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Proximal Femoral Nail design components overview
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Proximal Femoral Nail (PFN) - Overview & Design
What Is It?
The PFN is an intramedullary (IM) implant - more precisely, a type of cephalomedullary nail - used to fix fractures of the proximal femur, particularly intertrochanteric and subtrochanteric fractures. The nail sits inside the femoral medullary canal and is anchored proximally into the femoral head/neck, giving it a mechanical advantage over extramedullary devices like the sliding hip screw (DHS/CHS).
Core Components
| Component | Description |
|---|---|
| Main nail (intramedullary rod) | Titanium or stainless steel cannulated rod inserted into the femoral canal; proximal diameter ~17 mm, distal ~10 mm |
| Femoral neck screw (lag screw) | Large sliding screw (11 mm diameter, lengths 80-120 mm) that passes through the nail into the femoral head; CCD angles of 125° or 130° |
| Anti-rotation / hip pin | A secondary 6.5 mm self-tapping pin placed parallel and superior to the lag screw to prevent rotation of the femoral head fragment |
| Distal locking bolts | One or two 4.9 mm screws placed transversely through the nail at the distal end; can be placed statically (rigid, length-stable) or dynamically (allows axial compression) |
| End cap | Plugs the distal tip of the nail; prevents bone ingrowth and aids future removal |
Key Design Features
- Anatomical nail geometry: 6° mediolateral (ML) angle allowing entry at or just lateral to the tip of the greater trochanter (piriformis entry or trochanteric entry, depending on version); also has a ~10° anteversion built into the proximal portion
- Antecurvature (1.5 m radius): Matches the natural anterior bow of the femur to reduce stress concentration and ease insertion
- Cannulated throughout: Allows guide-wire-assisted insertion under fluoroscopic control
- Flexible distal tip: Reduces stress-riser effect at the nail tip, lowering the risk of peri-implant fracture
- Two proximal screws (lag + anti-rotation pin): This is the hallmark feature distinguishing classic PFN from a Gamma nail (which uses only one lag screw). The dual-screw design provides rotational control of the femoral head fragment
Short vs. Long PFN
| Short PFN | Long PFN | |
|---|---|---|
| Length | ~200-240 mm (3 sizes: 340/380/420 mm for standard) | Up to femoral condyles |
| Use | Intertrochanteric fractures not extending >3 cm below trochanteric region | Subtrochanteric fractures, fractures with long distal extension, pathologic fractures |
| Locking | May leave unlocked in stable patterns | Distal locking mandatory |
For most trochanteric fractures, current evidence recommends a short cephalomedullary nail - results are equivalent to long nails for fractures not extending below 3 cm of the trochanteric region.
Biomechanical Rationale
The IM position of the nail places it much closer to the mechanical axis of the femur compared to a lateral plate, resulting in:
- Shorter bending moment arm
- Better load sharing
- Less risk of implant failure under cyclic loading
- Reduced femoral medialization and shaft collapse compared to the sliding hip screw in unstable (AO/OTA 31-A2 and A3) patterns
The dual-screw configuration (lag screw + anti-rotation pin) creates a more stable fixation of the femoral head fragment, preventing rotation (the "egg-cup" effect seen with single-screw systems in osteoporotic bone).
AP radiograph of a cephalomedullary nail (PFN type) in the right proximal femur, showing the intramedullary rod, the lag screw in the femoral head, and distal locking bolts - Rockwood and Green's Fractures in Adults, 10th ed. 2025
PFN vs. Related Implants
| Implant | Proximal fixation | Key difference |
|---|---|---|
| Classic PFN (AO/Synthes) | Lag screw + anti-rotation pin (2 screws) | Original design; dual screw construct |
| PFNA (PFN Antirotation) | Single helical blade | Blade compacts bone rather than removing it; better in osteoporotic bone; 1 proximal element |
| Gamma Nail | Single large lag screw | First widely used IM nail for this indication; higher complication rate with early designs |
| InterTAN | Two integrated cephalomedullary screws with linear compression | Interlocking proximal screws resist rotation; may offer lower cutout rate |
| DHS (sliding hip screw) | Single lag screw + lateral plate | Extramedullary; still acceptable for stable A1 fractures |
Clinical Status
Current guidelines (supported by large registry data) favour cephalomedullary nails (including PFN and its derivatives) over the sliding hip screw for unstable intertrochanteric fractures (AO/OTA 31-A2, A3) because they reduce reoperation rates and may slightly lower mortality. For stable A1 fractures, both the sliding hip screw and short IM nail remain acceptable options.
- Rockwood and Green's Fractures in Adults, 10th ed. 2025 - Cephalomedullary Implants section
- Campbell's Operative Orthopaedics, 15th ed. 2026 - Intertrochanteric Fractures chapter
- AO Foundation PFNA overview
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