Arthroscopic mini tunnel suture bridge for ACL tibial avulsion fractures repair
The avulsion fracture at the tibial insertion of the anterior cruciate ligament (ACL) is a rare type of knee joint injury, commonly seen in adolescents, accounting for 2.5% of all pediatric knee injuries . Because the fracture occurs at the tibial attachment site of the ACL and the fracture fragment can be easily displaced due to the pull of the ligament, non-surgical treatment often yields poor results. In clinical practice, numerous instances of comminuted ACL avulsion fractures have been encountered, where simple screw fixation has proven to be inadequate for restoring the ligament’s tension . Consequently, displaced avulsion fractures at the tibial attachment require surgical treatment, either through open repair or arthroscopically assisted techniques, with the latter being considered the superior approach. In children, the tibial insertion of the ACL is not fully ossified, and the tendon-bone interface consists of only a thin layer of fibro-cartilage, making it difficult for screws to achieve effective fixation. Some surgeons had adapted the suture bridge technique, originally used for rotator cuff repair, for repairing avulsion fractures at the tibial insertion site of the ACL , . This technique uses cables to generate high contact pressure, providing robust fixation and achieving excellent therapeutic outcomes, without the need for a second surgery to remove the device. However, due to the requirement of inserting three or four anchors, and considering that the bone bed at the tibial insertion site in children is relatively small, the insertion of too many anchors might have a significant impact on the bone bed in children , . The purpose of this study was to evaluate the results of arthroscopic transosseous suture bridge for repairing tibial avulsion fractures of the ACL with a modified mini tunnel technique. The authors hypothesized that this mini tunnel and suture bridge technique could provide enough stability fixations and anatomical reduction for the fracture fragment, protect the contact surface of the bone bed, and successfully avoid injury to the epiphyseal plate. The refined surgical skills and clinical efficacy of this technique are reported in the subsequent findings. 

