3 things to watch for in athletes with femoroacetabular impingement

 2003. REUTERS/Patrick Price

Femoroacetabular impingement (FAI) primarily strikes young male athletes. The syndrome is often best managed with surgical correction. However, it’s important to understand how FAI affects the biomechanics of those who try a conservative approach.

Researchers at Marquette University realized that gait assessment alone doesn’t mimic the extreme hip motion needed in sport(1). Therefore, they enrolled 14 people in a cross-sectional, case-controlled study with two independent variables to help understand the biomechanics in subjects with FAI. Half of the participants had no hip pain. The other half received a diagnosis of FAI based on subjective complaints, clinical tests, radiographic and MRI findings, and pain relief in response to an injection into their hip joint.

Using video motion analysis and force plate measurements, the researchers evaluated each subject while performing a double-leg and a single-leg squat. They found that all subjects shared similar kinematics during the double-leg squat. However, those diagnosed with FAI demonstrated six degrees less hip adduction and four degrees less thigh adduction during the single-leg squat than those without hip pain.

Measurements of hip kinetics found that those with FAI had a 30% reduction (normalized to body weight) of their hip abduction moments than the control subjects during a single-leg squat. The FAI subjects also had significantly lower hip extension moments during the single-leg squat (70%) and the double leg squat (20%) when normalized to body mass. Additionally, those with hip pain performed the single-leg squat much slower than those without pain.

Practical implications

The double-leg squat is an exercise typically used for hip strengthening. Those with FAI may be able to complete this exercise with relatively few symptoms and apparent deviations. However, compensations and deviations become more apparent when the hip motion and strength are isolated to one side during a single-leg squat.

The single-leg squat isolates the hip motion and exaggerates the bony impingement between the femur and the acetabulum. An athlete with FAI may perform the exercise more slowly, as did the subjects in the study, to prevent the knee and femur from collapsing medially and causing pain. A lack of strength in the hip abductor and extensor muscles may explain the decreased force moments demonstrated in the study. Or, pain caused by a change in joint position upon activation of these muscles may have prevented their full use. Notably, the hip abductor and extensor muscles act eccentrically to control joint movement(1).  Slowing down the squat would also decrease the force production needed by these muscles. Clinicians should, therefore, work on strengthening these muscles eccentrically within a pain-free range and position.

The single-leg squat may be a helpful functional test of improvement in athletes with FAI. Watch for:

1. Deviations in the painful hip, such as decreased abduction, during the single-leg squat movement.

2. Slower execution of the movement on the affected side than the non-painful side.

3. Weakness or delayed recruitment of hip abductor and extensor muscles on the painful side.


  1. JOSPT. 2019 Dec;49(12):908-916
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