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Seventeen healthy elderly and 17 young adults walked and crossed obstacles of different heights, while sagittal angles (x) and angular velocities (x') of each joint were measured and their phase angles (phi) calculated as tan(-1)(x'/x). Relative phase angles (RPA) were also obtained, i.e., phi(hip-knee) and phi(knee-ankle). The standard deviations of the RPA curve points were averaged to obtain deviation phase (DP) values for the stance and swing phase for each obstacle height. Both groups had similar RPA patterns, for both the leading and the trailing limb. The elderly were found to cross obstacles with increased leading toe-clearance, but unaltered inter-joint coordination patterns. During the leading limb crossing, greater variability of the inter-joint coordination, correlated to the increased toe-clearance, indicates that aging increases the variability of the way the lower limb joints are controlled during obstacle-crossing. The elderly did not change the pattern and variability of the inter-joint coordination during the trailing limb crossing, possibly because it is relatively easy for the elderly to meet the mechanical demands despite increased age-related organismic constraints. The normal baseline inter-joint coordination data in the healthy aging population will be useful for future identification of coordination impairments and evaluation of subsequent treatment in those patients with diseases who may have an increased risk of falling.

To investigate the biomechanical strategy adopted by older adults with medial compartment knee osteoarthritis (OA) for successful obstacle crossing with the trailing limb, and to discuss its implications for fall-prevention, 15 older adults with bilateral medial compartment knee OA and 15 healthy controls were recruited to walk and cross obstacles of heights of 10%, 20%, and 30% of their leg lengths. Kinematic and kinetic data were obtained using a three-dimensional (3D) motion analysis system and forceplates. The OA group had higher trailing toe clearance than the controls. When the trailing toe was above the obstacle, the OA group showed greater swing hip abduction, yet smaller stance hip adduction, knee flexion, and ankle eversion. They showed greater pelvic anterior tilt and toe-out angle. They also exhibited greater peak knee abductor moments during early stance and at the instant when the swing toe was above the obstacle, while a greater peak hip abductor moment was found during late stance. Smaller knee extensor, yet greater hip extensor moments, were found in the OA group throughout the stance phase. In order to achieve higher toe clearance with knee OA, particular joint kinematic and kinetic strategies have been adopted by the OA group. Weakness in the hip abductors and extensors in individuals with OA may be risk factors for tripping owing to the greater demands on these muscle groups during obstacle crossing by these individuals.

Fifteen elderly subjects with bilateral medial knee osteoarthritis (OA) and 15 healthy elderly subjects walked and crossed obstacles with heights of 10%, 20%, and 30% of their leg lengths while sagittal angles and angular velocities of each joint were measured and their phase angles (ϕ) calculated. Continuous relative phase (CRP) were also obtained, i.e., ϕhip−knee and ϕknee−ankle. The standard deviations of the CRP curve points were averaged to obtain deviation phase (DP) values for the stance and swing phases. Significant differences between the OA and control groups were found in several of the peak and crossing angles, and angular velocities at the knee and ankle. Both groups had similar CRP patterns, and the DP values of the hip–knee and knee–ankle CRP curves were not significantly different between the two groups. Despite significant changes in the joint kinematics, knee OA did not significantly change the way the motions of the lower limb joints are coordinated during obstacle-crossing. It appears that the OA groups adopted a particular biomechanical strategy among all possible strategies that can accommodate the OA-induced changes of the knee mechanics using unaltered inter-joint coordination control. This enabled the OA subjects to accommodate reliably the mechanical demands related to bilateral knee OA in the sagittal plane during obstacle-crossing. Maintaining normal and reliable inter-joint coordination may be considered a goal of therapeutic intervention, and the patterns and variability of inter-joint coordination can be used for the evaluation of treatment effects.