Prospective Comparisons of Femoral Tunnel Enlargement With 3 Different Postoperative Immobilization Periods After Double-Bundle Anterior Cruciate Ligament Reconstruction With Hamstring Grafts Takuya Tajima, M.D., Ph.D., Etsuo Chosa, M.D., Ph.D., Katsuhiro Kawahara, M.D., Ph.D., and Nami Yamaguchi, M.D.
Purpose: To determine the effect of differing postoperative immobilization periods on femoral bone tunnel enlargement and clinical outcome after double-bundle anterior cruciate ligament (ACL) reconstruction with hamstring grafts. Methods: Fifty-one patients undergoing primary double-bundle ACL reconstruction with hamstring grafts were divided into 3 postoperative immobilization protocol groups: 2-day immobilization with the knee in 20 of flexion postoperatively (group A, n ¼ 18); 1-week immobilization (group B, n ¼ 17); and 2-week immobilization (group C, n ¼ 16). Bone tunnel enlargement was determined by computed digital radiographs taken on the first postoperative day and at 24 months in the anteroposterior (AP) and lateral views. Each tunnel diameter was shown as a percentage of the maximum joint width of the proximal tibia on the AP view or a percentage of the maximum diameter of the patella on the lateral view. To determine the incidence of tunnel enlargement, a percentage diameter change of more than 10% was defined as an enlarged tunnel. The standard clinical evaluation was also performed. This study used nonrandomized procedures. Results: In each group there were no significant differences in the incidence and magnitude of anteromedial and posterolateral bone tunnel enlargement on both the AP and lateral views (1-factor analysis of variance). Group C showed significantly less muscle strength in knee extension compared with the contralateral knee (85.3% 18.4%) than group A (93.7% 13.1%, P ¼ .049) and group B (96.8% 12.9%, P ¼ .044). Conclusions: This prospective radiographic study showed that femoral bone tunnel enlargement, in both the anteromedial and posterolateral tunnels, may occur after double-bundle ACL reconstruction with hamstring grafts despite different postoperative immobilization periods, with no significant difference in the incidence and magnitude among groups with differing postoperative immobilization periods. In addition, a 2-week immobilization period after surgery showed harmful effects, such as significantly less quadriceps muscle strength. Level of Evidence: Level II, prospective comparative study.
A
nterior cruciate ligament (ACL) injury is a common sports injury. In most cases ACL laxity causes knee joint instability in sports activities such as cutting or pivoting.1,2 A broad range of patients, including both
From the Division of Orthopedic Surgery, Department of Medicine of Sensory and Motor Organs, Faculty of Medicine, University of Miyazaki, Miyazaki, Japan. This study was supported by the University of Miyazaki and Japanese Ministry of Education, Culture, Sports, Science and Technology. The authors report that they have no conflicts of interest in the authorship and publication of this article. Received April 10, 2014; accepted October 24, 2014. Address correspondence to Takuya Tajima, M.D., Ph.D., Division of Orthopedic Surgery, Department of Medicine of Sensory and Motor Organs, Faculty of Medicine, University of Miyazaki, 5200 Kihara, Kiyotake, Miyazaki 889-1692, Japan. E-mail: [email protected] Ó 2015 by the Arthroscopy Association of North America 0749-8063/14302/$36.00 http://dx.doi.org/10.1016/j.arthro.2014.10.015
male and female patients, representing a large range of occupations and ages, have undergone ACL reconstruction in increasing numbers in recent years thanks to advances in surgical techniques, instruments, and basic research.3 The anatomy of the ACL is well known. There are at least 2 different bundles, the anteromedial (AM) bundle and the posterolateral (PL) bundle. Therefore anatomic double-bundle ACL reconstruction techniques with hamstring grafts were recently developed, and it has been proposed that they restore ACL function more closely to normal knee kinematics.4-6 However, potential complications associated with postoperative bone tunnel enlargement due to hamstring soft-tissue grafts have been reported.7-14 The most significant disadvantage after bone tunnel enlargement is difficulty in revision surgery; some cases require additional bone grafting before new bone
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tunnel creation in the anatomic position. Previously, Shelbourne and colleagues15,16 introduced the accelerated rehabilitation protocol, and this protocol extensively contributed to reducing the incidence of arthrofibrosis and loss of motion, thus improving functional outcomes. On the other hand, other authors showed that a non-aggressive rehabilitation protocol resulted in a lower increase in tunnel enlargement.17,18 Therefore a less aggressive rehabilitation protocol, such as a protocol using a longer postoperative immobilization period, may reduce the amount of bone tunnel enlargement after surgery. Cinar et al.19 reported that 88.2% of cases showed bone tunnel enlargement measured by computed tomography (CT) 24 months after single-bundle ACL reconstruction with hamstring grafting and EndoButton CL (Smith & Nephew, Andover, MA) fixation; Siebold and Cafaltzis9 reported AM bundle tunnel enlargement in 34% of cases and PL bundle tunnel enlargement in 46% of cases as measured by magnetic resonance imaging (MRI) at 7 months postoperatively; and Kawaguchi et al.20 reported that 21.6% to 36.1% of cases showed tunnel enlargement measured by digital radiography 24 months after double-bundle ACL reconstruction with hamstring grafting and EndoButton CL fixation. However, the postoperative knee immobilization periods were different depending on the authors or institutions; immediate knee motion after surgery was allowed in some cases, whereas 2 weeks of immobilization postoperatively was required in other cases. Unfortunately, the most suitable immobilization period or rehabilitation protocol after double-bundle ACL reconstruction with hamstring grafting remains unclear. The purpose of this study was to determine the effect of differing postoperative immobilization periods on femoral bone tunnel enlargement and clinical outcome after double-bundle ACL reconstruction with hamstring grafts. This prospective study was conducted to compare 3 different postoperative immobilization periods by assessing the clinical and radiologic results including bone tunnel enlargement at 2 years after surgery. We hypothesized that a less aggressive rehabilitation protocol (i.e. a protocol using a longer postoperative immobilization period) would prevent bone tunnel enlargement due to several biological events such as reduction of inflammation or filling of the bony tunnel with blood clots and fibrous tissue.
Methods Patients A prospective comparative study was conducted in 2008 involving patients who underwent double-bundle ACL reconstruction with hamstring tendon autografts, which was performed using the same procedures and fixation devices at our institution. The experimental
design was reviewed and approved by the ethics committee at our institution. The procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Declaration of Helsinki of 1975, as revised in 2000. Written informed consent was obtained from the patients for publication of this report and any accompanying images. We planned to examine all clinical and radiologic data available, including clinical scores, thigh muscle strength measurements, and measurements of femoral bone tunnel enlargement by digital radiography of the knee at 2 years after surgery. The exclusion criteria consisted of multiple-ligament injuries, such as posterior ligament involvement as indicated by the presence of the posterior drawer sign; abnormal varus/valgus laxity; open growth plates; ligament injury to the contralateral knee; concomitant treatment for articular cartilage defects, such as osteochondral autologous transplantation and microfracture; and ACL reconstruction in meniscal fixation cases because these patients followed a 3-week noneweight-bearing protocol postoperatively. Moreover, genu recurvatum cases were excluded from this study because of the effect of genu recurvatum on knee angle and extension moments in the gait pattern.21 In addition, patients who did not want to take part were not enrolled in this study. A total of 60 consecutive patients were initially enrolled in this study. During the follow-up period, 6 patients were lost to follow-up, 2 patients had another meniscal injury after primary ACL reconstruction, and 1 patient had a contralateral ACL injury after primary surgery. Therefore 51 patients who were undergoing primary double-bundle ACL reconstruction with hamstring grafts met the inclusion criteria and were finally matched in this study (Fig 1). They were allocated into 1 of 3 different postoperative immobilization protocol groups. The allocation was conducted in a serial consecutive manner, not by randomization: The first consecutive group of 20 patients received 2 days of immobilization with the knee in 20 of flexion postoperatively (group A; 2 cases lost to follow-up; n ¼ 18 [8 male and 10 female patients]); the second consecutive group of 20 patients received 1 week of immobilization (group B; 2 cases lost to follow-up and 1 case of new meniscal injury; n ¼ 17 [8 male and 9 female patients]); and the third consecutive group of 20 patients received 2 weeks of immobilization (group C; 2 cases lost to follow-up, 1 case of new meniscal injury, and 1 case of new contralateral knee injury; n ¼ 16 [7 male and 9 female patients]). The patients’ characteristics are shown in detail in Table 1. Surgical Procedures A complete diagnostic arthroscopy was first performed in every patient in this study to ensure that an
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FEMORAL BONE TUNNEL ENLARGEMENT AFTER ACLR
Fig 1. Participant flowchart. (ACL, anterior cruciate ligament.)
