Plantar flexor muscle weakness may cause stiff-knee gait.

AIM: The iterative simulation studies proclaim that plantar flexor (PF) muscle weakness is one of the contributors of stiff knee gait (SKG), although, whether isolated PF weakness generates SKG has not been validated in able-bodied people or individuals with neuromuscular disorders. The aim of the study was to investigate the effects of isolated PF muscle weakness on knee flexion velocity and SKG in healthy individuals.

METHOD: Twenty able-bodied young adults (23±3 years) participated in this study. Passive stretch (PS) protocol was applied until the PF muscle strength dropped 33.1% according to the hand-held dynamometric measurement. Seven additional age-matched able-bodies were compared with participants' to discriminate the influence of slow-walking. All participants underwent 3D gait analysis before and after the PS. Peak knee flexion angle, range of knee flexion between toe-off and peak knee flexion, total range of knee-flexion, and time of peak knee flexion in swing were selected to describe SKG pattern.

RESULTS: After PS, the reduction of plantar flexor muscle strength (33.14%) caused knee flexion velocity drop at toe-off (p=0.008) and developed SKG pattern by decreasing peak knee flexion (p=0.0001), range of knee flexion in early swing (p=0.006), and total knee flexion range (p=0.002). These parameters were significantly correlated with decreased PF velocity at toe-off (p=0.015, p=0.0001, p=0.005, respectively). The time of peak knee flexion was not significantly different between before and after stretch conditions (p=0.130).

CONCLUSIONS: These findings verified that plantar flexor weakness cause SKG pattern by completing three of SKG parameters. Any treatment protocol that weakens the plantar flexor muscle might impact the SKG pattern.