Although knee orthotics have become the preferred treatment method for rehabilitation and injury prevention, their biomechanical influence has not yet been quantified. A new type of knee joint orthosis (KJO) using a non-linear spring-loaded (NLSL) component was recently introduced to help prevent the growing number of knee injuries and aid during rehabilitation. The purpose of this case study is to quantify the lower extremity biomechanical effects and evaluate functional benefits of a new KJO as a precision treatment option. Kinematic and kinetic data obtained from two dynamic squat trials were recorded using VICON^Ⓡ motion capture system and an AMTI^Ⓡ force plate. This data was then applied to a modified computational musculoskeletal model. Inverse kinematics and dynamics were performed to calculate joint angles and joint moments while a static equilibrium problem was solved at each instant during the squat cycle, with and without the NLSL KJO to find individual muscle forces of the lower extremity. The NLSL KJO was seen to improve the activation in the subject's posterior chain musculature encouraging a more balanced synergy versus the inherent quadriceps dominant strategy during the squat movement, and encourage a more neutral behavior in the upright position by inhibiting movement towards terminal knee extension.

Musculoskeletal computational models provide a non-invasive approach to investigate human movement biomechanics. These models could be particularly useful for pediatric applications where in vivo and in vitro biomechanical parameters are difficult or impossible to examine using physical experiments alone. The objective was to develop a novel musculoskeletal subject-specific infant model to investigate hip joint biomechanics during cyclic leg movements. Experimental motion-capture marker data of a supine-lying 2-month-old infant were placed on a generic GAIT 2392 OpenSim model. After scaling the model using body segment anthropometric measurements and joint center locations, inverse kinematics and dynamics were used to estimate hip ranges of motion and moments. For the left hip, a maximum moment of 0.975 Nm and a minimum joint moment of 0.031 Nm were estimated at 34.6° and 65.5° of flexion, respectively. For the right hip, a maximum moment of 0.906 Nm and a minimum joint moment of 0.265 Nm were estimated at 23.4° and 66.5° of flexion, respectively. Results showed agreement with reported values from the literature. Further model refinements and validations are needed to develop and establish a normative infant dataset, which will be particularly important when investigating the movement of infants with pathologies such as developmental dysplasia of the hip. This research represents the first step in the longitudinal development of a model that will critically contribute to our understanding of infant growth and development during the first year of life.

The recent study by Walck et al., titled "A Patient-Specific Lower Extremity Biomechanical Analysis of a Knee Orthotic during a Deep Squat Movement," provides a novel insight into the biomechanical impacts of knee orthotics, particularly the non-linear spring-loaded (NLSL) knee joint orthosis (KJO)1. This commentary aims to delve into the implications, interpretations, and evaluations of the findings, contextualizing them within the broader discourse on knee orthotics.