Biomechanical comparison of three techniques for ... - Springer Link

Knee Surg Sports Traumatol Arthrosc (2012) 20:1470–1478 DOI 10.1007/s00167-011-1694-7

KNEE

Biomechanical comparison of three techniques for fixation of tibial avulsion fractures of the anterior cruciate ligament Yong In • Dai-Soon Kwak • Chan-Woong Moon Seung-Ho Han • Nam-Yong Choi

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Received: 7 April 2011 / Accepted: 27 September 2011 / Published online: 11 October 2011 Ó Springer-Verlag 2011

Abstract Purpose To evaluate the initial stability of a suture anchor fixation and to compare this with a screw fixation and pull-out suture fixation for anterior cruciate ligament tibial avulsion fracture. Methods The initial fixation strength of 3 different fixation techniques, antegrade cannulated screw fixation, pullout suture fixation with Ethibond and bioabsorbable knotless suture anchor fixation, was evaluated. Using 14 fresh cadavers (28 knees), the strength to failure, initial displacement and mode of failure were measured. Results The strength to failure of the suture anchor fixation was not significantly different from that of the screw fixation and was higher than that of the pull-out suture fixation. The initial displacement of the suture anchor fixation was lower than that of the screw fixation and the pull-out suture fixation. The majority of the suture anchor fixations and the screw fixations were failed by pull-out from the bone. Eight of the 56 suture anchor fixations failed by pull-out of the suture from the ligament proper.

Dai-Soon Kwak and Yong In contributed equally to this paper. Y. In C.-W. Moon N.-Y. Choi Department of Orthopedic Surgery, College of Medicine, The Catholic University of Korea, Seoul, Korea D.-S. Kwak S.-H. Han Department of Anatomy, Catholic Institute for Applied Anatomy, College of Medicine, The Catholic University of Korea, Seoul, Korea C.-W. Moon (&) Department of Orthopedic Surgery, Bucheon St. Mary’s Hospital, The Catholic University of Korea, 2, Sosa-Dong, Wonmi-Gu, Bucheon, Gyeonggi-Do 420-717, Korea e-mail: [email protected]

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And, one of the 7 screw fixations failed due to fracture of the avulsed bony fragment. All of the pull-out suture fixations failed by suture material rupture. Conclusions These biomechanical results suggest that the initial fixation strength of suture anchor fixation was not less than that of screw fixation or pull-out suture fixation. And, the initial displacement of suture anchor fixation was lower than that of screw fixation or pull-out suture fixation. The suture anchor fixation appears to be a good alternative fixation technique for repair of anterior cruciate ligament tibial avulsion fracture. Keywords Knee Anterior cruciate ligament Tibial eminence fracture Suture anchor Biomechanics

Introduction Many authors recommend that anatomical reduction and stable internal fixation for displaced anterior cruciate ligament tibial avulsion fracture (anterior cruciate ligament tibial avulsion fracture) are required to restore normal knee biomechanics [1, 8, 15, 17, 23, 26, 32–35, 40, 41]. Although many successful arthroscopic reduction and internal fixation (ARIF) techniques using a variety of fixation methods have been described in the literature, fixation is most commonly achieved with pull-out sutures or with screws [2, 8, 12, 13, 16, 17, 19, 27, 28, 31, 36, 44]. However, the screw fixation and the pull-out suture fixation with nonabsorbable sutures have several limitations [7, 14, 21, 42, 44, 45]. And they also raise concerns regarding possible physeal damage in skeletally immature patients, as they may need transepiphyseal drilling [3, 21, 22]. Thus, new fixation technique, the suture anchor fixation technique was reported and showed excellent clinical results

