Dysfunction of the posterior tibial tendon combined with pathologic changes in the spring ligament (Calcaneo-navicular ligament) result in loss of medial arch height
Aetiology
- Most often secondary to posterior tibial tendon elongation or rupture
- Overuse tenosynovitis
- Degenerative
- Traumatic
- Predisposing factors
- HTN
- DM
- Obesity
- Inflammatory arthropathies
- Foot surgery
- Steroid use
Anatomy
- Insertions
- Navicular tuberosity
- Sustentaculum tali
- All three cuneiforms
- Bases of the second, third and fourth metatarsi
- Blood supply
- Proximal portion of tendon receives blood supply from the mesotenon
- Distal portion of tendon receives blood from the periosteal vessels at insertion site
- There is a hypovascular area 1 – 1.5 cm distal to medial malleolus (3-5 cm proximal to navicular insertion)
- Actions
- Tarsal joint adduction
- Subtalar inversion
- Tibio-talar plantar flexion
- Functions
- Dynamic stabilizer of the medial longitudinal arch
- Initiator of hindfoot inversion when the ankle is in plantar flexion
- Provids stability during plantar flexion by adducting and locking the transverse tarsal joints
- Shifts the pull of the gastroc-soleus complex by inverting the subtalar joint; allowing Achilles to become the main inverter of the hindfoot
Pathology
- Typically a degenerative process
- Posterior Tibial Tendon (PTT) pathologic changes occur in the hypovascular area
- PTT only has an excursion of approximately 2 cm, therefore any pathologic lengthening has dramatic effect on function
- As PTT loses strength the peroneus brevis becomes unopposed causing increased stress on the spring ligament; esp. during mid-stance
- Ultimately the spring ligament undergoes pathologic changes
- Collapse of other supporting structures
- Plantar aponeurosis
- Deltoid ligament
- Talo-calcaneal ligament
- Long and short plantar ligaments
- Medial calcaneo-cuboid ligament
- Resulting deformities
- Hindfoot valgus
- Plantar flexion of talar head
- Heel cord contracture
- Transverse tarsal abduction
Classification
Stage I
- Swelling and pain along course of posterior tibial tendon due to tenosynovitis
- Patients are able to perform a single limb heel rise with corresponding normal hindfoot varus tilt. This may be initially painless, but repetitive toe raises cause pain
- Too many toes sign is absent
- Hindfoot valgus is absent
Stage II
- Degeneration and elongation of posterior tibial tendon
- Hindfoot valgus and potentially forefoot abduction
- Single limb heel rise may be possible in stage IIa
- Talo-navicular collapse
- Stage IIa
- Mild collapse with symptoms limited to medial side of foot
- < 40% of talar head uncovered on standing AP X-Ray
- Patient can still perform single limb heel rise
- Stage IIb
- Complete incompetence of posterior tibial tendon
- Fibular impingement
- > 40% of talar head uncovered on standing AP X-Ray
- Forefoot abduction
Stage III
- Rigid deformity
- Minimum 10-15 degrees of fixed forefoot varus
- Subtalar joint not reducible. Any attempt at reduction causes compensatory forefoot supination
- Tight heel cord
- Fibular impingement pain, often worse than medial pain
- Degenerative changes cause pain at rest
- Patient unable to perform single limb heel rise
Stage IV
- Osteoarthritis of lateral compartment of ankle, due to chronic valgus forces
- Valgus tilt of talus
- Deltoid ligament attenuation
Clinically
- Presents with pain and swelling of medial ankle
- Lateral ankle pain may be present if accompanied with fibular impingement
- Difficulty walking on uneven surfaces
- Progressive flatfoot
- In chronic cases (stages II & III), there is no correlation between symptoms and severity of deformity
- Too many toes sign : observing patient from backside, more than 2 lateral toes are visible
- Plano-valgus deformity
- Inability to perform single leg heel rise (except stage I)
- Tenderness behind medial malleolus
Imaging
Radiography
- Weight-bearing AP, Lateral and oblique views of foot plus AP of the ankle
- AP of ankle
- Look for degenerative changes and fibular impingement
- AP of foot
