Anatomic Study of Exposed Posterior Malleolus Using the Posterolateral Ankle Approach

Introduction

Posterior malleolus fracture (PMF) accounts for 7–44% of ankle fractures. The lack of proper fracture reduction may lead to early joint degeneration and poor ankle function [1, 2]. One of the commonly used PMF classification systems is the Haraguchi classification. According to this system, PMFs are divided into three categories: type I (posterior lateral oblique fractures, 67%), type II (medial extension fractures, 19%), and type III (small bone fractures, 14%) [3]. Open reduction and reliable internal fixation for intra-articular fractures is generally accepted, while debate persists about the surgical management of PMF [4, 5, 6]. Surgical approaches for ankle fractures generally include lateral, medial, posterolateral, and posteromedial incisions [7]. The success of the surgery depends on the patient’s clinical features and the design of the surgical incision. The surgical approach to PMF is determined based on the fracture location, extent, orientation, and safety [8]. The four mentioned methods are those most commonly used in clinical practice. The current references are mostly according to patients’ clinical symptoms and anatomical features of incision design, which is suitable and practical for clinical doctors’ scientific research work.

However, to provide better guidance regarding surgical approaches, here we conducted a comparative study of the exposed ankle surface of normal ankle joints via the posterolateral surgical approach and recorded the effect of different access approaches on the vascular nerves to determine how to reduce of surgical exposure difficulty and decrease vascular nerve damage risk.

Results

Distance from the tip of the lateral malleolus to incision A (a), incision B (b), or the midpoint of the sural nerve and small saphenous vein (c). There was no significant difference between distances (a) and (c) (P > 0.05), but a significant difference was observed between (b) and (c) (P < 0.05) (Figure 5).

Length and width of ankle bone block exposed through incisions A and B. The average length of the ankle bone block exposed through incision A was greater than that exposed through incision B, but the difference was not significant (P > 0.05). The average width of the ankle bone block exposed through incision A was significantly lesser than that exposed through incision B (P < 0.05) (Figure 6).

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Discussion

Ankle-related fracture, one of the most common intra- articular fractures that poses a high risk for young people, accounts for 14–44% of all ankle fractures [9]. The posterior malleolus, also known as the Volkmann nodule, forms the posterior lateral portion of the tibiotalar joint and is connected to the fibula by the posterior tibiofibular ligament [10, 11, 12]. Ankle fractures are often accompanied by internal and external malleolus fractures, which make the ankle joint unstable and prone to articular cartilage degeneration [13]. The incidence of traumatic arthritis of the ankle is significantly higher than the risk of ankle fractures and leads to poor functional foot recovery and prognosis [14]. The choice of the surgical approach used for ankle fractures is based on the following considerations: whether the lateral and lateral malleoli require open reduction at the same time; and internal fixation method [15, 16]. The condition of the soft tissue surrounding the proposed incision affects a surgeon’s ability to directly observe the fracture [17].

Olerud, et al. [18] suggested that ankle fracture fixation should be performed in the order of posterior malleolus, lateral malleolus, and medial malleolus, primarily because of the clear and safe exposure of the posterior malleolus and convenience and feasibility of fixation using the posterolateral incision. Talbot, et al. [19] reported in detail on the surgical procedure used to manage PMF, i.e., make a longitudinal incision in the posterior margin of the fibula, retract the tendon of the fibula to the inside to expose the posterior malleolus in a fixed order of lateral and posterior malleoli, and then make a medial incision to fix the medial malleolus. The main advantage of this approach is that it enables the direct visualization of the fractured bone block to facilitate the treatment of the posterolateral ankle fractures and is more conducive to post-anatomical reduction. With the help of gravity reduction and use of steel plate fixation, ankle fractures consist of osteochondral fragments; thus, a talus cartilage injury or compression injury could be more easily managed using a posterolateral approach [20].

Combined with the relevant literature, this anatomical study found that incision A was relatively closer to the lateral malleolus than incision B, similar to the lateral ankle approach used in clinical work. This incision was also closer to the sural nerve and small saphenous vein, which increases the risk of intraoperative injury [21]. Incision B was similar to the Achilles tendon lateral incision, which was positioned away from the vessels and nerves [22]. A comparison of the length and width of the posterior malleolus exposed through the two incisions revealed no significant differences in length, suggesting that the results may relate to the length of the incision. Since incision B was next to the posterior median line and resulted in greater exposure, the width of the exposed posterior malleolus was greater in this case than in case of incision A. Thus, the use of incision B could aid in fracture reduction and in ensuring upright positioning of hollow compression screws.