Song Joo Lee

Impaired varus–valgus proprioception and neuromuscular stabilization in medial knee osteoarthritis

Impaired proprioception and poor muscular stabilization in the frontal plane may lead to knee instability during functional activities, a common complaint in persons with knee osteoarthritis (KOA). Understanding these frontal plane neuromechanical properties in KOA will help elucidate the factors contributing to knee instability and aid in the development of targeted intervention strategies. The objectives of the study were to compare knee varus-valgus proprioception, isometric muscle strength, and active muscular contribution to stability between persons with medial KOA and healthy controls. We evaluated knee frontal plane neuromechanical parameters in 14 participants with medial KOA and 14 age- and gender-matched controls, using a joint driving device (JDD) with a customized motor and a 6-axis force sensor. Analysis of covariance with BMI as a covariate was used to test the differences in varus-valgus neuromechanical parameters between these two groups. The KOA group had impaired varus proprioception acuity (1.08±0.59° vs. 0.69±0.49°, p<0.05), decreased normalized varus muscle strength (1.31±0.75% vs. 1.79±0.84% body weight, p<0.05), a trend toward decreased valgus strength (1.29±0.67% vs. 1.88±0.99%, p=0.054), and impaired ability to actively stabilize the knee in the frontal plane during external perturbation (4.67±2.86 vs. 8.26±5.95 Nm/degree, p<0.05). The knee frontal plane sensorimotor control system is compromised in persons with medial KOA. Our findings suggest varus-valgus control deficits in both the afferent input (proprioceptive acuity) and muscular effectors (muscle strength and capacity to stabilize the joint).

A Pivoting Elliptical Training System for Improving Pivoting Neuromuscular Control and Rehabilitating Musculoskeletal Injuries

Knee injuries often occur in pivoting activities but most existing training and rehabilitation devices mainly involve sagittal movements. A pivoting elliptical training system (PETS) was developed to train and evaluate neuromuscular control in pivoting for the purposes of prevention and rehabilitation of musculoskeletal injuries. The PETS have capabilities of controlling two footplates individually or simultaneously through servomotor control so that the footplates behave like two torsional springs with adjustable offset and stiffness, slippery surface, or under external perturbations. Feasibility of the PETS in improving pivoting neuromuscular control and pivoting neuromechanical properties was demonstrated through experiments on healthy subjects, with reduced pivoting instability and reaction time, and improved proprioceptive acuity following training. The PETS can potentially be used as a therapeutic and research tool to investigate mechanisms underlying pivoting-related injuries and train human subjects for improving neuromuscular control during risky pivoting activities.

Offaxis neuromuscular training of knee injuries using an offaxis robotic elliptical trainer

The goal of this study was to use an offaxis robotic elliptical trainer to improve off-axis neuromuscular control in people with knee injuries. Thirteen individuals with knee injuries participated in the study. Among them, 8 individuals participated in 18 sessions of pivoting offaxis intensity-adjustable neuromuscular control training (POINT) (3 sessions/week for 6 weeks including 3 evaluation sessions) to improve offaxis neuromuscular control, specifically dynamic lower limb stability in pivoting. 5 individuals served as controls who only participated in the three evaluations. Following POINT patients in the training group reduced pivoting instability (p=0.024), while the control group did not (p=0.118). Individuals in the training group were able to hop farther in a single leg hop for distance task, take shorter in 12m hop time for time task, and reported reduced knee pain. The results suggest that subject-specific POINT utilizing the novel robotic elliptical trainer can be implemented as a rehabilitation protocol for patients with knee injuries to improve their lower limb functions and reduce knee symptoms.

