According to statistics, there are more than 250,000 cases of ACL rupture in the United States each year, and with technological advances, more and more patients are undergoing ligament reconstruction surgery. Generally, postoperative results of ACL reconstruction are good, but complications such as graft rupture, knee stiffness or instability, infection, and deep vein thrombosis still occur in some cases, and postoperative fractures of the proximal tibia or distal femur do occur as serious complications. In addition, intraoperative injury to the posterior femoral tunnel is a rare but certainly possible complication. In May 2014, the journal Arthroscopy reported on a case of fracture during ACL reconstruction provided by Mark D. Miller et al. The case involved a 32-year-old female who had injured her knee while skiing and had been experiencing knee pain and swelling for the following 2 weeks, with examination and MRI (Figure 1 A) suggesting an ACL tear without fracture (Figure 1 B). The preoperative decision was made to take an autologous tendon for ligament reconstruction, and due to the small size of the patient, the possibility of taking the contralateral tendon was considered preoperatively. Figure 1 Post-anesthesia examination and arthroscopy confirmed the tear of the anterior cruciate ligament, and tendon retrieval was performed immediately, but only a 6.5-mm-diameter graft could be prepared from the affected semitendinosus and thin femoral tendon, so contralateral tendon retrieval was performed, and a 9-mm-diameter graft was finally obtained. An anteromedial auxiliary incision was performed to prepare the bone tunnel, and a 10-mm drill was used to machine the tunnel on the femoral side under Beath guide pin positioning to a depth of approximately 27 mm, and the tibial side tunnel was approximately 9 mm in diameter (Figure 2 A-C). The lateral femoral graft was fixed with the INTRAFIX system, and a fracture of the lateral femoral condyle was found at the time of nail placement (Figure 2 D), and a coronal fracture was confirmed by the C-arm (Figure 1 C). Flexion and extension of the knee were performed 10 times and the lateral femoral fixation was found to be relatively firm despite the presence of the fracture, so the procedure was continued to complete the lateral tibial fixation. Figure 2 The fracture was repositioned and fixed through a postero-lateral incision in the distal femur, after which a repositioning forceps was placed along the posterior aspect of the femur, and two 5.5 mm hollow nails were driven perpendicular to the fracture line after clamping the fracture using this repositioning forceps for fixation, of which the first screw was treated as a tension screw, and the C-arm fluoroscopy again confirmed the anatomic repositioning of the fracture and the secure position of the internal fixation (Figure 1 D). Postoperatively, the patient underwent non-weight-bearing passive functional exercise first, and then weight-bearing exercise at approximately 50% of body weight after 10 days, along with adjunctive physical therapy. after 6 weeks, the range of motion of the joint was 80 degrees of flexion and -5 degrees of extension, and the range of motion gradually improved after 2 months. no bony healing was seen on the CT scan at February (Figure 3 A-D), and CT scans at April (Figure 4 A B) and August (Figure 4 C D) suggested fracture healing. One year after surgery, the patient had good knee stability and fully resumed daily activities. Figure 3 Figure 4 It is relatively rare that a coronal fracture of the lateral femoral condyle (Hoffa Fracture) occurred in this patient during the preparation of the femoral tunnel during the ACL reconstruction of the knee. In previous reports, in cases where the graft diameter was appropriate but the femoral tunnel was too far posterior, the patient may have experienced a break in the posterior wall of the femoral tunnel during postoperative exercise. However, the present case suggests that such a fracture may occur in the presence of an appropriately positioned tunnel, and it is speculated that the possible risk factor is that the patient’s femoral epicondyle was small and fractured while accommodating the thicker graft. Although the criteria for graft diameter are controversial, it is more recently accepted that a graft diameter of more than 8 mm is required to reduce the risk of surgical failure. In support of this view, grafts are customarily larger than in the past, and attention should be paid to the anatomic conditions of the prepared femoral tunnel, especially when applying interface screw fixation, and with increased vigilance if the patient is young, slender, or female (who may have a small femoral condyle or reduced bone density). The authors listed potential risk factors for fracture (Table 1), such as: increased graft diameter, increased tunnel diameter, small femoral condyles, need for tunnel expansion during fixation, and preparation of the tunnel through the anteromedial portal to bring it closer to the articular surface. Table 1 On this basis, the authors made several valuable recommendations to avoid intraoperative fractures (Table 2), including: paying attention to the tunnel, subchondral bone, and articular surface throughout the procedure to detect fractures in a timely manner; determining the stability of the graft immediately by inspection and microscopic observation if a fracture occurs; recommending incisional repositioning for intra-articular fixation; and avoiding the use of excessively thick In patients with risk factors, avoid the use of excessively thick grafts or switch to a suspension system for fixation to avoid dilated tunnels. Table 2