Background

Aetiology

 

Intrinsic

- inflammatory

- degenerative

 

Extrinsic

- traumatic

- spur

 

Epidemiology

 

F > 40

 

Associations 60% of cases  

- hypertension

- diabetes

- obese

- trauma 

- prior surgery

- steroids

 

Aetiology

 

RA 

- flat foot also secondary to synovitis TNJ and STJ

 

Hypermobile flat foot

 

Seronegative disorders

- Ankylosing spondylitis / psoriasis / reiter's

 

Anatomy Tibialis Posterior

 

Origin

- posterior tibia, fibula and inter-osseous membrane

- acute angle around medial malleolus

- flexor retinaculum holds TP in groove 

- no mesotenon

- relative hypo-vascular zone 1-2cm distal to medial malleolus

 

Insertion

- navicular tuberosity

- plantar cuneiforms

- 2,3,4 MT

- sustentaculum tali

 

Excursion 

- 2cm only

 

Nerve Supply

- tibial nerve (L4/5, S1)

 

Action

 

1.  Runs medial to axis STJ

- inverts STJ & adducts forefoot

 

2.  Runs posterior to axis AKJ

- plantar flexor

 

3.  Maintains longitudinal arch

 

4.  Locks the midtarsal joints

- allows T Achilles to perform heel raise

- otherwise T Achilles acts at TNJ

 

Opposed mainly by peroneus brevis

 

Pathophysiology

 

Avascular zone 

- behind medial malleolus

- paratenon is supplied by blood vessels from a mesotenon on its post aspect

- tendon is composed of fibrocartilage where it changes direction around the med malleolus 

 

Tendon Changes

 

Starts with varying combination

 

1. Paratendinitis

- fluid in sheath 

- synovial proliferation

 

2. Tendinosis 

- tendon degeneration 

- tendon enlarged

- longitudinal splits develop 

- becomes yellowish 

 

Tibialis Posterior Tendinosis

 

3. Elongation of tendon

 

4. Rupture

 

5. Deformity 

- loss TP function leads to acquired Planovalgus

- initial deformity is collapse of medial longitudinal arch

 

Dysfunction

 

1. Medial arch collapses

2. STJ everts

3. Valgus heel

4. Foot abducts at TNJ

5. Achilles tendon acts as evertor when heel in valgus

6. Calcaneus impinges on fibular causing lateral AJ pain

7. Attenuation of TNJ capsule, spring ligament and deltoid ligament

 

History

 

Pain medially at first

- swelling

 

Lateral pain with impingement of fibula

 

Foot shape changes / progressive deformity

 

Difficulty wearing shoes

 

Examination

 

Any sign of RA

 

Look

- flattened medial arch

- valgus heel

 

Too many toes sign

- abducted forefoot

- > 2.5 toes

- more than on other side when in symmetrical posture

 

Single Heel Raise

- unable to heel raise

- need T Post to invert STJ & lock hind foot rigid so T Achilles can pull up Calcaneus

 

Sit over edge

- AKJ

- STJ

 

Feel

- tender medial

- is tendon thickened

- may be tender laterally

 

STJ

- fixed or flexible

 

AKJ

- fixed or flexible

 

T Achilles

- silverskiold

 

Power

1.  T Post with foot inverted in equinus

2.  Foot equinus and everted

- ask patient to invert the foot

 

NV examination

 

X-ray

 

Lateral weight bearing

 

Early 

- reduced talo-metatarsal angle (Meary's angle  0-10°)

- medial cuneiform to floor distanced reduced (N= 2.5cm)

- talus plantar flexed

 

Late

- STJ OA

 

AP weight bearing of foot and ankle

 

Early - abduction of forefoot with navicular lateral to talus

 

Late - ankle OA / TNJ OA

 

MRI 

 

Enlarged T Post - tendinosis

 

Thickned Tibialis Posterior

 

Torn T Post - half size of FDL

 

Johnson Classification

 

Stage 1 

- T Post tendonitis 

- no deformity

 

Stage 2 

- T Post rupture

- unable SHR

- foot remains flexible

 

IIA - minimal forefoot abuction

IIB - forefoot abducted throught THJ / > 30% uncovered

 

Stage 3 

- fixed deformity of STJ (may have STJ OA)

 

Stage 4 

- valgus angulation of talus & OA of ankle joint