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
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
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