bone plug inside the tibial tunnel must be quite a little because the hardly-distorted bone plug snugly fits into the tunnel. Consequently, the distal bone plug is gradually incorporated with the tibial tunnel wall after surgery. Mechanical stress to the tunnel wall is generated from the tendinous portion of the graft and should be considered a rotational moment around the bone plug as a fulcrum. Thus, the mechanical stress increases gradually from the distal bone plug to the tunnel aperture. Therefore, the tibial tunnel forms from cylindrical into conical shape and the tendon length inside the tunnel positively correlates to the tibial tunnel enlargement after ACL reconstruction with a BTB graft as demonstrated in the present study. The clinical relevance of this study is that the proper tibial tunnel location in ACL reconstruction should be determined considering the tunnel enlargement in a postero-lateral direction after surgery. Although we performed anatomic ACL reconstruction with a lower initial tension and gentle postoperative rehabilitation, tibial tunnel enlargement in a postero-lateral direction occurred to some extent. Tunnel enlargement after ACL reconstruction may lead to increased knee laxity or worsen clinical outcome in the longer follow-up. Therefore, creation of the tibial tunnel within the antero-medial area in the tibial ACL footprint may be preferable. There were some limitations in the present study. First, the cohort in this study composed of mainly male patients with high activity level. The results may not be applicable to female patients or those with low activity level. Second, the tibial tunnel enlargement might already occur at 3 weeks after surgery [28], although our
Please cite this article as: Ohori T et al., Tibial tunnel enlargement after anatomic anterior cruciate ligament reconstruction with a boneepatellar tendonebone graft. Part 1: Morphological change in the tibial tunnel, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.01.004
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previous report demonstrated that the CSA of the tibial tunnel at 3 weeks was equivalent to that created intraoperatively after anatomic ACL reconstruction with hamstring tendon grafts [12]. Third, the patients were followed only for 1 year. The tibial tunnel enlargement after ACL reconstruction with a BTB graft occurs during 3e9 months after surgery and remains unchanged thereafter [2,5,27]. However, we need to continue to follow-up the patients over 1 year after surgery. Finally, the evaluation was performed on only one surgical procedure. Tibial tunnel enlargement after ACL reconstruction with hamstring tendon grafts is greater than that with a BTB graft on two-dimensional radiograph [3,25,29]. We need to compare the results of this study to those after anatomic ACL reconstruction with hamstring tendon grafts. 5. Conclusion The tibial tunnel enlarged at the aperture by 22% 1-year after anatomic ACL reconstruction with a BTB graft, and the tunnel morphology changed in a postero-lateral direction at the aperture and into conical shape inside the tunnel. Conflict of interest The authors declare that they have no conflict of interest. Acknowledgements The authors would like to thank Dr. Tsuyoshi Murase and Mr. Ryoji Nakao for developing the software. References [1] Fahey M, Indelicato PA. Bone tunnel enlargement after anterior cruciate ligament replacement. Am J Sports Med 1994 MayeJun;22(3):410e4. [2] Peyrache MD, Djian P, Christel P, Witvoet J. Tibial tunnel enlargement after anterior cruciate ligament reconstruction by autogenous boneepatellar tendonebone graft. Knee Surg Sports Traumatol Arthrosc 1996;4(1):2e8. [3] Clatworthy MG, Annear P, Bulow JU, Bartlett RJ. Tunnel widening in anterior cruciate ligament reconstruction: a prospective evaluation of hamstring and patella tendon grafts. Knee Surg Sports Traumatol Arthrosc 1999;7(3):138e45. [4] Zijl JA, Kleipool AE, Willems WJ. Comparison of tibial tunnel enlargement after anterior cruciate ligament reconstruction using patellar tendon autograft of allograft. Am J Sports Med 2000 JuleAug;28(4):547e51. [5] Fink C, Zapp M, Benedetto KP, Hackl W, Hoser C, Rieger M. Tibial tunnel enlargement following anterior cruciate ligament reconstruction with patellar tendon autograft. Arthroscopy 2001 Feb;17(2):138e43. [6] Wilson TC, Kantaras A, Atay A, Johnson DL. Tunnel enlargement after anterior cruciate ligament surgery. Am J Sports Med 2004 Mar;32(2):543e9. [7] Thomas NP, Kankate R, Wandless F, Pandit H. Revision anterior cruciate ligament reconstruction using a 2-staged technique with bone grafting of the tibial tunnel. Am J Sports Med 2005 Nov;33(11):1701e9. [8] Marchant Jr MH, Willimon SC, Vinson E, Pietrobon R, Garrett WE, Higgins LD. Comparison of plain radiography, computed tomography, and magnetic resonance imaging in the evaluation of bone tunnel widening after anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 2010 Aug;18(8):1059e64. [9] Robbrecht C, Claes S, Cromheecke M, Mahieu P, Kakavelakis K, Victor J, Bellemans J, Verdonk P. Reliability of a semi-automated 3D-CT measuring method for tunnel diameters after anterior cruciate ligament reconstruction: a comparison between soft-tissue single-bundle allograft vs. autograft. Knee 2014 Oct;21(5):926e31. [10] de Beus A, Koch JE, Hirschmann A, Hirschmann MT. How to evaluate bone tunnel widening after ACL reconstruction - a critical review. Muscles Ligaments Tendons J 2017 Sep 18;7(2):230e9.
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Please cite this article as: Ohori T et al., Tibial tunnel enlargement after anatomic anterior cruciate ligament reconstruction with a boneepatellar tendonebone graft. Part 1: Morphological change in the tibial tunnel, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.01.004