How is a Myerson type III adult flat foot deformity treated?

Treatment of Myerson Type III Adult Flatfoot Deformity

Myerson type III adult flatfoot deformity requires hindfoot arthrodesis as the primary surgical treatment, with double arthrodesis (talonavicular and subtalar fusion) being equally effective as triple arthrodesis but with significantly shorter operative time.

Surgical Management is the Standard of Care

Stage III flatfoot deformity represents a rigid, fixed deformity where the subtalar joint is no longer flexible 1. At this stage, conservative management with orthotics, bracing, or physical therapy will not correct the structural pathology. Arthrodesis is necessary because the rigidity of the deformity precludes joint-preserving procedures 1.

Choice of Arthrodesis Procedure

Double vs. Triple Arthrodesis

Double arthrodesis (talonavicular + subtalar fusion) should be your first-line surgical approach if the calcaneocuboid joint is unaffected 2. The evidence strongly supports this:

• Equivalent functional outcomes: Both procedures achieve similar AOFAS hindfoot score improvements (16.92 vs. 19.1 points, p=0.44) 2
• Equivalent deformity correction: No significant differences in radiographic correction of calcaneal pitch angle, Meary's angle, or Hibbs angle 2
• Equivalent union rates: Both achieve union by 4 months postoperatively 2
• Significantly shorter operative time: Double arthrodesis averages 55.77 minutes vs. 91.6 minutes for triple arthrodesis (p<0.001) 2

When to Add Calcaneocuboid Fusion (Triple Arthrodesis)

Proceed to triple arthrodesis only if:

• The calcaneocuboid joint shows arthritic changes on imaging
• There is significant lateral column pathology
• Intraoperative assessment reveals calcaneocuboid joint instability or degeneration

In the Swedish registry data, 83% of stage III cases underwent hindfoot arthrodesis 3, confirming this as standard practice.

Minimally Invasive Approach Option

For patients at high risk of wound complications (diabetes, peripheral vascular disease, obesity, smoking), consider minimally invasive surgery (MIS) technique for double arthrodesis 4. This approach demonstrated:

• Mean AOFAS score improvement of 54.27 points (p<0.0001)
• 89.5% union rate at mean 6.6-year follow-up
• Zero cases of superficial infection, wound dehiscence, or avascular necrosis
• Only 13.4% secondary surgery rate 4

The MIS technique significantly reduces soft tissue complications compared to traditional open approaches, making it particularly valuable in high-risk patients 4.

Critical Pitfalls to Avoid

1. Do not attempt joint-preserving procedures: Osteotomies and tendon transfers are contraindicated in rigid stage III deformity 1

2. Do not delay surgery: Stage III represents established arthritic changes; prolonged conservative management only allows progression and worsens outcomes 5

3. Assess calcaneocuboid joint carefully: Failure to address pathology at this joint leads to persistent lateral column pain and potential need for revision surgery (4 of 9 revision cases in the MIS series were for progression of deformity) 4

4. Plan for nonunion risk: Talonavicular nonunion occurred in 3 of 67 cases (4.5%) in the MIS series 4. Use adequate fixation and consider bone graft in osteoporotic patients.

Expected Outcomes

Patients should expect:

• Significant functional improvement with AOFAS scores increasing from 66-71 preoperatively to 85-88 postoperatively 2
• Correction of radiographic parameters: calcaneal pitch angle improves by 7-8 degrees, Meary's angle corrects by approximately 7 degrees 2
• Union by 3-4 months postoperatively 2
• Quality of life improvements, though baseline SF-36 scores are notably low in this population 3

Surgical Approach Selection Algorithm

1. Assess calcaneocuboid joint (weight-bearing CT or MRI if needed)

   • If normal → Double arthrodesis
   • If arthritic → Triple arthrodesis

2. Assess patient risk factors for wound complications

   • High risk (diabetes, PVD, obesity) → MIS technique 4
   • Standard risk → Traditional open approach

3. Perform talonavicular and subtalar arthrodesis with rigid internal fixation

4. Add calcaneocuboid fusion only if joint pathology present

This algorithmic approach prioritizes shorter operative time, equivalent outcomes, and reduced morbidity while maintaining excellent deformity correction 2.