TPLO planning workflow

A typical TPLO planning session in Librevet. The app handles the technical work of accurate measurement and templating; clinical decisions remain yours.

Before you start

Have your pre-operative radiographs ready, with a calibration marker visible in each.
Decide on your target TPA based on your standard practice. This determines the rotation you’ll need to plan.

Workflow

1. Open the case and calibrate

Calibrate the radiograph you’ll be planning on. See Calibrating radiographs. Every measurement that follows depends on this.

2. Measure the tibial plateau angle

Switch to Measurement and use TPA mode. Place the two construction lines:

The mechanical axis of the tibia, from the inter-condylar eminence to the centre of the talus.
The tibial plateau line along the joint surface.

A click drops the construction at the point you clicked; drag each handle onto its landmark. The TPA reading appears in degrees. Use the magnification loupe (its button is in the top bar) for precise endpoint placement on bony landmarks.

On a mediolateral view that reaches the talus, pressing TPA places it for you: the app finds the four points and drops the TPA on them, selected and ready to adjust. Where there is a small corner of bone just above the cranial edge of the plateau, the cranial point goes on that corner. That view need not be the selected film — with the craniocaudal view selected, the TPA goes on the mediolateral view beside it, as long as only one film on screen is such a view. Drag any handle to adjust it, or undo to take it away. Where no film qualifies, or two do, click to place as above. The first time you press TPA, the app downloads the model that finds the points, about 44 MB, once. It runs on your computer, so the film never leaves it.

3. Plan the osteotomy

Switch to Osteotomy and choose TPLO. On a film with a TPA, pressing TPLO places the cut for you: centred on the TPA’s tibial axis, halfway between the intercondylar eminence and where the axis crosses the plateau line — with its two ends where the circle meets the back and the front of the tibia. It chooses the blade too: the one that leaves closest to 30% of the tuberosity in front of the cut, and never less than 25%, measured on the TT line the app finds on the film. That TT line comes with the cut, so TT thickness, D1 and D2 read straight away. Where it cannot find the line, the cut opens at your default blade. It is selected and ready to adjust, like the TPA; undo takes it away. On a side view of the knee with no TPA yet, it places the TPA it finds as well: the plan reads its angle, and D1 is drawn square to its axis. When the whole film is on screen, it also zooms in on the knee so the cut is big enough to work on.

Check both ends against the bone, the back one especially: the fibula lies just behind the tibia there. Drag the centre, either end or the blade size to change it. On a film that does not qualify, or a second cut on the same film, click to place the arc as before.

Cut and Rotate traces the fragment round the tibia itself, from one end of the cut to the other, fibular head included. If the outline is wrong somewhere, drag it there (step 5).

4. Choose the blade radius

The slider offers 8, 10, 12, 15, 18, 20, 21, 24, 27, 30 and 33 mm — the catalogue radii, with the small and large ends included for cats and giant breeds. Choose based on tibial diameter at your planned cut location and your standard practice. The saw arc updates as you change the radius. A cut the app placed opens at the blade that leaves closest to 30% of the TT line in front of it, never under 25% — or at your default blade when the app could not find the TT line. The TT line comes with it, so the TT thickness tile shows the share it leaves.

5. Plan the rotation

The Current TPA box under Plateau Levelling decides how the cut is made, and the button below it tells you which you are about to get:

Cut and Rotate — the box has an angle in it, either taken from the TPA you measured in step 2 or typed in yourself. The app makes the cut, traces the fragment round the tibia, and turns it from that angle to your target. Trace Fragment sits beside it if you would rather draw the outline yourself.
Trace Fragment — the box is empty. You draw the fragment’s outline round the bone yourself, starting at one end of the cut; it closes when you come back to the other end, or when you press Finish Trace. Then turn it with the rotation handle.

If the traced outline is wrong somewhere, drag it: with the cut selected, take hold of the dashed outline where it is wrong and drop it where the edge should be. The app traces again through that point and leaves the rest alone; one undo puts it back. Trace Fragment, beside Reset Auto, replaces it with one you draw, keeping the plan’s rotation.

So measuring the TPA first gives you the automatic version, and clearing that box gives you the hand-traced one. Either way the rotation handle stays available afterwards, and the Plateau Levelling heading shows how far the fragment has turned as you drag it. If the plan came from a TPA measured on this film, turning it off the plan also brings up a note saying where the plateau now sits.

If you haven’t measured the TPA on the film, the app has nothing to read the plateau’s slope from, so it assumes the film is laid out the way a TPLO is normally planned — cranial to the left, distal end down — and turns the fragment accordingly. Check the plateau afterwards.

6. Place the implant

From the Implants tab, search for the plate you intend to use. Click to arm, then click to commit on the post-rotation position you plan to fix. See Placing implant templates.

Sister-variant swap lets you compare hole counts and sizes without re-aiming the implant.

The case auto-saves. To share with a colleague or referring vet, see Sharing and referrals.

Things to verify before surgery

Calibration is correct (do the cortices look the right thickness?).
TPA reading aligns with your visual sense of the joint.
The fragment outline follows the tibia all round — drag it where it does not.
Blade radius is appropriate for tibial diameter at your cut location.
Implant size and screw positions are anatomically reasonable.

The app’s automation is intended to reduce time spent on measurement, not substitute for surgical judgement. Verify every step.

Auto-features and their limits

Auto-calibration — finds the marker. Verify the picked marker is correct, especially with stacked or chained markers.
Auto-side detection — reads the L/R marker. Confidence varies with marker quality.
The automatic fragment from Cut and Rotate — traced round the tibia from the cut’s two ends and the TPA’s plateau points, about 2 mm outside the bone. Check its outline against the bone and drag it where it is wrong. With no TPA on the film it is a standard shape built from the arc instead, not traced.
The TPA placed for you — its points are found by a model on your computer. Check every point against the film before you rely on the angle.
The TPLO cut placed for you — centred on the TPA’s axis just below the eminence, its blade chosen from the TT line a model finds, its ends read off the film. Check both ends against the cortices, and the TT line against the tuberosity.
The TT line drawn for you — found by a model, as the TPA is. Check both ends, the insertion above all, before you rely on the thickness.

All of the automatic steps above can be wrong, and numerical outputs are only as good as the inputs.