Ischial Tuberosity – Definitiion, Anatomy, Causes, Symptoms, Fracture treatments

What is Ischial Tuberosity: Definition?

The term Ischial Tuberosity is made up of two words, namely Ischial (derived from Ischium, a pelvic bone) and tuberosity (tumor or lump). Collectively, it refers to tumor, lump or protrusion on the pelvic bone Ischium.

Ischial Tuberosity Synonyms

The Ischial Tuberosity is known by several other names such as, sit bones, sitting bones, tuber ischiadicum or tuberosity of theischium.

Location of Ischium Tuberosity

Ischium Tuberositities are bony protrusions that are situated on the posterior side (back) side of the hip bone ischium.
Location of Ischial Tuberosity

Anatomy of Ischial Tuberosity

To better understand the term Ischial Tuberosity it is necessary to understand some anatomical features of hip bone. Hip bone is made up of three main bones namely Ischium, Ilium and Pubis.  Ischium forms the lower and back part of the hip bone and located beneath the ilium and at the back of the pubis. Ischium is made up of three parts namely the body, the superior ramus and the inferior ramus. Now it is easy to understand the term Ischial Tuberosity which means “a bony protrusion or swelling on posterior (back in position) of the superior ramus of the ischium (Have a look on the picture to understand more precisely).
Anatomy of Ischial Tuberosity

Structure/division of Ischial Tuberosity

The Ischial Tuberosity is mainly composed of two different parts that is a lower, rough triangular shape part, and an upper, smooth, quadrilateral part. These parts are further subdivided into different subparts:

  • The lower triangular part is split by a longitudinal ridge or crest that comes across from base to top and divides the lower part into an outer and inner part.  
  1. The outer part shows origin of adductor magnus. It provides an anchor that helps to connect the thigh muscles known as adductor magnus to the Ischial Tuberosity.
  2. The inner part shows origin of sacrotuberous ligament. It gives attachment to the pelvic sacrotuberous ligament.
  • The upper  part  is split by an oblique downward and outward ridge into two parts:
  1. The upper and outer area shows origin of semimembranosus. It is associated with the hamstring muscle known as semimembranosus.
  2. While the lower and inner part shows origin of semitendinosus and long head of biceps femoris. This part is associated with the head of thigh muscles known as biceps femoris and the semitendinosus.

Structure of Ischial TuberosityStructure/division of Ischial Tuberosity

Ischial Tuberosity Function

Ischial Tuberosity is an anatomical term that is used to define part of the hip bone which holds or bears maximum body weight during sitting posture, thus helps in sitting. During standing position (upright posture), Ischial Tuberosity is completely covered by extensor gluteal muscle of the hip known as gluteus maximus. However, during sitting glutel maximus leaves Ischial Tuberosity completely free to stabilize and hold the body weight.

Ischial Tuberosity Function

Size of Ischial Tuberosity

The size or width of Ischial Tuberosity or sit bones depends upon bony architecture of pelvis. In fact, it does not have any correlation with pelvic width or mass that means a big butt can have a narrow sit bones while skinny butt can have a wide sit bones. The size of Ischial Tuberosity varies from individual to individual. Usually, sit bones are only 10-12 cm or in other words 4-5 inches in width. A narrow sit bone width is usually in the range of 10 cm or less, while medium range 10-13 cm and wide range over 13 cm.

Size of Ischial Tuberosity

Measurement of Ischial Tuberosity Width

There are several ways to measure the width or size of sit bones or Ischial Tuberosity. Usually, it is measured to get a perfect saddle for your bike for better comfort and easy drive. One can measure the size of sit bones by following ways:

  1. Use of gel pads, which is easily available on medical shops or bike shops. What you have to do is simply sit onto them to measure the distance between your sit bones.
  2. The process does not require any special-purpose equipment and you can do it at home too. What you require is a small piece of aluminium kitchen foil that can easily be placed on a carpeted stair or coffee table. Next, carefully sit on the foil as you sit when you ride (riding position) and lift your feet. Once you do this, it leaves an impression of your sit bones on the foil. The deepest impression helps the measurement of sit bone width easily.
  3. The measurement can also be performed with two small erasers by putting them on a chair so that one can sit on them with his/her sit bones.
  4. Alternatively, a fresh piece of ribbed or grooved cardboard can be used. Put the cardboard on a hard surface (i.e. carpeted stair or coffee table) and sit down in riding position.

