Healing distal femur fractures found robust, able to withstand high early loads
Click Here to Manage Email Alerts
Despite higher interfragmentary strains placed on distal femur fractures when weight-bearing during early healing exceeds 20% of a patient’s body weight, fracture models showed the fractures can likely withstand increased loads.
“The interfragmentary strain environment produced in clinical bridge plating is complex, but in vivo healing of distal femur fractures may be more robust to localized large shear-dominant strains than has been previously appreciated,” Peter Schwarzenberg, MS, told Healio Orthopedics.
At the Orthopaedic Research Society Annual Meeting, Schwarzenberg, a graduate research assistant at Lehigh University, presented findings from six patient-specific models of distal femur fractures he and his colleagues developed in consultation with orthopedic trauma surgeons.
Schwarzenberg discussed the various CT-based models and strain and load tests the researchers used to simulate the extent of weight-bearing seen clinically in patients with distal femur fractures. In his presentation, he said these took into consideration forces from the distal third of the femur not assessed with other distal femur fracture models, such as traditional osteotomy models, as well as bridge span — which is the distance between screws of an implant across the fracture line, construct stiffness, interfragmentary strain distribution and other factors.
“This study shows that strain is higher in patient-specific models compared to the osteotomy models that have traditionally been used to study distal radius fracture fixation,” Schwarzenberg said, noting the context of the study is the clinical debate regarding the safety of immediate weight-bearing as tolerated in patients with distal femur fractures.
“This study assumes that patients who have non-weight-bearing postoperative instructions will do no more than 20% light toe-touch weight-bearing. However, patients may be applying significantly more load to their implant. We know that strains will be higher at higher loads. This indicates that in vivo healing of distal femur fractures may be more robust to localized high strains than has been previously appreciated,” Schwarzenberg said.
Researchers used various virtual tests and finite element analysis techniques and studies to draw their conclusions. For example, they identified a wide variety of fracture patterns and relative magnitude of the 3D strain field during virtual 20% weight-bearing based on von Mises strain fields seen around the fracture line for the six patients.
Patients had bridge spans that ranged from 26 mm to 134 mm.
“We see a large and more intense strain field for patients that have a longer bridge span,” Schwarzenberg said.
Local hot spots were seen on strain simulations when strain exceeded a 10% threshold, which occurred in three patients, and there was a relationship between these and bridge span length, he said.
“We see that the [Orthopaedic Trauma Association] OTA 33-A3 osteotomy [model] does not produce peak strains that are similar to the patient-specific models, even at very high bridge spans,” Schwarzenberg said.
The patient-specific models all represented cases that went on to successful clinical union, he said.
Collapse
Read more about
Click Here to Manage Email Alerts