Step length after discrete perturbation predicts accidental falls and fall-related injury in elderly people with a range of peripheral neuropathy

Abstract

Aims: Distal symmetric polyneuropathy increases fall risk due to inability to cope with perturbations. We aimed to 1) identify the frontal plane lower limb sensorimotor functions which are necessary for robustness to a discrete, underfoot perturbation during gait; and 2) determine whether changes in the post-perturbed step parameters could distinguish between fallers and non fallers.

Methods: Forty-two subjects (16 healthy old and 26 with diabetic PN) participated. Frontal plane lower limb sensorimotor functions were determined using established laboratory-based techniques. The subjects' most extreme alterations in step width or step length in response to a perturbation were measured. In addition, falls and fall-related injuries were prospectively recorded.

Results: Ankle proprioceptive threshold (APrT; p=.025) and hip abduction rate of torque generation (RTG; p=.041) independently predicted extreme step length after medial perturbation, with precise APrT and greater hip RTG allowing maintenance of step length. Injured subjects demonstrated greater extreme step length changes after medial perturbation than non-injured subjects (percent change = 18.5 ± 9.2 vs. 11.3 ± 4.57; p = .01).

Conclusions: The ability to rapidly generate frontal plane hip strength and/or precisely perceive motion at the ankle is needed to maintain a normal step length after perturbation, a parameter which distinguishes between subjects sustaining a fall-related injury and those who did not.

Keywords: Falls; Gait; LP; Lateral Perturbed; MP; MVC; Maximum Voluntary Contraction; Medial Perturbed; Muscle strength; PN; Peripheral Neuropathy; Peripheral neuropathy; Proprioception; RTG; Rate of Torque Generation; SL; SW; Sensorimotor functions; Step length; Step width; UnP; Unperturbed.

Figure 1. Picture of the perturbing shoe

Anterior view of the sandal, unloaded by body weight and with the 18.4mm-high lateral flap (circled) deployed in the parasagittal plane so as to invert the foot during a single mid stance phase

Figure 2. Differences in the most aberrant post perturbed step length between Fallers and Non Fallers and between Fall Injured and No Fall injured individuals

The figures illustrate relative differences (in percentage on the y axis) in the most aberrant post perturbed step length between Fallers and Non Fallers and between Fall Injured and No Fall injured individuals (x-axis).