Summary

The Talus ("Astragalus") is a unique bone: it is 60% cartilage, has no muscular attachments, and relies on a precarious Retrograde Blood Supply. Fractures of the Talar Neck (most common) disrupt this supply, leading to Avascular Necrosis (AVN). The risk of AVN correlates directly with the degree of displacement (Hawkins Classification). High-energy trauma (Aviator's Astragalus - rudder bar injury) drives the tibial plafond into the talus. Treatment involves urgent anatomical reduction and rigid fixation (screws) to maximize revascularization chance. [1,2,3]

Key Facts

• The Blood Supply from Hell: The talus is supplied from Distal to Proximal. A neck fracture cuts off the flow to the body.
  1. Artery of the Tarsal Canal (br Posterior Tibial). Main supply.
  2. Deltoid Branch (br Posterior Tibial). Medial body.
  3. Artery of the Sinus Tarsi (br Peroneal/Dorsalis Pedis).
• Hawkins Sign: A prognostic sign seen on X-ray at 6-8 weeks. A subchondral radiolucent line in the talar dome indicates bone resorption. This is GOOD! It means the bone is alive (hyperaemic). Sclerosis (white bone) means death (AVN).
• Skin Threat: In Type III/IV fractures, the body of the talus dislocates posteromedially and tents the skin. If not reduced immediately, the skin dies.

Clinical Pearls

"The Canale View": A specific X-ray view (Ankle in 15° internal rotation + Beam angled 75° Cephalad). It is the only view that profiles the Talar Neck fully to assess displacement.

"Comminution Medially": Talar neck fractures often have comminution on the medial side (VARUS malunion risk). You must plate the medial side or use dual screws to prevent the talus collapsing into Varus.

"The Floating Talus": A Hawkins Type IV involves dislocation of the talus from the Tibia, Calcaneus, and Navicular. It is physically detached from all blood supply. AVN rate is 100%.

                  TALUS FRACTURE
                        ↓
             DISLOCATED? SKIN THREAT?
            ┌───────────┴────────────┐
           YES                      NO
            ↓                        ↓
      URGENT REDUCTION          CT SCAN
   (Sedation -> Open if fails)       ↓
            ↓                   HAWKINS TYPE?
       POST-REDUCTION CT        ┌────┼────┐
                                I    II  III/IV
                                ↓    ↓    ↓
                              CAST  ORIF ORIF
                              NWB   (Urgent)
                             8-12w

Indications

• Hawkins Type I: Strictly non-displaced (<2mm).
• Patient Unfit: Very high risk.

Protocol

• Cast: Below knee cast.
• Weight Bearing: Non-Weight Bearing (NWB) is mandatory for 8-12 weeks until union.
• Monitoring: Weekly X-rays for first 3 weeks to ensure no displacement.

Goals

• Anatomical reduction (restore joint congruity).
• Compression of fracture (promote healing).
• Preserve remaining blood supply.

Approaches

1. Anteromedial: Medial to Tibialis Anterior. Allows fixation of medial neck. Note: Avoid stripping the deep deltoid (blood supply).
2. Anterolateral: Lateral to Peroneus Tertius. Visualizes the sinus tarsi.
3. Combined: Often need both to fix neck.

Fixation Technique

• Lag Screws: 2x 3.5mm or 4.0mm screws.
• Direction: Posterior-to-Anterior (PA) screws are biomechanically stronger but harder to place (percutaneous from the back). Anterior-to-Posterior (AP) screws are easier but screw heads can impinge on the talar head cartilage.
• Plating: Essential if there is medial comminution (buttress plate).

Hawkins Sign (1970)

• Original paper described the subchondral radioluceny.
• Presence of sign = 100% predictive of survival.
• Absence of sign = Suggests AVN (but not 100% specific).

Timing of Surgery

• Old Dogma: "Operate within 6 hours to save blood supply".
• New Evidence: Immediate reduction of dislocation is critical. Definitive fixation can wait (days) for swelling to settle, provided the joint is reduced.

The Injury

You have broken the "keystone" of the foot. The Talus is a special bone because it connects the leg to the foot and is covered in slick cartilage. It has a terrible blood supply.

The Risk

Because the fracture cuts off the blood vessels, there is a high chance (up to 50-100% depending on severity) that the bone will "die" (Avascular Necrosis). If it dies, it crumbles like a sugar cube.

The Operation

We must fix it perfectly with screws to give the blood vessels a bridge to cross. You will be off your feet (crutches/scooter) for 3 months.

The "Hawkins Sign"

At 6 weeks, we will take an X-ray. If the bone looks "washed out" (dark), that is actually good news—it means blood is flowing. If it looks "bright white", it means no blood is getting there.

Q1: What is Hawkins Sign? A: Subchondral radiolucency seen in the talar dome on AP X-ray at 6-8 weeks post-injury. It indicates disuse osteopenia, which implies an intact vascular supply (bone is alive).

Q2: Name the blood supply of the Talus. A:

1. Artery of the Tarsal Canal (Posterior Tibial) - Major supply to body.
2. Deltoid Branch (Posterior Tibial) - Medial body.
3. Artery of the Sinus Tarsi (Peroneal/Dorsalis Pedis) - Head/Neck.

Q3: Why is Varus malunion common and why is it bad? A: Common due to medial neck comminution collapsing. Bad because it locks the subtalar joint and forces the patient to weight-bear on the lateral border of the foot, causing pain and instability.

Q4: Describe the Canale View. A: Ankle in maximum equinus, foot pronated 15° (internal rotation), beam angled 75° Cephalad. Profiles the talar neck.

(End of Topic)