The Synthes Femoral Neck System (FNS) is a specialized medical implant designed to repair fractures in the femoral neck, the narrow part of the thigh bone connecting the shaft to the ball of the hip joint. These fractures, often called hip fractures, are common, particularly among older individuals due to osteoporosis, a condition that weakens bones. The FNS offers an internal fixation solution, stabilizing broken bone fragments and promoting healing without replacing the entire hip joint.
How the Femoral Neck System Works
The Femoral Neck System is engineered to provide stability to the fractured femoral neck. It consists of a plate that rests on the lateral side of the femur, along with an integrated bolt and an anti-rotation screw that extend into the femoral neck and head. This system is made from a titanium alloy (specifically TAN, Ti-6Al-7Nb), a material known for its biocompatibility and strength, allowing it to function as an internal scaffold supporting the bone as it heals.
The FNS achieves both angular and rotational stability, which are crucial for successful fracture healing. The bolt provides angular stability, maintaining a fixed angle relative to the plate, while the anti-rotation screw, with its diverging design, prevents unwanted rotation of the femoral head. This combined stability helps hold the fractured pieces securely together. The system also allows for controlled dynamic compression, with up to 20 mm of collapse, which can promote bone healing by allowing the fracture fragments to settle together.
The Surgical Procedure and Recovery
The surgical procedure for implanting the Synthes FNS typically involves a minimally invasive approach. A small incision, often around 4-5 cm, is made on the side of the hip to access the fractured area. During the operation, surgeons use fluoroscopy, a live X-ray imaging technique, to guide the precise placement of the implant within the femoral neck and head.
Following the surgery, patients typically have a hospital stay, ranging from a few days to over a week, depending on their overall health and progress. Pain management is provided through various medications to ensure comfort during the initial recovery phase. Physical therapy begins soon after surgery, focusing on gentle range-of-motion exercises and gradual mobilization. Patients are often instructed to begin partial weight-bearing (around 30-50% of body weight) using assistive devices like walkers or crutches within 1-2 days post-operation. Adhering to the surgeon’s specific instructions regarding weight-bearing progression is important for promoting proper bone healing and preventing complications.
Comparing FNS to Other Treatment Options
The Synthes FNS is one of several methods used to fix femoral neck fractures, often compared to multiple cannulated screws (MCS) and the dynamic hip screw (DHS). The FNS offers enhanced rotational stability compared to traditional multiple cannulated screws, which can be less stable in certain fracture patterns. While MCS are minimally invasive, they may not provide the same resistance to varus collapse or femoral neck shortening as the FNS.
The FNS also shares similarities with the dynamic hip screw (DHS), which has long been a standard for hip fractures, particularly displaced ones. Both FNS and DHS allow for dynamic compression, but the FNS is sometimes considered to offer advantages such as a smaller incision, reduced blood loss, and potentially shorter operative times. Surgeons generally choose internal fixation methods, like the FNS, over hip replacement (arthroplasty) for younger patients or those with non-displaced fractures and good bone quality.
Potential Surgical Outcomes and Complications
While the Synthes FNS provides a method for repairing femoral neck fractures, like any surgical procedure, it carries risks. General surgical risks include infection, blood clots, or adverse reactions to anesthesia. Specific to femoral neck fracture fixation, complications include nonunion, where the bone fails to heal, occurring in approximately 4.7-9.1% of cases in some studies.
Another concern is avascular necrosis (AVN), a condition where the blood supply to the femoral head is disrupted, potentially leading to bone death. This complication has been reported in about 2.3-9.1% of FNS cases in early follow-up studies. Implant failure, such as screw cut-out or loosening, and peri-implant fractures, are also possibilities. Surgeons carefully evaluate each patient’s fracture type, bone quality, and overall health to determine the most suitable treatment approach, aiming to minimize these risks.