Tibialis posterior tendon

Function

The muscle behind the tendon

The tibialis posterior is the deepest muscle of the deep compartment at the back of the lower leg¹. Its belly arises from three places¹:

the back of the interosseous membrane, the sheet of tough tissue joining the two lower-leg bones¹;
the upper two-thirds of the fibula, the thin outer bone of the lower leg¹;
the upper part of the tibia (shinbone)¹.

The tibial nerve supplies the muscle, and the posterior tibial artery brings its blood¹. Its main jobs are plantar flexion, pointing the foot down, and inversion, turning the sole inward¹.

Where the tendon runs

The tendon forms in the lower third of the leg². It bends sharply behind the medial malleolus to enter the foot². That bend turns the line of pull from vertical to horizontal⁸.

Two views of the bones of the right foot with the tibialis posterior coloured orange. From the inner side, the lower end of the muscle and its tendon run down the back of the shin bone as a narrowing band. The tendon passes behind and then beneath the bony bump on the inner side of the ankle, turns forward, and reaches the inner side of the midfoot. From below, the tendon comes forward from behind the inner ankle, spreads out as it lands on the bones of the midfoot, and sends thin slips on toward the bases of the middle foot bones. — The tibialis posterior of the right foot, from the inner side and from belowRendered by Your Basic Trainer from the Open 3D Model by AnatomyTOOL, which builds on Z-Anatomy and BodyParts3D (Database Center for Life Science). (source, CC BY-SA 4.0). Rendered from the 3D model with only the bones and the tibialis posterior shown, the muscle and its tendon coloured orange as one piece, and the shin bones and muscle cut short above the ankle

The flexor retinaculum, a band of tissue, binds the tendon into a shallow groove on the malleolus and stops it slipping forward⁸. The tendon of the flexor digitorum longus, a deep calf muscle, lies beside it and shares its line of pull⁸.

Where it attaches

In a dissection study of 41 specimens, the main attachment was on the navicular in all 41³. In dissected feet, slips of tendon reached up to eight separate patches of bone³. After the navicular, the bones reached most often were these³:

Share of dissected feet (%). Bars start at zero; the table below gives each value with its source.

Bone	Share of dissected feet
Lateral cuneiform	93%³
Medial cuneiform	80%³
Bases of the metatarsals (long foot bones)	80%³
Cuboid	46%³
Intermediate cuneiform	19%³
Calcaneus (heel bone)	12%³

What it does for the arch

The arch has static supports and dynamic ones⁸. The tibialis posterior and the small muscles within the foot give the dynamic support⁸. When the muscle contracts, it raises the inner arch and locks the midfoot bones, which makes the back and middle of the foot rigid⁶. That lets the gastrocnemius, a calf muscle, act much more efficiently in walking⁶.

In 10 anatomical preparations, the muscle’s inversion moment arm, or leverage, at the subtalar joint was 19.1 mm, the largest measured⁹. For the tibialis anterior, the muscle at the front of the shin, it was 3.8 mm⁹. The subtalar joint lies just below the ankle joint.

Two cadaver experiments point different ways^10,11:

In 13 cadaver feet loaded as in mid-step, loading this tendon moved the foot bones toward restoring arch alignment¹⁰. Loads on the other tendons moved them toward flattening¹⁰.
In eight pairs of cadaver legs loaded as in single-leg standing, a 150 newton pull on the tendon did not restore the forefoot arch angle¹¹.

What it does in walking and running

Stance is the part of each step when the foot is on the ground. Early in stance, the muscle fires to steady the back of the foot and slow the inward roll of the midfoot⁸. At mid-stance it starts inversion, which locks the midfoot and gives the stiffness needed for toe-off⁸. In walking, the tendon tissue is stretched early in stance and shortens late in stance¹². The authors of that study conclude that it absorbs and returns elastic energy¹².

In 15 injury-free runners, the muscles at the back of the ankle, this one among them, were most active in midstance¹³. They worked eccentrically, that is while lengthening, to control the ankle as it bent¹³.

Breakdown

A stretch with few blood vessels

The tendon’s main blood supply comes from the posterior tibial artery¹⁴. Three studies describe a poorly supplied stretch, in different places^4,5,14:

In 28 injected limbs, every tendon had a zone of low blood supply behind and below the medial malleolus⁴.
The authors of a staining study call the front part of the tendon avascular, without blood vessels, where it passes behind the malleolus¹⁴. They note that ruptures are most frequent behind the malleolus¹⁴.
A third study saw a low-vessel region in every tendon examined under the microscope⁵. It ran from about 2.2 cm to about 0.6 cm above the malleolus⁵.

Whether the tendon has a low-blood-supply region that leaves it vulnerable has been a matter of controversy⁵. Where the tendon wraps around the malleolus, its pulley, the surface facing the bone is built like fibrocartilage, a tough, fibrous cartilage¹⁵. That study’s authors state that most spontaneous ruptures happen there¹⁵.

Wear more than sudden tears

Dysfunction of this tendon was once put down to inflammation¹⁶. Later tissue studies showed tendinosis, meaning tendon wear, with a nonspecific repair response¹⁶. It cannot be determined whether such changes come before the dysfunction or after it¹⁶.

The authors of a report on two athletes under 30 state that, unlike the Achilles tendon, this tendon does not typically rupture suddenly¹⁷. The tears they saw at surgery were chronic¹⁷. The tendon may rupture, but dysfunction can develop without a rupture⁶.

