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Keywords:

  • ankle;
  • CT;
  • macroscopy;
  • microscopy;
  • MRI;
  • tibiofibular syndesmosis;
  • ultrasound

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Syndesmotic bones and incisura fibularis
  5. Tibiofibular contact zone
  6. Syndesmotic recess (Recessus tibiofibularis)
  7. The syndesmotic ligaments
  8. Conclusion
  9. Acknowledgements
  10. References

A syndesmosis is defined as a fibrous joint in which two adjacent bones are linked by a strong membrane or ligaments. This definition also applies for the distal tibiofibular syndesmosis, which is a syndesmotic joint formed by two bones and four ligaments. The distal tibia and fibula form the osseous part of the syndesmosis and are linked by the distal anterior tibiofibular ligament, the distal posterior tibiofibular ligament, the transverse ligament and the interosseous ligament. Although the syndesmosis is a joint, in the literature the term syndesmotic injury is used to describe injury of the syndesmotic ligaments. In an estimated 1–11% of all ankle sprains, injury of the distal tibiofibular syndesmosis occurs. Forty percent of patients still have complaints of ankle instability 6 months after an ankle sprain. This could be due to widening of the ankle mortise as a result of increased length of the syndesmotic ligaments after acute ankle sprain. As widening of the ankle mortise by 1 mm decreases the contact area of the tibiotalar joint by 42%, this could lead to instability and hence early osteoarthritis of the tibiotalar joint. In fractures of the ankle, syndesmotic injury occurs in about 50% of type Weber B and in all of type Weber C fractures. However, in discussing syndesmotic injury, it seems the exact proximal and distal boundaries of the distal tibiofibular syndesmosis are not well defined. There is no clear statement in the Ashhurst and Bromer etiological, the Lauge-Hansen genetic or the Danis-Weber topographical fracture classification about the exact extent of the syndesmosis. This joint is also not clearly defined in anatomical textbooks, such as Lanz and Wachsmuth. Kelikian and Kelikian postulate that the distal tibiofibular joint begins at the level of origin of the tibiofibular ligaments from the tibia and ends where these ligaments insert into the fibular malleolus. As the syndesmosis of the ankle plays an important role in the stability of the talocrural joint, understanding of the exact anatomy of both the osseous and ligamentous structures is essential in interpreting plain radiographs, CT and MR images, in ankle arthroscopy and in therapeutic management. With this pictorial essay we try to fill the hiatus in anatomic knowledge and provide a detailed anatomic description of the syndesmotic bones with the incisura fibularis, the syndesmotic recess, synovial fold and tibiofibular contact zone and the four syndesmotic ligaments. Each section describes a separate syndesmotic structure, followed by its clinical relevance and discussion of remaining questions.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Syndesmotic bones and incisura fibularis
  5. Tibiofibular contact zone
  6. Syndesmotic recess (Recessus tibiofibularis)
  7. The syndesmotic ligaments
  8. Conclusion
  9. Acknowledgements
  10. References

A syndesmosis is defined as a fibrous joint in which two adjacent bones are linked by a strong membrane or ligaments. This definition also applies for the distal tibiofibular syndesmosis, which is a syndesmotic joint formed by two bones and four ligaments. The distal tibia and fibula form the osseous part of the syndesmosis and are linked by the distal anterior tibiofibular ligament (ATIFL), the distal posterior tibiofibular ligament (PTIFL), the transverse ligament and the interosseous ligament. Although the syndesmosis is a joint, in the literature the term syndesmotic injury is used to describe injury of the syndesmotic ligaments. To avoid confusion, we will do the same.

In an estimated 1–11% of all ankle sprains, injury of the distal tibiofibular syndesmosis occurs. Forty percent of patients still have complaints of ankle instability 6 months after an ankle sprain. This could be due to widening of the ankle mortise as a result of increased length of the syndesmotic ligaments after acute ankle sprain. As widening of the ankle mortise by 1 mm decreases the contact area of the tibiotalar joint by 42% (Harris & Fallat, 2004; Ramsey & Hamilton, 1976), this could lead to instability and hence early osteoarthritis of the tibiotalar joint.

Syndesmotic injury can occur after trauma to the ankle, both with and without a fracture of the osseous part. In fractures of the ankle, syndesmotic injury occurs in about 50% of type Weber B and in all type Weber C fractures, whereas in ankle sprains without fracture, syndesmotic injury accounts for 1–11% of all injuries (Hopkinson et al. 1990).

However, in discussing syndesmotic injury it seems the exact proximal and distal boundaries of the distal tibiofibular syndesmosis are not well defined. There is no clear statement in the Ashhurst & Bromer (1922) etiological, Lauge-Hansen (1950) genetic or Weber (1972) topographical fracture classifications, concerning the exact extent of the syndesmosis. This joint is also not clearly defined in anatomical textbooks, such as Lanz & Wachsmuth (1972). Kelikian & Kelikian (1985) postulate that the distal tibiofibular joint begins at the level of origin of the tibiofibular ligaments from the tibia and ends where these ligaments insert into the fibular malleolus.