Knee Surg Sports Traumatol Arthrosc (2012) 20:1470–1478

and anatomical reductions in the anterior cruciate ligament tibial avulsion fracture fragment without physeal damage [14]. Only a few studies have investigated the biomechanical performance of different arthroscopic fixation techniques for anterior cruciate ligament tibial avulsion fracture [7, 9, 22, 39]. To author’s knowledge, however, no study has compared the initial fixation strength of anterior cruciate ligament tibial avulsion fracture that was fixed with suture anchors with that of other fixation techniques. Moreover, because bone density and the types of bone are important variables affecting the biomechanical performance of suture anchors [4, 29, 37], differences in bone quality between shoulder and knee may instill a doubt as to whether a suture anchor fixation for repair of anterior cruciate ligament tibial avulsion fracture can provide sufficient initial fixation strength to maintain a reduction as for the repair of shoulder lesions. Thus, the biomechanical properties of suture anchors with the 2 most commonly used fixation devices such as sutures and screws were compared. The aim of this study is to evaluate the initial fixation strengths of different fixation techniques for anterior cruciate ligament tibial avulsion fracture under cyclic loading. The suture anchor fixation technique and 2 commonly used techniques (1) pull-out suture fixation and (2) antegrade screw fixation were tested. It was hypothesized that fixation of anterior cruciate ligament tibial avulsion fracture using 4 suture anchors would result in similar or superior fixation strengths when compared with fixations using a pull-out suture technique or a screw.

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the sizes of the fracture fragment be consistently 15 9 15 9 10 mm height (Fig. 1). Study groups To minimize the biases from bone quality and individual differences, including age and sex, the 14 cadavers were randomly divided into 2 study groups of 14 knees each. In the group 1, the right or left knee, which was selected randomly, was repaired by the suture anchor fixation technique, and the opposite knee of the same cadaver was repaired by the screw fixation technique. In this way, 7 matched pairs of specimens were prepared. In the group 2, 7 right or left knees were repaired by the suture anchor fixation and the remainder was repaired by the pull-out suture fixation technique as in the group 1. Thus, by mating the right knee with the left knee for the same cadaver, it was able to compare the fixation strength of each technique without bias due to bone quality and individual differences. The summary of study groups is described in Table 1. Surgical procedures For cannulated screw fixation, a 4 mm diameter and 28 mm length partially threaded titanium cannulated screw (U&I, Seoul, Korea) which has 12 mm thread length and 1.75 mm thread pitch was used. After the fracture fragment was reduced anatomically, a small guide pin (U&I) was drilled from the center of the fracture fragment to the posterolateral cortex of the tibia at an angle 45° to the coronal and sagittal axial plane. A cannulated reamer (U&I) was used for drilling through the fracture fragment

Materials and methods Specimen preparation Twenty-eight fresh-frozen human cadaveric knees from 14 cadavers were used. The cadavers ranged in age from 33 to 73 years (average 59.6 ± 10.4 years): 8 were men and 6 were women. The specimens had no ligamentous injury on clinical examination and no significant degenerative joint disease by visual inspection. During preparation and testing, the specimens were moistened with saline. After thawing for 24 h at room temperature, the femur and tibia were cut to 15 cm in length from the joint line. The soft tissues were dissected to isolate the knee joint capsule and ligaments, including medial collateral ligament, anterior and posterior cruciate ligaments. The tibial eminence, including the entire area of the anterior cruciate ligament (ACL) tibial attachment, was completely separated from the tibia with a sharp osteotome of 15 mm width to produce a Meyers and McKeever type III anterior cruciate ligament tibial avulsion fracture [24]. The fracture fragments were trimmed to make

Fig. 1 Created type III ACL tibial avulsion fracture with an osteotome. The fragment size was consistently 15 9 15 9 10 mm height

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Table 1 Summary of study groups Group

N

Age (year)

Gender

Fixation

Suture anchor

Male

Female

Suture anchor

Screw

Pull-out suture

Strength to failure (N)

Initial displacement (mm) 0.4 ± 0.2

1

14

61.9 ± 6.8

4

3

7

7

0

101.8 ± 29.0

2

14

57.4 ± 13.2

4

3

7

0

7

99.2 ± 30.5

0.6 ± 0.2

n.s.

n.s.

P value

n.s.

Each group consisted of 7 matched pairs of specimens

into the tibia. Then, a cannulated screw was inserted antegradely from the joint surface over the guide pin, not penetrating the distal tibial cortex (Fig. 2). For pull-out suture fixation, 2 bone tunnels of 2.7 mm diameter were created from just medial and lateral of the repositioned fracture fragment to the anteromedial cortex of the proximal tibia using an ACL tibial guide and a guide pin (Linvatec, Largo, FL, USA). The distal outlet of the 2 tunnels was more than 10 mm apart. Two No. 2 Ethibond (Ethicon, Somerville, NJ, USA) sutures were passed through the ACL just proximal to the fracture fragment anteriorly and posteriorly to the tunnels. Two sutures were passed through each tunnel using a 24 gauge wire loop. Then, the fracture fragment was reduced anatomically, and doubled sutures were pulled out tightly and tied with 5

