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The Science Behind Internal Fixation with Plates, Screws, and Nails

Internal fixation with plates, screws, and nails is a common surgical technique used to stabilize and repair fractured bones. This procedure involves the use of metal implants, such as plates, screws, and nails, to hold the broken bone fragments together and promote healing. The science behind internal fixation is based on the principles of biomechanics and the understanding of bone healing processes. In this article, we will explore the science behind internal fixation and delve into the various aspects of this surgical technique.

The Biomechanics of Internal Fixation

Biomechanics is the study of the mechanical properties of biological systems, including the human body. When it comes to internal fixation, biomechanics plays a crucial role in determining the type and placement of implants used to stabilize fractured bones. The goal of internal fixation is to provide stability to the fractured bone, allowing for proper healing while minimizing pain and complications.

One of the key factors in determining the biomechanics of internal fixation is the type of fracture. Fractures can be classified into different types, such as transverse, oblique, comminuted, or spiral fractures. Each type of fracture requires a specific approach to internal fixation, considering factors such as the direction of the fracture line, the number of bone fragments, and the stability of the fracture.

The choice of implant also depends on the biomechanical properties of the bone. Bones have different load-bearing capacities, and the choice of implant should be able to withstand the forces acting on the bone during daily activities. For example, in weight-bearing bones like the femur or tibia, stronger and larger implants may be required to provide adequate stability.

The Role of Plates in Internal Fixation

Plates are commonly used in internal fixation to stabilize fractures. These plates are made of biocompatible materials, such as titanium or stainless steel, which are strong and resistant to corrosion. The plates are designed to fit the contour of the bone and are fixed to the bone using screws.

One of the main advantages of using plates in internal fixation is their ability to provide rigid stability to the fractured bone. The plates act as a scaffold, holding the bone fragments in place and allowing for proper healing. The screws used to fix the plate to the bone provide compression, which helps to promote bone union.

There are different types of plates used in internal fixation, including compression plates, reconstruction plates, and locking plates. Compression plates are used to achieve compression across the fracture site, promoting bone healing. Reconstruction plates are used in complex fractures where multiple fragments need to be stabilized. Locking plates are designed to provide stability without relying on the friction between the plate and the bone.

The Role of Screws in Internal Fixation

Screws are an integral part of internal fixation and are used in conjunction with plates or as standalone implants. These screws are inserted into the bone to provide stability and hold the fractured fragments together. Similar to plates, screws are made of biocompatible materials and come in various sizes and designs.

The choice of screw depends on several factors, including the type of fracture, the bone quality, and the biomechanical requirements. For example, in osteoporotic bones, special screws with a larger thread pitch or self-tapping screws may be used to provide better fixation. In some cases, screws with a lag screw design may be used to achieve compression across the fracture site.

Screws can be inserted in different ways, such as cortical screws, cancellous screws, or lag screws. Cortical screws are used in the outer layer of the bone, providing stability in areas with dense bone. Cancellous screws are used in the spongy inner layer of the bone, providing stability in areas with less dense bone. Lag screws are used to achieve compression across the fracture site.

The Role of Nails in Internal Fixation

Nails, also known as intramedullary nails or rods, are another type of implant used in internal fixation. These nails are inserted into the medullary canal of long bones, such as the femur or tibia, and provide stability by acting as an internal splint.

The use of nails in internal fixation offers several advantages. Firstly, nails allow for load-sharing between the implant and the bone, reducing stress on the bone and promoting healing. Secondly, nails provide rotational stability, preventing the bone fragments from rotating and interfering with the healing process. Lastly, nails can be inserted through smaller incisions, resulting in less soft tissue damage and faster recovery.

Similar to plates and screws, nails come in different designs and sizes to accommodate different types of fractures and bone anatomy. For example, in femoral fractures, intramedullary nails with interlocking screws may be used to provide additional stability.

The Bone Healing Process

Understanding the bone healing process is essential in the science behind internal fixation. When a bone fractures, the body initiates a complex series of events to repair the damage and restore the bone’s integrity. The bone healing process can be divided into three main stages: the inflammatory stage, the reparative stage, and the remodeling stage.

In the inflammatory stage, blood vessels at the fracture site rupture, leading to the formation of a blood clot. This blood clot, known as a hematoma, serves as a scaffold for the influx of inflammatory cells, such as neutrophils and macrophages. These cells remove debris and initiate the inflammatory response, which is essential for the subsequent stages of healing.

In the reparative stage, specialized cells called osteoblasts and chondroblasts migrate to the fracture site and start producing new bone and cartilage. Osteoblasts lay down a collagen matrix, which serves as a framework for the deposition of minerals, such as calcium and phosphate, to form new bone. Chondroblasts produce cartilage, which eventually gets replaced by bone through a process called endochondral ossification.

In the remodeling stage, the newly formed bone undergoes remodeling and maturation. This process involves the removal of excess bone and the realignment of the bone’s structure to restore its strength and functionality. The remodeling stage can take several months to years, depending on the severity of the fracture and the patient’s overall health.


Internal fixation with plates, screws, and nails is a scientifically grounded surgical technique that aims to stabilize fractured bones and promote healing. The biomechanics of internal fixation, including the choice of implants and their placement, play a crucial role in achieving successful outcomes. Plates, screws, and nails provide stability to fractured bones, allowing for proper healing and restoration of function. Understanding the bone healing process is essential in optimizing the use of internal fixation techniques. By considering the principles of biomechanics and bone healing, surgeons can effectively utilize internal fixation to treat fractures and improve patient outcomes.

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