ACL tear was present and to examine for other possible findings, such as meniscal or chondral injury in the knee. In each group the semitendinosus and gracilis tendons were harvested. The semitendinosus tendon was prepared for the AM bundle, and the gracilis tendon was trimmed for the PL bundle. The EndoButton CL was attached on the femoral side. A baseball glove suture with FiberWire (Arthrex, Naples, FL) was performed on the tibial side to secure the graft. An additional accessory far AM portal was made. Two independent sockets and tunnels were created just posterior to the resident’s ridge22 in an inside-out fashion using a transportal technique. The AM and PL bundle tunnels were positioned according to Yasuda et al.3 The tunnel bridge between the AM and PL bone tunnels on the femur averaged 2.2 mm (range, 1 to 3 mm). The characteristics of graft size, tunnel length, and graft length inside the femoral bone tunnel are shown in
detail in Table 1. Two independent bone tunnels were created at the center of the AM and PL bundles on the tibia: a 6.0- to 7.5-mm-wide tunnel for the AM bundle and a 5.0- to 6.0-mm-wide tunnel for the PL bundle. The grafts for the PL and AM bundles were introduced through the tibial tunnel to the femoral tunnel. The EndoButton CL was flipped on the femoral cortical surface. An assistant surgeon (K.K., N.Y.) simultaneously applied tension of 20 N to both AM and PL grafts using a tensiometer, and the grafts were fixed to the tibia using a double-spike plate system (Meira, Aichi, Japan) with the knee positioned in 20 of flexion.23 Rehabilitation The knee was immobilized in 20 of flexion with a brace for each protocol. We wanted to keep the same angle as that used for graft fixation during surgery to avoid stress on the grafts. After each immobilization
Table 1. Patient Characteristics and Graft Size, Tunnel Length, and Graft Length Inside Tunnel No. of cases Mean age, yr (range) Male/female gender, n Height, cm Weight, kg Time between injury and surgery, mo Graft size (diameter), mm AMB PLB Femoral tunnel length, mm AMB PLB Graft length inside femoral tunnel, mm AMB PLB
Group A 18 28.6 (16-46) 8/10 164.5 7.8 63.4 7.7 23.0 25.5
Group B 17 25.0 (15-40) 8/9 163.5 7.9 62.4 12.6 20.1 16.9
Group C 16 28.4 (16-46) 7/9 165.2 8.7 62.1 9.8 22.1 18.6
Significance
6.67 0.6 5.47 0.4
6.33 0.6 5.38 0.5
6.38 0.5 5.41 0.3
NS NS
35.9 6.9 31.1 4.1
32.8 7.8 32.4 3.4
33.5 4.0 33.2 5.4
NS NS
14.6 1.8 13.3 2.1
13.9 1.9 13.5 1.8
14.2 2.2 13.6 1.4
NS NS
NOTE. Data presented as mean standard deviation unless otherwise indicated. AMB, anteromedial bundle; NS, not significant; PLB, posterolateral bundle.
NS NS NS NS NS
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Fig 2. Computed digital radiographs of knee after double-bundle anterior cruciate ligament reconstruction: (A) anteroposterior (AP) view and (B) lateral view on first postoperative day and (C) anteroposterior view and (D) lateral view 2 years after surgery. The radiolucent line on the AP view of the radiograph taken on the first postoperative day and the sclerotic lines of the tunnel wall are enhanced on the AP and lateral views at 2 years after surgery. On the lateral view of the radiograph taken on the first postoperative day, the radiolucent line was not confirmed clearly. Therefore the drill size was used as the initial bone tunnel size. The 2 white arrows show the femoral outlet of the anteromedial tunnel, and the 2 black arrows show the femoral outlet of the posterolateral tunnel. The 2 femoral tunnel diameters are shown as a percentage of the maximum joint width of the proximal tibia on the AP view or a percentage of the maximum diameter of the patella on the lateral view. To determine the incidence of tunnel enlargement, percentage diameter changes of more than 10% and less than 10% are defined as an enlarged tunnel and a reduced tunnel, respectively. The double-headed arrows in the AP views show the maximum joint width of the proximal tibia, and in the lateral views show the maximum diameter of the patella.
period, range-of-motion exercises were performed gradually: 10 of knee flexion was started with a locked hard brace (Breg X2K brace; Breg, Carlsbad, CA) for 1 week, and thereafter, full extension was allowed. Partial weight bearing was started 1 week after surgery, with full weight bearing at 4 weeks. The knee brace was used by all patients for the first 3 months after surgery. Running was allowed at 3 months after surgery, followed by a return to cutting actions and contact sports at no sooner than 8 months postoperatively. Clinical Evaluation Follow-up examinations were performed at 2 years postoperatively. The evaluated factors were the Lysholm score and peak isokinetic quadriceps and hamstring torque at 60 /s measured with a Biodex 4 (Biodex Medical Systems, Shirley, NY). Isokinetic peak torque values were compared with the values of the contralateral knee. Measurements of knee range of motion such as extension lag were also performed. Three experienced senior orthopaedic surgeons (T.T., K.K., N.Y.) performed these clinical examinations and collected the data. Radiographic Evaluation Patients underwent radiologic examination twice, on the first postoperative day and 2 years after surgery, so that we could evaluate bone tunnel enlargement of both the AM and PL bundles in each group. Computed
digital radiographs (Fujifilm, Tokyo, Japan) of the knee were taken in the anteroposterior (AP) and lateral views for the purpose of measuring tunnel enlargement according to Webster et al.10 The tunnel wall was enhanced on the computed digital radiograph, controlling contrast, intensity, and brightness of the image, and the diameter of the tunnel was measured. The tunnel measurement was taken at the intra-articular outlet of the femoral tunnel in each plane, perpendicular to the direction of the long axis of the tunnel. To compare the femoral tunnel diameters on radiographs taken in the 2 different periods, each diameter was shown as a percentage of the maximum joint width of the proximal tibia on the AP view or a percentage of the maximum diameter of the patella on the lateral view (Fig 2). However, on the digital radiographs obtained immediately postoperatively, the sclerotic margin was not confirmed. Instead of the sclerotic margin, the radiolucent area was confirmed on the AP view. Therefore we evaluated the tunnel width using the radiolucent margin. On the lateral view of the digital radiographs obtained immediately postoperatively, the radiolucent area was not confirmed clearly. So, we used the drill size as the initial bone tunnel width. Using a transportal technique to create the femoral bone tunnel makes the cross section of the tunnel nearly round. The percentage change in the diameter between the 2 periods was defined as the percentage tunnel enlargement in diameter. It was difficult to determine the percentage
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FEMORAL BONE TUNNEL ENLARGEMENT AFTER ACLR Table 2. Clinical Results at 2 Years Postoperatively ACL reinjury, n Lysholm score Preoperative score Postoperative score Quadriceps torque at 60 /s compared with contralateral knee, %
Group A (n ¼ 18) 0
Group B (n ¼ 17) 0
Group C (n ¼ 16) 0
P Value NS
66.8 3.8 97.4 7.1 93.7 13.1*
64.1 5.3 98.0 5.8 96.8 12.9y
63.5 3.9 97.7 6.3 85.3 18.4*y
90.3 16.2
91.1 18.8
86.1 17.6
NS NS P ¼ .049* P ¼ .044y NS
1 (5.6) 0 (0)
1 (5.9) 0 (0)
Hamstring torque at 60 /s compared with contralateral knee, % Knee extension deficiency, n (%) 5
2 (12.5) 0 (0)
NS
NOTE. Data presented as mean standard deviation unless otherwise indicated. ACL, anterior cruciate ligament; NS, not significant. *Significant difference between group A and group C (P < .05). y Significant difference between group B and group C (P < .05).
