JORT Journal

1.      Introduction

Femoroacetabular pathology has gained high importance in recent years, attracting greater levels of interest in the last decade, as is apparent from the number of publications about this pathology and about its treatment with hip arthroscopy [1]. It is currently one of the leading causes of hip pain in young adults, and is considered a potential cause of early hip Osteoarthritis (OA) [2-5].

Femoroacetabular Impingement (FAI) has been described as a deformity in the sphericity of the femoral head (cam type) or acetabular over coverage of the femoral head (pincer type) or a combination of both in mixed types. It remains difficult to diagnose, and its radiological evaluation remains controversial. The most common method used to evaluate FAI deformities radiologically, particularly the cam type, is the alpha angle

The deformities may lead to pain and functional impairments in some hips, but a very large proportion of hips remain asymptomatic from a clinical viewpoint despite the presence of radiological FAI deformities [8]. Consequently, there have been attempts to quantify the rate of these deformities in the population, the majority of whom may be asymptomatic [9-15]. Studies in Western countries have shown high rates of deformity, from 14% to 66%[9-20].  Studies in Asian countries appear to show lower rates, between 0.6% and 50% [2,18,21-24]. However some studies have pointed to the discordance between clinical and radiological findings, such that radiological deformities alone should not be considered FAI[16,25-29]. A very strong association has also been shown between the presence of FAI and sports, possibly due to lesions of soft tissue, especially of the acetabular labrum[30-39]. Furthermore, the rates of deformity as evaluated using the alpha angle are higher in these athletic populations [30,31,40,41].

The primary clinical consequence is evolution to OA[5,19,28,33,42,43]. A lower rate of hip OA has been reported in Asian countries[44,45], reinforcing the notion of a lower rate of FAI [18,24,46], nevertheless, studies have reported divergent findings [22,23,47]. The aim of our study was to obtain preliminary data on the proportion of football players with an abnormal alpha angle, in relation to different clinical situations, thereby laying the groundwork for future studies.

2.      Materials and Methods

The study population consisted of 121 males practicing association football as members of federation-affiliated clubs: 51 who underwent surgery for Osteitis Pubis (OP); 21 who underwent surgery for FAI; 15 who underwent ligamentoplasty for an Anterior Cruciate Ligament (ACL) lesion; 14 who underwent meniscal surgery; and 20 asymptomatic healthy volunteers. Data for OP and FAI patients were collected retrospectively; data for the other patient groups were collected prospectively. In OP patients, a weight-bearing AP pelvis radiograph had been performed as part of routine preoperative workup for this pathology at our center, in order to rule out a tumor process. FAI patients did not require any additional assessments beyond those performed for the purposes of their surgery. In both meniscus and ACL groups, the AP and axial radiographs on both hips were added to the preoperative workup, after consent to participate in our study was obtained from the patients. Previous hip pathology and previous knee surgery were exclusion criteria.

The asymptomatic group was drawn from a separate study evaluating the prevalence of abnormal alpha angles in subjects aged 12 to 14 years. The objective of our study was explained and consent was obtained from the players themselves, and from their parents or guardians, to perform AP and axial radiographs on both hips. Given the highly heterogeneous nature of our sample, in terms of pathology, we decided to reduce the impact of possible sex differences [48]by including only male subjects. All radiographs were read by two people: the study coordinator (who performed hip arthroscopic surgeries) and one of the other surgeons (who performed hip surgeries). The mean of the two measurements was used. The second readers did not know from which patient group the radiographs they evaluated belonged to. The AP radiographic view was selected as it was the one obtained in the pubis protocol and to minimize the costs of the study, in a population consisting exclusively of affiliated football players, who had been practicing for at least 5 years, with at least 4 training sessions or games per week. The AP views were considered correct when the coccyx tip and pubic
symphysis was aligned and the distance between them was 1 to 3 cm, and iliac wings and obturator foramina were symmetrical with a 15-20^° rotation of both hips [49] To calculate the cam, the alpha angle was measured using the methodology [6]. A line is drawn passing through the center of the femoral head and along the axis of the femoral neck. A circumference having as its center the center of the femoral head and a radius encompassing the entire head is drawn. The point where the transition between the head and neck crosses the circumference is taken as the section point; a radius is drawn from the center of the circumference passing through this section point. The angle formed by the two lines is the alpha angle (Figure 1).A normality test was performed in all groups then parametric or non-parametric tests used accordingly. Data were analyzed by a statistics specialist using the statistics program SPSS, version 18.0.