General data A retrospective analysis was conducted on 39 cases of various types of tibial avulsion fractures of the ACL admitted to our department from July 2016 to July 2023. They exhibited varying degrees of pain, swelling, and limited mobility, with positive anterior drawer test and Lachman test. Preoperatively, patients underwent thorough knee joint CT-3D and MRI examinations to ascertain the type of fracture and to check for any concomitant injuries (Table ). This is an retrospective study. The Research Ethics Committee of the Affiliated Hospital of North Sichuan Medical College has approved this study (2024ER0186). Adhering to the ethical principles of the 1964 Declaration of Helsinki, we obtained informed consent forms signed by all patients’ guardians prior to the operation. Technical methods Modified minimal bone tunnel creation method Initially, the anesthetic epidural needle was modified by straightening its tip to create a hollow steel needle for bone tunneling. The outer diameter of this needle was 1.8 mm, and the inner diameter was 1.2 mm, which was suitable for positioning with a 1.0 mm Kirschner wire (K-wire). Using an ACL reconstruction aiming device, 1 mm K-wires were placed on the medial and lateral sides at the anterior edge of the bone bed, with a minimum distance of 10 mm between the two wires. Subsequently, the epidural needle was fitted over the K-wire, and the tunnel was manually and slowly drilled open (Fig. ). This method results in a smaller diameter bone tunnel, positioned at the junction of the footprint area bone bed and the articular cartilage surface, thus having minimal impact on the bone bed . Intraoperative suture bridge technique All patients were operated by the same surgical team under arthroscopy. Anesthesia was performed using lumbar anesthesia, with the patient in a supine position and a tourniquet applied to the thigh. Surgical approaches included the anteromedial and anterolateral portals of the knee joint. Arthroscopy was conducted first to inspect the joint, and a probe was used to identify the location, size, and type of the bone fragment. The edges of the bone fragment and the interior of the bone bed were freshened with a shaver. Initially, the approach is made through the midline of the patellar tendon, with the arthroscope inserted as the observational portal. The anteromedial and anterolateral portals are utilized as the working portals, respectively, for inserting a suture anchor and passing sutures with a suture hook., At a knee flexion of 90°, through the anteromedial portal, an awl is inserted. The awl is then smoothly tapped into the harder bone quality at the posterior edge of the bone bed, followed by the successful placement of a suture anchor (InLoc anchor, Hangzhou Rejoin Mastin Medical Device Co, P.R. China). Suture hooks are used to pass two sutures through the anterior cruciate ligament on its medial and lateral sides, respectively. Then, PDS (polydioxanone) suture is utilized to pull both strands of the anchor sutures out. After the tail sutures are crossed, they are guided through the tissue between the ligament and the fracture fragment. Utilizing an ACL aiming device, two minimal bone tunnels are created on the medial and lateral sides of the anterior edge of the bone bed. PDS sutures are then used to pull the anchor suture tails out of these tunnels. Under the surveillance of arthroscopy, a small hemostat is introduced through the anteromedial approach to adjust the suture cable to the appropriate position. Then, the hemostat is pressed onto the bone fragment, forcefully pressing the fragment towards the bone bed while gradually tightening the suture cable, which is then secured outside the tunnel with a locking suture anchor (GripLoc knotless anchor, Hangzhou Rejoin Mastin Medical Device Co, P.R. China). Finally, check the reduction of the bone fragment and the stability of the fixation (Fig. ). If, after tightening the suture bundle, there is still poor alignment or contact between the bone fragment and the bone bed, additional steps can be taken. Two strands of high-strength suture can be added to wrap around the ACL ligament, followed by the creation of two more mini bone tunnels. After adjusting the position of the bone fragment and pulling the reinforcement sutures through, tightening them significantly enhances the stability of the bone fragment and the reliability of the reduction. Before the end of the surgery, the knee joint was flexed and extended to carefully check whether the bone fragment was firmly fixed and whether the ACL had regained its tension, ensuring that the bone fragment had close contact and no displacement during extension. After thorough hemostasis, the wound was irrigated with a large amount of physiological saline and then sutured. Large cotton pads and elastic bandages were wrapped from the foot to above the knee joint. Postoperative management and rehabilitation Postoperatively, the affected limb was bandaged with an elastic bandage, and a knee brace was used to keep the knee in an extended position for four weeks. Isometric contraction exercises for the quadriceps muscles began on the first postoperative day. The knee flexion should not exceed 30° within the first two weeks post-surgery, reach 90° by four weeks, and achieve full range of motion by eight weeks. Partial weight-bearing with crutches was allowed after four weeks, and full weight-bearing was achieved by eight weeks post-surgery. Whether to return to sports or activity should be based on the process of fracture healing. Follow-up and clinical evaluation During follow-up, the duration of the surgery and the amount of bleeding were recorded. Symptoms such as swelling, pain, joint effusion, postoperative fracture reduction, and joint mobility were observed. X-rays were taken at 1, 3, 6, and 12 months post-surgery to observe whether the fracture line had healed and whether the position of the fracture fragment had returned to normal. At the end of the follow-up, the stability of the ligament was assessed using the anterior drawer test and the Lachman test. The knee joint functional scores was evaluated based on the Lysholm scores and International Knee Documentation Committee (IKDC) functional scores . Statistical analysis Analysis was performed using the SPSS 22.0 statistical software. Data that conform to a normal distribution were represented as the mean ± standard deviation. The preoperative and postoperative Lysholm scores were compared using a paired t-test, with a P-value less than 0.05 indicating a statistically significant difference. 

A retrospective analysis was conducted on 39 cases of various types of tibial avulsion fractures of the ACL admitted to our department from July 2016 to July 2023. They exhibited varying degrees of pain, swelling, and limited mobility, with positive anterior drawer test and Lachman test. Preoperatively, patients underwent thorough knee joint CT-3D and MRI examinations to ascertain the type of fracture and to check for any concomitant injuries (Table ). This is an retrospective study. The Research Ethics Committee of the Affiliated Hospital of North Sichuan Medical College has approved this study (2024ER0186). Adhering to the ethical principles of the 1964 Declaration of Helsinki, we obtained informed consent forms signed by all patients’ guardians prior to the operation. 

