Introduction
Femoroacetabular impingement (FAI) has been described as the main cause of hip pain, altered joint range and decreased exercise performance in athletes.1 This condition is because of morphological alterations in the femoral head or acetabulum that leads to or predisposes labral and chondral injuries. Various conditions can lead to FAI presence, including congenital malformations, post-traumatic injuries, coxa profunda and acetabular retroversion and protrusion.2 These changes were initially described by Ganz et al,3 who separated them into two main groups: cam impingement, in which there is an alteration in the sphericity of the femoral head, and pincer impingement, which is characterised by changes to the acetabulum.
The causes and time course of the development of deformities found in FAI are not entirely clear. Some reports4 5 have revealed that participation in high-impact sports may play a role in the development of cam deformity; there is a higher prevalence of signs of cam impingement in asymptomatic adolescents who participate in soccer and basketball than in non-athlete controls.4 5 Current evidence regarding the initiation and development of deformities is scarce. Agricola et al 6 observed a group of elite soccer players aged 12–19 years over a 2-year period who demonstrated that the prevalence of cam deformity progressively increased until physis closure, during which the prevalence tended to stabilise. Based on these observations, we hypothesised that the prevalence of radiological signs of FAI in young elite soccer players who are skeletally immature would be lower than in adult soccer players.
The aim of this study was to compare the prevalence of radiographic hip abnormalities related to FAI pathology in young elite soccer players with that in a group of adult elite soccer players.
Subjects and methods
Research ethics board approval from our institution was obtained, and a prospective study was designed. One hundred and fifty elite footballers who belonged to a first-division club or the young national team were evaluated in two groups during the preseason period. Group 1 included 75 young players with incomplete skeletal maturity, and group 2 included 75 adult elite soccer players.
Inclusion criteria for group 1 were skeletal inmaturity defined by an open femoral physis and less than stage 4 of Risser’s iliac apophysis ossification.7 The mean age in group 1 was 15.4 years (SD 0.8, range 12–16). Inclusion criteria for group 2 were adult elite soccer players. The average age in group 2 was 24 years (SD 3.3, range 19–36).
Exclusion criteria for both groups were incomplete data, presence of symptoms related to the hip or history of hip pain (ie, moderate-to-severe pain that prevented the athlete to play or train normally) despite being asymptomatic at the time of the study, history of hip pathology and bad-quality X-rays after two attempts.
Each subject signed a consent form and voluntarily participated in this study. Seven patients were excluded from group 1 due to skeletal maturity, bad-quality X-rays or incomplete data, and five patients were excluded from group 2. Finally, 72 footballers were included in group 1 and 70 in group 2.
Anteroposterior pelvic and cross-table hip radiographs were taken for each subject. A radiology technician was responsible for obtaining the images using the recommended protocols for each projection.8 The quality of each image was analysed, and if it did not fulfil the requirements, it was repeated. A good radiograph was defined as the pelvis with the coccyx centreed on the pubic symphysis, with both legs internally rotated 15°, and with bony landmarks (teardrop and lesser trochanter) clearly visible. A radiograph was considered unacceptable when the coccyx was >1 cm lateralised with respect to the centre of the pubic symphysis or >3 cm above or below the superior edge of the pubis, or the obturator foramens were asymmetric.8 In cross-table hip radiographs, the anterior and posterior femoral head–neck junctions had to be clearly definable.8 A radiologist, a specialist in musculoskeletal radiology, analysed the films and evaluated signs of pincer or cam impingement (figure 1).
Anteroposterior pelvis and cross-table radiographs of a 14-year-old soccer player with skeletal immaturity and radiological signs of cam FAI. FAI, femoroacetabular impingement.
For pincer impingement, the lateral centre edge angle over was measured, and the presence of focal acetabular retroversion (in a figure-of-8 configuration, the ‘cross-over’ sign) was recorded.9 The cross-over sign is defined as the anterior rim line being lateral to the posterior rim in the cranial part of the acetabulum and crossing the latter in the distal part of the acetabulum, showing as a figure-of-8 on the anteroposterior radiograph.9 The lateral centre edge angle (Wiberg’s angle) is calculated by measuring the angle between two lines: (1) a line through the centre of the femoral head, perpendicular to the transverse axis of the pelvis, and (2) a line through the centre of the femoral head, passing through the most superolateral point of the sclerotic weight-bearing zone of the acetabulum.8
For cam impingement, the alpha angle and the anterior offset were measured.9 For measurement, first, a line following the longitudinal axis of the femoral neck is drawn. The alpha angle is the angle between the femoral neck axis and a line connecting the head centre with the point at which the head–neck contour begins to become aspherical.8 9 The anterior offset refers to the difference between the maximal anterior radius of the femoral head and the anterior radius of the adjacent femoral neck. To measure it, two lines parallel to the longitudinal axis are drawn. One must be tangential to the anterior border of the head, and the other must be tangential to the anterior border of the neck. The perpendicular distance between them corresponds to the anterior femoral offset.9 10 The measures and evaluations of the images were performed using Kodak Carestream software, V.10.2 (Carestream Health, 2008, Rochester, New York, USA).
Positive radiographic signs of cam-type FAI were defined as the presence of an increased alpha angle (>55°) or decreased anterior femoral offset (<8 mm) in at least one of the examined hips. Positive radiographic signs of pincer-type FAI were defined as the presence of a cross-over sign or lateral centre edge angle >40° in at least one of the examined hips. Positive radiographic signs of FAI were defined as the presence of any of the above mentioned specific signs.
The χ² test was used for comparison between groups of the presence or absence of radiographic signs. The remaining data (alpha angle, anterior femoral offset and Wiberg’s angle) were tested for normality using the D’Agostino-Pearson test and further analysed using Student’s t-test. A significance level of p<0.05 was considered to be statistically significant. Statistical analyses were performed using SPSS 21 (SPSS).
