3D Printed Osteotomy Plate and Custom Prosthesis for Reverse Shoulder Replacement

A reverse shoulder replacement flips the joint: the ball sits on the glenoid side and the cup on the humeral side. When a tumor or severe bone loss is involved, the surgeon also has to remove part of the scapula. That is where a patient-specific plate and prosthesis come in. The plate carries the osteotomy line and positions the glenoid component; the prosthesis fills the resected bone.

Both parts are derived from the patient's CT scan. A 3D printed osteotomy plate reproduces the planned cut plane on the bench, so the surgeon is not freehanding a curve through diseased bone. The custom prosthesis then matches the defect left behind. Get the fit wrong by a millimeter and the glenoid component sits at the wrong version angle.

Three inputs drive the whole design: bone stock quality, the resection margin the oncology team needs, and the fixation points that remain after resection. None of these are negotiable for the sake of a simpler part. They decide whether you can use a plate alone, a plate plus a graft, or a full hemi-scapular prosthesis.

Printing wins when the geometry is organic. A plate that wraps a scapular spine or bridges a curved defect has no flat fixturing surface. Add lattice or porous regions for bone ingrowth and machining becomes slow and wasteful. Titanium powder bed fusion (Ti-6Al-4V) builds those features in one piece, and the patient-matched contour comes straight from the model.

CNC wins on the mating surfaces. Screw holes, the glenoid taper, and any press-fit interface need a true position and a surface finish that as-built printing rarely holds. We machine printed near-net parts on our 5-axis centers to bring hole location, taper angle, and bearing surfaces into tolerance, then verify them on the CMM.

The practical route for most patient-specific shoulder parts is hybrid: print the body, machine the critical interfaces. A simple plate with flat faces and a short screw pattern is often faster and cheaper as a fully machined part. Reserve printing for the anatomy that cannot be reached with a cutter.

We run 16 simultaneous 5-axis machining centers and hold ±0.005 mm on printed-then-machined features, with finishes down to Ra 0.2–0.8 μm where a bearing surface calls for it. That combination is what makes a hybrid route workable instead of a compromise.

Ti-6Al-4V (TC4) is the default for both the plate and the prosthesis body. It has the fatigue strength a scapular implant needs and a well-documented record in orthopedic devices. Commercially pure titanium (TA1, TA2) is softer and easier to form, so it suits a thin guide plate that only carries a saw slot.

Stainless steel 316L works for instrumentation: cutting guides, trial components, and drill sleeves that never stay in the patient. It machines cleanly, takes a passivation finish, and costs less than titanium. Do not put a load-bearing 316L part into a permanent shoulder implant.

PEEK and carbon-fiber reinforced PEEK appear in custom prosthesis designs where imaging artifact matters. A radiolucent body lets the surgeon see bone healing around the implant on follow-up CT. The trade-off is lower stiffness and a weaker screw interface, so the fixation design has to change to match.

Every lot starts with a raw material certificate. We check chemistry and grain before a single cut, because a patient-specific part has no second chance at the material level.

Not every surface on a 3D printed osteotomy plate needs the same callout. The saw slot and the screw holes set the resection plane and the fixation position, so they carry the tight tolerance. The outer contour that only touches soft tissue can run looser. Splitting the callouts this way keeps the part manufacturable.

We hold ±0.005 mm on critical features and inspect 100% of parts before shipment. The route is raw material check, in-process monitoring, then final inspection on the CMM. Reports come on request, and a first-article report is standard for any new patient-specific design.

Sterilization matters too. Steam autoclave cycles and gamma doses can move a thin printed lattice or relax a machined taper. We review the sterilization route with the design team before finalizing wall thickness, because a part that fits on the bench but shifts after autoclaving is a failed part.