In older adults, surgical management of distal femur fractures can be challenging due to reduced bone mineral density, which results in inadequate implant anchorage. Mechanical testing of implant constructs designed to treat these injuries has been hampered by a lack of clinical data on the biomechanical properties of the distal femur in patients who sustain these fractures. Therefore, the purpose of this study was to apply asynchronous, quantitative computed tomography (qCT) to investigate the mechanical characteristics of fractured distal femurs with intent to inform the selection of appropriate synthetic materials for biomechanical testing of orthopaedic devices.

Distal femur fractures treated at St. Luke’s University Health Network, a Level I trauma center, were retrospectively reviewed and 43 cases with preoperative CT scans were identified for analysis. Scans were segmented and each bone fragment was reconstructed as a 3D model. Bone quality was determined from voxel-based radiodensity and reported as Young’s modulus in the distal femur for each patient.

The median patient age was 72 years (IQR = 57 – 81), with 26% males and 74% females. Young’s modulus in the distal femur was negatively correlated with patient age (R² = 0.50, p < 0.001). The distribution of patient-specific modulus values was also compared with the compressive modulus ranges, as stated by the ASTM F1839 standard for graded polyurethane foams for use as a standard material for testing orthopaedic devices and instruments. Bone quality varied dramatically from Grade 25 (25 lbs/in²) in younger individuals to Grade 5 (5 lbs/in²) in older individuals.

As a result, no single grade of synthetic polyurethane foam can be selected to model all clinically important scenarios for biomechanical testing of distal femur fracture fixation devices. Rather, this data can be used to select an appropriate material for a given clinical scenario. For example, a Grade 25 foam is appropriate for a younger individual where implant longevity in the clinical concern, whereas for an older patient where implant stability is the clinical concern, a Grade 5-15 is more appropriate.