Surgical screws represent one of the most fundamental tools in orthopedic and trauma surgery. These precision-engineered devices provide critical fixation for bone fragments, enable joint reconstruction, and support healing in countless procedures performed daily across operating rooms worldwide.
Understanding the distinct characteristics and optimal applications of these screws directly impacts patient outcomes and surgical success. That’s why we’ve put together this guide that covers the different types of surgical screws and what medical professionals should know about them.
Types of Surgical Screws
Surgical screws come in various designs and materials, each tailored to meet specific clinical needs. By selecting the appropriate type of screw, surgeons can address different anatomical challenges and ensure stability for effective healing. Below is an overview of some of the most commonly used types of surgical screws and their unique applications.
Cortical Screws
Cortical screws are specifically engineered for dense cortical bone, featuring a relatively shallow thread pitch and a smaller core diameter. These screws excel in providing compression across fracture sites and securing plates to bone surfaces. The fine threading pattern distributes load effectively across the dense outer bone layer, making them ideal for diaphyseal fractures and plate fixation applications.
The primary advantage of cortical screws lies in their exceptional holding power in hard bone tissue. Their design minimizes bone removal while maximizing thread engagement with cortical bone. However, cortical screws can be challenging to insert in dense bone and may cause stress concentrations that lead to bone splitting if not properly pre-drilled and tapped.
Cancellous Screws
Cancellous screws feature deeper, more aggressive threading designed to engage the softer, spongy cancellous bone found in metaphyseal and epiphyseal regions. The wider thread pitch and larger core diameter provide superior purchase in less dense bone tissue, making them particularly effective for metaphyseal fractures and areas where cortical bone thickness is limited.
These screws offer excellent fixation in soft bone and can often be self-tapping, reducing surgical time and complexity. The aggressive threading provides strong resistance to pullout forces in cancellous bone. The main disadvantage is their limited effectiveness in cortical bone, where the coarse threading may not offer adequate purchase and could potentially weaken the bone structure.
Cannulated Screws
Cannulated screws contain a central hollow channel that allows insertion over a guidewire, providing precise placement and trajectory control. This design proves invaluable in complex anatomical locations where accurate screw positioning is critical, such as femoral neck fractures, scaphoid fractures, and pedicle screw placement in spinal surgery.
The guided insertion capability significantly improves accuracy and reduces the risk of neurovascular injury. Cannulated screws allow for real-time fluoroscopic guidance, allowing surgeons to insert them through minimally invasive approaches. The hollow design does compromise some mechanical strength compared to solid screws, and the insertion technique requires additional steps, including guidewire placement and removal.
Lag Screws
Lag screws utilize a specific thread pattern that engages only the far cortex, while the smooth shank passes through the near cortex. This configuration creates compression across fracture lines or between bone fragments, promoting healing through interfragmentary compression. Lag screws are essential for oblique and spiral fractures where compression enhances stability.
The compression mechanism of lag screws provides excellent fracture reduction and promotes primary bone healing. Surgeons can use them alone or in combination with plates for enhanced fixation. Proper technique is crucial for lag screw effectiveness, as inadequate compression or over-compression can compromise fracture healing. Additionally, lag screws may loosen over time if the compression is lost.
Herbert Screws
Herbert screws feature a unique dual-thread design with different pitches on the leading and trailing portions of the screw. This configuration creates automatic compression as the screw advances, making them particularly useful for minor bone fractures such as scaphoid fractures, where compression is essential but space is limited.
The self-compressing mechanism eliminates the need for separate compression techniques and provides consistent interfragmentary pressure. Herbert screws are excellent for small bone applications where traditional lag screw techniques may be impractical. The specialized design makes them more expensive than standard screws, but surgeons won’t need them often since their application is primarily limited to specific anatomical locations and fracture patterns.
Interference Screws
Interference screws are specifically designed for soft tissue fixation, particularly in ligament reconstruction procedures such as ACL repair. These screws secure grafts within bone tunnels by creating interference between the graft and tunnel walls, providing immediate fixation strength.
The primary advantage of interference screws is their ability to provide immediate, strong fixation of soft tissue grafts without the need for additional fixation devices. They allow for tensioning of the graft during insertion, which means surgeons can place them through the same incision used for graft passage. Potential complications include graft laceration during insertion and the possibility of screw divergence from the tunnel axis, which can compromise fixation strength.
Bioabsorbable Screws
Bioabsorbable screws are more unique as they’re made from materials that gradually dissolve in the body over time, eliminating the need for removal surgery. These screws typically use polymers such as polylactic acid or polyglycolic acid and are common in pediatric applications. Most surgeons opt for these when working on areas where metal artifacts interfere with imaging, and situations where screw removal would be technically challenging.
The best part of bioabsorbable screws is that they eliminate long-term foreign body presence and avoid complications associated with permanent implants. They are particularly valuable in growing children, where permanent hardware could interfere with bone development. However, these screws provide less initial mechanical strength than metal screws and may cause inflammatory reactions as they dissolve. The degradation process can also create temporary weakness in the fixation construct during the absorption phase, so keep these things in mind.
Factors to Consider When Selecting Surgical Screws
Even once you understand the different types of surgical screws that exist, you still need to be familiar with the patient-specific factors that influence screw selection. That’s why bone quality assessment remains paramount, as osteoporotic patients require different considerations compared to those with normal bone density. Age impacts both bone quality and healing potential, while activity level influences the mechanical demands placed on the fixation.
The surgical site and specific procedure dictate many surgical screw selection parameters as well. Anatomical location determines available space, required screw length, and biomechanical loads. The nature of the fracture or repair influences whether compression, neutralization, or buttressing represents the primary fixation goal.
On top of that, biomechanical considerations encompass load distribution, stress concentration, and the mechanical environment at the surgical site. Understanding these forces helps optimize screw selection for long-term stability and successful healing.
Surgical Techniques and Screw Placement
Pre-drilling and tapping procedures ensure optimal screw placement and reduce insertion forces. Proper drill bit selection based on screw outer diameter and thread pitch prevents fracture during insertion and optimizes holding power.
The relationship between drill diameter and screw threads significantly affects fixation quality. Under-drilling increases holding power but raises fracture risk, while over-drilling reduces holding power and minimizes insertion forces. Achieving the optimal balance requires understanding bone quality and screw characteristics.
Most importantly, screw insertion techniques vary based on screw type and clinical situation. Proper torque application prevents over-tightening while ensuring adequate fixation. Sequential tightening in multi-screw constructs distributes loads evenly and prevents loss of reduction. Knowing this in advance will help with the entire insertion process.
