Reference: Heckmann, James, in Rockwood and Green, 1996, Chapter 32
The foot…. it’s an amazing thing…
Points of Interest
– the unique structure of the subtalar and Chopart’s joints (transverse tarsal joint) allows for both flexibility of the foot during heel-strike in order to soften the blow, and rigidity during toe-off to provide for a solid lever on which to push.
– The midtarsal joint (Chopart’s joint) is the confluence of the talonavicular and the calcaneocuboid joints. When the calcaneus is everted, as in during heelstrike, the talonavicular and calcaneocuboid joints are parallel and thus some motion can occur at the midtarsal joint. When the calcaneus inverts, as in toe-off, the joints are divergent, and the motion at the midtarsal joint is markedly restricted – “locked”. At heelstrike, the subtalar joint everts, unlocks the midtarsal joint, and creates a flexible midfoot; at toe-off, the subtalar joint inverts, locks the midtarsal joint, and creates a rigid lever at the midfoot to gain mechanical advantage for forward propulsion.
Compartment Syndrome of the Foot
– often seen in severe crush injuries
– different authors describe different compartments; Myerson – 4; Manoli – 9.
– Loeffler and Ballard – utilitarian plantar incision beginning posterior to the medial malleolus, extending laterally and distally to the midline, and ending between the first and second metatarsal heads.
– What are the compartments?
– almost all interosseous
– on the medial side, the posterior tibial artery gives off the artery of the tarsal canal, which gives off the deltoid branch going into the medial third of the body via the deltoid ligament
– on the lateral side, the anterior tibial artery gives off a number of branches to the neck and a branch to form the artery of the sinus tarsi.
– on the posterior side, the peroneal artery gives off some branches to the posterior body and a branch to form the artery of the sinus tarsi
– the artery of the sinus tarsi and the tarsal canal join to form a sling under the neck of the talus, which supplies the majority of the body
Fractures of the Neck
Hawkins I – undisplaced, with no displacement of the subtalar joint AVN – 0-13%
Hawkins II – displacement of the subtalar joint AVN – 20-50%
Hawkins III – displacement of the subtalar and ankle joint AVN – 80-100%
Canale & Kelly IV – talar neck fracture plus talar head dislocation
Best way to visualize this on x-ray is to take the film directed at 75o off horizontal towards the ankle, with the foot/ankle pronated 15o. (Canale and Kelly)
Hawkins I – cast (make sure it is truly a type I!!)
Hawkins II – ORIF – even 2 mm of displacement of the subtalar joint can cause problems!
– debatable how to fix: anteromedial incision will allow you to see the fracture well and reduce it, but it is not optimal for the screw insertion. Anterolateral allows you to get that little lip of the body and lag it back. Some go posterolaterally and insert it PA, but this is probably best done as a second incision so that you have one exposure to look at the fracture.
Hawkins III – ORIF – anticipate medial malleolar osteotomy to preserve the deltoid branch. Calcaneal traction pin is good.
– Nonunion is uncommon. Delayed union is common. Malunion is in varus and is a major problem if it occurs.
– Osteonecrosis – look for Hawkins sign – somewhere between 6-8 weeks, look for a bit of subchondral lucency, indicative of vascularization and resorption of bone. This is a good thing. If the bone becomes sclerotic, it is dead, and you should probably put them in a cast to protect them. This seems kinda crazy, as you would have to protect them for over 2 years, while the process of creeping substitution takes place.
If severe degenerative diseases occurs from AVN, options include arthrodesis of the ankle, or tibiocalcaneal arthrodesis, or Blair fusion (preserves the