As the syndesmosis of the ankle plays an important role in the stability of the talocrural joint, understanding of the exact anatomy of both the osseous and ligamentous structures is essential for interpretation of plain radiographs, CT and MR images in ankle arthroscopy and in therapeutic management.

With this pictorial essay we try to fill the hiatus in anatomic knowledge and provide a detailed anatomic description of the syndesmotic bones with the incisura fibularis, the syndesmotic recess, synovial fold and tibiofibular contact zone and the four syndesmotic ligaments. Each section below describes a separate syndesmotic structure, followed by its clinical relevance and discussion of remaining questions.

Syndesmotic bones and incisura fibularis

  1. Top of page
  2. Abstract
  3. Introduction
  4. Syndesmotic bones and incisura fibularis
  5. Tibiofibular contact zone
  6. Syndesmotic recess (Recessus tibiofibularis)
  7. The syndesmotic ligaments
  8. Conclusion
  9. Acknowledgements
  10. References

Anatomy

At the apex of the syndesmosis, the crista interossea tibiae, i.e. the lateral ridge of the tibia, bifurcates caudally into an anterior and posterior margin (Fig. 1). The anterior margin ends in the antero-lateral aspect of the tibial plafond called the anterior tubercle (Chaput’s tubercle). The posterior margin ends in the posterolateral aspect of the tibial plafond called the posterior tubercle. The anterior and posterior margins of the distal tibia enclose a concave triangle, with its apex 6–8 cm above the level of the talocrural joint (Kelikian & Kelikian, 1985). The base of the triangle is formed by the anterior and posterior tubercle of the tibia, with the incisura tibialis in between. The anterior tubercle is more prominent than the posterior tubercle and protrudes further laterally and overlaps the medial two thirds of the supramalleolar shaft of the fibula (Kelikian & Kelikian, 1985).

image

Figure 1.  Axial CT images at the level of the distal tibiofibular joint from (A) proximal to (D) distal (male, 53 years). The interosseous membrane (1) is visible between the tibial and fibular crest (A ). A little lower, the tibial crest forms an anterior and a posterior margin (2). The lateral aspect of the distal fibula is convex and fits into the concave tibial incisure. The fascicles of the interosseous ligament bridge the fibular incisure and run obliquely upward from the fibula towards the tibia. In the axial plane, the obliquely running fibres are depicted as small dots (3). The interosseous ligament extends till 1 cm above the tibiotalar joint. In (C) the full length and maximal depth of the incisure are visible. At the level of the tibiotalar joint, the anterior aspect of the fibular incisure flattens again to form the contact area with the fibula (4), which is also flat at its antero-medial border.

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The fibular part of the syndesmosis is congruent with its tibial counterpart. The crista interossea fibularis, i.e. the ridge on the medial aspect of the fibula, also bifurcates into an anterior and posterior margin and forms a convex triangle that is located above the articular facet on the lateral malleolus. The base of the fibular triangle is formed by the anterior tubercle (Wagstaffe–Le Fort tubercle) and the, almost negligible, posterior tubercle. The apex of the fibular triangle and the apex of the tibial triangle are situated at the same level. The convex shape of the distal fibula matches the concave incisura tibialis.

The incisura tibialis is also known under a variety of other names: the incisura fibulae, fibular incisure of the tibia, incisural notch, fibular notch of the tibia, peroneal groove of the tibia and syndesmotic notch. According to international terminology (Terminologia anatomica) its official name is incisura fibularis tibiae. Whenever the incisura tibialis is flattened, i.e. less concave, the distal fibula becomes less convex. The depth of the incisura tibialis increases from proximal to distal and its shape varies from concave (60–75%) to shallow (25–40%), giving the syndesmosis a rectangular shape with irregular forms (Hocker & Pachucki, 1989; Elgafy et al. 2010). Its depth varies from 1.0 to 7.5 mm (Grass, 2000; Sora et al. 2004) and is a little less in women than in men (Yildirim et al. 2003).

Clinical relevance

The size and shape of the incisura tibialis play an important role in ankle injury. The anterior tibial tubercle is larger than the posterior tubercle and prevents forward slipping of the distal fibula, while the diminutive posterior tubercle allows backward dislocation of the distal fibula. In fibula fractures caused by external rotation, the posterior tubercle functions as a fulcrum and the distal fibula spins around its longitudinal axis in a lateral direction (Kelikian & Kelikian, 1985).

A shallow incisura tibialis may predispose to recurrent ankle sprains (Mavi et al. 2002) or syndesmotic injury with fracture-dislocation (Ebraheim et al. 1998). After acute ankle fracture, good repositioning of the fibula is necessary to create a good alignment and rotation of the fibula in the incisura tibialis, in order to maintain a good position of the talus in the tibiofibular joint or ankle mortise. When the talus moves 1 mm laterally, the contact area of the tibiotalar articulation decreases by 42% (Ramsey & Hamilton, 1976). This could lead to early osteoarthritis of the tibiotalar joint.

