Quick answer
Ortho screw types are best understood in two overlapping ways: by design and by function. Design refers to the screw’s geometry and features, such as cortical, cancellous, cannulated, locking, or headless construction. Function refers to the job the screw performs within a fixation construct, including compressing a fracture, securing a plate to bone, creating a fixed-angle frame, or helping guide reduction. In practice, the same screw can serve different roles depending on how it is inserted and how it interacts with the plate, bone quality, and fracture pattern.
In most fracture fixation discussions, the core categories are cortical screws, cancellous screws, lag screws, locking screws, cannulated screws, and headless compression screws. Understanding these terms helps readers interpret operative reports, implant catalogs, regulatory descriptions, and fixation articles without assuming that one screw type is universally better than another.
Why screw type is not just a product label
Orthopedic screws are small implants, but their role in fracture fixation is mechanical and highly specific. A screw may pull two bone fragments together, secure a plate, hold an articular fragment below cartilage, or contribute to a bridge construct where the fracture zone is not compressed directly. A useful description therefore depends on both the screw design and the construct in which it is used.
This distinction matters because common terms are often mixed in everyday product and clinical discussions. A “lag screw” is primarily a mode of use, not only a separate product family. A cortical screw may be used as a lag screw if the near cortex is overdrilled so the threads engage only the far fragment. A cancellous screw may also create interfragmentary compression when its partially threaded design allows the near fragment to slide while the threaded portion gains purchase in the far fragment.
AO fracture fixation teaching commonly separates screw behavior by principles such as compression, neutralization, and fixed-angle support. U.S. FDA device descriptions, meanwhile, classify non-spinal metallic bone screws and washers as medical devices intended for applications such as fracture fixation, osteotomy, and small-joint fusion. These frameworks are different, but together they explain why an accurate overview needs to cover both design and intended function.
For more background on the wider fixation category, see the site’s fixation section.
Main ortho screw types by design
Cortical screws
Cortical screws are designed for dense cortical bone, especially in the diaphyseal region of long bones. They typically have a relatively fine thread and are commonly fully threaded. In many plate constructs, a non-locking cortical screw draws the plate toward the bone as it is tightened, creating stability through friction at the plate-bone interface.
A cortical screw can be inserted in neutral mode to hold a plate without intentionally compressing a fracture. It can also be used in lag mode when the near cortex is prepared as a glide hole and the far cortex receives the thread. In that situation, tightening the screw pulls the far fragment toward the near fragment, producing interfragmentary compression.
Cancellous screws
Cancellous screws are intended for less dense metaphyseal or epiphyseal bone. Compared with cortical screws, they generally use a deeper, coarser thread pattern to improve purchase in cancellous bone. They may be fully threaded or partially threaded, depending on the intended role.
Partially threaded cancellous screws are commonly associated with compression across cancellous fracture regions because the unthreaded shaft can allow one fragment to glide while the threaded portion anchors in the opposite fragment. Fully threaded cancellous screws are often used when the main goal is holding power rather than interfragmentary compression.
Locking screws
Locking screws are used with compatible locking plates. Instead of relying only on the screw head pressing the plate against bone, the screw head locks into the plate hole, creating a fixed-angle relationship between the screw and plate. This makes the construct less dependent on bone-plate compression.
Locking technology is especially relevant in osteoporotic bone, metaphyseal bone, periarticular fractures, and bridge plating concepts. Fixed-angle locking screws follow a predetermined path. Variable-angle locking screws allow a controlled range of screw angulation within the plate design, which may help surgeons avoid joint penetration, existing implants, fracture lines, or poor bone corridors.
Cannulated screws
Cannulated screws have a central channel that allows insertion over a guidewire. This design supports controlled placement when trajectory is important, such as in small bones, periarticular fragments, scaphoid fixation, femoral neck fixation, or other locations where imaging-guided positioning is required.
The main advantage is precision. The limitation is that cannulation changes the screw’s geometry, so implant selection still needs to account for diameter, thread length, insertion torque, and expected mechanical load. Cannulated does not automatically mean compressive, locking, or headless; it only describes the presence of the guidewire channel.
Headless compression screws
Headless compression screws are designed to sit below or flush with the bone surface, reducing problems caused by a prominent screw head. They are often used in small bone and intra-articular or periarticular applications where surface prominence can irritate soft tissue or interfere with joint movement.
Many headless compression screws create compression through differential thread pitch or other compression mechanics. A well-known historical example is the Herbert-style screw concept, but modern headless systems vary by diameter, cannulation, thread profile, and intended anatomical use.
Common screw roles in fixation constructs
Screw names become clearer when viewed through their role in the construct. The table below summarizes the practical differences between major terms often seen in orthopedic education, operative descriptions, and implant catalogs.
| Term | Primary meaning | Typical purpose | Key consideration |
|---|---|---|---|
| Cortical screw | Design for dense cortical bone | Plate fixation, bicortical purchase, lag technique when prepared correctly | Fine thread and bone quality influence holding power |
| Cancellous screw | Design for cancellous bone | Metaphyseal fixation, epiphyseal fixation, compression with partial threads | Thread depth and pitch support purchase in softer bone |
| Lag screw | Functional use | Interfragmentary compression | Requires correct glide and thread engagement principles |
| Locking screw | Plate-screw interface design | Fixed-angle support and bridge constructs | Must match the locking plate system |
| Cannulated screw | Insertion design | Guidewire-assisted placement | Trajectory accuracy is the main advantage |
| Headless compression screw | Head profile and compression design | Low-profile compression in small bone or joint-adjacent regions | Placement depth and joint clearance are critical |
How bone quality and fracture pattern influence screw selection
Bone quality strongly affects screw performance. Dense cortical bone can provide reliable thread engagement for cortical screws. Cancellous bone requires geometry that can gain purchase in a more porous structure. Osteoporotic bone may reduce holding power, making locking constructs, longer plates, additional fixation points, or alternative strategies more relevant depending on the fracture and patient factors. See also: Implants.
