As the foot contact progress from heel strike the center of pressure (COP) also progress from heel to in between balls of the great toe and the second toe. The COP progression is through the lateral aspect of the foot which comes in the contact with the ground.
Till the toes are off; the foot is in weight bearing at heel contact, foot flat, terminal stance (COP in between the balls of toes). The mid foot which contains maximum number of joints (refers to maximum flexibility) among other foot areas i.e. hind foot and fore foot; actually engages it’s small articulations in such a way that it behaves as a stud or a rigid lever.
Inversion sprains are the commonest of the injuries of the body. In many instances the intertarsal & tarsometatarsal (TM) joints on the lateral foot are injured. Anatomically the TM joints on the medial aspect of the foot are stronger & more rigidly build than lateral TM joints. The inversion injury easily disrupts the lateral TM joints. The spread of the anatomical disruption may be to multiple joints on that aspect.
Following article discuss injuries to TM joint & other mid-foot joints.
1. Injury to the tarsometatarsal joint complex.
Depending on the severity of the force to which the foot is subjected to decides the severity of the injury. According to Thompson MC et al Tarsometatarsal joint complex fracture-dislocations may result from direct or indirect trauma.
Direct injuries are usually the result of a crush and may involve associated compartment syndrome, significant soft-tissue injury, and open fracture-dislocation.
Indirect injuries are often the result of an axial load to the plantarflexed foot.
Midfoot pain after even a minor forefoot injury should raise suspicion; up to 20% of tarsometatarsal joint complex injuries are missed on initial examination. An anteroposterior radiograph with abduction stress may reveal subtle injury, but computed tomography is the preferred imaging modality.
The goal of treatment is the restoration of a pain-free, functional foot.
2. Injuries to talonavicular and calcaneocuboid joints
As we know from our above discussion the transverse tarsal plays a critical role in allowing the foot to transition from a flexible structure that dissipates impact as the foot strikes the ground and accepts the body's weight to the rigid structure that is required for efficient propulsion during toe off.
a. Injuries to talonavicular joint.
Medial longitudinal arch of the foot is controlled by the supportive structures of the talonavicular joint. A fine balance exists between muscular control and static support structures of the talonavicular joint. According to an article by Sammarco VJ; failure of one support structure is often followed by fatigue of the remaining support and loss of function of the entire joint complex.
b. Injury of the calcaneocuboid joint.
The selective rupture of the calcaneocuboid ligament is extremely rare and frequently misdiagnosed. The cuboid dislocation is a moderately common entity with inversion injuries which is also misdiagnosed that presents with mid-foot pain. Cuboid fractures are also not very rare too. Andermahr J et al clarify the mechanism, classification and treatment of this entity.
Discussions of the above said author are discussed on radiographs with varus stress. There are 4 recognized varieties of injuries & depending on the injuries the treatment varies. The following are his recommendations.
Type 1: On varus stress radiographs, there is a calcaneocuboid angle less than 10 degrees without a bony flake. It is treated conservatively by strapping for six weeks.
Type 2: On varus stress radiographs, a calcaneocuboid angle >10 degrees with or without a small bony flake of the ligament insertion is marked. Primarily, conservative treatment be treated with a shoe cast for 6 weeks; if there are persistent symptoms a secondary peroneus brevis tendon graft is recommended.
Type 3: On varus stress radiographs, a calcaneocuboid angle >10 degrees with a big flake is marked. Ideally it is treated by open reduction and refixation of the ligament.
Type 4: Complex injuries are characterised by cuboid compression fracture and ligament rupture. It is treated by open reduction method.