The main principle of the Proximal Femoral Nail (PFN) fixation device is its design as a load-sharing system.
Understanding the Core Principle
Based on the provided reference, the fundamental principle behind PFN fixation is:
- It utilizes a sliding screw placed in the femoral neck and head fragment.
- This sliding screw is attached to an intramedullary nail inserted into the femur.
Load Sharing vs. Load Bearing
A key aspect of the PFN's principle, as highlighted in the reference, is its function as a load-sharing device.
- Load Sharing: The implant shares the weight-bearing load with the surrounding bone. This allows for some controlled movement at the fracture site, which can promote healing (secondary bone healing).
- Load Bearing: In contrast, devices like the Dynamic Hip Screw (DHS) are considered load-bearing. They primarily bear the weight themselves, shielding the fracture site more completely.
Comparison Table:
| Feature | PFN (Proximal Femoral Nail) | DHS (Dynamic Hip Screw) |
|---|---|---|
| Primary Role | Load Sharing | Load Bearing |
| Mechanism | Sliding screw attached to intramedullary nail | Sliding screw attached to plate on bone surface |
| Biomechanics | Biomechanically stronger (intramedullary) | Less strong biomechanically than PFN |
| Fracture Type | Often used for trochanteric fractures, subtrochanteric fractures | Often used for intertrochanteric fractures |
Biomechanical Advantage
The reference notes that because PFN is an intramedullary fixation device (placed inside the bone marrow cavity), it is considered a biomechanically stronger implant compared to extramedullary devices like the DHS plate. This internal placement provides better support and leverage.
In essence, the sliding mechanism allows controlled collapse and impaction at the fracture site under weight-bearing, while the intramedullary nail and screw system distribute the load across the bone, encouraging stability and healing.
