The anterior medial tibia is covered by little and thin soft tissues, which is more obviously presented at the distal end. Fractures often occurred with concomitant local skin contusion and soft tissue injuries. In addition, blood supply to the distal tibia is generally poor and the extraosseous blood supply diminished under the fracture condition. Meanwhile reaming would eliminate the remain blood supply which may predispose the fracture to infection, delayed union and nonunion. Therefore, it is particularly crucial to choose an optimal internal fixation method that provides stable fixation and less interference with soft tissue simultaneously, thus can promote the recovery of limb soft tissue and fracture healing. External fixation is considered to be an effective fixation method. However, Ristiniemi et alrecently found that external fixation shows more complications when applied for the treatment of tibial fractures including nail trajectory infections, ankle stiffness and delayed fracture union. The authors treat 47 tibial fractures with combined external fixation, which brought the sequelae of delayed union for 25.5% of the patients. The advantages of applying open reduction and internal fixation were that the fracture site could be exposed sufficiently and the reduction could be fulfilled anatomically under direct vision. Researchers [3, 15–17] reported that the deformed union rate of fractures after plate fixation was less than 10%, but the risk of postoperative complications with soft tissues was higher, including superficial infections, deep infections, delayed wound healing, and necrosis of soft tissues. In the early 1940s, the intramedullary nail system was introduced to treat tibial shaft fractures, which can reduce the deformity union for tibial fracture and decrease the formation of pseudo-articular joints after the surgery, meanwhile promote the ossification of fractured callus. Moreover, the intramedullary nails have little interference with the soft tissue around the fracture site. Previous studies  noted that intramedullary nails have a shorter operative time in the treatment of tibial fractures and better postoperative function recovery. Therefore, in this study, we selected closed reduction and intramedullary nail fixation for tibial fractures. Currently, intramedullary nailing has become the popular treatment strategy for diaphyseal fractures of the tibia[5, 19]. We noticed the occurrence of angulation deformity for the distal fracture fragment during the nail insertion, it also has been reported that even a small amount of residual alters load through the knee and ankle joint , and the alternation in force could attribute a predisposition to osteoarthritis [21, 22]. Hence correctly estimating the occurrence of angulation deformity intraoperatively is the essential prerequisite to better clinical outcomes for the patients.
The reasons for the occurrence of distal tibia fragment valgus or varus deformity during the surgery
We assume the reasons for the valgus and varus deformity were complicated, mostly resulted from losing the balance of forces around the fracture site during inserting the nail. In the treatment of tibial fractures with open reduction and internal fixation, owing to the sufficiently exposed fracture site and reduction under direct vision, varus or valgus deformity of the distal fragment is hardly to occur unless there were existed varus and valgus deformities before the injury. However, when comes to closed reduction and intramedullary nail fixation, the reduction conditions of the fractures cannot be examined under direct vision since the fracture site would not be exposed. Moreover, because the full-length tibial imaging is currently not available during the surgery in most case scenarios, poor reduction including varus and valgus cannot be avoided. Based on the anatomical characteristics of the distal tibia, the compartment muscles and tendons formed by the extensor and flexor muscles passes through the anterior and posterior tibia, the lateral side is the fibula while the medial side has no muscle groups. This may result in a low probability of sagittal plane deformity of distal frament such as apex anterior after the traction and reduction due to the ligamentotaxis and blockage of anterior and posterior hinges. However, varus or valgus deformity is prone to occur due to the lack of soft tissue hinges on the medial and lateral sides which were not able to neutralize the forces. 1) For middle tibial shaft fractures, if the isthmus remains intact or just suffered simple transverse or spiral fracture, it can automatically reduce when inserting the tibial intramedullary nail and no valgus or varus deformity of the distal fragment will occur. However, when isthmus is comminuted such as AO fracture type 42-B3 and type C, the fracture cannot automatically reduce during the insertion of the tibial intramedullary nail. Under this circumstance the isthmus lost the physical restraint effect on the placement of intramedullary nails and resulted in the eccentric nail for distal fragment with the sequelae of valgus or varus deformity. 2) For the fracture at the distal 1/3 of the tibia, with the existence of the cavernous distal tibial metaphysis, the intramedullary nails could not achieve effective contact with the bone cavity. In other words, the cortical bone has no sufficient physical restraint effect on the tibial intramedullary nail during insertion and may result in possible deviations from the lateral or medial sides on the coronary plane, by which finally cause valgus or varus deformity of the distal fragment. 3) Currently, the intraoperative fluoroscopic imaging just provides local view of the tibia and hardly provides an entire view of the full-length tibia in a single film, hence the mild valgus or varus deformity emerged on the coronal plane cannot be detected.
