Overview
ISO 9585:1990 specifies a mechanical test method to determine the bending strength and bending stiffness of straight bone plates used as surgical implants. The standard describes a four-point bend test configuration with cylindrical rollers and procedures for placement, loading, measurement and reporting. It applies to straight plates and plates with a small initial curvature; it is not recommended for plates shorter than 50 mm or plates that form part of intramedullary devices.
Key Topics
- Test arrangement: Four-point bending rig with inner and outer roller supports. Axes of the four rollers remain parallel and rollers are constrained to prevent longitudinal movement.
- Roller dimensions: Cylindrical rollers of equal diameter are specified; mean diameters in the document fall in the 8 mm to 13 mm range (or profiled rollers suited to plate cross-section).
- Specimen placement: Plates are oriented with the surface intended for bone contact facing the inner rollers; alignment and screw‑hole placement are addressed to ensure representative loading and fracture location.
- Deflection measurement: Deflections are measured relative to the outer support and recorded as a load–deflection curve. The initial linear slope S of this curve is used in stiffness calculations.
- Calculations: The standard provides methods to compute an equivalent bending stiffness from geometry (inner/outer roller spacing) and the slope S of the linear portion of the load–deflection curve. It also defines the proof point (offset method) and gives expressions to calculate bending strength from the proof load or, if fracture precedes the proof point, from the maximum load.
- Test report requirements: Reports must include bending strength, offset used for the proof point, equivalent bending stiffness, fracture occurrence before proof deflection (if applicable), and full plate identification (type, length, catalogue and batch numbers).
Applications
ISO 9585:1990 serves practical needs in product development, regulatory support and quality control for surgical bone plates:
- Design validation and comparative assessment of plate geometry and materials.
- Preclinical mechanical evaluation to demonstrate mechanical performance and safety margins.
- Incoming inspection and production quality assurance where bending resistance and stiffness are critical.
- Supporting regulatory submissions and technical files with standardized test data.
The method helps engineers, R&D teams, testing laboratories and regulatory specialists evaluate how plates will behave under bending loads and supports decisions on material selection, thickness and hole layouts.
Related Standards
- Standards and guidance from ISO/TC 150 (Implants for surgery) are relevant for implant specific requirements.
- Medical device quality and management standards (for example ISO 13485) inform the overall quality system that governs testing and traceability.
- Relevant national or ASTM test methods for orthopedic implants may be consulted for complementary procedures or materials testing.
This standard focuses on practical, repeatable procedures and reporting to produce comparable bending performance data for surgical bone plates, aiding safe implant design and quality control.
Open preview (PDF)Implants for surgery — Determination of bending strength and stiffness of bone plates
