Bosworth Fracture-Dislocations

**Bosworth fracture-dislocation is a rare and severe ankle injury where the distal fibula dislocates posteriorly behind the posterior tibial tubercle and becomes entrapped. The fibula is "locked" in this position, making closed reduction accurately impossible without specific maneuvers or open surgery.

Historical Background: First described by David Bosworth in 1947 in a series of 5 cases. He identified the mechanism of the fibula becoming trapped behind the "posterior tibial ridge" (posterior tubercle). Before his paper, these were often misdiagnosed as simple fracture-dislocations that "failed reduction" due to soft tissue interposition. Bosworth correctly identified the bony block as the cause. Although rare, understanding this entity is critical because persistent forceful attempts at closed reduction can cause iatrogenic fracture of the fibula or posterior tibia, and massive soft tissue swelling.

Epidemiology:

• Incidence: Rare. Accounts for approximately 1-2% of ankle fractures.
• Demographics: Young adults, often high-energy trauma (sports, MVA).
• Pathognomonic Mechanism: External rotation of the foot with the ankle in plantarflexion (or neutral), with the tibia pushed anteriorly relative to the fibula.
• Association: Almost always associated with a fibula fracture (Weber B or C), but "pure" dislocations without fracture have been reported in flexible individuals.

Why is it Critical?

1. Irreducible: It will NOT reduce with standard traction.
2. Skin Risk: The skin over the medial malleolus is tented (Axilla sign) and the skin over the posterior fibula is compressed. Necrosis occurs rapidly.
3. Compartment Syndrome: The distortion of the deep posterior compartment can lead to ischemia. Pathophysiology:

• Mechanism: Severe External Rotation of the supinated foot.
• Sequence: The fibula rotates externally, snaps out of the incisura fibularis, moves posteriorly, and gets locked behind the posterior ridge of the tibia.
• Ligaments: The anterior inferior tibiofibular ligament (AITFL) is intact or avulsed (Tillaux-Chaput), acting as a hinge. The interosseous membrane is torn.

The Key Anatomic Checkpoint: The Incisura Fibularis. The distal tibia has a concave notch laterally (incisura) where the fibula sits. The posterior tubercle (Volkmann's triangle border) forms a buttress. In Bosworth injuries, the fibula jumps this buttress.

Detailed Osteology:

• Distal Tibia: The Lateral surface forms the incisura fibularis. It is bounded anteriorly by the anterior tubercle (Chaput) and posteriorly by the larger posterior tubercle (Volkmann).
• Distal Fibula: Fits into the incisura. It serves as the attachment for the syndesmotic ligaments (AITFL anteriorly, PITFL posteriorly, IOM medially).
• The Trap: The posterior tubercle acts as a "cam". Once the fibula rotates past it, the elastic recoil of the interosseous membrane snaps it medially against the posterior cortex of the tibia, locking it in place.

Pathomechanics of Entrapment: The entrapment occurs because the fibula is levered out of the incisura. The force vector is external rotation. The fibula acts as a lever arm.

1. Stage 1 - Ligament Failure: AITFL rupture or avulsion (Tillaux-Chaput or Wagstaffe). This releases the anterior constraint.
2. Stage 2 - Translation: Fibula rotates externally and translates posteriorly out of the groove.
3. Stage 3 - Crossing the Equator: The equator of the fibula passes the posterior colliculus of the tibia.
4. Stage 4 - The Lock: Elastic recoil of the soft tissues (or remaining interosseous membrane fibers superiorly) pulls the fibula tightly against the posterior cortex of the tibia.
5. Stage 5 - Irreducibility: The fibula is now "locked". The posterior tubercle prevents it from sliding forward. Traction alone simply tightens the IOM against the bone. Reducing it requires overcoming this posterior ridge by "unhooking" it laterally.

