Round Hole, Square Peg

Awareness of femoroacetabular impingement (FAI) has broken over the orthopaedic landscape like a tidal wave. How many of us saw this tsunami on our weather radar? As I think back decades ago, I realize FAI was one of those conditions that saw me, although I did not see it. Perhaps I deserve some partial credit: I saw it, but I didn’t see it. I remember telling more than one patient who had consulted me for hip pain, ‘‘The radiologist has read your films as normal. I agree that there are no overt signs of arthritis, but your proximal femur does have a mild ‘pistol grip’ configuration, like the handle of a Derringer pistol. ’’ That, however, was as far as I went with it. I assumed that the shape of the femoral head and neck was either the residuum of a mild undiagnosed epiphyseal slip, or perhaps a subtle osteophytic accretion, the early sign of a degenerative process that would become more flagrant with the passage of time. If the physical examination revealed a loss of internal rotation, I considered it as further evidence of nascent osteoarthritis. It did not occur to me that the rather innocuouslooking prominence could be a lead actor in the pathogenesis of the patient’s symptoms. I had no inkling that the deformity might be causing painful damage to the acetabular labrum or articular cartilage. It certainly never entered my mind to suggest that surgically removing the excess bone might produce a therapeutic effect. Times have changed. When I interview candidates for our orthopaedic sports medicine fellowship at the University of Chicago, I routinely ask them what they hope to gain during a fellowship that they won’t already have acquired by the time they complete their residency. When I posed this question to candidates last week, ‘‘more experience in hip arthroscopy’’ was the nearly universal response. A recent study of young surgeons taking the American Board of Orthopaedic Surgery (ABOS) certification examination gives more heft to my unscientific survey: Between 1999 and 2009, the average number of hip arthroscopies performed by ABOS candidates increased 18-fold. Surgeons who had completed an orthopaedic sports medicine fellowship were the most likely to be performing the surgery. It is safe to assume that the indication for many of these procedures was FAI. Around the world, the orthopaedic community has focused much attention on morphological variations of the hip joint, attempting to define their prevalence, etiology, clinical significance, and role in the pathogenesis of hip pain, labral damage, and osteoarthritis. Much of this scrutiny has been directed at the abnormalities of the femoral head-neck junction known as cam deformities. These lesions, usually quantified by the a angle or less frequently, the triangular index, have been shown to be quite common in the general population, especially males. Among an unselected cohort of over 3000 Danes averaging 59 years of age, Gosvig and colleagues reported a cam deformity in 17% of men and 4% of women. In a smaller MRI study of younger, asymptomatic Canadian volunteers, Hack et al noted that 14% had at least 1 hip with cam deformity, including 25% of men and 5% of women. In New Zealand, Kang et al evaluated computed tomograms of the hips from 50 individuals with no known history of hip problems. Assessing a broad range of anatomic parameters of both the proximal femur and acetabulum, they concluded that 33% of females and 52% of males had at least 1 factor predisposing to FAI. Cross-sectional studies in certain groups of athletes have produced even more striking findings. Gerhardt and colleagues studied a selected population of elite American soccer players of both sexes with conventional radiography. They found that 72% of men and 50% of women had a femoral or acetabular abnormality associated with FAI. Philippon and colleagues looked specifically at the a angle on MRI studies of 61 asymptomatic hockey players between the ages of 10 and 18 years, comparing them with a control group of 27 young skiers. They reported that 75% of the hockey players had an a angle 55 , compared with 42% of skiers. This difference was primarily the result of a markedly increased prevalence of elevated a angles in players 16 to 18 years old, a phenomenon not seen in skiers of the same age. If an elevated a angle is common in youth, it seems to imply a developmental cause for this morphology. Some authors have asserted that cam deformity represents a silent form of slipped capital femoral epiphysis (SCFE), but others have discounted this conclusion. Siebenrock and colleagues have undertaken a series of studies designed to pinpoint the origin of the cam lesion. In 2004, they proposed an abnormal extension of the femoral head epiphysis as a major cause of cam impingement, implicating the anterosuperior quadrant in particular. In a subsequent study, they compared a group of young basketball players with a control cohort who had not participated in athletic activities at a high level. Because they documented an elevated a angle, decreased internal rotation, and an increased prevalence of hip pain and positive impingement tests in the athletes, they concluded that the cam deformity arises in response to vigorous sports activity in childhood. In a later * 1986 WB Music Corp (ASCAP), Huey Lewis Music (ASCAP), Bedaah Music (ASCAP), and Sub-Par Music (ASCAP). All rights administered by WB Music Corp.