It is difficult to determine the correct alignment of the fibula on a plain X-ray of the ankle. Several measurements have been introduced to assess the integrity of the syndesmosis and stability of the ankle on X-rays, such as the tibiofibular overlap (TFO) (Pettrone et al. 1983; Harper & Keller, 1989), the tibiofibular clear space (TFCS) (Leeds & Ehrlich, 1984; Sclafani, 1985; Harper & Keller, 1989) and the ratio between the medial and superior clear space (MCS/SCS) (Beumer et al. 2004). However, compared with MRI, CT and peroperative findings, these measurements are not very accurate (Nielson et al. 2005; Miller et al. 2009). Therefore in patients with suspected instability of the distal tibiotalar joint, a CT scan or MRI should be performed to evaluate more accurately the position of the fibula in the incisura tibialis (Taser et al. 2006).

Tibiofibular contact zone

  1. Top of page
  2. Abstract
  3. Introduction
  4. Syndesmotic bones and incisura fibularis
  5. Tibiofibular contact zone
  6. Syndesmotic recess (Recessus tibiofibularis)
  7. The syndesmotic ligaments
  8. Conclusion
  9. Acknowledgements
  10. References

Anatomy

At the base of the syndesmosis there is a small area where the tibia and fibula are in direct contact. This area is called the tibiofibular contact zone. Its facets are covered with a small strip of hyaline cartilage about 0.5–1.0 mm thick (Lanz & Wachsmuth, 1972; Kelikian & Kelikian, 1985; Bartonicek, 2003; Ebraheim et al. 2006) (Figs 2 and 3). The tibial cartilage rim is a continuation of the cartilage covering the tibial plafond and is 3–9 mm in length and about 2–5 mm in height. The rim of fibular cartilage is continuous with the articular facet of the fibular malleolus.

image

Figure 2.  A 45° oblique slice through the right distal tibiofibular syndesmosis of a fresh frozen anatomic specimen (male, 85 years). A thin layer of cartilage (1) covers the lateral tibia and the medial fibula at the level of the tibiofibular contact zone. In between is the syndesmotic recess, which is filled with intra-articularly injected green coloured resin (2) and abuts the posterior margin of the ATIFL (3). In the middle of the recess and just anterior to the PTIFL (4), some fibres of the interosseous ligament (5) are visible. F, fibula; T, tibia.

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image

Figure 3.  A 45° oblique slice through the distal tibiofibular joint of a fresh frozen specimen (male, 86 years). The ATIFL has a triangular aspect and consists of multiple tight fibres interspersed with some fat (1). The fibres start at the broad-based anterior tibial tubercle (Chaput) (2) and converge towards the fibular tubercle (Wagstaffe–Le Fort) (3). Just behind the ATIFL is the small cartilage-covered tibiofibular contact zone (4), which abuts the fat pad (5) of the synovial recess (6). The posterior fibres of the interosseous ligament (7) gradually coalesce with the PTIFL (8). In (C) the network of thin fibrofatty fibres forming the interosseous ligament is visible.

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Clinical relevance

There is little information about the variation in size and presence of the cartilage-covered tibiofibular contact area and little is known about its function. The contact zone is not always present (Bartonicek, 2003).

The minimal size of the cartilaginous facets could be explained by the fact that the main forces acting on the distal tibiofibular articulation are strain forces (Tillmann et al. 1985). The two bones can come into direct contact in maximal plantar flexion when the fibula rotates internally and shifts anteriorly.

Although this articulation can be seen as only a minor joint considering the size of its cartilage surface, this bony connection can play an important role in the detection of malalignment of the malleolar mortise in ankle fractures or in anatomically based reconstructive surgery of the anterior syndesmosis. In this respect a detailed knowledge of the three-dimensional situation after fracture of this joint is of great importance. The articular facets might help as landmarks for accurate repositioning of the lateral malleolus in the incisura fibularis (Bartonicek, 2003).

Syndesmotic recess (Recessus tibiofibularis)

  1. Top of page
  2. Abstract
  3. Introduction
  4. Syndesmotic bones and incisura fibularis
  5. Tibiofibular contact zone
  6. Syndesmotic recess (Recessus tibiofibularis)
  7. The syndesmotic ligaments
  8. Conclusion
  9. Acknowledgements
  10. References

Anatomy

A syndesmotic recess is nearly always present between the distal tibia and fibula (Lanz & Wachsmuth, 1972; Sabacinski et al. 1990) (Figs 4 and 5). This synovial-lined plica extends from the tibiotalar joint and varies in size. Cranially, it is bordered by the distal aspect of the interosseous ligament. Medially, the plica is directly attached to the distal tibia with a small amount of connective tissue. Laterally, a fat-containing synovial fold is interposed between the synovial lining and the fibula, which contains loose connective tissue with an abundance of vessels and occasionally some small nerves (Bartonicek, 2003; Kim et al. 2007) (Figs 6 and 7). The synovial recess is attached to the fibula just proximal to the most superior border of the lateral malleolar articular surface and extends posteriorly with diffuse attachment to the entire posterior margin of the transverse ligament (Sabacinski et al. 1990; Karasick et al. 1997) (Fig. 8).

image

Figure 4.  Correlation between MR image (left) and plastinated slice (right) at the same level through the tibiofibular syndesmosis (female, 84 years). The intra-articularly injected green dye is visible in the tibiofibular recess (1), which extends between the anterior (2) and posterior (3) tibiofibular ligament. As the MR image is obtained without intra-articular contrast, the recess is not visible here. The incisura fibularis is shallow with an irregular contour.

