Operative treatment is the management of choice for most trochanteric hip fractures in current practice . Key decisions for the surgeon are fracture reduction, choice of implant, and implant positioning. To date, the dynamic mechanism instruments of sliding hip screw/blade clearly indicates that this type of implant has a lower fracture-healing complication rate. InterTan is a new type of cephalomedullary nail with a pre-loaded set-screw. As stated in the manufacturer’s guidance, using or not using the pre-loaded set-screw is optional. The resulting fixation with setscrew tightening and locking will be static with no opportunity for any collapse to occur at the fracture site. We want to argue this indication and advocate that the set-screw in InterTan nail should be seldom tightened in pertrochanteric fractures. The reasons are as follows:
Firstly, it is difficult to achieve an exact anatomic reduction in pertrochanteric fractures by closed maneuver and intraoperative fluoroscopic control. According to our investigation, a smooth cortex contact viewed in fluoroscopy is called neutral cortical apposition, which may actually contain three sub-conditions:(1)an exact real anatomic smooth cortex-to-cortex position, (2) a slightly positive extra-medullary buttressed position, or (3) a slightly intra-medullary negative position . However, as the image resolution of intra-operative fluoroscopy is limited, 2-mm cortical steps may not be identifiable. Therefore, those three sub-conditions are generally not able to be clearly distinguished, i.e. the so called anatomic reduction in fluoroscopy may not be really anatomic.
Secondly,though the head-neck fragment can be compressed primarily by the surgeon during operation through tightening the smaller compression screw (the lower worm screw). However, bone resorption does occur during fracture healing. There may be a gap at the fracture site, which may result in no cortical contact between the head-neck and the shaft. A gap between the medial calcar cortices may lead to a longer healing time, a delayed healing or even a non-healing, which is a risk factor for complications and treatment failure.
Thirdly,in the post-operative period, during the contraction of the muscles or the patient's weight bearing stage, continuous dynamic pressure is applied to the fracture site. The fracture gap can be eliminated by secondary sliding through impaction, which promotes the close contact of the head-neck fragment with the femoral shaft and achieve a secondary stability. Sliding provides an opportunity for the fracture site to re-adjust and re-sit firmly with each other, promote fracture consolidation and healing. In other words, postoperative secondary sliding can make up some technical shortcomings during the operation.
Fourthly, the aim of tightening and locking the set-screw is to prevent over-sliding and maintain the length of femoral neck. In our opinion, obtaining anteromedial cortex support through fracture reduction technique is a more safe and effective biomechanical approach to prevent excessive sliding. By direct cortical contact, the anteromedial cortex of the femoral shaft can resist the head-neck fragment from further sliding laterally, keep an almost normal neck length and neck-shaft angle . The cortical contact permits limited and controlled telescope, which has both mechanical (load sharing) and biological (healing) advantages .
Therefore, tightening the setscrew to prevent sliding as static constructs may keep a normal femoral neck length, but lose the possibility to make up technical shortcomings, and take the risk of fracture healing complications; on the other hand, not tightening the setscrew to allow head-neck dynamic sliding will promote fracture healing but take the risk of femoral neck shortening. Of two evils choose the lesser. Now, we prefer to accept a limited shortening femoral neck, rather than the risk of fracture nonunion, femoral head cutout, or implant breakage, which need further revision surgery. In the treatment of two-part intertrochanteric femur fractures (2018-AO/OTA: 31A1.2), Ricci et al. stated that they did not use set screws in the InterTan group, and if it was used in the TFN group (the head-neck can be fixed with either a lag screw or a helical blade), up to approximately 10 mm dynamic sliding was allowed.
There are some common features of these 4 cases. Firstly, although some technical deficiencies maybe exist, the overall fracture reduction quality and implant placement position are good or acceptable. Secondly, the set-screw is tightened and locked and no head-neck sliding happened after operation. The InterTan nail becomes a static implant. Thirdly, patient’s bone quality is relatively good, and can provide enough grasp with the screws to avoid cutout. Fourthly, the nail is thicker and stronger and there is no nail breakage. With the assistance of a stick, all patients can walk and care themselves in daily life, but with persistent pain in some degree. And lastly, the reason for delayed union or non-union is mostly attributed to the static fixation mechanism.