Lisfranc Injuries

The Lisfranc “joint” is usually used eponymously to mean the tarsometatarsal joint, although Lisfranc injuries often involve the tarsometatarsal, intermetatarsal, and intertarsal joints. The central stabilizing structure is the Y-shaped Lisfranc ligament, which runs from the medial cuneiform to the base of the second metatarsal; the ligament stabilizes the second metatarsal and is central to maintenance of the midfoot arch. The second metatarsal is the keystone of the transverse arch, and thus rupture of the Lisfranc ligament tends to be the key to Lisfranc injuries. Although initially described as a specific injury, Lisfranc injuries are now taken to refer to any injury defunctioning the Lisfranc joint. These injuries are usually caused by axial loading or indirect rotational forces through the Lisfranc joint in a plantar flexed foot. The plantar directed “V” shape of the second metatarsal makes it susceptible to dorsal dislocation. This family of injuries can also be caused by direct crush injuries when a heavy load lands on the foot, usually resulting in a plantarly displaced fracture.

First Metatarsal Fractures

The first ray is relatively rigid, providing a stable lever arm around which the windlass mechanism functions during the third rocker of gait. Shortening of as little as 7 mm from malunion of a first metatarsal fracture can lead to transfer of load to the lateral side of the foot. This can often result in pain, with transfer lesions of the lesser rays.

The first metatarsal is wider, shorter, and stronger than the lesser metatarsals. As a result of its relative size and strength, when fractures do occur in the first metatarsal they are often resultant on a high-energy injury, with more comminution and a higher incidence of being open.

Fifth Metatarsal Fractures

Injuries to the fifth metatarsal are common, comprising 25% of all metatarsal fractures. They are a significant burden for surgeons and patients alike, with a surprising number of unsatisfactory results and dissatisfied patients. The three common fractures of the base of the fifth metatarsal all occur by different mechanisms.

1. 
   

   1. Avulsion fractures are caused by the pull of peroneus brevis and are classically seen in dancers. Affecting the proximal 1.5 cm of the fifth metatarsal these injuries do not place the blood supply at risk.

   
   
2. 
   

   2. Jones’ fractures are more distal and are caused by inversion injuries. They involve the intermetatarsal facet between the fourth and fifth metatarsals, usually 1.5 to 3 cm from the styloid process.

   
   
3. 
   

   3. Stress fractures are the least common fracture and are seen in the diaphysis, distal to Jones’ fractures.

The fifth metatarsal has a relatively poor blood supply and therefore all three types of fracture risk non-union¹. The diaphyseal blood supply primarily comes from a single vessel entering the diaphysis at the junction of the proximal and middle thirds. Secondary arteries supply the tuberosity and base. This leaves a relatively avascular area in zone 2, where Jones’ fractures occur, and accounts for the high rates of non-union with these fractures. The only level 1 evidence available shows a non-union rate of 33% for those treated in cast, falling to 6% for those who have open reduction and internal fixation².

Second to Fourth Metatarsal Fractures

Acute fractures of the middle metatarsals are rarely isolated and often occur as a result of a high-energy injury, usually either as an extension of a Lisfranc injury, or as a result of the metatarsal bases being forced plantarward. Stress fractures are usually isolated and found in the second and third metatarsals, which are relatively fixed in comparison to the first, fourth, and fifth rays. In stress fractures low bone mineral density is a risk factor for occurrence and also an independent risk factor for non-union.

Together the metatarsal heads form a curved cascade when looked at from above (Lelièvre’s parabola). In the horizontal plane the plantar aspect of the second to the fourth metatarsal heads should all be on the same level. The first metatarsal head lies higher than the other four as the sesamoids are the weightbearing point.

Hallux Fractures and Dislocations

Intra-articular “corner” fractures of the proximal phalanx usually occur with a “stubbed toe” when the great toe is caught while walking barefoot or in sandals. Diaphyseal injuries are usually the result of direct trauma such as kicking a wall, and very high-energy axial loads can result in a pilon type fracture of the base of the toe. Patients commonly present late after the simpler great toe fractures.

Sesamoid Fractures

The two sesamoid bones of the hallux, which lie within the tendon of flexor hallucis brevis, and fibers of the abductor hallucis and adductor hallucis, also attach, respectively, to the tibial and fibular sesamoids. The two sesamoids are connected to each other by the intersesamoidal ligament. As a result of the lever arm of the first metatarsal head the sesamoids bear up to three times the body weight in the normal gait cycle, with the tibial sesamoid bearing a greater proportion of this due to its size and position.