From a sore tendon to a changed foot

Dysfunction of the tendon is linked with a collapsing inner arch, a heel that tilts outward and a forefoot that points outward¹⁶. Johnson and Strom described it as passing through stages¹⁸. Two published overviews describe the stages like this^6,8:

Stage	How the overviews describe it
I	Tendinopathy, local tendon pain with loading, and the arch is usually kept⁸
II	A flatfoot has developed, but it can still be corrected by hand⁶
III	The foot shape is fixed, with wear in the subtalar joint⁶
IV	Wear is also present in the ankle joint; Myerson added this stage later⁶

A consensus group stated that these staging systems have never been validated¹⁹. In 2020 it voted to rename adult acquired flatfoot deformity “progressive collapsing foot deformity”¹⁹. The group noted that many, but not all, of these feet have a ruptured posterior tibial tendon¹⁹. The new classification leaves out the tendon-only picture of stage I and part of stage II²⁰. A scoping review, which maps what research exists, calls that early picture tibialis posterior tendinopathy²⁰.

Who is affected

One overview names middle-aged women as the group most often affected⁶.
In a survey of women over 40 from one English general practice group, with 582 usable replies, 3.3% had stage I or II dysfunction²¹.
In 67 patients with rupture, rupture was statistically linked with obesity and, less strongly, with high blood pressure²².
A literature review of risk factors found no clear agreement on which matter most²³.

In runners and athletes

In a review of running injuries, this tendinopathy made up 1.1% of the injuries reported in prevalence studies of non-ultramarathon runners, with a range of 0.5% to 16.0% across studies²⁴. A systematic review of movement risk factors in runners found one study on this tendon’s dysfunction²⁵. A case-control study compared 12 runners with stage I dysfunction and 12 matched healthy runners²⁶. The affected runners’ heels tilted outward more, and for longer, when walking, with no difference in the strength of inversion²⁶. A review describes problems with this tendon as an uncommon source of disability in athletes²⁷.

One explanation offered for medial tibial stress syndrome, exercise-related pain along the inner shin, in runners involves this muscle²⁸. The idea is that repeated contraction of it, the soleus or the flexor digitorum longus overloads the tibia²⁸. In fifty dissected legs, the muscle did not attach at the site of the symptoms in any specimen²⁹. Those authors say this contradicts the idea²⁹.

Recovery

What is known about the course

The natural course of the dysfunction is not fully known, but most agree it is progressive⁸. A scoping review of the early stage found 97 articles on surgery against 12 on non-surgical approaches²⁰.

What exercise studies found

In a randomised trial, which assigns people to groups by chance, 36 adults with stage I or II tendinopathy were followed for 12 weeks³⁰. One group had orthoses (supports such as shaped shoe inserts) and stretching alone³⁰. Two added resistance exercise, concentric (while the muscle shortens) or eccentric³⁰. Scores on the Foot Functional Index, a questionnaire on foot pain, fell in all three groups, and the eccentric group improved most³⁰.
The systematic review did not pool its three trials⁷. Its moderate effects for eccentric exercise on pain and disability come from this trial⁷.
In an uncontrolled series of 47 patients with stage I or II dysfunction, 39 met the study’s success criteria after an orthosis and exercise programme³¹.

That review concluded that high-quality research on non-surgical approaches is scarce⁷.

What the tendon looked like afterwards

Ten people with early-stage tendinopathy did a 10-week programme of eccentric loading and calf stretching, with orthoses³². Symptoms and function improved, but the tendon still looked abnormal on ultrasound afterwards³². Ultrasound is a scan made with sound waves.

A meta-analysis, which pools earlier studies, of how symptom-free human tendons adapt to more loading found 27 studies³³. Each was on the Achilles or the patellar tendon, so none measured this tendon³³.

What surgical series found

One series followed 31 patients for a mean of 15.2 years after surgery for stage II dysfunction³⁴. The surgery moved the flexor digitorum longus tendon and reshaped the heel bone³⁴. Of them, 27 were pain free and functioning well³⁴. In six athletic patients with a full or partial rupture, surgery restored some but not all normal function³⁵. It did not restore the flattened arch³⁵.

Connections

Nerve, bone and neighbours

The tibial nerve supplies the muscle¹. Nerve and tendon share the tarsal tunnel, a passage on the inner side of the ankle³⁶. The tendon’s principal attachment is on the underside of the navicular³⁷.

What shares the work of the arch

The spring ligament, under the inner arch, is described as working together with this tendon in standing and walking³⁷. On MRI, a scan that shows soft tissue, the spring ligament complex was the ligament most often damaged in 31 people with an insufficient tendon³⁸. The deltoid ligament, spring ligament and this tendon are named as key supports of the inner ankle³⁹. The foot muscles share the dynamic support of the arch⁸.

Muscles that pull the other way

In five people with stage II dysfunction, muscle recordings suggested extra, compensating activity in three muscles⁴⁰. These were the peroneals, which oppose it, the tibialis anterior and the gastrocnemius⁴⁰. In eight cadaver feet, pulling on the peroneus longus tendon lowered the foot’s stiffness, and pulling on this tendon raised it⁴¹.

Exercises and stretches

Related exercise pages: running, calf raise and soleus stretch. In five healthy adults scanned by MRI, a single-leg heel raise raised the muscle’s signal by 27%, less than in the three other muscles measured⁴². In young adults without symptoms, the deep calf muscles, this one included, showed low stiffness as the foot was bent upward⁴³.