Medical Titanium Rod Description

The difference between a spinal rod that lasts 20 years and one that fails in 10 comes down to fatigue life. And in Ti-6Al-4V, fatigue life is controlled by oxygen content. That's why Grade 23 ELI exists.

Medical Titanium Rod ASTM F136 Gr5 ELI is Ti-6Al-4V with oxygen capped at 0.13% - not 0.20% like commercial Grade 5. Iron is also tighter: 0.25% max versus 0.30%. That small delta shifts fatigue strength up by 10–15% and raises fracture toughness from about 55–60 MPa√m to 75–80 MPa√m.

Commercial Grade 5 works for aircraft. ELI works for people. Regulators know the difference, and so do the implant systems that carry FDA product codes KWQ, KWP, and NKB.

Material Specifications

Property	Grade 23 ELI (ASTM F136)
Tensile (min)	860 MPa
Yield (min)	795 MPa
Elongation	≥10%
Reduction of area	≥25%
Density	4.43 g/cm³
Modulus	110 GPa

Chemical Composition (ASTM F136, max limits)

Element	Max %
Oxygen	0.13
Iron	0.25
Carbon	0.08
Nitrogen	0.05
Hydrogen	0.012
Aluminum	5.5 – 6.5
Vanadium	3.5 – 4.5

Grade 23 ELI is a damage-tolerant alloy. The lower interstitial content - oxygen, nitrogen, hydrogen - reduces the number of sites where fatigue cracks can start. ASTM F136 caps oxygen at 0.13%, compared to 0.20% for Grade 5 commercial. That extra purity translates to fatigue life roughly 10–15% longer than commercial Grade 5, fracture toughness suitable for extreme loads and cyclic use, and certification under ISO 10993 for implantable medical devices.

Grade 23 also performs at cryogenic temperatures down to -196°C, though that's more relevant to aerospace than orthopedics. The point is: this material is built for demanding environments.

FDA GUDID records confirm that Ti-6Al-4V ELI per ASTM F136 is the standard material for major spinal fixation systems. The Wiltrom Spinal Fixation System uses rods of 5.5mm diameter with tapered tips, manufactured from Ti-6Al-4V ELI complying with ISO 5832-3 and ASTM F136. These rods are indicated for degenerative disc disease and are cleared under product code NKB.

The Excella system also uses Ti-6Al-4V ELI rods under product codes KWQ, KWP, MNI, and NKB. The same material goes into bone-screw internal spinal fixation rods used for stabilization and fusion. When you spec Medical Titanium Rod ASTM F136 Gr5 ELI, you're buying material that already sits behind these cleared devices.

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Mechanical Properties (Annealed)

Property	Grade 23 ELI	Commercial Grade 5
Yield strength (0.2%)	795–860 MPa	830–880 MPa
Tensile strength	860–930 MPa	900–950 MPa
Elongation	10–15%	10–14%
Modulus	110 GPa	110 GPa
Fatigue life	10–15% higher	Baseline
Biocompatibility	ISO 10993 certified	General

Fatigue Strength

Fatigue strength at 10⁷ cycles for ELI is typically higher than commercial Grade 5. Data from additive manufacturing ELI shows fatigue strength exceeding 600 MPa at 10⁷ cycles after hot isostatic pressing. That's the material's capacity under cyclic load - the same load pattern a spinal rod or hip stem experiences in vivo.

Implant-grade bar uses minus-tolerance fits: the bar is never larger than nominal, only equal to or smaller within the stated micron band.

Nominal diameter	h6 tolerance	h7 tolerance	h8 tolerance
10 mm	0 / −9 µm	0 / −15 µm	0 / −22 µm
20 mm	0 / −13 µm	0 / −21 µm	0 / −33 µm
30 mm	0 / −13 µm	0 / −21 µm	0 / −33 µm

Values per ISO 286-2. OEMs drawing bar through carbide dies often require h6; high-speed Swiss turning may accept h7; multi-spindle setups sometimes use h8, but holding pressure becomes less uniform. Straightness for implant-grade stock is typically 0.2mm per 1000mm, tighter than commercial bar at 0.5mm per 1000mm.

Surface Finish	Ra	Use Case
Turned	≤1.6μm	Roughing stock
Ground	≤0.4μm	Screw blanks, Swiss machining
Polished	≤0.2μm	Tissue contact, finished implants

Medical-grade TC4 has stricter impurity controls than industrial-grade: O ≤0.13%, C ≤0.08%, H ≤0.012%, Fe ≤0.25%. These ensure mechanical properties suited to human load environments. Surface quality in turning depends on cutting parameters, and research on medical-grade TC4 has established relationships between cutting conditions and surface roughness, providing reference for improving manufacturing quality.

FDA Product Codes - What They Mean

KWQ - Appliance, Fixation, Spinal Intervertebral Body

KWP - Appliance, Fixation, Spinal Interlaminal

NKB - Orthosis, Spinal Pedicle Fixation, For Degenerative Disc Disease

All three accept Ti-6Al-4V ELI per ASTM F136 as standard material. If a spinal system has a 510(k) clearance with these codes, the rods are almost certainly ELI.

FAQ

Q: Can I substitute commercial Grade 5 for ELI if I run my own tests?
A: Commercial Grade 5 has higher oxygen and iron. Your tests will show differences - not a match. ELI has 10–15% better fatigue life.

Q: What diameter for a spinal rod?
A: Wiltrom uses 5.5mm with tapered tips. Most posterior fixation systems use 5.0mm to 6.5mm.

Q: What surface finish for screw blanks?
A: Ground at Ra ≤0.4μm. Feeds better through Swiss machines. Turned is for roughing only.

Q: What paperwork comes with the rod?
A: Heat number, Mill Test Report, ASTM F136 certificate, chemical and mechanical data. EN 10204 3.1 standard; 3.2 with third-party witness available.

Q: Lead time?
A: Stock sizes 7-10 days. Non-stock 3-5 weeks. Volume orders longer.

Q: Sample rod?
A: Yes. 300mm sample. Pay shipping. Material free. Credit back on first production order over $10,000.

Commercial Grade 5 is for aircraft. ELI is for implants. ASTM F136 makes it official. Medical Titanium Rod ASTM F136 Gr5 ELI is what you spec when fatigue life matters. Spinal rods. Hip stems. Trauma screws. The material behind devices that stay in the body for decades.