The Hip: Preservation, Replacement and Revision

Anatomy and Radiographs of the Midfoot

- See: Lisfranc's Frx

- Anatomy:
    - proximal end of the second metatarsal is tightly recessed between first and third cuneiforms;
          - this mortise configuration effectively locks entire tarsometarsal complex, preventing medial or lateral translation;
          - no significant dislocation of metatarsals or cuneiforms can occur unless this bone is disrupted;
          - for this reason, pure transmetatarsaltarsal dislocations rarely occur, & rather involve frxs through or around the second metatarsal base;
    - there are no ligaments binding together the first and second metatarsals;
          - this creates a relative weakness between 1st & other metatarsals;
          - the main stabilizer of the 1-2 intermetatarsal joint is Lisfranc's ligament;
    - Lisfranc's ligament:
          - strong oblique ligament which extends from plantar-lateral aspect of medial cuneiform, passes in front of the intercuneiform ligament, and inserts into the plantar-medial of second metatarsal;
          - variations:
                 - in about 20% of patients, two separate bands of the ligament are present (dorsal and plantar);
                 - in patients with two separate ligamentous bands, partial ligament injuries are possible;
          - function:
                 - acts to connect lateral metatarsals to the medial cuneiform;
                 - reinforces bony stability of base of the 2nd metatarsal between medial and lateral cuneiforms;
    - dorsalis pedis artery:
          - crosses Lisfranc's joint & dives deep between bases of the first and second metatarsals to form plantar arterial arch, making it susceptible to damage at time of injury or open reduction;

- Radiographs:  
    - lateral view:
            - metatarsal is never more dorsal than its respective tarsal bone but, on occassion, may be slightly plantar to tarsal bone;
    - AP view:
            - medial borders of 2nd metatarsal base & medial border of middle cuneiform, normally form a straight, unbroken line;
            - disruption of this line indicatives unstable TMT injury;
    - oblique view:
            - allows evaluation of the lateral midfoot;
            - medial border of 4th metatarsal base & medial border of cuboid, normally form a straight unbroken line;

- Equivocal Injury:
    - fractures of the base of the 2nd metatarsal should always rainse suspicions of tarsometatarsal injury;
    - any comminution or diastasis between the medial cunnieform and 2nd metatarsal indicates functional disruption of Lisfranc's ligamentous complex;
    - wt bearing AP:
           - w/ questionable injury, consider wt bearing AP view to assess 1-2 interval;
           - diastasis of the 2nd metatarsal-medial cuneiform articulation, or widening of the first 1-2 intermetatarsal interval greater than 2 mm (compared to the opposite foot) indicates subluxation and warrents closed reduction and percutaneous scew fixation;
                  - Potter, et al (1998) noted that normal separation of 1-5 mm may be found between the metatarsals, and therefore it is vital to compare the injured foot to the uninjured foot;
           - if standing AP is unacceptable to the patient then consider CT scan;
    - abudction stress AP:
          - in the study by Coss HS, et al (1998), cadavers had ligamentous sectioning and then underwent abduction stress AP x-rays;
          - motivation for the study is the observation that w/ Lisfranc strain, abduction stress will move the forefoot laterally;
          - in a control population a line tangential to the navicular and medial cuneiform (medial column line) intersected the base of the first metatarsal (even with abduction stress);
          - in cadavers w/ ligamentous sectioning and applied abduction stress, the medial column line falls medial to the metatarsal;
          - the authors also noted that the abduction stress AP needs to be taken w/o pronation or supination;
          - of note, these authors noted that cadavers w/ ligamentous sectioning, did not show more than 1.5 mm of widening w/ simulated wt bearing;
    - MRI:
           - use of MRI in Lisfranc fractures to evaluate the Lisfranc ligament was studied by HG Potter MD et al. 1998.
                  - axial views were used to visualize the Lisfranc ligament;
                  - these authors noted that all patients with complete ligament tears had at least 2 mm or more displacement between the second metatarsal and medial cuneiform (compared to the opposite side);
                  - they suggest that an MRI be ordered when there is equivocal widening and likewise that an MRI not be ordered when the diastasis is greater than 2 mm (since ligament disruption is most likely present)

Magnetic resonance imaging of the Lisfranc ligament of the foot.

Abduction stress and AP weightbearing radiography of purely ligamentous injury in the tarsometatarsal joint.

Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Tuesday, September 4, 2012 12:07 pm