When people think about the fit of an above-knee prosthesis, they usually think about walking. Does the socket feel secure? Is the prosthesis comfortable when standing? Does the knee feel stable? Can the person walk without pain?

Those things are obviously important. But there is another part of everyday life that deserves just as much attention: Sitting.

An above-knee amputee may spend hours every day sitting in a car, at work, at the dinner table, on the couch, or in a wheelchair. A prosthetic socket that works well while standing but becomes uncomfortable every time you sit can have a major effect on everyday comfort and prosthesis use.

Research has documented this problem. In one study of active transfemoral prosthesis users, 44% of those using traditional socket prostheses reported discomfort while sitting. The researchers also found that wearing the socket significantly reduced hip range of motion. That is why sitting comfort should be part of the conversation when designing and fitting an above-knee prosthesis.

Why Can an Above-Knee Socket Be Uncomfortable While Sitting?

A transfemoral, or above-knee, prosthetic socket surrounds a large portion of the residual limb and extends high around the upper thigh and pelvis. That height is necessary for several reasons, including suspension, stability, control of the prosthesis, and management of forces while walking. But your body also has to bend at the hip when you sit.

As you move from standing into a seated position, the relationship between your pelvis, residual limb, and socket changes. Areas of the socket that feel completely comfortable while standing may suddenly feel much more noticeable when your hip is flexed.

Research comparing transfemoral socket designs has specifically looked at these challenges because socket discomfort continues to be one of the major concerns reported by prosthetic users.

The Top Edge of the Socket Matters for Sitting Comfort

One of the biggest factors in sitting comfort is the shape of the upper portion of the socket.
Depending on the socket design and the individual patient, the socket may extend upward around areas near the pelvis, including the front of the groin and the area beneath or around the ischium, commonly referred to as the “sit bone.”
When sitting, these areas can experience different pressures than they do while standing.
If the socket edge is too high, poorly shaped, or does not match the person’s anatomy well, the wearer may experience:

• Pressure in the groin
• Pressure underneath the buttock
• Pinching when bending at the hip
• Discomfort around the pelvis
• Difficulty leaning forward
• Difficulty getting comfortable in certain chairs
• A feeling that the socket is pushing upward when seated

The solution is not necessarily to simply cut the socket lower. The upper socket also plays an important role in controlling the prosthesis.
Good socket design is a balance between support, stability, suspension, control, and comfort.

Hip Flexion Is a Big Part of Sitting Comfort

Try sitting in a chair without bending your hip very far. It does not work particularly well. Hip flexion is an essential part of getting into and maintaining a normal seated position.

A transfemoral socket can affect how freely the hip moves. In one study, 37% of the active transfemoral socket users evaluated had less than 90 degrees of hip flexion while wearing their prosthesis. Sitting discomfort was also more common among participants who had less than 90 degrees of hip flexion.

Modern socket design continues to explore ways to provide the stability an above-knee amputee needs while allowing greater freedom of movement around the hip. Research into subischial and other alternative socket designs has specifically examined comfort, mobility, and hip motion as important outcomes.

Why Some Chairs Are Worse Than Others

If you are an above-knee amputee, you may already know that not all chairs are created equal. A socket may feel fine in one chair and terrible in another.

Low Chairs

Low chairs require greater hip and knee flexion to sit down. That can increase pressure around the top of the socket. Deep couches can be especially difficult because your hips sink below your knees.

Hard Chairs

A hard chair provides very little cushioning and may make the rigid edges or contours of the socket more noticeable.

Bucket Seats

Vehicle seats can create their own challenges. Many car seats angle backward or have raised sides. Depending on the socket and the vehicle, this can affect pelvic position and place pressure on different parts of the socket.

Office Chairs

Someone who works at a desk may sit for many hours every day. Even relatively minor pressure can become a major problem when it is present for eight hours.

This is why your prosthetist needs to understand what you actually do during the day, not simply watch you walk down a hallway.

Sitting Unevenly Can Affect More Than Your Residual Limb

Sometimes an uncomfortable socket causes a person to change how they sit. They may:

• Lean toward the sound side
• Slide forward in the chair
• Rotate their pelvis
• Sit toward one edge of the seat
• Keep the prosthetic side farther forward
• Remove the prosthesis whenever sitting for longer periods

Compensations like these may make the socket more tolerable temporarily, but sitting asymmetrically for long periods can place different demands on the pelvis and lower back.

A VA report describing one transfemoral prosthesis user’s experience noted that sitting on a rigid above-knee socket contributed to an uneven seated posture and associated back discomfort.