tunnel enlargement in the tibial tunnels because the 2 intra-articular outlet images of the AM and PL bundles were overlapped in the radiographs. Therefore tibial bone tunnel measurements were excluded in this study. To determine the incidence of tunnel enlargement, percentage diameter changes of more than 10% and less than 10% were defined as an enlarged tunnel and a reduced tunnel, respectively, according to Kawaguchi et al.20 The tunnel enlargement grades were determined by a blinded, experienced orthopaedic surgeon. Statistical Analysis Intraobserver variability for the rate of femoral tunnel enlargement was satisfactory; the mean intraclass correlation coefficient was 0.92. On the basis of a power of 80% and a of .05, we calculated that the sample size required per group was 16. Statistical comparisons among the 3 groups were performed using 1-way factorial analysis of variance. When a significant difference was found by analysis of variance, we performed the Bonferroni-Dunn procedure as a post hoc test to determine which 2 of the 3 groups differed significantly for each parameter, including the clinical results and the magnitude and incidence of bone tunnel enlargement. Statistical analysis was performed with the statistical software package Ystat 2004 (Igaku Tosho Shuppan, Tokyo, Japan). The level of significance was set at P < .05.
Results Clinical Results There were 2 cases of meniscal injury after primary ACL reconstruction, and we excluded them from this study. These cases underwent another surgical procedure for treatment of the meniscus. The reconstructed ACL showed good results regarding tension, volume, and synovial coverage. There were no findings of ACL failure or laxity in either case. The mean follow-up period was 30.4 months (range, 24 to 48 months) in group A, 29.2 months (range, 24 to 38 months) in group B, and 28.5 months (range, 24 to 36 months) in group C. Muscle strength in knee extension at 2 years after surgery showed a significantly lower value in group C than in group A (P ¼ .049) and group B (P ¼ .044). The other clinical data showed no significant differences among the 3 groups (Table 2). Radiologic Results Concerning the femoral tunnels in group A, the incidence of AM tunnel enlargement was 66.7% and 61.1% on the AP view and lateral view, respectively, whereas the incidence of PL tunnel enlargement was 66.7% on both the AP and lateral views (Table 3). In group B the incidence of AM tunnel enlargement was 52.9% on the AP view and 58.8% on the lateral view, and the incidence of PL tunnel enlargement was 52.9%
Table 3. Incidence of Femoral Bone Tunnel Enlargement at 2 Years Postoperatively Anteromedial bundle Anteroposterior view Lateral view Posterolateral bundle Anteroposterior view Lateral view
Group A
Group B
Group C
Significance
12 of 18 (66.7) 11 of 18 (61.1)
9 of 17 (52.9) 10 of 17 (58.8)
9 of 16 (56.3) 10 of 16 (62.5)
NS NS
12 of 18 (66.7) 12 of 18 (66.7)
9 of 17 (52.9) 10 of 17 (58.8)
9 of 16 (56.3) 9 of 16 (56.3)
NS NS
NOTE. Data presented as number of cases (%). NS, not significant.
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Table 4. Magnitude of Percentage Femoral Bone Tunnel Enlargement at 2 Years Postoperatively Anteromedial bundle, % Anteroposterior view Lateral view Posterolateral bundle, % Anteroposterior view Lateral view
Group A
Group B
Group C
Significance
15.2 12.1 14.3 10.1
14.4 11.2 13.4 10.6
13.9 12.4 13.6 11.2
NS NS
14.5 13.4 14.4 10.3
14.0 11.4 13.8 11.3
14.2 12.7 14.5 13.2
NS NS
NOTE. Data presented as mean standard deviation. NS, not significant.
on the AP view and 58.8% on the lateral view. In group C, the incidence of AM tunnel enlargement was 56.3% on the AP view and 62.5% on the lateral view, and the incidence of PL tunnel enlargement was 56.3% on both the AP and lateral views. In each group no significant differences were observed. The magnitude of the percentage femoral bone tunnel enlargement also showed no significant differences in each group (Table 4). No cases of femoral bone tunnel reduction were found.
