Healing distal femur fractures found robust enough to withstand high early strains, loads

February 14, 2021

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Schwarzenberg P et al. Panel Presentation 0011. Presented at: Annual Meeting of the Orthopedic Research Society; 12-16 February 2021 (virtual meeting).

Disclosure:
Schwarzenberg does not report any relevant financial information.

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Despite higher interfragmental loads on the distal femoral fractures when the load exceeds 20% of a patient’s body weight during early healing, fracture models indicated that the fractures are likely to withstand increased loads.

At the annual conference of the Orthopedic Research Society, Peter Schwarzenberg, MRS, A research fellow at Lehigh University presented results from six patient-specific models of distal femoral fractures that he and his colleagues had developed in consultation with orthopedic trauma surgeons.

Schwarzenberg discussed the various CT-based models, as well as elongation and stress tests, which the researchers used to simulate the extent of clinical stress in patients with distal femoral fractures. He said these took into account forces from the distal third of the femur that weren’t assessed with other distal femoral fracture models such as traditional osteotomy models, as well as bridge span – which is the distance between the screws of an implant across the fracture line, stiffness, interfragmental strain distribution, and other factors.

“This study shows that the stress in patient-specific models is higher than in osteotomy models that have traditionally been used to study fracture fixation with a distal radius,” said Schwarzenberg. The context of the study is the clinical debate about the safety of immediate weight-bearing as tolerated in patients with distal femoral fractures.

“In this study, it is assumed that patients with postoperative instructions without weight bearing do not carry more than 20% light toe contact. However, patients can put much more stress on their implant. We know that the stretches are higher with higher loads. This indicates that the in vivo healing of distal femoral fractures may be more robust than previously thought to localized high loads, ”said Schwarzenberg.

The researchers used various virtual tests and finite element analysis techniques and studies to draw their conclusions. For example, they identified a variety of fracture patterns and the relative size of the 3-D strain field during 20% ​​virtual exposure based on von Mises strain fields seen around the fracture line for the six patients.

The patients had bridge spans ranging from 26 mm to 134 mm.

“We see a large and more intense exposure field for patients with a longer bridge span,” said Schwarzenberg.

Local hot spots were observed in elongation simulations when the elongation exceeded a 10% threshold that occurred in three patients, and there was a relationship between these and the length of the bridge span, he said.

“We see that the [Orthopaedic Trauma Association] OTA 33-A3 osteotomy [model] does not produce any peak loads similar to the patient-specific models, even with very high bridge spans, ”said Schwarzenberg.

The patient-specific models represented all of the cases that led to a successful clinical association, he said.

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Annual meeting of the Orthopedic Research Society

Annual meeting of the Orthopedic Research Society

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