Avulsion fractures of the tip of the lateral malleolus, which are classified by the AO/OTA as type 44A, occur when the foot is supinated and an adduction force is applied to the talus, causing the lateral structures to fail in tension, which corresponds to the supination-adduction type in the Lauge-Hansen classification. Approximately 60%-70% of ankle fractures are monomalleolar fractures, 15%-20% are bimalleolar fractures and 7%-12% are trimalleolar fractures [4, 5]. Most of the cases (n = 14) in this study were monomalleolar fractures of AO/OTA types 44A1.2 and 44A1.3. Only 3 cases were bimalleolar fractures of AO/OTA types 44A2.2 and 44A2.3. This was consistent with the incidence of ankle fracture.
Conservative treatment is quite effective in treating acute ankle sprain. Nonsurgical treatment is widely accepted even by young athletes [2, 3]. However, some articles have reported the incidence of complications with conservative treatment in ankle injuries with avulsion fracture of the lateral malleolus. Haraguchi et al.  found in 44 patients with avulsion fracture of the lateral malleolus that, even after 3 to 7 weeks of strict cast immobilization, 35% of the fractures failed to heal. El Ashry et al.  reported that in 2 cases of ankle sprain, the avulsion fracture fragment of the distal fibula did not heal after conservative treatment and had clinical symptoms, making secondary operation necessary. The reason for this is that the ATFL and CFL are attached to the fracture fragment of the distal fibula, and the retracting force of the ligament makes it difficult for the fracture site to contact; meanwhile, in the case of insufficient stability of external fixation, even mild foot movements may cause fracture fragments to move, thus causing fracture nonunion . Diallo et al.  reported that the displacement of the fragment from the insertion site on the fibula was larger than suspected radiographically; therefore, spontaneous bone-to-bone healing would have been unlikely. In the cases included in this study, it was found intraoperatively that all distal fragments were connected to the ATFL and CFL.
Osseous union is the strongest. Therefore, some scholars tend to adopt operative treatment of fresh and old avulsion fractures of the distal lateral malleolus to reduce and fix the fracture [7–9, 13]. As observed in this study, these therapies have been shown to restore the anatomical position of the ligaments and have achieved good stability of the ankle intraoperatively and postoperatively. The patients regained their previous exercise ability and did not experience repeated ankle sprains. In these articles, most researchers used 1 or 2 2.5- to 3.0-mm cannulated screws for fixation. However, in screw fixation, it will often be difficult to achieve accurate reduction and rigid fixation when the distal fragment is too small or when the bone is osteoporotic . Meanwhile, the fixation of avulsion fractures with screws causes other complications, including irritation by the screw head, injury of the peripheral nerve, bone nonunion because of small diameter, and secondary fractures because of large diameter . In addition, any screw with threads causes further complications in patients whose distal fibula growth plate has not been closed . A Kirschner wire tension band is another alternative fixation method, but complications such as skin and soft tissue irritation, loosening and hardware breakage are likely to occur . Moreover, these fracture fragments are often not large enough to be suitable for a distal fibula anatomical LCP. Since the common distal fibula anatomical LCP is placed in a superior position, not enough screws can be inserted into the distal fracture fragment.
The anatomical contouring, low profile, obtuse edge and polished surface of the 2.0-mm LCP distal ulna hook plate help reduce the irritation of soft tissue. Between the two most distal screw holes, there is a groove to assist shaping, which can allow the plate to attach to the contour of the outer surface of the distal fibula (Fig. 1). The 2 pointed hooks at the distal end of the plate can be embedded in the tip of the lateral malleolus through the CFL attachment site to form an embrace-like grip and exert multidirectional stress. The operative fixation of intra-articular fracture may be more challenging if the fragment is connected to tendons and ligaments. Nevertheless, the pointed hooks fixed in the attachment site of the lateral collateral ligament of the ankle can effectively resist its tension, restore the rotational displacement, eliminate dynamic factors that cause fracture redisplacement, and create conditions for early functional training without damaging ligament connections. These are unique advantages of hook plates. Based on confidence in the stability, all patients in this study began passive and active ankle functional exercise just 2 or 3 days after the operation. No fracture displacement was observed. A 2.0-mm miniature angle stabilization screw system can secure a small fragment of the tip of the lateral malleolus. The combination of the proximal sliding compression hole and the locking hole facilitates the fixation of osteoporotic fractures and avoids bone loss due to the insertion of cannulated screws. The sustained pressure exerted by the elastic recovery of pointed hooks and the design of the proximal sliding compression holes constitute advantages compared with the other internal fixations. For some cases fixed with screws, if a technical secondary fracture occurs at the distal fragment during the operation, the plate can also be used as a remedy. According to the above thinking, many scholars have used this plate for the fixation of fractures at the base of the fifth metatarsal [10, 16, 17], but its application to the lateral malleolus has not been reported.
We compared this plate with two commonly used types of distal fibula anatomical plates that are manufactured by DePuy Synthes and Zimmer (Fig. 4). As measured, the penultimate distal screw hole of the DePuy Synthes anatomical plate is 10 mm from the distal end of the plate, while that of the Zimmer anatomical plate is 13 mm. According to the instruction manual, they were placed 5 mm proximal to the tip of the lateral malleolus. Therefore, theoretically, the two kinds of plates can be used only when the fracture line is at least 15 mm (10 + 5) and 18 mm (13 + 5) from the tip of the lateral malleolus, such that at least two 2.7-mm screws can be inserted into the distal fracture fragment to obtain sufficient purchase. The distance between the most distal screw hole of the 2.0-mm LCP distal ulna hook plate and the distal end of the plate is 6 mm. Therefore, a 2.0-mm screw can be inserted as long as the fracture line is not less than 6 mm from the tip of the lateral malleolus, securing the distal fragment together with the pointed hooks. For this reason, we suggest that the use of this plate is indicated if the fracture line is 6 to 15 mm from the distal end of the tip of the lateral malleolus. Such a design also provides the possibility of safe internal fixation for some patients with fractures of the distal fibula when the growth plate is not closed.
Although the hook plate provides rigid fixation, as with other techniques, it is not always possible to obtain accurate fracture fragments and anatomical consistency. In particular, when the fragment is wide or large, to achieve better reduction and fixation effects, independent 2.4- or 3.0-mm cannulated screws or 2.0-mm cortex screws may be added as appropriate. In addition, as mentioned above, the best indication for the use of this plate is the fracture line 6–15 mm from the distal end of tip of the lateral malleolus, which also limits its range of application to a certain extent. If the fracture line is greater than 15 mm, some distal fibula anatomical LCP may be used; if the fracture line is less than 6 mm, other fusion methods, such as cannulated screws , the Broström operation, or other ligament reconstruction methods [18, 19], should be considered.
The lack of a control group to compare the outcomes is another limitation of this study. However, the main objective of this study was to introduce a new feasible fixation rather than compare 2 treatment methods.