Geoffrey Wilkin et al., 2017

This is a summary of a research article that describes un updated definition of hip dysplasia and delves into the different ways that hip dysplasia can present and be classified. You can read the written summary or visit our video:

The goals of this article were to:

1) Provide an updated definition for hip dysplasia

2) Provide a new classification system for hip dysplasia based on current understanding of different types of hip structure and patterns of instability

Hip dysplasia is even more complex than we thought!

In the past, a hip dysplasia diagnosis in teens and adults was mostly based on how well the head of the femur (ball) was covered by the acetabulum (socket) on the side on a 2D pelvis x-ray. This measurement is called the lateral center edge angle or “LCEA.” Normal LCEA is > 25 degrees.

When the LCEA is decreased with dysplasia, there is increased stress on the labrum and the joint. This can cause pain and early joint damage and arthritis.

However, we now have more advanced 3D imaging like Computed Tomography (“CT”) that helps surgeons understand hip dysplasia in new ways. It turns out there are different kinds of hip dysplasia! Some people may have instability from dysplasia even with a normal lateral center edge angle.

The definition for hip dysplasia is expanding, and there is still some lack of consensus on what imaging measurements are most important. Positioning during x-rays and other tests is also important since this can impact measurements.

Surgeons may look at a lot of different x-ray measurements when trying to determine if someone has dysplasia. Many also now use 3D CT or other advanced imaging in addition to x-rays.

Some of these measurements give information about how the socket is positioned and how it is shaped. Other measurements give information about how well the socket covers the femur on the side, front, and back.

The authors of this article propose a hip dysplasia classification system based on patterns of instability. It is called the “Ottawa Classification for Symptomatic Acetabular Dysplasia” and includes 3 classifications.

These include:

1) Anterior (front) instability

2) Posterior (back) instability

3) Lateral (side)/global (all around) instability

What are some of the differences between these types of dysplasia?

Anterior Instability: People with anterior instability may have a normal LCEA but have decreased coverage in the front of the hip and may have increased coverage in the back of the hip. Some patients have hips that developed this way and others may develop anterior instability after hip arthroscopy “scopes,” especially if too much of the socket was shaved down during surgery or if the capsule was not repaired or did not heal.

People with anterior instability may experience pain or apprehension when the hip is extended behind the body.  They may complain about pain when taking longer strides and when wearing high heel shoes.

Posterior Instability:  People with posterior instability may have a normal LCEA but have decreased coverage in the back of the hip. Some people with posterior instability may have sacroiliac (SI) joint pain, piriformis syndrome, or sciatic nerve pain.

People with posterior instability may experience pain in the front or the back of the hip. Pain may be increased when the hip is flexed and rotated in. They may complain about pain when doing activities like going up stairs or walking up hills. This can often mimic symptoms of hip impingement. This is one of the rare instances where dysplasia and impingement occur together.

Lateral or “Global” Instability: This is the most “traditional” type of dysplasia. People with lateral/global instability have a decreased LCEA and may show other signs of dysplasia on x-rays. Some may also have relatively decreased coverage on the front or back of the hip depending on how the socket is aligned.

People with lateral or global instability may experience general activity-related pain and may experience muscle fatigue and overuse symptoms, especially in the abductor muscles on the side of the hip. They may also have symptoms of anterior instability.

How can I figure out what kind of hip dysplasia I have?

Your surgeon can help you figure out what kind of dysplasia you have. They will do this by:

• Asking about your symptoms
• Physical examination
• Imaging such as x-rays and 3D CT Scans

Why is it important to know what kind of dysplasia I have?

This information can:

1) Help decrease misdiagnosis

2) Help your surgeon plan how to position the socket for a PAO or similar surgery

3) Help your physical therapist know what soft tissue structures and motions may need extra work before and after surgery

How is hip dysplasia treated?

While some people may have improvements in their hip dysplasia symptoms with physical therapy and other non-surgical treatments, others may benefit surgery. Hip preservation surgery like periacetabular osteotomy (PAO) can change the hip alignment to improve hip coverage and stability and protect the native hip joint. Total hip replacement may also be an option for people who are not good candidates for PAO surgery.

Reference:

Wilkin GP, Ibrahim MM, Smit KM, Beaulé PE. A Contemporary Definition of Hip Dysplasia and Structural Instability: Toward a Comprehensive Classification for Acetabular Dysplasia. J Arthroplasty. 2017;32(9S):S20-S27. doi:10.1016/j.arth.2017.02.067