knots over a tibial bony bridge between tunnels (Fig. 3). Because No. 2 Ethibond sutures were used more frequently in previously reported studies [9, 22, 39, 45], though No. 5 Ethibond sutures are thicker and preferable, we chose No. 2 Ethibond sutures as a fixation material. For suture anchors fixation, 4 BioKnotless suture anchors (DePuy Mitek, Raynham, MA, USA) with Ethibond were used. This biodegradable anchor is made of poly-L-lactic acid and is a toggle anchor of which body has a nub on the tip of the lower distal anchor prong and comes with the suture loop engaged in the distal anchor prong. This triangular-shaped anchor is 3.9 mm at the widest part, 9 mm long, and is inserted into a 2.9-mm drill hole (Fig. 4). The anterior cruciate ligament tibial avulsion fracture was repaired using the technique described by In et al. [14].

Fig. 2 Antegrade cannulated screw fixation of ACL tibial avulsion fracture. The direction of screw is from the center of the fracture fragment to the posterolateral cortex of the tibia at an angle 45° to the coronal and sagittal axial plane

Fig. 3 Pull-out suture fixation of ACL tibial avulsion fracture using two No. 2 Ethibond sutures

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Fig. 4 Shape and size of the BioKnotless suture anchor (DePuy Mitek). This triangular-shaped anchor is 3.9 mm at the widest part, 9 mm long, and is inserted into a 2.9-mm drill hole

While maintaining the anatomical reduction, a guide suture was introduced into the inferior anteromedial part of the ACL. A 17.8 mm deep drill hole was then created using a 2.9 mm arthroscopic drill (DePuy Mitek) in the tibial plateau just medial from the fracture site (Fig. 5a). A utility loop of a BioKnotless suture anchor (DePuy Mitek) assembly was then passed through the ACL by pulling the guide suture. One strand of the anchor loop was captured in the channel at the tip of the anchor (Fig. 5b). The anchor was then inserted and slowly tapped into the drill hole to the desired depth to achieve appropriate tissue tension (Fig. 5c). Similar procedures were performed for the anterolateral, posteromedial and posterolateral parts of the ACL until all four suture anchors were inserted (Fig. 5d). Measurements All tests were performed at room temperature. The proximal and distal parts of the specimens were fixed in a custom-made device mounted in a materials testing machine, Instron 5567 (Instron Corp, Canton, MA, USA), at 30° of knee flexion and neutral rotation (Fig. 6). The material testing machine used in this test had enough measurement accuracy of ±0.05 N at load and ±0.02 mm at displacement. The results were rounded off to one decimal place. The custom-made device also had no measureable compliance under maximum test load (200 N). The angle of tension was 30° to simulate an anterior tibial translation. All remaining ligaments, except the repaired ACL, were transected at the mid-substance level just prior to biomechanical testing. After applying a 5 N preload to reduce the loads across the joint surface and isolate the eminence repair, tension was applied to the specimen by a series of 10 cycles at 1 Hz from 0 to 30 N, in order to estimate initial displacement from the second to the ninth cycle (Fig. 7b) and then it was extended at a rate of 200 mm per minute until failure. The resulting load–displacement curve and the strength to failure were recorded. The strength to failure was determined to be that point of the load–displacement curve where the first ultimate failure load was documented (Fig. 7a). The mode of failure was recorded macroscopically.

Fig. 5 Surgical techniques of fixation of ACL tibial avulsion fracture using BioKnotless suture anchor (DePuy Mitek) (a) Prepare the drill hole (b) Pull the anchor loop through the ACL and capture one strand in the channel at the tip of the anchor (c) Insert and tapped the anchor into the drill hole (d) Finally, the anteromedial, anterolateral, posteromedial and posterolateral parts of the ACL were fixed by 4 suture anchors

Statistical analysis Statistical comparisons between experimental groups were performed using Mann–Whitney U test and Spearman’s correlation test. The level of significance was set at P \ 0.05.

