Thomas Test

The Thomas Test evaluates the length of several muscles that cross the hip joint. The three primary muscles assessed by the Thomas Test are the iliopsoas muscle complex, the tensor fascia lata and the rectus femoris. Shortness in these muscles can affect the range of motion in the hip, knee and spine and can play a role in pain and dysfunction in these areas.

When it comes to the care of musculoskeletal injuries of the lower back, hip and leg, proper assessment of the hip joint complex is imperative. There are many tests and measures designed to evaluate muscle strength, muscle length and joint range of motion that can provide a target for treatment.

In this article we will discuss the anatomy of the muscles involved in the Thomas Test, the procedure for performing the Thomas Test and review how to interpret and document the results.

A review of the anatomy

To utilize and interpret the Thomas Test correctly, one must understand the musculoskeletal anatomy of the pelvis, hip and femur.

Let’s review the anatomy of the three primary muscles that are assessed by the Thomas Test:

• Iliopsoas muscle complex: The iliopsoas muscle complex is composed of two separate muscles: the iliacus and the psoas major muscles. The psoas major originates from the transverse processes and lateral vertebral bodies of L1-L4 or T12-L5. The iliacus originates within the upper two thirds of the iliac fossa. These two muscles join together and insert on the lesser trochanter of the femur. Their primary function is to flex the hip but they also contribute to hip external rotation. Iliopsoas is a single joint muscle because it only crosses a single joint–the hip joint.

• Rectus Femoris: Rectus femoris originates on the anterior inferior iliac spine (AIIS) of the ilium and inserts at the patella and the tibial tuberosity along with the vastus lateralis, vastus medialis and vastus intermedius. This is a two-joint muscle as it crosses both the hip joint and the knee joint and thus acts on both. It acts as a flexor of the hip joint and an extensor of the knee joint.

• Tensor Fascia Lata: The Tensor Fascia lata (TFL) originates from the anterior superior iliac spine (ASIS) then descends inferiorly between and attaches to the deep and superficial fascia of the iliotibial band which inserts at Gerdy’s tubercle distal to the knee joint.

It lies superficial to the greater trochanter on the anterolateral aspect of the thigh. The TFL works in conjunction with several muscle groups to move and stabilize the hip and knee. It assists with internal rotation, abduction and flexion of the hip. It also works at the knee to laterally rotate the tibia, stabilize the knee in extension and assist with knee flexion beyond 30 deg. Though the muscle itself only crosses the hip joint, because of its insertion and effect on the IT band, the TFL is considered a two joint muscle.

Other muscles to consider

While the iliopsoas, rectus femoris and TFL are the three muscles primarily measured during the Thomas Test, it is important to remember that there are several other muscles that also cross the hip that could impact these results. The adductor longus, brevis and magnus muscles, the pectineus muscle and the sartorius muscle all cross the hip joint, and if significantly shortened, could contribute to abnormal results in the Thomas Test.

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How to perform the Thomas Test

To perform the Thomas Test correctly, explain these steps first to the patient and then follow them in sequence:

1. Ask the patient to stand at the end of an adjustable table
2. Raise the table height until the edge of the table is just below the patient’s gluteal fold
3. Reach with one arm around the patient’s back and the other beneath their knees and guide them back into supine with their knees toward their chest. Note: if your patient has good balance they can raise one leg and hug the knee toward their chest as you lower them.
4. With the hips still flexed, palpate the pelvis or lumbar spine and flex/extend the hips to achieve lumbar neutral. Note the degree of hip flexion needed to achieve this position
5. Either have the patient hold their non-test leg at that same angle of hip flexion or stabilize it on your side or hip as you begin to lower the test leg toward the ground
6. Do not allow the non-test leg to move out of its original position as it will change the results of the test
7. Slowly lower the test leg toward the ground until it comes to a natural resting position
8. Observe the position of the test leg to determine if any muscle shortness is present

Note, this test should not be performed on a patient with a posterior hip replacement or a lower extremity fracture and should be used with caution on those with acute lumbar instability or a suspected hip flexor injury.

Interpreting results of the Thomas Test

By observing the position of the test thigh and flexion angle of the test knee, you can determine where muscle length impairments exist:

• Normal Test: Back of the test thigh rests on the table and the knee flexes to ~80 degrees

• Shortness of one joint hip flexors (iliopsoas): Back of thigh rests off the table and knee flexes to >80 degrees

• Shortness of two hip flexors (rectus femoris): Back of thigh rests on table but knee flexion angle is <80 degrees

• Shortness of one and two joint hip flexors (iliopsoas and rectus femoris): Back of thigh rests off the table and knee flexion angle is <80 degrees

• Shortness of TFL: Abduction of the thigh as it extends, lateral deviation of the patella. Internal rotation of the thigh. If ab/adduction is prevented when thigh is extended, the knee will extend instead

Taking measurements

While observation of hip and knee angles is enough to tell you which muscles are shortened, taking goniometric measurements turns this into a measurement you can track. To help with intrarater reliability, after determining which muscles are shortened, place the non-test hip at 90 degrees flexion and take your measurements of the test leg in this position. This allows you to standardize the position of the pelvis each time you measure so you can be sure any changes you see are accurate.