Operative Management of Bimalleolar Equivalent Fractures: Deltoid Ligament Repair and Lateral Malleolus Fixation

INTRODUCTION AND BIOMECHANICAL PRINCIPLES

The anatomical reduction of fractures and ligamentous disruptions around the ankle is the cornerstone of achieving acceptable, long-term functional results and preventing post-traumatic osteoarthritis. The "bimalleolar equivalent" ankle fracture—characterized by a fracture of the lateral malleolus combined with a complete rupture of the medial deltoid ligament complex—represents a significant destabilization of the ankle mortise.

Historically, the necessity of primary deltoid ligament repair in the presence of rigid lateral malleolar fixation has been a subject of debate. However, contemporary orthopedic consensus, supported by advanced biomechanical studies, emphasizes that failure to address medial instability or unrecognized soft-tissue interposition can lead to chronic medial clear space widening, valgus instability, and catastrophic joint wear.

Clinical Pearl: A lateral displacement of the talus by merely 1 millimeter reduces the tibiotalar contact area by 42%, exponentially increasing peak contact stresses. Restoration of the deep deltoid ligament—the primary restraint to lateral talar excursion and external rotation—is paramount in restoring native joint kinematics.

This masterclass delineates the precise surgical techniques for the repair of the deltoid ligament in conjunction with internal fixation of the lateral malleolus, alongside advanced strategies for managing irreducible fracture-dislocations.

SURGICAL ANATOMY OF THE DELTOID LIGAMENT

A profound understanding of medial ankle anatomy is non-negotiable for successful repair. The deltoid ligament is a robust, multifascicular structure traditionally divided into two distinct components:

1. The Superficial Deltoid: A broad, fan-shaped structure originating from the anterior colliculus of the medial malleolus. It comprises the tibionavicular, tibiocalcaneal, and superficial tibiotalar ligaments. It primarily resists hindfoot eversion and acts as a secondary restraint to external rotation. Tears here typically occur mid-substance or as avulsions from the medial malleolus.
2. The Deep Deltoid: A short, thick, and intra-articular structure originating from the intercollicular groove and posterior colliculus, inserting onto the medial surface of the talus. It is composed of the deep anterior and deep posterior tibiotalar ligaments. This is the primary stabilizer of the medial ankle. It may be avulsed from the talus, torn mid-substance, or avulsed from the medial malleolus.

PREOPERATIVE PLANNING AND PATIENT POSITIONING

Indications for Operative Intervention

• Widened medial clear space (>4 mm) on static or stress radiographs.
• Lateral malleolar fracture with clinical or radiographic evidence of deltoid rupture (bimalleolar equivalent).
• Irreducible ankle fracture-dislocations with suspected soft-tissue interposition.

Positioning

The patient is placed supine on a radiolucent operating table. A bump is placed under the ipsilateral hip to internally rotate the leg, bringing the lateral malleolus anteriorly for easier access, while still allowing the leg to be externally rotated for the medial approach. A well-padded thigh tourniquet is applied. Fluoroscopy must be positioned to allow seamless anteroposterior (AP), mortise, and lateral imaging.

SURGICAL TECHNIQUE: DELTOID LIGAMENT REPAIR AND LATERAL MALLEOLUS FIXATION

Surgical Warning: The sequence of fixation is critical. Medial dissection and suture placement must often precede lateral fixation, but the medial sutures must never be tied until the lateral malleolus is anatomically reduced and rigidly fixed. Premature tying of the deltoid will result in suture pull-out during fibular manipulation.

Step 1: Medial Approach and Exposure

1. Incision: Make an anteromedial curved incision, approximately 6 to 8 cm in length. The trajectory should be similar to the standard approach for medial malleolus fixation but extended slightly more distal to expose the talonavicular joint and the sustentaculum tali.
2. Superficial Dissection: Carefully protect the saphenous nerve and vein, which run in the anterior flap of the incision.
3. Identify the Superficial Deltoid: Expose the fan-shaped superficial portion. Note the pathology: it is almost always torn across its mid-substance or avulsed directly from the medial malleolus. The broad, fanned-out inferior attachment on the calcaneus and navicular makes an inferior avulsion exceedingly rare.

