Treatment of Anterior Cruciate Ligament Tibial Avulsion Fracture in Children with Suture Anchor Fixation Outside The Tunnel: A Retrospective study


 Background: Anterior cruciate ligament (ACL) tibial avulsion fractures are a special ACL injury type, classified as intra-articular fractures. Presently, the main treatment method is arthroscopic surgery, and various fixation methods are available, including use of steel wires, high-strength sutures, cannulated screws, anchors, Kirschner wires, etc. Joint fixation using wire binding could cut through the bone tunnel. We aimed to evaluate the clinical efficacy of a novel method involving suture anchor fixation outside the tunnel to treat anterior cruciate ligament (ACL) tibial avulsion fractures in children.Methods: This retrospective study analyzed the data of 42 pediatric patients (26 boys and 16 girls; age: 7–13 years) with ACL tibial avulsion fractures. Based on the Meyers–McKeever–Zaricznyj classification of fractures, 22, 14, and 6 patients had types II, III, and IV fractures, respectively. All patients underwent arthroscopic surgery for ACL tibial avulsion fracture; during surgery, double tibial tunnels were established, and high-strength sutures were passed through the tunnels and fixed externally with an anchor. The clinical outcome was evaluated by assessing the pre- and post-operative knee joint range of motion (ROM) and by using the Lysholm knee function score and International Knee Documentation Committee (IKDC) score. Post-operative computed tomography and magnetic resonance images were reviewed to determine the status of fracture displacement, healing, and epiphyseal damage.Results: All 42 patients were followed up for 20–36 months (average of 27.8 months). Knee ROM increased from 48.2°±21.7° pre-operatively to 131.6°±8.7° at the final follow-up (t=23.119, P=0.000). The Lysholm knee function score increased from 37.6±5.2 points pre-operatively to 90.1±6.3 points post-operatively, representing a significant improvement (t=41.651, P=0.000). The IKDC score improved from 43.3±7.5 points pre-operatively to 91.3±5.7 points post-operatively (t=45.521, P=0.000). The imaging findings indicated that the fractures healed with displacement and there was no significant epiphyseal damage.Conclusions: Suture anchor fixation outside the tunnel to treat ACL tibial avulsion fracture in children reduces the cutting action of the sutures on the tunnel, minimizes epiphyseal damage, involves a simple procedure, offers firm fixation, and effectively improves knee function. This approach can enable early functional rehabilitation and achieve satisfactory clinical efficacy.

reports. [2][3][4][5] However, as children are still growing and developing, and their treatment principles differ from those of adults, special techniques in fracture reduction and xation, with the aim of avoiding iatrogenic injuries to the epiphysis during surgery when possible, need to be developed. The suture binding technology is widely used for ACL tibial avulsion fracture at present. 6 Previous studies showed that it is safe and feasible to reconstruct the ACL through the epiphyseal tunnel without varus or valgus deformity and leg shortening. [7][8] The use of suture anchors outside the tunnel is a novel method, and it can prevent high-strength sutures from cutting through the bone tunnel. This study aimed to evaluate the clinical e cacy of using suture anchor xation outside the tunnel in treating ACL tibial avulsion fractures in children. Our hypothesis was that the application of suture anchors outside the tunnel to x ACL tibial avulsion fractures would have advantages and would result in good fracture reduction.

General information
This retrospective study analyzed the data of 42 children with ACL tibial avulsion fractures who were admitted to our hospital between March 2014 and November 2017. This study was approved by the ethics committee of Fuzhou Second Hospital (No: FZSE2014039). Written informed consent was provided by the patients and their parent or legal guardian prior to participating in the study.

Inclusion criteria
The inclusion criteria were as follows: (1)

Exclusion criteria
The exclusion criteria were as follows: (1) old fractures (≥ 3 weeks) with a healing deformity that ends with an unreducible fracture; (2) other ligament injuries or type III meniscus injuries; and (3) cartilage injuries in other parts of the knee joint.

