What orthopedic implant screws do in fracture fixation
In fracture fixation, screws are among the most common orthopedic implants used to hold bone fragments, plates, rods, or other fixation constructs in position while healing occurs. In search language, orthopedic implants screws usually refers to bone screws used in internal fixation, not ordinary hardware. Their value is not determined by diameter or length alone. A screw may compress a fracture, anchor a plate, lock into a fixed-angle construct, guide a cannulated technique, or help maintain fixation in weaker bone.
The appropriate choice depends on the fracture pattern, bone quality, anatomical site, implant system, surgical plan, and regulatory-cleared indication. No single screw type is universally better. The practical question is whether the design, material, instrumentation, and performance evidence match the intended fixation task.
This article is an educational overview for industry and clinical readers. It does not replace surgeon judgment, device labeling, regulatory review, or patient-specific medical advice. For related implant category coverage, see the Implants section.
Main screw types and why design matters
Orthopedic bone screws look simple, but their geometry changes how they interact with cortical bone, cancellous bone, plates, washers, and instruments. Thread pitch, thread depth, core diameter, head design, drive recess, tip shape, cannulation, and surface finish can all affect insertion, pullout resistance, compression, and removal. Public educational material from the American Academy of Orthopaedic Surgeons notes that screws are used very frequently in internal fracture fixation. Regulatory and standards documents also treat them as engineered medical devices requiring defined specifications and testing.
| Screw category | Typical role | Key design issue | Common limitation |
|---|---|---|---|
| Cortical screw | Purchase in dense cortical bone or fixation through a plate | Finer thread profile and firm engagement with the outer bone layer | Performance depends on bone quality, pilot hole preparation, and insertion technique |
| Cancellous screw | Purchase in softer cancellous bone, often near metaphyseal regions | Deeper, coarser threads intended to engage trabecular bone | Can lose purchase in poor bone if loading or technique is unsuitable |
| Cannulated screw | Placement over a guide wire for controlled trajectory | Central channel enables guided insertion | Reduced core area may affect mechanical properties, depending on design |
| Locking screw | Threaded engagement with a locking plate to create angular stability | Screw head locks into the plate rather than only compressing plate to bone | Construct stiffness and screw placement must be planned carefully |
| Lag screw technique | Compression across a fracture line | Near fragment is over-drilled or otherwise prepared so threads engage the far fragment | Requires suitable fracture geometry and accurate reduction |
Cortical, cancellous and cannulated screws
Cortical screws are commonly associated with dense outer bone. Their threads are generally shallower and more closely spaced than those of cancellous screws. Cancellous screws are designed for softer trabecular bone and often have deeper threads. Cannulated screws are not defined by bone type alone; their central channel allows insertion over a guide wire, which can be useful when trajectory control is critical. In each case, the term describes a design strategy, not an automatic clinical result.
Locking and non-locking screws
Conventional non-locking screws can draw a plate toward bone and depend partly on friction between the plate and bone. Locking screws mechanically engage the plate, creating a fixed-angle relationship between screw and plate. This can be important in comminuted fractures, periarticular fixation, osteoporotic bone, or bridge plating strategies.
Locking technology, however, is not a substitute for reduction, alignment, or construct planning. Excessive stiffness can reduce beneficial micromotion in some healing situations, while insufficient stability can increase the risk of fixation loss.
Lag screws are a function, not only a label
A lag screw compresses two bone fragments by allowing the screw threads to engage the far fragment while the near fragment can slide under the screw head. Some screws are sold or described as lag screws, but the clinical effect depends on technique, drilling, fracture orientation, and thread engagement. This distinction matters when reading product literature: a screw name alone does not prove that compression was achieved in a specific case.
Materials used in orthopedic implant screws
Most permanent orthopedic fixation screws are metallic. Common materials include surgical stainless steel and titanium alloys, both widely used because they combine strength, manufacturability, and a long clinical history. Cobalt-chromium alloys are used in some orthopedic applications but are less commonly discussed for general fracture screws than stainless steel and titanium. Material choice affects strength, stiffness, imaging artifacts, compatibility with plates and instruments, corrosion behavior, and labeling considerations.
