In the field of veterinary orthopedics, selecting the right material for internal fixation is a balance between mechanical strength, biocompatibility, and long-term corrosion resistance. While 316L has long been the industry standard, Grade 317 is an increasingly utilized alloy in specialized applications.
Below is an objective analysis of how these two austenitic stainless steels compare.
Chemical Composition and Metallurgy
Both 316 and 317 belong to the 300-series of austenitic stainless steels. The defining difference lies in the concentration of alloying elements, specifically Molybdenum (Mo) and Chromium (Cr).
- 316L: Contains 2.0% – 3.0% Molybdenum.
- 317: Contains 3.0% – 4.0% Molybdenum and a higher percentage of Chromium.
The Role of Molybdenum: Molybdenum is added to enhance resistance to “pitting”—a localized form of corrosion that can occur in chloride-rich environments, such as the saline-heavy physiological environment of a canine or feline patient.
Corrosion Resistance (PREN Analysis)
The Pitting Resistance Equivalent Number (PREN) is a scientific measurement used to rank the corrosion resistance of stainless steels.
- Grade 316L typically yields a PREN of 23–26.
- Grade 317 typically yields a PREN of 28–33.
The higher PREN of Grade 317 indicates a more robust passive layer on the metal’s surface. In clinical terms, this provides an extra margin of safety against crevice corrosion, which can sometimes occur at the interface where a screw head meets the plate hole.
Mechanical Properties
There is a trade-off between corrosion resistance and workability:
- Strength: Grade 317 generally exhibits higher tensile and yield strength than 316. This provides excellent structural integrity for thin-profile implants, such as 1.5mm plates, which must endure repetitive stress during the early stages of bone healing.
- Ductility & Hardness: Grade 317 is a “tougher” material. While this makes it highly durable, it also means the material is slightly harder to contour (bend) compared to 316. For surgeons, this translates to an implant that feels more “rigid” and holds its shaped contour very effectively once placed.
Objective Comparison Table
| Feature | 316 Stainless Steel | 317 Stainless Steel |
| Pitting Resistance | Standard/Reliable | Enhanced (due to higher Mo) |
| Tensile Strength | Moderate | Higher |
| Malleability | High (Easier to bend) | Moderate (Higher spring-back) |
| Clinical Track Record | Decades of universal use | Growing use in specialized/high-load cases |
| Biocompatibility | Excellent | Excellent |
Why Use Grade 317 for Cuttable Plates?
Choosing Grade 317 for a 30-hole cuttable plate is a specific engineering decision. Because a cuttable plate is often used in small patients where the implant must be thin (1.5mm) to avoid soft-tissue tension, the material must compensate for its thinness with higher inherent strength.
Grade 317 provides that extra structural “backbone” and enhanced chemical stability, ensuring that even when the plate is cut and contoured, the material remains stable and resistant to the biological environment.
Conclusion
Neither material is “better” in a vacuum; rather, they serve different clinical needs. Grade 316 remains a versatile, easy-to-manipulate standard for general use. Grade 317 offers a more robust alternative for surgeons seeking higher corrosion resistance and increased material strength in demanding orthopedic applications.