Femoroacetabular Impingement

Other Names for Femoroacetabular Impingement

• Femoroacetabular Impingement Syndrome
• FAI, an English abbreviation for femoroacetabular impingement
• Conflict associated with a cam-type, pincer-type, or mixed-type bone deformity

What is Femoroacetabular Impingement?

Femoroacetabular impingement syndrome is a hip condition characterized by a combination of symptoms, physical examination findings, and a specific bony pattern visible on medical imaging.¹ The femoral head is the rounded end of the thigh bone. The acetabulum is the socket in the pelvis that houses it. Certain shapes of these bones can cause them to come into contact too early during movement, which may limit mobility and cause pain. The same shape may also be present in a person who experiences no pain.²

The hip joint resembles a ball in a socket. The ball represents the head of the femur, and the socket, the acetabulum. Cartilage, a smooth tissue that covers the bone surfaces, facilitates movement. Depending on the shape of the bones and the position of the hip, the neck of the femur—the part that connects the head to the rest of the bone—may come into contact with the edge of the socket sooner.³

This syndrome can affect active adults, particularly athletes, but also less active individuals.¹

Repeated contact can put strain on the cartilage and the labrum—the ring of tissue surrounding the acetabulum—and contribute to damage to these structures.³ The cam shape is associated with an increased riskof hip osteoarthritis, a condition that affects the tissues of the joint. The link to the pincer shape is less clear.⁴ This progression is not inevitable, and treatments for impingement have not been shown to prevent osteoarthritis.¹

What are the types of femoroacetabular impingement?

The three types of femoroacetabular impingement are the CAM type, related to the shape of the femur; the pincer type, related to the coverage provided by the acetabulum; and the mixed type, which combines the two.¹

The "cam" shape refers to a bump or a less rounded area between the head and the neck of the femur. It can cause the femur to come into contact with the edge of the acetabulum when the hip is bent or the thigh is rotated inward. These movements are called flexion and internal rotation.¹

The pincer-shaped acetabulum provides greater coverage of the head of the femur. The rim of the “cup” may then come into contact with the femoral neck sooner during certain movements.¹

The mixed type combines the CAM and pincer forms. Treatment also depends on your symptoms and goals. In a study of 90 hip surgeries performed on 85 patients, outcomes were better for the CAM type alone than for the mixed type after an average follow-up of 32.8 months. This comparison between groups does not allow for predicting the individual outcome of a surgery.⁵

What causes femoroacetabular impingement?

Femoroacetabular impingement results from an interaction between the shape of the hip bones and the movements or positions that trigger symptoms. The shape of the bones influences contact within the joint, but it does not, on its own, explain why a person experiences pain.¹

Bone shape develops primarily during growth. It depends on several factors. A study compared young basketball players to people of the same age who did not play the sport intensively. Its results suggest that sports-related stress during growth may contribute to the formation of a cam bump.⁸

Certain movements or changes in activity may worsen your symptoms, depending on what your hip can tolerate:

• Repeated movements in a position that triggers your pain
• An increase in the duration or number of workouts beyond what your hip can handle
• Sports that require bending or rotating the hip close to its limit

Physical therapy can improve symptoms even if it does not change the shape of the bones. A review of five trials, involving a total of 124 people followed for 6 to 12 weeks, found better outcomes in terms of functional ability. The comparisons favored core strengthening over care without such strengthening, active exercises over care received without active participation, and supervision by a professional over unsupervised care.⁹

What are the risk factors?

Intensive sports participation during growth and certain hip conditions in childhood can contribute to bone shapes associated with impingement. The link between intensive sports participation and the “cam” shape has been studied, in particular, among young basketball players.⁸ However, a cam deformity does not necessarily mean that pain will develop.

• Ice hockey
• Soccer
• Basketball
• Dance (especially ballet)
• Martial arts

The movements in these sports often involve repetitive motions, a bent hip, or rotations. If certain movements trigger your pain, their range of motion—that is, how far you go through the movement—and their frequency can be adjusted in consultation with your physical therapist.¹⁰

Certain childhood diseases can alter the shape of the hip. Impingement is notably described following Legg-Calvé-Perthes disease, which weakens the femoral head during childhood, or following slippage of the femoral head at the growth plate.^{11, 12} Other problems, such as dysplasia—inadequate coverage of the femoral head by the acetabulum—can also cause hip pain or coexist with a cam deformity. Dysplasia and impingement are two distinct conditions associated with osteoarthritis, each requiring appropriate evaluation.^{13, 3}

• Hip dysplasia: the hip socket does not adequately cover the head of the femur
• Congenital hip dislocation: the head of the femur is displaced from its socket at birth
• Legg-Calvé-Perthes disease: a blood circulation problem that temporarily weakens the head of the femur during childhood
• Slippage of the femoral head at the growth plate, known as superior femoral epiphysiolysis

Be sure to mention this history during your appointment. Knowing how it affects the shape and function of your hip will help the team choose the appropriate tests and treatment.³

What are the symptoms of femoroacetabular impingement?