Titanium is often associated with a lower elastic modulus than stainless steel and favorable biocompatibility, but that does not make it automatically superior for every fixation task. Stainless steel remains widely used and can offer high strength and cost-effective manufacturing. Mixing metals within a construct is generally governed by the implant system’s labeling and compatibility data, not by informal assumptions. Surgeons and procurement teams should confirm whether screws, plates, drill bits, taps, drivers, and washers are intended to be used together as a system.
Absorbable screws and plates occupy a separate category. FDA-recognized consensus standards have included ASTM F2502 for absorbable plates and screws for internal fixation implants. These devices raise additional questions about degradation profile, mechanical retention during healing, local tissue response, and sterilization. They should not be evaluated using the same assumptions applied to permanent metallic screws.
Performance checks before a screw reaches surgery
Bone screws are evaluated through a combination of design description, material controls, mechanical testing, biocompatibility assessment, sterilization validation when supplied sterile, packaging validation, labeling, and regulatory submission evidence where applicable. In the United States, FDA guidance issued in November 2024 addresses orthopedic non-spinal bone plates, screws, and washers in 510(k) submissions. The guidance covers non-resorbable, non-spinal systems and stand-alone screws and is intended to support more consistent review of device information and performance data.
ASTM F543 is a central standard for metallic medical bone screws. The standard addresses requirements and test methods related to metallic screws implanted into bone, including torsional properties, driving torque, axial pullout strength, and self-tapping performance. These tests do not simulate every clinical condition, but they help compare worst-case designs and demonstrate that a screw can withstand defined mechanical demands. ISO 5835, confirmed by ISO in 2022, addresses dimensions and tolerances for certain metal bone screws with hexagonal drive connection, spherical under-surface of the head, and asymmetrical thread.
| Evidence area | What it helps answer | Why readers should care |
|---|---|---|
| Material specification | What alloy or absorbable material is used | Material affects strength, corrosion behavior, compatibility, and labeling |
| Dimensional controls | Whether thread, head, drive, and length meet defined tolerances | Small changes can affect insertion, plate fit, and removal |
| Torsional testing | How the screw behaves under twisting loads | Important during insertion and removal |
| Pullout testing | How strongly the screw resists axial extraction in a test medium | Relevant to fixation strength, while not replacing clinical judgment |
| Driving torque | How much torque is needed to insert the screw | High insertion torque may damage the screw, driver, or bone |
| Biocompatibility and sterilization | Whether patient-contacting materials and sterile supply claims are supported | Essential for patient safety and regulatory compliance |
The important editorial point is that a standard test result is not a clinical guarantee. Bench tests are controlled comparisons. Human bone varies by age, anatomy, disease, medication history, fracture energy, and surgical technique. A well-tested screw can still fail if used outside its indication, paired with an incompatible plate, inserted with the wrong instrument, or subjected to loads beyond the construct plan.
Clinical and design factors that influence screw selection
The same screw may perform differently in dense diaphyseal cortical bone, metaphyseal cancellous bone, osteoporotic bone, small fragments, or periarticular fixation. For that reason, orthopedic screw selection starts with the biological and mechanical problem rather than the catalog page. A transverse fracture needing compression, a comminuted fracture needing bridge fixation, and a periarticular fracture needing trajectory control may require different screw strategies.
- Fracture pattern: Simple patterns may benefit from compression, while multifragmentary patterns may require relative stability and bridging.
- Bone quality: Osteoporotic or weak bone can reduce purchase and may influence the use of locking constructs, longer screws, alternative trajectories, augmentation, or different fixation methods.
- Anatomical site: Small bones, long bones, periarticular regions, and spine-related applications have different load environments and regulatory categories.
- Construct design: Screw number, working length, plate span, screw density, and placement sequence all affect stiffness and load sharing.
- Instrumentation: Drill size, tapping, countersinking, driver fit, and torque control influence whether the intended mechanical design is actually achieved.
- Indication and labeling: A screw cleared for one general use should not be assumed appropriate for another anatomical or loading environment without supporting labeling.
Locking technology illustrates the trade-off. A fixed-angle screw-plate interface can help when conventional screw purchase is limited, but a construct with too many screws or too short a working length may become very stiff. Orthopedic literature on fracture fixation often discusses the balance between absolute stability, relative stability, compression, and controlled micromotion. The best choice depends on the healing strategy, not on a single product feature.