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image

Figure 5.  MR-arthrography of the tibiotalar joint with a coronal view of the syndesmotic recess (female, 43 years). This recess is visible as a vertical, contrast-filled pouch between the distal part of the tibia and fibula (arrow). F, fibula; T, tibia; Ta, talus.

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image

Figure 6.  Coronal proton-density-weighted MR image (female, 23 years). The fat-containing synovial fold (1) protrudes from the incisura fibularis into the lateral superior tibiotalar joint space. During dorsal flexion of the foot, the talus pushes the tibia and fibula outwards, therewith increasing the space of the tibial incisure. This leads to retraction of the fat pad, as can be seen during arthroscopy.

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image

Figure 7.  Microscopy (haematoxylin–azophloxin; female, 89 years). Oblique slice at the level of the anterior (A) and posterior (B) distal tibiofibular syndesmosis. The tibial and fibular facets of the tibiofibular contact zone are covered with a thin layer of cartilage (1). The small recess (2) between the two facets extends anteriorly to the posterior aspect of the ATIFL (3), and posteriorly almost to the anterior aspect of the PTIFL (4). The synovial fold (5), consisting of fat and loose connective tissue, is attached to the fibula and is continuous with the anterior aspect of the PTIFL. The synovial recess (2) is covered by a single cell layer of synoviocytes and is directly attached to the tibia. F, fibula; T, tibia.

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image

Figure 8.  Exposure of syndesmotic ligaments in a dissected right ankle (male, 92 years). (A) The trapezoid multifascicular anterior tibiofibular ligament (ATIFL) (1) runs obliquely upwards from the anterior fibular tubercle towards the anterior tibial tubercle. (B) The band-like posterior tibiofibular ligament (PTIFL) (2) runs obliquely upwards from the posterior fibular tubercle towards the posterior tibial tubercle. (C) View from below after removal of the talus shows the curved and horizontally running transverse ligament (3) and the inferior margin of the ATIFL. In (D) fat (4) from the synovial fold is visible in the tibial incisure between the transverse ligament and the small contact area between the tibia and fibula (5). F, fibula; T, tibia.

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The antero-posterior borders of the syndesmotic recess are variable and depend on the presence of a tibiofibular contact area anteriorly and a synovial fold or fat pad posteriorly. Regarding the anterior border, the plica extends to the posterior aspect of the ATIFL when the tibiofibular contact area is absent (Fig. 9). Posteriorly, when the fat pad is small or absent, the plica borders on the anterior lining of the PTIFL (Fig. 10). Its antero-posterior length varies from 10 to 15 mm (Bartonicek, 2003). The width of the syndesmotic recess is 2 mm and its height varies from 4 to 25 mm (Kopsch, 1922; Arner et al. 1957; Olson, 1981; Pavlov, 1982; Kelikian & Kelikian, 1985; Bartonicek, 2003; Kim et al. 2007).

image

Figure 9.  Correlation between detailed view of ATIFL (1) in a 45° oblique plastinated slice (A) and an MR image (B) taken at exactly the same level (male, 71 years). Green coloured resin is visible in the syndesmotic recess (2) which abuts the posterior margin of the multifascicular ATIFL (1). There is a small tibiofibular contact zone devoid of cartilage just posterior to the ATIFL (3). F, fibula; T, tibia.

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image

Figure 10.  Correlation between detailed view of PTIFL in a 45° oblique plastinated slice (A) and an MR image (B) taken at exactly the same level (male, 71 years). Green coloured resin is visible in the syndesmotic recess (1) which abuts the anterior margin of the multifascicular PTIFL (2). T, tibia. F, F, fibula; T, tibia fibula.

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Clinical relevance

In acute injury to the syndesmosis, i.e. injury mostly to the ATIFL, the syndesmotic recess can tear. In the acute setting, arthrography of the tibiotalar joint would demonstrate leakage of contrast fluid into the incisura tibialis or, depending on the extent of injury, into the interosseous ligament between the tibia and fibula, or even outside the borders of the ATIFL and PTIFL (van Moppes et al. 1980; Wrazidlo et al. 1988).

The syndesmotic recess runs the risk of being traversed during the insertion of fine wires when using external fixators for the treatment of fractures or placement of a set screw. To minimize the risk of septic arthritis of the ankle due to pin tract infections, it is best to avoid areas of capsular extensions (Lee et al. 2005).

In chronic injury of the syndesmosis, the synovial lining may become irregular due to inflammation. Kim et al. (2007) speculated that in contrast-enhanced MRI, an abnormal upward extension of enhancing tissue surrounding the syndesmotic recess could be an ancillary sign of syndesmotic instability caused by syndesmotic disruption.

