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Taking Great TPLO Radiographs

Taking Great TPLO Radiographs

TPLO

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Learn how to take great TPLO radiographs with proper positioning, imaging tips, & techniques. Watch videos to improve accuracy for better surgical planning

By 

Sustainable Vet Group

Updated on

August 13, 2026

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This article is for informational purposes only and is not a substitute for professional veterinary advice. Every case is unique, so always consult your veterinarian for guidance specific to your pet.

This content is intended for veterinary professionals for educational purposes. It does not replace clinical judgment or tailored advice. Always rely on your training, expertise, and the specific context of your patients.

Taking Great TPLO Radiographs

High-quality radiographs are the foundation of TPLO planning and post-operative assessment. The tibial plateau angle (TPA) measurement that determines plate size, osteotomy arc, and rotation amount depends entirely on image quality.

A poorly positioned radiograph produces inaccurate TPA measurements, which can lead to undercorrection, overcorrection, or incorrect implant selection.

Understanding what makes a TPLO radiograph diagnostically reliable is essential for any veterinary professional involved in TPLO cases.

 

Quick answer: A diagnostic TPLO lateral radiograph requires: stifle and hock at approximately 90 degrees; tibia and fibula superimposed throughout; femoral condyles superimposed; the entire tibia visible; and the beam centered over the stifle. Femoral condyle non-superimposition is the most common cause of TPA measurement error.

 

Key takeaways

  • Limb positioning is the single most important variable for TPA accuracy: limb positioning affects the appearance of anatomic landmarks used for TPA determination
  • The femoral condyles must be superimposed on the lateral view: MDPI research confirms 3 mm non-superimposition produces 90.6% of measurements within 1 degree of true TPA; error increases substantially beyond 3 mm
  • The stifle and hock should both be at approximately 90 degrees for the lateral view: this is required for accurate tibial plateau angle measurement
  • Sedation is recommended: a sedated dog allows accurate limb placement without motion artifact; an unsedated dog in pain cannot maintain the required positioning
  • The TPA averages 23 to 29 degrees in most dogs: some small breeds average higher; dogs with TPA over 30 degrees may be poor candidates for extracapsular repair or TTA
  • Post-operative TPA target is 5 to 6.5 degrees: achieving this angle eliminates cranial tibial thrust; post-operative radiographs confirm whether the target was achieved

Why radiograph quality matters for TPLO

TPLO planning is based entirely on the pre-operative lateral stifle radiograph. From this image, the surgeon:

  • Measures the TPA (tibial plateau angle)
  • Selects the appropriate osteotomy saw blade radius
  • Plans the rotation amount needed to achieve the target post-operative TPA (5 to 6.5 degrees)
  • Selects the implant size (plate and screw dimensions)

A 2-degree error in TPA measurement from a poorly positioned radiograph can result in a plate one size too small or large, or an osteotomy rotation that undercorrects or overcorrects the joint.

Today's Veterinary Practice confirms: a well-positioned lateral stifle radiograph is essential for accurate diagnostic interpretation and TPA measurement; correct tibial alignment is most important for TPA measurement.

The lateral (mediolateral) projection

This is the critical image for TPA measurement.

Patient positioning

Body position: the dog is placed in lateral recumbency with the limb of interest (affected stifle) closest to the table. The limb is extended slightly away from the body.

Stifle angle: the stifle is positioned at approximately 90 degrees of flexion.

Hock angle: the hock (tarsus) is positioned at approximately 90 degrees of flexion.

Cave Vet Specialists confirms: ensure the stifle and hock are collimated into the area of interest; keep the leg in a natural position; place an appropriate-sized plate under the limb.

Femoral condyles: both femoral hemicondyles should be precisely superimposed. This is the most technically demanding aspect of lateral stifle radiography. To achieve superimposition, the opposite limb is elevated with foam wedges or a triangular positioning aid to allow the limb of interest to lie flat and parallel to the table.

Cave Vet Specialists confirms: place the non-interest limb onto wedges to tilt the limb of interest centrally; place a triangular wedge or sandbag on the opposite side.

Tibia-fibula superimposition: the tibia and fibula should be superimposed throughout their full length. If the tibia and fibula are not superimposed, the tibia is rotated relative to the plate -- and this same rotation is captured in the TPA measurement.

What to include

The radiograph must include the entire tibia from the tibial plateau (top) to at least the distal metaphysis (ideally the entire bone).

Today's Veterinary Practice confirms: the x-ray beam should be centered over the stifle joint with collimation to include the entire tibia.

The most common positioning errors

Femoral condyle non-superimposition: the most frequent and most impactful error. Caused by the hindquarters tilting, the contralateral limb not elevated sufficiently, or the dog being unsedated and shifting position.

The MDPI Animals research quantified the impact: 3 mm of non-superimposition produces about 1 degree of TPA error; errors increase substantially beyond 3 mm.

Tibial rotation: the tibia is internally or externally rotated relative to the true mediolateral plane. This occurs when the hock is not held in a natural position. Rotation changes the apparent slope of the tibial plateau and produces a falsely high or low TPA.

Today's Veterinary Practice confirms: the tibia can easily be rotated with CCL injury even when the femur appears straight.