How to read orthopedic screw specifications without overinterpreting them
Product descriptions often emphasize diameter, length, material, head style, thread type, cannulation, self-tapping capability, and compatibility with plates. These details are useful, but they should be read with care. A 3.5 mm screw from one system is not automatically interchangeable with another 3.5 mm screw. Head geometry, thread form, driver recess, locking interface, pitch, and instrument tolerances may differ.
Readers evaluating orthopedic implant screws should look for several pieces of information before drawing conclusions:
- Intended use: Confirm whether the screw is for non-spinal fracture fixation, spinal fixation, cranio-maxillofacial use, external fixation, arthrodesis, or another category.
- System compatibility: Determine which plates, washers, drivers, drill bits, taps, and guides are listed as compatible.
- Material and standard references: Check whether the material and testing references are identified clearly, such as ASTM or ISO standards where applicable.
- Sterile or non-sterile supply: Sterility, packaging, shelf life, and reprocessing instructions matter for hospital handling.
- Warnings and contraindications: Labeling may limit use in infection, poor bone stock, excessive load, noncompliant patients, or other risk conditions.
- MRI and imaging information: MR safety labeling should be based on device-specific evaluation, not assumed from material alone.
For procurement and technical writing, the safest approach is to describe what the device is designed and cleared to do, then separate that from clinical outcome claims. Phrases such as designed for fixation, intended to provide stabilization, or evaluated under ASTM F543 are more defensible than unsupported claims that a screw prevents failure, accelerates healing, or is the best option for a broad patient group.
Information gaps that matter in industry coverage
Many online explanations of orthopedic screws stop at basic definitions. A more useful review should also identify what is not proven by a brief specification sheet. Diameter does not reveal fatigue behavior in a full construct. Material does not prove compatibility with every plate. Locking does not guarantee better healing. Cannulation does not guarantee safer placement. A recognized standard does not replace indication-specific evidence, regulatory review, or surgical planning.
Another important distinction is the difference between stand-alone screws and screw-plate systems. A screw used alone for interfragmentary compression has a different mechanical role from a screw used to anchor a plate, lock into a fixed-angle construct, or secure an intramedullary device. Device submissions and labeling often treat the system as a whole, so the screw cannot be evaluated apart from its mating components. This is especially relevant when hospitals consider substitutions or when writers compare products across manufacturers.
Finally, time matters. FDA guidance and recognized consensus standards are periodically updated. As of the latest public information reviewed for this article, FDA’s final guidance for orthopedic non-spinal bone plates, screws, and washers was issued in November 2024, and FDA’s recognized standards database reflected updates into 2026. Readers should verify the current version before relying on a standard number, recognition status, or regulatory pathway in purchasing, submission planning, or clinical documentation.
Frequently asked questions
Are orthopedic implant screws permanent?
Many metallic orthopedic screws are designed to remain in the body permanently, but some may be removed if they cause symptoms, interfere with another procedure, become associated with complications, or if the surgeon determines removal is appropriate. Absorbable screws are designed to degrade over time, but their use depends on indication, material, and labeling.
What is the difference between locking and non-locking screws?
A non-locking screw usually compresses a plate toward bone or compresses bone fragments, depending on technique. A locking screw mechanically engages the plate, creating a fixed-angle construct. Locking screws can be useful in certain fracture patterns or poor bone quality, but they are not automatically better for every case.
Are titanium screws better than stainless steel screws?
Not universally. Titanium alloys and stainless steel both have long histories in orthopedic fixation. Titanium may offer advantages in some compatibility and imaging contexts, while stainless steel may provide favorable strength and manufacturing characteristics. The appropriate material depends on the device system, indication, surgeon preference, and labeling.
Can orthopedic screws break or loosen?
Yes. Screws can loosen, bend, back out, or break if fixation is overloaded, bone purchase is poor, healing is delayed, the construct is not suitable for the fracture, or the device is used outside its intended parameters. Mechanical testing reduces uncertainty, but it cannot eliminate all clinical risk.
Do ASTM or ISO standards prove that a screw will work clinically?
No. Standards help define specifications and repeatable test methods. They support consistency, comparison, and regulatory review, but they do not prove success in every patient. Clinical performance depends on indication, surgical technique, anatomy, patient factors, postoperative loading, and the complete fixation construct.