STJ FUSION (SUBTALAR JOINT ARTHRODESIS) CHEAT SHEET
1. How are the major tarsal joints affected with a fusion? : TN fusion limits STJ motion the most (8%). STJ fusion still allows 25% TN and 55t% CC motion (astion). -the take home is that an isolated STJ fusion (vs triple) preserves 50% of mid tarsal joint motion.
2. Do TAL before fusion? YES
3. What type of Incision: inferior posterior tip of fibula to CC joint OLLIER approach (sinus tarsi approach) – advantageous because it can be curved along langer’s lines for good healing:
a. What should you be careful to protect during the incision? incision is superior to the 1. peroneals and 2. sural nerve and inferior to 1. intermedial dorsal cutaneous nerve so be careful! ****communicating branch from sural nerve to the intermedial dorsal cutaneous nerve may exist and therefore needs to be completely transected to avoid any neuritis!
b. What ligaments are usually transected? sinus tarsi is cleaned out, interosseus talocalcaneal ligament is transected, lateral TC and CF ligaments incised. crego elevator is positioned at the lateral aspect of talocalcaneal joint and directed posterior -> exposes posterior subtalar joint
4. Should all facets of the STJ fusion be performed? No. Fusion of middle facet is not necessary (FHL injury)
5. What are some techniques to prepare the joint to encourage bleeding? Subchondral k-wire drilling VS “Fish scaling” – using a small osteotome to the subchondral bone to ensure exposure of cancellous substrate and increase surface for fusion across joint vs simple curettage – least effective according to podiatrytoday.com articles
6. What are two techniques to prepare the joint via cartilage removal? Wedge resection (adding bone to the fusion site in severe deformities ) vs contour resection (most common – it maintains natural joint contours)
7. What is the most important step in STJ ARTHRODESIS AS PER McGlamry: proper reduction and positioning. TWO-hand technique: :first hand: “heel is grasped with the palm of one hand, while the thumb of the same hand is placed on the talar head, next an inversion force with the palm on the heel and a medial to lateral pressure with the thumb over the talar head is applied -> this allows the heel to be in neutral position (5-7degrees of valgus and 10 degrees of external rotation) this lines up the mechanical axis for proper weightbearing -> the TN joint is reduced. second hand: grasp the forefoot and any residual forefoot varus is reduced or “dialed down” to ensure plantigrade foot.
- in summary – 1. rotate the heel into a neutral position while pushing against the talar head to reduce the talonavicular joint 2. reduce any forefoot supinatus simultaneously 3. drill k-wire to fixate this position
8. **What to look for on fluoro**? lateral: normal cyma line, unmasking of cuboid, good apposition of STJ. AP: adequate talar head coverage without a tendency toward excessive forefoot abduction. calc axial: IMPORTANT VIEW THAT MANY SURGEONS FAIL TO DO: look for neutral alignment of the heel in relation to bisection of tibia .
b. what position do you want the heel on a calcaneal axial to be fused? slight valgus position of the calcaneus in relation to the tibia
9. What is the non union rate for STJ fusion? 10%
10. What factors usually complicate STJ fusions? – patient usually has poor bone stock, scar tissue/fibrosis can limit reduction of STJ and since it is avascular can cause wound problems
11. most common complication of arthrodesis? non-union or fibrous union(pseudoarthrosis)