Extra excitation of biceps femoris during neuromuscular electrical stimulation reduces knee medial loading

Prediction of in vivo hip contact forces during common activities of daily living using a segment-based musculoskeletal model

Background: Quantifying in vivo hip muscle and contact forces during activities of daily living (ADL) provides valuable information for diagnosis and treatment of hip-related disorders. The objective of this study was to utilize Freebody, a segment-based musculoskeletal model, for the prediction of hip contact forces using a novel objective function during seven common ADLs and validate its performance against the publicly available HIP98 dataset. Methods: Marker data, ground reaction forces, and hip contact forces during slow, normal, and fast walking, stair ascent and descent, and standing up and sitting down were extracted for 3 subjects from the HIP98 dataset. A musculoskeletal anatomical dataset was scaled to match the dimensions of each subject, and muscle and hip contact forces were estimated by minimizing a novel objective function, which was the summation of the muscle stresses squared and body weight-normalised hip contact force. The accuracy of predictions were quantified using several metrics, and muscle forces were qualitatively compared to experimental EMGs in the literature. Results: FreeBody predicted the hip contact forces during the ADLs with encouraging accuracy: The root mean squared error of predictions were 44.0 ± 8.5, 47.4 ± 6.5, and 59.8 ± 7.1% BW during slow, normal, and fast walking, 44.2 ± 16.8% and 53.3 ± 12.2% BW for stair ascent and descent, and 31.8 ± 8.2% and 17.1 ± 5.0% BW for standing up and sitting down, respectively. The error in prediction of peak hip contact forces were 14-18%, 24-28%, 17-35% for slow, normal, and fast walking, 7-25% and 15-32% in stair ascent and descent, and around 10% for standing up and sitting down. The coefficient of determination was larger than 0.90 in all activities except in standing up (0.86 ± 0.08). Conclusion: This study has implemented a novel objective function in a segment-based musculoskeletal model, FreeBody, for the prediction of hip contact forces during a large range of ADLs. The model outputs compare favourably for all ADLs and are the best in standing up and sitting down, while muscle activation patterns are consistent with experimental EMGs from literature. This new objective function addresses one of the major limitations associated with musculoskeletal models in the literature, namely the high non-physiological predicted hip joint contact forces.

The effect of modifying foot progression angle on the knee loading parameters in healthy participants with different static foot postures

BACKGROUND

Studies have found that toe-in gait reduced the peak knee adduction moment (KAM) during early stance, while toe-out gait reduced the peak KAM during late stance. However, some other studies found that toe-in or toe-out gait could reduce the KAM throughout stance phase. There is still a divergence of opinion on the use of toe-in or toe-out gait for reducing the KAM.

RESEARCH QUESTION

This study aimed to investigate whether static foot posture affected participants' biomechanical responses to three self-selected foot progression angles (FPA): neutral, toe-out and toe-in.

METHODS

Twenty-seven healthy participants were recruited for this FPA gait modification experiment and classified into three groups: neutral (n = 8), supination (n = 9) and pronation (n = 10), based on the Foot Posture Index (FPI). The kinematic and kinetic data were recorded with Vicon motion capture system and three force plates. The knee adduction moment and ankle eversion moment were calculated using an inverse dynamics model. The effect of the FPA modification on the knee loading parameters was analysed by the Friedman non-parametric test.

RESULTS

The KAM results in the neutral group showed that the toe-in gait modification reduced the first peak of the KAM (KAM1), while the KAM1 was increased in the supination group. The effect of the FPA modification on the KAM1 did not reach significance in the pronation group. The toe-out gait modification reduced the second peak (KAM2) regardless of the static posture.

SIGNIFICANCE

Different static foot postures were correlated with different peak KAM during the early stance phase due to FPA modification. These data suggest that the assessment of static foot posture provides a reference on how to offer adequate FPA modification for knee OA patients with different foot postures.