A femoral neck fracture affects the bone connecting the ball of the hip joint to the main shaft of the femur. This is a highly common injury, particularly among older adults. These fractures disrupt the structural integrity of the upper thigh bone and often compromise the blood supply to the femoral head, necessitating prompt and stable internal fixation. The Synthes Femoral Neck System (FNS) is a contemporary advancement in fracture care, specifically designed to stabilize this particular injury. This system offers a unique combination of features to achieve a strong, dynamic fixation that balances mechanical stability with the biological need for compression at the fracture site.
Defining the Synthes FNS Device
The Synthes FNS is an internal fixation implant constructed from a titanium alloy, designed specifically for treating femoral neck fractures. This device is categorized as a fixed-angle gliding system, meaning it maintains a set angle between the main bone shaft and the neck fragment while allowing controlled movement.
Its hardware consists of three primary components: a lateral plate, a central bolt, and an anti-rotation screw (ARScrew). The small, single-hole lateral plate is secured to the side of the femur, providing a stable platform. The central load-bearing element is the bolt, inserted into the head and neck of the femur, acting as the main anchor.
Parallel and adjacent to the bolt is the ARScrew, which has a diverging, non-parallel trajectory relative to the bolt. When the system is assembled, the bolt and the ARScrew are locked together within the barrel of the plate, forming a single, fixed-angle unit. This integrated design is engineered to resist forces that typically cause fixation failure.
How the FNS Achieves Fracture Stabilization
The mechanical performance of the FNS relies on rotational stability and controlled dynamic compression, which are superior to older, static fixation methods. The diverging paths of the central bolt and the ARScrew are linked together to prevent the fractured head fragment from rotating independently. This feature is helpful in unstable fractures, where rotation can compromise healing and lead to hardware failure. By eliminating this unwanted movement, the FNS maintains a precise anatomical reduction.
Controlled dynamic compression is provided by the FNS design. The bolt and ARScrew are engineered to slide together within the lateral plate’s barrel, allowing up to 20 millimeters of controlled collapse at the fracture site. This controlled movement permits the bone fragments to compress against each other when the patient bears weight, which stimulates fracture healing. The system allows this axial compression without the implant protruding excessively from the side of the femur. Biomechanical studies have shown that the FNS provides stability comparable to larger sliding hip screws while also exhibiting greater resistance to shortening than fixation with multiple cannulated screws.
The Surgical Approach and Procedure Overview
The implantation of the Synthes FNS is typically performed using a minimally invasive surgical technique, contrasting with the larger incisions sometimes required for other hip fracture surgeries. The procedure begins with the patient positioned on a specialized fracture table, allowing the surgeon to apply gentle traction to the leg to help realign the fractured bone fragments. This process, known as fracture reduction, is monitored continuously using fluoroscopy (mobile X-ray) to ensure precise anatomical restoration.
Once the fracture is properly aligned, a small incision, often only four to six centimeters in length, is made on the side of the upper thigh. This limited approach helps minimize trauma to the surrounding muscles and soft tissues. The surgeon then uses specialized instruments and fluoroscopic guidance to drill and ream the path for the implant.
The pre-assembled plate, bolt, and ARScrew component is inserted through this small opening and positioned across the fracture line into the femoral head. The image intensifier confirms the correct depth and position of the hardware throughout the procedure. After the bolt and ARScrew are fully seated and locked, a final locking screw secures the lateral plate to the femur shaft. The entire process, from incision to closure, is often completed in under an hour.
Post-Operative Recovery and Expected Timeline
Recovery following FNS implantation is often accelerated due to the fixation’s stability and the minimally invasive nature of the surgery. Patients typically begin mobilization the day after the operation, starting with gentle range-of-motion exercises. The initial hospital stay generally lasts between nine and fifteen days.
A key advantage of the FNS system is its ability to allow early weight bearing, which is important for preventing muscle atrophy and encouraging bone healing. Depending on the fracture pattern and the surgeon’s protocol, patients are commonly instructed to begin protected or full weight bearing as tolerated immediately after surgery. Physical therapy starts promptly to focus on gait training and restoring strength. While full fracture healing can take approximately three months, the robust nature of the FNS allows many patients to return to daily activities and greater independence much earlier.