Ischial Tuberosity 101

You’re walking for a long time with your new above-the-knee (AK) prosthesis, and you notice pain in the buttocks area. The pain you're feeling could be related to the ischial tuberosity in your pelvis. 

So, what is the ischial tuberosity? And how can the pain surrounding this bone be avoided?

Ischial Tuberosity: What is it?

Your prosthetist can refer to the ischial tuberosity as your sitting or seat bone. This term comes from the fact that the ischial tuberosity absorbs your weight when you sit or wear your above-knee (AK) prosthesis.

However, if you continuously feel discomfort in this area, regardless of how new or old your prosthesis is, you may have an irritated ischial tuberosity or an inflammation of the ischial bursa. The ischial bursa is a fluid-filled sac located between the ischial tuberosity and the tendons that connect the hamstring muscle to the bone. Severe pain or inflammation in this area is called ischial bursitis, which is also known as weaver’s bottom or tailor’s seat.

The anatomy of ischial tuberosity

The ischium refers to the curved bone that makes up the bottom of your pelvis. And the ischial tuberosity refers to the rounded bone that extends from your ischium. 

Your hamstring—a muscle in the back of your thigh—is connected to the ischial tuberosity by three tendons. You can further identify your tuberosity by bending forward at the hip. When you do this, the gluteus maximus muscle moves out of the way and exposes your ischial tuberosity. 

This movement of large muscles groups explains why those above-knee amputees with muscular limbs struggle with deep ischial seats within a prosthetic socket design. For some, deep ischial seats can irritate the origin point of your hamstring from constantly sliding over deep seats when your hip flexes and extends. 

Ischial bursitis

Another thing that you have watch to out for are the bursas, which are fluid-filled sacs that act as the cushion between tendons and bones in joints. These sacs can be found in all the joints within your body. If one of these bursas becomes inflamed, this very uncomfortable condition is referred to as bursitis.

In some cases, active people who wear an ill-contoured socket can eventually experience bursitis. A bursa can become irritated from constant pressure. In particular, sitting on a deep, hard surface within your prosthetic socket can irritate your ischial bursa, causing ischial bursitis.

Symptoms that you may have ischial bursitis include:

- Aching or stiffness in your pelvis

- Pain when you take your seat

- Trouble sleeping on your prosthetic side

- Redness or swelling around the bursa

Diagnosing ischial bursitis starts with a visit to your prosthetist to have your socket along the ischial area checked. If upon examination your prosthetist determines that your socket is contoured well around your ischium, they may suggest visiting a physician for an X-ray. Your physician may want to take a small fluid sample from the affected bursa for further analysis.

How to relieve pain in the ischial tuberosity

Bursitis usually resolves on its own with proper rest. However, ischial bursitis may take longer to heal since it’s hard to avoid ischial pressure when using your prosthesis, considering this bone is important in providing side-to-side stability. As you recover, there are several things you can do to manage discomfort in the area.

Socket Contours

One way to reduce pressure over your ischial tuberosity is by having the shape of the ischial area of your prosthetic socket adjusted. This is ideal since everyone’s anatomy is unique, requiring a socket that can contour around the different curves and angles of the pelvis.

For those AK amputees with powerful hamstrings and glutes, they require more refined and less dramatic contours around the ischium. This is because it's difficult for the tendons of these powerful muscles to slide continuously over deep shelves and steep angles.

Meanwhile, amputees with less muscular residual limbs—who are considered by prosthetists as more “skeletally weight-bearing”—can benefit from more substantial ischial seats (shelves), as well as gel or foam padding to absorb repetitive shock.

Exercise

Another way to relieve ischial tuberosity pain is by strengthening your muscles and improving flexibility through exercise or physical therapy. Climbing stairs is a great exercise—just be sure there are railings for you to hold on to in case the pain affects your balance.

Stretching exercises can also help increase flexibility in your hamstring, as well as relieve pressure on your ischial bursa. Here are some stretches that you can include in your daily routine:

a. Gluteus Stretch

i. Lie on your back, with your head supported by a cushion. Then, bend one knee.

ii. With both hands around the knee, pull the knee slowly toward your chest. Hold this position for 5-10 seconds.

iii. Slowly straighten your leg. Do the same with your other knee. 

iv. Repeat 5-10 times.

b. Piriformis Stretch

i. Sit on the floor and extend both legs. 

ii. Cross one leg over the other. Put your foot along the opposite knee.

iii. With your opposite hand, gently pull your bent knee across the middle of your body. Hold this position for 10-30 seconds. You should feel a stretch in the muscles of your outer thigh.

iv. Repeat with the other leg.

In Summary

Your ischial tuberosity is the lower part of your pelvis. It's sometimes referred to as your sit or seat bone. Two of its functions is to absorb your weight when you sit and provide side-to-side stability when you're in "single limb support" phase of walking. However, you can experience pain, especially when a nearby bursa (fluid-filled sac) becomes inflamed and causes ischial bursitis. While ischial bursitis usually resolves on its own, you can also rely on over-the-counter pain relievers, prosthetic adjustments, as well as gentle stretching exercises to help ease the discomfort.