Gauging force by tapping tendons? Inaccurately in the human patellar tendon

Area of Science:

• Biomechanics
• Musculoskeletal Research
• Biomedical Engineering

Background:

• Non-invasive estimation of in vivo tendon load is a significant challenge in biomechanics.
• Shear-wave tensiometry offers a potential solution by measuring tendon shear wave speed using skin-mounted accelerometers.

Purpose of the Study:

• To evaluate the feasibility and accuracy of shear-wave tensiometry for estimating in vivo patellar tendon load.
• To determine the relationship between shear wave speed and patellar tendon force during knee extensor contractions.

Main Methods:

• Two experiments were conducted with 8 participants each, measuring patellar tendon shear wave speeds during voluntary knee extensor contractions.
• Participants performed sustained or ramp contractions at various knee joint angles and torque levels.
• Data analysis involved correlating normalized wave speed squared with normalized torque and comparing mean absolute errors.

Main Results:

• Experiment one showed no significant correlation between wave speed squared and estimated patellar tendon force within participants (r = -0.19, p = 0.278).
• Experiment two revealed variable correlations (r = 0.43 to 0.94) between normalized wave speed squared and torque, with time-varying correlations near +/- 1.00.
• Mean absolute errors for wave speed squared were larger than those for summed EMG amplitude, indicating lower accuracy.

Conclusions:

• A simple relationship between shear wave speed squared and patellar tendon load was not established.
• The feasibility of shear-wave tensiometry for accurately estimating in vivo tendon load at the knee joint is severely limited by these findings.