Hannah Dailey and her team at Lehigh University in the USA has developed a novel approach to determine when patients with tibial fractures can bear weight
Until now, there’s never been a tool that could determine how long it will take a patient to heal from a tibial fracture.
“What was exciting about our project was that all the mechanical analysis was done blinded to the clinical treatment of the patients, and the surgeon never saw any of our data,” says Hannah Dailey, an assistant professor of mechanical engineering and mechanics at Lehigh University’s PC Rossin College of Engineering and Applied Science.
“When we put it all together, we were able to answer the question, ‘Can the virtual mechanical test predict how long it will take the patient to heal?’ We found that it could.”
Dailey, who is also affiliated with Lehigh’s Institute for Functional Materials and Devices (I-FMD) is the lead author of “Virtual Mechanical Testing Based On Low-Dose Computed Tomography Scans for Tibial Fracture.” The paper was published in the Journal of Bone and Joint Surgery.
Most people who break their tibia proceed along a normal healing timeline. As the weeks go by, more and more callus forms along the fracture line. Callus starts out as a spongy material that over time hardens into bone that is just as strong – or stronger – than it was before the break. Patients typically come in for X-rays at regular intervals, and as long as the images reveal there’s increasingly more callus in the region, all is well.
But some people don’t heal normally. This failure to heal is called a nonunion, and it can be utterly debilitating.
“Musculoskeletal injuries are very painful,” says Dailey. “And when a bone isn’t healing properly, patients can be in pain for weeks or months.”
Ideally, she says, surgeons would re-operate early on a patient with a nonunion. But differentiating between a true nonunion, where no new bone is forming at all, and a bone that is healing, just very slowly, is difficult. And that difference is critical. If it’s the former, a second surgery is imperative. If it’s the latter, it may be better for the patient to wait and avoid the risk and expense of another operation.
Pinpointing that crucial difference between who needs additional surgery and who does not is difficult because surgeons typically rely on X-rays to determine the extent of bone healing. X-rays, however, are two-dimensional, often fuzzy, and can reveal an incomplete picture.
“Our approach was, ‘Can we measure healing in a structural way, and put a number on how healed a bone is?’” says Dailey. “Instead of using X-rays to determine, ‘Yes, healed,’ or ‘No, not healed,’ can we be more accurate? By using engineering tools, the answer was, yes. We could.”
In this study, adults with tibial shaft fractures were prospectively recruited for observation following standard reamed intramedullary nailing, a procedure in which a titanium rod is inserted in the hollow space of the tibia and secured at the top and bottom with screws. The screws allow the patient to bear weight soon after surgery by keeping the upper bone fragment from collapsing onto the lower bone fragment.
Patient follow-up included radiographs and completion of patient-reported outcome measures, all performed at 6, 12, 18, and 24 weeks post-surgery. Low-dose computed tomography (CT) scans were done at 12 weeks. These scans provided a detailed, three-dimensional picture of what was going on inside each patient.
Using specialised, commercially available software on the scans, Dailey’s PhD student and study co-author, Peter Schwarzenberg, built 3D mechanical structural models that identified the regions of bone and new bone. Schwarzenberg then ran the models through finite element analysis software – the same program used by civil engineers to simulate how much deformation happens to a bridge when a load (like cars or pedestrians) is applied to it. Schwarzenberg and Dailey wanted to do the same thing for bones – apply a force and see how much the bone flexed. The less it flexed, the more healed it was.
Schwarzenberg used the finite element software to divide each bone model into tiny zones called tetrahedra that all have a mathematical relationship to each other. He and Daile