3D Printed Porous Vertebral Body Cage for Anterior Cervical Corpectomy

In an anterior cervical corpectomy, the surgeon removes a vertebral body and the discs on either side, then rebuilds that column. The implant has to hold the load, sit in a defined position and give bone a route to grow through and around it. A 3D printed porous vertebral body cage does all three in one part, which is why the design keeps moving from solid machined blocks toward lattice structures.

The porous region is not decoration. Pore size, strut thickness and pore interconnectivity set how fast bone can bridge the cage. Open cells around 400–800 μm are common in published orthopedic work, with struts thick enough to survive handling and insertion. The solid endplates and the screw or plate interface stay dense so they can be machined, tapped or clamped without crushing.

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  Load pathSolid rims carry the column load; the lattice only carries what the surgeon leaves it.
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  Pore sizeSmall pores slow bone ingrowth, large pores cut strut strength.
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  InterconnectivityClosed cells block vascular flow and defeat the purpose.

Start with the anatomy, not the lattice. Get the footprint from the CT or MRI data, then set the sagittal profile and the height in 1 mm steps. Only after the outer envelope is fixed does the porous zone get defined. If the lattice drives the envelope, the cage will not seat properly and the surgeon will have to remove more bone.

For laser powder bed fusion on Ti-6Al-4V, struts below roughly 200 μm are hard to keep clean and tend to warp. A 250–400 μm strut gives a better build window on most machines. Pores should be open and connected in all three axes. Overhang angles under 45° need support, and support scars on a lattice cannot be sanded away later.

Keep a dense band where the screws or the plate meet the cage. Threads and locking features do not belong in porous material. A tapped hole in a lattice will strip. Machine the thread into solid metal, or bond a solid insert after printing.

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  Wall thicknessKeep outer walls at 0.8 mm or more where the cage is handled.
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  DatumAdd a machinable boss or flat as a print datum and a post-print reference.
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  ClearanceLeave 0.2–0.3 mm for post-print finishing on any mating face.
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  MarkingLaser mark size and lot; keep character height at 1.5 mm or above.

A printed cage comes off the machine attached to a build plate and covered in loose powder. Cut it off with a wire EDM or a saw, then stress relieve before any finish machining. Ti-6Al-4V holds residual stress from the melt, and a cage that is machined first can move during the final cut. A vacuum or inert stress relief at the material supplier's recommended cycle is the safe route.

Powder removal is the step that decides whether the porous region is actually porous. Use ultrasonic cleaning in a compatible bath, then verify by weight or by flow. Trapped powder adds mass and can come loose in the body. Keep the cleaning record with the lot.

The dense faces then go to the mill. Flat the endplates, cut the screw holes and tap the locking features. For a Ti-6Al-4V cage, use sharp carbide or PVD-coated tooling, low cutting speed and plenty of coolant. Titanium moves under heat. Take light passes and check flatness between them.

Finish with bead blasting on the solid surfaces only, then passivate. Do not blast the lattice; media lodges in the pores. Laser mark the lot on a solid face at 1.5 mm minimum character height so it stays readable after cleaning.

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  Cut-offWire EDM leaves a cleaner edge on a lattice than a band saw.
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  Stress reliefDo it before the finish cuts, not after.
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  Powder checkWeigh the part against the CAD mass and flag any gain.
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  PassivationFollow ASTM F86 for titanium surgical implants.

Dimensional checks on a cage go beyond a caliper. Use a CMM for the solid envelope, the screw hole pattern and the endplate flatness. For the lattice, optical or CT inspection shows strut breaks and blocked pores that touch probes cannot reach. If a build has a strut break in the load-bearing rim, scrap the part. A lattice defect inside the porous zone is a judgement call between the design owner and the surgeon, not the machine shop.

Every lot should carry a material certificate for the Ti-6Al-4V powder or bar, a build record, a cleaning record and a final inspection report. We run 100% inspection before shipment and hold raw material, in-process and final checks. Reports go out on request. Our quality system is certified to ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022, so the documentation trail matches what a medical device file needs.

Keep the print and the machining under one lot number. If the cage is printed at one supplier and finished at another, the traceability chain breaks at the exact point where the implant touches the patient.