Effects of Pivoting Neuromuscular Training on Pivoting Control and Proprioception

PURPOSE Pivoting neuromuscular control and proprioceptive acuity may play an important role in anterior cruciate ligament injuries. The goal of this study was to investigate whether pivoting off-axis intensity adjustable neuromuscular control training (POINT) could improve pivoting neuromuscular control, proprioceptive acuity, and functional performance. METHODS Among 41 subjects, 21 subjects participated in 18 sessions of POINT (three sessions per week for 6 wk), and 20 subjects served as controls who did their regular workout. Both groups received pre-, mid-, and postintervention evaluations. Propensity score analysis with multivariable regression adjustment was used to investigate the effect of training on pivoting neuromuscular control (pivoting instability, leg pivoting stiffness, maximum internal, and external pivoting angles), proprioceptive acuity, and functional performance in both groups. RESULTS Compared with the control group, the training group significantly improved pivoting neuromuscular control as reduced pivoting instability, reduced maximum internal and external pivoting angles, increased leg pivoting stiffness, and decreased entropy of time to peak EMG in the gluteus maximus and lateral gastrocnemius under pivoting perturbations. Furthermore, the training group enhanced weight-bearing proprioceptive acuity and improved the single leg hop distance. CONCLUSION Improvement of pivoting neuromuscular control in functional weight-bearing activities and task performances after POINT may help develop lower limb injury prevention and rehabilitation methods to reduce anterior cruciate ligament and other musculoskeletal injuries associated with pivoting sports.

Gender differences in offaxis neuromuscular control during stepping under a slippery condition

PurposeFemales are at greater risks of musculoskeletal injuries than are males, which may be related to decreased neuromuscular control in axial and/or frontal planes, offaxis neuromuscular control. The objective of this study was to investigate gender differences in offaxis neuromuscular control during stepping under a slippery condition.MethodsForty-three healthy subjects (21 males and 22 females) performed different stepping tasks under a slippery condition, namely, free pivoting task (FPT) to control axial plane pivoting, free sliding task (FST) to control frontal plane sliding, and free pivoting and sliding task (FPST) to control axial pivoting, and frontal sliding on a custom-made offaxis elliptical trainer.ResultsCompared to males, females showed significantly higher pivoting instability, higher max internal and external pivoting angles, higher mean max medial and lateral sliding distance, and higher entropy of time to peak EMG in the medial and lateral gastrocnemius muscles during the FPST and higher entropy of time to peak EMG in the lateral gastrocnemius muscle during the FPT and FST.ConclusionsThe findings may help us understand potential injury risk factors associated with gender differences, and provide a basis for developing targeted neuromuscular training to improve offaxis neuromuscular control, and reduce musculoskeletal injuries associated with excessive offaxis loadings.

Pivoting neuromuscular control and proprioception in females and males

PurposeNoncontact ACL injuries occur most commonly in pivoting sports and are much more frequent in females than in males. However, information on sex differences in proprioceptive acuity under weight-bearing and leg neuromuscular control in pivoting is scarce. The objective of this study was to investigate sex differences in pivoting neuromuscular control during strenuous stepping tasks and proprioceptive acuity under weight-bearing.Methods21 male and 22 female subjects were recruited to evaluate pivoting proprioceptive acuity under weight-bearing, and pivoting neuromuscular control (in terms of leg pivoting instability, stiffness, maximum internal and external pivoting angles, and entropy of time-to-peak EMG in lower limb muscles) during strenuous stepping tasks performed on a novel offaxis elliptical trainer.ResultsCompared to males, females had significantly lower proprioceptive acuity under weight-bearing in both internal and external pivoting directions, higher pivoting instability, larger maximum internal pivoting angle, lower leg pivoting stiffness, and higher entropy of time-to-peak EMG in the gastrocnemius muscles during strenuous stepping tasks with internal and external pivoting perturbations.ConclusionsResults of this study may help us better understand factors contributing to ACL injuries in females and males, develop training strategies to improve pivoting neuromuscular control and proprioceptive acuity, and potentially reduce ACL and lower-limb musculoskeletal injuries.

Real-time tracking of knee adduction moment in patients with knee osteoarthritis.

