Summary

Available evidence suggests that Syndesmosis injuries, commonly known as "High Ankle Sprains", account for 1-18% of all ankle sprains but cause significantly more disability and prolonged recovery (2x longer than ATFL sprains). The injury involves disruption of the ligaments holding the distal tibia and fibula together (AITFL, PITFL, IOM). While Grade I injuries are stable and treated conservatively, Grade II/III injuries result in Diastasis (widening of the mortise) and require surgical stabilization to prevent early osteoarthritis. The Squeeze Test and External Rotation Stress Test are key clinical signs. [1,2,3]

Key Facts

• The Anatomy: The syndesmosis is a complex of 4 ligaments:
  1. AITFL: Anterior Inferior Tibiofibular Ligament. (Weakest, 1st to tear).
  2. PITFL: Posterior Inferior Tibiofibular Ligament. (Strongest).
  3. Transverse Ligament: Deep part of PITFL.
  4. Interosseous Ligament: Thickening of the IOM.
• Recovery Time: Unlike a simple ankle sprain (2-3 weeks), a high ankle sprain takes 6-12 weeks to return to sport.
• The Trap: X-rays often look normal in Grade II injuries. MRI or Weight-Bearing CT is the gold standard for diagnosis.

Clinical Pearls

"The Hop Test": If a patient can hop 10 times on the injured leg without pain, the syndesmosis is stable. If they cannot hop due to pain localized above the ankle joint, think Syndesmosis.

"Tape is Useless": You cannot tape a syndesmosis instability. The forces during weight-bearing (3-5x body weight) spread the tibia and fibula apart like a wedge. Bracing or Surgery is required.

"Look for the Flake": An avulsion fracture of the tibial tubercle (Chaput Tubercle) or fibula (Wagstaffe Fragment) is pathognomonic for AITFL avulsion.

                 SYNDESMOSIS INJURY
                        ↓
            X-RAY: FRANK DIASTASIS? (>5mm)
           ┌────────────┴─────────────┐
          YES                         NO
           ↓                          ↓
        SURGERY            STRESS TEST / MRI +ve?
      (Fixation)           ┌──────────┴──────────┐
                          NO                    YES
                  (Grade I: Stable)      (Grade II: Unstable)
                           ↓                     ↓
                    CONSERVATIVE              SURGERY
                   (Boot 2-4 wks)           (Fixation)

Indications

• Grade I injuries (Stable).
• Grade II injuries with negative stress views (Latent instability - controversial).

Protocol

• Phase 1 (1-3 weeks): Walking boot. Partial weight bearing.
• Phase 2 (3-6 weeks): Wean boot. Proprioception. Avoid External Rotation.
• Phase 3 (6+ weeks): Return to run.

Indications

• Frank Diastasis (Grade III).
• Unstable Grade II (Widening on stress views/arthroscopy).
• Failed conservative management (Persistent pain >3 months).

Options

1. Syndesmotic Screws:
   • Construct: 1 or 2 screws (3.5mm/4.5mm). Tricortical (3 cortices) or Quadricortical (4 cortices).
   • Position: 2-3cm above joint line.
   • Post-op: Non-weight bearing 6-8 weeks (or screw will break).
   • Removal: Routine removal at 12 weeks is debated but common.
2. Suture Button (TightRope):
   • Construct: Heavy FiberWire suture tensioned between two titanium buttons.
   • Pros: Flexible fixation (allows physiologic motion). No need for removal. Earlier weight bearing.
   • Cons: Cost. Button irritation.
3. AITFL Repair:
   • Direct repair of the ligament avulsion (Tape/Suture anchor) + Screw/Button augmentation.

TightRope vs Screw (Systematic Reviews)

• TightRope fixation results in better functional outcomes (AOFAS scores) and faster return to work compared to screws. It avoids the complications of broken screws and second surgeries.

Screw Removal

• Mora et al: Showed that leaving screws in (letting them break) or taking them out had no difference in outcome, provided the syndesmosis had healed first.

The Injury

You have a "High Ankle Sprain". This is not a normal sprain. The ligaments that hold your two shin bones together have snapped. It is like the zipper on your jeans breaking—the two bones split apart when you stand on them.

Why is it slower?

Normal sprains heal in 2 weeks. High ankle sprains take 6-12 weeks because every time you step, your body weight forces the bones apart, stressing the healing ligament.

The Operation

We need to put a "zip-tie" (TightRope) or a screw between the bones to hold them tight while the ligament heals. This takes about 3 months.

Q1: Name the 4 ligaments of the syndesmosis. A:

1. AITFL (Anterior Inferior Tibiofibular Ligament) - 35% stability.
2. PITFL (Posterior Inferior Tibiofibular Ligament) - 40% stability (Strongest).
3. Transverse Ligament.
4. Interosseous Ligament.

Q2: What is the Squeeze Test? A: Compression of the tibia and fibula at the mid-calf level. A positive test elicits pain distally at the syndesmosis (ankle). Specificity is high, sensitivity is low.

Q3: Why is malreduction common with syndesmosis screws? A: Because the fibula naturally sits slightly posterior in the incisura. If the surgeon uses a reduction clamp perpendicular to the floor, it can pull the fibula too far anteriorly. The clamp should be angled 30 degrees.

Q4: What is the risk of leaving a syndesmosis screw in? A: Screw breakage. The syndesmosis is a dynamic joint (fibula moves during gait). If a rigid screw is left in and the patient weight bears, the metal fatigue will cause it to snap. (Though broken screws are often asymptomatic).

(End of Topic)