- Lateral subluxation of talo-navicular joint
- Lateral of foot
- Talo-navicular sag
- First metatarso-cuneiform joint sag
- Subtalar subluxation evident by indistinct joint surface
- Increased lateral talo-metatarsal angle "Meary’s angle"
- Angle formed between a line drawn through longitudinal axis of talus and another through the axis of the first metatarsal diaphysis
- Normal: -4 to +4 degrees
- Decreased cuneiform height
- Measured between the medial cuneiform and the fifth metatarsal base/ground
- Best inter-observer reliability
CT Scan: only used when MRI is contraindicated
MRI
- Study of choice for showing longitudinal splits, inflammation and enlargement of PTT
- Magic angle effect
- Seen on T1 images where the acute angle of the posterior tibial tendon exiting the medial malleous simulates tendon rupture on MRI
- Avoid this by obtaining images in a true axial plane perpendicular the tendon at the level of medial malleolus. This plane is approximately 45 degrees between true axial and true coronal planes or perpendicular to the posterior facet of the subtalar joint
Ultrasound
- Potentially as effective as MRI for evaluating the posterior tibial tendon
- Requires an experienced operator
Treatment
Nonoperative treatment
- Three to six months of conservative treatment is indicated before operative management is considered
- Exceptions:
- Severe structural deformity
- Seronegative spondyloarthropathy with tenosynovitis in which case surgical treatment should be considered after failure of 6 weeks of conservative treatment
- Steroid injections are to be avoided
- Runners are to replace shoes at least every 400 miles
- NSAIDS
- Immobilization (cast, brace)
- Isolated strengthening of PTT when pain subsides
- Bracing
- Mild symptoms
- Rigid stirrup, lace-up sport brace
- Limits hindfoot valgus, but doe not limit sagittal motion
- Moderate symptoms
- CAM (controlled-ankle-motion) walker boot or short leg cast for 4 – 6 weeks
- Weight bearing allowed if it does not cause pain
- Mild symptoms
- Orthotics can be used after initial symptoms subside
- Flexible deformity:
- Corrective orthosis that places the subtalar joint in a neutral position
- Semi-rigid orthosis with medial heel wedge and medial column post
- UCBL (University of California Biomechanics Laboratory) brace
- Stabilizes heel in neutral and prevents forefoot abduction
- Used for flexible stage II disease
- Arizona brace
- Can restore arch and midfoot kinematics
- Can be used for all stages
- Fixed deformity:
- Accommodative orthosis made by molding
- Marzano articulated ankle brace
- Solid ankle AFO; useful for patients with degenerative, painful ankle joints
- Flexible deformity:
- Footwear modifications include :
- Offset heel
- Flanged heel
- Extended Thomas heel
- Medial heel
- Sole posts (1/4 to 1/2 inch)
Operative treatment
Stage I
- Tenosynovectomy
- Repair of small longitudinal split tears
- Patients with advanced degenerative changes or irreparable lesions may require tendon transfer and side to side tenodesis using the flexor digitorum longus
Stage II
- Flexor digitorum longus transfer
- Prerequisites: adequate subtalar (15 degrees of inversion) and transverse tarsal (10 degrees adduction) motion
- Contraindications
- Subtalar osteoarthritis
- Hypermobility
- Older than 60 y/o
- Flexor tendon transfer is rarely done as an isolated procedure. Typically performed in conjunction with one or more of the following:
- Achilles tendon lengthening or gastrocnemius recession if equinus present
- Medial slide calcaneal osteotomy
- Opening-wedge medial cuneiform osteotomy
- Closing-wedge planar flexion first metatarso-cuneirom arthrodesis
- Naviculo-cuneiform arthrodesis
- Repair of spring ligament
- Lateral column lengthening (stage IIb disease)
- Evans procedure (calcaneal lengthening osteotomy)
- Calcaneo-cuboid distraction arthrodesis
Stage III
- Triple arthrodesis
- Subtalar arthrodesis; indicated for fixed/restricted subtalar joint, correctable transverse tarsal joint and fixed forefoot varus less than 10 degrees
Stage IV
- Tibio-talo-calcaneal fusion
- Pantalar fusion