Foot and Ankle Instability: A Clinical Guide to Diagnosis and Surgical Management

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021

B. Hintermann, R. RuizFoot and Ankle Instabilityhttps://doi.org/10.1007/978-3-030-62926-7_1

1. Introduction

Beat Hintermann¹   and Roxa Ruiz¹

(1)

Centre of Excellence for Foot and Ankle Surgery, Clinic of Orthopaedics and Traumatology, Kantonsspital Baselland, Liestal, Switzerland

The ankle joint complex and its surrounding ligaments represent a complex mechanical structure with its mechanical properties highly dependent on the integrity of the ligaments. While an acute inversion/supination trauma may typically result in lateral ankle instability, a trauma that includes an acute adduction of the foot may cause an additional loss of stability of the lateral Chopart joint. An external/abduction trauma, while the foot is fixed in a neutral to dorsiflexed position, may cause injuries to the inferior tibiofibular (syndesmotic) ligaments. Injuries to the medial side, as is the case for an eversion/pronation trauma, in contrast, may lead to various types of instability patterns depending on different preexisting conditions such as deformities and function of the posterior tibial muscle. On the lateral side, inappropriate treatment may typically result in chronic instability, whereas on the medial side, it may result in progressive destabilization of the hindfoot as can be seen in an acquired flatfoot deformity. Therefore, proper diagnosis and appropriate treatment is mandatory to prevent the patient from experiencing chronic instability and progressive destabilization of the ankle and foot, respectively.

Proper medical history taking and physical examination remain the single most important tool in the diagnostic process of an unstable foot and ankle. Though tremendous progress has been made in the last two decades, current imaging modalities are not able to replace the clinical workup. While MRI may be helpful in assessing acute injuries, weight bearing CT scans offer better information in most chronic conditions. The introduction of arthroscopy brought new insights on articular pathologies, mainly of the ankle joint; but, with this, the surgeons learned to avoid the anatomy. Knowledge of the anatomy is mandatory for any surgical procedure, however. Therefore, in this book emphasis is given on describing the anatomy so the surgeon can understand the pathology to successfully plan the surgeries and estimate their effect.

The talus has a unique function coupled to its anatomical shape. It provides the functional coupling between the lower leg and foot. As this bone does not have direct muscle attachments, it is often called bony meniscus. This unique construct may explain why the joints around the talus are highly exposed to injuries that, if not properly treated, may result in an unstable foot and ankle. The key for successful treatment is the full understanding of the resulting pathomechanics and involved morphologic structures. Therefore, emphasis is also given to work up the current knowledge on the biomechanics of the foot and ankle as well as the changes caused by instability. This, in turn, will help the surgeon to plan and to perform successful reconstructive surgeries.

Finally, the best treatment results from thoroughly understanding the pathology, knowing the expectations of the patient and being aware of the availability of various surgical and nonsurgical techniques. When considering surgical treatment, knowing their possibilities and limitations is mandatory for success. Main focus of this book is thus given to step-by-step instructions—in form of an operational manual, based on the authors’ lifelong experience.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021

B. Hintermann, R. RuizFoot and Ankle Instabilityhttps://doi.org/10.1007/978-3-030-62926-7_2

2. Lateral Ankle Instability

Beat Hintermann¹   and Roxa Ruiz¹

(1)

Centre of Excellence for Foot and Ankle Surgery, Clinic of Orthopaedics and Traumatology, Kantonsspital Baselland, Liestal, Switzerland

Lateral ankle ligament injuries are the most common injuries in sports and recreational activities [1–4] and account for about 25% of the injuries that occur in running and jumping sports [5]. Seventy-five percent of all ankle injuries are ankle sprains [2–4, 6–9], and 85% of these sprains are caused by an inversion trauma [10]. Although most of these ligamentous ankle injuries can be treated successfully with physical rehabilitation and nonoperative treatment, 20–40% of the patients with these injuries will go on to experience chronic instability and subsequent disability [4, 11–18].

Some of these patients can be treated satisfactorily with late repair or reconstruction of the lateral ligaments [16, 19–29]. However, in spite of surgery, some patients will be left with persistent disability including subjective or objective instability, persistent talar tilt, stretching of the ligaments, pain, stiffness, or limitation of the range of motion [16, 30]. Some of the reasons for these displeasing results may be attributed to a lack of respecting the biomechanics of the unstable ankle joint complex when operative treatment is carried out. In case of nonanatomic ligament reconstructions, the altered joint anatomy changes the kinematics, which may lead to several unsatisfactory results [20, 31]. These may include having residual subtalar instability [32, 33] or having highly restricted subtalar motion with an increased development of arthrosis [30, 34, 35].

