Hip osteoarthritis (OA) is a major cause of pain, disability and reduced quality of life. 

Cam morphology – excess bone at the anterolateral femoral head-neck junction – contributes to femoroacetabular impingement (FAI) syndrome and hip OA, although progression is complex and multifactorial. 

Our review published in Nature Reviews Rheumatology synthesised contemporary evidence on cam morphology, including its development, diagnosis, clinical relevance and management, with emphasis on early intervention and physiotherapy-led treatment.

What is cam morphology? 

Cam morphology refers to excess bone or cartilage at the femoral head-neck junction, resulting in loss of the femoral head’s spherical shape. 

This asphericity can lead to abnormal joint contact during hip movements, increasing stress on the acetabular cartilage and labrum. Importantly, cam morphology is not a disease. 

It is common in both the general population and athletes and frequently occurs without symptoms. 

Primary and secondary cam morphology is distinctly different. 

Primary cam morphology, the form most often seen clinically, develops during adolescence in otherwise healthy hips, likely in response to repetitive high-impact loading. 

Secondary cam morphology arises from prior hip disease or trauma, such as slipped capital femoral epiphysis or Perthes disease.

Terminology 

Clear terminology is essential. 

Cam morphology should be distinguished from FAI syndrome, which is a clinical diagnosis requiring symptoms, signs and imaging findings. 

Terms such as ‘deformity’, ‘lesion’ or ‘abnormality’ should be avoided, as they may promote unhelpful beliefs about pathology rather than reflecting a bony adaptation. 

When talking about these symptoms and syndromes, use the following terminology: 

• cam morphology
• FAI syndrome
• FAI syndrome with cam morphology. 

Avoid using:

• symptomatic/asymptomatic femoroacetabular impingement
• cam-type morphology or impingement
• femoroacetabular impingement morphology
• deformity, lesion, abnormality or pathology (for cam morphology). 

Defining FAI syndrome 

AI syndrome is a motion-related clinical disorder affecting young to middle-aged active adults. According to the 2016 Warwick Agreement, diagnosis requires a triad of:

• symptoms – hip or groin pain aggravated by activity or sustained positions; mechanical symptoms (eg, clicking, catching) may occur
• clinical signs – reduced hip internal rotation and symptom reproduction during tests such as the FADIR (flexion, adduction, internal rotation) test and prone internal rotation
• imaging findings – cam morphology, pincer morphology or both. 

FAI syndrome can be classified into three subtypes: cam, pincer and mixed morphology. 

Cam morphology is the most common. 

Distinguishing symptomatic individuals from those without pain and cam morphology is critical to avoid overdiagnosis and unnecessary intervention. How does cam morphology develop? 

Evidence indicates that cam morphology develops during adolescence, when the proximal femoral growth plate is highly responsive to mechanical load. Repetitive high-intensity activities, particularly sports involving deep hip flexion, rotation and rapid directional changes (eg, football, ice hockey and basketball), are associated with its development. 

Longitudinal studies show that cam morphology forms while the growth plate is open and does not develop after skeletal maturity. Cam morphology is less common in women, possibly due to earlier physeal closure, though sex differences in morphology suggest distinct developmental pathways. 

Prevalence also varies by ethnicity, with lower rates reported in East Asian populations, indicating potential genetic, hormonal or cultural influences. 

The key points to know are:

• Early changes may occur between the ages of eight and 10, initially as soft tissue hypertrophy.
• Development largely ceases once the growth plate closes. 
• High training volume and intensity increase risk, particularly in men. 

Diagnosis and imaging 

Clinical tests such as FADIR are sensitive but not specific, making them useful for screening rather than confirming FAI syndrome.

Reduced or painful hip internal rotation, especially in neutral or prone positions, is a more clinically informative finding. Imaging is important for identifying cam morphology but must always be interpreted alongside symptoms and examination findings. 

The most common radiological measure is the alpha angle, which quantifies femoral head asphericity. 

An alpha angle (greater than or equal to 60 degrees) is widely used to define cam morphology. 

However, there is considerable overlap between symptomatic and asymptomatic individuals, limiting its diagnostic utility in isolation. 

When using imaging to inform a diagnosis, consider that: 

• X-ray (anteroposterior pelvis and Dunn 45 degrees view) is first-line imaging
• MRI provides additional information on cartilage, labrum, femoral and acetabular version, and early OA changes
• imaging alone cannot diagnose FAI syndrome. 

Why do only some people develop symptoms? 

Most individuals with cam morphology remain asymptomatic. 

Symptom development appears to reflect interactions between multiple factors: 

• morphology characteristics (size, shape, location) 
• coexisting pincer morphology
• femoral version (eg, reduced version limiting internal rotation)
• spinopelvic alignment influencing hip mechanics
• load exposure from sport or occupation
• biological factors, including inflammatory processes
• labral tears and cartilage defects. 

Labral and cartilage abnormalities are also common in asymptomatic individuals with cam morphology, indicating that structural findings alone do not explain pain. 

Cam morphology, FAI syndrome and hip OA 

Prospective studies indicate that cam morphology is a causal risk factor for hip OA, approximately doubling to tripling risk over eight to 10 years. 

In some people, structural joint changes may begin in late adolescence or early adulthood. 

Different cam morphology subtypes (eg, pistol grip deformity, flattened head-neck junction) show varying associations with OA. 

FAI syndrome appears to be a stronger predictor of OA progression. 

In one large cohort, older adults with FAI syndrome had markedly increased their odds of developing end-stage OA over 10 years.

Management 

Non-surgical management

Physiotherapist-led care is recommended as first-line treatment. 

• Core components include:
• patient education and reassurance
• activity modification and load management
• progressive hip and trunk strengthening
• movement retraining
• adjuncts such as injections where appropriate.

Randomised controlled trials show that physiotherapy improves pain and function, although differences compared with surgery are often modest in the short term. 

Given the high prevalence of cam morphology in individuals without pain, education is particularly important as a way of addressing misconceptions and reducing fear. 

Surgical management Hip arthroscopy aims to reshape cam and/or pincer morphology and to address labral or cartilage pathology. 

Some trials report slightly greater improvements in patient-reported outcomes compared with physiotherapy, although findings are inconsistent. 

Evidence for surgery altering OA progression remains inconclusive. 

Limited imaging data suggest possible structural benefits but longterm outcomes are uncertain. 

Can cam morphology be prevented? Given its developmental origins, cam morphology is a target for primary prevention. Reducing high-load sporting exposure during adolescence may theoretically lower risk. 

However, current evidence is insufficient to recommend restricting youth sport, particularly given its broad health benefits.

Conclusion

The key take-home messages for physiotherapists are: 

• Cam morphology is common and often asymptomatic.
• It typically develops during adolescence in response to mechanical loading.
• FAI syndrome requires symptoms, signs and imaging – not imaging alone.
• Cam morphology increases OA risk but not all individuals will develop OA.
• Physiotherapy-led care should be first-line management. 
• Hip arthroscopy is an effective treatment in those who do not benefit from physiotherapy-led care.  
• Clear communication is essential to avoid fear and overtreatment.

>>Dr Joshua Heerey MACP is an APA Titled Sports and Exercise Physiotherapist. In addition to clinical practice at Alphington Sports Medicine, Joshua is a senior research fellow at La Trobe Sport and Exercise Medicine Research Centre.