Know what each implant does—and why it sometimes fails. Clear clinical explanations with implant photographs, X-rays, implant comparisons and a decision guide.
Start here: A plate, screw or nail is not a treatment plan by itself. Choose an implant that supports the intended reduction, fracture biology, stability and rehabilitation—then verify the construct in the real patient.
1. What do orthopaedic implants actually do?
Orthopaedic implants hold the skeleton in a planned position while tissue heals or a joint is reconstructed. Their performance depends on material, shape, size, location, bone quality and how they are applied.
| Device | Core job | Typical application |
|---|---|---|
| Screw | Obtains bone purchase or produces interfragmentary compression | Lag fixation, plate-to-bone fixation |
| Plate | Controls bending, rotation, shear; may compress or bridge | Periarticular and selected shaft fractures |
| Intramedullary nail | Central load-sharing support, often locked for length/rotation | Many femoral or tibial shaft fractures |
| K-wire / tension band | Pin fixation or fixation with a tension-band construct | Selected small-bone or avulsion fracture patterns |
| External fixator | Transmits force through pins/wires and an external frame | Temporary damage control, selected definitive/reconstructive uses |
For the underlying healing mechanics, see Principles of Fracture Fixation and Fracture Healing.
2. Implant materials and mechanical properties
Stainless steel and titanium alloys are common implant materials. Metal composition matters, but construct geometry and the mechanical environment can matter just as much.
| Property | Stainless steel | Titanium alloy |
|---|---|---|
| Typical elastic modulus | Approximately 190–210 GPa | Approximately 100–120 GPa |
| Relative stiffness (same size) | Higher | Lower |
| Useful considerations | Cost, strength and familiar instrumentation | Good corrosion resistance; lower elastic modulus; widely used in locked systems |
| Important limitation | Can be associated with stress shielding in some constructs | Not automatically more flexible or fatigue-resistant once total implant geometry is considered |
Stiffness is not strength: stiffness is resistance to deformation, yield strength marks onset of permanent deformation, and fatigue failure results from repetitive cyclic loading. An implant that repeatedly carries too much load while the fracture remains ununited can eventually fail.
3. Bone screws — identification and functions
Screws can act as interfragmentary compression devices or as anchors for an implant. They are characterized by diameter, thread depth, pitch, core, head and the way threads engage bone.
↗ Enlarge imageCortical screw
Typically has fine, relatively shallow threads suited to cortical bone. May obtain bicortical purchase in suitable diaphyseal situations. Screw diameter, intact cortices, trajectory and bone quality all affect fixation.
↗ Enlarge imageCancellous screw
Typically has coarser, deeper threads designed to engage cancellous bone, such as selected metaphyseal sites. Partially threaded variants may produce compression if their threaded portion lies fully beyond the fracture.
| Screw concept | How it works | Common pitfall |
|---|---|---|
| Conventional cortical screw | Screw head compresses plate against underlying bone when tightened | Poor plate contour may displace reduction |
| Lag screw (technique) | Near fragment glides; far-fragment threads pull fracture surfaces together | Threads crossing both fragments prevent the intended lag effect |
| Partially threaded cancellous screw | Thread purchase beyond fracture; smooth shaft in near fragment can allow lag effect | Threads across fracture → limited compression |
| Locking screw | Threaded head engages compatible plate hole | Does not independently compress the fracture |
Screw purchase and pull-out
Pull-out resistance depends on bone density, outer thread diameter, thread geometry, engaged cortical thickness and insertion quality. Osteoporotic bone can fail despite a correctly sized screw. Longer screws are not universally better: extra length may injure tendons, neurovascular structures or a joint.
4. Standard versus locking plates and screws
A conventional screw creates stability through plate-to-bone friction. A locking screw engages the plate itself, forming a fixed-angle screw–plate construct. Both may be appropriate—depending on the fracture.
↗ Enlarge imageLocking interface — implant photograph
Notice the locking screw head seated in a compatible plate. This construct can preserve reduction without drawing the plate tightly against the bone, but needs correct trajectory and reliable screw purchase.
| Conventional screw / plate | Locking screw / plate |
|---|---|
| Draws plate to bone; shape and contour critical | Fixed-angle screw–plate connection; less reliance on plate–bone friction |
| May permit useful compression or plate adjustment | Useful in selected metaphyseal or osteoporotic fracture patterns |
| Can displace reduction if plate poorly contoured | Does not automatically reduce or compress fracture |
| Requires appropriate bone purchase | Threaded head does not rescue a stripped bone hole |
5. Plate design, plate function and screw distribution
Plate design refers to the implant shape/hole system; plate function describes how the surgeon applies it. A locking compression plate may perform different roles depending on reduction and screw sequence.