Discussion Previously, comparative studies on bone tunnel enlargement associated with the immobilization period concluded that bone tunnel enlargement after ACL reconstruction using hamstring autograft can be increased by an accelerated, brace-free rehabilitation protocol.17,18 However, the mean follow-up period of these reports was only 10 months (range, 9 to 11 months). The most important finding of our study was that a high incidence of femoral tunnel enlargement occurred not only in the 2-day immobilization group but also in the 2-week immobilization group; in group C, the incidence of AM tunnel enlargement was 56.3% on the AP view and 62.5% on the lateral view, whereas the incidence of PL tunnel enlargement was 56.3% on both the AP and lateral views. Our results showed a higher incidence of enlargement than that reported by Kawaguchi et al.20 and lower incidence than that reported by Cinar et al.19 These previous reports may have included ACL reconstruction with meniscal repair or recurvatum cases, which may have influenced the differences in the results. At our institution, we provide different protocols in cases with meniscal repair and recurvatum, such as a longer immobilization period, another immobilization angle, and a noneweightbearing period. In this study, therefore, cases of ACL reconstruction with meniscal repair and recurvatum were completely excluded. Moreover, in this study the 2-week immobilization group included 2 cases of slight knee extension deficiency and significant loss of muscle strength in knee extension 2 years after surgery compared with the contralateral knee. On the basis of these results, the 2-week postoperative immobilization protocol did not significantly reduce femoral bone tunnel enlargement after double-bundle ACL
reconstruction with hamstring grafts. This study suggested that double-bundle ACL reconstruction with hamstring grafts yields the potential risk of postoperative femoral bone tunnel enlargement on both the AM and PL views despite different postoperative immobilization periods. On the other hand, there was no clinically significant difference in tunnel enlargement based on clinical outcome scores among the 3 different immobilization periods. However, our results showed that the 2-week immobilization period after surgery had harmful effects, such as significantly less quadriceps muscle strength associated with longer immobilization. Many previous studies have reported the incidence of tunnel enlargement after single- or double-bundle ACL reconstruction with hamstring grafts in the femur.7-14,17-20 However, the postoperative knee immobilization periods were different, depending on the authors or institutions; some studies had an accelerated program, whereas other studies had a slow rehabilitation protocol, such as a 1- or 2-week postoperative immobilization period. Therefore the information from our study is clinically of value to clarify the most suitable postoperative immobilization period after doublebundle ACL reconstruction with hamstring grafts. The mechanism of tunnel enlargement is not yet fully understood. Previously, several possible factors contributing to tunnel enlargement after ACL reconstruction with soft-tissue grafts were proposed. These factors fall into 2 broad categories, biomechanical factors and biological factors. Biomechanical factors relate to the motion of the graft within the tunnel, with graft motion abrading the edge of the tunnel; a longer distance between the graft fixation points results in significantly greater longitudinal graft motion, called the bungee-cord effect, and transverse graft motion, called the windshield-wiper effect. Biological factors are related to bone resorption induced by biological activity. Several biological theories have been proposed: synovial fluid propagation within bony tunnels, localized bone necrosis possibly caused by the drilling process due to thermogenic effects that induce a nonspecific inflammatory response, biochemical mediators, and so on.12-14,24 Zysk et al.25 studied synovial fluid samples collected from patients after ACL
FEMORAL BONE TUNNEL ENLARGEMENT AFTER ACLR
reconstruction and reported that patients with bone tunnel enlargement had higher concentrations of tumor necrosis factor a, interleukin 6, and nitric oxide, indicating the involvement of these mediators in tunnel enlargement. Kawaguchi et al.20 reported that there was significantly less femoral tunnel enlargement after anatomic double-bundle ACL reconstruction with hamstring grafts than after single-bundle reconstruction; the potential mechanisms were less tension on the tunnel edge due to force sharing by the 2 bundles, less synovial fluid propagation because of a smaller tunnel diameter, and earlier graft remodeling and revascularization because of smaller grafts. In an animal model study, delayed application of cyclic axial loading after ACL reconstruction resulted in improved mechanical and biological parameters of tendon-to-bone healing compared with those associated with immediate loading.26,27 On the other hand, arthroscopic findings and clinical results after ACL reconstruction have been found to be satisfactory with both accelerated and less aggressive rehabilitation programs.28-30 The advantage of an accelerated rehabilitation protocol after ACL reconstruction is earlier normal function of the knee. On the basis of our results, a less aggressive protocol, such as a 2-week immobilization period, showed satisfactory clinical scores, but there were also a few cases of slight extension deficiency and significantly less knee extension strength. In the first 2 weeks after ACL reconstruction, several biological events are expected to prevent tunnel enlargement and/or stimulate tendon-bone healing, such as reduction of inflammation or filling of the bony tunnel by blood clots and fibrous tissue. However, our findings showed that 2 weeks of immobilization induced less muscle strength and a slight extension deficiency instead of preventing femoral tunnel enlargement. Therefore the most suitable immobilization period after double-bundle ACL reconstruction with hamstring grafts was shorter than 2 weeks. The radiologic and clinical evaluations showed satisfactory results in both the 2-day immobilization and 1-week immobilization groups with no significant difference. Limitations Several limitations of this study must be taken into consideration. First, the sample size in each group was small. Second, an important limitation is the lack of randomization. Third, MRI or CT was not used for measurement of tunnel enlargement in this study. CT scans may be more sensitive to detect early signs of bone tunnel enlargement than digital radiographs because the sclerotic margins are not present on radiographs until approximately 3 months after surgery.7 However, in the previous literature, digital radiography has been shown to have the same ability to identify bone tunnel enlargement after ACL reconstruction as
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CT.10,20,31 Moreover, digital radiography provides a time- and cost-effective means for documenting bone tunnel enlargement compared with MRI and CT. Fourth, tibial bone tunnel enlargement was not measured. After anatomic double-bundle ACL reconstruction, the 2 tibial intra-articular outlets of the AM and PL bundles were usually overlapped on the AP and lateral radiographic views.20 Fifth, we did not determine the interobserver variation in the radiographic evaluation. However, despite these limitations, this study provides important information on the postoperative immobilization period after ACL reconstruction with hamstring grafts.
Conclusions This prospective radiographic study showed that double-bundle ACL reconstruction with hamstring grafts yields the potential risk of postoperative femoral bone tunnel enlargement in both the AM and PL tunnels despite different postoperative immobilization periods, with no significant difference in the incidence and magnitude among groups with differing postoperative immobilization periods. In addition, a 2-week immobilization period after surgery showed harmful effects, such as significantly less quadriceps muscle strength. A postoperative immobilization period shorter than 2 weeks is recommended.
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prospective evaluation of hamstring and patella tendon grafts. Knee Surg Sports Traumatol Arthrosc 1999;7:138-145. Jansson KA, Harilainen A, Sandelin J, Karjalainen PT, Aronen HJ, Tallroth K. Bone tunnel enlargement after anterior cruciate ligament reconstruction with the hamstring autograft and EndoButton fixation technique. A clinical, radiographic and magnetic resonance imaging study with 2 years follow-up. Knee Surg Sports Traumatol Arthrosc 1999;7:290-295. Siebold R, Cafaltzis K. Differentiation between intraoperative and postoperative bone tunnel widening and communication in double-bundle anterior cruciate ligament reconstruction: A prospective study. Arthroscopy 2010;26:1066-1073. Webster KE, Feller JA, Hameister KA. Bone tunnel enlargement following anterior cruciate ligament reconstruction: A randomized comparison of hamstring and patellar tendon grafts. Knee Surg Sports Traumatol Arthrosc 2001;9:86-91. Wilson TC, Kantaras A, Atay A, Johnson DL. Tunnel enlargement after anterior cruciate ligament surgery. Am J Sports Med 2004;32:543-549. Silva A, Sampaio R, Pinto E. Femoral tunnel enlargement after anatomic ACL reconstruction: A biological problem? Knee Surg Sports Traumatol Arthrosc 2010;18:1189-1194. Achtnich A, Stiepani H, Forkel P, Metzlaff A, Hänninen EL, Petersen W. Tunnel widening after anatomic double-bundle and mid-position single-bundle anterior cruciate ligament reconstruction. Arthroscopy 2013;29:1514-1524. Järvelä T, Moisala AS, Paakkala T, Paakkala A. Tunnel enlargement after double-bundle anterior cruciate ligament reconstruction: A prospective, randomized study. Arthroscopy 2008;24:1349-1357. Shelbourne KD, Nitz P. Accelerated rehabilitation after anterior cruciate ligament reconstruction. Am J Sports Med 1990;18:292-299. De Carlo MS, Shelbourne KD, McCarroll JR, et al. Traditional versus accelerated rehabilitation following ACL reconstruction: A one-year follow-up. J Orthop Sports Phys Ther 1991;15:309-316. Iorio R, Vadala A, Argento G, et al. Bone tunnel enlargement after ACL reconstruction using autologous hamstring tendons: A CT study. Int Orthop 2007;31: 49-55. Vadala A, Iorio R, De Carli A, et al. The effect of accelerated, brace free, rehabilitation on bone tunnel enlargement after ACL reconstruction using hamstring tendons: A CT study. Knee Surg Sports Traumatol Arthrosc 2007;15:365-371. Cinar BM, Akpinar S, Hersekli MA, et al. The effects of two different fixation methods on femoral bone tunnel enlargement and clinical results in anterior cruciate ligament reconstruction with hamstring tendon graft. Acta Orthop Traumatol Turc 2009;43:515-521 [in Turkish].