There is, apparently, need for a better understanding of the anatomy and function of the ligament structures, as well as their susceptibility to injury and resultant instability. This will give an overall understanding of the biomechanics of the ankle. Furthermore, it may then allow to establish a rational for the daily practice when dealing with patients suffering from an acute or chronic unstable condition of the ankle joint complex.

2.1 Anatomy of the Lateral Ligaments of the Ankle

The lateral ankle ligaments form a complex construct that spans the ankle and subtalar joint.

Each ligament has its isometric position to guide motion and to provide stability.

The anterior talofibular and calcaneofibular ligaments are confluent and have a common insertion area on the anterior aspect of the distal fibula.

Anatomy textbooks and the orthopedic literature contain various descriptions of lateral ankle ligament anatomy [36–42]. The major lateral ligaments are the anterior talofibular ligament (ATFL), the calcaneofibular ligament (CFL), and the posterior talofibular ligament (PTFL).

2.1.1 Anterior Talofibular Ligament

The anterior talofibular ligament (ATFL) can be considered as being an intra-articular reinforcement of the anterolateral part of the rather weak ankle joint capsule. The ATFL is a broad flat ligament between 15 and 20 mm long, 6 and 10 mm wide, and 2 mm thick. It runs 45° medially from the fibula towards the talus in the coronal plane. The ATFL originates at the anterior edge of the fibula, just lateral to the articular cartilage of the lateral malleolus (Fig. 2.1). The center of its attachment is 10 mm proximal to the tip of the fibula as measured along the long axis of the fibula [36]. The insertion on the talus begins directly distal to the articular surface and the center is 18 mm proximal to the subtalar joint.

Fig. 2.1

The anterior talofibular ligament (ATFL) runs from the anterior border of fibula to the neck of talus with an angle of 105° to the ground. Its fibular insertion is 10 mm above the tip of the fibula and its talar insertion 18 mm above the subtalar joint

2.1.2 Calcaneofibular Ligament

The calcaneofibular ligament (CFL) is a cylindrical structure that lies deep to the peroneal tendons, underneath the tendon sheath, and superficial to the joint capsule. Structurally, the CFL is 2.5 times stronger than the ATFL and is 20–30 mm long, 4–8 mm wide, and 3–5 mm thick. In contrary to popular belief, the CFL does not originate from the apex of the tip of the lateral malleolus. Its attachment on the anterior edge of distal fibula is centered 8.5 mm from the distal tip just below the origin of the ATF ligament [36] (Fig. 2.2). As is the case for the ATFL, the CFL has most of its attachment fibers running on the lateral surface of the fibula. The calcaneal insertion begins 13 mm distal to the subtalar joint with its proximal edge on a line nearly perpendicular to the joint [36, 43].

Fig. 2.2

The calcaneofibular ligament (CFL) crosses the subtalar joint perpendicularly, originating from the lateral calcaneus 13 mm below the subtalar joint. Its insertion on the anterior aspect of the fibula is 8.5 mm above its tip. The fan-shaped lateral talocalcaneal ligament (LTCL, asterisk) is contiguous with the CFL inferiorly, broadening to insert along the entire inferior portion of the ATFL

The angle between the CFL and ATFL was measured on 50 cadavers. In the sagittal plane, the average angle was 105° ranging from 70° to 140° (Fig. 2.3). In the coronal plane, the average angle was 100° ranging from 60° to 140° [44].

Fig. 2.3

The LTCL is a completely discrete ligament (asterisk). Notice the angulation between the CFL and the ATFL of 105° (varying from 70° to 140°)

2.1.3 Lateral Talocalcaneal Ligament

The lateral talocalcaneal ligament (LTCL) varies in configuration, from a distinct rectangular structure spanning the subtalar joint to a fan-shaped ligament contiguous with the CFL inferiorly and broadening to insert along the entire inferior portion of the ATFL. Burks et al. [36] found three basic ligament patterns: a ligament combined with the CFL (Fig. 2.1), a completely discrete ligament (Fig. 2.2), and a missing ligament.