Ligamentous Structures:

• Anterior Inferior Tibiofibular Ligament (AITFL): Always torn or avulsed. This is the first restraint to fail.
• Posterior Inferior Tibiofibular Ligament (PITFL): Often intact, attached to the posterior malleolus, pulling it off (Volkmann fracture) or torn. If intact, it contributes to the posterior tethering.
• Interosseous Membrane (IOM): Extensive tearing proximally, depending on the level of the fibular fracture (Maisonneuve variant). The level of the IOM tear often determines the level of the fibular fracture.
• Deltoid Ligament: Universally injured (either tear or medial malleolus fracture) allowing the talus to shift laterally and externally rotate.
• Lateral Ligament Complex (ATFL/CFL): Usually intact, as the fibula moves with the talus.

Neurovascular Anatomy at Risk:

• Posterior Structures: The neurovascular bundle (Posterior Tibial Artery/Nerve) runs just medial to the Achilles tendon but lateral to the medial malleolus. In a severe posterior dislocation, the bundle can be tented or stretched over the posterior aspect of the tibia.
• Anterior Structures: The Superficial Peroneal Nerve (SPN) runs anteriorly in the subcutaneous tissue. It is at risk during the lateral approach if not identified and retracted.
• Posterior Approach Risks: The Sural Nerve runs with the small saphenous vein posterior to the peroneal tendons. It must be identified and protected during the posterolateral approach.

History:

• High-energy twisting injury (sports, fall).
• Patient reports inability to stand, severe pain.
• "The ankle looks twisted around backward."

Physical Exam:

• Deformity: Foot is in severe external rotation relative to the leg.
• Axilla Sign: A skin dimple/pucker over the medial malleolus (resembling an axilla). This is due to the tibia buttonholing through the capsule or severe deltoid tethering.
• Neurovascular: Check dorsalis pedis/posterior tibial pulses. Tibial nerve stretch injury is possible and should be documented carefully.
• Swelling: Rapid and massive soft tissue swelling occurs due to the violent nature of the injury and significant tearing of the IOM. This further compromises the skin.
• Skin: Look for tenting posteriorly (fibula) or medially (tibia). Skin necrosis is a major risk.
• Tenderness: Diffuse tenderness, maximal over the syndesmosis and posterior fibula.
• Gait: Patient is unable to bear weight and unable to hop.

Pre-Hospital Care:

• Analgesia: Assessment of pain score. Methoxyflurane or IV opioids.
• Deformity Check: Document neurovascular status BEFORE and AFTER any movement.
• Splintage: Don't forcefully reduce on the field. Apply a pillow splint in the position of deformity (which is usually significant external rotation) to support the limb. Attempting to force the ankle into a standard backslab without disengaging the lock is dangerous and futile.
• Transport: Urgent transport to a center capable of surgical intervention. This is a time-critical ischemia injury for the skin.
• Documentation: Clearly document "Non-reducible deformity" to alert ED staff immediately upon arrival.

Emergency Department Assessment:

• Triad of Signs:
  1. Severe external rotation of foot (often 90 degrees).
  2. Impossible closed reduction.
  3. "Axilla Sign" (medial skin pucker).
• Reduction Attempt:
  • Typical Quigley maneuver (lift toe, internally rotate) feels locked.
  • Elastic resistance ("bouts back") when trying to internally rotate.
  • STOP if this sensation is felt. Repeated attempts damage the articular surface of the posterior tibia.

Differential Diagnosis:

• Pilon Fracture: Distal tibial explosion.
• Standard Ankle Fracture-Dislocation: Usually reducible.
• Subtalar Dislocation: Foot deformity but ankle mortise is intact on AP X-ray.
• Total Talar Dislocation: Talus is extruded (open injury usually).