Results The average age for group 1 was 61.9 ± 6.8 year and 57.4 ± 13.2 year for group 2. Each group had same sex ratio of 4 men and 3 women. The average strength to failure for the suture anchor fixation was 101.8 ± 29.0 N in group 1 and 99.2 ± 30.5 N in group 2. The average initial displacement for the suture anchor fixation was 0.4 ± 0.2 mm in group 1 and 0.6 ± 0.2 mm in group 2. There was no statistically significant difference between

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groups in age, sex, strength to failure and initial displacement for the suture anchor fixation (Table 1). Five of the 7 cannulated screw fixations showed higher strength to failure than that of the suture anchor fixations but there was no significant difference between the average strength to failure for the cannulated screw fixation (126.6 ± 69.0 N) and suture anchor fixation (101.8 ± 29.0 N) (Fig. 8). The average initial displacement for the cannulated screw fixation (0.7 ± 0.2 mm) was significantly longer

than suture anchor fixation (0.4 ± 0.2 mm, P = 0.018) (Fig. 9). None of the cannulated screw fixations showed lower initial displacement than that of the suture anchor fixations (Table 2). The average value of strength to failure for the pull-out suture fixation (77.9 ± 29.4 N) was significantly lower than suture anchor fixation (99.2 ± 30.5 N, P = 0.048) (Fig. 8). The average value of initial displacement for the pull-out suture fixation (0.9 ± 0.4 mm) was longer than suture anchor fixation (0.6 ± 0.2 mm, P = 0.025) (Fig. 9). None of the pull-out suture fixations using Ethibond sutures showed higher strength to failure and lower initial displacement than that of the suture anchor fixations (Table 3). The details of mode of failure are outlined in Table 4. Eight of the 56, 14% of the suture anchor fixations failed by cutting of the ACL proper at the suture site, and the remainder failed by pull-out of the suture anchors from the bone. The suture anchors failed by ACL cutting at the suture site usually occurred in suture anchor fixations located at posteromedial and posterolateral aspects of ACL for specimens from younger donors. And, higher failure loads were achieved when ACL cutting at the suture site occurred before the suture anchor pulled out from the bone. But, there were no significant correlations between specimen’s age and strength to failure or initial displacement. One of the 7 screw fixations failed due to fracture of the avulsed bony fragment and that failure also occurred in the youngest specimen with good bone quality. The remainder failed by pull-out of the screws from the bone. All of the pull-out suture fixations failed by suture material rupture following tightening or slippage at the suture knots or suture material elongation.

Fig. 6 The test setup. The specimen was fixed in a custom-made device mounted in Instron 5567. The angle of tension was 30° to imitate an anterior tibial translation and the upward traction force (arrow) acted as a force to make the tibia translate anteriorly in this setup

Discussion

Fig. 7 Obtained load– displacement curve by Instron (a) The strength to failure was determined to be that point of the load–displacement curve where the first ultimate failure load was documented (b) The initial displacement was defined as displacement from the second to the ninth cycle after a series of 10 cycles of tensioning from 0 to 30 N

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The most important finding of this study is that bioabsorbable knotless suture anchor fixation has similar or


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higher strength to failure and lower initial displacement as compared with antegrade cannulated screw fixation and pull-out suture fixation using Ethibond. The results of the current study support its initial hypothesis. To author’s knowledge, this is the first study that investigates the initial

Fig. 8 Histogram of strength to failure in N (mean ± SD). * indicates statistically significant differences (P \ 0.05)

Fig. 9 Histogram of initial displacement in mm (mean ± SD). * indicates statistically significant differences (P \ 0.05)

fixation strength of a suture anchor for repair of anterior cruciate ligament tibial avulsion fracture in the English medical literature. In spite of the reported successful outcomes with arthroscopic repairs of anterior cruciate ligament tibial avulsion fracture, some follow-up studies have shown a disturbing amount of residual laxity [3, 5, 13, 21, 23, 32, 33, 40, 45]. Residual laxity may result from secondary dislocation of the bony fragment attributable to insufficient fixation technique. Unreliable fixation techniques carry the risk for a loss of reduction and require prolonged postoperative immobilization, which makes early rehabilitation impossible, and may result in arthrofibrosis and limitation in range of motion [23, 25]. For these reasons, strong initial fixation strength at the fixation site is the key for reducing motion complications. The strength to failure, which was measured as the upper limit of the fixation construct during the single cycle load to failure test, is the useful information because it could give pertinent information with regard to the behavior of the fixation during unexpected loading events, such as those associated with the loss of balance or a fall [6]. The results of this study show that the average strength to failure of the suture anchor fixation was higher than that of the pull-out suture fixation using Ethibond. And, there were no significant biomechanical differences between suture anchor fixation and antegrade screw fixation. It seems that suture anchor fixation can provide similar or higher fixation strength as compared with the other fixations during unexpected loading events. The initial displacement of fixation, which was measured as the amount of fracture displacement after repetitive submaximal force loadings, could be a predictor of potential loss in reduction during healing and rehabilitation [22], though it actually means displacement of fixation immediately after the surgery in this study. Initial displacement may contain the creep of the ACL and fixation devices. Because this study design is the comparison between matched right and left knee for the same cadaver, the effect of the creep of the ACL could be ignored. However, the creep of used fixation devices may be different from the others so it could have influence on the result and we could consider the initial displacement is an

