TFS injuries accompanying ankle fractures are highly heterogeneous. They can occur through various mechanisms and are associated with fractures of differing morphologies. TFS injuries may manifest as purely ligamentous, purely bony, or combined bony and ligamentous injuries [21]. This diversity necessitates careful consideration when selecting the appropriate method for internal fixation. Options range from universal fixation techniques, such as syndesmotic screws, to injury-specific approaches.

Fixation of posterior malleolus fractures represents an injury-specific stabilization method for TFS. However, posterior malleolus fractures are not a homogeneous group of injuries. Various classifications differentiate these fractures based on morphology and pathophysiology [22,23,24]. Commonly, these classifications identify three types: small shell fractures without an articular surface (usually unsuitable for fixation), posterolateral fragments, and posterolateral fragments with additional posteromedial fragments. Stabilization of the posterolateral fragment, which anchors the intact posterior tibiofibular ligament (PITFL), partially restores TFS stability by reconstituting PITFL function.

Our study demonstrates that almost all (97%) posterior malleolus fractures, regardless of morphology or mechanism, are accompanied by complete AITFL injury. These findings align with Nelson’s study, which reported AITFL injury in all cases of unstable TFS [25]. However, Nelson did not specify how many of these cases involved posterior malleolus fractures. Based on preoperative CT scans, Mason et al. reported a much lower incidence of anterior TFS injuries (42%) in posterior malleolus fractures [24]. This discrepancy likely arises because static CT is less sensitive in diagnosing ligament injuries without accompanying diastasis [26]. Our results underscore the importance of intraoperative assessment for detecting ligamentous injuries.

Fisher et al. concluded that the average location of LeFort-Wagstaffe fractures only partially overlaps with the AITFL footprint, suggesting that ligamentous failure must accompany the fracture for syndesmosis instability to occur [27]. However, our findings challenge this conclusion in the context of posterior malleolus fractures. We observed complete AITFL damage in all patients with posterior malleolus fractures and concurrent LeFort-Wagstaffe fractures. This suggests that the degree of syndesmotic instability after posterior malleolus fixation depends on the extent of additional injuries to the interosseous ligament (IOL), interosseous membrane (IOM), and deltoid ligament.

Our findings align with those of Nielson et al., who identified IOM damage in 30 of 73 surgically treated ankle fracture patients [28]. Given that the IOM is a proximal extension of the IOL, IOL damage is likely in such cases. This highlights the multifactorial nature of TFS instability and emphasizes the need for a comprehensive assessment of all stabilizing structures.

The incidence of AITFL avulsion fractures in general ankle fractures ranges from 13 to 26% [29, 30]. Our study, focusing specifically on posterior malleolus fractures, found a much higher incidence (53%), suggesting that posterior malleolus fractures are more strongly associated with anterior TFS injuries than other types of ankle fractures.

Intraoperative diagnosis of TFS instability in the case of its complete damage is usually not difficult and does not raise controversy as an indication for internal fixation. However, the situation is different in the case of instability resulting from partial damage - as is most often the case after stabilization of posterior malleolus fracture. It has been proven that damage to the AITFL, IOL and PITFL is necessary for the development of diastasis above 2 mm in the frontal plane [31]. Therefore, the hook test performed after stabilization of the posterior malleolus is usually negative. For radiological detection of TFS instability caused by damage to the AITFL and IOL with preserved PITFL, it is necessary to perform tests assessing stability in the direction of external rotation or in the sagittal plane. However, it has been proven that stress tests assessed under fluoroscopy are less sensitive in detecting partial TFS instability than arthroscopic or direct visual assessment [32,33,34]. Gosselin-Papadopoulos et al. showed that damage to the AITFL and 10 cm IOM (with preserved deltoid ligament) results in an average of 3 mm of diastasis on the anterior side observed during stress tests under direct vision [34]. Interestingly, Lauge-Hansen, in his work, also observed 2–3 mm of diastasis on the anterior side in the first phase of SER fracture (after complete damage to the AITFL) [21].

Although the threshold of TFS instability requiring fixation remains unclear, achieving full stability during surgery may improve clinical outcomes. Subtle, hidden chronic instability in the ankle joint may be a potential cause of pain, decreased joint function, and secondary degenerative changes. Vega et al. described microinstability associated with damage to the upper bundle of the anterior talofibular ligament (ATFL) and its clinical consequences [35]. In the work by Ryan et al., subtle TFS instability (as a consequence of a so-called high ankle sprain) was described as clinically symptomatic and difficult to recognize [36]. An unhealed AITFL injury may result in scar tissue formation, which potentially causes anterolateral soft tissue impingement [37]. Such impingement is one of the causes of pain in patients after ankle fractures [38]. In the author’s observation, the stumps of the injured AITFL often remain wrapped posteriorly and distant from each other, which may impede healing and increase the risk of irregular scar formation. Direct visualization of the anterior TFS allows for approximation and suturing of the injured ends of the ligament.

The author’s approach to treating TFS injuries with posterolateral fragments of posterior malleolus fractures is to stabilize the fracture and then stabilize the anterior part of the TFS. Posterior malleolus fractures are most often stabilized percutaneously in the posterior-anterior direction [39]. For AITFL avulsion fractures of fixable size, we recommend internal fixation. For smaller fractures or predominant ligamentous injuries, suturing the ligament and reinforcing the anterior TFS with tape (anchored in the lateral malleolus and Chaput tubercle) is preferred (Fig. 6). These procedures can be performed with a direct lateral approach and do not require extensive tissue dissection.

Intraoperative image after stabilization of the anterior TFS with tape (on the lateral malleolus side anchored in the posterolateral plate and on the tibia side fixed with a knotless anchor)

This approach aims to avoid the consequences of damage to the anterior part of the TFS (nonunion of avulsion fractures, chronic instability of the TFS, minimizing the risk of anterolateral impingement) and promote the early introduction of range-of-motion exercises and weight bearing on the operated limb. Additionally, direct visualization of the TFS could reduce the risk of syndesmosis malalignment.