Summary

Talonavicular (TN) Arthritis affects the "Coxa Pedis" (Hip of the Foot)—the ball-and-socket joint formed by the Talus head and the Navicular. This single joint is responsible for 80-90% of all complex hindfoot motion (inversion/eversion/rotation). Consequently, arthritis here is profoundly disabling, causing deep midfoot pain and a stiff, flat foot. It is a classic target for Rheumatoid Arthritis and is the end-stage result of Muller-Weiss Syndrome or PTTD. Treatment almost exclusively involves Fusion (Arthrodesis). Because isolated TN fusion has a high non-union rate, it is often combined with Subtalar fusion (Double Arthrodesis) to lock the entire hindfoot block. [1,2,3]

Key Facts

• The Acetabulum Pedis: The TN joint is not just two bones. The "socket" is formed by the Navicular, the Spring Ligament, and the Sustentaculum Tali. It is a complex suspension bridge.
• The Motion Killer: Fusing the TN joint eliminates virtually all subtalar motion (cross-locking mechanism). Conversely, fusing the Subtalar joint leaves about 25% of TN motion.
• The Rheumatoid Target: The TN joint is often the first joint in the foot to be destroyed by RA, leading to a valgus drift and flatfoot.

Clinical Pearls

"The Circle of Pain": Patients grasp the foot with a 'C-clamp' grip (thumb on medial arch, fingers on lateral sinus tarsi). They describe pain "deep inside" the foot.

"Ortho-Biologics": The TN joint is notoriously hard to fuse (small surface area, high shear forces). Use of Bone Graft (Autograft) and rigid fixation (Plates + Screws) is mandatory.

"Double Trouble": If you fuse the TN joint alone in a patient with a valgus heel, the heel will remain valgus and painful. You must address the Subtalar joint (Double Arthrodesis) to align the heel.

                 MIDFOOT PAIN
                       ↓
              X-RAY: TN ARTHRITIS
            ┌──────────┴──────────┐
          ISOLATED              MULTI-JOINT
          (TN Only)           (TN + ST + CC)
             ↓                      ↓
       CONSERVATIVE           CONSERVATIVE
     (UCBL / Brace)          (Gauntlet Brace)
             ↓                      ↓
          FAILED?                FAILED?
             ↓                      ↓
      DOUBLE ARTHRODESIS     TRIPLE ARTHRODESIS
      (TN + ST Fusion)       (TN + ST + CC)

Protocol

• Bracing:
  • UCBL: A hard plastic cup that holds the heel and arch. Good for flexible deformity.
  • Arizona Brace (Gauntlet): Gold standard for rigid arthritis. Leather lace-up that locks the ankle and hindfoot.
• Shoe: Rocker bottom essential.
• Injection: Ultrasound guided steroid.

1. Isolated TN Fusion

• Indication: Isolated arthritis with minimal deformity.
• Technique:
  • Medial incision.
  • Compression screws or Dorsal Plate.
• Risk: High non-union rate (10%). Hard to control heel valgus.

2. Double Arthrodesis (TN + ST)

• The Modern Workhorse.
• Rationale: Fusing the ST joint along with the TN joint allows powerful correction of heel valgus and improves fusion rates by creating a stable block. It spares the Calcaneocuboid joint (Lateral column), preserving lateral foot length.
• Outcome: Equivalent correction to Triple Arthrodesis with fewer complications (CC non-union).

3. Triple Arthrodesis

• Indication: If the CC joint is also arthritic.

Double vs Triple

• Sammarco et al: Showed that Double Arthrodesis provides reliable correction of Grade 3/4 PTTD and Arthritis without the need to violate the CC joint, reducing surgical time and lateral column stiffness.

Fixation Methods

• Biomechanics: A combination of a compression screw and a dorsal neutralization plate provides the highest stability for the TN joint.

The Condition

The "universal joint" of your foot (the ball and socket) is worn out. This is why you can't walk on cobbles or uneven paths.

The Surgery

We need to lock this joint.

• The Sacrifice: You will lose the side-to-side wiggle of your foot. It will be stiff.
• The Gain: The deep aching pain will stop, and the arch will be straight.
• The Recovery: 3 months in a boot. It takes a long time for this bone to knit.

Q1: What percentage of hindfoot motion is lost after isolated Talonavicular fusion? A: ~90%. Locking the TN joint (the head of the Chopart "key") effectively locks the Subtalar joint due to their coupled mechanics. Fusing the Subtalar joint only limits TN motion by ~25%.

Q2: What is the primary indication for Double Arthrodesis over Triple? A: Sparing the Calcaneocuboid (CC) joint. This preserves the lateral column length and some mobility, reducing the risk of lateral foot pain/stiffness, while still achieving powerful hindfoot realignment.

Q3: Describe the "Spring Ligament" complex. A: The Calcaneonavicular Ligament. It forms the floor of the Acetabulum Pedis (TN joint), supporting the head of the talus. Failure leads to PTTD.

Q4: Which structure is at risk during medial approach to the TN joint? A: The Saphenous Nerve and Great Saphenous Vein. Also the Tibialis Anteior tendon (superiorly) and Tibialis Posterior tendon (inferiorly).

(End of Topic)