How Surgical Planning Works: From CT Scan to the OR

Ask most patients what “surgical planning” means, and you’ll get a shrug. Ask most surgeons, and they’ll describe the PDF and the VR headset they get before a case. Almost no one, patient or surgeon, sees what happens in between.

That gap is the entire reason this post exists. We sat down with Lauren Crockett, Kinomatic’s Production Manager for Surgical Planning, to walk through exactly what her team does between the moment a CT scan arrives and the moment a surgeon opens a finished plan.

What is surgical planning, exactly?

Surgical planning is the process of building a custom, 3D digital model of a patient’s anatomy that helps a surgeon prepare for implant placement before surgery begins.

In practice, that means turning a single imaging scan into a fully personalized blueprint tailored to a specific patient’s bones, a specific surgeon’s preferences, and the specific implant they’ve chosen, before anyone ever sets foot in the OR.

From CT scan to surgeon-ready plan

Every plan starts the same way and follows the same disciplined path:

1. CT scan. We capture a bilateral CT scan of the patient’s lower anatomy, both the operative and non-operative side, lower back to ankle.
2. CT approval. Before anything else happens, the scan is checked against strict quality specs. If it doesn’t meet the bar for building an accurate 3D model, it doesn’t move forward.
3. Segmentation. A CT scan is hundreds of x-ray slices stacked together. Our team, with an AI-driven first pass then a human review, goes slice by slice and “paints” each bone, building a 3D model accurate to the patient as they were actually scanned.
4. Landmarking and measurement. Biomedical engineers place anatomical landmarks on the model and take a defined set of measurements, establishing a precise preoperative reference for that patient’s anatomy.
5. Implant placement. For a primary hip or knee replacement, the surgeon’s chosen implant is placed on the patient’s model, weighing their preferences alongside the anatomy in front of us. The team works within the implant system that surgeon uses, finding the size and position that fit the patient best.
6. Final review and flagging. The team steps back and asks what the surgeon needs to know: irregular anatomy, existing hardware, anything that deserves a second look before surgery.
7. Delivery. The finished plan goes to the surgeon in VR, where they can review it in 3D before surgery. In addition, a patient-specific model is sent to the patient so they can review their custom plan, too.

How long does it take to produce a surgical plan?

A typical knee or hip plan takes between 1.5 to 2.5+ hours. What drives the difference, and the variability within each, depends on how irregular the patient’s anatomy is and how many surgeon-specific requirements the plan needs to accommodate.

Quality checks at every handoff, not just at the end

One thing that stood out in our conversation: quality isn’t a single checkpoint at the end. It’s built into every stage.

• The CT scan is checked before segmentation ever begins.
• AI-assisted segmentation is reviewed, slice by slice, by a person.
• Auto-placed landmarks are validated by a biomedical engineer before any measurement is generated from them.
• Before a plan ever reaches a surgeon, we conduct a peer review with a second engineer, a neutral party who didn’t complete the plan. They review it against the surgeon’s preferences and confirm every flag and note is in place.
• The surgeon then has final say, with the ability to request adjustments before approving.

“It’s an internal review at every step,” is how Lauren described it, deliberately redundant, so nothing reaches a surgeon without proper quality and validation in place.

Why do 3D and bilateral scans change everything?

Today’s standard approach to joint replacement is 2D templating off a diagnostic x-ray. It works, but it’s inherently limited: a 2D image can’t accurately capture angular measurements like femoral anteversion, femoral rotation, or tibial slope, details that matter once a surgeon is actually placing an implant. In studies that compare the two, 3D CT-based planning has predicted implant size far more accurately than 2D templating.^[1]

Kinomatic’s process is built around two things standard x-rays can’t offer:

Three-dimensional imaging. A 3D model surfaces information a flat x-ray simply can’t, the true shape and orientation of a patient’s bones, not just an outline.

Bilateral scanning. Because we scan both the operative and non-operative side, the team can compare the two. If the non-operative side has existing hardware, the surgeon sees it. If the operative joint is significantly more worn or diseased, the healthier side gives a reference for what “normal” looked like for that specific patient before disease progressed.

One recent example: a knee replacement case where wear on the operative-side tibia had distorted the natural tibial varus angle. By referencing the patient’s own healthier, non-operative knee, the team planned the tibial component to match what that angle would have naturally been, rather than replicating a worn, diseased shape.

Bilateral scanning also enables something patients ask about directly: leg length discrepancy, which affects an estimated 3% to 30% of hip replacement patients.^[2] Because both sides are measured, at the pelvic level and the full-leg level, surgeons get real data to work from when deciding how to balance leg length against joint stability and implant fit, instead of estimating.

What’s the hardest part that nobody sees?

Ask Lauren what’s most technically demanding about her team’s work, and it isn’t the imaging or the software, it’s the balancing act. Each plan accounts for roughly 15 distinct surgeon preferences at once, and adjusting one variable frequently shifts several others. Getting all 15 to align for one patient’s specific anatomy takes real iteration, not a single pass.

The other underrated part: stepping back before delivery to look at the plan as a whole, not just piece by piece, making sure everything that should be flagged for the surgeon actually is, and that the plan reflects the full clinical picture, not just a set of measurements in isolation.

What this means once the surgeon is in the OR

A common misconception is that a surgeon executes a plan exactly as it’s built. In reality, the plan is created in an ideal, unconstrained environment: full visibility, unlimited time, every measurement available. The OR is different by design. Incisions are kept intentionally small to support minimally invasive surgery and faster recovery, which naturally limits a surgeon’s direct view and the precision of the instruments they’re working with.

Lauren’s way of putting it: think of the plan like a GPS. It maps the ideal route through a patient’s anatomy, but the surgeon is still the one navigating the terrain in front of them in real time. The plan is a highly informed guide and reference point that hands the surgeon as much certainty as possible walking into an environment that will always require some in-the-moment judgment.

What this means for the patient

For patients, the value shows up as confidence. Knowing that a surgeon has reviewed a complete, personalized model of their own anatomy, not a generic template, before ever making an incision offers real peace of mind. It also opens the door to something patients don’t always expect: the chance to review their own game plan with their surgeon beforehand, and go into surgery as an informed partner in the decision rather than a passenger.

That collaboration, more than any single measurement or technology, is what custom planning is ultimately in service of: fewer surprises, more preparation, and a surgical team that walked in already knowing what they were working with.

See surgical planning in action

Want to see the process for yourself? Watch how a plan comes together, from CT scan to finished 3D model:

Learn more about how Kinomatic’s planning works, or find a Kinomatic surgeon near you.

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