Syme Amputation (Ankle Disarticulation)

Surgical Indications

Absolute Indications

• Unsalvageable forefoot or midfoot infection / gangrene (e.g., severe diabetic foot infection that cannot be managed with a partial foot amputation)
• Severe distal foot trauma (crush injuries or blast injuries where the forefoot cannot be reconstructed but the heel pad is pristine)
• Tumours of the forefoot or midfoot (where adequate oncological margins can be achieved by ankle disarticulation)
• Congenital foot deformities (e.g., fibular hemimelia, severe untreated clubfoot) where a Syme amputation provides a superior base for a prosthesis compared to the native deformed foot

Prerequisites for Success

• Vascular: Palpable posterior tibial pulse, Doppler biphasic flow, or TcPO2 greater than 30 mmHg. The posterior tibial artery is the sole supply to the heel pad via the medial calcaneal branches.
• Soft Tissue: The heel pad skin must be completely intact, without deep ulceration, necrosis, or active infection. It must be mobile and healthy enough to bear the entire body weight.
• Functional: The patient must have the cognitive and physical capacity to participate in prosthetic rehabilitation.

Contraindications

Absolute:

• Absent posterior tibial artery flow (unless reconstructable via surgical or endovascular bypass)
• Heel pad necrosis or deep ulceration (the pad cannot serve as a weight-bearing surface)
• Inadequate tissue oxygenation (TcPO2 less than 20 mmHg universally predicts failure)
• Ascending gas gangrene (requires a higher level, open amputation for life salvage)

Relative:

• Severe neuropathy leading to unrecognised heel pad trauma (requires strict patient compliance and specialized prosthetic care)
• Bedbound non-ambulatory status (though a Syme is end-bearing and can assist with pivot transfers, a transtibial amputation often heals more reliably and faster in severe dysvascular bedbound patients)

Biomechanics of the Syme Amputation

• Energy Expenditure: Ambulation with a Syme amputation increases energy expenditure by only 10 to 15 percent compared to a normal gait. In contrast, a transtibial amputation increases energy expenditure by 20 to 40 percent. This is particularly crucial for elderly or dysvascular patients who have limited cardiopulmonary reserve.
• Proprioception: Preservation of the natural heel pad provides excellent proprioceptive feedback to the patient. The thick fibrous septa and fat lobules compress and distribute load uniformly across the distal tibial metaphysis.
• Lever Arm: The Syme stump provides a very long lever arm for the prosthesis, reducing the force required by the quadriceps and hip extensors to control the limb during the stance phase of gait.

Evidence for One-Stage vs Two-Stage Syme

One-Stage Syme

• The classical approach described by James Syme in 1843.
• Indicated in trauma, congenital deformities, and controlled dysvascular cases without active infection.
• Definitive bony resection and soft tissue closure are performed in a single operation.
• Excellent outcomes in non-infected patients but carries an unacceptably high failure rate if performed in the presence of severe forefoot sepsis due to contamination of the broad cancellous bone surface of the distal tibia.

Two-Stage Syme (Pinzur and Smith)

• Developed specifically for the diabetic patient with an infected forefoot.
• Stage One: Ankle disarticulation, removal of infected forefoot, but the malleoli are left INTACT. The oversized heel pad is loosely approximated over the malleoli. This avoids exposing cancellous bone to infection and provides a biological dressing over the joint.
• Stage Two: Performed 2 to 6 weeks later when the infection is clinically resolved and inflammatory markers are normal. The wound is reopened, the malleoli are resected, and definitive closure is performed.
• Evidence shows the two-stage technique significantly reduces stump infection and revision to transtibial amputation in the diabetic population, making it the standard of care for infected cases.

The Heel Pad

Architecture and Function

• The heel pad is highly specialised tissue designed for weight bearing and shock absorption, unique in the human body.
• It consists of closed fat compartments separated by thick, vertically oriented fibrous septa that anchor the skin to the underlying calcaneus.
• Surgical rule: These septa must not be violated. Dissection must remain strictly subperiosteal on the calcaneus to preserve the integrity of the fat lobules. If the septa are cut, the fat lobules necrose and the pad loses its shock-absorbing capacity.