X-rays (Trauma Series):

• AP View:
  • "Cortical Overlap Sign": The proximal cortex of the distal fibula fragment overlaps with the lateral cortex of the distal tibia. The overlap is significantly greater than the normal tibiofibular overlap (greater than 6mm).
  • Joint Space: The medial clear space is often widened due to deltoid rupture.
  • Deception: It may look like a "well-reduced" ankle fracture if not scrutinized, but the patient has severe pain and deformity.
• Lateral View:
  • "The Diagnostic View": This is the single most important film.
  • Posterior Displacement: The distal fibula is seen completely posterior to the tibia. (Normally, the fibula superimposes on the posterior third of the tibia).
  • Empty Notch: The tibial incisura is empty.
  • Double Shadow: If the fibula is fractured, the proximal shaft may be seen in normal position while the distal fragment is posterior.

CT Scan:

• Indication: Often obtained after failed reduction or if the diagnosis is suspected but X-rays are equivocal. Recommended for surgical planning in all cases if resources allow.
• Bone Window Findings:
  • Shows the "fibular head locked behind tibial plume".
  • Identifies associated marginal fractures (Volkmann, Chaput).
  • Assesses the size of the posterior malleolus fragment (important for fixation).
• 3D Reconstruction:
  • Extremely useful for understanding the rotational deformity and planning the "unhooking" maneuver.
• Soft Tissue Window:
  • Can show entrapment of the FHL or Peroneus Brevis tendons, which may block reduction.

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Major Complications

1. Skin Necrosis and Wound Issues

• Incidence: High (up to 17% in some series), especially with delayed reduction.
• Mechanism: The entrapped fibula tents the posterior skin, causing pressure necrosis. Alternatively, the "axilla sign" medially causes skin compromise due to extreme tension.
• Risk Factors: Time to reduction greater than 24 hours, older age, smoking, diabetes.
• Prevention: Urgent reduction (within hours). Handle soft tissues gently. Avoid "searching" for the nerve in compromised skin.
• Management: Debridement, negative pressure wound therapy (VAC), or flap coverage (sural flap/free flap) if defect is large.

2. Compartment Syndrome

• Risk: Significant soft tissue trauma from the dislocation and forceful reduction attempts. The deep posterior compartment is most at risk.
• Mechanism: Bleeding + edema from the torn IOM and muscles.
• Signs: Pain out of proportion, pain with passive toe stretch (especially great toe), tense compartments, paresthesia.
• Action: High index of suspicion. Emergent 4-compartment fasciotomy if pressures are elevated (greater than 30 mmHg or delta pressure less than 30 mmHg).
• Sequelae: Claw toes, sensory loss, weakness.

3. Post-Traumatic Osteoarthritis

• Mechanism: Chondral damage occurs as the fibula "grinds" across the posterior tibia during dislocation and reduction. "Scuffing" of the cartilage is inevitable.
• Prevalence: Up to 50% at long-term follow-up show radiographic arthritis.
• Symptoms: Chronic pain, stiffness, weather-related ache, swelling.
• Treatment: Non-operative (bracing, injections) initially. Ankle arthrodesis or Total Ankle Arthroplasty (TAA) for end-stage disease.

4. Neurovascular Injury

• Posterior Tibial Nerve: Can be stretched around the tibia or injured during reduction. Leads to paresthesia in the sole of the foot.
• Sural Nerve: At risk during the posterolateral approach (crossing the incision). Numbness in lateral foot.
• Superficial Peroneal Nerve: At risk during lateral approach. Numbness in dorsum of foot.
• Management: Careful dissection and protection. Document deficits pre-op if possible.

5. Missed Diagnosis

• Problem: Often mistaken for a "bad sprain" or simple fracture if only AP X-ray is seen. The "Cortical Overlap" is subtle.
• Consequence: Delayed treatment leads to irreducible contractures, severe arthritis, and "Chronic Bosworth Injury" which is very difficult to treat (often requires fusion).
• Pearl: The "Lateral View" rule: You must see the fibula centered in the tibia. If it's behind, it's out.

