Hip Impingement

Hip impingement, also known as femoroacetabular impingement (FAI), is a condition where the bones of the hip joint come into mechanical conflict with each other in certain hip positions. In hip impingement, extra bone grows on the ball, the socket, or both. This abnormal shape causes the bones to rub against each other during movement.

Over time, this repeated contact can damage the smooth cartilage that lines the joint and the labrum, which is the ring of cartilage that helps stabilise the hip. Hip impingement is a common cause of hip pain in young and middle-aged adults and can lead to early hip osteoarthritis if left untreated.

How Does Hip Impingement Impact Your Hip Joint?

Hip impingement affects both the structure of the hip joint and its function. A healthy hip joint allows smooth, pain-free movement through a wide range of motion, while maintaining excellent stability. When impingement is present, this range of movement can become restricted and painful.

From an anatomical perspective, the abnormal bone shape of the ball, socket or both reduces the clearance between the femoral head and the acetabulum. When the hip bends, twists, or rotates, the bones collide prematurely. This repeated collision places excessive stress on the labrum and the joint cartilage.

Over time, this can lead to:

Labral tears: The labrum can fray or tear, reducing hip stability and causing pain or catching sensations
Cartilage damage: The smooth cartilage covering the bones can wear away, leading to early arthritis
Reduced range of motion: Movements such as sitting in a low chair, squatting, or turning the leg inward may become difficult or painful
Muscle compensation: Surrounding muscles may tighten or weaken as they try to protect the joint

From a broader health perspective, hip impingement can limit physical activity, affect participation in work and sports, and reduce overall quality of life. If the condition progresses, it increases the risk of developing hip osteoarthritis at a younger age than usual.

Risk Factors for Hip Impingement

Hip impingement can affect people of all activity levels, but certain groups are at higher risk due to anatomy, lifestyle, or past activities.

People more likely to develop hip impingement include:

Young and middle-aged adults: Symptoms often appear between the late teens and 50s
Athletes: Sports involving repetitive hip flexion and rotation, such as football, soccer, hockey, dance, martial arts, and weightlifting
People with childhood hip conditions: Conditions such as slipped capital femoral epiphysis (SCFE) or Perthes disease can alter hip shape
Men: Cam-type impingement is more common in males
Women: Pincer-type impingement is more common in females
People with a family history: Genetics can influence hip shape and joint development

Importantly, not everyone with risk factors will develop symptoms. Some people have hip impingement changes on imaging but remain pain-free throughout their lives.

Causes of Hip Impingement

Hip impingement, especially ‘cam type’, typically results from abnormal bone growth during development, rather than from injury later in life. The exact reason why this extra bone forms is not always clear, but several contributing factors are recognised.

Common causes include:

Abnormal hip development: Changes in bone shape during adolescence, when the skeleton is still growing
High-impact sports during growth years: Repetitive stress on the hip joint in teenage athletes may influence bone formation
Genetic factors: Inherited traits can affect hip structure and alignment
Previous hip disorders: Childhood hip conditions that alter joint shape
Structural variations: Naturally deep hip sockets or developmental variations in the direction the bones are facing, such as femoral retroversion or acetabular retroversion, can lead to hip impingement
Functional hip impingement: certain sports such as martial arts, dance and gymnastics may lead to impingement symptoms despite relatively normal hip anatomy due to the extreme range of hip motion required. Unlike arthritis, hip impingement is not caused solely by wear and tear. Instead, the abnormal structure causes damage over time due to repeated movement and contact.

Symptoms of Hip Impingement

Symptoms of hip impingement often develop gradually and may initially be mild or intermittent. Pain usually becomes more noticeable with certain movements or activities.

Common symptoms include:

Groin pain: The most typical symptom, often felt deep in the front of the hip and commonly misdiagnosed as a hip flexor strain
Hip stiffness: Especially after sitting for long periods or first thing in the morning
Pain with movement: Discomfort during bending, squatting, twisting, or prolonged sitting
Reduced range of motion: Difficulty rotating the hip inward or bringing the knee toward the chest
Clicking, catching, or locking: Sensations caused by labral damage
Pain radiating: Discomfort may spread to the outer hip, thigh, or buttock

Symptoms are often worse during or after physical activity and may temporarily improve with rest. As the condition progresses, pain may become more constant and affect daily activities, such as walking, driving, or sleeping.

