Northwestern University Feinberg School of Medicine

Northwestern University Prosthetics-Orthotics Center

Study of Residual Limb/Prosthetic Socket Compliance in Transtibial Amputees

Principal Investigator: Steven A. Gard, PhD

Student Investigator: Erin Boutwell, MS

Co-Investigators: Andrew Hansen, PhD; Rebecca Stine, MS; Kerice Tucker, BS

Funded by: Department of Veterans Affairs; National Science Foundation Graduate Research Fellowship

Status: Completed

Purpose

Shock absorption is a critical consideration for lower-limb prosthesis users. The able-bodied locomotor system is capable of providing effective shock absorption through compression of soft tissues, kinematic adaptations in the lower limb and pelvis, and eccentric muscle contractions. In individuals with a transtibial amputation, the structure of the residual limb has been drastically altered, and many of the mechanisms utilized by able-bodied individuals are either no longer present or compromised by the amputation. Thus, the prosthetic limb must incorporate appropriate shock absorption to promote comfort and reduce pain arising from large impact forces during gait.

As a result, many prosthetic components have been designed or updated to assist in restoring shock absorption to the prosthetic-side limb. These components include energy-storage-and-return (ESAR) feet and shock-absorbing pylons. The effect of these shock-absorbing prosthetic components has been investigated to assess their influence on walking speed, energy consumption, and ground reaction forces, but no consistent difference related to shock absorption has been documented for any intervention type. One hypothesis is that the compliance of the components is much lower than that of the soft tissue within the residual limb-prosthetic socket interface. Thus, the soft tissue compresses more substantially during loading and thereby dictates the overall compliance of the limb.

The mechanical interaction between the prosthetic socket and the residual limb should be further examined to analyze the contribution of residual limb soft tissue to total limb compliance. One way to accomplish this objective is to introduce additional compliance at the limb-socket interface. If the low stiffness of the residual limb soft tissue is driving the compliance of the prosthetic-side limb, then reducing the stiffness further by introducing a thick gel liner may result in considerable changes to overall limb compliance and the shock-absorbing capacity of the prosthetic-side limb.

Methods

The effect of compliance at the residual limb-prosthetic socket interface was tested using two thicknesses of gel liner. Eleven subjects with unilateral transtibial amputation participated in a walking and a loading protocol while wearing one of two liners: a thin 3mm liner and a thick 9mm liner. The relative displacement of the socket from the residual limb and a quasi-stiffness measurement of the liner were determined from a coronal-plane side-to-side loading experiment. Subjects also participated in a gait evaluation at slow, normal, and fast freely selected walking speeds; temporal-spatial, kinematic, kinetic, and intrasocket pressure data were acquired and analyzed.

Results

Subjects were divided into three categories: bony residual limbs (BRLs, n=5), average residual limbs (ARLs, n=1), and padded residual limbs (PRLs, n=5). A decreased peak pressure found over the fibular head was significant (p = 0.01). The temporal-spatial data exhibited little difference between the two liner thicknesses for the BRL group, while the PRL group experienced an increase in walking speed (p = 0.04) and a decrease in prosthetic-side stance phase duration (p = 0.01) with the 9mm liner. No differences between the two liners were found in stance-phase knee flexion or prosthetic-side pelvic obliquity range of motion, both of which are anatomical shock-absorbing mechanisms. An overall increase in vertical ground reaction force peaks were found (p = 0.02), but no other kinetic changes were noted. A small and statistically insignificant reduction in quasi-stiffness was observed with the 9mm liner.

PRL subjects may be more accustomed to compliance at the limb-socket interface and may therefore be able to take advantage of the compliance offered by the 9mm liner. While BRL subjects indicated a reduction of pain with the 9mm liner, their unaltered gait parameters may suggest a perception of instability associated with more relative motion between the socket and the limb. It was concluded that the greater compliance afforded by the 9mm liner may allow increased comfort within the limb-socket interface through redistribution of peak pressures in persons with bony residual limbs, while individuals with padded residual limbs may benefit from a thicker liner depending on activity level and limb physiology.

Related Publications

Boutwell E, Stine R, Hansen AH, Tucker K, and Gard SA. (2012) "Effect of Prosthetic Gel Liner Thickness on Gait Biomechanics and Pressure Distribution within the Transtibial Socket." Journal of Rehabilitation Research & Development. 49(2): 227-240.

Gard SA, Boutwell EV, Stine RL, Hansen AH, and Tucker KA. (2010) "Study of Residual Limb/Prosthetic Socket Compliance in Transtibial Amputees." International Society for Prosthetics and Orthotics (ISPO) 13th World Congress. May 10-15. Leipzig, Germany.

Boutwell E, Stine R, Hansen AH, Tucker K, and Gard SA. (2010) "Study of Residual Limb-Prosthetic Socket Compliance in Transtibial Amputees." American Academy of Orthotists and Prosthetists (AAOP) Annual Meeting & Scientific Symposium. February 24-27. Chicago, IL.

Boutwell E. (2009) "Study of Residual Limb/Prosthetic Socket Compliance in Transtibial Amputees." Annual Summer Symposium of the Midwest Chapter American Academy of Orthotists and Prosthetists (AAOP). June 12-13. Lake Geneva, WI.

Stine R, Hansen AH, Tucker K, Boutwell E, and Gard S. (2008) "A Preliminary Study of the Effects of Gel Liner Thickness on In-Socket Residual Limb Pressures in Trans-tibial Prosthesis Users." (Poster) 11th EMED Scientific Meeting (ESM). July 28-30. Dundee, Scotland, UK.