Anterior ankle impingment syndrome is less frequent, but associated with a longer absence and higher re-injury rate compared to posterior syndrome: a prospective cohort study of 6754 male professional soccer players

Data collection was undertaken in accordance with the 2006 consensus statement on how to conduct injury surveillance research in soccer [22] and in line with the recent 2020 International Olympic Committee (IOC) consensus statement [2]. The overall study methodology has previously been described in detail [7].

In brief, all first team players in the included teams were invited to participate in the study. At the beginning of every season, teams appointed a contact person within their medical team to be responsible for collecting data and communicating with the study group. Player baseline data were collected at inclusion on an annual basis. All individual player exposures during supervised training sessions and matches were recorded on standard attendance records. Time loss injuries were registered on standard injury cards containing information about the type, location and circumstances of the injury. The appointed contact person reported attendance records and injury cards monthly to the study group that checked the reports and sent feedback to the teams to clarify any missing or unclear data. No specific diagnostic criteria for AAIS and PAIS were used, and it was up to the medical staffs to classify the injuries and refer for imaging or any other consultations needed. All injuries were given a diagnostic code by the study group per the Orchard Sports Injury Classification System (OSICS) 10 [19]. Injury was defined as any physical complaint sustained by a player that resulted from a soccer match or soccer training and led to the player being unable to take a full part in future soccer training or match play. Other relevant injury definitions for this substudy are highlighted in Table 1.

Data were analyzed using SPSS (IBM SPSS Statistics for Windows, V.26.0, IBM Corp, Armonk, New York, USA). Player demographics are reported with descriptive statistics using mean ± standard deviation (SD) and proportions. Injury incidence was calculated as the number of injuries per 1000 h of exposure ((Σ injuries/Σ exposure hours) × 1000) with corresponding 95% confidence interval (CI). Injury burden was calculated as the number of absence days per 1000 h of exposure ((Σ days absence/Σ exposure hours) × 1000). Rate ratio (RR) was calculated with 95% CI and tested for significance with Z-statistics. Injury severity was defined as the number of days of absence and presented as median with interquartile range (IQR). The Mann–Whitney U test was used to compare days of absence for different injury categories. The χ² test was used to compare the proportions of categorical variables, while Students t test was used to compare the mean age, height, and weight between players suffering AAIS and PAIS. The significance level was set at P < 0.05.

AAIS and PAIS represented 35 (38%) and 58 (62%) of the ankle impingement cases, with the majority having a gradual onset (both n = 51, 55%) and occurred during training (Table 3). Sixteen (18%) cases were considered as exacerbation of symptoms. AAIS and PAIS were similar with regard to injury characteristics with the exception of a greater proportion of AAIS being re-injuries [11 (32%) vs. 5 (9%); P < 0.01] and having a gradual onset [24 (69%) vs. 27 (47%); P = 0.03]. Information about player contact was collected from the 2004/05 season onward and was available for 76 of 93 injuries. Out of those 76 impingement injuries, there was a noncontact injury mechanism in 53 (69%) of the injuries with no difference in the mechanisms between AAIS and PAIS (Table 3).

The median absence following an ankle impingement injury was 7 (IQR 16) days and 15 (16%) of the injuries were severe with > 28 days on the sidelines (Fig. 1 and Table 4).

The median absence was significantly longer in AAIS than PAIS [10 (22) vs. 6 (11) days; P = 0.023]. Gradual-onset injuries had significantly longer median absence compared with acute-onset injuries [8 (22) vs. 5 (11) days; P = 0.014].

The overall incidence of ankle impingement was 0.03 injuries (95% CI 0.02–0.03) per 1000 h. The incidence during match play was fivefold higher than during training [0.08 (95% CI 0.06–0.10) injuries per 1000 match hours vs. 0.02 injuries (95% CI 0.01–0.02) per 1000 training hours, RR 4.7 (95% CI 3.1–7.1)].

The incidence of PAIS was almost twofold higher than AAIS [0.02 (95% CI 0.001–0.02) injuries per 1000 h vs. 0.01 (95% CI 0.01–0.01) injuries per 1000 h, RR 1.7 (95% CI 1.1–2.5)]. This difference was mainly seen during match play [0.05 (95% CI 0.04–0.08) vs. 0.02 (95% CI 0.01–0.04) injuries per 1000 match hours, RR 2.5 (95% CI 1.3–4.9)]. No difference was seen during training [0.01 (95% CI 0.01–0.01) vs. 0.01 (95% CI 0.00–0.01) injuries per 1000 training hours, RR 1.2 (95% CI 0.7–2.1)]. A total of 1517 days of absence were reported due to ankle impingement (1046 days due to training injuries and 471 days due to match injuries). This represents an overall injury burden of 0.4 days per 1000 h, with 0.2 days per 1000 h calculated for both AAIS and PAIS (Table 5).