The feasibility to determine the occurrence of distal tibia fragment valgus or varus deformity intraoperatively
For patients with existed knee joint deformity before injury (knee valgus or valgus), the included angle between the axis of the distal horizontal interlocking screw and the horizontal line of the tibiotalar articular surface in the AP X-ray film cannot be used to determine whether the distal tibia fragment combine valgus or varus deformity. Because for such case scenario there existed deviations in the entry point of the tibia intramedullary nail, and the standard entry point for the nails cannot be obtained as shown in Fig. 2. Which means that the intramedullary nail may not get into the center of the tibial bone marrow cavity in the coronal plane when it enters the proximal end of the medullary cavity.
During the surgery, the C-arm fluoroscopy can easily obtain the AP images of the distal tibia. It is preferable to get standard AP films, by which the included angle between the axis of the distal horizontal interlocking screw and the horizontal line of the tibiotalar articular surface on the AP view represents the actual value, which is more accurate when correcting the valgus or varus deformity and adjusting the implant position. We preferred the fibular bisector line (overlap of the lateral border of the tibia bisecting the fibula head) as a reliable intraoperative fluoroscopic confirmation of appropriate rotation .
If an included angle emerged by the projections of the distal horizontal interlocking screw and the tibiotalar articular surface on the coronal plane, it is demonstrated that the valgus or varus deformity occurs at the distal fragment of the tibia. Meanwhile the fibula can be used as a reference. If the included angle points to the fibular side, the valgus deformity exists, and if the angle faces away from the fibula, then varus deformity exists. In this study, 33 patients with tibial comminuted fractures were evaluated by this method during the surgery, and the postoperative alignment and clinical outcomes were satisfactory.
The distal end of the tibial intramedullary nail is designed as two locking holes on the sagittal plane. With regard to the dynamic locking hole, to the best of our knowledge, there is currently no tibial intramedullary nail with a dynamic hole at the distal end. Oblique interlocking angulation may occur when the screw is locked through the dynamic hole by freehand technique, which means the interlocking screw is not perpendicular to the main nail. However, the oblique interlocking phenomenon would not occur when locking through the static locking hole. Therefore, the freehand locking technique does not create the bias to our method when it is applied to the tibial intramedullary nail through a static hole.
The Significance Of Developing This Convenient Approach
Previous studies [23–25] showed the application of a femoral distractor to maintain the tibial alignment. During the surgery, the traction pins are placed posterior to the central axis of the proximal tibial metaphysis and the distal end of the tibia. The perpendicular relationship between the intramedullary nail and the traction pins or the tibiotalar articular surface is used to verify the validity of fracture reduction. We have also tried to apply this method, however we found it has some limitations. Firstly, the inserted traction pin must be perpendicular to the tibial force line which is difficult to operate on the fractured tibia; secondly, the distractor is fixed with a single pin at the proximal and distal site which implies poor ability on anti-rotation and later reduction. Therefore, it is not practical to apply this method. In addition, some authors[10, 11] suggest that the guide wire of the intramedullary nail at the distal end must be centered before reaming so that central reaming can ensure that the distal fracture fragment can be well controlled after the insertion of intramedullary nails, and diminishing the probability of poor postoperative alignment or deformity. However, based on our clinical experience, eccentric placement of the intramedullary nail still occurs in some patients even the guide wire is in the center of cavity during reaming for the elderly patients with osteoporosis. This is likely resulted from insufficient cancellous bone mass of the distal tibia. Therefore, it has certain limitations for elderly patients with tibial fractures who combines osteoporosis. Of the 33 patients in our study, 5 patients over 60 years old with osteoporosis were estimated by our method. Postoperative full-length X-ray films demonstrated no valgus or varus deformity of the distal fragment. Hence we believe that this method is a simple and convenient approach to determine the occurrence of distal tibia fragment valgus or varus deformity intraoperatively and allow the surgeons to correct the angulations immediately without using additional tools.