POSNA One Day Course 2012: Adolescent and Young Adult Hip Disorders May 16, 2:00-2:10 The natural history of osteoarthritis after a slipped capital femoral epiphysis / The pistol grip deformity. Pablo Castañeda, MD • A relationship between subtle deformity of the proximal femur and the subsequent development of osteoarthritis (OA) has been suggested since the earlier part of the last century. • These deformities were termed “pistol grip deformity” and are now grouped under the term of femoroacetabular impingement (FAI) • The role of FAI in OA remains controversial because a clear causal relationship has not been rigorously established and proven by evidence.