3.      Results

In the group of asymptomatic volunteers, aged between 12 and 14 years (mean 12.7 years, SD 0.6), who had been practicing their sport as an affiliate for a mean period of 6.9 years (SD 2.1), the alpha angle was abnormal (>55^°) in 20% of them in the AP view. This group also underwent an axial study, which showed a 32% rate of abnormal alpha angle. In the meniscus group (mean age 24.2 years, SD 7.3), 12 of the 28 (42.8%) analyzed hips had an abnormal alpha angle. In the ACL group (mean age 24.7 years, SD 8.3), the overall rate was 60% and a statistically significant difference was seen by laterality:  the rate was 73% in the hip ipsilateral to the lesion versus 46% in the contralateral hip. In the osteitis pubis group (mean age 26.8, SD 5.6), an abnormal angle was found in 88.2% of them, and was bilateral in 84% of them. In the FAI group (mean age 26.5 years, SD 7.1), 100% of patients had an abnormal angle (Figure 2).

None of the groups displayed a normal distribution on the basis of the Kolmogorov-Smirnov test (p<0.05), hence non-parametric tests were performed (Mann-Whitney U test).

4.      Discussion

In this series, we demonstrated a clear relationship between abnormal alpha angle and specific pathologies. Correlation was complete (100%) in patients who required hip corrective surgery, 88.2% in patients who required surgery for osteitis pubis, 73% in ipsilateral hip in patients who required anterior cruciate ligament reconstruction surgery. The abnormality was present in less than half of contralateral hips in ACL patients and patients requiring meniscus surgery (42% and 46% respectively). The prevalence of hip OA in the European population is around 10% of the general population [50]and anatomic abnormalities are present in more than 90% of these patients[51,52]. There is a close relationship between hip OA and an abnormal alpha angle[53]. In fact, bone deformities are a common finding in patients with hip pain[54], and FAI is considered a precursor to OA[33,43,55]. Some authors have found a correlation between FAI and reduced internal rotation[56]. The main way of diagnosing a cam-type deformity is an abnormal alpha angle[57]. Correction of the alpha angle is associated with clinical improvement and is considered predictive of outcome  [1,58]. The abnormal angle criterion has been described in studies [6,20]it is considered abnormal above 50^°. The rate of this deformity in the general population is calculated to be around 14% if they are asymptomatic, but the figure is much higher in the symptomatic population [11]. It has been calculated that around 80% of hips with a clinical picture of pain could have a FAI deformity [13,53]. Even in cases of hip OA, the risk of having a deformity in the contralateral hip is higher than 80%, even though symptoms are only found in slightly more than 10% of them [59].

Although plain radiographic studies find lower rates than CT or MRI, they are a much cheaper and simpler option for evaluating asymptomatic patients [9-11,13,20,60-62]. The cam-type deformity is usually defined in two ways: i) alpha angle >55^° in the anterolateral area[6,63,64]and (ii) alpha angle >83^° in any part of the femoral neck circumference[65]. There is a relationship between FAI and the practice of sport [63,64,66,67], and this is attributed to vigorous activity at ages at which bone is growing [41,48,68]. In fact, there is a direct relationship between practice of intense sports and a higher risk of cam deformity and hence higher risk of developing hip OA secondary to FAI [39,51,69,70]. It has been calculated that the risk of developing OA is 3 to 8.5 times higher in practitioners of intense sports than in the non-athletic population, for sports such as football, basketball, handball, athletics, martial arts and generally all those that involve running around a playing area[36-38,69,71-73]. The primary mechanism promoting this deformity is the effect of the mechanical impact [32,74-76].described that 16% of American football players had FAI-type modifications, but with significant variations between different playing positions.