Surgical technique
After successful induction of anesthesia, a tourniquet was applied at the proximal thigh of the affected limb. The patient was then placed in a supine position, routinely disinfected, and draped, and the knee arthroscopy anteromedial and anterolateral approaches were established. Second, the synovial membrane, adipose tissue, and hematoma surrounding the fracture end were debrided. The meniscus and transverse ligament were retracted using a probe hook to fully expose the ACL tibial avulsion fracture ( Fig. 1A).Third, using the Lasso technique, two high-strength sutures of different colors were passed posteriorly around the ACL; then, both ends of the sutures were pulled anteriorly. Fourth, the anterior and anteromedial edges of the tibial avulsion fracture were xed using ACL xators (Fig. 1B), drilled using 2.0mm Kirschner wires, and pierced with a lumbar puncture needle. Then, a thin wire (Lasso suture) was guided through the tunnel with both ends of the same high-strength suture passing though the same tunnel to apply downward pressure on the upturned bone (Fig. 1C). Fifth, an absorbable anchor (DepuySynthes, Raynham, MA, US) was implanted at the tunnel exit, and the fracture was reduced by a downward traction of the pull sutures (Fig. 1D). The pulley technique was used to knot the pull sutures and anchor sutures of the same color, and the two pull sutures were xed on the anchor (Fig. 1E). Finally, the fracture end was stable after mobilizing the knee joint, and the wound was closed layer by layer.

Post-operative care
To protect the knee, an extension splint was used for 4 weeks with partial weight-bearing and crutches were used after the surgery. Quadriceps strength training and passive joint exion exercises began on the rst day after the surgery. The passive range of motion (ROM) of the knee joint was maintained within 0°-90°. Full ROM and full weight-bearing exercises were allowed on the fourth week after surgery.

Outcome evaluation indicators
Post-operative computed tomography and magnetic resonance images were reviewed to determine the status of fracture displacement, healing, and epiphyseal damage. Preoperative and nal follow-up joint ROM, the Lysholm score, and the International Knee Documentation Committee (IKDC) score were assessed to evaluate the clinical outcomes.

Statistical methods
The SPSS19.0 (SPSS Inc., Chicago, IL, US) statistical software package was used to perform statistical analyses on the data. Measurement data that were normally distributed or approximately normally distributed were expressed as mean ± standard deviation. Comparisons of pre-and post-operative observational indicators were performed using paired samples t-test. The signi cance level of testing was set at α = 0.05.

General information
There were 26 boys and 16 girls, with a mean age of 12 years (range, 7-13 years). Based on the Meyers-McKeever-Zaricznyj classi cation of fractures, 22, 14, and 6 patients had type II, III, and IV fractures, respectively.

Basic operative conditions
All patients in this study successfully completed the surgery, and the operative time ranged from 0.5 h to 1 h. There were no abnormalities or complications postoperatively in all cases, and the length of hospital stay was 3-5 days.
E cacy evaluation All 42 patients were followed up for 25-36 months. The imaging ndings at the nal follow-up showed the absence of fracture displacements, deformities in healing, or damages to the epiphysis (Fig. 2).

