TPLO Surgery Complications in Dogs: The Numbers Tell Different Stories
If you’ve looked up TPLO surgery complications in dogs, you may have found very different rates in different places—and wondered which one to believe. New research suggests those differences may have little to do with how the surgeries went. They may simply reflect how complications were counted.
A study published in Frontiers in Veterinary Science compared two grading systems used to classify complications after TPLO surgery in 79 dogs (85 procedures total). The result was striking: one system reported that 28.2% of cases had complications, while another reported 54.1%—even though they were evaluating the same surgeries.
TPLO stands for tibial plateau leveling osteotomy. It’s the most common surgery to repair a torn CCL (cranial cruciate ligament), the dog equivalent of the ACL in humans. It’s a significant procedure, so the complication numbers owners read online carry a lot of weight when they’re deciding whether to go ahead.
What a Grading System Actually Does
Not every complication after surgery is equally serious. A small bruise near the incision is very different from an infection that requires hospitalization. Grading systems are meant to sort complications by how serious they are, so researchers and surgeons can compare outcomes fairly across different clinics and studies.
This study compared two different grading tools:
- The adapted Clavien–Dindo system — originally designed for human surgery and adapted for veterinary use, this system categorizes complications based on the treatment required (for example, whether the dog needed extra medication, a second procedure, or intensive care).
- The Cook system — built specifically for veterinary surgery, this system uses its own set of categories and definitions.
Both tools were applied to the exact same 85 procedures. The Clavien–Dindo system labeled 28.2% of them as complications. The Cook system labeled 54.1% of them as complications.
That’s a gap of more than 25 percentage points—nearly double the rate.
What the Researchers Did
The team conducted a prospective study, meaning they followed patients forward in time as they recovered from TPLO surgery—rather than looking back at old records. They then applied both grading systems to each case and compared what each one found.
This kind of head-to-head comparison is useful because it removes variables. The same surgeries, the same dogs, the same recovery periods—just two different lenses for interpreting what happened.
Why the Same Surgeries Produced Such Different Numbers
The gap comes down to definitions. Each grading system draws the line in a different place when deciding what counts as a complication, and how serious it needs to be to qualify.
Think of it like two teachers grading the same exam with different rubrics. One marks off points for every small mistake; the other only notes major errors. The exam hasn’t changed—only the scoring guide has.
Under one system, a bit of mild swelling or minor discharge at the incision site might not register as a complication at all. Under another system, it might count as one. Neither system is necessarily wrong—they’re asking slightly different questions about the same data.
The research conclusion is clear: when you read a complication rate for TPLO surgery, that number is only meaningful if you know which grading system produced it.
How to Make Sense of the Numbers You Find Online
Different Sources May Not Be Measuring the Same Thing
When you come across a statistic like “TPLO surgery has a 30% complication rate” in one place and “50% complication rate” in another, those numbers may not be in conflict. They may simply be using different grading systems with different thresholds. A lower number might only count serious complications that required intervention. A higher number might include minor, short-lived events that resolved on their own.
Neither figure is automatically the one to worry about—but they’re not directly comparable.
Questions Worth Asking Your Veterinary Surgeon
Before or after your dog’s TPLO surgery, it’s worth having a direct conversation with your vet about what to expect. Some useful questions:
- What does your practice count as a complication? Does it include minor events that heal without treatment, or only ones that need active management?
- What are the most common things you see after TPLO at this clinic? Your surgeon’s real-world experience may be more relevant than a published average.
- What signs should I watch for at home, and when should I call? Practical guidance is more useful than any percentage.
When to Call Your Vet After TPLO Surgery
Reach out to your veterinary surgeon promptly if your dog shows any of the following:
- Increased swelling, warmth, or redness around the incision that gets worse instead of better
- Discharge that is cloudy, discolored, or has an odor
- Significant lameness that worsens after the first few days
- Refusal to bear any weight on the leg
- Signs of pain—such as whining, panting, or restlessness—that aren’t managed by the prescribed medication
- Fever, unusual tiredness, or loss of appetite
What the Study Doesn’t Answer
This research focused specifically on comparing grading systems—not on comparing surgical techniques or testing whether better complication classification leads to better care. The study used a specific patient group, so the findings may not apply to every TPLO case, clinic, or surgeon.
The researchers also did not determine which grading system is more clinically useful or better at predicting long-term outcomes. That’s an important open question. Broader research will be needed before veterinary medicine settles on a single standard for reporting TPLO outcomes.
The Bottom Line
When you read that TPLO surgery in dogs has a certain complication rate, the number you see is shaped heavily by how complications are defined. The same 85 procedures, reviewed with two different grading systems, produced rates of 28.2% and 54.1%—a difference that has nothing to do with how the surgeries actually went.
For pet owners, the most useful step isn’t memorizing a percentage. It’s asking your veterinary surgeon what they count as a complication, what they see most often, and what warning signs to watch for at home. That direct conversation will tell you far more than any statistic in a published study.
This article summarizes peer-reviewed research for educational purposes. Always consult with your veterinarian for personalized advice about your pet’s health and behavior.