Table 2 Summary of group 1 results Fixation

N

Suture anchor

7

Screw

7

Age (year)

61.9 ± 6.8

Gender


Initial displacement (mm)

Male

Female

4

3

101.8 ± 29.0

0.4 ± 0.2

4

3

126.6 ± 69.0

0.7 ± 0.2

n.s.

0.018*

P value Cannulated screw fixation versus bioabsorbable suture anchor fixation * Statistically significant differences

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Table 3 Summary of group 2 results Fixation

N

Suture anchor

7

Pull-out suture

7

Age (year)

57.4 ± 13.2

Gender


Initial displacement (mm)

Male

Female

4

3

99.2 ± 30.5

0.6 ± 0.2

4

3

77.9 ± 29.4

0.9 ± 0.4

P value

0.048*

0.025*

Pull-out suture fixation versus bioabsorbable suture anchor fixation * Statistically significant differences

Table 4 Details of mode of failure Mode

Suture anchor (n = 56)

Screw (n = 7)

Pull-out suture (n = 14)

Pull-out from bone

48 (86%)

6 (86%)

0

Rupture of suture material

0

0

14 (100%)

Fracture of fragment

0

1 (14%)

0

Cutting of ACL

8 (14%)

0

0

n: Total number of used fixation devices

end result including difference in creep of fixation device. In this study, the suture anchor fixation showed significantly less initial displacement than either antegrade screw fixation or pull-out suture fixation using Ethibond. It seems that the initial stability of the suture anchor fixation is superior to that of the other fixations. Because only the strength to failure and initial displacement of antegrade screw fixation (or pull-out suture fixation) to those of suture anchor fixation were compared in this study design, direct differences between antegrade screw fixation and pull-out suture fixation could not be estimated. Seon et al. [32] reported that both the screw and the suture fixation techniques for the anterior cruciate ligament tibial avulsion fracture produced relatively good results in terms of functional outcomes and stability without any significant differences. Because available human cadaveric resources were limited and there are several already reported studies comparing antegrade screw fixation and pull-out suture fixation [7, 9, 22, 32, 39], it was not planned to make the third group to compare antegrade screw fixation and pull-out suture fixation directly. But it would be desirable that further studies about comparison between antegrade screw fixation and pull-out suture fixation should be done, because the previous studies showed conflicting results. Although Tsukada et al. [39] reported that antegrade screw fixation had greater stability than pull-out suture fixation using Ethibond, other studies [9, 22] reported that there were no significant differences between antegrade screw fixation and pull-out suture fixation using Ethibond. The superior stability of antegrade screw fixation in Tsukada’s study [39] may have resulted from their use of screw fixation penetrating far cortex

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rather than screw fixation engaged only cancellous bone used in the other studies. Two modes of failure were observed in the specimens fixed with suture anchors. The primary mode of failure was suture anchor pull-out from the bone. But, 14% of the suture anchors failed by ACL cutting at the suture site, which mostly occurred in suture anchor fixations located at posteromedial and posterolateral aspects of ACL for specimens from younger donors. During testing, higher failure loads were achieved when ACL cutting at the suture site occurred before the suture anchor pulled out from the bone. While pull-out of a suture anchor may result from improper insertion, it is likely that poor bone quality contributed to the pull-out before suture and tissue failure [4, 10, 18, 29, 30, 37, 38]. The age and bone quality of the specimens used in this study were the potential factors for influencing the mode of failure, though there was no significant correlation between the specimen’s age and strength to failure or initial displacement. One of the 7 screw fixations was failed by breakage of the fracture fragment instead of pulling out from the bone. This occurred in the youngest specimen with good bone quality and showed much higher strength to failure. All of the pullout suture fixations using No. 2 Ethibond failed due to suture material rupture following tightening or slippage at the suture knots or suture material elongation. This may be due to the lower stiffness of No. 2 Ethibond [9, 39, 43] and the requirement of knot tying for pull-out suture fixations [18]. Although use of stronger suture materials such as No. 5 Ethibond and Fiberwire (Arthrex, Naples, Fl, USA) instead of No. 2 Ethibond could vary these results [7, 9], in light of these observations, these kinds of displacement of