20. Kawaguchi Y, Kondo E, Kitamura N, Kai S, Inoue M, Yasuda K. Comparisons of femoral tunnel enlargement in 169 patients between single-bundle and anatomic doublebundle anterior cruciate ligament reconstructions with hamstring tendon grafts. Knee Surg Sports Traumatol Arthrosc 2011;19:1249-1257. 21. Kawahara K, Sekimoto T, Watanabe S, et al. Effect of genu recurvatum on the anterior cruciate ligamentdeficient knee during gait. Knee Surg Sports Traumatol Arthrosc 2012;20:1479-1487. 22. Shino K, Suzuki T, Iwahashi T, et al. The resident’s ridge as an arthroscopic landmark for anatomical femoral tunnel drilling in ACL reconstruction. Knee Surg Sports Traumatol Arthrosc 2010;18:1164-1168. 23. Mae T, Shino K, Nakata K, et al. Optimization of graft fixation at the time of anterior cruciate ligament reconstruction. Part II: Effect of knee fixation angle. Am J Sports Med 2008;36:1094-1100. 24. Dave LY, Leong OK, Karim SA, Chong CH. Tunnel enlargement 5 years after anterior cruciate ligament reconstruction: A radiographic and functional evaluation. Eur J Orthop Surg Traumatol 2014;24:217-223. 25. Zysk SP, Fraunberger P, Veihelmann A, et al. Tunnel enlargement and changes in synovial fluid cytokine profile following anterior cruciate ligament reconstruction with patellar tendon and hamstring tendon autografts. Knee Surg Sports Traumatol Arthrosc 2004;12:98-103. 26. Bedi A, Kovacevic D, Fox AJ, et al. Effect of early and delayed mechanical loading on tendon-to-bone healing after anterior cruciate ligament reconstruction. J Bone Joint Surg Am 2010;92:2387-2401. 27. Brophy RH, Kovacevic D, Imhauser CW, et al. Effect of short-duration low-magnitude cyclic loading versus immobilization on tendon-bone healing after ACL reconstruction in a rat model. J Bone Joint Surg Am 2011;93:381-393. 28. Janssen RP, Scheffler SU. Intra-articular remodelling of hamstring tendon grafts after anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 2014;22:2102-2108. 29. Janssen RP, Du Mee AW, Valkenburg VJ, et al. Anterior cruciate ligament reconstruction with 4-strand hamstring autograft and accelerated rehabilitation: A 10-year prospective study on clinical results, knee osteoarthritis and its predictors. Knee Surg Sports Traumatol Arthrosc 2013;21: 1977-1988. 30. Marumo K, Saito M, Yamagishi T, et al. The ‘ligamentization’ process in human anterior cruciate ligament reconstruction with autogenous patellar and hamstring tendons. Am J Sports Med 2005;33:1166-1173. 31. Webster KE, Feller JA, Elliott J, et al. A comparison of bone tunnel measurements made using computed tomography and digital plain radiography after anterior cruciate ligament reconstruction. Arthroscopy 2004;20: 946-950.
Purpose: To determine the effect of differing postoperative immobilization periods on femoral bone tunnel enlargement and clinical outcome after double-bundle anterior cruciate ligament (ACL) reconstruction with hamstring grafts. Methods: Fifty-one patients undergoing primary double-bundle ACL reconstruction with hamstring grafts were divided into 3 postoperative immobilization protocol groups: 2-day immobilization with the knee in 20 of flexion postoperatively (group A, n ¼ 18); 1-week immobilization (group B, n ¼ 17); and 2-week immobilization (group C, n ¼ 16). Bone tunnel enlargement was determined by computed digital radiographs taken on the first postoperative day and at 24 months in the anteroposterior (AP) and lateral views. Each tunnel diameter was shown as a percentage of the maximum joint width of the proximal tibia on the AP view or a percentage of the maximum diameter of the patella on the lateral view. To determine the incidence of tunnel enlargement, a percentage diameter change of more than 10% was defined as an enlarged tunnel. The standard clinical evaluation was also performed. This study used nonrandomized procedures. Results: In each group there were no significant differences in the incidence and magnitude of anteromedial and posterolateral bone tunnel enlargement on both the AP and lateral views (1-factor analysis of variance). Group C showed significantly less muscle strength in knee extension compared with the contralateral knee (85.3% 18.4%) than group A (93.7% 13.1%, P ¼ .049) and group B (96.8% 12.9%, P ¼ .044). Conclusions: This prospective radiographic study showed that femoral bone tunnel enlargement, in both the anteromedial and posterolateral tunnels, may occur after double-bundle ACL reconstruction with hamstring grafts despite different postoperative immobilization periods, with no significant difference in the incidence and magnitude among groups with differing postoperative immobilization periods. In addition, a 2-week immobilization period after surgery showed harmful effects, such as significantly less quadriceps muscle strength. Level of Evidence: Level II, prospective comparative study.
A
nterior cruciate ligament (ACL) injury is a common sports injury. In most cases ACL laxity causes knee joint instability in sports activities such as cutting or pivoting.1,2 A broad range of patients, including both
From the Division of Orthopedic Surgery, Department of Medicine of Sensory and Motor Organs, Faculty of Medicine, University of Miyazaki, Miyazaki, Japan. This study was supported by the University of Miyazaki and Japanese Ministry of Education, Culture, Sports, Science and Technology. The authors report that they have no conflicts of interest in the authorship and publication of this article. Received April 10, 2014; accepted October 24, 2014. Address correspondence to Takuya Tajima, M.D., Ph.D., Division of Orthopedic Surgery, Department of Medicine of Sensory and Motor Organs, Faculty of Medicine, University of Miyazaki, 5200 Kihara, Kiyotake, Miyazaki 889-1692, Japan. E-mail: [email protected] Ó 2015 by the Arthroscopy Association of North America 0749-8063/14302/$36.00 http://dx.doi.org/10.1016/j.arthro.2014.10.015
male and female patients, representing a large range of occupations and ages, have undergone ACL reconstruction in increasing numbers in recent years thanks to advances in surgical techniques, instruments, and basic research.3 The anatomy of the ACL is well known. There are at least 2 different bundles, the anteromedial (AM) bundle and the posterolateral (PL) bundle. Therefore anatomic double-bundle ACL reconstruction techniques with hamstring grafts were recently developed, and it has been proposed that they restore ACL function more closely to normal knee kinematics.4-6 However, potential complications associated with postoperative bone tunnel enlargement due to hamstring soft-tissue grafts have been reported.7-14 The most significant disadvantage after bone tunnel enlargement is difficulty in revision surgery; some cases require additional bone grafting before new bone
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tunnel creation in the anatomic position. Previously, Shelbourne and colleagues15,16 introduced the accelerated rehabilitation protocol, and this protocol extensively contributed to reducing the incidence of arthrofibrosis and loss of motion, thus improving functional outcomes. On the other hand, other authors showed that a non-aggressive rehabilitation protocol resulted in a lower increase in tunnel enlargement.17,18 Therefore a less aggressive rehabilitation protocol, such as a protocol using a longer postoperative immobilization period, may reduce the amount of bone tunnel enlargement after surgery. Cinar et al.19 reported that 88.2% of cases showed bone tunnel enlargement measured by computed tomography (CT) 24 months after single-bundle ACL reconstruction with hamstring grafting and EndoButton CL (Smith & Nephew, Andover, MA) fixation; Siebold and Cafaltzis9 reported AM bundle tunnel enlargement in 34% of cases and PL bundle tunnel enlargement in 46% of cases as measured by magnetic resonance imaging (MRI) at 7 months postoperatively; and Kawaguchi et al.20 reported that 21.6% to 36.1% of cases showed tunnel enlargement measured by digital radiography 24 months after double-bundle ACL reconstruction with hamstring grafting and EndoButton CL fixation. However, the postoperative knee immobilization periods were different depending on the authors or institutions; immediate knee motion after surgery was allowed in some cases, whereas 2 weeks of immobilization postoperatively was required in other cases. Unfortunately, the most suitable immobilization period or rehabilitation protocol after double-bundle ACL reconstruction with hamstring grafting remains unclear. The purpose of this study was to determine the effect of differing postoperative immobilization periods on femoral bone tunnel enlargement and clinical outcome after double-bundle ACL reconstruction with hamstring grafts. This prospective study was conducted to compare 3 different postoperative immobilization periods by assessing the clinical and radiologic results including bone tunnel enlargement at 2 years after surgery. We hypothesized that a less aggressive rehabilitation protocol (i.e. a protocol using a longer postoperative immobilization period) would prevent bone tunnel enlargement due to several biological events such as reduction of inflammation or filling of the bony tunnel with blood clots and fibrous tissue.