↗ Enlarge imageWrist plate and screws
This is a physical implant for wrist fracture fixation. An anatomically shaped plate may reduce contouring requirements, but plate fit, tendon clearance, safe screw lengths and joint avoidance remain essential.
| Plate application mode | Clinical purpose | Fracture environment |
|---|---|---|
| Compression | Generates interfragmentary compression for suitable simple fracture | Mostly absolute stability |
| Neutralization | Protects a previously compressed lag-screw construct from bending/torsion | Depends on underlying fixation |
| Bridge | Spans multifragmentary region, minimizes soft-tissue stripping | Relative stability with callus |
| Buttress / antiglide | Resists a shear fragment sliding in the relevant direction | Pattern dependent |
| Reconstruction plate | Easier to contour to complex surfaces | Depends on method of application |
| Locking compression plate (LCP) | Combi holes allow appropriate conventional/locking screw options | Not one predetermined stability mode |
Working length, screw density and plate position
The working length generally refers to the plate span between the innermost fixation points adjacent to the fracture zone. A longer effective working span may make a bridge construct less stiff in some configurations. Excessive plate–bone offset, short plates, concentrated screws or wide fracture gaps may promote fatigue or malalignment. The best number and distribution of screws is fracture- and implant-specific; filling every hole is not routinely necessary.
6. Sliding hip implants and angular-stable options
A dynamic hip screw (DHS) is a sliding screw–side-plate system. In suitably selected stable intertrochanteric fractures, controlled sliding can permit fracture impaction under load. Fracture morphology—not familiarity with one implant—guides choice.
↗ Enlarge imageDHS hardware
The lag screw component interfaces with a side-plate barrel, permitting controlled telescoping. It is not simply a generic cortical screw, and it is not preferred for every proximal femoral fracture.
↗ Enlarge imageDHS on a clinical radiograph
Use the AP/lateral radiographs to assess reduction, implant trajectory, tip position and available lateral wall support. This published film illustrates a DHS construct, not universal treatment guidance for all femoral-neck fracture types.
7. Intramedullary nails: structure, locking and reaming
Intramedullary nails sit closer to the limb mechanical axis than plates and often act as load-sharing devices. Locking bolts control rotation and length in selected patterns. Suitability depends on site, fracture pattern, canal, skeletal maturity, entry point and soft tissues.
↗ Enlarge imageTibial interlocking nail
This implant demonstrates a central nail with locking capability. Static interlocking can control both rotation and length in unstable patterns; some systems offer dynamic slots for selected controlled axial movement.
| Feature | Concept / decision |
|---|---|
| Reamed vs unreamed | Reaming changes canal fit and biology; choice is injury-specific, not universally superior |
| Static interlocking | Often used when axial length and rotation are unstable |
| Dynamic locking | Selected stable fracture patterns; evaluate risk of shortening |
| Dynamization | Not an automatic answer to every delayed union; check gap, alignment and infection first |
| Entry point | Incorrect entry may drive malalignment or injury to nearby structures |
8. K-wires and tension-band constructs
Kirschner wires (K-wires) are relatively slender smooth pins, widely used for temporary reduction or selected definitive fixation. Their small diameter gives limited resistance to rotation and bending unless a suitable configuration is used.
↗ Enlarge imageK-wire instrumentation
Used in wrist/hand and selected paediatric injuries. Protect tendons and neurovascular structures. Consider pin migration, skin/pin-site care, and whether fixation stability permits early movement.
↗ Enlarge imagePatella tension-band construct on an X-ray
The classic anterior figure-of-eight tension-band construct was designed to resist tensile forces at the anterior patella and promote compression in suitable fracture geometries. Hardware irritation and migration are recognized issues, and modern plating or other methods may be selected when appropriate.
9. External fixation: unilateral versus circular frames
External fixators connect percutaneous bone pins or wires to external rods/rings. They provide a valuable method of temporary stabilization when soft tissues or physiology do not permit immediate definitive fixation; selected frames are also definitive treatment.
