Minimally Invasive Techniques for Foot Deformity Correction

Minimally Invasive Techniques for Foot Deformity Correction

Susan T. Mahan

Collin J. May

Insertion of Subtalar Extra-Articular Screw Arthroereisis for Treatment of Flexible Flatfoot in Children

Operative indications: Symptomatic flexible pes planovalgus and ankle pronation in an ambulatory child that has been recalcitrant to conservative methods of treatment (Figure 28.1).

  • Need dorsiflexion at least past neutral (ideally >20° past neutral when the foot is supinated and knee is extended)

    • Challenge the child preoperatively to obtain sufficient dorsiflexion using daily stretching and nighttime dorsiflexion boot

    • If not achieved, then should add Achilles lengthening (typically Vulpius type)

  • Age range in normal kids is typically 9 to 17 years

    • Most common age in normal children is 12 years

    • Ambulatory neuromuscular children with very severe pes planus can be treated as young as 6 years of age (almost always need Vulpius)

Equipment: Synthes 6.5-mm cannulated partially threaded screw (typically 30 mm for about 90% of patients). In very young (<10 years, or very small feet), the 4.5-mm cannulated system can be used. Smooth Kirschner wire (K-wire) (3/32 when using the 6.5-mm cannulated system). Schnitt or snap. Fluoroscopy.

Positioning: Supine with a bump under the hip so the leg sits naturally with patella forward. Tourniquet on involved limb. Sural nerve block.

Surgical Approach: The subtalar extra-articular screw arthroereisis (SESA) screw goes in through a small <1 cm incision just over the sinus tarsi on the anterolateral aspect of the foot. The SESA screw will go vertically in the calcaneus just distal to the isthmus; properly placed, it will impinge on the lateral talar process and lateral talus and prevent the talus from hyperpronation.

Techniques in Steps

  • If a Vulpius or other type of Achilles lengthening needs to be done, then that should be done first

  • Leg position during insertion

    • Very important!

    • Foot in neutral dorsiflexion and maximum supination (Figure 28.2)

    • Important to have patella forward (Figure 28.3)

    • Bump under the ankle/foot

  • Surgical incision

    • 5 to 8 mm lateral foot over sinus tarsi in Langer lines (Figure 28.4)

    • Spread down with snap or scissors to the sinus tarsi (Figure 28.5). If in correct place, will have 1 in of snap/scissors deep in the space (Figure 28.6)

  • Screw insertion

    • Large K-wire (3/32 fits through the 6.5-mm screw) placed first (Figure 28.7)

    • Starting point

      • Medial third of the calcaneal cuboid joint—about 1 cm medial from lateral edge of calcaneus

      • Just distal to the calcaneal isthmus

    • Trajectory

      • Press against the fibula with the wire

      • Aim a little anteriorly 15° to 20° and slightly medially—this angle is slightly forgiving if not perfect

      • Check fluoroscopy to confirm position of the guide pin (Figures 28.8 and 28.9)

    • Overdrill—just the near cortex—typically cannulated drill for 6.5-mm system (Figure 28.10)

    • Screw insertion (Figure 28.11)

      • Usually, Synthes 6.5-mm cannulated partially threaded screw

      • Length 3.0 cm in most all feet 90% to 95%

        • 3.5 in bigger feet

        • 2.5 in smaller feet

      • Confirm position of screw on fluoroscopy—anteroposterior (AP) and lateral (Figures 28.12 and 28.13)

      • Confirm clinically (Figure 28.14)

        • Weakest part of the procedure is how deep to put in the screw

        • Too proud will be undercorrected—needs to tuck under talus

        • Too deep will also undercorrect

        • When properly placed, can see screw head just under the skin level

        • Impinges on lateral talar process (cannot see this directly though)

  • Closure

    • Deep stitch

    • Skin

    • If no Achilles lengthening, then place soft dressing

    • If Vulpius done, then placed in solid short leg cast and may weight bearing in cast until follow-up

Postoperative Care

  • If no Vulpius and in soft dressing,

    • Non-weight bearing 3 days

    • First day post-op, patients are instructed to do 100 dorsiflexion eversion exercises

    • Follow-up day 3 to 5 for wound check

      • Exercises are also started

        • Skier exercises with feet apart and shift weight from one foot to the other—must have plantargrade stance (Figure 28.15)

        • Cannot weight bearing until 300 skier exercises