Modified minimal bone tunnel creation method Initially, the anesthetic epidural needle was modified by straightening its tip to create a hollow steel needle for bone tunneling. The outer diameter of this needle was 1.8 mm, and the inner diameter was 1.2 mm, which was suitable for positioning with a 1.0 mm Kirschner wire (K-wire). Using an ACL reconstruction aiming device, 1 mm K-wires were placed on the medial and lateral sides at the anterior edge of the bone bed, with a minimum distance of 10 mm between the two wires. Subsequently, the epidural needle was fitted over the K-wire, and the tunnel was manually and slowly drilled open (Fig. ). This method results in a smaller diameter bone tunnel, positioned at the junction of the footprint area bone bed and the articular cartilage surface, thus having minimal impact on the bone bed . Intraoperative suture bridge technique All patients were operated by the same surgical team under arthroscopy. Anesthesia was performed using lumbar anesthesia, with the patient in a supine position and a tourniquet applied to the thigh. Surgical approaches included the anteromedial and anterolateral portals of the knee joint. Arthroscopy was conducted first to inspect the joint, and a probe was used to identify the location, size, and type of the bone fragment. The edges of the bone fragment and the interior of the bone bed were freshened with a shaver. Initially, the approach is made through the midline of the patellar tendon, with the arthroscope inserted as the observational portal. The anteromedial and anterolateral portals are utilized as the working portals, respectively, for inserting a suture anchor and passing sutures with a suture hook., At a knee flexion of 90°, through the anteromedial portal, an awl is inserted. The awl is then smoothly tapped into the harder bone quality at the posterior edge of the bone bed, followed by the successful placement of a suture anchor (InLoc anchor, Hangzhou Rejoin Mastin Medical Device Co, P.R. China). Suture hooks are used to pass two sutures through the anterior cruciate ligament on its medial and lateral sides, respectively. Then, PDS (polydioxanone) suture is utilized to pull both strands of the anchor sutures out. After the tail sutures are crossed, they are guided through the tissue between the ligament and the fracture fragment. Utilizing an ACL aiming device, two minimal bone tunnels are created on the medial and lateral sides of the anterior edge of the bone bed. PDS sutures are then used to pull the anchor suture tails out of these tunnels. Under the surveillance of arthroscopy, a small hemostat is introduced through the anteromedial approach to adjust the suture cable to the appropriate position. Then, the hemostat is pressed onto the bone fragment, forcefully pressing the fragment towards the bone bed while gradually tightening the suture cable, which is then secured outside the tunnel with a locking suture anchor (GripLoc knotless anchor, Hangzhou Rejoin Mastin Medical Device Co, P.R. China). Finally, check the reduction of the bone fragment and the stability of the fixation (Fig. ). If, after tightening the suture bundle, there is still poor alignment or contact between the bone fragment and the bone bed, additional steps can be taken. Two strands of high-strength suture can be added to wrap around the ACL ligament, followed by the creation of two more mini bone tunnels. After adjusting the position of the bone fragment and pulling the reinforcement sutures through, tightening them significantly enhances the stability of the bone fragment and the reliability of the reduction. Before the end of the surgery, the knee joint was flexed and extended to carefully check whether the bone fragment was firmly fixed and whether the ACL had regained its tension, ensuring that the bone fragment had close contact and no displacement during extension. After thorough hemostasis, the wound was irrigated with a large amount of physiological saline and then sutured. Large cotton pads and elastic bandages were wrapped from the foot to above the knee joint. 

Initially, the anesthetic epidural needle was modified by straightening its tip to create a hollow steel needle for bone tunneling. The outer diameter of this needle was 1.8 mm, and the inner diameter was 1.2 mm, which was suitable for positioning with a 1.0 mm Kirschner wire (K-wire). Using an ACL reconstruction aiming device, 1 mm K-wires were placed on the medial and lateral sides at the anterior edge of the bone bed, with a minimum distance of 10 mm between the two wires. Subsequently, the epidural needle was fitted over the K-wire, and the tunnel was manually and slowly drilled open (Fig. ). This method results in a smaller diameter bone tunnel, positioned at the junction of the footprint area bone bed and the articular cartilage surface, thus having minimal impact on the bone bed . 