Associated Medical Conditions with Ischial Tuberosity

The Ischial Tuberosity or sit bones are strong, widening that frequently hold body weight when one is sitting. Ischial Tuberosity is attached to various pelvic and thigh muscles i.e. adductor and hamstring muscles, sacrotuberus ligaments. Ischial Tuberosity is susceptible to a wide variety of physical exertion caused by any activity that directly or indirectly (by means of associated muscles) affects them. Following is a list of different illness or ailments associated with Ischial Tuberosity:

Ischial Tuberosity pain

The best way to describe Ischial Tuberosity pain is “sharp, pain in the butt “as the pain experiences in the base of the buttock. The pain feels like a dull ache and spread to the larger area than the sit bone itself. The pain becomes more severe with prolonged sitting, running and folding forward. In more severe cases, Ischial Tuberosity becomes tender, swollen and sensitive to touch.

  • Ischial Tuberosity pain is a common problem that can occur in any individual at any age.
  • It commonly occur in sportspeople and athletes as they participate in various physical activities that cause stress (strain or injury) on sit bones and associated muscles i.e. running, over stretching (tearing), jumping, weight lifting, stretching, soccer, cycling, skating,  etc.
  • It can also occur by yoga especially if overdoing forward bends.
  • All these activities put forth constant strain on the muscles of the legs, which may result in injury, inflammation, muscle pull, avulsion fracture, ligament tearing and muscle detachment.
  • In some cases, Ischial Tuberosity pain can occur with wrong or incorrect posture while sitting or working for prolonged duration of time.

Ischial Tuberosity avulsion fracture

    1. The Ischial Tuberosity avulsion fracture (fragment of bone is pulled away from the rest of the ischium bone) is a fracture of the ischium that occurs due to acute hamstring injuries i.e., by a ligament or tendon as a result of injury.
    2. In most of the cases the causes of an avulsion fracture is trauma such as car accident or sport injury, high speed impact or collision with other objects or surfaces, people, or due to a fall.
    3. The key symptoms of Ischial Tuberosity avulsion fracture comprise pain in the buttocks as well as in surrounding area such as groin area. The pain is aggravated and prolonged during movement and surrounding area becomes tender to touch and becomes swollen.
    4. Most common Ischial Tuberosity avulsion fractures are linked with acetabular fractures and affect the posterior column.

Ischial Tuberosity avulsion fracture

Ischiofemoral impingement syndrome

Ischiofemoral impingement syndrome is known as painful arc in which ischium and femur muscles get irritated and inflamed (impingement) and causes hip pain. Due to impingement of ischium and femur, the space between the Ischial Tuberosity and the femur narrow down and causes a squeezing of the soft tissue between the bones. The ischiofemoral impingement is caused by a combination of multiple factors such as

  1. Joints instability (hip instability and pelvic/spinal instability)
  2. Physical trauma (extreme hip motion or over stretching)
  3. Abductor/adductor imbalance
  4. Ischial Tuberosity enthesopathies (stress reaction on the ligament and tendon attachment to the bone)
  5. Pain caused by post surgical procedure
  6. Tumors and other pathologies

Ischiofemoral impingement syndrome

Ischial Bursitis

Ischial Bursitis is inflammation of luid-filled sac (countering friction at a joint also known as bursa) located between the Ischial Tuberosity and the tendon of a hamstring muscle. It is caused by its own or in concurrence with hamstring tendinitis (inflammation of tendon). The symptoms mainly involved are pain and tenderness at the Ischial Tuberosity. The pain also occurs during stretching the hamstring muscles as well. The pain is experienced following a sprinting training session and become more aggravated with prolonged sitting.

Ischial Bursitis

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