Original article by Jason T. Kahle, CPO, and M. Jason Highsmith, DPT, CP
Translated into plain language by Helen Osborne of Health Literacy Consulting

woman with walkerProstheses, prosthoses, crutches and wheelchairs all must fit right and be used correctly. This article has facts to know.

Solving one problem sometimes causes others. As prosthetists, we see this when amputees ask us to adjust their prostheses. Sometimes, there is no perfect solution and what seems to be an easy fix may lead to other problems.

Requests to cut down prostheses
Below-knee amputees often ask to have the top back section of their prostheses cut back so it is easier to bend the knee. Or they may want the sides cut down to reduce pain or improve how the prosthesis looks (when the socket’s trim line sticks too far up). Likewise, above-knee amputees often want the inside top of the socket cut down to increase comfort and also improve looks.

We agree to these requests if doing so does not hurt the prosthesis’ fit or function. But sometimes this is not in the person’s best interests. Here are some reasons why prostheses are designed as they are:

  • Figure 1The height of the trim line is designed to help amputees with common problems such as muscle weakness, abnormal bone structure, or abnormal bone alignment.
  • A high trim line on the sides of the top can help stabilize (steady) the knee. This is a help for people with short below-knee amputations who need knee support during gait (walking). (See Figure 1).
  • Figure 2 The top of prostheses is kept high and tight on the inside and outside to stabilize the femur and pelvis. This helps people with above-knee amputations who do not have enough muscle support. (See Figure 2).

Prostheses are also designed to help prevent back pain, knee problems, foot injuries, muscle injuries, falls and other common gait problems. Here are some things that can go wrong if the trim line is cut down:

  • For people with below-knee amputations, cutting the trim lines can decrease needed support and increase force to one side of the knee. This can lead to instability and pain. One way to then fix this is by adding a knee orthosis section to the prosthesis.
  • For people with above-knee amputations, cutting the trim lines may affect pelvic stability and lead to extra wear of the hip joint, spine problems, or poor gait habits. To fix these types of problems, the person may need a Silesian belt, hip joint with pelvic band orthosis, extra spinal support, or other orthotic device. Sometimes, the person needs hip or spinal surgery or may lose his or her ability to walk.

Prosthoses: Combined Prostheses and Orthoses
Some prostheses problems can be helped by orthoses (support or bracing to help with weight-bearing, proper body alignment, and protection). It is called “prosthoses” when prostheses and orthoses are used together.

We often find that prosthoses help when people complain that their prostheses are painful, do not fit well, or just “aren’t working.” Here are some ways that joint and corset prosthoses can help:

  • The most common prosthosis is the joint and corset below-knee prosthesis. It is often used by people who have knee-joint problems. It is a below-knee prosthesis that has a socket (interface), pylon (shin), and foot plus orthotic joints with a thigh corset. The orthotic joints help the knee’s ligaments prevent harmful movements and prevent extra stress from going to the anatomic knee (See Figure 3).
  • Another type of joint and corset prosthosis has the top half of a knee orthosis (KO) attached to it. This helps people fully bear weight when they have very short residual limbs with only a small amount of surface area. The KO helps by transferring some weight-bearing to the person’s thigh.
  • People with short residual limbs may also have knee instability. This is because the “lever arm” (part of the limb below the knee) is too short to support the force of weight-bearing. The KO extends the “lever arm” well above the knee to assist against these forces.
  • Prosthoses can also help people who have very short or highly sensitive residual limbs. They help by placing most of the person’s body weight on the thigh through the prosthetic foot rather than the residual limb.

Crutches and Wheelchairs
Crutches, wheelchairs, and other mobility devices need to fit properly and be used correctly. If not, they can harm a person’s nervous, muscular, or skeletal system. Here are some examples:

Axillary crutches. We know that most people do not like learning how to use crutches. But we also know how important this learning can be. As prosthetists, we feel that it is a must, not a luxury, that crutches fit well and people know how to use them. Here are two reasons why:

  • When crutches do not fit well or are not used correctly, they can cause damage to nerves in a person’s armpit (axilla) from excess pressure. This often happens because the crutches are not properly adjusted and allow people to bend (flex) their elbows too much. This puts too much pressure on the armpit, not hands (where the pressure should be).
  • People who bend their elbows too much while walking with crutches, may have a less-efficient gait. But if they know to bend their elbows just slightly, people can use their arm muscles to vary gait speed and change the length of their stride.

Wheelchairs. Just like with crutches, wheelchairs need to fit right and be used correctly. Here are some common problems and ways to avoid them:

  • Wheelchairs are very helpful for moving people around, but most are not designed for long-term sitting. A person may get a deformity or skin break-down if he or she sits too long or is not sitting in the right position.
  • Most wheelchairs have hammock-like seats, limited back support, and improper hip flexion angles. This may cause people to slump forward and have poor spinal posture from pelvis to skull. It can also cause people to over-rotate and over-flex their hips.
  • Footrests need to fit properly. When they do not, the person may slide forward putting extra pressure on the sacrum (tailbone).
  • foot x-raySometimes, people slump forward even though the wheelchair and footrests fit just right. This may be due to muscle weakness, spinal deformity, or other medical problems. A spinal orthosis can help with healthy spinal positioning and weight-bearing. People may also need ankle-foot orthoses (AFOs) to keep their feet flat on the footrests while keeping good body posture. (See Figure 4.)


About the Authors

Jason T. Kahle Jason T. Kahle is a certified and licensed prosthetist/orthotist. He is the director of lower-extremity prosthetics at Westcoast Brace & Limb in Tampa, Florida.
M. Jason Highsmith M. Jason Highsmith is a physical therapist and certified prosthetist. He is an assistant professor in the School of Physical Therapy at the University of South Florida.

Translated from Special Report: Orthotic and Pedorthic Care
When a Prosthesis or Mobility Device Isn’t Enough

Last updated: 01/01/2017
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