Fracture pattern is equally important. Simple oblique and spiral fractures may be suitable for lag screw compression if anatomical reduction is achievable. However, a lag screw alone may not resist bending and torsional loads in many long-bone settings. In those cases, a neutralization plate can protect the compressed fracture. Comminuted fractures usually cannot be compressed fragment by fragment without disrupting biology or alignment, so bridge plating with locking or non-locking screws may be considered instead.
Anatomical location also changes the choice. Diaphyseal fixation often relies on cortical purchase and plate mechanics. Metaphyseal and periarticular fixation may require cancellous screws, locking screws, raft-like subchondral support, or variable-angle options to avoid a joint surface. Small bones may benefit from cannulated or headless compression screws when precision and a low profile matter.
Regulatory and material context
Orthopedic screws are regulated medical devices, not generic hardware. In the United States, FDA materials for non-spinal metallic bone screws and washers describe Class II device pathways and performance expectations for screws used in fracture fixation, osteotomy, and small-joint fusion or arthrodesis. The FDA’s November 2024 guidance on non-spinal metallic bone screws and washers is particularly relevant for understanding how performance criteria are framed for safety and effectiveness review.
Common metallic materials include stainless steel and titanium alloys, selected for mechanical strength, biocompatibility, corrosion resistance, imaging considerations, and compatibility with the overall implant system. Absorbable and bioresorbable fixation concepts also exist, but they are not interchangeable with metallic screws and should be evaluated within their specific indication, material behavior, degradation profile, and regulatory clearance.
Industry readers should be cautious when comparing screws only by diameter or catalog name. Thread profile, core diameter, head design, drive interface, material standard, locking mechanism, instrumentation, and compatible plate system can all affect performance. A 3.5 mm cortical screw from one system should not be treated as equivalent to every other 3.5 mm screw without reviewing the manufacturer’s approved specifications and surgical technique documentation.
Practical comparison for non-clinical readers
For implant buyers, medical writers, distributor teams, and healthcare content editors, the most useful way to describe ortho screw types is to connect each type to a mechanical problem. If the problem is dense shaft bone fixation, cortical screws are central. If the problem is purchase in metaphyseal cancellous bone, cancellous geometry matters. If the problem is compression across a simple fracture, lag technique is the key. If the problem is maintaining alignment in weaker bone or periarticular regions, locking constructs may be important.
It is also important to avoid overgeneralized claims. Locking screws are not automatically superior to non-locking screws. Cannulated screws are not automatically safer or stronger. Headless screws are not appropriate simply because they are low profile. Each design solves a particular mechanical or anatomical problem while introducing its own constraints.
Another common misunderstanding is the belief that more screws always mean more stability. In plate fixation, screw number, screw position, working length, fracture pattern, bone quality, and biological preservation all interact. Filling every plate hole is not always necessary or desirable. Construct planning aims to maintain reduction and stability while respecting soft tissue and bone biology.
Frequently asked questions
What are the most common ortho screw types?
The most common categories are cortical screws, cancellous screws, locking screws, lag screws, cannulated screws, and headless compression screws. Some terms describe design, while others describe function. For example, “cannulated” describes guidewire-assisted insertion, while “lag” describes compression across a fracture.
What is the difference between cortical and cancellous screws?
Cortical screws are intended for dense cortical bone and typically have finer threads. Cancellous screws are intended for porous cancellous bone and generally use deeper, coarser threads to improve purchase. The choice depends on bone region, density, and fixation goal.
Is a lag screw a separate type of screw?
Not always. A lag screw is best understood as a compression function. A screw becomes a lag screw when it is inserted so that the near fragment can glide and the far fragment is engaged by the threads, allowing tightening to compress the fracture surfaces.
When are locking screws used?
Locking screws are used with compatible locking plates to create a fixed-angle construct. They are often considered when bone quality is poor, when periarticular fixation needs angular stability, or when a bridge plating strategy is used. Their value depends on the whole construct, not the screw alone.
Why use a headless compression screw?
A headless compression screw can provide compression while reducing implant prominence. This is useful in small bones or near joint surfaces where a screw head could irritate soft tissue or interfere with motion. Correct sizing, depth, and trajectory remain essential.
Key takeaway
The phrase “ortho screw types” covers more than a list of implants. It includes screw geometry, bone purchase, plate interaction, insertion method, and intended mechanical role. Cortical and cancellous screws describe how threads engage different bone structures. Lag screws describe compression. Locking screws describe a fixed-angle plate-screw interface. Cannulated screws describe guidewire-assisted placement. Headless compression screws describe low-profile compression. The safest and most accurate interpretation always considers the fracture pattern, bone quality, anatomical site, implant system, and documented indication.