Cam morphology (femoroacetabular impingement)

Last revised by Dr Yuranga Weerakkody on 26 Sep 2021

Cam morphology refers to an abnormal morphology of the femoral head-neck junction interlinked with an osseous asphericity of the femoral head. It is one possible cause of femoroacetabular impingement (FAI).

Cam morphology is also commonly referred to as 'cam deformity', 'cam lesion' or 'cam abnormality'. According to the Warwick agreement ‘cam morphology’ is the preferred term 1.  

There is a significantly higher prevalence of cam morphology in athletes compared to non-athletes. Cam morphology is more common in males than in females.  

A higher incidence of cam morphology has been found in high-impact sports 1-6:

  • football (soccer)
  • hockey
  • American football, rugby
  • basketball
  • baseball

Cam morphology itself can be and remain asymptomatic or can cause clinical signs and symptoms as typical motion or position-dependent hip or groin pain and is then referred to as femoroacetabular impingement 1,2. A painfully decreased range of motion during hip flexion, internal rotation and adduction, locking and stiffness are also described.

Cam morphology causes increased shear forces at the chondrolabral junction, possibly leading to the following 1-3:

The deformity usually involves the anterosuperior aspect of the proximal femur more precisely the head-neck junction and is characterized by a loss of sphericity of the femoral head 4  and a flat or convex in cases even ‘bumpy‘  head neck-junction 1-6.

This leads to a restriction in range of motion especially during hip flexion, internal rotation and adduction with associated shear at the chondrolabral junction 3,6.

Not yet completely understood, a combination of several factors seems to cause cam morphology 2-6:

The cam morphology is usually most prominent in the anterosuperior position of the femoral head-neck junction 7 usually between 0:30 and 2:30 on the clock face of the hip ref.

The predilection site for possible injury in cam deformity is the chondrolabral junction of the anterosuperior acetabulum 6.

For initial identification of cam morphology, an AP view of the pelvis and a lateral femoral neck view is recommended 1. Cross-sectional imaging is advised for better characterization, the detection of chondral and labral lesions and preoperative planning 1,6.

AP view pelvis: the typical finding is the pistol grip appearance of the proximal femur.

Dunn view: for evaluation of contour abnormalities of the head-neck junction including femoral head-neck offset.

Bone morphology and abnormalities in particular of the proximal femur can be nicely depicted 1:

  • loss of sphericity, flattening or a bump at the femoral head-neck junction, often found in the anterosuperior location
  • associated findings e.g. cysts or degenerative changes
  • alpha angle
  • femoral head-neck offset

The following morphological features can be assessed 1- 6:

  • loss of sphericity or a bump at the femoral head-neck junction especially in the anterosuperior location
  • associated findings e.g. cysts, bone marrow edema
  • alpha angle
    • >55° considered a risk factor in the anterior position
    • >60° in the anterosuperior position* is a recommended threshold 7
  • chondrolabral separation or avulsion
  • anterosuperior cartilage lesions e.g. carpet lesion
  • improved detection of acetabular chondral defects 5,6
  • better sensitivity for the detection of labral tears 5,6

A report for preoperative should include the following 6:

  • description of abnormalities in the femoral head-neck junction: bump, cysts
  • possible coexisting pincer morphology
  • associated findings e.g. bone marrow edema
  • chondrolabral detachment and other labral pathology
  • chondral lesions e.g. carpet lesion
  • alpha angle including the plane and position
  • femoral anteversion
  • signs of early osteoarthritis: subchondral sclerosis, cysts, osteophytes
  • associated soft tissue injuries: musculotendinous injury

Cam morphology itself can be managed with preventive measures in high-risk populations e.g. athletes but should not be treated surgically if asymptomatic. 

Symptomatic femoroacetabular impingement with cam morphology can be treated conservatively or surgically. Conservative treatment approaches include activity and /or lifestyle modifications, physiotherapy, watchful waiting. Surgical treatment aims at restoring hip morphology and repair or reconstruction of chondral and labral damage with arthroscopic and open surgical approaches 1,8.  The indication for surgery warrants not only morphological changes but also typical clinical signs and symptoms indicative of femoroacetabular impingement 1,9.

Possible considerations in some situations include. 

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Cases and figures

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