What is the fovea capitis?

The fovea capitis is a small, oval-shaped dimple on the ball-shaped end (head) on top of your femur (thigh bone).

Your hip is a ball-and-socket joint. The femoral head is the ball. It fits into a cup-shaped “socket” called the acetabulum in the lower part of your pelvic bone. Together, the femoral head and acetabulum make up your hip joint.

“Fovea capitis” is sometimes confused with the term “fovea capitis femoris.” That’s another name for the femoral head.

The fovea capitis is often used as a landmark when doctors evaluate your hips on X-rays or during less invasive hip surgeries called hip arthroscopy.

What’s the function of the fovea capitis?

The fovea capitis is the site where the ligamentum teres (LT) resides. It’s one of the large ligaments that connect the femoral head to the pelvis.

This ligament is also called the round ligament or the ligament capitis femoris.

It’s shaped like a triangle. One end of its base is attached to one side of the hip socket. The other end is attached to the other side. The top of the triangle is shaped like a tube and attached to the femoral head at the fovea capitis.

The LT stabilizes and carries the blood supply to the femoral head in newborns. Doctors used to think it lost both of these functions by the time we reached adulthood. In fact, the LT was often removed during open surgery to repair a hip dislocation.

Doctors now know that along with the three ligaments surrounding your hip joint (together called the hip capsule), the LT helps stabilize your hip and keep it from pulling out of its socket (subluxation) no matter how old you are.

Its role as a hip stabilizer is especially important when there’s a problem with your hip bones or surrounding structures. Some of these problems are:

  • Femoroacetabular impingement. Your hip joint bones rub together because one or both have an abnormal irregular shape.
  • Hip dysplasia. Your hip dislocates easily because the socket is too shallow to completely hold the femoral head in place.
  • Capsular laxity. The capsule becomes loose, which leads to overstretching of the LT.
  • Joint hypermobility. The bones in your hip joint have a larger range of motion than they should.

The LT contains nerves that sense pain, so it plays a role in hip pain. Other nerves help make you aware of your body position and movements.

The LT also helps produce the synovial fluid that lubricates the hip joint.

What are the most common fovea capitis injuries?

In a 2018 review article, researchers estimate up to 90 percent of people who undergo hip arthroscopy have an LT problem.

About half of LT problems are tears, either complete or partial. The LT can also become frayed rather than torn.

Synovitis, or painful inflammation, of the LT makes up the other half.

LT injuries can occur alone (isolated) or with injuries to other structures in your hip.

What causes injuries to the fovea capitis?

Severe traumatic injuries can cause an LT injury, especially if it causes hip dislocation. Examples include:

  • a car accident
  • a fall from a high place
  • injuries from high-contact sports like football, hockey, skiing, and gymnastics

Frequent, recurring microtrauma due to capsular laxity, joint hypermobility, orfemoroacetabular impingement can also case an LT injury.

How are injuries of the fovea capitis diagnosed?

LT injuries are hard to diagnose without actually seeing it with arthroscopic or open surgery. This is because there aren’t any specific signs or symptoms that occur when it’s present.

Some things that might make your doctor consider an LT injury are:

  • an injury that occurred while your leg was twisting or you fell on a flexed knee
  • groin pain that radiates to the inside of your thigh or your buttocks
  • your hip hurts and locks, clicks, or gives out
  • you feel unstable when squatting

Imaging tests aren’t very helpful for finding LT injuries. Only about 2 percent get diagnosed because they were seen on an MRI or MRA scan.

LT injuries are most often diagnosed when your doctor sees it during arthroscopy.

What’s the treatment for fovea capitis injuries?

There are 3 treatment options:

  • steroid injection into your hip for temporary pain relief, especially for synovitis
  • removing the damaged LT fibers or areas of synovitis, called debridement
  • reconstruction of a completely torn LT

Surgical repairs are usually performed arthroscopically, which works well no matter what caused the injury.

The treatment you need will depend on the type of injury.

Partial tears and frayed LTs are usually treated with arthroscopic debridement or radiofrequency ablation. That uses heat to “burn” and destroy the tissue of the damaged fibers.

One 2014 study showed more than 80 percent of people with an isolated LT injury improved with arthroscopic debridement. About 17 percent of the tears reoccurred and needed a second debridement.

If the tear is complete, the LT can be surgically reconstructed.

The cause of the injury is also treated when possible. For example, tightening the capsule ligaments can prevent another tear if it was caused by stretched ligaments, loose hips, or hypermobility.

The takeaway

The fovea capitis is a small, oval-shaped dimple on the ball-shaped end of the top of your thigh bone. It’s the spot where a large ligament (the LT) connects your thigh bone to your pelvis.

If you experience a traumatic event like a car accident or a major fall, you may injure your LT. These types of injuries are hard to diagnose and may require arthroscopic surgery to diagnose and repair.

Once treated with debridement or reconstruction, your outlook is good.