A musculoskeletal model was developed to analyze the tensions of the knee joint ligaments during walking and to understand how they change with changes in the muscle forces. The model included the femur, tibia, patella and all components of cruciate and collateral ligaments, quadriceps, hamstrings and gastrocnemius muscles. Inputs to the model were the muscle forces, estimated by a static optimization approach, the external loads (ground reaction forces and moments) and the knee flexion/extension movement corresponding to natural walking. The remaining rotational and translational movements were obtained as a result of the dynamic equilibrium of forces. The validation of the model was done by comparing our results with literature data. Several simulations were carried out by sequentially removing the forces of the different muscle groups. Deactivation of the quadriceps produced a decrease of tension in the anterior cruciate ligament (ACL) and an increase in the posterior cruciate ligament (PCL). By removing the hamstrings, the tension of ACL increased at the late swing phase, while the PCL force dropped to zero. Specific effects were observed also at the medial and lateral collateral ligaments. The removal of gastrocnemius muscles produced an increase of tension only on PCL and lateral collateral ligaments. These results demonstrate how musculoskeletal models can contribute to knowledge about complex biomechanical systems as the knee joint.

The purpose of this retrospective study was to quantify the three-dimensional knee and ankle joint kinematics and kinetics during walking in young participants with different degrees of obesity and to identify the associated effects by stratifying the obese participants according to their BMI. Thirty-two young obese individuals (mean age 30.32 years) and 16 normal-weight age-matched individuals were tested using 3D gait analysis. Analysis of kinematic and kinetic data revealed significant differences in mechanics at knee and ankle joints in all the evaluated planes of movement. Compared to the healthy-weight participants, obese adults demonstrated less knee flexion, greater knee ab-adduction angle during the entire gait cycle and abnormalities at the knee flex-extension moment. At the ankle joint, reduced range of motion was observed together with a lower peak of ankle plantarflexor moment and power during terminal stance. These results provide insight into a potential pathway by which obesity predisposes a healthy adult for increased risk of osteoarthritis.

The actual need for surgical reconstruction of an injured anterior cruciate ligament (ACL) is still a matter of debate. The aim of this study was to quantify and analyze the knee kinematics and the ligament force redistribution resulting from the ACL sacrifice and the consequent effects of changing the quadriceps and hamstring activity during walking. A three-dimensional musculoskeletal model was used to simulate the behavior of the knee joint during the gait cycle, in different testing conditions: an ACL-deficient knee, an ACL-deficient knee with hamstrings inactivated and an ACL-deficient knee with quadriceps inactivated. Our results showed that in the ACL-deficient knee, the medial collateral ligament (MCL) was the main passive stabilizer of the anterior translation of the tibia. Furthermore, the compensation effects produced by the hamstrings and quadriceps in the ACL-deficient knee during walking were quantified and analyzed. In the case of ACL sacrifice, reducing the quadriceps activity would allow for relieving all ligaments in general, except for the posterior cruciate ligament, which required more consistent recruitment in the support phase. Meanwhile, hamstring activity was crucial not only to compensate for the absence of ACL in limiting the anterior tibial displacement but also to reduce the risk of MCL injury.

Inertial technology has spread widely for its comfortable use and adaptability to various motor tasks. The main objective of this study was to assess the validity of inertial measurements of the cervical spine range of motion (CROM) when compared to that of the optoelectronic system in a group of healthy individuals. A further aim of this study was to determine the optimal placement of the inertial sensor in terms of reliability of the measure, comparing measurements obtained from the same device placed at the second cervical vertebra (C2), the forehead (F) and the external occipital protuberance (EOP). Twenty healthy subjects were recruited and asked to perform flexion–extension, lateral bending, and axial rotation movements of the head. Outcome measurements of interest were CROM and mean angular velocities for each cervical movement. Results showed that inertial measurements have good reliability (0.75 < ICC < 0.9). Excellent reliability (ICC > 0.9) was found in both flexion and right lateral bending angles. All parameters extracted with EOP placement showed ICC > 0.62, while ICC < 0.5 was found in lateral bending mean angular velocities both for F and C2 placements. Therefore, the optimal sensor’s positioning emerged to be EOP. These results suggest that inertial technology could be useful and reliable for the evaluation of the CROM.

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