Blood Supply

• The lifeline of the Syme amputation is the medial calcaneal artery, a major branch of the posterior tibial artery.
• It branches off proximal to the flexor retinaculum and travels inferiorly and laterally into the heel pad.
• Lateral calcaneal branches from the peroneal artery provide a secondary, but much smaller, contribution to the lateral aspect of the pad.
• The anterior tibial artery supplies the anterior flap but does not perfuse the critical heel pad. Loss of the anterior tibial artery does not compromise the procedure.

Bone and Articular Anatomy

The Tibial Plafond and Malleoli

• The distal tibia and fibula form a mortise. In a classical Syme amputation, the medial and lateral malleoli are resected along with a thin slice of the tibial plafond.
• Preserving the broad metaphyseal flare of the distal tibia is essential. This wide surface area distributes weight-bearing forces effectively and helps suspend the prosthesis by creating a bulbous stump end.
• The bony cut must be perfectly horizontal (parallel to the ground) in both coronal and sagittal planes to prevent asymmetric loading on the heel pad, which would lead to pressure ulceration.

The Achilles Tendon

• The Achilles tendon inserts into the posterior tuberosity of the calcaneus.
• During the Syme amputation, it must be divided close to its insertion.
• The posterior skin flap (part of the heel pad) is extremely thin directly over the Achilles insertion.
• Surgical rule: Great care must be taken not to buttonhole the skin when detaching the Achilles tendon, as a defect here will compromise the entire posterior flap and expose the deep tissues to infection.

Nerves of the Ankle

Five distinct sensory nerves cross the ankle joint and must be proactively managed to prevent neuroma formation within the rigid prosthetic socket:

1. Tibial Nerve: Travels posteromedially with the posterior tibial artery. It is a large nerve; it must be identified early and cut high. Ligation may be necessary due to a large accompanying vasa nervorum.
2. Superficial Peroneal Nerve: Travels anteriorly; supplies the dorsum of the foot. Found in the anterior subcutaneous tissue.
3. Deep Peroneal Nerve: Travels anteriorly with the anterior tibial artery between the extensor hallucis longus and extensor digitorum longus.
4. Sural Nerve: Travels posterolaterally behind the lateral malleolus.
5. Saphenous Nerve: Travels anteromedially with the great saphenous vein.

All nerves should be isolated, placed under gentle traction, cut sharply, and allowed to retract proximal to the weight-bearing stump end to avoid terminal neuromas.

Positioning and Preparation

• Position: Supine with a sandbag under the ipsilateral buttock to internally rotate the leg to a neutral position, bringing the lateral malleolus anteriorly.
• Tourniquet: A thigh tourniquet may be used in trauma or congenital cases, but is generally avoided in severe peripheral vascular disease to prevent further ischaemic insult to compromised tissues.
• Preparation: Paint and drape the entire leg from the knee down to allow accurate assessment of alignment and rotation during the procedure.

The Classical Syme Amputation (One-Stage)

Step 1: Incision Marking

The incision consists of two continuous limbs that meet at the malleoli, creating a U-shaped plantar flap and a slightly curved anterior flap.

• Anterior limb: Extends straight across the anterior aspect of the ankle from the tip of the lateral malleolus to a point 1.5 cm inferior to the tip of the medial malleolus. The medial starting point is slightly lower to protect the posterior tibial neurovascular bundle.
• Plantar limb: Extends vertically across the sole of the foot, connecting the two ends of the anterior limb. It must pass directly under the heel, straight down to bone.

Step 2: Anterior Exposure

Deepen the anterior incision straight down to the bone and anterior ankle joint capsule.

• Identify and ligate the anterior tibial artery and vein.
• Identify the superficial peroneal nerve, deep peroneal nerve, and saphenous nerve. Apply gentle traction, transect them cleanly, and let them retract proximally into the soft tissues.
• Divide the extensor tendons (tibialis anterior, extensor hallucis longus, extensor digitorum longus) while applying distal traction, allowing them to retract out of the field.

Step 3: Ankle Disarticulation

Incise the anterior joint capsule to enter the ankle joint.

• Plantarflex the foot firmly to open the anterior joint space.
• Divide the medial (deltoid) and lateral collateral ligaments from inside the joint, cutting closely against the talus to protect surrounding soft tissues.
• The talus is now free to subluxate anteriorly, exposing the posterior capsule which is then incised.