2.1.4 Posterior Talofibular Ligament

The posterior talofibular ligament (PTFL) is a thick and rather long ligament. On average, it is 30 mm long, 5 mm wide, and 5–8 mm thick. The PTFL originates from the medial surface of the fibula and runs medially in a horizontal fashion to the posterior aspect of the talus (Fig. 2.4). The fibular attachment is centered 10 mm proximal to the tip in the digital fossa [36]. The attachment on the talus involves nearly the entire non-articular portion of the posterior talus up to the groove for the flexor hallucis longus tendon. The ligament is confluent with the joint capsule and is well vascularized by vessels which supply the talus and the fibula via the digital fossa [42].

Fig. 2.4

The strong posterior talofibular ligament (PTFL) originates 10 mm above the tip of fibula and runs in a horizontal direction to the posterior aspect of the talus (CFL, asterisk)

2.2 Biomechanics of Lateral Ankle Instability

Loss of ligamentous support results in mechanical changes of the ankle joint complex.

Lateral ankle instability is in most instances a rotational one, given by the freedom of the talus to move laterally, out of the ankle mortise.

Ankle instability occurs in the absence of radiographically demonstrable talar tilt.

Besides providing stability, the ankle ligaments also have a significant role in preserving the mechanics of the ankle joint complex.

2.2.1 Stabilizing Function

Each of the lateral ligaments has a role in stabilizing the ankle and/or subtalar joint, depending on the position of the foot (Fig. 2.5). In dorsiflexion, the PTFL is maximally stressed and the CFL is taut, while the ATFL is loose. On the opposite, in plantarflexion the ATFL is taut, and the CFL and PTFL become loose [42, 45, 46].

Fig. 2.5

Lateral view of the ankle joint complex while the foot is (a) in dorsiflexion, (b) in neutral position, and (c) in plantarflexion. While in dorsiflexion the PTFL and CFL are taut and the ATFL is loose, in plantarflexion the ATFL is taut, and the CFL and PTFL become loose

Sequential sectioning of the lateral ligaments in cadavers has demonstrated the function of these ligaments in different positions and under various loading conditions. Johnson and Markolf [47] studied the laxity after sectioning the ATFL and found the most changes to occur in plantarflexion. They observed a smaller change in laxity in dorsiflexion, suggesting that the ATFL limits talar tilt throughout motion but has greatest influence on stability in plantarflexion. Others further confirmed the above findings, stating that talar tilt is limited in plantarflexion and in neutral position by the ATFL, and in dorsiflexion by the CFL plus the PTFL [46, 48]. In conclusion, the ATFL and CFL appear to synergistically work together to provide lateral stability to the ankle throughout the full range of motion, in such a way that when one is relaxed the other is strained and vice versa [20, 43, 49, 50].

2.2.2 Mechanical Changes with Loss of Ligamentous Support

In an attempt to elucidate how the ligaments contribute to this functional interplay with the bone structures of the ankle joint complex [13, 51–55], most reports have focused on the lateral ligaments and the role they play in maintaining lateral ankle stability [1, 46, 56, 57]. Although the magnitude of talar tilt has been shown to vary significantly [46, 58], there is a consensus that some tilt occurs with the loss of stabilization through these ligaments [1, 17, 56] (Fig. 2.6).

Fig. 2.6

After dissection of the ATFL and CFL, the talus will show some varus tilt and anterolateral extrusion out of ankle mortise when supination forces are applied to the foot

Recently it was reported in a study of ten matched pairs of specimens that stiffness and peak torque did not significantly decrease after sectioning the ATFL but decreased significantly after sectioning of the CFL [59]. Peak pressure in the tibiotalar joint decreased and mean contact area increased significantly after CFL release. Significantly more inversion of the talus and calcaneus as well as calcaneal medial displacement was seen with weight-bearing inversion after sectioning of the CFL.

2.2.3 Rotational Instability

Cass and Settles [58] studied the kinematics of ankle instability after lateral ligament sectioning in a model where axial rotation was not constrained. They found no tilting of the talus to occur in the mortise with isolated release of the ATFL or CFL. However, after both ligaments were released, an average talar tilt of 20.6° occurred. External rotation of the leg occurred with inversion averaging 11.1° in the intact specimen. A further external rotation of 4.9° occurred after ATFL release when compared to the intact inverted specimen and 12.8° further after an additional CFL release. The authors concluded that the ATFL and CFL ligaments work in tandem to prevent tilting of the talus, and that the articular surfaces themselves do not seem to prevent tilting of the talus in the mortise.