pull-out suture fixation before failure could have a negative impact upon early rehabilitation and fracture healing [25]. There were several limitations to the present study. First, this study was a test of biomechanical comparisons involving an isolated portion of the knee and the tensile force applied in the study acted only in the anterior drawing direction. This setting may not reflect actual situations in vivo that rotational forces act on, and the results of this study should be interpreted as a part of a more complex system in vivo. And, there are many factors that influence the clinical outcome in addition to the biomechanical properties of a fixation device. It is important to fix a fracture with the most stable fixation in order to begin early motion and weight bearing, while keeping in mind the tolerances of the implants used and quality of the repair performed. Second, the average age of donors for the specimen was much older than the average age of patients with anterior cruciate ligament tibial avulsion fracture [11]. And, the age range for the cadaveric donor in this study was relatively wide. Specimens from older donors may have had poorer bone quality than younger donors. Poor bone quality contributes to fixation failures by pulling out before suture failure [7, 18]. But, human cadaveric materials from young age group are difficult to obtain. Osteoporotic bone quality of older specimens could have adversely affected the strength of screw fixation and suture anchor fixation. Third, as mentioned above, the third group to compare antegrade screw fixation and pull-out suture fixation directly was not made because of limited cadaver resources and known references [7, 9, 22, 39]. Fourth, the fixations used in this study were performed in open procedures rather than arthroscopic procedures, which could adversely or beneficially influence the stability of some fixation techniques. And, No. 2 Ethibond was used instead of No. 5 Ethibond for pull-out suture fixation. Because No. 5 Ethibond is thicker and stiffer than No. 2 Ethibond, it could be preferable and used in many clinical situations. But, as mentioned above, No. 2 Ethibond was chosen as a fixation material because No. 2 Ethibond was used more frequently in previously reported comparative studies [9, 22, 39]. Last, a small number of load cycles were used in this study, and this obviously influenced the initial displacement. It was desirable that use more cycles up to at least 1,000, but results of this study could represent the displacement in the early stage of postoperative immobilization. This study showed that 4 bioabsorbable knotless suture anchor fixation has similar or higher strength to failure and lower initial displacement as compared with antegrade cannulated screw fixation engaged only cancellous bone and pull-out suture fixation using No. 2 Ethibond. These findings could provide biomechanical advantages for suture anchor fixation for treatment of anterior cruciate ligament tibial avulsion fracture. But considering the cost of 4 suture

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anchors with regard to 1 cannulated screw when there is no comminution of anterior cruciate ligament tibial avulsion fracture, there are significant cost increase for a technique that does not provide a higher biomechanical performance compared with simple screw fixation. However, screw fixation and pull-out suture fixation may need transepiphyseal drilling [3, 21, 22] that raises concerns regarding possible physeal damage in skeletally immature patients. While sutures and screws are not applicable to all types of anterior cruciate ligament tibial avulsion fracture, suture anchors can be used in repair of anterior cruciate ligament tibial avulsion fracture regardless of size or comminution of fracture fragment and presence of open physis [14, 20, 42, 44]. So it would be a good choice to use suture anchor fixation for anterior cruciate ligament tibial avulsion fracture in spite of its high cost when screw fixation is unsuitable or impossible, especially in case of skeletally immature patient.

Conclusions These biomechanical results suggest that the initial fixation strength of suture anchor fixation for anterior cruciate ligament tibial avulsion fracture was not less than that of screw fixation or pull-out suture fixation. And, the initial displacement of suture anchor fixation for anterior cruciate ligament tibial avulsion fracture was lower than that of screw fixation or pull-out suture fixation. The suture anchor fixation appears be a good alternative fixation technique for anterior cruciate ligament tibial avulsion fracture, especially in case of small, comminuted fracture fragment or presence of open physis. Acknowledgments This work was supported by the National Research Foundation of Korea grant funded by the Korea government (MEST) (KRF-2008-359-E00001).

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