Methods Patients A prospective comparative study was conducted in 2008 involving patients who underwent double-bundle ACL reconstruction with hamstring tendon autografts, which was performed using the same procedures and fixation devices at our institution. The experimental
design was reviewed and approved by the ethics committee at our institution. The procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Declaration of Helsinki of 1975, as revised in 2000. Written informed consent was obtained from the patients for publication of this report and any accompanying images. We planned to examine all clinical and radiologic data available, including clinical scores, thigh muscle strength measurements, and measurements of femoral bone tunnel enlargement by digital radiography of the knee at 2 years after surgery. The exclusion criteria consisted of multiple-ligament injuries, such as posterior ligament involvement as indicated by the presence of the posterior drawer sign; abnormal varus/valgus laxity; open growth plates; ligament injury to the contralateral knee; concomitant treatment for articular cartilage defects, such as osteochondral autologous transplantation and microfracture; and ACL reconstruction in meniscal fixation cases because these patients followed a 3-week noneweight-bearing protocol postoperatively. Moreover, genu recurvatum cases were excluded from this study because of the effect of genu recurvatum on knee angle and extension moments in the gait pattern.21 In addition, patients who did not want to take part were not enrolled in this study. A total of 60 consecutive patients were initially enrolled in this study. During the follow-up period, 6 patients were lost to follow-up, 2 patients had another meniscal injury after primary ACL reconstruction, and 1 patient had a contralateral ACL injury after primary surgery. Therefore 51 patients who were undergoing primary double-bundle ACL reconstruction with hamstring grafts met the inclusion criteria and were finally matched in this study (Fig 1). They were allocated into 1 of 3 different postoperative immobilization protocol groups. The allocation was conducted in a serial consecutive manner, not by randomization: The first consecutive group of 20 patients received 2 days of immobilization with the knee in 20 of flexion postoperatively (group A; 2 cases lost to follow-up; n ¼ 18 [8 male and 10 female patients]); the second consecutive group of 20 patients received 1 week of immobilization (group B; 2 cases lost to follow-up and 1 case of new meniscal injury; n ¼ 17 [8 male and 9 female patients]); and the third consecutive group of 20 patients received 2 weeks of immobilization (group C; 2 cases lost to follow-up, 1 case of new meniscal injury, and 1 case of new contralateral knee injury; n ¼ 16 [7 male and 9 female patients]). The patients’ characteristics are shown in detail in Table 1. Surgical Procedures A complete diagnostic arthroscopy was first performed in every patient in this study to ensure that an
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Fig 1. Participant flowchart. (ACL, anterior cruciate ligament.)
ACL tear was present and to examine for other possible findings, such as meniscal or chondral injury in the knee. In each group the semitendinosus and gracilis tendons were harvested. The semitendinosus tendon was prepared for the AM bundle, and the gracilis tendon was trimmed for the PL bundle. The EndoButton CL was attached on the femoral side. A baseball glove suture with FiberWire (Arthrex, Naples, FL) was performed on the tibial side to secure the graft. An additional accessory far AM portal was made. Two independent sockets and tunnels were created just posterior to the resident’s ridge22 in an inside-out fashion using a transportal technique. The AM and PL bundle tunnels were positioned according to Yasuda et al.3 The tunnel bridge between the AM and PL bone tunnels on the femur averaged 2.2 mm (range, 1 to 3 mm). The characteristics of graft size, tunnel length, and graft length inside the femoral bone tunnel are shown in
detail in Table 1. Two independent bone tunnels were created at the center of the AM and PL bundles on the tibia: a 6.0- to 7.5-mm-wide tunnel for the AM bundle and a 5.0- to 6.0-mm-wide tunnel for the PL bundle. The grafts for the PL and AM bundles were introduced through the tibial tunnel to the femoral tunnel. The EndoButton CL was flipped on the femoral cortical surface. An assistant surgeon (K.K., N.Y.) simultaneously applied tension of 20 N to both AM and PL grafts using a tensiometer, and the grafts were fixed to the tibia using a double-spike plate system (Meira, Aichi, Japan) with the knee positioned in 20 of flexion.23 Rehabilitation The knee was immobilized in 20 of flexion with a brace for each protocol. We wanted to keep the same angle as that used for graft fixation during surgery to avoid stress on the grafts. After each immobilization
Table 1. Patient Characteristics and Graft Size, Tunnel Length, and Graft Length Inside Tunnel No. of cases Mean age, yr (range) Male/female gender, n Height, cm Weight, kg Time between injury and surgery, mo Graft size (diameter), mm AMB PLB Femoral tunnel length, mm AMB PLB Graft length inside femoral tunnel, mm AMB PLB
Group A 18 28.6 (16-46) 8/10 164.5 7.8 63.4 7.7 23.0 25.5
Group B 17 25.0 (15-40) 8/9 163.5 7.9 62.4 12.6 20.1 16.9
Group C 16 28.4 (16-46) 7/9 165.2 8.7 62.1 9.8 22.1 18.6
Significance
6.67 0.6 5.47 0.4
6.33 0.6 5.38 0.5
6.38 0.5 5.41 0.3
NS NS
35.9 6.9 31.1 4.1
32.8 7.8 32.4 3.4
33.5 4.0 33.2 5.4
NS NS
14.6 1.8 13.3 2.1
13.9 1.9 13.5 1.8
14.2 2.2 13.6 1.4
NS NS
NOTE. Data presented as mean standard deviation unless otherwise indicated. AMB, anteromedial bundle; NS, not significant; PLB, posterolateral bundle.
