Summary

Peroneal Tendon Dislocation (Subluxation) is the anterior displacement of the Peroneus Brevis and/or Longus tendons out of the retromalleolar groove. It is caused by the failure of the Superior Peroneal Retinaculum (SPR), usually during a forceful contraction of the peroneals while the foot is dorsiflexed (e.g., Skiing injury, "caught an edge"). Acute injuries are frequently misdiagnosed as "just a sprain". Chronic cases present with a painful "snapping" sensation. Surgical reconstruction (Groove Deepening + SPR Repair) is the gold standard for active patients, as conservative management has a high failure rate (>50%). [1,2,3]

Key Facts

• The Restraint: The SPR does not tear in the middle; it strips off the fibula. In 90% of cases, the retinaculum pulls a distinct periosteal sleeve (or bone fleck) off the lateral malleolus, allowing the tendons to slide underneath it into a "false pouch".
• The Groove: The retromalleolar groove is often shallow or flat in 20% of the population, predisposing to dislocation.
• Fleck Sign: A small avulsion fracture seen on the lateral border of the distal fibula X-ray. It is pathognomonic for SPR rupture.

Clinical Pearls

"The Snapping Ankle": If a patient says their ankle "pops out", ask them to reproduce it. They will Circle the foot (Circumduction) and evert. You will see the tendons snap over the bone.

"Mistaken for ATFL": Initial exam often shows swelling over the lateral malleolus. The key is that the tenderness is Posterior to the fibula (Peroneals), not Anterior (ATFL).

"Prognostic Failure": Treating a true dislocation in a standard moon boot fails because the tendons remain subluxed anteriorly inside the boot. They must be reduced and held in a cast in slight plantarflexion/inversion.

                 LATERAL ANKLE SNAP
                        ↓
             ACUTE OR CHRONIC?
            ┌─────────┴─────────┐
          ACUTE              CHRONIC
       (First time)        (Recurrent)
           ↓                    ↓
     ELITE ATHLETE?          SURGERY
      ┌────┴────┐          (Reconstruction)
     NO        YES
     ↓          ↓
    CAST      SURGERY
   (6w)      (Repair)
     ↓
  FAILED?
     ↓
  SURGERY

Indications

• Acute injury (Grade I/II).
• Low demand patient.
• Sedentary lifestyle.

Protocol

• Cast: Below knee cast.
• Position: Slight Plantarflexion (relaxes tendons) and Inversion (keeps them in groove).
• Duration: 6 weeks Strict.
• Success Rate: Poor compared to ligaments. 50% re-dislocation rate reported in athletes.

Indications

• Acute: Grade III (Bone avulsion), High level athlete.
• Chronic: Painful snapping, failed conservative.

Techniques

1. Direct Repair:
   • Drill holes in fibula. Re-attach the baggy SPR.
2. Groove Deepening (Gould):
   • If the fibula is flat.
   • The cancellous bone is scooped out, and the cortical "lid" is tapped down to create a trench.
   • Prevents recurrence.
3. Bone Block:
   • Creating a bony bumper (Osteotomy). (Old technique, rarely used now).
4. Tendon Repair:
   • Almost always need to fix an associated longitudinal split tear (tubularization).

Post-Op

• NWB Cast 2 weeks.
• Walker Boot 4 weeks.
• Sport at 3-4 months.

Deepening vs Repair

• Porter et al (2005): Showed that adding a Groove Deepening procedure significantly reduced recurrence rates compared to SPR repair alone, especially in athletes. It is now standard.

Acute Surgery?

• Saxena et al: Recommend acute surgical repair for high-demand athletes to avoid the high failure rate of casting and prolonged time off sport.

The Injury

The "seatbelt" (Retinaculum) that holds your tendons behind your ankle bone has ripped off. Now, every time you lift your foot, the tendons jump over the bone.

Why not just a cast?

Tendons are slippery. They rarely stick back down in the right place with just a plaster. If they heal "loose", you will have a snapping ankle forever.

The Surgery

We will drill the seatbelt back into the bone. If your bone groove is shallow (flat), we will carve a deeper channel for the tendons to sit in comfortably.

Q1: What is the Fleck Sign? A: A cortical avulsion fracture of the posterolateral fibula, representing the attachment of the Superior Peroneal Retinaculum (Grade III injury).

Q2: Describe the Eckert & Davis Grade I injury. A: The most common type. The SPR is stripped from the fibula along with the periosteum, creating a "False Pouch" into which the tendons dislocate. The SPR itself is technically intact but incompetent due to the periosteal stripping.

Q3: Which test is most sensitive for verifying dislocation? A: Dynamic Ultrasound. MRI is static and may show the tendons reduced. Ultrasound shows the mechanical instability during movement.

Q4: What must you check for inside the tendon during surgery? A: A Longitudinal Split. The chronic friction of snapping over the fibula causes the Peroneus Brevis to split down its length. This must be sutured (tubularized).

(End of Topic)