Femoroacetabular impingement often causes pain in the groin, in front of the hip, during certain movements or after prolonged immobility. This location was common in a group of people who underwent surgery for this condition.¹⁴ The pain may worsen when you bend your hip, but symptoms vary from person to person.

• Mainly in the groin (front of the hip)
• May extend toward the buttock
• Can be felt on the side of the hip
• Sometimes in the thigh

• Running
• Walking with long strides
• Do squats by bending at the hips and knees as if you were sitting down, especially when going down very low
• Climbing stairs or hiking uphill
• Sitting for long periods (at work, in the car)
• Getting up from a sitting position

• Stiffness and reduced hip mobility
• A sensation of cracking, "clicking," or "popping" during certain movements
• Feeling of occasional locking
• Difficulty putting on socks or shoes

Some people have a form of cam or pinching that is visible on imaging but causes no symptoms.² This condition alone does not constitute a painful syndrome. In the absence of pain, preventive surgery is rarely indicated; follow-up depends on your specific situation.¹

How is femoroacetabular impingement diagnosed?

A diagnosis of femoroacetabular impingement is based on your symptoms, the results of a physical exam, and imaging studies of the hip.¹ The FADIR test involves bending the hip, bringing the thigh toward the other leg, and rotating it inward. It may reproduce your pain, but it is not sufficient on its own to confirm the diagnosis.¹⁵

• Questions about the location and circumstances of your pain
• Assessment of your hip mobility
• Tests to determine which movements trigger your usual pain
• Assessment of the strength of the muscles that help control the hip

X-rays show the shape of the bones and can help identify other causes of pain, such as osteoarthritis. They are interpreted in conjunction with your symptoms and physical exam. Your healthcare provider may measure, among other things:

• The alpha angle (femur shape)
• The center-edge angle (acetabular coverage)

Magnetic resonance imaging (MRI), a test that uses a magnet to produce detailed images, can help examine the labrum and cartilage. It may be ordered, in particular, when surgery is being considered.³

When to consult a physiotherapist?

A physical therapy appointment is recommended when hip pain persists, recurs, or limits your activities. The physical therapist will assess your symptoms and also look for signs of other problems.

In Quebec, you can see a physical therapist in a private practice without a doctor's referral. If your situation requires a medical evaluation, the physical therapist can refer you to the appropriate care.¹⁶

See a doctor if your groin pain persists, if it limits your sports or daily activities, or if you have difficulty sitting down.

Non-surgical treatments, such as exercises and physical therapy, are generally recommended first. Sufficient improvement may make it possible to avoid surgery.¹⁰ A trial randomly assigned 348 people aged 16 or older to either physical therapy or surgery. These participants did not have osteoarthritis and were considered likely to benefit from surgery. Both groups experienced an improvement in their hip-related quality of life. At 12 months, the average adjusted score favored surgery by 6.8 points out of 100, with a margin of uncertainty ranging from 1.7 to 12 points. Five serious complications were associated with surgery, compared with none in the physical therapy group.¹⁷

Seek medical attention immediately if you experience sudden, severe pain without any injury, if your hip is warm and swollen, or if the skin around your hip changes color. Also seek medical attention if you have hip pain, feel generally unwell, and also have a fever, an unusual sensation of heat or cold, or chills.

Go to the emergency room if you have severe pain after a fall or injury, if you can’t walk or put weight on your leg, or if you experience tingling or a loss of sensation in your hip or leg after an injury.¹⁸

What physiotherapy treatments are available?

Physical therapy combines hip and core exercises, activity modifications, and—depending on your needs—manual mobilization techniques. Active, supervised treatment can improve your symptoms and your ability to perform daily activities.⁹ Mobilization techniques—movements guided by the physical therapist—can complement the program. Their effectiveness on their own has been less well studied than that of programs that combine them with exercises.¹⁰

Your physical therapist will examine your hip and the surrounding areas to determine what is limiting your activities:

• How easily your hip moves in different directions
• Signs of nerve irritation, if your symptoms suggest it
• Movements and positions that are difficult or painful
• Your strength and your ability to maintain balance and control your hips
• The way you walk, run, or perform the movements of your sport

Based on the assessment results, your physiotherapist will be able to:

• Gently guide the movements of your hip with your hands to help relieve pain and make it easier to move
• To give you exercises to strengthen your glutes, hip muscles, and core
• To teach you exercises that will help you coordinate your muscles better during movements
• Help you temporarily modify activities that irritate your hip
• Give you advice for your posture and daily movements

Duration of treatment: The British guidelines often describe a course of 6 to 10 sessions spread over 12 to 24 weeks. They recommend a follow-up assessment after about three months. The number of sessions and the pace of progress are tailored to your needs; there is no one-size-fits-all “optimal” duration.¹⁰

What to do at home?

