Femoroacetabular impingement: question-driven review of hip joint pathophysiology from asymptomatic skeletal deformity to end-stage osteoarthritis

Journal of Orthopaedics and Traumatology

Official Journal of the Italian Society of Orthopaedics and Traumatology

Table 1 Cam and pincer, similarities and differences

	Cam	Pincer
Common location	Femoral head–neck junction	Acetabular rim
Primary damage	Acetabular cartilage wear	Labrum squeezing
Prevailing gender and age	Post-adolescent males	Middle-aged females
Development of osteoarthritis	Frequent	Rare
Pathomechanics	Sliding friction (shear contact stress)	Rim-to-neck impact (normal contact stress)
Pathobiology	Inflammation	Scarcely relevant
Pathoanatomy	Primary cam: physeal scar hypertrophy or subclinical SCFE Secondary cam^a: malunion of femoral neck fracture; SCFE; Legg–Calvè–Perthes disease; femoral head and neck neoplasms; malrotation of the femoral epiphysis; coxa vara	Primary pincer: Protrusio acetabuli (global overcoverage); acetabular retroversion (anterolateral overcoverage) Secondary pincer: acetabular retroversion after periacetabular osteotomy

SCFE slipped capital femoral epiphysis
^aTheoretically, all the secondary cam deformities might be classified alternatively as femur-based pincer deformities, depending on the likelihood of articular penetration. If the lesion may intrude easily into the joint, it will behave like a cam; otherwise, it will behave like a pincer