NS NS NS NS NS
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Fig 2. Computed digital radiographs of knee after double-bundle anterior cruciate ligament reconstruction: (A) anteroposterior (AP) view and (B) lateral view on first postoperative day and (C) anteroposterior view and (D) lateral view 2 years after surgery. The radiolucent line on the AP view of the radiograph taken on the first postoperative day and the sclerotic lines of the tunnel wall are enhanced on the AP and lateral views at 2 years after surgery. On the lateral view of the radiograph taken on the first postoperative day, the radiolucent line was not confirmed clearly. Therefore the drill size was used as the initial bone tunnel size. The 2 white arrows show the femoral outlet of the anteromedial tunnel, and the 2 black arrows show the femoral outlet of the posterolateral tunnel. The 2 femoral tunnel diameters are shown as a percentage of the maximum joint width of the proximal tibia on the AP view or a percentage of the maximum diameter of the patella on the lateral view. To determine the incidence of tunnel enlargement, percentage diameter changes of more than 10% and less than 10% are defined as an enlarged tunnel and a reduced tunnel, respectively. The double-headed arrows in the AP views show the maximum joint width of the proximal tibia, and in the lateral views show the maximum diameter of the patella.
period, range-of-motion exercises were performed gradually: 10 of knee flexion was started with a locked hard brace (Breg X2K brace; Breg, Carlsbad, CA) for 1 week, and thereafter, full extension was allowed. Partial weight bearing was started 1 week after surgery, with full weight bearing at 4 weeks. The knee brace was used by all patients for the first 3 months after surgery. Running was allowed at 3 months after surgery, followed by a return to cutting actions and contact sports at no sooner than 8 months postoperatively. Clinical Evaluation Follow-up examinations were performed at 2 years postoperatively. The evaluated factors were the Lysholm score and peak isokinetic quadriceps and hamstring torque at 60 /s measured with a Biodex 4 (Biodex Medical Systems, Shirley, NY). Isokinetic peak torque values were compared with the values of the contralateral knee. Measurements of knee range of motion such as extension lag were also performed. Three experienced senior orthopaedic surgeons (T.T., K.K., N.Y.) performed these clinical examinations and collected the data. Radiographic Evaluation Patients underwent radiologic examination twice, on the first postoperative day and 2 years after surgery, so that we could evaluate bone tunnel enlargement of both the AM and PL bundles in each group. Computed
digital radiographs (Fujifilm, Tokyo, Japan) of the knee were taken in the anteroposterior (AP) and lateral views for the purpose of measuring tunnel enlargement according to Webster et al.10 The tunnel wall was enhanced on the computed digital radiograph, controlling contrast, intensity, and brightness of the image, and the diameter of the tunnel was measured. The tunnel measurement was taken at the intra-articular outlet of the femoral tunnel in each plane, perpendicular to the direction of the long axis of the tunnel. To compare the femoral tunnel diameters on radiographs taken in the 2 different periods, each diameter was shown as a percentage of the maximum joint width of the proximal tibia on the AP view or a percentage of the maximum diameter of the patella on the lateral view (Fig 2). However, on the digital radiographs obtained immediately postoperatively, the sclerotic margin was not confirmed. Instead of the sclerotic margin, the radiolucent area was confirmed on the AP view. Therefore we evaluated the tunnel width using the radiolucent margin. On the lateral view of the digital radiographs obtained immediately postoperatively, the radiolucent area was not confirmed clearly. So, we used the drill size as the initial bone tunnel width. Using a transportal technique to create the femoral bone tunnel makes the cross section of the tunnel nearly round. The percentage change in the diameter between the 2 periods was defined as the percentage tunnel enlargement in diameter. It was difficult to determine the percentage
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FEMORAL BONE TUNNEL ENLARGEMENT AFTER ACLR Table 2. Clinical Results at 2 Years Postoperatively ACL reinjury, n Lysholm score Preoperative score Postoperative score Quadriceps torque at 60 /s compared with contralateral knee, %
Group A (n ¼ 18) 0
Group B (n ¼ 17) 0
Group C (n ¼ 16) 0
P Value NS
66.8 3.8 97.4 7.1 93.7 13.1*
64.1 5.3 98.0 5.8 96.8 12.9y
63.5 3.9 97.7 6.3 85.3 18.4*y
90.3 16.2
91.1 18.8
86.1 17.6
NS NS P ¼ .049* P ¼ .044y NS
1 (5.6) 0 (0)
1 (5.9) 0 (0)
Hamstring torque at 60 /s compared with contralateral knee, % Knee extension deficiency, n (%) 5
2 (12.5) 0 (0)
NS
NOTE. Data presented as mean standard deviation unless otherwise indicated. ACL, anterior cruciate ligament; NS, not significant. *Significant difference between group A and group C (P < .05). y Significant difference between group B and group C (P < .05).
tunnel enlargement in the tibial tunnels because the 2 intra-articular outlet images of the AM and PL bundles were overlapped in the radiographs. Therefore tibial bone tunnel measurements were excluded in this study. To determine the incidence of tunnel enlargement, percentage diameter changes of more than 10% and less than 10% were defined as an enlarged tunnel and a reduced tunnel, respectively, according to Kawaguchi et al.20 The tunnel enlargement grades were determined by a blinded, experienced orthopaedic surgeon. Statistical Analysis Intraobserver variability for the rate of femoral tunnel enlargement was satisfactory; the mean intraclass correlation coefficient was 0.92. On the basis of a power of 80% and a of .05, we calculated that the sample size required per group was 16. Statistical comparisons among the 3 groups were performed using 1-way factorial analysis of variance. When a significant difference was found by analysis of variance, we performed the Bonferroni-Dunn procedure as a post hoc test to determine which 2 of the 3 groups differed significantly for each parameter, including the clinical results and the magnitude and incidence of bone tunnel enlargement. Statistical analysis was performed with the statistical software package Ystat 2004 (Igaku Tosho Shuppan, Tokyo, Japan). The level of significance was set at P < .05.
Results Clinical Results There were 2 cases of meniscal injury after primary ACL reconstruction, and we excluded them from this study. These cases underwent another surgical procedure for treatment of the meniscus. The reconstructed ACL showed good results regarding tension, volume, and synovial coverage. There were no findings of ACL failure or laxity in either case. The mean follow-up period was 30.4 months (range, 24 to 48 months) in group A, 29.2 months (range, 24 to 38 months) in group B, and 28.5 months (range, 24 to 36 months) in group C. Muscle strength in knee extension at 2 years after surgery showed a significantly lower value in group C than in group A (P ¼ .049) and group B (P ¼ .044). The other clinical data showed no significant differences among the 3 groups (Table 2). Radiologic Results Concerning the femoral tunnels in group A, the incidence of AM tunnel enlargement was 66.7% and 61.1% on the AP view and lateral view, respectively, whereas the incidence of PL tunnel enlargement was 66.7% on both the AP and lateral views (Table 3). In group B the incidence of AM tunnel enlargement was 52.9% on the AP view and 58.8% on the lateral view, and the incidence of PL tunnel enlargement was 52.9%
Table 3. Incidence of Femoral Bone Tunnel Enlargement at 2 Years Postoperatively Anteromedial bundle Anteroposterior view Lateral view Posterolateral bundle Anteroposterior view Lateral view
Group A
Group B
Group C
Significance
12 of 18 (66.7) 11 of 18 (61.1)
9 of 17 (52.9) 10 of 17 (58.8)
9 of 16 (56.3) 10 of 16 (62.5)
NS NS
12 of 18 (66.7) 12 of 18 (66.7)
9 of 17 (52.9) 10 of 17 (58.8)
9 of 16 (56.3) 9 of 16 (56.3)
NS NS
NOTE. Data presented as number of cases (%). NS, not significant.
