Tibialis Posterior Anatomy

Tibialis posterior is the deepest and most central muscle of the deep posterior compartment of the leg. It arises from the interosseous membrane and the adjoining posterior surfaces of both the tibia and the fibula, so it is the only muscle in the leg that takes origin from both bones and from the membrane between them. Its tendon runs behind the medial malleolus, turns sharply forward beneath the sustentaculum tali, and fans out onto almost every bone of the midfoot.

Functionally it is far more than an invertor. During stance it is the dynamic locker of the transverse tarsal joint: by inverting the hindfoot it brings the talonavicular and calcaneocuboid axes out of parallel, converting the flexible midfoot into a rigid lever against which the gastrocsoleus can push. Its loss produces the single most common acquired deformity of the adult foot.

Actions by plane

• Frontal: inversion (supination) of the subtalar and transverse tarsal joints - its dominant and defining action. It is the strongest invertor of the foot, roughly twice as strong as its direct antagonist peroneus brevis.
• Sagittal: weak ankle plantarflexion; the tendon passes posterior to the ankle axis but its moment arm is small.
• Transverse: adduction of the forefoot, resisting the abduction that characterises the collapsing flatfoot.
• Arch: elevation and dynamic support of the medial longitudinal arch through its broad plantar insertion, acting as a dynamic sling under the talonavicular joint and augmenting the static spring ligament.

Timing within gait

• Active from just after heel strike through to heel rise - an early and mid-stance muscle.
• Eccentric early: it decelerates the physiological pronation that occurs after heel strike, controlling the rate of arch flattening.
• Concentric at heel rise: it inverts the calcaneus, locks the transverse tarsal joint, and hands the foot over to the gastrocsoleus as a rigid lever.
• It is essentially silent in swing, which is why it is a poor donor for a swing-phase role such as dorsiflexion without phase conversion.

Excursion and strength - the numbers that matter for transfers

• Excursion approximately 1 to 1.5 cm in its working range - the shortest useful excursion of any of the major tendons about the hindfoot.
• Flexor digitorum longus excursion is roughly 2 to 3 cm and its strength is only around one-third that of tibialis posterior.
• Consequence: flexor digitorum longus is not a strength-matched substitute for tibialis posterior. The FDL transfer works not by replacing lost inversion power but by acting as a tenodesis and a proprioceptive checkrein, and by supplementing a bony realignment. This is exactly why the transfer must be combined with a medial displacement calcaneal osteotomy - the osteotomy does the mechanical work; the tendon transfer holds the correction and provides some dynamic support.

Static versus dynamic support of the arch

Palpation

• The tendon is palpable immediately behind and inferior to the medial malleolus, running forward to the prominent navicular tuberosity, which sits roughly 2.5 to 3 cm distal and anterior to the malleolar tip.
• Ask for resisted inversion with the foot in plantarflexion (which relaxes tibialis anterior) - this isolates tibialis posterior better than any other manoeuvre.
• Swelling and tenderness along the tendon course, with a boggy fullness behind the malleolus, is the earliest physical sign of stage I disease.

Named tests and signs

Interpreting the single heel-raise properly

• The test has two components. First, can the patient rise? Second, does the heel invert as they rise?
• A patient may rise onto the toes using the gastrocsoleus alone yet the heel remains in valgus - that is a positive test and indicates tibialis posterior insufficiency.
• Fatigue variant: ask for ten repetitions. Early dysfunction shows as progressive loss of height and loss of heel inversion with repetition, when a single attempt looked normal.
• Fingertip balance support is permitted; without it, balance failure produces false positives.

Additional assessment required before surgery

• Flexibility of the hindfoot - stage II versus stage III. This is the single most important determinant of treatment.
• Forefoot varus (supination) - after correcting the hindfoot to neutral, look at the plane of the forefoot. A fixed forefoot varus of more than about 10 to 15 degrees needs a medial column procedure (Cotton opening wedge medial cuneiform osteotomy or a naviculocuneiform or first tarsometatarsal fusion), otherwise the corrected hindfoot will simply fall back into valgus to get the first ray to the ground.
• Forefoot abduction - assess talonavicular uncoverage on a weightbearing anteroposterior radiograph. Uncoverage of more than about 40 per cent suggests the need for lateral column lengthening.
• Gastrocnemius contracture - a Silfverskiold test in every case.
• Ankle valgus - a weightbearing ankle radiograph or weightbearing CT to exclude stage IV.

Radiographic parameters

• Weightbearing lateral: Meary line (talus-first metatarsal angle) breaks plantarwards at the talonavicular or naviculocuneiform level; the calcaneal pitch falls below about 18 degrees; the lateral talocalcaneal angle increases.
• Weightbearing anteroposterior: increased talonavicular uncoverage, increased talus-first metatarsal angle, forefoot abduction.
• Hindfoot alignment (Saltzman) view: quantifies valgus of the calcaneus relative to the tibial axis.
• Weightbearing CT increasingly demonstrates peritalar subluxation, sinus tarsi and subfibular impingement, and middle facet subluxation, which correlates strongly with the clinical deformity.
• MRI: tenosynovial fluid, tendon thickening or attenuation, longitudinal split tears, and integrity of the spring ligament and deltoid.