Incomplete tibia: if the distal tibia is cut off by collimation, the surgeon cannot assess the full tibial axis -- which is required for TPA measurement.

The caudocranial (CrCd or AP) projection

The caudocranial view assesses limb alignment, varus and valgus deformity, and tibial torsion. It is a standard part of the pre-operative TPLO radiograph set.

Patient positioning

The dog is placed in sternal recumbency or dorsal recumbency with the affected limb extended caudally (toward the x-ray plate). The stifle and hock should be visible.

Rita Leibinger confirms: the AP projection must have the stifle and tarsus included for the attending surgeon to assess limb alignment.

DVM360 confirms: on the caudocranial view, the medial margin of the tuber calcis should align with the center of the distal tibia, confirming the absence of tibial torsion.

Calibration for surgical planning

When radiographs will be used for surgical planning (plate size selection), a calibration marker must be placed at the same level as the stifle joint.

This allows the surgeon to scale the digital image to real-world measurements.

Rita Leibinger confirms: image calibration does not alter TPA measurement (the angle is size-independent), but it enables radiographs to be used for surgical plate-size planning.

Post-operative radiographs

After TPLO, radiographs are taken:

  • Immediately post-surgery: to confirm osteotomy position, plate position, screw placement, and achieved post-operative TPA
  • At 6 to 8 weeks: to assess early bone healing and callus formation
  • At 12 weeks: to confirm bone union before lifting activity restrictions

What a good post-operative radiograph shows

  • Post-operative TPA of approximately 5 to 6.5 degrees
  • No screws violating the joint space
  • Plate in correct medial position on the tibia
  • Osteotomy gap that is progressively narrowing on follow-up films (callus formation)

Warning signs on post-operative radiographs

  • Screw tip in the joint space (requires removal of that screw)
  • Plate migration from original position
  • Peri-implant radiolucent halos (suggests implant loosening or infection)
  • Osteotomy gap not narrowing by 8 weeks (suggests delayed union or infection)

For the TPA measurement guide, see what causes TPLO surgery in dogs. For post-operative complications, see 15 common complications after TPLO surgery.

For the plate infection guide, see TPLO plate infection signs and treatment. For bone healing information, see TPLO bone healing time in dogs.

Frequently asked questions

Does the dog need to be sedated for TPLO radiographs?

Sedation is strongly recommended and preferred. An unsedated dog -- particularly one in pain from CCL disease -- cannot maintain the precise positioning required for accurate TPA measurement.

Even minor position changes between preparation and exposure produce significant error. Sedation allows the technician to position the limb correctly and hold it in place without the dog shifting.

Why does the hock position matter for the lateral view?

The hock angle affects the position of the tibia relative to the table and the imaging plate.

When the hock deviates from approximately 90 degrees, the tibia is either elevated or depressed at the distal end, which changes the apparent angle of the tibial plateau.

This error is captured in the TPA measurement.

What is a normal TPA range and when should TPLO be recommended?

Today's Veterinary Practice confirms the average TPA in most dogs is 23 to 29 degrees. Some small breeds have higher averages.

Dogs with TPA greater than 30 degrees may be poor candidates for extracapsular repair or TTA.

TPLO is appropriate for dogs of all TPA values -- the procedure specifically corrects whatever TPA angle the dog presents with.

Can the same radiograph be used for both diagnosis and surgical planning?

Yes, if it is of adequate quality and includes a calibration marker.

Diagnostic-only radiographs taken without a calibration marker can confirm CCL disease and measure TPA, but cannot be used for plate-size surgical planning.

Including a calibration marker at the time of acquisition allows a single radiograph to serve both purposes.

What happens if the TPA is measured incorrectly pre-operatively?

If the pre-operative TPA is underestimated, the surgeon may under-rotate the osteotomy and fail to reach the target 5 to 6.5 degree post-operative TPA.

This results in residual cranial tibial thrust and potentially ongoing instability. If overestimated, overcorrection is possible.

This underscores why positioning accuracy at the time of radiography is critical -- errors propagate through the entire surgical plan.

Resources

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Taking Great TPLO Radiographs

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Let's take your infection control to the next level

Watch these videos!

Step #1

Getting Ready

Ensuring a clean surgical field starts with proper skin preparation. This video demonstrates the best practices for:

  • Shaving the patient – Achieving a close, even shave while minimizing skin irritation
  • The Dirty Scrub – The initial skin prep step to remove surface debris and reduce bacterial load before the sterile scrub.

Following these techniques helps reduce infection risk and improve surgical outcomes. Watch the video to see how it’s done effectively!

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Many surgeons are shocked to find out that their patients are not protected from biofilms and resistant bacteria when they use saline and post-op antibiotics.

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Why leave these risks and unmanaged?  Just apply Simini Protect Lavage for one minute. Biofilms and resistant bacteria can be removed, and you can reduce two significant sources of infection.

Step #3

Take the Course

Preventing surgical infections is critical for patient safety and successful outcomes. This course covers:

  • Aseptic techniques – Best practices to maintain a sterile field.
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  • ​Antibiotic stewardship – When and how to use perioperative antibiotics effectively.

Stay up to date with the latest evidence-based protocols. Click the link to start learning and earn CE credits!

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