An internal fixation device is a specialized medical implant used in orthopedic surgery to stabilize and hold broken bone fragments in their correct anatomical alignment. Placed inside the body, these devices ensure the fracture remains stable during the natural healing process. This technique is often necessary when casting or splinting alone cannot maintain proper alignment.
Fundamental Purpose and Function
The primary role of internal fixation is to provide a stable mechanical environment that promotes bone healing. Internal devices stabilize the fracture site directly, reducing uncontrolled movement between bone fragments. Reducing micro-motion across the fracture line is crucial for encouraging the formation of new bone tissue.
This stable environment allows for earlier mobilization and function of the injured limb, which aids rehabilitation. The devices bear some load, protecting the healing bone while the patient begins guided movement. This approach reduces the risk of complications such as nonunion, where the bone fails to heal, or malunion, where it heals in an incorrect position.
Fixation devices apply specific mechanical forces to achieve stability. Some implants are designed for compression, drawing bone ends tightly together to accelerate healing. Other devices, such as neutralization plates, protect the fracture from bending and twisting forces.
Diverse Categories of Fixation Hardware
Orthopedic surgeons utilize a variety of hardware designs suited to different bone shapes and fracture patterns.
Screws and Plates
Screws are the most common component, used alone for compression or with other implants. Cortical screws anchor into the dense outer layer of long bones. Cancellous screws feature wider, deeper threads for purchase in the softer, spongy bone near joints. Plates function as internal splints, applied to the bone surface and secured with screws. Locking plates offer enhanced stability by having the screws thread directly into the plate, creating a fixed-angle construct resistant to angular forces.
Nails and Wires
Intramedullary nails or rods are used primarily for fractures in long bones, such as the femur or tibia. Inserted down the hollow center of the bone, they provide central alignment and load-sharing support. Pins and wires are thinner, needle-like implants often used to temporarily hold fragments together or to fix small bones.
Device Composition and Material Selection
Materials selected for internal fixation devices must meet strict criteria, including high strength, resistance to corrosion, and biocompatibility. Surgical-grade metals, primarily stainless steel and titanium alloys, are the standard. Stainless steel offers excellent strength and durability, making it reliable for high-stress applications.
Titanium alloys are favored for their lower density and superior corrosion resistance. Titanium also possesses a lower modulus of elasticity compared to stainless steel, meaning it is slightly more flexible. This flexibility helps minimize stress shielding, which occurs when a stiff implant carries too much load, hindering the bone’s natural healing response.
A newer class of materials includes bioabsorbable polymers, which are designed to slowly break down and dissolve harmlessly in the body over time. These polymers gradually transfer the stress back to the healing bone as the fracture mends, eliminating the need for a second surgery to remove the implant. They are typically reserved for fractures under lower mechanical stress.
Factors Determining Device Retention or Removal
After the bone has completely healed, a decision is made regarding whether the internal fixation device should remain in place or be surgically removed. Many implants are designed to be permanent and do not require removal if they are asymptomatic. Leaving the device in place is often preferred for older patients, as this avoids the risks associated with a second operation.
However, a device may need to be removed if it causes symptoms such as persistent pain, soft tissue irritation, or skin prominence. Removal is also necessary if the patient develops an allergic reaction to a metal component, or if there is infection around the hardware or interference with growth plates in children.
The removal procedure itself carries risks, including infection, nerve damage, or re-fracture of the weakened bone. The decision is individualized, balancing the patient’s symptoms and age against the potential complications of an additional surgical intervention.