Preventing Hip Impingement

Because hip impingement is largely related to bone shape, it cannot always be fully prevented. However, steps can be taken to reduce symptoms, slow progression, and lower the risk of joint damage.

Preventive and protective strategies include:

Activity modification: Avoiding repeated deep hip bending or twisting movements that trigger pain
Early assessment: Seeking medical advice for persistent hip or groin pain, especially in active individuals
Strength and flexibility training: Maintaining balanced strength in the core, gluteal, and hip muscles
Good movement technique: Proper form during sports, lifting, and exercise to reduce joint stress. An experienced physiotherapist or exercise physiologist can be very helpful in assessing and optimising form to improve hip symptoms
Managing training loads: Gradually increasing activity intensity and allowing adequate recovery
Weight management: Reducing excess load on the hip joint, where appropriate

For adolescents involved in high-level sports, monitoring hip pain and addressing symptoms early may help limit long-term joint damage. While bone shape cannot be changed without surgery, early diagnosis and appropriate management can significantly reduce the risk of developing early hip osteoarthritis.

Types of Hip Impingement

Hip impingement is classified into types based on the location of the abnormal bone shape within the hip joint.

The main types of hip impingement are:

Cam Impingement: This occurs when the femoral head is not perfectly round. Ideally, the top of the femur consists of a nice round ball on top of a relatively narrow neck, like a lightbulb. This allows an optimal range of motion before the neck comes in contact with the edge of the socket. In cam impingement, a bony bump forms at the junction between the femoral head and neck. During hip movement, especially bending and rotation, this bump wedges into the socket and grinds to a halt, increasing the pressure on the cartilage. Cam impingement is more common in males and younger athletes and is strongly associated with cartilage damage inside the joint.
Pincer Impingement: This occurs when the acetabulum (hip socket) covers too much of the femoral head. The rim of the socket and its attached labrum pinch against the femoral neck during movement, particularly with deep hip flexion. Pincer impingement is more common in females and is often associated with labral tears rather than widespread cartilage damage.
Mixed Impingement: Often, features of both cam and pincer impingement coexist in the same patient, and, most commonly, both sides of the joint need to be addressed during hip impingement surgery.
Extra-articular impingement: As our understanding of hip biomechanics continues to evolve, other forms of hip impingement have been identified, including:
Sup-spine impingement. There is a bony bump on the pelvis just above the hip called the anterior inferior iliac spine (AIIS), which is the site of attachment of the rectus femoris muscle. Abnormal prominence of the AIIS (due to healed avulsion fracture, repetitive traction or acetabular/femoral retroversion) may cause it to impinge on the femur in deep flexion. Typically, this occurs lower down the anterior aspect (front) of the femoral neck.
Ischiofemoral impingement. This describes abnormal contact of the ischium part of the pelvis (the sitting bone) with the lesser trochanter of the femur. It typically causes buttock and sciatic-type pain, though it can also have groin pain and is usually worse when walking quickly, with long strides. There are many causes, including high femoral anteversion, a naturally wide pelvis, leg length difference and gluteal dysfunction, to name a few.

Other anatomical factors above and below the hip joint can also contribute to restricted range of motion and pain, such as:

Spinopelvic stiffness. When the spine is stiff, excessive demands are placed on the hips to accommodate the required range of motion.
Acetabular retroversion. If the opening of the hip joint socket is oriented slightly backward, rather than forwards, the front edge of the socket can impinge early on the femur in deep hip flexion.
Femoral retroversion. The thigh bone (femur) usually has 10-20 degrees of ‘twist’ between the hip and knee, such that the femoral neck is pointing slightly forwards. When the twist is reduced, internal rotation and flexion of the hip may be restricted.

Many people have multiple types of impingement, and the pattern of damage can vary with activity level, movement patterns, and symptom duration.

Stages of Hip Impingement

Hip impingement is not a single moment in time but a condition that typically progresses in stages. The rate of progression varies between individuals and depends on anatomy, activity level, and early management.

