Anterior Ankle Arthroscopy: Advantage of a Preoperative Ultrasound Mapping to Prevent Neurovascular Complications

Abstract

Purpose

The aim of this study is to verify the usefulness of ultrasound-assisted mapping of the vascular and neurological structures in the anterior compartment of the ankle just before an anterior arthroscopic procedure to reduce these kinds of complications.

Methods

Various complications can be present in anterior arthroscopy of the ankle. The structures most prone to iatrogenic damage are vessels and nerves. They are macroscopically visible and palpable in a little more than 50% of cases, but arterial ramifications are not visible because they are located deeper.

Results

The authors have investigated how to reduce potential iatrogenic damage to the complex and variable neuro-vascular network of the anterior aspect of the ankle. They have completed the classic routine marking of the bony and tendinous structures with an ultrasound mapping of the neurovascular structures.

Conclusions

The authors concluded that ultrasound-assisted mapping is a non-invasive, fast, and safe procedure that can help to reduce potential iatrogenic damage when performing anterior arthroscopic surgery.

Introduction

The neurovascular complications described in literature after an anterior ankle arthroscopic procedure have a global incidence ranging from 3.7 to 17%. Most of them affect peripheral nervous structures [1–5]. Many factors could influence the percentage of post-arthroscopic complications. We have distinguished them as:

Modifiable factors They are related to standardized surgical steps of the procedure. They have been defined as “modifiable” as they depend on the practical competence of the surgeon.

Unmodifiable factors They concern the position of the anatomical elements (bones, tendons, nerves, veins, arteries).

Among the modifiable factors, we must consider the arthroscopic setup (joint distention, ankle with or without fixed traction and therefore free to be mobilized or not), the technique of performing the portals (position of the ankle and foot, the technique of introduction of the arthroscope and instruments), and the operative dynamics (orientation and use of motorized instruments in the anterior ankle compartment). Among the unmodifiable factors, we must consider the neurological and vascular periarticular network in the anterior area of the ankle. In ankle arthroscopic surgery, the identification of the limits of the safe spaces where the portals should be performed is the first step to avoid complications. These spaces have anatomical limits (bone, tendons, and neurovascular structures), but they also depend on other factors linked to surgical manoeuvres (position of the foot and ankle, modality of performing incision and penetration of the instruments). The most critical portal is the lateral one: it is the site of the largest number of post-arthroscopic complications. The anterolateral area is a complex and variable crossroad of nervous and vascular structures. The identification of these anatomical structures at the beginning of the procedure is the first step in performing a safe procedure. The bony structures (medial and lateral malleolus), the joint line, and the saphenous vein medially are quite evident and therefore easier to mark with a dermographic pen. Vascular structures, especially the thin arterial ramifications, are invisible. As regards the nervous structures, only the intermediate dorsal cutaneous nerve is sometimes visible and palpable in plantarflexion and inversion of the foot, as it is subcutaneous. The marking of this nerve structure is often impossible (in 43% of patients), especially in patients with well-represented subcutaneous tissue or some sort of subcutaneous oedema [6] (Figs. 1, 2).

Fig. 1.

a “Thin foot”. b “Fat foot”. No evidence of the IDCN with inversion of the ankle, plantarflexion of the foot and flexion of the fourth toe

Fig. 2.

Question marks. Where IDCN will be proximal, near and distal to the distal line and antero-lateral portal (red circle)

Standard Arthroscopic Operative Setup

The patient lies in a supine position, with the foot perpendicular to the floor and exceeding the edge of the operating table by a few centimetres. No traction is used. The medial and lateral malleolus, the medial border of the tibialis anterior, the lateral border of the peroneus tertius, and the joint line are marked with a dermographic pen. As regards the neurovascular structures, only the great saphenous vein and other palpable veins can be marked.

The intermediate dorsal cutaneous nerve (IDCN), a branch of the superficial peroneal nerve, may be visible. Often it’s visible only at the anterolateral part of the mid-forefoot and lost at the joint line level where we perform the anterolateral portal. The IDCN can be seen in thin patients with “thin foot” with a combination of inversion of the foot, plantarflexion of the ankle, and flexion of the fourth toe [6] (Fig. 1a). In patients with a “fat foot”, even with a combination of inversion, plantarflexion, and fourth toe flexion, the IDCN is invisible (Figs. 1b, 2).

The proper anteromedial portal is located just medial to the anterior tibial tendon at the level of the joint line. The latter is easily palpable with passive dorsi- and plantarflexion of the joint, and the point of entry is marked with the dermographic pen whilst maintaining the ankle in slight dorsiflexion. The tibialis anterior tendon medially, the anterior margin of the medial malleolus, the distal medial border of the tibia, and the great saphenous vein (with the parallel saphenous nerve) delimit the medial safe area where the portal should be located.