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Table 4. Magnitude of Percentage Femoral Bone Tunnel Enlargement at 2 Years Postoperatively Anteromedial bundle, % Anteroposterior view Lateral view Posterolateral bundle, % Anteroposterior view Lateral view
Group A
Group B
Group C
Significance
15.2 12.1 14.3 10.1
14.4 11.2 13.4 10.6
13.9 12.4 13.6 11.2
NS NS
14.5 13.4 14.4 10.3
14.0 11.4 13.8 11.3
14.2 12.7 14.5 13.2
NS NS
NOTE. Data presented as mean standard deviation. NS, not significant.
on the AP view and 58.8% on the lateral view. In group C, the incidence of AM tunnel enlargement was 56.3% on the AP view and 62.5% on the lateral view, and the incidence of PL tunnel enlargement was 56.3% on both the AP and lateral views. In each group no significant differences were observed. The magnitude of the percentage femoral bone tunnel enlargement also showed no significant differences in each group (Table 4). No cases of femoral bone tunnel reduction were found.
Discussion Previously, comparative studies on bone tunnel enlargement associated with the immobilization period concluded that bone tunnel enlargement after ACL reconstruction using hamstring autograft can be increased by an accelerated, brace-free rehabilitation protocol.17,18 However, the mean follow-up period of these reports was only 10 months (range, 9 to 11 months). The most important finding of our study was that a high incidence of femoral tunnel enlargement occurred not only in the 2-day immobilization group but also in the 2-week immobilization group; in group C, the incidence of AM tunnel enlargement was 56.3% on the AP view and 62.5% on the lateral view, whereas the incidence of PL tunnel enlargement was 56.3% on both the AP and lateral views. Our results showed a higher incidence of enlargement than that reported by Kawaguchi et al.20 and lower incidence than that reported by Cinar et al.19 These previous reports may have included ACL reconstruction with meniscal repair or recurvatum cases, which may have influenced the differences in the results. At our institution, we provide different protocols in cases with meniscal repair and recurvatum, such as a longer immobilization period, another immobilization angle, and a noneweightbearing period. In this study, therefore, cases of ACL reconstruction with meniscal repair and recurvatum were completely excluded. Moreover, in this study the 2-week immobilization group included 2 cases of slight knee extension deficiency and significant loss of muscle strength in knee extension 2 years after surgery compared with the contralateral knee. On the basis of these results, the 2-week postoperative immobilization protocol did not significantly reduce femoral bone tunnel enlargement after double-bundle ACL
reconstruction with hamstring grafts. This study suggested that double-bundle ACL reconstruction with hamstring grafts yields the potential risk of postoperative femoral bone tunnel enlargement on both the AM and PL views despite different postoperative immobilization periods. On the other hand, there was no clinically significant difference in tunnel enlargement based on clinical outcome scores among the 3 different immobilization periods. However, our results showed that the 2-week immobilization period after surgery had harmful effects, such as significantly less quadriceps muscle strength associated with longer immobilization. Many previous studies have reported the incidence of tunnel enlargement after single- or double-bundle ACL reconstruction with hamstring grafts in the femur.7-14,17-20 However, the postoperative knee immobilization periods were different, depending on the authors or institutions; some studies had an accelerated program, whereas other studies had a slow rehabilitation protocol, such as a 1- or 2-week postoperative immobilization period. Therefore the information from our study is clinically of value to clarify the most suitable postoperative immobilization period after doublebundle ACL reconstruction with hamstring grafts. The mechanism of tunnel enlargement is not yet fully understood. Previously, several possible factors contributing to tunnel enlargement after ACL reconstruction with soft-tissue grafts were proposed. These factors fall into 2 broad categories, biomechanical factors and biological factors. Biomechanical factors relate to the motion of the graft within the tunnel, with graft motion abrading the edge of the tunnel; a longer distance between the graft fixation points results in significantly greater longitudinal graft motion, called the bungee-cord effect, and transverse graft motion, called the windshield-wiper effect. Biological factors are related to bone resorption induced by biological activity. Several biological theories have been proposed: synovial fluid propagation within bony tunnels, localized bone necrosis possibly caused by the drilling process due to thermogenic effects that induce a nonspecific inflammatory response, biochemical mediators, and so on.12-14,24 Zysk et al.25 studied synovial fluid samples collected from patients after ACL
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reconstruction and reported that patients with bone tunnel enlargement had higher concentrations of tumor necrosis factor a, interleukin 6, and nitric oxide, indicating the involvement of these mediators in tunnel enlargement. Kawaguchi et al.20 reported that there was significantly less femoral tunnel enlargement after anatomic double-bundle ACL reconstruction with hamstring grafts than after single-bundle reconstruction; the potential mechanisms were less tension on the tunnel edge due to force sharing by the 2 bundles, less synovial fluid propagation because of a smaller tunnel diameter, and earlier graft remodeling and revascularization because of smaller grafts. In an animal model study, delayed application of cyclic axial loading after ACL reconstruction resulted in improved mechanical and biological parameters of tendon-to-bone healing compared with those associated with immediate loading.26,27 On the other hand, arthroscopic findings and clinical results after ACL reconstruction have been found to be satisfactory with both accelerated and less aggressive rehabilitation programs.28-30 The advantage of an accelerated rehabilitation protocol after ACL reconstruction is earlier normal function of the knee. On the basis of our results, a less aggressive protocol, such as a 2-week immobilization period, showed satisfactory clinical scores, but there were also a few cases of slight extension deficiency and significantly less knee extension strength. In the first 2 weeks after ACL reconstruction, several biological events are expected to prevent tunnel enlargement and/or stimulate tendon-bone healing, such as reduction of inflammation or filling of the bony tunnel by blood clots and fibrous tissue. However, our findings showed that 2 weeks of immobilization induced less muscle strength and a slight extension deficiency instead of preventing femoral tunnel enlargement. Therefore the most suitable immobilization period after double-bundle ACL reconstruction with hamstring grafts was shorter than 2 weeks. The radiologic and clinical evaluations showed satisfactory results in both the 2-day immobilization and 1-week immobilization groups with no significant difference. Limitations Several limitations of this study must be taken into consideration. First, the sample size in each group was small. Second, an important limitation is the lack of randomization. Third, MRI or CT was not used for measurement of tunnel enlargement in this study. CT scans may be more sensitive to detect early signs of bone tunnel enlargement than digital radiographs because the sclerotic margins are not present on radiographs until approximately 3 months after surgery.7 However, in the previous literature, digital radiography has been shown to have the same ability to identify bone tunnel enlargement after ACL reconstruction as
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CT.10,20,31 Moreover, digital radiography provides a time- and cost-effective means for documenting bone tunnel enlargement compared with MRI and CT. Fourth, tibial bone tunnel enlargement was not measured. After anatomic double-bundle ACL reconstruction, the 2 tibial intra-articular outlets of the AM and PL bundles were usually overlapped on the AP and lateral radiographic views.20 Fifth, we did not determine the interobserver variation in the radiographic evaluation. However, despite these limitations, this study provides important information on the postoperative immobilization period after ACL reconstruction with hamstring grafts.
Conclusions This prospective radiographic study showed that double-bundle ACL reconstruction with hamstring grafts yields the potential risk of postoperative femoral bone tunnel enlargement in both the AM and PL tunnels despite different postoperative immobilization periods, with no significant difference in the incidence and magnitude among groups with differing postoperative immobilization periods. In addition, a 2-week immobilization period after surgery showed harmful effects, such as significantly less quadriceps muscle strength. A postoperative immobilization period shorter than 2 weeks is recommended.
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