In inflammation of the syndesmosis, such as rheumatoid arthritis, scalloping of the medial border of the distal fibula can occur due to chronic erosion, secondary to hyperplastic synovial villi and invasive pannus in a ‘bare area’ devoid of articular cartilage. The scalloped defects measured 7–23 mm in length (Karasick et al. 1997).

With dorsiflexion, the synovial fold retracts between the tibia and fibula, and it is pushed downward during plantar flexion of the foot. This movement of the fat pad can be seen easily during ankle arthroscopy. In healthy volunteers the height of the fat pad protruding from the incisura tibialis into the tibiotalar joint varied from 0 to 7 mm (Hermans JJ, Beumer A, Kleinrensink GJ, unpublished MRI data). The synovial fold or fat pad is therefore a normal finding and should not be mistaken for synovial thickening. Both its gross appearance and histologic structure may indicate that this fold functions like a meniscus and is needed for stability and proper function (Sabacinski et al. 1990).

The syndesmotic ligaments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Syndesmotic bones and incisura fibularis
  5. Tibiofibular contact zone
  6. Syndesmotic recess (Recessus tibiofibularis)
  7. The syndesmotic ligaments
  8. Conclusion
  9. Acknowledgements
  10. References

Anterior tibiofibular ligament (Ligamentum tibiofibulare anterius)

Anatomy

About 20% of the distal anterior tibiofibular ligament (ATIFL) is intra-articular (Stoller, 2007). The ATIFL extends in an oblique way from the anterior tubercle of the distal tibia, on average 5 mm above the articular surface, to the anterior tubercle of the distal fibula, running from proximal-medial to distal-lateral and crossing the antero-lateral corner of the talus (Fig. 8). The angle formed by a line along the tibial plafond in the coronal view and a line along the ATIFL varies between 30 and 50° (Kapandji, 1985; Grass, 2000; Bartonicek, 2003; Ebraheim et al. 2006). Posteriorly, it forms an angle of 65° with the sagittal plane (Ebraheim et al. 2006). The ATIFL has a multifascicular aspect, caused by fatty tissue interposed between the multiple collagen bundles (Figs 3, 4 and 9). Viewed in a coronal plane, it is composed of three bundles, separated by 2-mm-wide gaps that converge slightly in the latero-distal direction and consequently give the ATIFL a trapezoidal shape (Bartonicek, 2003; Ebraheim et al. 2006).

The upper part is the shortest (6.0–8.9 mm), with a width of 4.0–4.9 mm and a thickness of 1.8–3.0 mm. It originates just above the anterior tubercle of the tibia and is attached just above the anterior tubercle of the fibula. Sometimes it is divided into two stronger fascicles. The middle, and strongest, part runs between the anterior tubercle of the tibia and fibula. Its measures about 12.0–15.5 mm in length, 8.3–10.0 mm in width and 2.6–4.0 mm in thickness. It is sometimes divided into three or four smaller ligaments. The lower part, which is the longest, extends just below the anterior tubercles and measures 17.0–20.6 mm in length, 3.8–4.0 mm in width and 2.0–2.2 mm in thickness.

An accessory antero-inferior tibiofibular ligament, also called Bassett’s ligament, which runs inferior and parallel to the ATIFL, is described in the literature. This accessory ligament, not demonstrated in this pictorial essay, can be identified in 21–92% of dissected ankles of human anatomic specimen or MRI studies (Nikolopoulos, 1982; Bassett et al. 1990; Ray & Kriz, 1991; Akseki et al. 1999,  2002; Nikolopoulos et al. 2004; Subhas et al. 2008). The fibular attachment of Bassett’s ligament is distal-medial to the ATIFL and its fibres blend with the tibial attachment of the distal fibres of the ATIFL. The ligament is 17–22 mm in length, 1–2 mm in thickness, and 3–5 mm in width (Nikolopoulos et al. 2004; Subhas et al. 2008). It is not covered by synovial tissue, is intra-articular, and crosses the proximo-lateral margin of the ankle and comes into contact with the lateral talar trochlea during dorsiflexion.

Clinical relevance

Bartonicek (2003) described a meniscoid structure just behind the ATIFL. It is possible that he in fact thereby encountered one of the shorter deep fibres of the ATIFL. On axial MRI the ATIFL is triangular-shaped and shows more than one fascicle. Nikolopoulos et al. (2004) demonstrated that in five ankles the ATIFL appeared to consist of two layers, one deep and one superficial, which were separated by a thin fibrofatty septum. Brostroem (1964) mentioned that the superficial anterior fibres are 2–3 cm long and the deeper posterior fibres somewhat shorter. As 20% of the ATIFL lies intra-articularly, the most inferior and deepest fibres are easily seen with arthroscopy and should not be interpreted as a meniscus or scar tissue.

