Unilateral transfemoral amputees walk with increased trunk lateral flexion in comparison with able-bodied individuals, and a new study has identified four distinct positive power phases at the low back that occur just before and after each heel strike.
Researchers Brad D. Hendershot, PhD, of the Center for Rehabilitation Sciences Research (CRSR) and Erik J. Wolf, PhD, of the DOD-VA Extremity Trauma and Amputation Center of Excellence (EACE), both located at the Walter Reed National Military Medical Center conducted a retrospective analysis of biomechanical gait data on 20 patients with unilateral transfemoral amputation, as well as 20 uninjured controls.
“We aimed to quantify mediolateral joint powers at the low back in this population, since joint powers are commonly used to understand the flow of mechanical energy (i.e., generation or absorption) and infer the causes of segmental motions,” Hendershot told O&P Business News.
During each gait evaluation, participants walked at a self-selected speed between 1.25 meters and 1.40 meters per second without assistive devices or powered prostheses, across a 15-meter level walkway. A camera motion capture system was used to track full-body kinematics, while force platforms embedded within the walkway recorded ground reaction forces. Mediolateral joint powers were determined as a product of the net coronal joint moment at L5/S1 and relative joint angular velocity.
The researchers identified four phases of positive joint power in people with transfemoral amputation, which were distinct from those in uninjured controls. The phases taking place before the heel strike support increased trunk movements as an active movement strategy. The power phases occurring during stance help to return the trunk toward an upright posture for subsequent steps while the lateral bend moment at L5/S1 still is acting opposite to the support limb. The final power phases also may assist hip musculature in controlling pelvic tilt while facilitating adequate toe clearance during contralateral swing.
“While the joint powers among persons with transfemoral amputation were still relatively small, the distinct phases of positive power in this population are a novel and interesting finding,” Hendershot said.
Additionally, the total generation energies throughout the gait cycle were larger for those with transfemoral amputation than among controls. Two distinct negative power phases at L5/S1 also were found in both groups at the onset of single-limb stance. This finding was consistent with the idea that eccentric activity of the contralateral trunk musculature helps control pelvic lateral tilt and maintain an upright trunk posture in single-limb stance. Total absorption energies showed no significant difference in the groups.
Trunk movement strategy
Hendershot and Wolf hope their findings will provide an increased understanding of the effect of an active trunk movement strategy on a patient’s metabolic energy expenditures and association with lower back pain.
“Although much more work is needed, these results may guide future developments of rehabilitation regimens targeted at specific trunk postural control strategies in persons with lower extremity amputation, leading to more efficient gait and/or reductions in secondary musculoskeletal complications of limb loss (e.g., low back pain),” Hendershot said.
Several elements of the study could be explored with further research, as the study was limited to young military personnel with traumatic amputations. Additionally, Hendershot said, “The methods used to calculate joint powers cannot distinguish the individual muscle contributions; they represent the net overall response to the joint. Therefore, one important area for future research is collecting muscle activities, as these would improve our understanding of the relationship between muscle input and kinematic output.”
For example, joint powers cannot distinguish responses from active or passive tissues, nor can they differentiate between the contributions of agonist, antagonist or biarticular muscles. Future studies also need to examine other possible contributors to the positive joint powers.
“Joint powers at the low back could be correlated with other factors, such as hip abduction strength and/or residual limb length, to further improve the clinical implications and guide future studies,” Hendershot said.
He added, “I would like to thank my coworkers at Walter Reed National Military Medical Center and the Center for Rehabilitation Sciences Research for their support, as well as the injured service members for their continued interest and participation in our research projects.” — by Amanda Alexander
Disclosure: Hendershot and Wolf declare no financial or personal relationships with other persons or organizations that might inappropriately influence the work presented in the study. This work was supported by the Center for Rehabilitation Sciences Research, of the Department of Physical Medicine and Rehabilitation at the Uniformed Services University of the Health Sciences. The views expressed in the article do not necessarily reflect the official policy of the Departments of the Army, Navy and Defense, nor the U.S. government.