BACKGROUND The external knee adduction moment (EKAM) is closely associated with the presence, progression, and severity of knee osteoarthritis (OA). However, there is a lack of convenient and practical method to estimate and track in real-time the EKAM of patients with knee OA for clinical evaluation and gait training, especially outside of gait laboratories. NEW METHOD A real-time EKAM estimation method was developed and applied to track and investigate the EKAM and other knee moments during stepping on an elliptical trainer in both healthy subjects and a patient with knee OA. RESULTS Substantial changes were observed in the EKAM and other knee moments during stepping in the patient with knee OA. COMPARISON WITH EXISTING METHOD(S) This is the first study to develop and test feasibility of real-time tracking method of the EKAM on patients with knee OA using 3-D inverse dynamics. CONCLUSIONS The study provides us an accurate and practical method to evaluate in real-time the critical EKAM associated with knee OA, which is expected to help us to diagnose and evaluate patients with knee OA and provide the patients with real-time EKAM feedback rehabilitation training.

Improvement in off-axis neuromuscular control through pivoting elliptical training: Implication for knee injury prevention

The goal of this study was to investigate the efficacy of off-axis neuromuscular control training using a pivoting elliptical machine. Although knee motion is mainly in flexion/extension, injuries to the knee are usually associated with excessive off-axis movement (tibial axial rotation and valgus/varus). A pivoting elliptical training system was developed to improve neuromuscular control about the off-axes. Six week training was conducted in nine healthy individuals and seven healthy individuals served as control and only participated in evaluation sessions. Our results showed that following the pivoting elliptical training, individuals were able to reduce pivoting instability across different phases of the elliptical cycle (p<0.01) and also mediolateral instability at mid and terminal swing phase (p<0.05). A trend of reduced response time and phase dependent changes in EMG patterns were also observed. The results showed that the pivoting elliptical training is effective to improve off-axis neuromuscular control in healthy individuals and such training protocol can potentially be implemented to prevent knee injury.

Real-Time Knee Adduction Moment Feedback Training Using an Elliptical Trainer

The external knee adduction moment (EKAM) is associated with knee osteoarthritis (OA) in many aspects including presence, progression, and severity of knee OA. Despite of its importance, there is a lack of EKAM estimation methods that can provide patients with knee OA real-time EKAM biofeedback for training and clinical evaluations without using a motion analysis laboratory. A practical real-time EKAM estimation method, which utilizes kinematics measured by a simple six degree-of-freedom goniometer and kinetics measured by a multi-axis force sensor underneath the foot, was developed to provide real-time feedback of the EKAM to the patients during stepping on an elliptical trainer, which can potentially be used to control and alter the EKAM. High reliability (ICC(2,1): 0.9580) of the real-time EKAM estimation method was verified through stepping trials of seven subjects without musculoskeletal disorders. Combined with advantages of elliptical trainers including functional weight-bearing stepping and mitigation of impulsive forces, the real-time EKAM estimation method is expected to help patients with knee OA better control frontal plane knee loading and reduce knee OA development and progression.

Development of an elliptical trainer with real-time knee adduction moment feedback

The external knee adduction moment (EKAM) is associated with knee osteoarthritis (OA) in many aspects including its presence, progression, and severity. Despite of its importance, there is a lack of EKAM estimation methods that can provide patients with knee OA a real-time EKAM biofeedback during training and be used for routine clinical evaluations outside motion analysis laboratories. Thus, a practical real-time EKAM estimation method, which utilizes kinematic variables from a simple 6-DOF goniometer, was developed to provide patients with knee OA a real-time feedback of their EKAM during stepping on elliptical trainers (ETs) to reduce the damaging EKAM. Feasibility of the proposed method was verified on seven healthy subjects. Combined with advantages of ETs (e.g., functional weight-bearing stepping, mitigation of delivery of impulsive forces), the real-time EKAM estimation method is expected to benefit patients with knee OA.