Patients with transtibial amputation experienced decreased voluntary body inclination with backward movements when testing the limits of stability of prosthetic alignments compared with controls, according to a study recently published in the Archives of Physical Medicine and Rehabilitation. Changes in prosthetic foot settings through rotation in the sagittal plan also affected movement strategy more than changes in the prosthesis length.

“Postural instability is a major limiting factor of activities of daily living for persons with lower limb amputation and is reflected in both static and dynamic aspects of balance,” the researchers wrote. “The purpose of this study was to evaluate the limits of stability of patients with transtibial amputation and the influence of changes in prosthetic alignment.”

Limits of stability

Researchers recruited 10 male participants with transtibial amputation (TTA) and a minimum of 1 year history of daily prosthesis use and 17 healthy control participants without lower limb amputation. The inclusion criterion for all participants was the ability to stand unassisted without any support during common everyday activities for at least 30 minutes.

Using dynamic computer posturography, participants’ limits of stability (LOS) were evaluated with five different prosthetic alignments: optimal prosthesis alignment, prosthesis shortened by 1 cm, prosthesis lengthened by 1 cm, prosthetic foot in 5° extra dorsiflexion and prosthetic foot in 5° extra plantarflexion. Main outcome measures for the LOS test included the maximum excursion, endpoint excursion, direction control, movement velocity and reaction time with inclination in the forward direction, toward the amputated leg/right leg and in the backward direction and toward the nonamputated leg/ left leg.

Participants with TTA demonstrated significantly lower maximum excursion and direction control scores in the backward direction for all tested prosthetic alignments vs. controls. Direction control in backward inclination was also reduced compared with other tested directions for all assessed prosthetic alignments, according to study results.

Although researchers found no significant differences within each direction tested for the different prosthetic alignments, when comparing both groups, they found differences in endpoint excursion they attributed to prosthetic alignment. Endpoint excursion was significantly lower in the extra dorsiflexion and extra plantarflexion alignments compared with the controls in the backward direction and toward the amputated leg. Study results also showed a significant difference in endpoint excursion with the prosthetic foot in extra dorsiflexion for the amputated and nonamputated legs. Endpoint excursion was only significantly lower in the backward inclination when the prosthesis was shortened by 1 cm.

“Even though the prosthetic alignment changes tested were not large, they represented changes that prosthesis users encounter in daily life,” the researchers concluded. “Changes in prosthetic foot settings by means of rotation in the sagittal plane have greater effects on movement strategies within the LOS in patients with TTA than changes in the length of the prosthesis. The generalizability of our findings might be limited to men with TTA who are nonfallers.”

Study limitations

The researchers acknowledged the experimental group was not a random sample, was small and consisted of all men. They also were unable to separate the roles of intact and amputated limbs using the force platform; they speculated that separating the roles may have provided greater insight into the postural control mechanisms used by patients with TTA. Limits of stability should also be measured in more than just the anteroposterior and mediolateral directions and the influence of more prosthetic components should be considered, they wrote.

Finally, the order in which the tests were conducted may have affected the results.

“We assumed that the order of testing the different prosthetic alignment conditions would be attenuated by both the provision of practice trials and familiarity to the settings from daily exposure,” the researchers stated. “However, this assumption may not be correct, and random order should be used in future studies.” — by Casey Murphy