Step 2: Deep Deltoid Exploration

1. Tendon Sheath Release: Open the retinacular sheath of the posterior tibial tendon (PTT). Retract the PTT anteriorly or posteriorly to gain unimpeded access to the deep deltoid ligament and the medial ankle gutter.
2. Pathology Assessment: Inspect the deep, heavy portion of the deltoid. Identify whether it is avulsed from the tip of the malleolus, torn mid-substance, or avulsed from the medial aspect of the talus. Clear any hematoma or osteochondral debris from the medial gutter.

Step 3: Suture Placement for Talar Avulsions (Trans-Talar Technique)

If the deep portion has been avulsed from the medial aspect of the talus:
1. Pass two No. 0 or No. 2 ultra-high-molecular-weight polyethylene (UHMWPE) nonabsorbable sutures through the robust stumps of the deep ligament.
2. Drill two small converging holes diagonally across the body and neck of the talus, aiming from the medial avulsion footprint to exit laterally in the sinus tarsi area.
3. Using a suture passer or Keith needle, shuttle the suture limbs through these trans-talar tunnels.
4. Crucial Step: Clamp the lateral ends of the sutures with a hemostat. Do not tie them at this stage.

Alternative Modern Technique: In contemporary practice, if bone stock permits, small metallic or biocomposite suture anchors (2.5 mm to 3.5 mm) may be placed directly into the medial talar body footprint instead of drilling trans-talar tunnels. Again, the sutures are passed through the ligament but left untied.

Step 4: Lateral Malleolus Internal Fixation

1. Lateral Approach: Make a standard lateral longitudinal incision over the fibula, extending distally to expose the sinus tarsi area (where the trans-talar sutures have exited).
2. Fracture Reduction: Anatomically reduce the lateral malleolus. Restore fibular length, alignment, and rotation. This is the key to restoring the lateral buttress of the ankle mortise.
3. Fixation: Utilize standard AO principles. For a typical Weber B fracture, place an interfragmentary lag screw followed by a lateral neutralization plate or a posterolateral antiglide plate. Ensure rigid, absolute stability.
4. Syndesmotic Assessment: Perform a Cotton test (lateral hook test) under fluoroscopy to assess the distal tibiofibular syndesmosis. If unstable, place syndesmotic screws or flexible fixation devices.

Step 5: Tensioning the Deep Deltoid

1. With the lateral malleolus rigidly fixed and the talus anatomically reduced within the mortise, return to the lateral incision.
2. Locate the trans-talar sutures exiting the sinus tarsi.
3. Hold the ankle in neutral dorsiflexion and slight inversion to approximate the medial structures.
4. Snugly tie the sutures over the lateral cortical bridge of the talus (or over a small button if bone quality is poor).
5. Close the lateral incision in layers.

Step 6: Medial Closure and Superficial Deltoid Repair

1. Return to the medial side of the ankle.
2. Replace the posterior tibial tendon into its anatomical groove behind the medial malleolus and meticulously repair its sheath to prevent postoperative subluxation.
3. Superficial Repair: Repair the superficial portion of the deltoid ligament using multiple interrupted, nonabsorbable sutures (e.g., 2-0 or 0 braided polyester).
4. Medial Malleolar Avulsions: If the entire deltoid complex (deep and superficial) was avulsed from the medial malleolus, drill two or three small osseous tunnels in the malleolus. Pass interrupted sutures through these holes and the avulsed ligament end. Alternatively, utilize suture anchors placed at the anterior and posterior colliculi.
5. Perform a layered closure of the medial wound.

MANAGEMENT OF THE IRREDUCIBLE FRACTURE OR FRACTURE-DISLOCATION

While most ankle fractures can be provisionally reduced in the emergency department, certain injury patterns present as irreducible. A widened ankle mortise—defined by lateral displacement of the talus and fibula leaving a pathological interval between the talus and an intact medial malleolus—is a crippling lesion if left unreduced.

Forcible, repeated closed reduction attempts in these scenarios are contraindicated, as they cause severe iatrogenic chondral damage and exacerbate soft-tissue trauma. Immediate operative intervention is required.