Posterior tibial tendon dysfunction and progressive collapsing foot deformity

The condition is now widely termed progressive collapsing foot deformity (PCFD) to acknowledge that the tendon is one component of a multiplanar deformity, but the Johnson and Strom staging with the Myerson modification remains the language of the exam.

• Stage II is subdivided in common practice into IIA (minimal forefoot abduction, treated with medial displacement calcaneal osteotomy and FDL transfer) and IIB (significant forefoot abduction with more than about 40 per cent talonavicular uncoverage, requiring lateral column lengthening in addition).
• Risk factors: female sex, age over 40, obesity, hypertension, diabetes, seronegative and inflammatory arthropathy, prior local steroid injection, and pre-existing pes planus.
• Presentation: medial hindfoot pain and swelling early; as the deformity progresses the pain often migrates laterally to the sinus tarsi and the subfibular region as the calcaneus impinges beneath the fibula. A patient describing lateral hindfoot pain with a flat foot has advanced disease, not a new problem.

Acute rupture and traumatic injury

• Acute traumatic rupture is uncommon and follows a forced eversion injury or a medial malleolar fracture with entrapment. It is often missed in the trauma setting.
• Tendon entrapment or incarceration within a medial malleolar fracture or a subtalar dislocation prevents reduction; the tibialis posterior tendon is the classic block to reduction of a lateral subtalar dislocation, while the peroneals block a medial dislocation.
• Look specifically for the tendon in any medial malleolar fracture that will not reduce, and in any open reduction of a pilon or plafond injury approached medially.

Tarsal tunnel syndrome

• Compression of the tibial nerve beneath the flexor retinaculum (laciniate ligament) between the medial malleolus and the calcaneus.
• Causes: space-occupying lesions (ganglion, lipoma, varicosities, accessory muscle such as an accessory flexor digitorum accessorius longus), post-traumatic scarring and malunion, tenosynovitis of the adjacent flexor tendons, and hindfoot valgus, which stretches the nerve.
• Findings: burning plantar pain, positive Tinel over the tunnel, a positive dorsiflexion-eversion test (sustained maximal dorsiflexion and eversion with toe extension for 5 to 10 seconds reproduces symptoms), and sensory disturbance in the medial or lateral plantar territory. Heel sensation is often spared because the medial calcaneal branch may arise proximal to the retinaculum.
• Important link: a valgus hindfoot from tibialis posterior dysfunction can itself produce a traction tarsal tunnel syndrome, and correcting the deformity may relieve the neuropathy.

Deep posterior compartment syndrome

• The deep posterior compartment contains tibialis posterior, flexor digitorum longus, flexor hallucis longus, the tibial nerve and the posterior tibial and peroneal vessels.
• Clinical signs: pain on passive toe extension and passive foot eversion, deep calf tenderness that is hard to appreciate because the compartment is covered by soleus, and plantar sensory disturbance.
• It is the compartment most often missed because the deep transverse fascia is not opened. The late consequence is a fibrotic, contracted deep compartment with claw toes, a cavovarus foot and plantar sensory loss.

Accessory navicular and the Kidner procedure

• A symptomatic type II accessory navicular causes medial midfoot pain over a prominent bony bump, worse in stiff footwear and with activity, typically in an adolescent.
• Non-operative management with activity modification, orthoses and immobilisation succeeds in the majority.
• Kidner procedure: excision of the accessory ossicle with advancement and re-attachment of the tibialis posterior tendon plantarwards onto the navicular. Modern practice usually re-attaches with a suture anchor. Debate persists as to whether simple excision without formal advancement gives equivalent results.

The medial hindfoot approach

• Incision: a curved incision centred 1 cm posterior to the medial malleolus, curving distally toward the navicular tuberosity, roughly 8 to 10 cm long. This single exposure gives access to the tibialis posterior tendon, the flexor digitorum longus, the spring ligament and the navicular.
• Structures at risk: the saphenous vein and nerve anteriorly, the posterior tibial neurovascular bundle posteriorly (it lies immediately deep and posterior to flexor digitorum longus), and the medial calcaneal branches of the tibial nerve crossing the distal part of the wound.
• Key relation: the flexor digitorum longus lies directly posterior to tibialis posterior and anterior to the neurovascular bundle. The safe plane in which to harvest FDL is therefore between the two tendons, staying strictly anterior to the bundle.