The sesamoids are commonly injured during sport, usually as a result of either a direct axial loading force resulting in a comminuted fracture, or forced hyperextension of the first MTPJ. Stress fractures are seen three times more commonly than acute fractures, often in long-distance runners. The risk of a sesamoid fracture is increased by cavus deformity of the foot and hallux valgus deformity of the great toe.

Misdiagnosis is common, as bipartite or multipartite sesamoids are present in 20%³ of the population as a result of the ossification centers failing to fuse. A bipartite or multipartite sesamoid is only bilateral in 25% of patients and so unilaterality is not a useful sign for assessing a fracture. To compound matters, when a bipartite sesamoid is fractured, it often does so through the fibrocartilagenous junctional zone making detection very difficult. It should therefore be more accurately termed a “diastasis” injury. Diagnosis may be aided by either MRI scanning or more traditionally bone scanning with areas of high signal or tracer uptake indicative of fracture.

Turf Toe

The term “turf toe” was coined in 1976 to describe a plantar capsulo-ligamentous injury of the hallux MTPJ⁴. The condition commonly affects athletes and ballet dancers, and is caused by hyperdorsiflexion of the first MTPJ, usually with an axial load applied with the foot in fixed equinus (such as when a ballerina attempts to land “en pointe”). This results in tearing of the plantar plate and the surrounding structures. Injuries have become commoner in sports people as the use of hard synthetic sports surfaces and soft-soled shoes has become commoner. Astroturf has a higher coefficient of friction than living grass and loses some of its shock absorbency over time. This results in the forefoot being “fixed” to the playing surface, making hyperdorsiflexion injury more likely.

Turf toe is associated with significant morbidity with as many as 50% of athletes complaining of persisting symptoms five years following injury⁵. Once torn, unrestricted motion of the proximal phalanx causes significant compression of the dorsal articular surface of the metatarsal head. Turf toe may be associated with a sesamoid fracture.

Phalangeal Dislocations and Fractures

Fractures of the lesser toe phalanges are seen four times as frequently as those of the hallux⁶. Fractures of the proximal phalanx and dislocations of the proximal interphalangeal joint are usually sustained when barefoot, as the toe can easily catch and be forced into abduction. Distal phalangeal fractures are usually caused by a direct crushing injury or an axial loading force (a “stubbed” toe). Great care must be made not to miss a nailbed injury or open fracture as these injuries need thorough washout and repair of the nail bed.

Lisfranc Injuries

Sprains of the Lisfranc joint are relatively common and have been classified by the grade of injury to the Lisfranc ligament⁷. Differentiation of the grades is aided by weightbearing AP films, to demonstrate instability.

• 
  

  Grade 1: Pain at the site of the Lisfranc ligament with minimal swelling and no instability.

  
  
• 
  

  Grade 2: Pain and swelling with associated laxity, but no instability. Diastasis present between the first and second metatarsals, but no collapse of the medial arch.

  
  
• 
  

  Grade 3: Complete ligamentous disruption with diastasis and loss of the longitudinal arch.

Grade 3 injuries are usually a fracture dislocation, which can also be classified as below.

Complete injuries of the Lisfranc joint, with ligament rupture and defunctioning of the base of the second metatarsal, were originally classified by Quénu and Küss in 1909⁸, a classification that was subsequently modified in 1982 by Hardcastle⁹ and finally updated in 1986 by Myerson¹⁰. The Myerson classification is in common use as it guides treatment and also indicates prognosis (Figure 23.1).

• 
  

  A: Homolateral

  
  
  
  
  • 
    

    A1: total incongruity medial displacement

    
    
  • 
    

    A2: total incongruity lateral displacement.

  
  
• 
  

  B: Isolated

  
  
  
  
  • 
    

    B1: partial incongruity medial displacement

    
    
  • 
    

    B2: partial incongruity lateral displacement.

  
  
• 
  

  C: Divergent

  
  
  
  
  • 
    

    C1: partial divergent displacement

    
    
  • 
    

    C2: total divergent displacement.

It is important to bear in mind that in the normal foot radiograph:

• 
  

  The lateral border of the medial cuneiform should align with the lateral aspect of the first metatarsal.

  
  
• 
  

  The medial aspect of the second metatarsal should align with the medial cortex of the middle cuneiform.

  
  
• 
  

  The medial aspect of the third metatarsal should align with the medial edge of the lateral cuneiform.

  
  
• 
  

  The medial aspect of the fourth metatarsal should align with the medial edge of the cuboid.