It is easier to get a good depiction of the transverse cross-sectional area of the ATIFL with MRI than with gross macroscopy. Although the ATIFL is described as a flat band on dissection (Muhle et al. 1998), on a transverse cross-section with MRI or plastination it looks more triangular (Hermans et al. 2009). In our experience, we have never seen a separate superficial and deep layer of the ATIFL. In the coronal, axial and oblique MR images the ATIFL consists of a variable number of contiguous fibrous fibres separated by fat, which could give the impression of a multilayered structure. The number of fascicles can vary from a few thick fibres to up to seven thin fibres.

The ATIFL is the weakest of the four syndesmotic ligaments and is the first to yield to forces that create an external rotation of the fibula around its longitudinal axis (Kelikian & Kelikian, 1985).

It is important to distinguish the accessory ligament from the ATIFL because it can potentially cause antero-lateral ankle impingement and pain in the presence of a normal ATIFL due to synovitis and scarring in the antero-lateral groove and cartilage abnormalities in the antero-lateral talar dome (Subhas et al. 2008). Resection of the accessory ligament does not lead to instability and relieves pain in patients with chronic ankle complaints after ankle sprain (Akseki et al. 1999).

In patients with chronic instability of the syndesmosis, an anatomical reconstruction of the anterior syndesmosis can be considered. The widened syndesmosis can be reduced, followed by medial reinsertion of a bone block with the tibial insertion of the intact but elongated ATIFL (Beumer et al. 2000).

As the ATIFL is located superficially, just beneath the skin, it can be well visualized with ultrasound. With high frequency ultrasound (15 MHz), injuries of the ATIFL can be detected with an accuracy of 85% (Milz et al. 1999). As the ATIFL runs obliquely, MR images in an axial plane could lead to depiction of a partly interrupted ligament, leading to a false positive diagnosis of a ruptured ligament. Using an additional oblique image plane of about 45° reduces this problem (Hermans et al. 2010).

Posterior tibiofibular ligament (Ligamentum tibiofibulare posterius)

Anatomy

The PTIFL is a strong ligament that extends from the posterior tibial malleolus to the posterior tubercle of the fibula and runs from proximal-medial to distal-lateral (Fig. 8). It forms a 20–40° angle with the horizontal plane and a 60–85° angle with the sagittal plane (Grass, 2000; Ebraheim et al. 2006). Its lower part, or transverse ligament, runs more horizontally than the PTIFL (Bartonicek, 2003). The PTIFL has a similar shape and structure as the ATIFL. It is triangular with a broad base at the tibial insertion. Its fascicles more or less converge at the posteromedial aspect of the fibula (Figs 4 and 10). Therefore the length of the proximal fibres is shorter than the distal fibres; respectively 9.7 ± 6.9 mm (3.4–21.2 mm) and 21.8 ± 7.5 mm (6.4–32.5 mm). The mean width of the ligament is 17.4 ± 3.5 mm (11.1–21.2 mm), with a tibial insertion thickness of 6.4 ± 1.9 mm (4.4–9.0 mm) and a fibular insertion thickness of 9.7 ± 1.7 mm (8.0–11.4 mm) (Nikolopoulos et al. 2004; Ebraheim et al. 2006). The PTIFL, like the ATIFL, is multifascicular and consists of multiple collagen bundles interspersed with fat. Its most distal fibres are in close contact with the transverse ligament and fibres from the fibular insertion sometimes even appear to be continuous with it (Ebraheim et al. 2006).

Clinical relevance

According to the fracture classification of Lauge-Hansen, rupture of the posterior syndesmosis, i.e. the PTIFL or avulsion fracture of the PTIFL, can occur in supination-eversion, pronation-eversion or pronation-abduction injury of the ankle. As the PTIFL is a thick and strong ligament, excessive stress results more often in a posterior malleolus avulsion fracture than in a rupture of the ligament (Van de Perre et al. 2004). With direct reduction of the posterior malleolus avulsion fracture, the syndesmosis can be stabilized. However, this is only feasible when the PTIFL is intact (Miller et al. 2009).

Transverse ligament (Ligamentum tibiofibulare transversum)

Anatomy

The transverse ligament runs horizontally between the proximal margin of the fibular malleolar fossa and the dorso-distal rim of the tibia and may extend as far as the dorsal aspect of the medial malleolus (Figs 11 and 12). Its length varies from 22 to 43 mm (Nikolopoulos et al. 2004; Ebraheim et al. 2006). It is a thick, round ligament that deepens the postero-inferior rim of the tibia and forms a labrum analogue (Figs 8 and 13). Some fibres of the posterior talofibular ligament coalesce with the most distal fibres of the transverse ligament and form the so-called tibial slip, or intermalleolar ligament (IML) (Fig. 14). According to Oh et al. (2006) the intermalleolar ligament is a separate anatomic entity and was almost invariably present in 81.8% of 77 specimens (Golano et al. 2002). The IML arises slightly proximal to the origin of the posterior talofibular ligament in the malleolar fossa and distal to the origin of the transverse ligament (Rosenberg et al. 1995). Its shape varies from a thick string to a band, with a length of 39.2 mm (28.2–44.9 mm), a width of 3.7 mm (0.8–8.8 mm), and a thickness of 2.8 mm (0.4–5.8 mm), and it occasionally extends into the joint. The medial insertion sometimes consists of two or three slips. The medially arising sites of the IML include both the medial and lateral border of the medial malleolar sulcus, through the septum between the M. flexor digitorum longus and M. tibialis posterior, or the medial part of the posterior margin of the tibia (Oh et al. 2006). The IML runs parallel to the transverse ligament, from which it is always separated by a triangular- or quadrilateral-shaped soft tissue space. During plantar flexion the IML becomes less taut and approximates the transverse ligament (Golano et al. 2002).

