Stabilizing lateral ankle instability by suture tape – a cadaver study

Ankle sprain is the most common injury in the physically active population and development to chronic ankle instability (CAI) is frequent [1]. About one out of five osteoarthritic ankles results from lateral ankle sprain [1]. The role of the mechanical component in CAI is a matter of ongoing debate [2]. Most studies originating from a kinesiology or sport scientific perspective do not report “a definitive association of ankle laxity with CAI” [3]. In the orthopaedic literature, however, CAI and mechanical ankle instability (MAI) are often used interchangeably [4‐8]. When MAI exceeds a certain amount and functional deficits cannot adequately be restored by conservative approaches, operative interventions have to be taken into consideration. In principle, tenodeses, anatomic reconstructions, and combined procedures are used to stabilize against ligamentous lateral ankle instability [9, 10]. Repair using local tissue has been shown to effectively stabilize the lateral ankle joint [8, 11]. Suture tape is a recent development to augment a Brostrom repair at least during the healing phase of the native tissues used for stabilization of the lateral ankle ligaments [12, 13]. Although there are concerns for progressive elongation of suture-tape, unclear long-term stability (longevity of mechanical stability), and unexpected complications such as foreign body reaction, this procedure is increasingly used for various ligament reconstructions.

A clinical study examined the effectiveness of suture tape to stabilize the ankle against a manually performed anterior drawer test. Results led to the conclusion that using an additional suture tape might be favoured compared to an isolated modified Brostrom repair [14]. Until now, only three cadaver experiments were published to demonstrate the stability of anterior talofibular ligament (ATFL) suture tape augmentation [13, 15, 16]. These experiments either investigated load to failure of the isolated ATFL [13], or rotation of the tibia, respective to the calcaneus [15, 16]. These experiments were designed to only load the ATFL (or the respective reconstructions), and specimens were therefore rigidly fixed to the testing apparatuses. In contrast, our ankle arthrometer applied only low load to the unconstrained heel in an anterior direction. Due to the complex anatomy of the hindfoot, this load is transferred into a complex motion of the calcaneus and the talus with respect to the fixed leg. In contrast to previous cadaver experiments, we therefore aimed to more functionally test the whole lateral ankle ligament complex in a clinically relevant situation (anterior talar drawer), its contribution to stability, and the effect of suture tape ATFL augmentation (Table 1). In previous experimental approaches, the loading of the ankle joint complex was quantified externally with specific measurement devices, which can be applied only to cadavers. Until now, no study compared the specific motion between the interacting bones (fibula and calcaneus) and its functional representation in an ankle arthrometer, which is validated for experimental and clinical use in a native condition, following incremental lateral ligament dissection, and following suture tape application.

The purpose of this study was to evaluate the effect of ATFL suture tape augmentation using a previously validated anterior talar drawer arthrometer in a cadaver experiment. Additionally, the spatial bone-to-bone movement was examined by motion analyses using intraosseous markers.

This investigation is part of a larger research project, which also aims to experimentally evaluate and validate the ankle arthrometer for assessing ankle laxity (anterior talar drawer).

The local Ethics Commission approved the study.

Macroscopically, there was no failure of the suture tapes or the anchor fixations during the testing procedures.

Ankle arthrometry (Fig. 3): Measured with the ankle arthrometer, the median anterior translation of the intact specimens was 4.0 ± 1.1 mm. Following the dissection of the ATFL median displacement increased to 6.1 ± 2.9 mm (p = 0.003) and to 7.6 ± 3.6 mm when the CFL was additionally cut (p = 0.001). With suture tape reconstruction, anterior translation was 5.0 ± 1.2 mm and 5.0 ± 2.1 mm, when solely the ATFL or both, ATFL and CFL were cut, respectively. Both reconstructed conditions were not different from the intact condition (p = 0.173 and 0.078, respectively).

Bone pin measurements (Table 2): Compared to the intact condition (0.2 ± 0.6 mm), anterior translation increased following the dissection of the ATFL (2.4 ± 4.9 mm; p = 0.004) and additionally the CFL (2.9 ± 6.5 mm; p < 0.001). Adding the suture tape reduced the anterior translation to 0.9 ± 1.0 mm when solely the ATFL was cut (p = 0.173) and to 0.7 ± 1.3 mm when additionally the CFL was cut (p = 0.007).

The correlation for the comparison between the exact motion of interacting bones (fibula vs. calcaneus) and its functional representation in the ankle arthrometer for the 20–40 N anterior talar drawer load was r = 0.851 (p < 0.001).

This study clearly demonstrates that an experimentally created anterolateral ankle instability (ATFL dissection) can effectively be reduced to anterior talar drawer baseline values by suture tape implantation. When compared to the intact condition and for the tested load (20–40 N), the CFL does not seem to play a relevant role for stabilizing against the anterior talar drawer, if the ATFL is reconstructed by suture tape. This behaviour is interesting, because our experimental setup tested for anterior translation, but the CFL is thought to protect mainly against ankle inversion [24, 25]. Because a large portion of patients with chronic ankle instability have insufficiency of both ligaments, further study regarding the suture tape ATFL and CFL reconstruction can be important and interesting.