Home care involves activities you can tolerate, adapted exercises, and temporarily avoiding movements that increase your pain. The goal is to keep moving by adjusting your effort and body positions, and then to gradually progress based on how your body responds.¹⁰

• Swimming, with a style and intensity that don't trigger pain
• Whether you're riding a bike or using a stationary bike, adjust the seat and handlebars to avoid bending your hip too much if that causes pain
• Elliptical trainer
• Moderate walking on flat ground

• Standing with your weight shifted to one hip
• Sitting with your legs crossed
• Performing deep squats
• Forcing your knee towards your chest

If you sleep on your side, you can try placing a pillow between your thighs and knees. Maintain the position that allows you to sleep best, without forcing your hip into a painful position.

• Incorporate walking breaks into your running sessions
• Temporarily reduce the intensity, duration, or number of workouts
• Do glute strengthening exercises regularly
• Avoid movements that reproduce your pain

If changing your activities does not reduce your pain, see a physical therapist.

How long does it take to improve?

An exercise program can improve symptoms within 6 to 12 weeks, but progress varies and may take several months.⁹ A follow-up study found that improvements persisted after a 12-week program: of the 26 initial participants, 19 had not undergone surgery and still reported improved daily and athletic functioning after an average of 4.6 years. However, their athletic performance remained below pre-symptom levels.¹⁹

• The duration of symptoms and their progression since the start of treatment
• The ability to complete the exercises and the challenges encountered
• Your Physical Activity Level
• The intensity of the pain and the activities it limits

A physical therapist can help you maintain an appropriate strengthening routine and gradually resume the activities that are important to you. Follow-up visits allow for adjustments to this routine if pain returns or if your goals change.¹⁰

Hip surgery is generally considered when your symptoms continue to limit your activities despite having tried non-surgical treatment. The right time to seek a surgical evaluation also depends on your examination, the condition of your hip, and your goals.²⁰ Surgery can improve outcomes for some people, but it isn’t necessary for everyone.¹⁷ The decision is made in consultation with your healthcare team after discussing the benefits, risks, and other options.¹

Sources

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2. Frank JM, Harris JD, Erickson BJ, Slikker W, Bush-Joseph CA, Salata MJ, et al. Prevalence of Imaging Findings Suggestive of Femoroacetabular Impingement in Asymptomatic Volunteers: A Systematic Review. Arthroscopy. 2015;31(6):1199-204. (Back to sections: 1, 2, 3, 4)
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5. Said HG, Masoud MA, Morsi MMA, El-Assal MA. Outcomes of hip arthroscopy for femoroacetabular impingement: The effect of morphological type and chondral-labral damage. SICOT J. 2019;5:16. (Back to section: 1)
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7. Morales-Avalos R, Tapia-Náñez A, Simental-Mendía M, Elizondo-Riojas G, Morcos-Sandino M, Tey-Pons M, et al. Prevalence of Morphological Variations Associated With Femoroacetabular Impingement According to Age and Sex: A Study of 1,878 Asymptomatic Hips in Nonprofessional Athletes. Orthop J Sports Med. 2021;9(2):2325967120977892. (Back to section: 1)
8. Siebenrock KA, Ferner F, Noble PC, Santore RF, Werlen S, Mamisch TC. The cam-type deformity of the proximal femur develops during childhood in response to vigorous athletic activity. Clin Orthop Relat Res. 2011;469(11):3229-40. (Back to sections: 1, 2)
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12. Millis MB, Lewis CL, Schoenecker PL, Clohisy JC. Legg-Calvé-Perthes disease and slipped capital femoral epiphysis: major developmental causes of femoroacetabular impingement. J Am Acad Orthop Surg. 2013;21 Suppl 1:S59-63. (Back to section: 1)
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15. Reiman MP, Goode AP, Cook CE, Hölmich P, Thorborg K. Diagnostic accuracy of clinical tests for the diagnosis of femoroacetabular impingement and labral tears of the hip: a systematic review with meta-analysis. Br J Sports Med. 2015;49(12):811. (Back to section: 1)
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