The anterolateral portal is identified under arthroscopic control with the out-in insertion of a needle in the ankle joint. The point of introduction of the needle must be located inside the previously marked limits of the lateral safe area: lateral to the peroneus tertius tendon, usually medial to the intermediate dorsal cutaneous nerve previously marked on the skin (in cases it can be identified), at the level of the joint line.

The statistically more frequent complications are related to this step of setting up. Arthroscopic transillumination of the anterolateral area can sometimes be used to highlight the vascular and nervous structures which can cross this area, but this trick is not always effective. The only way to avoid lesions is to respect the structures which are marked on the skin [2].

Methods

The authors decided to further improve the precision of the mapping of the anterior neurovascular structures to decrease the incidence of possible complications.

We tried to obtain greater precision in the mapping step with the use of the ultrasounds [33] (Figs. 3, 4, 5).

Fig. 3.

Ultrasound mapping of the IDCN (yellow arrow) and of the artery (red arrow). Proximal to the joint line (a, b) at the joint line level (c, d), distal to the joint line (e, f)

Fig. 4.

Final IDCN map

Fig. 5.

a Vascular structures in the antero-lateral aspect of the ankle. b Echo-colour-Doppler exam

The ultrasound scan was performed with a linear transducer (13–6 MHz, MyLab One, Esaote) in the pre-surgery room during anaesthesiology setup. To highlight the nerve structures, the probe was kept transverse to the course of the nerve and highlighted in an oval-shaped section. The nerve was observed on a short axis, and it usually appeared as a hypoechoic dot. It could be difficult to see in a few cases, mainly in the patients who had abundant subcutaneous fat tissue (Fig. 3).

It was possible to highlight the vascular structures with the echo-colour-doppler by longitudinal and transverse scans. The position of the central and anterolateral arteries (the anterior tibial/dorsalis pedis artery and the peroneal or anterior perforator artery) and the main anastomotic branches, especially in the anterolateral area, were highlighted and marked on the skin. In a short time and without great difficulty, we obtained a mapping that could be more detailed than the usual one, with more precision in identifying the safe areas where the portals should be localized (Fig. 4).

After this mapping, the arthroscopic surgery was carried on as usual, and the treatment was performed on the basis of the pathology identified.

Discussion

Main arterial vessels and secondary branches create a complex and often variable network on the anterior aspect of the ankle, especially in the anterolateral area. The normal arterial vascular network includes two main axes, roughly perpendicular to the ankle joint line: a central axis represented by the anterior tibial artery (which continues with the dorsalis pedis artery) and an anterolateral axis represented by the anterior peroneal artery (also called the perforating artery or ramus perforans), a branch of the peroneal artery. These two main axes are connected by anastomotic branches, which run in a direction more parallel to the joint line. Particularly, two arterial branches arise from the central arterial axis, one medial and one lateral: they are described as malleolar branches and are more or less horizontal in relation to the joint line. As they approach the respective malleolus, they divide into more thin terminal branches. In the proximity of the lateral malleolus, an anastomotic complex web is formed by the branches of the lateral malleolar artery and of the perforating anterior artery. This classical anterolateral arterial network structure is found in about 50% of cases. Many variants can be present in the architecture and distribution of the arteries and of their terminal or collateral branches. In 4.2–5.5% of cases the central axis is moved laterally beyond the limit of the extensor digitorum longus, or the anterior axis is the continuation of the anterior perforating artery [7–14].

The most frequent vascular complication is represented by the development of a pseudo-aneurysm of an artery, also called “false aneurysm”. This is due to localized but full-thickness damage of the wall. The incidence of pseudo-aneurysms reported in the literature is only 0.008%, but perhaps this percentage is underestimated due to the difficulty of correctly diagnosing this kind of complication [15]. For a pseudo-aneurysm to occur, the entire arterial wall must be injured but in a localized manner: the consequent release of blood is contained by a fibrous pseudo-wall [12]. The cause of this event can be a pathology of collagen, but many times its origin is traumatic (traction or direct localized trauma) [16–20].

Peripheral neurological damage is much more frequent than vascular complications in the anterior arthroscopy of the ankle [4]. The anterior peripheral nervous network of the ankle is formed by two main nerves, the two branches of the superficial peroneal nerve: one is directed medially on the foot (the medial dorsal cutaneous nerve), and one laterally. The latter is the intermediate dorsal cutaneous nerve or Lemont’s nerve and is the most frequently damaged nervous structure during arthroscopy [22, 23]. Nerve complications have an overall incidence of approximately 14% [21].

Like the vascular structures, the anatomy of the peripheral nervous network at the level of the ankle is extremely variable. Many variants of the bifurcation of the superficial peroneal nerve are described in the literature [24–26]. In their anatomical dissections, Takao and Saito confirm that in most cases the bifurcation occurs at the site where the nerve perforates the fascia, about 10 cm proximally to the joint line [27, 28].

