"articolazione di Lisfranc": anatomia e patologia

Definizione e Anatomia

Il complesso articolare di Lisfranc  viene riferito all'articolazione tra I e II osso metatatarsale con l'osso cuneiforme mediale (I) ed intermedio (II)  (vedi schema anatomico sottostante).

Il complesso legamentoso di  Lisfranc  è una  larga banda del tessuto collageno plantare che si espande ad unire l'articolazione tra  cuneiforme mediale e la base del secondo osso metatarsale; mentre il legamento trasverso unisce la porzione laterale della base  tra II e V osso metatarsale,  non esiste il legamento trasverso tra I e II osso metatarsale. La capsula articolare ed il legamento dorsale formano soltanto il minimorinforzo dorsale di tale complesso articolare.  L'architettura ossea di questa "articolazione", specificalmente l'incastro  tra seconda base metatarsale e cuneiforme, forma il punto  focale che supporta l'intero complesso articolare. 

Lo stiramento capsulare è il riscontro traumatico più frequente. La severità della distrazione dipende dall'energia assorbita nel trauma. Most tarsometatarsal ligament injuries are grade I (pain at the joint, with minimal swelling and no instability) or grade II (increased pain and swelling at the joint, with mild laxity but no instability). TLa distrazione di III grado representa la  completa interruzione del complesso legamentoso, spesso accompagnata ad avulsione ossea della bratta inserzionale sulla II base metatarsale (vedi RM sottostante).

Meccanismo di lesione 

La lesione del complesso di Lisfranc può avvenire per trauma diretto od indiretto. Il trauma diretto avviene quando una forza esterna determina lo stiramento del mesopiede; il trauma indiretto  avviene quando la forza si trasmette sul piede bloccato  che diventa il fulcro di rotazione su cui  il peso del corpo diventa la forsa determinante per la torzione, rotazione o compressione.

Per la sua limitata mobilità, l'articolazione di Lisfranc  assicura uno stabile asse di rotazione  del piede, ed svolge un ruolo importante per la flessione e dorsiflessione del piede. The horizontal axis, about which plantar flexion and dorsiflexion occur, passa direttamente attraversola giunzione metafisi-diafisi della base del II ossometatarsale. Pertanto , con la perdita del supporto plantare e l'immobilità del II metatarso, mettendo il piede in estrema flessione plantare a causa di una spinta assiale si può determinare lo stress che causa la lesione del complesso legamentoso di Lisfranc.

Diagnosi clinica

 Evidente sub-lussazione o deviazione laterale del mesopiede è raro. Tumefazione della regione del mesopiede, impotenza funzionale e inabilità a sostenere il peso del corpo sono i segni clinici che suggeriscono la diagnosi.

PHYSICAL EXAMINATION

When Lisfranc joint complex injury is suspected, palpation of the foot should begin distally and continue proximally to each tarsometatarsal articulation. Tenderness along the tarsometatarsal joints supports the diagnosis of midfoot sprain with the potential for segmental instability.4

Pain can localize to the medial or lateral aspect of the foot at the tarsometatarsal region on direct palpation, or it can be produced by abduction and pronation of the forefoot while the hindfoot is held fixed.4 Another diagnostic clue is the patient's inability to bear weight while standing on tiptoe.3

The dorsalis pedis pulse and capillary refill should also be evaluated. The dorsalis pedis artery courses over the proximal head of the second metatarsal. Thus, it is susceptible to disruption in a severe dislocation.11

RADIOGRAPHS

The initial radiographs of a suspected Lisfranc joint injury should include weight-bearing anteroposterior and lateral views, as well as a 30-degree oblique view.1,4,9,12 A weight-bearing radiograph is necessary, because a non–weight-bearing view may not reveal the injury. As an example, Figure 6 is a non–weight-bearing radiograph of the foot shown in Figure 2. Note that the patient's foot appears to be normal in the non–weight-bearing view. The diastasis between the base of the first and second metatarsals or the medial and middle cuneiforms should be evaluated carefully and compared with the unaffected side.

On the radiographs, dislocation of the tarsometatarsal joint is indicated by the following: (1) loss of in-line arrangement of the lateral margin of the first metatarsal base with the lateral edge of the medial (first) cuneiform; (2) loss of in-line arrangement of the medial margin of the second metatarsal base with the medial edge of the middle (second) cuneiform in the weight-bearing anteroposterior view1(Figure 2) and (3) the presence of small avulsed fragments (fleck sign), which are further indications of ligamentous injury and probable joint disruption5 (Figure 3).