The present study found that soccer players with ankle impingement were able to return to play (RTP) at a median of 7 days (10 days in AAIS and 6 days in PAIS, respectively) following the injury occurrence, with only 16% of the injuries requiring longer than 28 days to recover. Importantly, our data included both injuries with nonsurgical and surgical treatment, whereas a few other studies have reported RTP details on surgically treated PAIS in soccer players exclusively. For example, Lopez-Valerio et al. [12] reported on 20 professional soccer players in Brazil who were treated arthroscopically for PAIS, and reported a mean RTP to the previous level of activity at an average of 46.9 days. Similarly, Calder et al. [4] reported an average of 34 days to return to training and 41 days to RTP in elite soccer players following arthroscopic surgery of PAIS. They also reported a sooner return in players with soft tissue rather than bony impingements. Finally, Kudaş et al. [10] reported an average RTP at 36 days of nonsurgical treatment in elite Turkish soccer players with PAIS. Murawski and Kennedy [17] reported RTP at a mean of 7 weeks (5–13 weeks) post-arthroscopic debridement of AAIS in a mixed population. The days of absence in the current study are fewer than reported in the literature and are to be interpreted with caution due to the lack of treatment data and detailed pathology (e.g., soft tissue vs bony impingement).

In the present study, AAIS led to significantly greater days of absence than PAIS. While such a comparison was not the main objective of this study, it could potentially be explained by the treatment strategy. In a previous study, AAIS had a higher probability of failure of nonsurgical management and thus requiring surgery, in comparison to 60% chance of success in PAIS after nonsurgical treatment [20]. Another possible cause for our findings is that soft tissue impingement, which is more common in PAIS, results in quicker recovery than bony causes of impingement. In the aforementioned series of 27 professional soccer players who underwent PAIS arthroscopic treatment, Calder et al. [4] reported a quicker return to training in soft tissue impingement in comparison to bony impingement (28 days vs. 40 days, respectively). Moreover, arthroscopic management of PAIS is considered to be safer in terms of nerve injuries than anterior arthroscopy needed for AAIS [12, 20, 23, 26].

The overall incidence of symptomatic ankle impingement was 0.03 cases per 1000 h, with PAIS being 1.7 times more common than AAIS. Interestingly, the incidence was almost five times higher during match play compared with training. This could be attributed to the more unpredictable and aggressive style of play during matches, and similar findings were described by Lubberts et al. [13] who found that syndesmotic ankle injuries in professional soccer players were 13 times more frequent during match play compared with training.

Re-injury was identified as a repeated period of time loss due to AAIS or PAIS within the same season as a previous identical injury. In this paper, the re-injury variable was based on what was reported by teams. Teams were instructed to report injuries as re-injuries when a player suffered a second period of absence due to an injury of the same type and affecting the same location as a previous index injury.

Multiple theories have been proposed regarding the etiology of AAIS, and a significant contribution to our understanding of the pathology has been done by Tol and van Dijk [24] in the 1990s and early 2000s. The earlier theory, first described by McMurray in 1950, attributed it to the traction forces on the anterior ankle capsule during forced plantar flexion, leading to the formation of anterior tibiotalar osteophytes and subsequent soft tissue proliferation and impingement [15, 25]. However, this theory has its limitations and has been disputed in favor of repetitive dorsiflexion and microtrauma [10, 15, 29]. An anatomical study by Tol and van Dijk [25] found the attachment of the anterior capsule to be on average 4 mm proximal to the cartilage. Likewise, a few other studies found the capsule to also be around 6 mm proximal to the site of the tibial spur, and arthroscopic examination has shown the spurs to be within the ankle joint and not in the joint capsule. Our results that the majority of ankle impingements had a gradual onset and AAIS was more common than PAIS support the subsequent theory of direct repetitive microtrauma and the findings of the biomechanical study by Tol et al. [25], where they concluded that the impact of a soccer ball to the anteromedial side of the cartilaginous rim generated sufficient forces to cause damage [5, 30].

Walls et al. highlighted the importance of injury and re-injury prevention and early recognition of ankle injuries in soccer players to optimize outcomes and reduce absence from sport [29]. Proper warmup, stretching, sufficient recovery, proprioception, and neuromuscular exercises are paramount for injury prevention. Additionally optimizing field conditions can further reduce injury incidence, especially non-contact injuries. Artificial turf, longer cleats, and dry hardened turf can increase the shoe–surface friction and thus increase the risk of ankle injuries [29]. An 18% recurrence rate and total a of 1517 days of absence due to ankle impingement were shown by our results, which represent an injury burden of 0.4 days absence per 1000 h. Hence, more organized efforts to prevent ankle impingement syndromes are required.

The clinical relevance of the findings in this study is that the provided epidemiological data on AAIS and PAIS in elite soccer can guide the clinician toward the best evidence-based ankle impingment management.

Unfortunately, this study presents several limitations. First, the injury form did not record the diagnostic tests and examination findings of all players and was not able to record data of all potentially important variables. The diagnosis was made by the medical teams of each soccer team and is consequently subject to biases, different experiences of different physicians, and availability of resources. Second, there was no information on how players with either AAIS or PAIS were treated, and if they had associated arthroscopic findings if they underwent surgical treatment. The type of impingement, whether bony or soft tissue, was also not recorded. Third, we did not capture data on the players’ medical history, such as ankle instability or fractures. Fourth, AAIS led to time loss in our study compared to PAIS. This might also be because AAIS more frequently requires surgery. Fifth, we acknowledge the limitation of our injury definition that could clarify why PAIS was a more frequent cause of time loss in professional football, while we are unaware of the total prevalence of symptomatic ankle impingement in the cohort, since many symptomatic AAIS and PAIS may not be captured when using a time loss injury definition given that players may have symptoms but are not taken out of play. Sixth, even though the study sample of professional players was large, some sub-analyses were limited by a small number of injuries and there is a risk of type 2 error. Finally, we utilized in-season time loss as an indicator of the severity of the injury. Consequently, injuries with off-season rest, treatment, or surgery might be missed.