The "Neglected" Bosworth:

• Definition: Cases presenting or diagnosed after 3-4 weeks.
• Problem: Significant soft tissue contracture (triceps surae), formation of distinct facet on posterior tibia (false articulation), and extensive osteopenia.
• Management:
  1. Open Reduction: Extensive release required. Often need to lengthen Achilles tendon.
  2. Osteotomy: Removal of the posterior tibial tubercle (buttress) to allow the fibula to slide forward.
  3. Arthrodesis: In cases greater than 6 weeks with cartilage destruction, primary fusion may be the better option to avoid painful stiffness.

Pediatric Bosworth:

• Rare: Even rarer than in adults.
• Variant: Often involves a Salter-Harris type separation of the distal fibular physis.
• Trap: The distal fibular epiphysis may be trapped behind the tibia while the metaphysis looks aligned (if separated).
• Treatment: Gentle reduction under anesthesia. If closed reduction fails (common due to periosteal entrapment), open reduction is required. Fixation with smooth K-wires is preferred to avoid growth arrest, crossing the physis only if necessary, and removing them early (3-4 weeks).

Geriatric Considerations:

• Bone Quality: Porotic bone makes the "locking" mechanism less secure, but associated fractures (posterior malleolus) are more comminuted. The posterior wall may be crushed, making the lock less distinct but the joint more unstable.
• Skin Risk: Extreme risk of sloughing. Minimally invasive techniques should be used if possible.
• Fixation: Augment with locking plates (distal fibula LCP) or fibular nail if soft tissue allows. Primary fusion nail (hindfoot nail) is a salvage option for non-reconstructable locking injuries with poor skin.

Immediate Post-Op (0-2 Weeks):

• Immobilization: Backslab or bulky dressing applied in the operating room. Foot is held in neutral dorsiflexion to prevent equinus contracture.
• Elevation: Strict elevation (toes above nose) for 48-72 hours to minimize swelling and reduce wound complications.
• DVT Prophylaxis: Chemical prophylaxis (LMWH, Xarelto) is standard due to NWB status and trauma risk.
• Weight Bearing: Strict Non-Weight Bearing (NWB).
• Wound Check: Review at 2 weeks. Suture removal if healed. Check for marginal necrosis especially at the corners of the incision.

Early Rehab (2-6 Weeks):

• Immobilization: Transition to a removable CAM boot (Moon boot) once wounds are healed.
• ROM Exercises: Gentle active dorsiflexion/plantarflexion out of boot 3-4 times daily. Avoid inversion/eversion to protect ligaments and syndesmosis.
• Muscle Activation: Isometric calf, quad, and gluteal exercises.
• Weight Bearing: Remain NWB generally. Some protocols allow touch-down weight bearing (TDWB) if fixation is rigid, but caution is advised due to syndesmotic injury.

Progressive Loading (6-12 Weeks):

• X-ray Check: Confirm callus formation and maintenance of reduction. Ensure no diastasis of syndesmosis.
• Weight Bearing: Progress to partial weight bearing (PWB) then full weight bearing (FWB) in boot over 2-3 weeks.
• Proprioception: Begin wobble board and balance training once FWB.
• Strength: Theraband resistance exercises for peroneal and tibialis posterior strengthening.

Long Term (3+ Months):

• Hardware Removal:
  • Syndesmosis Screws: Traditionally removed at 12-16 weeks before full sport return to prevent breakage. Current trend is to leave them unless symptomatic or removing due to breakage risk in athletes.
  • Suture Buttons: Do not need removal.
• Return to Sport: Impact activities (jogging) at 4-6 months. Cutting sports (football/rugby) at 6-9 months pending functional testing (single leg hop).
• Work: Return to sedentary work at 2-3 weeks; manual labor at 4-6 months.

General Prognosis: Bosworth fractures historically have poorer outcomes than standard ankle fractures due to the severity of soft tissue injury and chondral damage. However, early recognition and anatomical reduction can yield good results.

Factors Influencing Outcome:

1. Time to Reduction: The most critical factor. Delays (greater than 24 hours) correlate with poor AOFAS scores and higher complication rates.
2. Cartilage Damage: The "grinding" of the fibula against the posterior tibia causes osteochondral defects (OCDs) which predispose to arthritis.
3. Syndesmosis Reduction: Malreduction leads to rapid joint degeneration.

