Orthopedics 3D Printing: What a Launch Really Changes

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  Why orthopedics 3D printing took over the cage
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  Where orthopedics 3D printing stops working
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  How additive and CNC share a medical part
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  Titanium, PEEK, and the stiffness question
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  What ISO 13485 means on the shop floor
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  Additive or machined: pick by feature

A spinal interbody cage has one hard job: sit between two vertebral bodies, hold them apart, and let bone grow through it. For decades that meant a solid block of PEEK or titanium with a few windows cut into it. Bone could enter the windows, but it could not enter the material itself.

Additive manufacturing changed the geometry, not the biology. Laser powder bed fusion builds the cage layer by layer from Ti-6Al-4V powder, typically in 30–60 μm layers. Because the part grows rather than gets carved, the walls can be a lattice with 300–800 μm pores instead of a solid shell.

That pore size range is the whole point. Below roughly 100 μm, cells struggle to migrate and blood vessels cannot form. Above about 1,000 μm, the lattice loses stiffness and the cage can collapse under load. The 300–800 μm window is where bone ingrowth and mechanical strength overlap.

Porous titanium also drops the effective stiffness. Solid Ti-6Al-4V sits near 110 GPa, far above the 10–30 GPa of cortical bone. A 60–80% porous lattice brings the implant closer to bone, which reduces stress shielding and the bone resorption that follows it.

So the launch itself is not the news. The news is that a lattice cage passed the same fatigue and subsidence testing a solid cage passes, and that the process can repeat it at volume.

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  Layer thickness30–60 μm typical for LPBF titanium
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  Pore window300–800 μm for bone ingrowth
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  Stiffness targetMatch 10–30 GPa cortical bone

Additive is not free. A build chamber runs a full thermal cycle whether it holds one cage or two hundred, so the cost per part falls hard with quantity. For a five-piece prototype, that is fine. For a 50,000-piece run, the same geometry machined from bar stock is usually cheaper.

Surface finish is the second limit. As-built LPBF titanium lands around Ra 8–15 μm with loosely bonded particles on downfacing surfaces. Those particles must come off before the part touches tissue. Bead blasting, chemical etching, or machining of the bearing surfaces handles it, but each step adds handling and inspection.

Internal channels are where additive has no rival. A lattice, a gyroid, or a curved cooling passage simply cannot be cut with a rotating tool. If the design needs a feature that a tool cannot reach, additive is the only route. If it does not, you are paying a premium for nothing.

Dimensional accuracy is the third boundary. LPBF holds roughly ±0.1 mm on a well-supported part, and thin lattice struts can warp during cooling. Threads, taper locks, and mating bores usually get machined after printing to reach ±0.005 mm.

There is also a powder problem. Ti-6Al-4V powder is expensive, it degrades with reuse, and every build leaves unsintered material that must be sieved and requalified. That loop is why medical additive stays in controlled facilities rather than general job shops.

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  Low volume winsOne to a few hundred pieces per design
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  High volume losesMachined bar stock is cheaper at scale
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  Post-processing is mandatoryBlast, etch, or machine every load-bearing surface

Most production implants are not purely printed. They are printed, then finished on a mill or a lathe. The printed blank carries the lattice and the rough outer profile; the machined features carry the tolerances that matter to the surgeon.

A typical sequence starts with LPBF to near-net shape, leaving 0.3–0.5 mm of stock on the machined faces. The part then goes to a 5-axis center for the taper, the locking screw holes, and the endplate geometry. That step is where a screw hole gets its position and its depth.

On our floor, 16 simultaneous 5-axis machining centers handle that finishing work, with a Ø400 mm rotary table for parts that need access from several sides. Tolerance holds at ±0.005 mm on the machined features, and fine finishes reach Ra 0.2–0.8 μm where a bearing surface calls for it.

Machined titanium cages are still common, and they are not obsolete. A solid cage with machined windows is faster to make, easier to inspect, and cheaper at volume. For a straightforward fusion case with no need for a porous scaffold, it does the job.

The split is a design decision, not a fashion. Ask which features carry load, which features carry bone, and which features only need to be the right shape. Additive earns its place on the second group. Machining earns it on the first and third.

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  Print to near-netLeave 0.3–0.5 mm on machined faces
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  Finish on 5-axisTaper, screw holes, endplate geometry
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  Inspect 100%Reports on request before shipment

Titanium is the default for porous cages because it is biocompatible, strong, and printable. Ti-6Al-4V covers most spinal and trauma work. Commercially pure TA1 and TA2 show up where ductility matters more than strength.

PEEK solves the stiffness problem differently. Its modulus sits near 3–4 GPa, close to bone, so a solid PEEK cage causes little stress shielding. It is machined, not printed, and it shows up clearly on X-ray, which some surgeons prefer for follow-up.

The trade-off is bone attachment. PEEK is bioinert. Bone does not bond to it, so fixation depends on the geometry and on any coating applied to the surface. Titanium lattice invites bone in, which is why the two materials keep competing rather than one replacing the other.

Stainless grades 316L and 17-4PH appear in trauma plates and instruments, where cost and toughness beat weight. Cobalt chrome shows up in bearing couples. Each material changes the finishing route, and the finishing route changes the lead time.

Whichever alloy you pick, the material certificate and the heat lot follow the part. That traceability is not optional in a medical device, and it is a large part of why medical work costs more than general machining.

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  Ti-6Al-4VPrintable, load bearing, bone ingrowth
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  PEEKMachined, low modulus, bioinert
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  316L / 17-4PHTrauma plates and instruments

ISO 13485:2016 is the medical device quality standard. It is not a badge on a website. It changes how a shop runs: documented process validation, traceable material lots, controlled calibration, and a complaint file that stays open until the issue closes.

For a machined or printed component, that means the inspection record travels with the part. Raw material is checked on arrival. In-process dimensions are monitored at set intervals. Final inspection happens before shipment, and reports go out on request.

We hold ISO 9001:2015, IATF 16949:2016, ISO 13485:2016, and ISO 27001:2022. The last one matters more than people expect. Implant geometry and patient-specific scan data are sensitive, and ISO 27001 covers how that data is stored and who can open it.

Confidentiality is part of the same system. Uploads stay secure, and an NDA is available on request before any file changes hands. For a hospital or an OEM, that step usually comes before the first drawing is shared.

None of this makes a shop a device manufacturer. It makes the shop a supplier that a device manufacturer can audit without finding a hole in the paper trail.

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  Traceable lotsMaterial certificate follows every part
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  Calibrated inspectionGauges and CMMs on a schedule
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  Data controlISO 27001:2022 for scan and design files