Imaging Sports Medicine Injuries of the Foot and Toes

Hilary R. Umans, MD

Albert Einstein College of Medicine, Division of Musculoskeletal Radiology, Jacobi Medical Center, Bronx, New York 10461, USA

The Lisfranc joint, aka the tarsal-metatarsal (TMT) joint, marks the transition between the more rigid midfoot and the relatively flexible forefoot. It provides critical stability in maintenance of both the transverse and longitudinal arch of the foot. That stability is derived from both its osseous geometry and complex capsuloligamentous architecture.

The second metatarsophalangeal (MTP) joint is recessed with respect to the neighboring first and third MTP joints. Multiple facets at the second metatarsal base articulate with all three cuneiforms. The second metatarsal base is shaped like a keystone at the apex of the transverse arch of the foot. Intermetatarsal ligaments connect the second through fifth metatarsal bases, but there is no in-termetatarsal ligament bridging the first and second. Instead, the Lisfranc ligament, the most substantial and strongest at the TMT joint, courses obliquely from the lateral surface of the medial cuneiform in a plantar and lateral direction to insert on the plantar medial base of the second metatarsal [1] (Fig. 1). Disruption or avulsion of the Lisfranc ligament, or fracture of the second meta-tarsal base, results in TMT instability. Left untreated, a Lisfranc injury can result in collapse of the longitudinal arch of the foot.

Although the majority of Lisfranc fracture/dislocations result from highvelocity trauma or crushing injuries, sports-related Lisfranc injuries typically occur as a result of low-velocity indirect force. In athletes, the typical mechanism of injury is an axial load on a plantar flexed and slightly rotated foot [2]. These injuries are particularly common in but not unique to American Football, with offensive linemen most commonly affected [3]. Sports-related Lisfranc injuries are considered in a spectrum of midfoot sprains. Midfoot sprains may or may not include diastasis or fracture at the first intermetatarsal space or second metatarsal base, respectively, and therefore may elude conventional radiographic detection.

Nunley and Vertullo [4] proposed a classification for midfoot sprains that differs from the standard classification systems used for high-velocity traumatic Lisfranc injury. Stage I injury is characterized by a dorsal capsular tear without

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Fig. 1. Axial T1 weighted MR image demonstrates the normal, intact Lisfranc ligament coursing between the lateral aspect of the medial cuneiform to its insertion onto the medial second metatarsal base (curved arrow).

elongation of the Lisfranc ligament; weight-bearing radiographs are normal. Stage II injury includes elongation or disruption of the Lisfranc ligament, with an intact plantar capsular ligament; weight-bearing radiographs demonstrate 2- to 5-mm diastasis at the first intermetatarsal space. Stage III injury includes disruption of the dorsal capsule as well as the Lisfranc ligament and the plantar capsuloligamentous structures; weight-bearing radiographs demonstrate greater than 5 mm diastasis at the first intermetatarsal space, loss of the longitudinal arch height, and, often, associated fracture.

Even in the context of high-velocity traumatic Lisfranc injury, approximately 20% of cases are prospectively missed on conventional foot radiographs [5]. Although alignment may be assessed by evaluating cortical registration across each TMT joint, congruent alignment is most reliably evaluated at the medial cortex of the middle cuneiform and second metatarsal base on anteroposterior (AP) and oblique radiographs. Given a high index of suspicion based on mechanism of injury, midfoot tenderness/swelling, or TMT instability on examination, further imaging is indicated. Although some authors advocate stress views under fluoroscopy, weight-bearing radiographs more effectively stress the TMT joint and permit detection of subtle diastasis at the first intermetatarsal space [4,6] (Fig. 2). If pain precludes weight bearing, ankle block may facilitate the examination.

Overlapping structures about the TMT joint often obscure midfoot fracture on conventional radiographs. Computed tomography (CT) permits improved fracture detection and, although it is a non-weight-bearing examination, may facilitate detection of subtle osseous malalignment [7]. An advantage of MRI over CT is that it can detect trabecular microfracture and bone bruise, and permits direct visualization of the Lisfranc ligament and the capsuloligamentous

Lisfranc Subluxation

Fig. 2. AP weight-bearing radiographs of both feet. There is pathologic widening of the first intermetatarsal space with lateral subluxation of the second metatarsal with respect to the middle cuneiform (curved arrow); this is a grade II Lisfranc injury as described by Nunley and Ver-tullo [4]. Note the normal alignment in the comparison view of the right foot.

Fig. 2. AP weight-bearing radiographs of both feet. There is pathologic widening of the first intermetatarsal space with lateral subluxation of the second metatarsal with respect to the middle cuneiform (curved arrow); this is a grade II Lisfranc injury as described by Nunley and Ver-tullo [4]. Note the normal alignment in the comparison view of the right foot.

structures about the TMT joint [8,9]. It is important to realize that the Lisfranc ligament may appear intact on magnetic resonance imaging (MRI) in the context of mechanically significant injury (Fig. 3). Soft tissue edema on T2-weighted imaging in and around the ligament should be considered suspicious for injury, as should associated bone bruise or fracture at the ligamentous origin and insertion at the medial cuneiform and second metatarsal base (Fig. 4).

Mri Lisfranc Injury

Fig. 3. Axial STIR image through the mid and forefoot demonstrates an apparently intact Lisfranc ligament with surrounding soft tissue edema indicative of midfoot sprain.

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Images Leg Stress Fracture

Fig. 4. Axial T1-weighted (A) and STIR (B) images of the mid and forefoot demonstrate an oblique intra-articular Lisfranc fracture (curved arrows) at the medial base of the second metatarsal. The STIR image demonstrates vague residual marrow edema.

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