Supination at the Subtalar Joint and the Distal Intertarsal Joints

날짜:

 


Supination at the Subtalar Joint

At approximately 15–20% of the gait cycle, the transverse plane motion of the supporting limb transitions from internal rotation to external rotation. The external rotation of the tibia, while the foot remains fixed on the ground, generally coincides with the initiation of the swing phase in the opposite limb. With the supporting foot firmly stabilized on the ground, the external rotation of the tibia along the femur gradually shifts the motion of the talus in the transverse plane from internal rotation to external rotation.

As a result, around 35% of the gait cycle, the subtalar joint, which was in eversion (pronation), begins a rapid transition toward inversion (supination). As the rearfoot undergoes supination, the midfoot and forefoot must simultaneously rotate in relative eversion to maintain full contact with the ground. In late stance, the supinated subtalar joint and the elevated, tensioned medial longitudinal arch transform the midfoot into a more rigid lever, which is crucial for propulsion.

The posterior lower leg muscles, including the gastrocnemius and soleus, actively utilize this structural stability to efficiently transfer the powerful forces generated through the Achilles tendon from the midfoot to the metatarsal heads during walking or running propulsion. However, if excessive pronation persists until the late stance phase, achieving proper midfoot stability becomes difficult. As a result, intrinsic and extrinsic foot muscles compensate by overworking to maintain the medial longitudinal arch, leading to chronic overuse of these muscles over time. This prolonged muscular overactivity can contribute to widespread muscle fatigue and pain-related overuse syndromes throughout the lower limb and foot.

Distal Intertarsal Joints

The distal intertarsal joints are a group of three joints or joint complexes within the midfoot that play a crucial role in maintaining stability and flexibility. Each of these joints is responsible for specific regions of the midfoot and collectively contributes to both structural integrity and adaptability.

Structure and Function

As an integrated system, the distal intertarsal joints serve two primary functions:
  1. Assisting Transverse Tarsal Joint Movements – They support the transverse tarsal joint in facilitating adaptable movements during midfoot pronation and supination.
  1. Maintaining Transverse Arch Stability – They contribute to forming the transverse arch, which is essential for structural support in the midfoot.
The individual range of motion of these joints is relatively limited, and their subtle movements are often not easily distinguishable in standard clinical observations. However, despite their minimal motion, these joints play a significant role in allowing the midfoot to efficiently distribute loads and maintain overall foot mechanics.