Biomechanics
Able to achieve relatively high level of function after STJ fusion
- previously believed that isolated STJ fusion should not be performed
- believed that triple arthrodesis was operation of choice for hindfoot
- STJ fusion has superior result with less stress on AJ
Average loss of DF 30% / PF 10%
Position of hindfoot determines flexibility of transverse tarsal (CCJ & TNJ) joints
- imperative that fusion be positioned in ~ 5o valgus
- permits TTJ mobility
- if varus TTJ locked & patient tends to walk on lateral aspect of foot
Indications for STJ arthrodesis
Post traumatic / calcaneal fracture
RA
Primary OA
Coalition
Tibialis posterior dysfunction
Neuromuscular disorders
- instability
- CMT / polio / nerve injury
Indication for Triple Arthrodesis
Valgus deformity
OA of CCJ / TNJ
Technique STJ Fusion
Approach
Position
- patient supine
- roll under hip to expose lateral aspect foot
- tourniquet, IV Abx, radiolucent table, II available
Incision
Direct lateral approach - Tip of fibula toward base of 4th MT
- internervous plane between SPN and sural nerve
Superficial dissection
- peroneal tendons lifted dorsally
- elevate EBD
- fatty tissue over sinus tarsi
- expose STJ / CCJ / sinus tarsi
Deep dissection
- remove TC interosseous ligament
- clear out sinus tarsi
- diathermy artery of tarsal sinus
- insert lamina spreader to expose posterior facet
- need to expose medial facet medially
Debridement
- curette / osteotomes / burr
- simply remove cartilage if no deformity
- otherwise remove bone to correct deformity
- recreate 2 flat surfaces that come together in 5o valgus
- drill holes to stimulate bleeding +/- bone graft
- if previous calcaneal fracture, decompress lateral wall
(5 - 10mm removed)
Reduction technique in valgus foot
Deformity
- talus internally rotated on calcaneum
- navicular abducted on talus
Issues
- need T Achilles lengthening
(assess at end)
- need to perform TNJ and CCJ fusion
- likely need to have open reduced TNJ / CCJ before STJ reduction
- may need lateral bone block
- often deficient skin laterally
STJ
- reducing calcaneum back under talus difficult
- calcaneum also abducted like navicular
- lamina spreader between lateral process talus and anterior aspect of calcaneum
- open it up
- calcaneum internally rotates / talus externally rotates
- screw like motion
- need to have all joints opened and exposed for this to occur
- need care to ensure don't place foot into varus
Fixation
Insert K wires for 6.5 mm/ 8.0 mm cannulated screw
- One or two from inferior calcaneum via stab incisions into body and neck of talus
Check position of K wires on II before screw insertion
Bone graft
- local usually sufficient
http://www.boneandjoint.org.uk/content/jbjsbr/87-B/2/175.full.pdf
- if large correction take from proximal lateral or medial tibia
TNJ fusion
Indications
- isolated TNJ OA (lose 80% subtalar joint motion)
- as part of triple arthrodesis
Incision
- medial to T anterior, anterior to T posterior
- talar neck to naviculo-cuneiform joint
- protect saphenous nerve and vein
- Tibialis posterior guide to navicular
Exposure
- can sometimes only expose 2/3 of joint medially
- may need to utilize the lateral approach for full exposure
- inserting lamina spreader aids exposure to debride
- reduce forefoot onto navicular by adducting /plantar flexing and pronating it
- must not leave in varus
- provisionally fix with K wires
Fixation
- 2 x 4.0 mm cannulated screws
- from navicular into talus
- parallel or triangular
- may need to make notch in medial cuneiform
CCJ fusion
Incision
- exposed through continuation of lateral approach
Fixation
- 2 x screws
- must hug lateral border
- alternatively can use specific plates
T Achilles lengthening
Indication
- tight T Achilles
- if don't will have to take a lot of bone to get foot plantigrade
Technique
A. Formal Z lengthen
B. Hoke lengthening
- want to lengthen laterally more than medially
- 2 incisions halfway laterally
- 1 half incision medially between them
- stretch out the T Achilles
Post-operative
Back-slab for 2/52
Wound inspection at 10 - 14/7
NWB in full cast for 4/52
WBAT in walking cast for a further 6/52
6/52 radiologic assessment until union
(pain-free WB with evidence radiologic union)