Thus, inversion is accompanied by a mandatory external rotation of the leg [44, 60–62]. In the intact specimen, this external rotation occurs at the subtalar joint [58, 63]. After loss of ligamentous support, the external rotation increases, but not at the subtalar joint [58, 64]. Rather, this increase occurs between the tibia and the talus. One may thus speculate that ankle instability, at least in one form, is an axial rotational one (Fig. 2.7).

Fig. 2.7

Loss of the ATFL support results in anterolateral rotational instability of the ankle

This rotational concept may explain why symptoms of ankle instability occur in the absence of radiographically demonstrable talar tilt. The role of the subtalar joint, therefore, also needs to be considered in ankle joint instability [65, 66].

2.3 Conclusions and Clinical Implications

No tilting is necessary at either the ankle or subtalar level to experience functional instability.

Repair of the anterior talofibular ligament alone can provide successful clinical results for treatment of ankle instability.

There is general agreement that motion between the tibia and the foot is a complex combination of ankle and subtalar joint motion limited by osseous shape and soft tissue interaction. The complex pattern of ankle joint motion is guided by the close relationship between the geometry of the ligaments and the shape of the articular surfaces [60]. The slackening and tightening of the ankle ligaments may be explained in terms of their instantaneous position with respect to the moving axis of rotation. The pattern of rotation has been shown to be more isometric for the CFL and talocalcaneal ligament (TCL) with respect to all others.

Obviously, besides maintaining lateral ankle stability, the lateral ankle ligaments play a significant role in maintaining rotational ankle stability (Fig. 2.8). It has been shown that loss of the ATFL and/or CFL leads to a measurable increase in inversion without any additional tilting of the talus or subtalar gapping (Fig. 2.7). It has also been shown that the loss of the ATFL allows an increase in external rotation of the leg to occur. The loss of the ATFL restraint unlocks the subtalar joint, allowing for further inversion. It is this increase in inversion which may lead to symptomatic instability. Considering this, no tilting is necessary at either the ankle or subtalar level to nevertheless experience functional instability.

Fig. 2.8

The lateral ankle ligaments play an important role in maintaining rotational stability of the ankle. (a) pronation position, (b) neutral position, and (c) supination position of the foot

These rotational concepts may explain why repair of the ATFL alone can provide successful clinical results for treatment of ankle instability [12, 19]. It may also explain why reconstructions that simply tenodese the fifth metatarsal to the fibula, thereby preventing external rotation, cure ankle instability [67]. Most of the common tenodesis procedures [68–70], however, do significantly restrict subtalar motion and thus alter the physiological interplay of the ankle and subtalar joint motion. As they interfere with the hindfoot mechanics, these tenodesis procedures should be avoided [20, 71].

In conclusion, appreciating the anatomy and mechanics of the rearfoot complex aids in understanding the pathomechanics of lateral ankle sprains and chronic ankle instability. Mechanical instability of the ankle may be due to the specific insufficiencies of pathologic laxity, arthrokinematic restrictions, synovial irritation, or degenerative changes to the joints of the ankle complex. Functional instability is driven by insufficiencies in proprioception, neuromuscular control, postural control, and strength [72].

2.4 Injury Pattern of Lateral Ankle Ligaments

Most frequently, the tear is located at the proximal insertion along the fibula, thus involving both the anterior talofibular and calcaneofibular ligaments.

The posterior talofibular ligament is rarely affected by the injury.

Associated injuries to the peroneal tendons are common.

The most common tear site of the ATFL and CFL are their proximal attachments, with the deep layers being more often affected than the superficial layers [36, 43] (Fig. 2.9). The rupture typically starts at the proximal site of the common insertion area and continues distally, leaving the ATLF/CFL complex intact, however detached from the fibula (Fig. 2.10). A special type of injury is an avulsion fracture of the lateral ankle ligaments at the fibula that is most commonly seen among children and patients over 40 years of age [73] (Fig. 2.11). The clinical characteristics are different from those of ligament rupture, and, unlike nonoperative treatment of lateral ligament rupture, nonoperative treatment of avulsion fractures does not yield satisfactory results [74]. Tears at the talar end of the ATFL (Fig. 2.12), in contrast, are less common since bone density is greater than at the fibular enthesis, and stress is dissipated away from the talar enthesis by the wrap-around fibrocartilaginous character of the ligament near the talar articular facet [75].