FDL transfer with medial displacement calcaneal osteotomy - the operation to know

Tibialis posterior as a tendon transfer donor

• Transfer for foot drop is the classic use: the tibialis posterior tendon is transferred anteriorly through the interosseous membrane to the dorsum of the foot (usually the lateral cuneiform, or split between the cuneiforms) to restore dorsiflexion in a common peroneal nerve palsy, in leprosy, or in post-polio paralysis.
  • Circumtibial routing (around the medial border of the tibia subcutaneously) is an alternative but gives a less direct line of pull and a poorer vector.
  • The interosseous route requires a generous window in the membrane - at least 3 to 4 cm - to prevent the tendon binding, and the anterior tibial neurovascular bundle must be protected.
  • Limitations: excursion of only 1 to 1.5 cm against a required 3 cm, and the muscle is out of phase (a stance-phase muscle asked to do a swing-phase job). Results are best regarded as producing a dynamic tenodesis rather than true active dorsiflexion, and most patients are converted from a flail foot to a plantigrade one rather than to normal.
  • Consequence to warn about: harvesting tibialis posterior in a foot with any pre-existing planovalgus tendency will accelerate arch collapse.
• Split posterior tibial tendon transfer (SPOTT) is used for spastic equinovarus in which the tibialis posterior is the deforming muscle - varus present through stance rather than only in swing. Half the tendon is passed behind the tibia and fibula and attached to peroneus brevis.

Terminology and consensus

• An international consensus group has recommended replacing the term adult-acquired flatfoot deformity with progressive collapsing foot deformity (PCFD), and has proposed a classification describing the deformity by its components - hindfoot valgus, midfoot and forefoot abduction, forefoot varus, peritalar subluxation and ankle instability - rather than by a single linear stage. Both systems are examinable; the Johnson and Strom stages with the Myerson modification remain the common clinical language, and a candidate should be able to speak both.
• Weightbearing CT has changed the assessment of peritalar and middle facet subluxation, and is increasingly regarded as the reference standard for quantifying three-dimensional deformity where available.

Anatomical variation across populations

• Accessory navicular is present in roughly 10 to 15 per cent of feet across most populations, with reported prevalence varying by imaging modality and by population, and is bilateral in the majority.
• The number and distribution of the plantar insertional slips varies considerably; the navicular slip is universal, the cuneiform and metatarsal slips vary.
• Flexible flatfoot is far more common than symptomatic PCFD and, in the absence of a tight Achilles or a tarsal coalition, is a normal variant in children that requires reassurance, not treatment.

Side-by-side guidance

Resource-dependent practice

• Well-resourced settings: weightbearing CT, MRI, custom orthoses, arthroereisis implants and total ankle replacement for stage IV.
• Limited-resource settings: the diagnosis of PCFD is entirely clinical - too-many-toes, single heel raise, passive correctability - and weightbearing radiographs suffice for planning. Medial displacement calcaneal osteotomy with FDL transfer requires only a saw, two screws and basic instruments, and is entirely deliverable at district hospital level. Where implants are limited, a well-executed triple arthrodesis remains a reliable and durable operation for rigid deformity.
• Tibialis posterior transfer for drop foot is one of the highest-value operations in leprosy and post-polio programmes worldwide, and is performed in enormous numbers in South Asia and sub-Saharan Africa.

Registry and outcome signals

• There is no dedicated international registry for flatfoot reconstruction. Institutional cohorts consistently show durable improvement after combined tendon transfer and bony realignment for flexible stage II deformity, with the principal causes of failure being under-correction, an unaddressed gastrocnemius contracture, and unrecognised fixed forefoot varus.
• Total ankle replacement registries show that pre-operative coronal-plane deformity greater than about 10 to 15 degrees is associated with higher failure rates, which is why hindfoot realignment must precede or accompany arthroplasty in stage IV disease.

The condition this tendon causes when it fails: Adult Flatfoot Deformity, with Flexible Flatfoot and Rigid Flatfoot as the two ends of the correctability question the hindfoot examination is actually asking.

The structures that fail alongside it - and the reason a tendon transfer alone does not hold: Spring Ligament Insufficiency and Deltoid Ligament Injuries. The deltoid is what separates stage III from stage IV.

The contracture that must be looked for at every reconstruction: Gastrocnemius Equinus Contracture and Gastrocnemius Anatomy - the Silfverskiold test is only interpretable if the hindfoot is held neutral.

Conditions that present as the same painful medial foot and are not tendon dysfunction: Accessory Navicular, Navicular Stress Fracture, Talonavicular Arthritis, Subtalar Arthritis and Tarsal Coalition - a stiff hindfoot in a young adult is a coalition until proven otherwise, not a stage III deformity.

The opposite deformity, and the neurological cause that produces it: Cavovarus Foot and Charcot-Marie-Tooth Disease. Charcot Neuroarthropathy is the collapse that must never be mistaken for a failing tendon.