Figure 23.1 Myerson classification of Lisfranc injuries.

Fractures of the Base of the Fifth Metatarsal

Fractures of the base of the fifth metatarsal are most commonly classified using the Dameron–Lawrence–Botte zonal classification^11–12. The classification (Figure 23.2) divides injuries into three zones: avulsion fractures of the tubercle (zone 1); Jones’ fractures at the metadiaphyseal junction (zone 2); and diaphyseal stress fractures (zone 3). While this classification is useful, in that it does predict the likelihood of fracture union, it does suffer from the problem that in vivo many injuries cross more than one zone.

Figure 23.2 Dameron–Lawrence–Botte zonal classification of fractures of the base of fifth metatarsal.

Jones’ fractures and stress fractures within 1.5 cm of the tuberosity are also subclassified by the Torg classification¹³:

X-Ray

X-ray is the standard investigation for the forefoot with anteroposterior, oblique, and lateral views (Figure 23.3). These will adequately show most injuries. Acutely radiographs are normally taken with the patient non-weightbearing as a result of pain or for fear of causing further damage. Nevertheless significantly more information, particularly in defining Lisfranc instability and collapse, can be garnered from weightbearing films and stress views. It is essential to correlate radiological and clinical findings. X-rays are often normal in stress fractures from two to six weeks of symptom onset, though they usually progress to show either the stress fracture itself or evidence of healing.

Figure 23.3 A standard radiological trauma series. (a) AP, (b) oblique, and (c) lateral. If the series can be obtained weight bearing this is ideal.

Special Views

Weightbearing Views. AP and lateral x-rays with the patient weight bearing can be useful to show displacement of the Lisfranc joint where there has been complete ligament rupture. This is often missed on standard non-weightbearing films. Where there remains any doubt weightbearing films of the uninjured side may be useful.

Stress Views of the Lisfranc Joint. Stress views can be used to ascertain the extent of the injury if this remains unclear after weightbearing x-rays. They are rarely performed in the emergency department in the acute setting, as to do so would usually require an anesthetic and interpretation can be difficult. They can, however, be very informative at the start of an operation if for no other reason than to document the degree of instability. The widespread availability of preoperative CT and MRI scanning has rendered these views obsolete in many centers.

Sesamoid Views. When assessing the sesamoids two sets of views are useful:

• 
  

  – The medial oblique view, to assess the tibial sesamoid, and the lateral oblique view, to assess the fibular sesamoid, show each sesamoid in a near AP or PA view (depending on technique) and clear the metatarsal head from the projection. The two views are taken with the foot in the AP position and the x-ray beam directed 15° cephalad with the MTPJ extended to 50°.

  
  
• 
  

  – Axial views, with the hallux held dorsiflexed, and a radiograph taken along the longitudinal axis of the sole of the foot to profile the two sesamoids, can also be helpful.

Contralateral x-rays should not be used for interpretation due to the significant variation in bipartite and multipartite sesamoids between sides.

CT Scan

A CT scan is commonly used to assess the extent of injury, especially of the Lisfranc joint. The complex overlapping geometry of the forefoot and midfoot can be clearly viewed with cross-sectional imaging and 3D reconstructions assisting in the assessment of the metatarsal arcade and other fracture patterns. CT is particularly useful in assessing the degree of plantar comminution, which may not be appreciated on plain radiographs. The use of volume rendered images (Figure 23.4) is particularly helpful in understanding fracture patterns, and hence in surgical planning. When assessing fractures using 3D-rendered views there is a risk of missing fractures, or oversimplification of fracture configurations, as these are inherently lower resolution images and should be carefully compared to plain slices.

Figure 23.4 (a) An AP x-ray and (b) a 3D volume-rendered image of the same injury looking at the plantar aspect. While some comminution can be appreciated on the AP x-ray the comminution of the bases of the second to fourth metatarsals can be fully appreciated on the CT scan.

MRI Scan

An MRI scan can aid in the diagnosis of metatarsal stress fractures, as x-rays can remain normal for up to six weeks. MRI may also show a stress reaction within the metatarsal, showing low signal on the T1 and high signal intensity on T2 and STIR sequences, but with no evidence of extension into the cortices. A stress reaction should be treated in the same way as a stress fracture. The diagnosis of a stress reaction is never made on x-ray.

Sesamoid fractures can also be diagnosed on MRI, and the technique is particularly useful in identifying those patients with a diastasis injury of a bipartite or multipartite sesamoid. It may also reveal avascular necrosis of the sesamoid¹⁴.