Cancellous Screw vs. Cortical Screw

Attribute	Cancellous Screw	Cortical Screw
Usage	Primarily used in cancellous bone	Primarily used in cortical bone
Thread Design	Coarse thread design	Fine thread design
Thread Pitch	Higher thread pitch	Lower thread pitch
Thread Diameter	Thicker thread diameter	Thinner thread diameter
Head Design	Usually has a larger head	Usually has a smaller head
Indications	Fractures in cancellous bone, osteoporotic bone	Fractures in cortical bone, non-osteoporotic bone
Insertion Technique	Usually self-tapping	May require pre-drilling
Stability	Provides good stability in cancellous bone	Provides good stability in cortical bone

Introduction

When it comes to orthopedic surgeries and fracture fixation, screws play a crucial role in providing stability and promoting bone healing. Two commonly used types of screws are cancellous screws and cortical screws. While both serve the purpose of fixation, they have distinct attributes that make them suitable for specific applications. In this article, we will explore and compare the attributes of cancellous screws and cortical screws, shedding light on their differences and highlighting their respective advantages.

Thread Design

The thread design of a screw greatly influences its performance and application. Cancellous screws typically have a coarse thread with larger pitch and deeper threads. This design allows for better purchase in softer bone, such as cancellous bone found in the metaphysis or epiphysis of long bones. The deep threads provide excellent pull-out resistance, preventing the screw from loosening or backing out over time.

On the other hand, cortical screws have a finer thread with a smaller pitch. This design is more suitable for dense cortical bone, which is found in the diaphysis or shaft of long bones. The finer thread allows for better engagement with the dense bone, providing increased stability and reducing the risk of screw pull-out.

Diameter and Length

Another important attribute to consider is the diameter and length of the screws. Cancellous screws are typically larger in diameter compared to cortical screws. This is because cancellous bone has a lower density and requires a larger screw to achieve adequate fixation. The larger diameter provides better load-bearing capacity and reduces the risk of screw breakage.

On the other hand, cortical screws have a smaller diameter, as cortical bone is denser and can provide sufficient stability with a smaller screw. The smaller diameter allows for easier insertion and reduces the risk of damaging the bone during the drilling process. Additionally, cortical screws are available in various lengths to accommodate different bone thicknesses and fixation requirements.

Head Design

The head design of a screw determines the method of insertion and the type of screwdriver required. Cancellous screws typically have a hexagonal or square head, allowing for easy insertion using a corresponding screwdriver. The larger head provides better grip and torque transmission during insertion.

On the other hand, cortical screws often have a countersunk or conical head design. This allows the screw head to sit flush with the bone surface, reducing the risk of soft tissue irritation and facilitating a smoother post-operative recovery. The countersunk head also allows for easy removal of the screw if necessary.

Indications

Both cancellous screws and cortical screws have specific indications based on the type of bone and fracture being treated. Cancellous screws are commonly used in metaphyseal fractures, such as those involving the distal radius or proximal humerus. They are also suitable for fixation in osteoporotic bone, as the deep threads provide excellent purchase in low-density bone.

On the other hand, cortical screws are primarily used in diaphyseal fractures, where the dense cortical bone requires a smaller diameter screw for adequate fixation. They are also preferred for fixation in non-osteoporotic bone, as the finer thread design engages better with the dense bone structure.

Conclusion

In conclusion, cancellous screws and cortical screws have distinct attributes that make them suitable for specific applications in orthopedic surgeries. The thread design, diameter and length, head design, and indications differ between the two types of screws. Understanding these differences is crucial for surgeons to choose the appropriate screw for each patient and fracture type, ensuring optimal fixation and promoting successful bone healing. By considering the unique attributes of cancellous screws and cortical screws, orthopedic surgeons can achieve better outcomes and improve patient care.