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Figure 11.  Axial (A) and oblique images (B) at the level of the tibiotalar joint with the posterior inferior tibiotalar ligament (PTIFL) (1) and, in front of it, the transverse ligament (2) (female, 30 years). The PTIFL runs from the posteromedial aspect of the fibula towards the posterior tibial tubercle. The transverse ligament originates postero-medially from the fibula just above the fibular malleolar fossa and inserts onto the dorsal ridge of the tibia up to the level of the medial malleolus. In (C) the posterior talofibular ligament (3) runs from the fibular malleolar fossa towards the posterior talar tubercle and is only partly depicted. F, fibula; LM, lateral malleolus; MM, medial malleolus; T, tibia; Ta, talus.

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Figure 12.  Axial proton density MR images (A,B) and axial T1-weighted MR images with fat suppression with intra-articular contrast (C,D) at the level of the tibiotalar joint, in the same patient (female, 47 years). The transverse ligament (1) originates postero-medially from the fibula, just above the fibular fossa, and inserts on the dorsal ridge of the tibia. It forms a labrum-like structure to keep the talus from moving posteriorly (A). The posterior tibiofibular ligament (PTIFL) (2) is visible 5 mm above this level, which originates from the postero-medial corner of the fibular malleolus and inserts on the posterior tibial tubercle (B). The transverse ligament (3) extends like a thick band along the entire border of the posterior tibial ridge, where it serves as a labrum for the talus (C). The PTIFL (4) is short and triangular-shaped and bridges the fibula and tibia posteriorly (D). MM, medial malleolus; LM, lateral malleolus; Ta, talus.

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Figure 13.  MR arthrogram with an oblique image at the level of the tibiotalar joint shows the curved transverse ligament (1) running from the posteromedial aspect of the fibula to the posterior inferior rim of the tibia (female, 16 years). F, fibula; T, tibia; Ta, talus.

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Figure 14.  MR-arthrogram: coronal T1-weighted image with fat suppression and with intra-articular contrast in the tibiotalar joint (male, 23 years). The fibula (F), the posterior malleolus of the tibia (T) and the posterior body of the talus (Ta) are visible. The posterior talofibular ligament (TFP) (1) runs more or less horizontally from the fibular fossa to the posterior process of the talus. Just above the origin of the TFP in the fibular fossa, the intermalleolar ligament originates (2), extending medially and fusing with the transverse ligament (3) at the medial aspect of the posterior ridge of the distal tibia. The transverse ligament runs between the posteromedial fibula, just above the fibular fossa, and the posterior ridge of the distal tibia. F, fibula; T, tibia; Ta, talus.

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Clinical relevance

In the literature there is controversy about whether the transverse ligament and distal posterior tibiofibular ligament form one anatomic unit or are two distinct structures. Golano et al. (2002) stated that the transverse ligament is the deep part of the posterior tibiofibular ligament, whereas Lee et al. (1998) demonstrated that MR arthrography allowed resolution of the superficial and deep component of the posterior tibiofibular ligament.

Even more controversy exists about the tibial slip and intermalleolar ligament. Bartonicek (2003) considered the tibial slip to be a reinforced strip of the joint capsule, whereas others showed that the intermalleolar ligament is a separate anatomic structure with diverse morphologic features (Golano et al. 2002; Oh et al. 2006). The observed frequency of the IML varies from 19% in MRI of the ankle to 82% in dissected anatomical specimens (Rosenberg et al. 1995; Milner & Soames, 1998; Golano et al. 2002; Oh et al. 2006). This difference could be due to the use of different techniques, such as MRI, dissection, cryosection or arthroscopy, the number of patients or specimens used or the position of the foot during investigation.

The space between the transverse ligament and IML makes the posterolateral approach in ankle arthroscopy the most suitable for avoiding ligamentous structures. During anterior ankle arthroscopy with standard antero-medial or antero-lateral ports, the transverse and intermalleolar ligament are visible but not the posterior tibiofibular ligament. To visualize the PTIFL, posterior arthroscopy or endoscopy is necessary. The intermalleolar ligament can be the cause of posterior impingement syndrome in ballet dancers, where in extreme plantar flexion, entrapment or even a bucket handle tear of the ligament can occur (Rosenberg et al. 1995; Oh et al. 2006).

