Prosthetic Categories

Benefits of Using an Adjustable Subischial Above-Knee Prosthesis

    The problem with conventional prostheses is that they come with a hard prosthetic socket that cannot be easily adjusted to fit residual limb changes. But in the first year after limb loss, the residual limb is expected to change significantly in size and shape. In addition, limb volume fluctuates daily for many individuals, particularly those with heart and renal disease.

     The new adjustable subischial prosthetic leg could be better for above-knee amputees.

    Although there are ways to accommodate residual limb volume changes while using hard prosthetic sockets, adding or removing prosthetic sock layers is often time-consuming. And if the individual isn’t wearing adaptive clothing, adjusting the socket fit will require finding a private area to remove their clothing before they begin adjusting the socket.

    Hard prosthetic sockets present not only convenience issues but also comfort problems. According to a U.S. Department of Veterans Affairs survey, 45% of individuals with above-knee limb loss expressed interest in switching to a different socket type. Additionally, 60% of respondents sought care from multiple prosthetists due to dissatisfaction with the fit of their conventional devices or the prosthetic services provided.

    The new prosthetic socket  

    Since around the 1970s, prosthetists have used the quadrilateral socket and ischial containment socket for their patients. However, both sockets are known to restrict the range of motion in the residual limb. So, iFIT Prosthetics, based in Wisconsin, developed an adjustable subischial transfemoral prosthetic limb to enhance user comfort and function.

    The adjustable subischial prosthesis has a unique design different from traditional prosthetic sockets. It is lower in profile and extends up the leg to just below the ischium. This design allows the adjustable socket to grasp the soft tissues firmly but comfortably and provide a stable support base for safe and steady walking.

    The study  

    Eighteen individuals with above-knee limb loss—16 men and two women—tested the new socket. The goal was to examine the practicality of a subischial adjustable socket for people with above-knee limb loss.

    According to the researchers, the participants preferred the subischial above-knee prosthetic limb to the traditional prosthesis. The participants rated the subischial prosthetic as being significantly better in areas such as adjustability, accommodating changes in limb volume, the weight of the prosthesis, standing stability, and providing comfort while sitting and standing.

    In addition, none of the study participants reported skin breakdown, a fall, and other adverse events while using the subischial prosthesis. One study participant even biked for exercise again because the new prosthetic socket improved his sitting comfort.

    During the two-month follow-up, the researchers found that 11 out of the 18 participants wore the adjustable socket often. The six remaining participants reported that they used the adjustable socket along with their regular prosthetic limb.

    Benefits of the subischial prosthesis  

    The research concluded that the adjustable subischial above-knee prosthesis was more comfortable for standing and sitting. The prosthesis was flexible and strong, providing adequate support and compliance for various residual limb circumferences and lengths.

    Another advantage of the subischial adjustable socket is it allows users to fit their prosthesis and begin gait training as soon as their surgical wounds heal. Even patients with bulbous residual limbs and edema can start rehabilitation immediately. They can simply adjust the socket when their limbs mature, and the edema resolves.

    Experts agree that starting walking early after an amputation is beneficial, as it can reduce joint stiffness and muscle weakness and increase the likelihood of using a prosthetic device. A study by Miller et al. showed that getting a prosthetic device within three months after amputation can save up to $25,000 in healthcare costs in the following year. Getting a comfortable and functional prosthetic device quickly is also associated with greater satisfaction, increased usage, and better long-term outcomes.

    Another group that can benefit from using the subischial prosthesis are children with limb deficiencies who have problems with traditional sockets as they grow. They may find relief using the prosthesis, which can be easily adjusted to accommodate their growth.

    The bottom line  

    The researchers concluded that persons with above-knee limb loss could use the adjustable ischial prostheses safely. However, they noted that the small sample size used in the study might not be enough, proposing that a more extensive multi-center study would be best.