Fig. 2.9

(a) The most common injury site of the lateral ankle ligaments is at the proximal insertion of the ATFL/CFL complex. Very often the superficial layers remain intact, while the deep layers are detached. (b) After dissecting the superficial layers that remained connected to the periosteum, the extent of the tear with complete detachment from the fibula becomes visible

Fig. 2.10

Another case showing the complete detachment of the ATFL/CFL complex from the fibula with some superficial layers remaining intact while the deep layers are torn

Fig. 2.11

Avulsion of the lateral ankle ligaments (arrow) in a chronically unstable ankle after experiencing a severe sprain. (a) AP radiograph showing the detached fragment (arrow). (b) In the lateral view, the fragment is seen at the anterior aspect of distal fibula. (c) Under fluoroscopy, the fragment is seen to be close to its origin when the foot is in neutral position (arrow); whereas (d) when varus stress is applied, the fragment is seen to move away from the fibula (arrow). (e) Arthroscopy shows a complete detachment of the fragment with the ATFL/CFL complex. (f) Surgical exploration evidences the detached fragment at the fibular site with an intact ATFL/CFL complex

Fig. 2.12

An acute tear of the ATFL at its distal insertion on the talar neck (asterisk)

2.5 History and Clinical Presentation

Patients most commonly report on having sustained a supination sprain.

In the acute situation, pain and swelling can help the surgeon identify the location and extent of the lesion.

Stress testing should be done with hanging feet.

Patients with an acute injury of the lateral ankle ligaments usually report on a sustained inversion-supination trauma and pain in the anteromedial part of the ankle joint. After a fracture has been ruled out, a careful physical examination is carried out starting with examining the swelling, deformity, and ecchymosis, as they are indicative of acute injury (Fig. 2.13). In cases where lateral ankle instability has become a chronic problem, making an accurate diagnosis may be more demanding, as pain is often missing and local symptoms may be subtle. To assess stability of the lateral ankle ligaments, two provocative maneuvers are essential, best done with the patient sitting upright with their feet hanging. The anterior drawer test assesses the integrity of the ATFL (Fig. 2.14) [49, 76–81] but its reliability was found to be poor, likely because the average amount of clinically meaningful talocrural laxity is small and varies considerably, making it difficult to perceive with a manual test [82]. If the ATFL is ruptured, in 50% of the cases a dimple sign can be seen in the anterior aspect of the joint (Fig. 2.15). The talar tilt test for the ATFL and CFL are shown in Fig. 2.16.

Fig. 2.13

Swelling and ecchymosis after an acute ankle sprain. (a) lateral view, (b) anterior view

Fig. 2.14

Anterior drawer test. (a) With the foot hanging, the distal tibia is held with one hand while the other hand holds the foot at the heel. (b) While the foot is in slight plantar flexion, the heel is then pulled towards anterior

Fig. 2.15

Dimple sign. (a) While supination stress is applied, a dimple sign can often be seen at anterior ankle. (b) It can also be seen when the distal tibia and the heel are taken by the investigator, and (c) then the foot is pushed towards medial

Fig. 2.16

Talar tilt test. While the foot is taken in slight plantar flexion by the heel and varus stress is applied, the investigator can feel the opening of the lateral ankle. Important for correct testing is that the patient is relaxed. This can be best achieved when the patient is sitting with hanging feet

The foot’s shape and overall alignment of the hindfoot are assessed with the patient standing (Fig. 2.17a–c). Any deformity is reassessed with the patient in the tiptoe position to determine if the deformity is affected by the eccentric pull of the Achilles tendon (Fig. 2.17d). To exclude that the hindfoot varus is not forefoot driven, the Coleman bloc test can be done [83] (Fig. 2.17e).

Fig. 2.17

Clinical assessment of the foot shape and hindfoot alignment is done with the patient weight-bearing. (a) Anterior view showing the peek-a-boo of the calcaneus due to the cavovarus deformity (arrow). (b) The high-arch configuration with shortening and some adduction of the forefoot. (c) Varus malalignment of the hindfoot that is associated with an external rotation of the foot is seen from posterior; typically, the lateral malleolus is very prominent, whereas the medial malleolus has disappeared. (d) In tiptoe position, while the heel cord is activated, no further varus malalignment is seen, meaning that it is a fixed deformity. (e) When performing the Coleman bloc test, no decrease of varus can be seen, which confirms that the hindfoot varus is not driven by a forefoot pronation

2.6 Imaging

Radiographs serve to rule out a fracture.

MRI may help