The previous post in this series discussed the rearfoot considerations of pronation and supination of the foot, and continuing with the theme of breaking down and simplifying the process into three parts from posterior to anterior, this post will address the midfoot considerations. The necessity of a good biomechanical exam and gait evaluation, along with other aspects of any given individual patient's needs, such as intended shoe gear, activity, body morphology, gender, age and weight in help determining which orthotic corrections will prove to be the most beneficial to the patient, in a timely and efficient manner.
Pronation is the natural inward roll of the foot after heel strike. It helps absorb shock and adapt to uneven surfaces. Movements involved (tri-planar) include eversion (frontal plane), sole of the foot turns outward, abduction (transverse plane), foot moves away from the midline, and plantar flexion (sagittal plane), top of the foot moves downward in the closed kinetic chain. Midfoot role in pronation, unlocks to allow the foot to adapt to the ground (increased mobility), Talonavicular and Calcaneocuboid joints become more flexible, essential for shock absorption during the loading response of gait.
Supination is the outward roll of the foot during push-off. It makes the foot more rigid to act as an efficient lever for propulsion. Movements involved (tri-planar) are inversion (frontal plane), sole of the foot turns inward, adduction (transverse plane), foot moves toward the midline, and dorsiflexion (sagittal plane), top of the foot moves upwards in the closed kinetic chain. Midfoot role in supination, locks into a rigid structure to allow efficient force transfer, Talonavicular and Calcaneocuboid joints become stable, essential for terminal stance and pre-swing phases of gait.
Key midfoot considerations include mobility vs. stability and balance. The midfoot needs to shift between being mobile during pronation of heel contact and rigid during supination entering the propulsive phase of the gait cycle and eventually toe off. Common dysfunctions include excessive pronation (midfoot collapse): which leads to overuse injuries like plantar fasciitis, shin splints and Posterior Tibial Tendinitis, limited pronation (rigid midfoot) which leads to poor shock absorption, and excessive stress on knees and hips, and excessive supination (rigid Pes Cavus foot) which leads to poor ground adaptation, and increased stress fracture and ankle sprains risk.
These muscles help control and decelerate pronation, preventing collapse of the arch and excessive motion; Peroneus Longus and Brevis which everts and plantarflexes the foot, Extensor Digitorum Longus assists with dorsiflexion and eversion, Tibialis Anterior dorsiflexes and can assist in controlling pronation eccentrically, and intrinsic foot muscles (like Abductor Hallucis, Flexor Digitorum Brevis) which helps maintain arch integrity while allowing mobility.
These muscles lock the midfoot and rearfoot, allowing forceful push-off in gait; Tibialis Posterior is a key supinator, inverting and plantarflexing the fore foot, and supports the medial arch, Tibialis Anterior (concentrically) assists with inversion and dorsiflexion of the ankle, Flexor Hallucis Longus plantarflexes and assists medial arch support, Flexor Digitorum Longus plantarflexes the toes and also supports the medial arch.
Joint mobility testing to assess Subtalar, Talonavicular and Calcaneocuboid mobility which should allow movement during pronation and stiffening in supination. First ray (1st metatarsal) mobility ,important for push-off mechanics, should lock when the midfoot is supinated and unlock when the midfoot is pronated. Hypo- or hypermobility of a patient's foot can affect foot function. Laterally the Lisfranc’s joint can also be hypermobile at the level of the Cuboid-4th, 5th metatarsal base causing subluxation and pain.
Muscle testing for Tibialis Posterior strength includes resisted inversion and plantarflexion. Tibialis Anterior strength includes resisted dorsiflexion and inversion. Weakness leads to poor arch control, pronation issues. Peroneal Longus strength involves resisted eversion of the foot and plantarflexion of the first ray. Weakness leads to poor lateral foot stability, over-supination tendency, and pronatory arch instability at the same time. Intrinsic foot muscles are tested with toe curls to evaluate/control arch height and stability.
Static foot posture evaluation should include Navicular drop test: Measures arch collapse when moving from seated to standing (difference in Navicular height) or the Navicular drift/drop test, as well as overall arch height observation. The dynamic assessment (walking/gait analysis) should include looking for excessive medial collapse (overpronation), rigid high arch and poor shock absorption (underpronation or oversupination),adequate heel strike to toe-off progression. Ideally, the foot should move from a pronated (mobile) to a supinated (rigid) position during the midstance phase. A good test is the single-leg stance test, watch for medial or lateral sway indicating instability.
Determining the medial arch height is the most critical decision regarding the midfoot portion of the orthotic. The relative rigidity or flexibility of the frame material should also be determined at this point, as well as the potential use of a frame filler, to help determine the level of arch support of the orthotic device. Additional corrections to the medial middle portion of the orthotic, such as the scaphoid pad are available. A wide arch profile or a medial flap are both capable of increasing the medial support in the hypermobile flat foot. A Navicular button out can be used to accommodate enlarged or accessory Navicular bones. A fascial groove can be used with or without the presence of plantar fibromatosis, when maintaining a tight medial arch support is important while simultaneously avoiding irritation of a bowstrung plantar fascia. In the case of desired additional lateral support of the midfoot, one should consider using a lateral frame reinforcement, with or without additional corrections. Cuboid offloading pads are available in various heights for cases of Cuboid subluxation. A cutout for a prominent 5th metatarsal base is also valuable in cases associated with metatarsus adductus or post 5th metatarsal fracture.
