Navicular, medical cuneiform, intermediate cuneiform, lateral cuneiform, cuboid
What is midfoot fusion and why is this surgery performed?
Midfoot fusion is also called arthrodesis. This surgery will fuse the separate bones in the midfoot so that the fused bones act like a single mass of bone.
Normally, just a few of the joints are fused, but entire bones in the midfoot can sometimes be fused.
It is usually done to remove the painful motion of the arthritic joints and to restore the normal positions of these bones (i.e, reconstructing the arch).
The joint surface cartilages are usually completely removed for a successful fusion.
Metal implants are used to achieve stability as well as bone graft if necessary.
Clinical management after the surgery
An immobilizing cast is normally placed for 6 - 10 weeks after the surgery.
Weight bearing is not recommended until after 12 weeks of the surgery date. X-ray investigation is usually performed every 4 weeks to ensure successful fusion.
To assist with gradual weight bearing, a pre-fabricated boot is usually provided.
Neuromechanical Impact of the midfoot fusion specific to gait
Although intra-joint motion of the midfoot is absent, it does not significantly affect the mobility in the forefoot, hindfoot, and ankle. The gait is performed relying on the motion of these structures.
Decreased joint perception is expected as the capsular sensory receptors were removed. This can negatively affect the ability to coordinate intrafoot muscles and joints.
Contribution of midfoot for eversion would significantly decrease. According to Takabayashi et al. (2017), midfoot is the dominant everter (compared to forefoot or rearfoot) during a stance phase of the gait.
Given that foot eversion in stance phase is important for shock absorption and dispersion, decreased contribution of midfoot for eversion could lead to increased stress in other joints (distally to the forefoot and proximally up the kinetic chain).
Sanchis-Sales et al. (2016) also found that midfoot majorly deals with externally generated dorsiflexion moment throughout the stance phase of the gait (except for heel strike to foot plant). This means that midfoot plays such an important role of generating a plantar flexor torque to counter the external dorsiflexion moment while spreading out to absorb the impact force. It has been speculated that passive structures within the midfoot structure aid in generating the plantar flexion torque. Reduced plantar flexion moment through midfoot would impose more demand to posterior calf muscles for generating plantar flexion.
Given the above-mentioned neuromechanical impact of the midfoot fusion, what does Kinesiologist need to assess?
Gait analysis (Is here an indication of shortened stance phase?)
Split stance: weight shifting back and forth (Observe the natural ability to flatten and reshape the arch)
Weight bearing multi-segmental rotation (Observe the natural ability to supinate one side as pronating the other side)
Toe walk (Functionally stable supination? / What is the endurance of the ankle plantar flexors?)
Heel walk (If midfoot eversion is possible, what is the endurance of it?)
Single leg balance (eyes opened & closed)
Seated rearfoot internal / external rotation with the feet on the floor (Observe the ratio between tibial rotation and rearfoot rotation) - Decreased motion of the rearfoot relative to tibial rotation was associated with running-related ankle injuries (Nawoczenski et al., 1998)
Test the ability for 2 point discrimination or light touch (Conscious somatosensation through dorsal medial lemniscus ascending pathway)
Test the ability for a foot tapping following changing metronome beats (unconscious spinocerebellar pathway is involved - Although this wouldn't let us rule out the involvement of descending tract)
Check the mobility of the 1st ray, big toe extension / flexion
Manual muscle testing, active / passive physiological ROM of the foot and ankle
Passive Accessory motion of horizontal forefoot flexion / extension
Passive Accessory motion of subtalar joint
Y balance (or star excursion) balance test (Chronic ankle instability is correlated with low score: Filipa et al., 2010)
What movement may need to be retrained?
Basic non-wieght bearing foot control drills that emphasizes separation among rearfoot, midfoot and forefoot motion.
Eccentric supination of the foot in weight bearing position
Active dorsiflexion while pushing the midfoot into the ground
Forefoot control (toe separation) in weight bearing