Internal fixation in orthopedic surgery involves the use of implants to repair bones. This surgical approach stabilizes fractured bones and corrects deformities. The primary goal is to restore the bone’s proper alignment and stability, promoting effective healing and patient mobility.
Understanding Screw Fixation
Screw fixation is a fundamental internal fixation technique that uses screws to hold bone fragments together or secure other orthopedic implants. Screws generate compression between bone fragments or provide stable anchoring for devices like plates, which is beneficial for bone healing and reduces stress on the implant.
Orthopedic screws are made from biocompatible materials. Common materials include stainless steel and titanium or titanium alloys, such as Ti-6Al-4V. These materials are selected for their high strength and corrosion resistance.
Types and Functions of Orthopedic Screws
Orthopedic screws come in various designs, each tailored for specific bone types and surgical objectives. Cortical screws, for example, are designed for dense, hard bone, typically found in the shafts of long bones. They have fine, tightly pitched threads along their entire length, providing a strong grip in compact bone. These screws are often used to secure plates to bone or as positional screws.
Cancellous screws are made for softer, spongy bone, often found near joints or in the ends of long bones. They feature coarser, deeper threads with a wider pitch, allowing for better purchase in less dense bone. Partially threaded cancellous screws are frequently used as lag screws to compress two bone fragments together, promoting faster healing.
Cannulated screws have a hollow central shaft, allowing them to be inserted over a guide wire for precise placement. This design is useful in intricate surgeries, as it minimizes trauma to surrounding tissues and can reduce surgical time. Both cortical and cancellous screws can be cannulated, making them versatile for various fracture patterns.
Locking screws have threaded heads that engage with corresponding threaded holes in a plate, creating a fixed-angle construct. This construct enhances stability, especially in complex fractures or in bones with poor quality, such as osteoporotic bone. Unlike traditional screws, locking screws do not rely on compression between the plate and bone for stability, which helps preserve the bone’s blood supply.
Headless screws, also known as Herbert screws, lack a traditional screw head and are designed to be fully buried within the bone. They often feature threads with different pitches at each end, allowing for compression between bone fragments as the screw is inserted. These screws are commonly used in small bones or around joint surfaces where a low-profile implant is desired to minimize soft tissue irritation.
Common Applications of Screw Fixation
Screw fixation is used for various orthopedic conditions. A primary use is in fracture fixation, where screws directly hold broken bone fragments in alignment. This is common for fractures in long bones like the femur, tibia, and humerus, as well as in smaller bones such as those in the ankle and wrist. Screws can be used alone to stabilize a fracture or in conjunction with plates, rods, or nails to create a more robust construct.
Screws also play a role in joint fusions (arthrodesis), a procedure that joins two bones forming a joint. For instance, screw fixation is used to stabilize the subtalar joint in the foot to relieve pain caused by arthritis or instability. The screws compress the joint surfaces, encouraging them to fuse into a single, solid bone.
Screws are regularly used to secure plates and other implants to bone. Locking plates, for example, rely on screws that thread directly into the plate, creating a rigid system that helps stabilize complex fractures, particularly in areas with compromised bone quality. Pedicle screws are a specialized application in spinal surgery, inserted into the vertebrae and connected by rods to stabilize the spinal column during fusion procedures.
The Surgical Process and Post-Operative Care
Screw fixation begins with the patient receiving anesthesia. The surgeon makes an incision to access the fractured bone. The bone fragments are repositioned into their correct anatomical alignment using specialized tools like clamps or reduction forceps.
Once the bone is aligned, a pilot hole is drilled into the bone at a precise angle, often guided by fluoroscopy for accuracy. In dense bone, the hole might be tapped to create threads before the screw is inserted. The chosen screw is inserted using a screwdriver, ensuring it is fully seated without overtightening. After the screws are placed and stability is confirmed, the incision is closed with stitches or staples.
Post-operative care includes managing pain, caring for the wound, and often immobilizing the affected area. Pain medication is prescribed to manage discomfort. The surgical site requires wound care, including dressing changes, to prevent infection. Immobilization, often with a cast or brace, helps protect the healing bone from movement that could disrupt the fixation. Physical therapy and rehabilitation are recommended to restore strength, range of motion, and function, with recovery timelines varying from weeks to several months depending on the fracture’s severity and location.
When Screw Removal is Considered
Orthopedic screws remain in the body permanently after the bone has healed. However, screw removal is considered in certain situations. The decision to remove screws depends on factors such as the screw’s location, the patient’s symptoms, and the surgeon’s judgment.
Common reasons for removal include pain or discomfort caused by the hardware, especially if it is prominent under the skin or irritates surrounding soft tissues. Infection around the implant, or mechanical issues like screw loosening or breakage, are also reasons for removal. In growing children, hardware may be removed to prevent interference with bone growth. If removal is needed, it involves a surgical procedure using specialized tools to loosen and extract the screws.