Discussion
In this study, arthroscopy was used to perform suture anchor xation outside the tunnel to treat children with ACL tibial fractures. The follow-up period was 25-36 months. No deformities or fracture nonunion were found in the affected limb; thus, the clinical outcome was satisfactory. The key points of this technique are as follows: (1) synovial tissue and hematoma surrounding the fracture were debrided, and the bone bed was freshened to avoid affecting fracture reduction; (2) xation was performed using ACL tibial xators, with the anterior and medial edges of the fracture as the chosen xation sites. Fine Kirschner wires were used to establish the tunnels, and sutures were guided through the tunnels.
Following the direction of the ACL, traction was rst applied to the medial pull suture to correct the lateral displacement, then to the anterior pull suture to apply downward pressure on the fractured bone; (3) during reduction, the anterior meniscus and transverse ligament are retracted using probe hooks to avoid affecting fracture reduction; and (4) under arthroscopic monitoring, the double pulley technique was used to adjust the tension of the high-strength suture.
An ACL tibial avulsion fracture is a type of ACL injury. The exion and rotational force of the knee joint can result in an ACL tibial avulsion fracture and displacement, ligament contracture, limited exion and extension of the knee joint, and impaired movement. Currently, such displaced fractures are often treated using arthroscopic surgery, and a wide variety of xation methods are available, including steel wires, high-strength sutures, cannulated screws, anchors, Kirschner wires, and so on. Steel wires offer poor toughness and non-elastic xation; hence, breakage can occur easily during knee exion and extension. 9,10 Kirschner wire xation causes minimal damage, but it does not offer su cient holding power, which can easily lead to the loosening or detachment of internal xation, thereby resulting in fracture re-displacement and affecting the function of the affected limb. 11 Currently, the most commonly used method in clinical settings is the technique of using cannulated screws, which generally involves utilizing two screws to x the fractured bone. This method is especially effective in the xation of larger bone fractures. 12 However, for pediatric patients, the relatively large diameter of cannulated screws means that the cutting action of the thread when inserting the screw can cause a more signi cant damage to the epiphysis. Moreover, ACL tibial fractures are smaller in children than in adult patients, which implies that screwing in and removing the xators will cause a greater damage to the ACL tibial spine. Therefore, this method should be used with caution in pediatric patients. 13 Fracture xation with high-strength sutures are also widely used in clinical practice. It is advantageous for the xation of comminuted ACL tibial fractures and does not require a second surgery to retrieve the xator. However, slippage of the sutures may occur to different degrees during knee exion and extension, which may cause cutting to the tunnel, thereby preventing early functional recovery. 14,15 Internal xation with suture anchors is one of the surgical approaches for treating ACL tibial avulsion fracture. In et al. used intraarticular suture anchors to x the fractured bone and obtained a satisfactory clinical e cacy. 16 However, they encountered di culty in adjusting the tension of the intra-articular suture, and excessively large knots may irritate the synovium or affect joint extension. Yao et al. used intra-articular xation with double row anchors to treat ACL tibial fractures and achieved satisfactory clinical e cacy. 17 However, for pediatric patients, the relatively large diameter of the lateral row anchors implies that pre-drilling and screwing in the anchor may lead to epiphyseal damage.
Unlike in adults, the proximal tibial epiphyseal plate in children plays a crucial role in the growth and development of the lower limbs. This is of particular importance when selecting the surgical method and xation for intra-articular fractures in this group. Jang et al. found that the 8-mm bone tunnel only damages 2.5% of the growth area of the tibial epiphyseal plate, and the damage area will decrease with age. 18 Thus, avoiding epiphyseal damage as much as possible is our top priority. Not only should we consider the healing of the fracture during the post-operative follow-up, but we should also pay attention to whether there is an epiphyseal damage and an abnormal development in the affected limb. The followup period should, therefore, be extended accordingly. Sinha et al. adopted an epiphyseal plate evasion method for the suture xation of ACL tibial avulsion fractures in children, and the early clinical outcomes were satisfactory. 19 Using arthroscopic techniques, Liu et al. drilled across the epiphyseal plate and performed gure-8 suture xation to treat ACL tibial avulsion fractures in children. 20 No deformities were found in the lower limbs of the patients during the 2-year follow-up.
The surgical method adopted in the present study has the following advantages: (1) drilling with smooth, ne Kirschner wires can avoid epiphyseal damage caused by the drilling of coarse screw threads; (2) the same suture remains in the same tunnel, which prevents cutting of the tunnel during knee exion and extension; (3) the surgical procedures are simple and do not require complicated winding of sutures. The two high-strength sutures are passed around posteriorly to the ACL tibial spine and pulled anteriorly. Then, the same high-strength suture is passed through the same tunnel to apply downward pressure on the upturned bone, which was subsequently followed by reduction and xation; (4) suture anchor xation outside the tunnel avoids the epiphysis, which only causes minimal damage to the epiphysis, and allows the tightening of the high-strength sutures for the effective xation of the fractured bone; and (5) it involves an extra-articular knot that will not irritate the synovium or affect the exion and extension of the joint.

Limitations
Given that the sample size of this study is relatively small, further large-scale follow-up studies are still needed. Furthermore, our technique has only been used in a clinical setting. To con rm the superiority of the extra-tunnel suture anchor xation method, further biomechanical studies are required.

Conclusions
The use of arthroscopic reduction monitoring and suture anchor outside the tunnel to treat children with ACL tibial fractures involves simple procedures, results in reliable reduction and xation, causes minimal epiphyseal damage, and reduces the cutting effect of the high-strength sutures on tissues. Therefore, this approach can enable early functional rehabilitation and achieve satisfactory clinical e cacy. Consent for publication: The manuscript does not contain any individual's data in any form (including personal or identifying details, images, or videos), and consent for publication has been obtained from the parent or legal guardian of the children. Availability of data and materials: All data analyzed in this study has been provided in the manuscript.

List Of Abbreviations
Competing interests: The authors declare that they have no competing interests.