All patients were operated by the same surgical team under arthroscopy. Anesthesia was performed using lumbar anesthesia, with the patient in a supine position and a tourniquet applied to the thigh. Surgical approaches included the anteromedial and anterolateral portals of the knee joint. Arthroscopy was conducted first to inspect the joint, and a probe was used to identify the location, size, and type of the bone fragment. The edges of the bone fragment and the interior of the bone bed were freshened with a shaver. Initially, the approach is made through the midline of the patellar tendon, with the arthroscope inserted as the observational portal. The anteromedial and anterolateral portals are utilized as the working portals, respectively, for inserting a suture anchor and passing sutures with a suture hook., At a knee flexion of 90°, through the anteromedial portal, an awl is inserted. The awl is then smoothly tapped into the harder bone quality at the posterior edge of the bone bed, followed by the successful placement of a suture anchor (InLoc anchor, Hangzhou Rejoin Mastin Medical Device Co, P.R. China). Suture hooks are used to pass two sutures through the anterior cruciate ligament on its medial and lateral sides, respectively. Then, PDS (polydioxanone) suture is utilized to pull both strands of the anchor sutures out. After the tail sutures are crossed, they are guided through the tissue between the ligament and the fracture fragment. Utilizing an ACL aiming device, two minimal bone tunnels are created on the medial and lateral sides of the anterior edge of the bone bed. PDS sutures are then used to pull the anchor suture tails out of these tunnels. Under the surveillance of arthroscopy, a small hemostat is introduced through the anteromedial approach to adjust the suture cable to the appropriate position. Then, the hemostat is pressed onto the bone fragment, forcefully pressing the fragment towards the bone bed while gradually tightening the suture cable, which is then secured outside the tunnel with a locking suture anchor (GripLoc knotless anchor, Hangzhou Rejoin Mastin Medical Device Co, P.R. China). Finally, check the reduction of the bone fragment and the stability of the fixation (Fig. ). If, after tightening the suture bundle, there is still poor alignment or contact between the bone fragment and the bone bed, additional steps can be taken. Two strands of high-strength suture can be added to wrap around the ACL ligament, followed by the creation of two more mini bone tunnels. After adjusting the position of the bone fragment and pulling the reinforcement sutures through, tightening them significantly enhances the stability of the bone fragment and the reliability of the reduction. Before the end of the surgery, the knee joint was flexed and extended to carefully check whether the bone fragment was firmly fixed and whether the ACL had regained its tension, ensuring that the bone fragment had close contact and no displacement during extension. After thorough hemostasis, the wound was irrigated with a large amount of physiological saline and then sutured. Large cotton pads and elastic bandages were wrapped from the foot to above the knee joint. 

Postoperatively, the affected limb was bandaged with an elastic bandage, and a knee brace was used to keep the knee in an extended position for four weeks. Isometric contraction exercises for the quadriceps muscles began on the first postoperative day. The knee flexion should not exceed 30° within the first two weeks post-surgery, reach 90° by four weeks, and achieve full range of motion by eight weeks. Partial weight-bearing with crutches was allowed after four weeks, and full weight-bearing was achieved by eight weeks post-surgery. Whether to return to sports or activity should be based on the process of fracture healing. 

During follow-up, the duration of the surgery and the amount of bleeding were recorded. Symptoms such as swelling, pain, joint effusion, postoperative fracture reduction, and joint mobility were observed. X-rays were taken at 1, 3, 6, and 12 months post-surgery to observe whether the fracture line had healed and whether the position of the fracture fragment had returned to normal. At the end of the follow-up, the stability of the ligament was assessed using the anterior drawer test and the Lachman test. The knee joint functional scores was evaluated based on the Lysholm scores and International Knee Documentation Committee (IKDC) functional scores . 

Analysis was performed using the SPSS 22.0 statistical software. Data that conform to a normal distribution were represented as the mean ± standard deviation. The preoperative and postoperative Lysholm scores were compared using a paired t-test, with a P-value less than 0.05 indicating a statistically significant difference. 

