Inclusion of a skeletal model partly improves the reliability of lower limb joint angles derived from a markerless depth camera.

A single depth camera provides a fast and easy approach to performing biomechanical assessments in a clinical setting; however, there are currently no established methods to reliably determine joint angles from these devices. The primary aim of this study was to compare joint angles as well as the between-day reliability of direct kinematics to model-constrained inverse kinematics recorded using a single markerless depth camera during a range of clinical and athletic movement assessments.A secondary aim was to determine the minimum number of trials required to maximize reliability.

A Two-Degree-of-Freedom Knee Model Predicts Full Three-Dimensional Tibiofemoral and Patellofemoral Joint Motion During Functional Activity.

Six kinematic parameters are needed to fully describe three-dimensional (3D) bone motion at a joint. At the knee, the relative movements of the femur and tibia are often represented by a 1-degree-of-freedom (1-DOF) model with a single flexion-extension axis or a 2-DOF model comprising a flexion-extension axis and an internal-external rotation axis. The primary aim of this study was to determine the accuracy with which 1-DOF and 2-DOF models predict the 3D movements of the femur, tibia and patella during daily activities.

Articular contact motion at the knee during daily activities.

We combined mobile biplane X-ray imaging and magnetic resonance imaging to measure the regions of articular cartilage contact and cartilage thickness at the tibiofemoral and patellofemoral joints during six functional activities: standing, level walking, downhill walking, stair ascent, stair descent, and open-chain (non-weight-bearing) knee flexion. The contact centers traced similar paths on the medial and lateral femoral condyles, femoral trochlea, and patellar facet in all activities while their locations on the tibial plateau were more varied. The translations of the contact centers on the femur and patella were tightly coupled to the tibiofemoral flexion angle in all activities (r  > 0.

Moment arm of the knee-extensor mechanism measured in vivo across a range of daily activities.

We measured the moment arm of the knee-extensor mechanism as ten healthy young individuals performed six functional activities: level walking, downhill walking, stair ascent, stair descent, open-chain (non-weight-bearing) knee flexion, and open-chain knee extension. The moment arm of the knee-extensor mechanism was described by the moment arm of the patellar-tendon force, which acts to rotate the tibia about the instantaneous axis of rotation (screw axis) of the knee. A mobile biplane X-ray imaging system enabled simultaneous measurements of the three-dimensional movements of the femur, tibia and patella during each activity, from which the position and orientation of the screw axis and the patellar-tendon moment arm (PTMA) were determined.

Load Distribution at the Patellofemoral Joint During Walking.

We combined computational modelling with experimental gait data to describe and explain load distribution across the medial and lateral facets of the patella during normal walking. The body was modelled as a 13-segment, 32-degree-of-freedom (DOF) skeleton actuated by 80 muscles. The knee was represented as a 3-body, 12-DOF mechanical system with deformable articular cartilage surfaces at the tibiofemoral (TF) and patellofemoral (PF) joints.

Six-Degree-of-Freedom Tibiofemoral and Patellofemoral Joint Motion During Activities of Daily Living.

The purpose of this study was to measure the three-dimensional movements of the femur, tibia and patella in healthy young people during activities of daily living. A mobile biplane X-ray imaging system was used to obtain simultaneous measurements of six-degree-of-freedom (6-DOF) tibiofemoral and patellofemoral kinematics and femoral condylar motion in ten participants during standing, level walking, downhill walking, stair ascent, stair descent and open-chain (non-weightbearing) knee flexion. Seven of the eleven secondary motions at the knee-three translations at the tibiofemoral joint, three translations at the patellofemoral joint, and patellar flexion-were coupled to the tibiofemoral flexion angle (r ≥ 0.

Three-dimensional motion of the knee-joint complex during normal walking revealed by mobile biplane x-ray imaging.

Accurate knowledge of knee kinematics is important for a better understanding of normal joint function and for improving patient outcomes subsequent to joint reconstructive surgery. Limited information is available that accurately describes the relative movements of the bones at the knee in vivo, even for the most common of all activities: walking. We used a mobile X-ray imaging system to measure the three-dimensional motion of the entire knee-joint complex-femur, tibia, and patella-when humans walk over ground at their natural speeds.

Normalized patellofemoral joint reaction force is greater in individuals with patellofemoral pain.

Patellofemoral pain is a disabling, highly prevalent pathology. Altered patellofemoral contact forces are theorized to contribute to this pain. Musculoskeletal modeling has been employed to better understand the etiology of patellofemoral pain.