The stages commonly include:

Early Stage (Structural Changes Without Symptoms): Extra bone is present, but the person has little or no pain. The hip may feel tight, but daily activities are usually unaffected. Many people remain in this stage for years without knowing they have impingement.
Symptomatic Stage (Mechanical Irritation): Pain develops with specific movements, particularly during sitting, squatting, twisting, or sports. Labral irritation or small tears may be present. Stiffness and reduced range of motion become noticeable.
Progressive Joint Damage: Ongoing bone contact leads to worsening labral tears and cartilage damage. Pain becomes more frequent, recovery after activity takes longer, and daily tasks may be affected.
Early Osteoarthritis: Cartilage loss leads to joint space narrowing and more constant pain. At this stage, symptoms are less activity-dependent and more persistent.

Not everyone progresses through all stages. Early diagnosis and appropriate management can slow or halt progression in many patients.

Diagnosis of Hip Impingement

Diagnosing hip impingement involves combining clinical assessment with imaging. No single test alone confirms the diagnosis.

The diagnostic process usually includes:

Detailed Medical History: Dr Williams will ask about the location of pain, activity triggers, stiffness, clicking, and how symptoms affect work, sport, and daily life.
Physical Examination: Specific hip movements are gently tested to reproduce symptoms. Reduced internal rotation, pain with hip flexion, and mechanical catching are common findings.
X-rays: Standard hip X-rays assess bone shape, socket depth, and joint alignment. They help identify cam and pincer deformities, as well as early signs of arthritis.
Dr Williams routinely asks patients to have a special series of X-rays to assess the Young Adult Hip, including:
Standing pelvis x-ray. An upright X-ray will uncover any pelvic tilt caused by leg length difference.
Modified Dunn view. Cam deformity usually occurs at the front of the femoral neck and cannot be seen on AP (front-on) imaging.
False profile view. This is a functional lateral of the hip, which will reveal over-coverage of the front of the joint or a prominent AIIS.
MRI or MRI Arthrogram: MRI shows soft tissues such as the labrum and cartilage. An MRI on a 3T machine is usually adequate to diagnose most pathologies. Occasionally, an MRI arthrogram (with contrast dye injected into the joint) is required.
CT Scan (Selected Cases): CT scans provide detailed 3D views of bone anatomy and are sometimes used for surgical planning.

Importantly, imaging findings must match symptoms. Many people have hip impingement features on scans, but do not have pain. Diagnosis focuses on correlating structural findings with clinical symptoms.

Treatment Options for Hip Impingement

Treatment depends on symptom severity, joint damage, age, activity level, and personal goals. Management usually begins with non-surgical options.

Non-Surgical Treatment

Activity Modification: Avoiding movements that repeatedly load the hip in deep flexion or rotation
Physiotherapy: Improving hip strength, core stability, and movement control to reduce joint stress
Pain Management: Short-term use of anti-inflammatory medications when appropriate
Injections: Corticosteroid injections may reduce inflammation and help confirm the hip as the pain source
Education: Learning safe movement patterns and load management strategies

Many people experience meaningful improvement with conservative care, particularly when treatment starts early.

Surgical Treatment

Dr Williams may discuss surgical options with you when symptoms persist despite appropriate non-surgical care and imaging shows treatable structural abnormalities. Dr Williams is trained in all forms of hip preservation surgery and will choose the most appropriate intervention for you, taking into account your age, activity goals and individual anatomy.

Hip Arthroscopy: A minimally invasive procedure used to reshape bone, repair labral tears, and treat cartilage damage
Open Hip Surgery: May be necessary for complex cases with severe deformities

Surgery aims to improve joint mechanics and reduce further damage rather than reverse arthritis. Outcomes are generally better when surgery is performed before significant cartilage loss occurs.

What if Hip Impingement is Untreated?

If hip impingement is left untreated and symptoms persist, ongoing joint damage may occur. The consequences vary with the severity of impingement and the demands of activity.

Potential outcomes include:

Progressive Pain: Symptoms may become more frequent and less activity-dependent
Labral Degeneration: Repeated pinching can lead to extensive labral tearing
Cartilage Loss: Continued bone contact accelerates cartilage wear
Early Hip Osteoarthritis: Structural damage increases the likelihood of needing hip replacement later in life
Reduced Activity and Quality of Life: Pain may limit work, exercise, and recreational activities

However, not everyone with hip impingement requires treatment. Some people remain stable with minimal symptoms for many years, particularly with activity modification and good hip strength.

What is Hip Impingement?