In the present study, athletes with anterior ankle impingement syndrome had frequent tram-track lesions, and more than half had ICRS grades 2 and 3 cartilage injuries. Furthermore, the most critical finding in the present study was that the osteophyte size and protrusion into the joint space were related to the severity of tram-track lesions.

The frequency of tram-track lesions in the present study (76.5%) was higher than that reported in previous studies (8.8% and 31.6%) [11, 13]. Regarding the severity of tram-track lesions, we compared the frequency of ICRS grade 3 in the present study to that of Outerbridge classification grade 4, almost equivalent to ICRS grade 3 in a previous study [13]. The result showed that the frequency of ICRS grade 3 (26.5%) in the present study was higher than that of Outerbridge grade 4 (17.5%) in a previous study [13]. A change in subject characteristics can cause these differences; however, the difference in the cartilage lesion evaluation can also affect the results. The subjects of the previous study consisted of four professional athletes (7.0%), 31 recreational athletes (41.3%), and 22 nonparticipants in sports (38.6%) [13]. However, the subjects of the present study consisted of 22 professional athletes (64.7%) and 12 student-athletes (35.3%); this shows that sports activity levels can affect the frequency and severity of cartilage lesions of tram-track lesions. In other words, athletes with anterior ankle impingement syndrome can have relatively severe tram-track lesions.

We could not find significant differences in osteophyte size and ICRS grade between the three types of sports in the present study; however, we believe that by conducting evaluations that include more sports and more participants, we will be able to clarify the differences in the impact of each sport on anterior ankle impingement syndrome. In addition, the present study’s main finding was that the ICRS grade in the protrusion-type group was higher than that in the non-protrusion-type group. The proportion of males was significantly higher in the protrusion-type group than in the non-protrusion-type group. In fact, all female athletes were in the non-protrusion-type group. As for differences between males and females in terms of anterior ankle impingement syndrome, it has been suggested that females have a higher percentage of combined anterior ankle impingement with chronic instability than males [19]. In addition, it has also been reported that females have higher rates of traumatic ankle sprains associated with anterior ankle impingement than males [20]. These findings indicate a possibility of sex-related differences in the mechanism of presenting symptoms of anterior ankle impingement. Considering the high incidence of anterior/anterolateral synovitis in patients with chronic lateral ankle instability [21], female athletes may present symptoms and undergo surgery in the earlier stage of anterior ankle impingement syndrome without developing larger or protruding osteophyte than male athletes.

Contrarily, male athletes may present symptoms in the relatively late stage of anterior ankle impingement syndrome with large or protruding osteophyte formation. Information regarding ankle instability was unavailable in the present study; however, the age of female participants was significantly low, and the osteophyte size of female participants was significantly small. These differences may be caused by sex-related differences such as ankle stability, dynamic postural control [22], and coordination and variability among foot joints [23]. Furthermore, a previous study suggested that female patients have higher rates of chondral injury in anterior ankle impingement syndrome [10]. No other studies have reported the relationship between sex and cartilage injury in anterior ankle impingement syndrome. Therefore, we considered that the difference in sex ratio between the two groups is unlikely to make us overestimate the effect of protrusion on cartilage lesion severity. There were no significant differences in the osteophyte size of these two groups. These findings showed that osteophyte morphology influences the severity of tram-track lesions independent of osteophyte size. In the present study, 53.8% of athletes in the protrusion-type group had ICRS grade 3 tram-track lesions. In addition, seven of nine athletes with grade 3 cartilage lesions had osteophyte protrusion into joint space. It has been suggested that the severity of cartilage lesions affects the long-term clinical outcome of arthroscopic treatment for anterior ankle impingement syndrome [6, 9]. Based on these findings, osteophyte protrusion should be assessed when considering an indication of arthroscopic treatment for anterior ankle impingement syndrome in athletes. The tram-track lesions can be detected by 3.0-tesla magnetic resonance imaging [24]; however, the information demonstrated in the present study will be useful for decision-making. We believe that if athletes experiencing anterior ankle impingement syndrome have protrusion-type osteophytes, arthroscopic resection can help them continue their careers with good performance for an extended time.

This study had some limitations. First, the number of subjects was small. Second, we did not assess ankle joint instability, clinical score, foot posture, and years of experience in the athletic field, which could have affected the degree of cartilage lesions. Therefore, considering these factors, a large cohort study is required to evaluate the relationship between osteophyte morphology and the severity of tram-track lesions in athletes.