All patients had been followed up. Patients were followed for 12–18 months, averaging 15.6 months. The surgical duration averaged 52.7 min, ranging from 45 to 62 min. Approximately 10–30 mm of bleeding occurred during surgery. No neurovascular injuries were found. Three cases of postoperative joint swelling occurred and were alleviated with needle aspiration. By two months after surgery, swelling had decreased, pain had become less intense, and there were no restrictions on knee extension. Additionally, all patients achieved knee flexion beyond 120°. Fractures healed within 6–12 months postoperatively, with no instances of loosening, refracture, or displacement, and both the anterior drawer test and the Lachman test were negative (Fig. ). By the end of the follow-up period, all patients could safely return to their previous level of sports or activity. The Lysholm and IKDC knee joint functional scores had significantly improved from preoperative levels. (Table ). 

The findings of this study demonstrate that all fractures achieved healing within the six to twelve-month postoperative period, with no incidences of loosening, re-fracture, or displacement. Furthermore, there was a notable recovery in knee joint function, all patient could safely return to their previous level of sports or activity, as evidenced by significant improvements in Lysholm and IKDC functional scores at the final follow-up compared to preoperative levels. These outcomes are consistent with those reported in other studies , . Tibial avulsion fractures of the ACL are relatively uncommon, typically affecting adolescents and young adults in the context of sports-related injuries . The evolution of treatment approaches has shifted from conventional open reduction and internal fixation to less invasive arthroscopic techniques. These modern methods utilize a variety of fixation devices, including sutures, screws, wires, anchors, and buttons – . Early fixation techniques, such as those employing screws, wires, or loop plates, were found to be less suitable for the comminuted fractures and thin bone fragments often encountered in the adolescent population. These methods were associated with complications like bone fragment displacement, fragmentation, and rotational instability, primarily due to improper ACL tension restoration and inadequate fixation of bone fragments . In response, many in the surgical community have adopted the suture bridge technique, initially developed for rotator cuff repairs, for the treatment of ACL tibial avulsion fractures. This technique has shown promise . Hapa et al. , through biomechanical studies using an ovine model, confirmed that under cyclic loading, the strength of high-strength suture weaving fixation was significantly superior to screw and simple suture anchor fixation. Eggers et al. reported in biomechanical tests that the suture bridge technique, utilizing multiple anchors and high-strength sutures, could withstand a higher load to failure than screw and suture fixation. However, the use of multiple anchors can significantly increase surgical costs. Therefore, the arthroscopic suture bridge technique, combined with transosseous tunnels and tail suture locking anchor fixation, may offer a highly suitable alternative. Boutsiadis et al. described an enhanced arthroscopic suture fixation technique for ACL avulsions, involving the creation of four angled 2.9 mm tibial tunnels and secure fixation with pegs after pulling the tail sutures through. This technique provides stable fixation and reduces the risks associated with bone bridge and tunnel issues, accommodating various fragment sizes. However, it might affect the fracture contact surface and carries the risk of growth disruption due to traversal of the epiphyseal area. Our study combines the arthroscopic transosseous tunneling technique with the suture bridge technique, achieving a three-point fixation pattern. By employing this modified mini-tunnel technique, we are able to reduce the use of anchors and have the opportunity to choose multiple bone tunnels. This approach can anatomically reduce and immediately stabilize fixation, irrespective of the size of the avulsed bone fragments. Particularly in adolescents, where the avulsed bone fragments at the ACL tibial insertion site are often thin and prone to fragmentation, the strong tensile force from the high-strength sutures provides adequate support, allowing the ACL to regain tension. This is beneficial to rehabilitation training and recovery of joint function. This retrospective study has a small sample size, potentially biasing the reliability of the findings. It also lacks long-term follow-up data, being based on short-term outcomes. Future large-scale and long-term studies are needed to bolster the research’s credibility. In conclusion, the suture bridge technique adheres to the principle of tension-side fixation, with internal anchors capable of closing the inner edge of the bone block. The minimal impact of the mini tunnel on the bone bed is advantageous for fracture healing at the interface. The tail sutures are fixed on the distal side of the bone tunnel, successfully avoiding the epiphyseal plate. The arthroscopic transosseous suture bridge for repairing ACL tibial avulsion fractures with this mini tunnel technique has demonstrated a definite therapeutic effect, stable fixation, minimal impact on the bone bed, and is particularly well-suited for the treatment of ACL tibial avulsion fractures in adolescents (Fig. ). 

Below is the link to the electronic supplementary material. Supplementary Material 1 Supplementary Material 2 

