Femoral intertrochanteric fracture is mainly caused by fall, car accident and other reasons, which is called the last fracture in life[4]. Although conservative treatment has the advantages of non-trauma and low cost, it needs to be bedridden for a long time and has many complications. Although surgical treatment is traumatic, it is beneficial for patients to get out of bed and exercise in the early stage, so it has become the first choice for the treatment of intertrochanteric fractures [5]. PFNA, as the representative of the intramedullary system, plays an important role in the treatment of intertrochanteric fractures. It has the following advantages: (1) the force arm is short and close to the gravity line, which can reduce the stress bending of gravity on the nail after weight bearing, and at the same time has the effect of local direct compression, which is in line with the biomechanical characteristics, which greatly reduces the pressure of the femoral calcar and reduces the stress shielding effect, and is conducive to fracture healing; (2) the minimally invasive incision has small tissue injury and less bleeding during the operation; (3) the helical blade has the effect of anti-rotation and compression, which can reduce the cutting of the femoral neck, and the helical blade implantation can better compress the cancellous bone and reduce the loss of bone mass, it provides a strong guarantee for patients to get out of bed in the early stage after operation[6, 7]. However, during the clinical follow-up, it was found that 6–21% of the patients with PFNA had internal fixation failure, which led to complications such as nail withdrawal, cutting and so on [8]. In essence, the cutting of the helical blade is caused by the micro fracture of the surrounding cancellous bone, especially the fragile and loose bone trabecula of osteoporosis, the fracture of the surrounding large bone trabecula after the injury accumulation, and the local instability and movement of the unsupported helical blade. If excessive osteoporosis, it needs to be treated with other treatments. According to previous reports, the failure of PFNA internal fixation can be divided into controllable factors and uncontrollable factors [9]. The controllable factors include the mode of anesthesia, the time of operation, the amount of intraoperative blood loss and postoperative rehabilitation measures. The uncontrollable factors mainly include age, sex, basic diseases, fracture types and bone quality, etc. When TAD (Tip-apex distance) > 30 mm, severe osteoporosis, poor fracture reduction and severe underlying diseases are the high risk factors for the failure of PFNA [10].
The case reported in this paper, the helical blade was over-unlocking during the operation, resulting in inability to lock. If it is not handled or ignored, the compression effect will be lost after the operation, and at the same time, it will lead to rotation instability and increase the risk of internal fixation failure. Although the helical blade is locked successfully through a distal screwdriver in our operation, it is still necessary to pay attention to the recurrence of similar problems. Wang report similar case with us and suggest to use the SW4.00 mm Cannulated hexagonal screwdriver to lock the helical blade, which the same as we used, however, they don’t discuss what’s the problem about the helical blade and why has that happened [11]. In this paper, we propose the concept of over-unlocking of spiral blade. PFNA helical blades from different equipment companies are not consistent, but no matter which kind. All need to be tested before inserting the helical blade to prevent the helical blade from being over-unlocking and unable to lock during the operation. Intraoperative fluoroscopy should not only pay attention to the position of the helical blade, but also pay more attention to the abnormal shape of the helical blade itself. When the helical blade is over-unlocking, if the aiming arm is not disassembled, you can try to take out the helical blade and fix it again. If the aiming arm has been removed, it is not recommended to remove the helical blade, which can easily lead to loss of reduction, loss of bone mass and prolongation of operation time. We suggest that we should consider adding a screw from the lateral wall through the femoral neck for anti-rotation, or you can observe the tail of helical blade and find suitable screw driver to fix it if there is one.