The tibialis posterior is a powerful muscle of the lower leg, often called the “deep stabilizer” of the leg and foot. Though difficult to see or feel, its function is foundational to every step you take. This muscle and its strong tendon provide the necessary movement and stability for walking, running, and standing. Understanding its location and function is important for overall foot and ankle health.
Anatomical Location Deep in the Lower Leg
The tibialis posterior muscle belly is situated deep within the calf, shielded by superficial muscles like the soleus and gastrocnemius. It occupies the deep posterior compartment of the lower leg, sharing space with nerves and blood vessels that supply the foot. The muscle originates from the back surfaces of both the tibia (shin bone) and the fibula.
It also attaches to the interosseous membrane, a thick sheet of tissue between the tibia and fibula. This deep, central location makes the muscle nearly impossible to palpate directly. This position allows it to act as a central anchor point, connecting the two bones of the lower leg to the foot.
The Path and Insertion Point
As the muscle fibers travel downward, they converge into the posterior tibial tendon. This tendon runs along the inner side of the ankle, passing directly behind the medial malleolus. The medial malleolus, or inner ankle bone, acts like a pulley, redirecting the tendon’s force into the foot.
After passing this pulley system, the tendon fans out into multiple attachment points across the bottom of the foot. Its primary insertion is on the tuberosity of the navicular bone, located on the inner side of the arch. Smaller slips of the tendon also attach to the medial, intermediate, and lateral cuneiform bones, and the bases of the second, third, and fourth metatarsals. This broad insertion allows the muscle to exert influence over the structure of the entire midfoot.
Essential Role in Foot and Ankle Stability
The tibialis posterior muscle is responsible for two main movements of the foot: plantar flexion and inversion.
Plantar Flexion
Plantar flexion involves pointing the foot and toes downward, helping to propel the body forward during walking.
Inversion
Inversion is the movement that turns the sole of the foot inward, necessary for navigating uneven terrain.
The muscle’s most important function is acting as the primary dynamic stabilizer of the medial longitudinal arch. This arch is the main curve on the inner side of the foot, providing spring and shock absorption. By contracting, the tibialis posterior actively supports the arch during the weight-bearing phase of walking and standing. This action prevents the foot from excessively rolling inward, a motion called overpronation, which maintains proper alignment of the leg.
Common Injuries and Dysfunction
The persistent demands placed on the tendon make it susceptible to overuse injuries, most commonly Posterior Tibial Tendon Dysfunction (PTTD). PTTD is a progressive condition that begins when the tendon becomes inflamed (tendonitis). This initial inflammation is often followed by gradual degeneration and weakening of the tendon structure.
As the tendon weakens, it loses its ability to support the medial longitudinal arch. This failure causes the arch to slowly collapse, leading to acquired flatfoot in adults. Since the tendon cannot hold the foot in proper alignment, the foot and ankle begin to roll inward. A visible sign of this is often referred to as the “too many toes” sign when viewed from behind. Early treatment is important because the condition is progressive and can lead to significant pain, difficulty walking, and arthritis in the foot and ankle joints.