Regarding the anatomical limits of the safe areas where the portals should be performed, they can be barely modified by technical manoeuvres (Fig. 4). Articular distension with physiological saline solution does not appear to change the position of vessels and nerves, and therefore the safe work areas are not modified [29]. The traction of the ankle brings the anterior tibial artery closer to the capsule; on the contrary, in dorsiflexion the artery moves away. However, the extent of this displacement is minimal: Gentile [29] quantifies the distance of the artery from the anterior capsule as 0.7 cm and 0.9 cm, respectively. The same findings are confirmed by Jang [30]. Despite this minimal change of position, the neurovascular complications rate goes from 3.7 to 10.3% if the ankle is fixed in traction according to a study by the Dutch school [31]. The position of the ankle is also extremely important for a safe location of the portals, especially the lateral one. The relationship between the neurovascular structures and the anterior working chamber varies by placing the ankle in plantar- or dorsiflexion, in inversion or neutral position.

It should be pointed out that the displacement of the neurovascular structures verified on cadavers in dorsi- or plantarflexion changes according to the type of dissection that is performed [6]. In anatomical dissections of cadavers, the maintenance or not of the anatomical constraints with the neighbouring structures can modify the displacement of the anatomical structures. The greater the loss of constraints, the greater the possibility of changes in the course/orientation of the nervous and vascular structures [31].

De Leeuw et al. demonstrated that the superficial peroneal nerve moves laterally (mean 3.6 mm) from the peroneus tertius (the more lateral extensor tendon) in relation to the skin when passing from inversion to a neutral position of the foot and from plantar- to dorsiflexion of the ankle [6]. The structures which have a course parallel to the axis of rotation of the joint, like the arterial branches, undergo more positional changes from the plantarflexion to the dorsiflexion position, becoming more vulnerable to accidental direct trauma during the introduction of the instruments [32]. Slight dorsiflexion of the ankle (about 10°) and a neutral inversion-eversion position of the foot guarantee a sufficiently large lateral safe area. The plantarflexed position is not recommended [2, 32].

Other factors like performing vertical skin-only incisions, blunt dissection with a mosquito clamp of the subcutaneous tissues, and an accurate introduction of the trocar and instruments inside the joint are surgeon-dependent factors. Training and expertise are the keys to avoiding damage to the surrounding neurovascular structures, so we consider them as modifiable factors. Meanwhile, the neurovascular anatomy and the abovementioned possible variants of it are specific to each patient and so unmodifiable.

Some authors stress the importance of an accurate pre-operative topographic mapping, but the literature only includes papers on specimens [17, 22, 33]. To our knowledge, no paper has been published until now on a practical application on patients that will undergo surgery.

Instrumental methods which can help to map the neurovascular structures and delimit the safe area (especially on the lateral side) can help to avoid complications in case of anatomical variants unknown to the surgeon at the moment of the intervention. The ideal method must be simple, not invasive, reproducible, and carried out in a location near the operating theatre. Ultrasounds and echo-colour-Doppler combine these characteristics.

Limitations to the application of the technique can relate to the practical implementation. The first limit is the required presence of an expert in ultrasound imaging just before the beginning of the arthroscopy. This issue can be solved through collaboration with a consultant anaesthetist who has expertise in peripheral nervous blocks (frequently dedicated to orthopaedic surgery) and is competent in this technique. Orthopaedic surgeons who have expertise in ultrasound diagnostic imaging can manage the mapping by themselves. Another practical limit is the requirement of an ultrasound diagnostic device with echo-colour-Doppler in the pre-surgery room.

The technique will have to be validated with prospective and comparative studies to demonstrate the possibility of decreasing the percentage of postoperative complications due to the arthroscopic approach.

Conclusions

We believe that ultrasound and echo-colour-Doppler mapping of neuro-vascular structures just before an anterior ankle arthroscopy must be considered a useful, reproducible, low-cost technique which is quick to perform. The role of ultrasound imaging can be especially useful in the mapping of neurovascular structures that are not palpable or visible and are often atypically positioned, mostly in the area of the lateral portal. We think that this could be an easy and feasible technique to reduce postoperative complications due to the surgical approach, especially during the location of the lateral portal.

Declarations

Conflict of interest

All the Authors declare that they have no conflict of interest.

Ethical approval

All procedures performed in studies involving human partecipants were in accordance with the ethical standards of the institutional and/or national research committee and with 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Data obtained in this study did not interfere with course of treatment for patients included.

Informed consent

Informed consent was optained from all individual partecipants included in the study.

Funding

This study received no funding.

Availability of data and material

Material and data are all available.

Code availability

Not Applicable.

Consent for publication

Additional consent for publication was optained from all individual partecipants included in the study.

Author contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Marcello Lughi. The first draft of the manuscript was written by Marcello Lughi and all authors participated in drafting the manuscript. All author read and approved the final manuscript.