Transarticular external fixation versus deltoid ligament repair in treating SER IV ankle fractures: a comparative study

The deltoid ligament is an important structure to stabilize the ankle and maintain the normal anatomical position of the talus, inappropriate treatment for the ruptured deltoid ligament may cause ankle instability and traumatic arthritis [1‐4]. Supination external rotation type IV (SER IV) ankle fractures are one of the most common and unstable fractures in the clinical which need surgical treatment [3, 5‐9]. When the medial malleolus is intact, this type of fractures represents the ones with the injury of the deltoid ligament (AO/OTA classification 44-B3.1). Whether the ruptured deltoid ligament should be repaired or not is still controversy.

In recent years, suture-anchor was widely used for patients treated with deltoid ligament repair (DLR) [9‐11], and plaster casts were most often used in treatment without DLR. Previous studies had shown that transarticular external fixators might raplace the plaster casts well by offering the opportunity for self-healing of deltoid ligament and allowing early weight bearing [12‐14]. Our previous study had also shown that open reduction and internal fixation (ORIF) with transarticular external fixation (TEF) but no DLR could achieve satisfactory outcomes in treating SER IV ankle fractures [15].

Up to now, studies about ORIF, TEF but no DLR versus ORIF and DLR in the treatment of SER IV ankle fractures are rare. In this study we focused to compare the clinical and radiographic outcomes of these two methods.

The deltoid ligament is an important structure to limit the anterior and posterior translation of the talus and restrain talar abduction, with a relative contribution ranging from 50 to 80% [2, 21].

The acute deltoid ligament injury is commonly associated with ankle joint fractures. There are two most commonly used classification systems, the Lauge–Hansen, and Danis–Weber (AO/OTA) systems. The former relates the suspected mechanism of injury, the latter is based on the location of fibular fracture with respect to syndesmosis. According to the Lauge–Hansen classification, SER IV ankle fractures with an intact medial malleolus represent the ones with a deltoid ligament injury and corresponds to the type B fracture in the Danis–Weber classification (AO/OTA classification type 44-B3.1). They are one of the most common and unstable fractures in the clinical which need surgical treatment [3, 5‐9]. Whether the ruptured deltoid ligament should be repaired or not is still controversy.

Many studies suggested that it was not necessary to repair the ruptured deltoid ligament in ankle fractures [1, 6, 22‐25]. In Baird and Jackson’s research [22], 24 patients were diagnosed as ankle fractures with the deltoid ligament rupture, 21 patients with no DLR reached a good or excellent rate of 90%, the other 3 were treated with DLR, but 2 of them had unfavorable results. In de Souza’s study [23], 22 patients were diagnosed as the deep deltoid ligament rupture, all underwent ORIF and no DLR, all patients had satisfactory outcomes. Stromsoe et al. [24] designed a RCT, symptoms and clinical findings during follow-up showed no differences between two groups. Harper [25] reported 36 patients treated without DLR, the results showed no morbidity or evidence of ligamentous instability, he suggested that when the fibula was anatomic fixed and the medial space was maintained, DLR was not necessary.

However, some studies suggested that repair of the deltoid ligament could reduce long-term complications, patients may develop chronic ankle instability without DLR [7, 21, 25, 26]. Jones and Nunley [7] designed a retrospective comparative study including 27 patients, 12 were treated with lateral malleolus ORIF and DLR, the author concluded that repairing the deltoid ligament at the time of lateral malleolus fixation demonstrates subjective, functional, and radiologic outcomes for bimalleolar equivalent ankle fractures. Zhao et al. [21] reported 74 ankle fractures with deltoid ligament rupture, 20 patients were treated with DLR, this comparative study showed that DLR could decrease the widen medial clear space and malreduction rate. Johnson and Hill [26] reported 30 patients, treated with lateral malleolus ORIF, no DLR, the final outcome was poor in 41% of them.

As mentioned before, our previous study had shown that ORIF with TEF could achieve satisfactory outcomes in treating SER IV ankle fractures [15]. The present study retrospectively analyzed the results of 43 patients with SER IV ankle fractures who received ORIF with TEF (group 1) or ORIF with DLR (group 2).

For functional recovery and pain relieving, in both groups, AOFAS, SF-36, and VAS achieved satisfactory results after surgery, and with the numbers available, the difference between the two groups was not significant for all the three indexes. As for the total dorsiflexion/plantarflexion arc of motion, at the time of 6 weeks after surgery, patients in group 2 got significantly improved ankle ROM than patients in group 1. We considered that in the early stage, the ankle was fixed by transarticular external fixator and could not start early exercise, it brought unfavorable ankle functional results. When the fixator was removed after 6 weeks postoperatively, patients in group 1 could start ankle mobilization. Although patients in group 2 toke the exercise much earlier, there was no difference at 12 months postoperatively compared with patients in group 1. No cases of bone nonunion or post-traumatic arthritic changes were seen during the follow-up. So, patients who underwent ORIF with TEF could achieve comparable functional results and pain relieving to those who underwent ORIF with DLR.

According to biomechanical and animal studies, early weight bearing protocols is beneficial that it could optimize fracture healing [27]. For ankle fracture, early weight bearing after ORIF is feasible biomechanically without loss of reduction or fixation failure [28]. Dehghan et al. [16] designed a multicenter RCT, 110 patients with an unstable ankle fracture underwent ORIF, they were randomly divided into two groups, in the early weightbearing group, patients started full weightbearing at 2 week after operation, in the late weightbearing group, patients kept nonweightbearing for 6 weeks. The author recommended early postoperative weightbearing because it brought early improved functional outcome and did not increase complication rate. Papachristou et al. [29] designed a prospective study and suggested that early weight bearing could facilitate recovery and promote fracture union after ORIF for posterior malleolar fracture. In the present study, as ORIF and TEF could provide rigid stability and support, patients in group 1 spent less time to start weightbearing and achieve fracture union.

Both methods brought inconvenience to patients’ daily life. A majority of patients in group 2 complained that it was weary to repeat the process of taking on and off the plaster cast when cleaning the affected lower extremity. In group 1, the external fixator provided an open space that did not cover the skin, few patients thought that it was a little difficult to keep the skin clean around the external apparatus. It could also be noticed that most patients in group 1 thought it inconvenient for clothing because special trousers were needed to cope with the external apparatus, few patients in group 2 thought it difficult to wear trousers when the plaster cast was not removed.

There were several limitations in the present study. This was a retrospective study, and it was not randomized when assigning patients to different groups. We just analyzed SER IV fractures without other types of ankle fractures combined with deltoid ligament injury, the sample size was relatively small. Prospective comparative studies involving more samples are necessary for better illustration. However, in our study, the baseline data of the two groups were similar, most patients achieved satisfactory results, this study could provide reference for the management of SER IV fractures which have not been reported before. Regardless of fixation strategy, the ultimate goal is to have patients quickly and painlessly return to their preinjury activities and minimize the incidence of postoperative traumatic arthritis [5, 11, 30].

In conclusion, compared with ORIF with DLR, ORIF with TEF but no DLR is an optional strategy to manage SER IV ankle fractures (AO/OTA classification 44-B3.1) as it results in favorable postoperative functional recovery and pain relieving. It also allows patients to start relatively earlier weightbearing and may promote fracture union.