Anatomy of the distal tibiofibular syndesmosis in adults: a pictorial essay with a multimodality approach

Abstract

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.

Fig. 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.

Fig. 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.

Fig. 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.

Fig. 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.

Fig. 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.

Fig. 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.

Fig. 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.

Fig. 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.

Fig. 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.

Fig. 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.

Fig. 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.

Fig. 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.

Fig. 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.

Fig. 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.

Fig. 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.