Normative Achilles and patellar tendon shear wave speeds and loading patterns during walking in typically developing children

Abstract

Background: Motion analysis is commonly used to evaluate joint kinetics in children with cerebral palsy who exhibit gait disorders. However, one cannot readily infer muscle-tendon forces from joint kinetics. This study investigates the use of shear wave tensiometry to characterize Achilles and patellar tendon forces during gait.

Research question: How do Achilles and patellar tendon wave speed and loading modulate with walking speed in typically developing children?

Methods: Twelve typically developing children (9-16 years old) walked on an instrumented treadmill with shear wave tensiometers over their Achilles (n = 11) and patellar (n = 9) tendons. Wave speeds were recorded at five leg length-normalized walking speeds (very slow to very fast). Achilles and patellar tendon moment arms were measured with synchronized ultrasound and motion capture. The tendon wave speed-load relationship was calibrated at the typical walking speed and used to estimate tendon loading at other walking speeds.

Results: Characteristic Achilles and patellar tendon wave speed trajectories exhibited two peaks over a gait cycle. Peak Achilles tendon force closely aligned with peak ankle plantarflexor moment during pushoff, though force exhibited less modulation with walking speed. A second peak in late swing Achilles loading, which was not evident from the ankle moment, increased significantly with walking speed (p < 0.001). The two peaks in patellar tendon loading occurred at 12 ± 1% and 68 ± 6% of the gait cycle, matching the timing of peak knee extension moment in early stance and early swing. Both patellar tendon load peaks increased significantly with walking speed (p < 0.05).

Significance: This is the first study to use shear wave tensiometry to characterize Achilles and patellar tendon loading during gait in children. These data could serve as a normative comparison when using tensiometry to identify abnormal tendon loading patterns in individuals who exhibit equinus and/or crouch gait.

Keywords: Pediatric gait database; Shear wave tensiometry; Subject-specific calibration; Tendon force; Tendon stress.

Figure 1.

Average (solid line) and standard deviation (shading) of Achilles and patellar tendon moment arm quadratic fits as a function of joint angle.

Figure 2.

Average (solid line) Achilles and patellar wave speeds and standard deviation (shading) across five normalized walking speeds. Vertical line indicates end of stance phase.

Figure 3.

Average Achilles and patellar tendon stress (top row) and ankle plantarflexion and knee extension moment (bottom row) across speeds presented over the average stride time. A second peak in Achilles tendon stress (AL2) is present during late swing, corresponding with the passive Achilles tendon loading due to tibialis anterior activation in preparation for heel strike. This is undetected in the ankle plantarflexion moment. The patellar tendon stress curves show two distinct peaks, the first corresponding with early stance (PL1) and the second with pre-swing/early swing phase (PL2). Peak knee extension moments are observed at these two instances as well (KM1, KM3). Vertical ticks along the x-axis indicate end of stance phase.