The lateral radiographic view of the foot may show a diagnostic “step-off,” which means that the dorsal surface of the proximal second metatarsal is higher than the dorsal surface of the middle cuneiform(Figure 1). On an oblique view, the medial edge of the fourth metatarsal base should be aligned with the medial edge of the cuboid.12 The radiographic evaluation may be negative in the patient who, in attempting ambulation, has caused the dislocation to spontaneously reduce.7

Computed tomographic (CT) scanning or bone scanning is helpful in diagnosing difficult cases of Lisfranc joint injury. The CT scan may also be useful in formulating the surgical treatment plan.10,12

Some investigators13 have suggested that radiographic displacement or flattening of the longitudinal arch of the foot is associated with a poor prognosis. This finding may also correlate well with the patient's functional result, even after treatment.13 Other physicians caution that this radiographic abnormality pertains specifically to subtle injuries of the Lisfranc joint.14

TREATMENT

Early diagnosis of a Lisfranc joint injury is imperative for proper management and the prevention of a poor functional outcome.3 With a general knowledge of both conservative and operative treatment options, the primary care physician can decide whether to treat the injury nonoperatively or refer the patient to an orthopedist.

NONOPERATIVE TREATMENT

If the clinical evaluation indicates the probability of a mild or moderate sprain and the radiograph shows no diastasis, immobilization is suggested. Treatment with a short-leg walking cast,6 a removable short-leg orthotic or a non–weight-bearing cast4 is continued for four to six weeks or until symptoms have resolved. The potential for disability following a Lisfranc joint injury justifies the use of a non–weight-bearing cast.

After the period of immobilization, ambulation and rehabilitation exercises should be progressive. If the symptoms persist up to two weeks after rehabilitation has begun, a repeat weight-bearing radiograph must be obtained to evaluate the joint articulation for instability5 and evidence of delayed separation (i.e., disarticulation worsened after weight-bearing).

NONOPERATIVE VS. OPERATIVE TREATMENT

The treatment of Lisfranc joint complex fracture–dislocations remains controversial. Some investigators5,6,11 believe that nonoperative management of fractures and fracture-dislocations is ineffective, because the reduction and alignment that occur with casting are lost when soft tissue swelling decreases.

According to some investigators,3,6 a displacement of more than 2 mm requires open reduction and internal fixation to avoid a poor outcome,3,6 especially in athletes.4 Others13 report no correlation between the degree of diastasis and the eventual functional outcome. All studies indicate that timely diagnosis facilitates treatment and decreases long-term disability.

OPERATIVE TREATMENT

If surgical repair is warranted, it should be done within the first 12 to 24 hours after the injury. Alternatively, surgery can be performed after seven to 10 days to allow the reduction of swelling.4,5,15

While some orthopedists3,4,6 prefer closed fixation with percutaneous K-wires (Kirshner wires), others5,11 report that this method does not hold anatomic reduction and fixation. An alternative method involves the use of open reduction and internal fixation with AO screw fixation (i.e., meets Arbeitsgemeinschaft für Osteosynthesefragen international standards). An open surgical field allows easier removal of fragments or soft tissue that may be hindering reduction of the dislocation.3,5,6

After open reduction and internal fixation, most orthopedists suggest that the foot be immobilized in a cast for eight to 12 weeks with minimal (toe-touch) weight-bearing.3,5,11 Noncasted, full weight-bearing usually is not allowed until the AO screw or similar device is removed at eight to 12 weeks.3,5 For three months after cast removal, the patient should wear a protective shoe with a well-molded orthotic.11

COMPLICATIONS

Post-traumatic arthrosis is the most common complication of Lisfranc joint injury.2,11 This complication is directly related to the degree of comminution of the articular surface in the joint.11

No consensus exists regarding the most effective treatment for Lisfranc joint injury when the diagnosis is delayed.3 Whether delayed treatment will prevent post-traumatic arthrosis and chronic pain is also controversial.3,13 The three factors that appear to be most important in predicting the occurrence of complications with Lisfranc joint injuries are the extent of local trauma, a delay in injury recognition and the degree of displacement.16 In general, procedures such as arthrodesis for post-traumatic arthritis should not be performed until at least one year after the initial injury.4,13,16