Impact of bone health on the mechanics of plate fixation for Vancouver B1 periprosthetic femoral fractures.

Background: Condyle-spanning plate-screw constructs have shown potential to lower the risks of femoral refractures after the healing of a primary Vancouver type B1 periprosthetic femoral fracture. Limited information exists to show how osteoporosis (a risk factor for periprosthetic femoral fractures) may affect the plate fixation during activities of daily living.

Methods: Using total hip arthroplasty and plate-implanted finite element models of three osteoporotic femurs, this study simulated physiological loads of three activities of daily living, as well as osteoporosis associated muscle weakening, and compared the calculated stress/strain, load transfer and local stiffness with experimentally validated models of three healthy femurs.

Impact of periprosthetic femoral fracture fixation plating constructs on local stiffness, load transfer, and bone strains.

Secondary femoral fractures after the successful plate-screw fixation of a primary Vancouver type B1 periprosthetic femoral fracture (PFF) have been associated with the altered state of stress/strain in the femur as the result of plating. The laterally implanted condyle-spanning plate-screw constructs have shown promises clinically in avoiding secondary bone and implant failures as compared with shorter diaphyseal plates. Though the condyle-spanning plating has been hypothesized to avoid stress concentration in the femoral diaphysis through increasing the working length of the plate, biomechanical evidence is lacking on how plate length may impact the stress/strain state of the implanted femur.

Simplified Mechanical Tests Can Simulate Physiological Mechanics of a Fixation Construct for Periprosthetic Femoral Fractures.

Plate fractures after fixation of a Vancouver Type B1 periprosthetic femoral fracture (PFF) are difficult to treat and could lead to severe disability. However, due to the lack of direct measurement of in vivo performance of the PFF fixation construct, it is unknown whether current standard mechanical tests or previous experimental and computational studies have appropriately reproduced the in vivo mechanics of the plate. To provide a basis for the evaluation and development of appropriate mechanical tests for assessment of plate fracture risk, this study applied loads of common activities of daily living (ADLs) to implanted femur finite element (FE) models with PFF fixation constructs with an existing or a healed PFF.

Development of axial compression and combined axial compression and torque loading configurations to reproduce strain in the implanted femur during activities of daily living.

Femoral strain is indicative of the potential for bone remodeling (strain energy density, SED) and periprosthetic femoral fracture (magnitude of principal strains) after total hip arthroplasty (THA). Previous modeling studies have evaluated femoral strains in THA-implanted femurs under gait loads including both physiological hip contact force and femoral muscle forces. However, experimental replication of the complex muscle forces during activities of daily living (ADLs) is difficult for in vitro assessment of femoral implant or fixation hardware.

Quantitative ultrasound mapping of regional variations in shear wave speeds of the aging Achilles tendon.

Objectives: Evaluate the effects of aging on healthy Achilles tendon and aponeurosis shear wave speed (SWS), a quantitative metric which reflects tissue elasticity.

Methods: Shear wave elastography was used to measure spatial variations in Achilles tendon SWS in healthy young (n = 15, 25 ± 4 years), middle-aged (n = 10, 49 ± 4 years) and older (n = 10, 68 ± 5 years) adults. SWS was separately measured in the free Achilles tendon, soleus aponeurosis and gastrocnemius aponeurosis in resting (R), stretched (dorsiflexed 15° from R) and slack (plantarflexed 15° from R) postures.