3D Printed Titanium Cage: How Porous Implants Fix Infected Bone

• 1
  Why infected nonunion resists standard fixation
• 2
  How a porous titanium lattice carries load and grows bone
• 3
  What the engineer needs before modeling the cage
• 4
  When a 3D printed titanium cage is the wrong choice
• 5
  From CAD file to finished implant: the production chain
• 6
  Comparing fixation options for a segmental bone defect

A tibial shaft that fails to unite after infection is a geometry problem as much as a biology problem. The debridement that clears infection removes bone, leaving a gap that plates and nails cannot bridge without stress risers. The remaining bone is often sclerotic and poorly vascularized, so it heals slowly even when the fixation holds.

Standard hardware assumes a continuous cortex. When a segment is missing, a plate spans the gap and carries the entire load through screws at each end. Those screws concentrate stress in bone that is already compromised. Loosening follows, and the revision rate climbs.

An antibiotic spacer keeps the space open but does not restore load-bearing. The patient waits in a protected state while the defect stays unresolved. Something has to fill the void, share the load, and allow bone to grow back through it.

That is the niche a 3D printed titanium cage fills. It is not a replacement for every fixation. It is a targeted answer to a segmental defect where the bone cannot bridge itself.

• 1
  Segmental defectBone missing over a length, not just a crack
• 2
  Compromised boneSclerotic or avascular ends that heal slowly
• 3
  Load transfer neededThe implant must carry weight while bone regrows

Titanium alloy Ti-6Al-4V ELI has an elastic modulus around 110 GPa, far stiffer than cortical bone at 10–20 GPa. A solid implant shields the surrounding bone from stress, and the bone resorbs. A lattice changes that. By removing 60–80% of the volume as pores, the effective stiffness drops toward the bone range.

The pores do two jobs at once. They lower stiffness to reduce stress shielding, and they give bone cells a scaffold to colonize. Pore sizes between 300 and 800 μm support vascular ingrowth and bone deposition. Below 200 μm, tissue cannot penetrate reliably. Above 1,000 μm, the struts get thin and the structure weakens.

The lattice is not uniform. A typical cage uses graded porosity: denser at the load-bearing ends where screws and host bone meet, more open in the middle where bone needs to fill in. The gradient is built into the CAD model before printing, not added after.

Printing is usually laser powder bed fusion. A laser melts Ti-6Al-4V powder layer by layer, typically 30–60 μm per layer, in an inert argon atmosphere. The struts come out at 200–500 μm diameter. Post-processing includes stress relief, powder removal from internal channels, and sometimes hot isostatic pressing to close internal porosity.

• 1
  Graded porosityDense ends, open middle
• 2
  Layer thickness30–60 μm in laser powder bed fusion
• 3
  Strut diameter200–500 μm typical range

Start with a CT scan at 0.5 mm slice thickness or finer. The defect geometry drives everything. A thicker slice loses the cortical shell detail you need for a press-fit margin. The scan also reveals the quality of the remaining bone, which determines how much load the cage must carry versus how much the host bone can share.

The defect length sets the cage length. A 30 mm gap and a 60 mm gap are different design problems. Longer spans need more wall thickness or a central strut to resist bending. Shorter spans can use a thinner shell. The surgeon should confirm the planned resection margins before modeling starts, because a 5 mm change in length changes the whole frame.

Screw trajectories matter as much as the lattice. The cage must accept locking screws at angles that reach solid bone, not the infected zone. Plan those paths in the model. Off-the-shelf plates force the surgeon to adapt. A patient-specific cage adapts to the anatomy.

Material certification is not optional. Ti-6Al-4V ELI powder must meet ASTM F136 or an equivalent standard. Traceability from powder lot to finished implant is required for regulatory submission. If your supplier cannot show that chain, the implant cannot be used clinically.

• 1
  CT slice thickness0.5 mm or finer for margin detail
• 2
  Powder standardASTM F136 or equivalent
• 3
  Screw pathsPlanned to reach solid bone

A cage is not a first-line treatment for a fresh fracture. If the bone can heal with a plate or nail, use those. The cage adds cost, lead time, and a custom design cycle. It makes sense when the defect is segmental, the bone ends are compromised, and standard hardware has already failed or cannot bridge the gap.

Active infection changes the timeline. Printing a cage does not sterilize the field. The surgeon must confirm infection control before implantation, often with a staged procedure. A cage placed into an infected bed will not integrate. The lattice becomes a surface for biofilm, not bone.

Small defects under 10 mm rarely need a custom cage. A bone graft or a standard spacer handles those. The custom approach earns its cost when the geometry is complex, the load is high, or the anatomy does not match any catalog part.

Regulatory pathway matters. A patient-specific implant may fall under a different submission route than a mass-produced device. The engineer should confirm the intended pathway before finalizing the design, because it affects documentation, testing, and timeline.

• 1
  Fresh fractureUse standard fixation first
• 2
  Active infectionControl infection before implantation
• 3
  Defect under 10 mmGraft or spacer is usually enough

The workflow starts with the CT data converted to a solid model. The engineer designs the cage with the lattice, screw holes, and mating surfaces. The file goes to the printer as an STL or a sliced build file. Build orientation affects surface finish and support removal, so it is chosen with the post-processing steps in mind.

After printing, the part is stress-relieved to reduce residual stress from the melt cycle. Powder is removed from internal channels, often with compressed air and vibration. Some designs include escape holes sized for powder evacuation. If those holes are missing, trapped powder becomes a regulatory and biological problem.

Machining may follow for the mating surfaces. The bone contact faces often need a specific flatness or a locking thread. A 5-axis machining center can hold ±0.005 mm on those features. The lattice itself is left as-printed, because machining would close the pores.

Final steps include cleaning, passivation, and inspection. Dimensional checks cover the screw holes and the overall envelope. Porosity is verified by micro-CT or by sectioning a witness coupon from the same build. The implant is then packaged and sterilized.

• 1
  Build orientationChosen for support removal and finish
• 2
  Powder evacuationEscape holes prevent trapped powder
• 3
  Mating surfacesMachined to ±0.005 mm where needed