Anatomic repair/reconstruction is currently the mainstay for operative treatment of MAI [10, 14, 26, 27]. In the last decade, anchor systems have been introduced to secure transplants [28] or as a knotless fixation for sutures [8]. Suture anchors are most important for the evolving arthroscopic Brostrom techniques [29, 30]. The stability of anchor systems has been tested in cadaver studies, but the strength of these repairs was inferior to native ATFL [31‐34]. Recently, suture tape techniques for augmentation of the ATFL were described [12, 35] and are proposed at least for patients with generalized ligamentous laxity [26], athletes, or patients with poor local tissue quality, e.g., following failed previous repair or reconstruction [13, 14].

An advantage of these techniques is the additional mechanical stability, provided by the suture tape which is securely fixed to cover the ATFL from its anatomic fibular origin to its talar insertion [13, 15, 16]. So, safer and faster rehabilitation is thought to be possible [12, 14, 27]. Compared with tenodesis, no “donor site morbidity” can occur [35].

In a clinical study, young females with MAI underwent an isolated minimally invasive suture tape augmentation of the ATFL and CFL. After a minimum follow-up of 2 years, “91.2% achieved satisfactory functional results” [35]. In another study, patients “were able to quickly return to activity and sports” [14].

A disadvantage of the suture tape procedure is the “possibility of progressive elongation over time” [35]. But otherwise, this could turn into an advantage by “allowing the natural tissues to progressively strengthen” [12]. An uncontrolled study described “favourable” short-term outcome [27]. The most critical point for the suture tape implementation until now is that no long-term follow-up is available to determine effects and side effects.

There are few reports to demonstrate the stability of the suture tape augmentation in cadaver experiments. Previous cadaver experiments tested load to failure of suture tape augmentation (Table 1). In these experimental setups, the talofibular joints were extensively dissected and isolated. The specimens were rigidly fixed in the test apparatuses while internal rotation load was applied to the calcaneus relative to tibia/fibula [13, 15, 16, 31, 32]. That highly standardized procedure tries to apply the load exactly in the direction of the suture tape. Contrasting to this, our investigation was performed following only minimal dissection of the specimens to mimic the specific motion of the involved bones during anterior talar drawer. The measurements were performed between 20 and 40 N anterior talar drawer load with our arthrometer which was developed, validated, and used for testing in the clinical situation [2, 17‐20]. However, our arthrometer does not evaluate the coronal plane motion (varus/valgus) of the ankle, but this motion has been analysed in a different approach within the same project [25].

Discussion is open whether additional CFL repair or augmentation is necessary. The effect of suture tape ATFL augmentation on talar tilt has not been addressed in cadaver studies (Table 1). However, a cadaver study demonstrated no difference in initial varus instability between isolated ATFL and combined CFL and ATFL repair with a Brostrom-Gould procedure [36]. This conclusion is also supported by an uncontrolled clinical study in an athletic population using a modified Brostrom procedure without CFL reconstruction [37]. When compared to the intact condition and for the tested load (20–40 N), the CFL does not seem to play a relevant role for stabilizing against the anterior talar drawer load, if the ATFL is stabilized by suture tape (Table 2). Recently, a minimally invasive technique was presented to anatomically augment both ATFL and CFL [35]. To further elucidate the role of the CFL, we addressed specifically the frontal plane instability in another approach [25].

Limitations to this study could be the higher age of our donors resulting in reduced bone and ligament quality. However, due to intraindividual comparisons of the different testing conditions, these differences were not likely to influence the results. Ankle degeneration could also influence the mobility during our tests, but all our specimens were free from degenerative findings. To get information about the isolated suture tape effect, we performed no Brostrom repair and therefore the individual quality of the lateral ankle ligaments does not play a role for the comparisons. However, this procedure is different from the standard clinical setting. We do not suggest that this study should be interpreted to promote isolated suture tape reconstruction to replace the modified Brostrom repair. It can be expected that an additional repair of the local tissue by a Brostrom procedure would lead to even more stability if the balance of load between the suture tape and the repair were properly set. Interestingly, isolated suture tape augmentation without addressing the ligaments has been recently shown to be effective in a clinical MAI study [35]. An additional limitation is that the cadaver study design only determines the response to the tape at the time of implantation. The stability measures would likely change over time due to wear out of the tape. Furthermore, this study evaluates the lateral ankle instability executed by an anteriorly applied load to the posterior calcaneus. The lateral ankle ligaments, however, stabilize the hindfoot in more complex and three-dimensional ways. That behaviour should be subjected to further analyses.

In principle, differences between ankle arthrometer and bone pin measurements are to be expected. The arthrometer provides an external instrumented measure, while the bone pins approach directly assesses the relative bone-to-bone movement between calcaneus and fibula. However, both measures demonstrated a strong relationship (r = 0.851). Our previous validation studies for the ankle arthrometer were done in a 2D radiographic approach in cadavers [19] or by in vivo comparison with a manual stress testing [2, 18]. As we were interested in having the most possible accuracy for the spatial bone-to-bone interaction, and to further evaluate the functional representation of the bone-specific movements, we decided to also investigate the ankle arthrometer against measurements obtained from a very precise biomechanical measuring tool. Consequently, in further studies, intraosseous markers can therefore be omitted.

In summary, the presented data demonstrate the effectiveness of ATFL suture tape augmentation in a cadaver experiment and the validity of the arthrometer to measure anterior talar drawer. This arthrometer therefore is recommended at least for quality management in the treatment of MAI patients and for preventive experimental and epidemiologic evaluations to further study CAI.

Suture tape augmentation of the ATFL effectively protects the unstable anterolateral ankle in the sagittal plane. For additional CFL lesions, the stabilizing effect in the sagittal plane was reduced.