↗ Enlarge imageIlizarov circular frame
Circular frames use rings and tensioned wires or half-pins for multiplanar stability. They may support complex deformity correction, infected bone-defect management or selected difficult fractures—but require meticulous pin-site surveillance and specialized planning.
| Unilateral frame | Circular frame |
|---|---|
| Half-pins with rod/clamps; commonly modular | Rings connected by rods; wires or half-pins |
| Often rapid for damage control | Useful for deformity correction and complex reconstruction |
| Stability increases with appropriate pin diameter, spread, reduced bone–rod distance and frame geometry | Wire tension, crossing angles, ring dimensions and number of fixation points affect stability |
| Monitor pin loosening and soft-tissue access | Monitor wire/pin care, alignment and neurovascular safety |
10. Common implant complications and practical prevention
| Failure / complication | Likely contribution | Clinical prevention / response |
|---|---|---|
| Screw loosening or pull-out | Poor bone stock, inadequate hold, cyclic overload | Confirm purchase, length, trajectories and load-sharing |
| Plate fatigue breakage | Persistent unhealed gap, excessive cyclic loading, unsuitable construct | Address fracture biology and alignment—not just plate thickness |
| Nail malalignment | Entry-point error, poor reduction, metaphyseal instability | Check AP/lateral alignment and locking technique |
| Joint penetration | Incorrect screw trajectory or excessive length | Multiple safe intraoperative fluoroscopic views |
| Tendon irritation/rupture | Hardware/screw prominence, notably at wrist | Safe plate position and screw length verification |
| Pin-site infection | External frame or exposed wires | Safe insertion corridors and appropriate care |
| Stress shielding / peri-implant fracture | Stiffness transition or implant-related loading changes | Individualized implant planning and follow-up |
A practical implant-choice pathway
Consider anatomical reduction, lag fixation and suitable protection/compression.
Consider nail, bridge construct or temporary/definitive external fixation.
11. High-yield revision in 60 seconds
12. Interactive viva — click to reveal
Short surgical decision-making questions. Answers remain hidden until opened.
1. What is the single most important distinction between a locking and a conventional screw?
2. How can a fully threaded cortical screw create interfragmentary compression?
3. Why can a plate compress or bridge depending on technique?
4. Why are screws not routinely placed in every plate hole?
5. What is the difference between static and dynamic interlocking in a nail?
6. What does a DHS barrel allow?
7. When might an intertrochanteric fracture need a cephalomedullary nail rather than a DHS?
8. What are common K-wire complications?
9. How can a unilateral external fixation frame become stiffer?
10. Why does a seemingly strong plate break after months?
13. Interactive 20-question implant mock test
One question at a time. Choose A–D for immediate feedback and option-by-option explanation. Next unlocks after selection; score and answers stay on this browser.
Select an option to reveal explanation and unlock Next.
14. References & image credits
Show references and complete image source addresses
Clinical reference framework
- Orthobullets — Orthopaedic Implants
- AO Surgery Reference — Basic Principles of Plating
- AO Surgery Reference — Locking Plate Principles
- AO — Principles of Fracture Management
Clinical photograph and radiograph sources
Each media item is reproduced unmodified with attribution and a license link. Please check the linked source before publishing; third-party availability can change. All pictured cases illustrate specific implant concepts, not universal treatment recommendations.
- Cortical screw — closer-spaced threads designed for dense cortical bone — Netha Hussain. Original source · CC BY-SA 3.0 licence · Direct image URL
- Cancellous screw — deeper, widely spaced threads for metaphyseal cancellous purchase — Netha Hussain. Original source · CC BY-SA 3.0 licence · Direct image URL
- Fixed-angle locking screw engages a threaded plate hole — Fry72 (Karel Frydrýšek). Original source · CC BY-SA 4.0 licence · Direct image URL
- An anatomical wrist fixation plate with its screws (implant photograph) — Wouter Hagens. Original source · CC BY-SA 3.0 licence · Direct image URL
- Dynamic hip screw component for a sliding hip fixation system — Netha Hussain. Original source · CC BY-SA 3.0 licence · Direct image URL
- Postoperative radiograph showing a DHS construct (case-specific example) — Drvaram. Original source · CC BY-SA 4.0 licence · Direct image URL
- Tibial interlocking nail (implant specimen) — Netha Hussain. Original source · CC BY-SA 3.0 licence · Direct image URL
- Kirschner wire instrumentation used in distal radius fracture management — Ardo191. Original source · Public domain licence · Direct image URL
- Patellar tension-band fixation radiograph — Hellerhoff. Original source · CC BY-SA 3.0 licence · Direct image URL
- Clinical Ilizarov circular external fixation frame — Pagemaker787. Original source · CC BY-SA 4.0 licence · Direct image URL
Educational information only. Surgical technique and implant selection require patient-specific assessment and professional supervision. No affiliation with Orthobullets or AO Foundation is implied.
0 Comments