Pathoanatomy of the Irreducible Medial Clear Space

When the mortise remains widened despite manipulation, soft-tissue interposition must be suspected. Several structures can block reduction:

1. Inverted Deltoid Ligament: The avulsed end of the deltoid ligament may flip proximally and become incarcerated between the medial malleolus and the medial articular facet of the talus.
2. Posterior Tibial Tendon (PTT) Entrapment: A severe deltoid tear or an avulsion fracture of the medial malleolar tip can disrupt the PTT retinaculum. The tendon can dislocate anteriorly and become trapped within the medial joint space. Occasionally, the tendon is interposed directly between the torn fascicles of the deltoid ligament, completely impairing healing.
3. Neurovascular Entrapment: In high-energy trauma, the tibial nerve and posterior tibial vessels may be dragged into the joint space alongside the PTT.
4. Lateral Displacement of the PTT: In catastrophic fracture-dislocations, the PTT may be displaced entirely across the joint, lodging laterally between the distal tibia and fibula (syndesmotic interval).

Clinical Pearl: The "Dimple Sign" on the anteromedial skin of the ankle is a classic indicator of soft-tissue interposition (often the deltoid ligament or joint capsule being pulled into the joint). If this sign is present, closed reduction will fail, and open reduction is mandatory.

Surgical Management of Entrapment:
The medial approach is utilized first. The incarcerated structures (deltoid, PTT, or neurovascular bundle) are carefully extracted from the joint using blunt retractors and nerve hooks. Once the medial clear space is cleared of obstructions, the talus will easily reduce. The surgeon then proceeds with lateral malleolar fixation and deltoid repair as described in the standard technique.

The Bosworth Lesion: A Unique Posterior Fracture-Dislocation

First described by David Bosworth in 1947, the Bosworth lesion is a rare but notorious cause of an irreducible posterior fracture-dislocation of the ankle.

Mechanism and Anatomy:
In this severe supination-external rotation injury, the distal end of the proximal fibular fragment is forcefully displaced posterior to the tibia. It becomes anatomically locked behind the prominent posterolateral ridge of the distal tibia.

Why Closed Reduction Fails:
The intact proximal interosseous membrane acts as a tether. When longitudinal traction is applied during closed reduction attempts, the interosseous membrane tightens, pulling the fibular shaft tighter against the posterior tibia, making closed reduction biomechanically impossible.

Surgical Extrication:
1. Approach: A standard or slightly posterior-based lateral longitudinal incision is made over the fibula.
2. Identification: The distal fibular fragment is identified, but the proximal shaft will be conspicuously absent from the lateral compartment, buried deep in the posterior compartment.
3. Release: A heavy periosteal elevator (e.g., a Cobb elevator) or a bone hook is introduced between the tibia and the entrapped fibula.
4. Reduction: Considerable, controlled anteriorly directed force is required to lever the proximal fibular fragment over the posterolateral tibial ridge and back into the fibular incisura.
5. Fixation: Once unlocked, the fibular fracture is anatomically reduced and rigidly fixed using standard plate osteosynthesis. The syndesmosis must be rigorously tested, as it is universally disrupted in a Bosworth lesion.

POSTOPERATIVE CARE AND REHABILITATION

The postoperative protocol following deltoid ligament repair and lateral malleolus fixation must balance the need for ligamentous healing with the prevention of joint stiffness.

1. Phase I (0-2 Weeks): The ankle is placed in a well-padded posterior splint or a short-leg cast in neutral dorsiflexion. The patient is strictly non-weight-bearing (NWB). Elevation and edema control are prioritized.
2. Phase II (2-6 Weeks): Sutures are removed at 14 days. The patient is transitioned to a controlled ankle motion (CAM) boot. NWB status is maintained. Gentle, active range of motion (ROM) exercises (plantarflexion and dorsiflexion) are initiated out of the boot. Inversion and eversion are strictly prohibited to protect the deltoid repair.
3. Phase III (6-12 Weeks): Radiographs are obtained to confirm fibular union and maintenance of the medial clear space. Progressive weight-bearing is initiated in the CAM boot. Physical therapy focuses on proprioception, peroneal strengthening, and restoring full sagittal plane ROM.
4. Phase IV (3-6 Months): Transition to regular footwear, often with a medial arch support or an ankle brace for high-impact activities. Return to sports is permitted once functional testing demonstrates >90% symmetry with the contralateral limb.