Angle changes have been detected during the adolescent growth phase [77], but it is not possible to determine changes over time when one compares a population of adults aged under 40 years with others aged over 60 years[17]. However it has been demonstrated that intense athletic activity under the age of 12 years promotes a higher rate of abnormal alpha angle[78]. This is why we focused the present study on the highly specific population of affiliated football players. In this respect, the first group we analyzed, aged between 12 and 14 years, with 20% rate of abnormal angle in the AP view and 32% in the axial view, which is consistent with published data for the general population with asymptomatic hips[11,20]. It is possible that the results obtained in this age group rise from values closer to 14% described previously[11]to the values observed in the adult athletic population which fluctuates above 40% [11]. In populations of football players, a 40% rate of cam deformities was found [11], while a rate of 19.6% was found in non-athletic populations [20], but in some series a rate of up to 75% of cam-type deformities was found[31]. It is generally accepted that the rate of abnormal alpha angles in the normal population is around 20%, and double that in the athletic population, around 40-50% [66]. Consequently, it has been concluded that a higher alpha angle of the hip is associated with a higher rate of hip OA [77,79-82].

The meniscus patients had similar rates to the athletic population with asymptomatic hips [11], and similarly for the hip contralateral to the torn anterior cruciate ligament. Several authors have looked at the relationship between ACL lesions and hip modifications [83-86], and found a clear relationship between greater FAI-type deformity, with or without movement restriction, and a higher risk of ACL lesion. Although there are several possible causes of ACL lesions, an abnormal alpha angle could be a contributory factor to this lesion. In this respect, the patients in our series displayed a statistically significant difference in the side ipsilateral to the ACL lesion, with rates clearly higher to those of the contralateral side (73% vs 46%), which could influence the pathophysiology of the ACL lesion. Patients treated for OP had a very high correlation with hip deformities, which could include joint symptoms secondary to FAI, in our series (88.6%). Studies in a similar population found near identical results (86%) [31,87]. Although these studies point to subclinical FAI as the leading cause of OP, three elements should be borne in mind. First, that the success rate of OP surgery is very high, with a greater than 95% rate of resumption of athletic activity at the same level and revision rates below 5%, most of which are for insufficient initial tenotomy. As regards the rate of revision surgery for OP following surgery for FAI, we do not have these data and the few publications that exist simply establish a connection between both pathologies[31]. The second element is something that should not be overlooked: the studies that we have performed, the studies that have been published, and the follow-up we perform in sports clubs do not go beyond the period of affiliation of the players and we cannot perform a follow-up sufficiently long to see whether pathology manifests. The third very important element is that the rate of abnormal alpha angle in this population is 88.2%. This finding should lead one to suspect that it plays an important role in the pathophysiology of OP, and although we cannot consider these patients as clinical FAI, it is probable that the greater deformity of their hips contributes to impaired joint mobility and hence modifies adductor longus tone, as the studies by Williams suggested[88].

5.      Limitations

Our study has significant limitations. The primary one concerns the selection of the study population. The design of the study did not go beyond its stated aim of describing the population of affiliated football players. Given the higher rate of deformity of the femoral head, we wanted to verify the situation with our patients. In view of the significant costs associated with additional investigations and the ethical considerations, we decided to carry out studies prospectively in patients requiring various surgeries. To avoid unnecessary irradiation and to obtain information on the prevalence of this angle, the study also included patients who had already undergone surgery and in whom the radiographs had already been obtained, in the OP and FAI groups. Another limitation we considered was that of including a population of healthy volunteers to compare similar ages. Given that the figures in meniscus surgery patients were very similar to those observed in similar studies, we considered that the ethical and economic limitations outweighed the information that we could have obtained in this group. Another major limitation concerns the calculation of the angle itself. The alpha angle is calculated on the basis of a single plane and can vary significantly according to the radiological position, providing estimates different to actual values [62,89], with underestimations in many cases. For a better calculation, the 3-dimensionality of the hip must be taken into account[90]. Use of CT or MRI would improve the calculation of the angle[65], but these additional investigations were ruled out because of the significant additional cost. In any case, the high rates we obtained underestimate the reality.

6.      Conclusions

The present study describes the abnormal alpha angles in a population of football players, ranging from 20-30% in growing players, becoming established at around 40% in the adult population, but which can be higher, possibly exceeding 80%.

7.      Future Studies

It is obvious that this descriptive study lays the groundwork for prospective studies evaluating the relationships between frequent pathologies in footballers or athletes in general and hip impairment, whether this be a radiological deformity or a functional impairment in terms of mobility.

Figure 1:Calculation of the alpha angle in a normal and pathological hip in a X-ray study (Nötzli 2002 JBJS).

Figure 2: Percentage of patients with abnormal alpha angle (above 55^°) in AP radiographs.

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