Long-Term Complications:

• Post-Traumatic Osteoarthritis: Rates reported between 20-50% at 10 years.
• Chronic Pain / Stiffness: Reduced range of motion, particularly dorsiflexion.
• Hardware Issues: Prominent plates laterally may require removal.

Evidence-Based Discussion

Historical Context and Relevance: David Bosworth's 1947 paper, "Fracture-dislocation of the Ankle with Fixed Displacement of the Fibula Behind the Tibia," remains accurate in its description of the pathomechanics. He noted that once the fibula is entrapped, "no amount of traction will pull it down and no amount of rotation will untwist it." The key insight was that the posterior tibial ridge acts as a fulcrum.

Diagnostic Delays: A common theme in the literature (Schepers et al., Bartoníček et al.) is the high rate of missed diagnosis. In Schepers' series, 30% were delayed. A delay over 24 hours significantly increases the risk of skin necrosis and compartment syndrome.

• Why is it missed? On the AP view, the overlap just looks like a "badly reduced" ankle fracture.
• Solution: Any ankle fracture that does not reduce easily with a standard Quigley maneuver should be suspected of being a Bosworth injury. The lateral X-ray is mandatory.

Controversies in Management:

1. Approach Selection:

   • Posterolateral: Advocated by Lui, Bartoníček, and most modern trauma surgeons. It allows direct visualization of the entrapment, protection of the sural nerve, and easier "prying" of the fibula.
   • Anterolateral: Some older texts describe an anterior approach to "push" the fibula back. This is generally harder as the block is posterior.

2. Syndesmotic Fixation:

   • Given the mechanism involves complete disruption of the interosseous membrane and syndesmotic ligaments, some debate exists on whether every case needs fixation if the fibula fracture is fixed anatomically.
   • Consensus: Most authors recommend syndesmotic stabilization (screw or suture button) because the extensive soft tissue stripping makes the construct inherently unstable even with fibular plating.

3. Cartilage Damage:

   • The "grinding" of the fibula against the posterior tibia during the dislocation event causes significant osteochondral damage (OCDs).
   • Even with perfect reduction, rates of post-traumatic arthritis are higher than standard ankle fractures. Patients should be counseled about this guarded prognosis early.

Epidemiology in Australia: Bosworth fracture-dislocations are rare (estimated less than 2% of ankle fractures), but are over-represented in major trauma centers.

• Sporting Injuries: High-velocity contact sports like Australian Rules Football (AFL) and Rugby League/Union act as common mechanisms. The "tackle with foot planted + severe external rotation" is a classic mechanism.
• Motor Vehicle Accidents: High-energy trauma remains a key cause in rural and regional areas.

Referral Pathways:

• Complexity: These injuries are prone to complications (skin necrosis, compartment syndrome, poor reduction).
• Transfer Criteria: Should be transferred to a center with orthopaedic specialists comfortable with complex ankle trauma (e.g., foot and ankle subspecialists).
• Rural Support: Telehealth consultation with major trauma centers (e.g., The Alfred, Royal Brisbane, Royal Adelaide, Royal North Shore) is recommended before attempting forceful reductions in a rural ED, which may maximize soft tissue injury.
• Retrieval: MedSTAR/Ambulance services may be required for urgent transfer if vascular compromise is present.

Treatment Trends:

• Syndesmosis Fixation: Australian surgeons heavily utilize the "TightRope" (suture button) technology for syndesmotic fixation. This allows for physiological motion of the distal tibiofibular joint earlier than screw fixation.
• Rehabilitation Funding: Funding through private health or sporting clubs (e.g., AFL injury schemes, WorkCover) often supports intensive physiotherapy, which is critical for restoring range of motion.
• Post-Op protocol: Trend towards "functional rehabilitation" with early ROM in a boot, rather than prolonged casting.