If you find yourself constantly shifting away from your prosthesis just to sit comfortably, mention that to your prosthetist.

The Socket Has to Do Two Different Jobs

One of the challenges of designing an above-knee socket is that your body asks very different things from it depending on what you are doing.

When you are standing and walking, you want: Control. Stability. Suspension. Security.

When you sit, you want: Flexibility. Space. Hip movement. Comfort.

Those goals can sometimes compete with each other.

A socket that is extremely rigid and supportive may provide excellent control while standing, but certain designs may feel more restrictive while sitting.

A socket that allows greater movement around the hip may feel better during certain activities, but it still has to provide adequate stability and control during walking.

There is no single socket design that is automatically best for every above-knee amputee. A randomized clinical trial comparing different transfemoral socket designs found no single design universally superior for comfort and skeletal movement, reinforcing the importance of matching socket design to the individual patient.

Your Residual Limb Shape Makes a Difference

No two residual limbs are exactly alike. The length and shape of the residual limb, available soft tissue, muscle development, bone structure, skin condition, scars, sensitivity, and other anatomical factors can affect how a socket needs to be designed. A socket that works extremely well for one above-knee amputee may not work well for another.

That is why prosthetic socket design should be individualized rather than based entirely on a standard shape. The goal is to create an interface between the person and the prosthesis that provides the necessary control without creating unnecessary pressure or restricting movement more than necessary.

Socket Fit Can Change Throughout the Day

Even a well-designed socket can become uncomfortable if the fit changes. Residual limb volume can fluctuate, which can change how deeply a person sits inside the socket and where pressure is applied. If the limb sinks farther into the socket than intended, the upper edges of the socket may begin contacting areas differently. If the limb is sitting too high in the socket, other areas may become excessively tight.

Changes in socket fit can affect both walking and sitting comfort. A recent randomized controlled trial evaluating adjustable-volume transfemoral sockets found that socket design and fit can affect comfort and prosthetic utility, although not every socket design worked successfully for every participant.

Again, individualized fitting matters.

Tell Your Prosthetist About Sitting Problems

During a prosthetic appointment, patients naturally tend to focus on walking. But your prosthetist needs to know what happens during the other hours of your day too.

Tell them if:

• Driving is uncomfortable
• Your socket digs into your groin when sitting
• You cannot comfortably sit upright
• You constantly shift toward your sound side
• Your socket presses into your buttock
• You struggle in low chairs
• Sitting causes numbness or tingling
• You develop redness or skin irritation
• You have to remove your prosthesis for sitting comfort
• Your job requires you to sit for long periods

These details can help your prosthetist determine whether adjustments to the socket, alignment, suspension, or another part of the prosthetic system should be considered.

Bring Real-Life Problems Into the Prosthetic Office

One of the most useful things you can tell your prosthetist is: “Here is exactly when it bothers me.”

Maybe it only happens when you drive. Maybe it happens at your desk. Maybe getting into a restaurant booth is difficult. Maybe you are fine walking all day, but sitting through your child’s two-hour baseball game becomes miserable. Those details matter.

Sometimes it can even be helpful to show your prosthetist how you normally sit, how you position your leg in a vehicle, or what motion causes the discomfort. A prosthesis is not designed only for the few minutes you spend walking in a prosthetic office. It has to work in your real life.

Sitting Comfort Doesn’t Mean Giving Up Stability

The goal of socket design is not simply to make the socket loose or remove material anywhere something feels uncomfortable. An above-knee socket still needs to securely connect the person to the prosthesis and allow appropriate control during standing and walking.

Instead, the prosthetist has to determine why the discomfort is occurring. Is it the socket shape? Is the trim line too high in a particular area? Is the person sitting too deeply in the socket? Has residual limb volume changed? Is the socket rotating? Is suspension affecting the position of the limb? Is the alignment contributing to the problem? Is a different socket design worth considering?

Those questions require an individual evaluation.

A Prosthesis Should Work When You’re Sitting Too

Walking is understandably one of the biggest priorities in lower-limb prosthetic care, but walking is only part of life.

You also have to drive to work.

Sit through meetings.

Eat dinner.

Watch your kids play sports.

Travel.

Go to a movie.

Sit on the couch.

Live your life.

If your above-knee prosthesis works well when you are walking but becomes painful or uncomfortable every time you sit, that is worth discussing with your prosthetist.

At Leimkuehler Orthotic-Prosthetic Center, we believe prosthetic care should consider the entire person and the activities they perform throughout their day. Because a successful prosthesis should not only help you get where you’re going. It should also let you sit down comfortably once you get there. Contact us if it’s time to schedule a prosthetic evaluation.