Volumetric Depression Can Predict Risk of Subsidence in Patients with Tibial Plateau Fractures

An ePoster presented at the AAOS 2024 Annual Meeting by Abhishek Ganta, MD, assistant professor of orthopaedic surgery at NYU Langone Health and director of foot and ankle surgery and codirector of orthopaedic trauma at Jamaica Hospital Medical Center in Queens, New York, found that current measurements of tibial plateau fractures often underestimate trauma severity. His study used a database to measure volumetric depression, finding that larger preoperative subsidence increases the risk of postoperative subsidence. AAOS Now Editorial Board member Stuart A. Green, MD, FAAOS, sat down with Dr. Ganta to discuss the results of his study and their potential impact on clinical practice.

Dr. Green: What stimulated your research assessing tibial plateau depression?
Dr. Ganta: When we measure depression on tibial plateaus, it’s on a plane film or a single cut on the CT scan. I think that these measurements underestimate the severity of trauma. I thought, “How can we really quantify exactly how much bone volume is actually being depressed from these injuries?”

How did you quantify subsidence volume?
I figured that measuring volume is a more accurate predictor of exactly what’s going on. We took a negative space on a single cut and measured by the thickness of the slice, which gives you a volume measurement, and repeated it on every other cut. We were able to determine how much negative space there is, [representing] the amount of volume loss.

[Our study found that] patients with a very large amount of subsidence or volumetric depression will have a risk of postoperative subsidence. Now, whether or not that makes a clinical difference is to be told.

Would you use that information to determine how much bone graft you need to fill the space?
We’re basically estimating the amount of volume that we’re going to put in. But sometimes that volume is not enough.

Can the data you’ve generated help figure out whether you need to put some supplementary struts or a screw to hold up the plateau, in addition to the bone graft?
Yes, absolutely. I’ve adjusted my techniques; sometimes I’ll put in a large cortical allograft. And I’ll put in filler, like a tricalcium phosphate around it, just to give it more support.

At what level of volumetric loss do you see an increased risk of subsidence?
2,000 cubic millimeters

After that volume, do you have to insert some additional supplementation?
Yes, exactly. So basically, that was a cut-off; anything after this point is a risk of subsidence. Now, calculating subsidence postoperatively can be a little bit challenging, too.

So now, we get routine CTs on these patients 6 months to a year or so after the injury. But we know that there are certain patients in which the subsiding is so severe that they’ll get a valgus thrust or some sort of balance deformity that’s going to need an arthroplasty in the future.

Under the circumstances, has it changed your practice significantly, besides the fact that you might use a tricortical graft to support the plateau? When a patient shows up in the emergency room and you get a CT scan, do you do the volumetric analysis and say, “Based on this 2,000 cubic millimeters, I’m going to do this instead of that”?
Nowadays, the protocol is that we treat tibial plateau fractures, especially Schatzker II, in such a manner. Overall, the [management] has not really differed. In the future, we’re going to be able to guide patients [about] their outcomes.

Do you think this measurement be automated for wider clinical application?
Yes, absolutely. A radiologist has the ability to look at Hounsfield units, which have been predictors of bone quality.

It is daunting, at first, to try to figure out ways that we can automate these things, but I think that this is something that can be achieved in the next 2 to 3 years.

Stuart A. Green, MD, FAAOS, is cofounder and past president of the Limb Lengthening and Reconstruction Society; past president of the Association of Bone and Joint Surgeons; and an attending surgeon at the Tibor Rubin Long Beach VA Medical Center. He is the son, first cousin, and father of AAOS Fellows. Dr. Green is a member of the AAOS Now Editorial Board.