Interosseous ligament (Ligamenta tibiofibularia)

Anatomy

The interosseous membrane (Membrana interossea cruris) extends between the tibia and fibula, and at its lowermost end thickens and gives rise to a spatial network of pyramidal shape. This network is filled with fatty tissue and steep running fascicles and forms the interosseous ligament (Figs 1, 2 and 4). Most fibres run in a latero-distal and anterior direction from the tibia to the fibula, although some fibres on the anterior aspect run in the reverse direction. The most distal fibres attach to the tibia at the anterior tubercle level and descend straight to the fibula, where they attach just above the level of the talocrural joint. The most proximal fibres attach to the tibia at the apex of the incisura tibialis (Bartonicek, 2003; Ebraheim et al. 2006). The length of fibres gradually increases from proximal to distal, with a proximal length of 6.6 ± 1.3 mm (5.8–7.6 mm) and distal length of 10.4 ± 3.1 mm (8.2–12.6 mm). The thickness of the interosseous ligament is 4.7 ± 1.1 mm (3.8–5.3 mm), its width at the fibular attachment is 21.2 ± 1.7 mm (20.0–22.5 mm) and its width at the tibial attachment is 17.7 ± 1.0 mm (17.1–18.5 mm). The measurements of Nikolopoulos et al. (2004) differ a little from these values (length 3–6 mm, thickness 2–4 mm and width 2–4 mm). However, the trend of these data is the same. The presence of the interosseous ligament is variable. In some individuals it is absent, whereas in others it is rather markedly present, especially in those with a flattened incisura of the tibia and fibula. The area underneath the interosseous ligament is generally filled with the synovial plica from the tibiotalar joint (Bartonicek, 2003; Ebraheim et al. 2006).

Clinical relevance

Not only is there a gradual transition of the interosseous membrane into the interosseous ligament (Kopsch, 1922), but there also appears to be a continuous transition between the interosseous tibiofibular ligament and the ATIFL and PTIFL. However, Bartonicek (2003) describes that on a sagittal section the ATIFL is sharply separated from the anterior surface of the interosseous ligament by a narrow gap.

The interosseous ligament is thought to act as a ‘spring’, allowing for slight separation between the medial and lateral malleolus during dorsiflexion at the talocrural joint, and thus for some wedging of the talus in the mortise. This is also reflected in the change of shape, reflecting the tension in the ATIFL and PTIFL, as can be observed with ultrasound during plantar- and dorsiflexion of the foot (Fig. 15).

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Figure 15.  Ultrasound images of anterior (1) (A,B) and posterior (2) (C,D) tibiofibular ligament (female, 20 years). F, fibula; T, tibia. In plantar flexion the ATIFL is slack (A). In dorsiflexion the talus pushes the tibia and fibula outwards, with stretching of the anterior tibiofibular ligament as a result (B). The same mechanism applies for the PTIFL. In plantar flexion the ligament is slack with a resulting increase in echogenicity (C). In dorsiflexion the fibres are stretched and are more longitudinally aligned (D). F, fibula; T, tibia.

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The interosseous ligament not only functions as a buffer, neutralizing forces during for instance the ‘heel strike’ phase in walking, but also has a function in stabilizing the talocrural joint during loading (Heim, 1983; Hocker & Pachucki, 1989; Grass, 2000). Haraguchi et al. (2009) described that the distal tibiofibular ligaments and interosseous membrane were loaded throughout the stance phase, which provides a theoretical basis for evidence of syndesmosis screw breakage or loosening. In anatomical specimens the relative importance of the individual syndesmotic ligaments to syndesmotic stability was found to be 35% for the ATIFL, 33% for the transverse ligament, 22% for the interosseous ligament and 9% for the PTIFL (Ogilvie-Harris et al. 1994).

Conclusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Syndesmotic bones and incisura fibularis
  5. Tibiofibular contact zone
  6. Syndesmotic recess (Recessus tibiofibularis)
  7. The syndesmotic ligaments
  8. Conclusion
  9. Acknowledgements
  10. References

As the syndesmosis plays an important role in stability after acute or chronic osseoligamentous injury, understanding of the anatomy is essential in both diagnostic imaging and therapeutic management. In this article we described in detail the anatomy of the separate osseoligamentous structures of the distal tibiofibular joint, which is a complex syndesmotic joint, and discussed the clinical relevance of these structures.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Syndesmotic bones and incisura fibularis
  5. Tibiofibular contact zone
  6. Syndesmotic recess (Recessus tibiofibularis)
  7. The syndesmotic ligaments
  8. Conclusion
  9. Acknowledgements
  10. References

We thank Wolter Oosterhuis, MD, PhD, from the Department of Pathology of the Erasmus University Medical Center, for his description of the microscopy of the syndesmosis. We also thank Sjors Moonen, orthopaedic surgeon at the Amphia Hospital Breda, for his thorough reading of the manuscript.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Syndesmotic bones and incisura fibularis
  5. Tibiofibular contact zone
  6. Syndesmotic recess (Recessus tibiofibularis)
  7. The syndesmotic ligaments
  8. Conclusion
  9. Acknowledgements
  10. References
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