Step 4: Calcaneal Dissection (The Danger Zone)

This is the most critical and technically demanding step of the operation.

• Use a bone hook placed into the dome of the talus to pull the foot strongly anteriorly and downwards. This places the posterior soft tissues under tension.
• Using a heavy knife or a sharp periosteal elevator, dissect the soft tissues off the superior, posterior, and inferior aspects of the calcaneus.
• CRITICAL: The dissection must be strictly subperiosteal. Hug the bone tightly. Straying into the fat pad will destroy its septal architecture and blood supply, inevitably leading to pad necrosis.
• Take extreme care on the posteromedial corner of the calcaneus. The posterior tibial artery and its medial calcaneal branches are immediately adjacent. Stay firmly on bone to avoid damaging these vital vessels.
• Divide the Achilles tendon close to its insertion on the calcaneal tuberosity, ensuring the posterior skin is not buttonholed.
• Complete the subperiosteal dissection inferiorly until the entire calcaneus and foot are delivered from the heel pad.

Step 5: Bony Resection

Clear the soft tissues 1 to 2 cm proximally from the articular margin of the distal tibia and fibula. Use retractors to protect the anterior and posterior flaps.

• Use a broad oscillating saw to remove the medial and lateral malleoli and a thin (3 to 5 mm) slice of the distal tibial articular surface.
• The cut must be perfectly parallel to the ground in both the coronal and sagittal planes. Check this alignment with the knee fully extended. A non-parallel cut will cause shear forces and pressure sores in the prosthesis.
• Ensure the broad metaphyseal flare is preserved; do not cut too proximally. A cut that is too proximal loses the end-bearing surface area.
• Smooth all sharp bony edges with a rasp, especially the anterior tibial cortex.

Step 6: Nerve Management

Identify the tibial nerve and the sural nerve in the posterior flap.

• The tibial nerve is often thick and may require careful ligation to prevent bleeding from its vasa nervorum.
• Transect the nerves high under tension so they retract well above the weight-bearing surface to prevent neuroma pain.

Step 7: Anchoring the Heel Pad

To prevent the heel pad from migrating posteriorly or medially when weight is applied, it must be firmly anchored to the bone.

• Drill several small holes (usually 3 to 5) in the anterior and anterolateral cortex of the distal tibia and fibula, about 1 cm proximal to the cut edge.
• Pass heavy non-absorbable sutures (e.g., #2 FiberWire or Ethibond) through the deep fascia of the anterior edge of the heel pad and secure them through the drill holes.
• The pad should sit squarely and centrally beneath the cut end of the tibia.

Step 8: Closure

• Insert a deep suction drain to prevent haematoma formation, which can compromise flap viability and increase infection risk.
• Trim any small 'dog ears' medially and laterally, taking great care not to narrow the base of the flap or compromise its blood supply. Often, dog ears remodel over time and are best left alone if excision threatens the flap.
• Close the skin and subcutaneous tissue with interrupted monofilament sutures (e.g., 3-0 nylon) to avoid tissue strangulation.
• Apply a rigid or semi-rigid dressing (such as a plaster cast) to maintain the pad in the correct central position and control post-operative oedema.

The Two-Stage Syme Technique

For diabetic patients with active forefoot infection.

Stage One

• Perform the incisions, anterior exposure, and ankle disarticulation exactly as described above.
• Subperiosteally remove the calcaneus.
• DO NOT resect the malleoli or the articular cartilage of the distal tibia.
• Leave the oversized heel pad loosely draped over the malleoli. Do not attempt to anchor it.
• Insert a drain and close the skin loosely with a few interrupted sutures, or leave it partially open if heavily contaminated.
• Treat the infection with targeted intravenous antibiotics based on deep tissue cultures.

Stage Two

• Once the infection is cleared (typically 2 to 6 weeks later), and inflammatory markers have normalised, return to theatre.
• Reopen the wound completely.
• Proceed with Step 5 (Bony Resection), Step 6 (Nerve Management), and Step 7 (Anchoring the Heel Pad) as described in the definitive one-stage procedure.
• Perform a definitive meticulous closure over a drain.

Post-operative Protocol

Early Phase (Weeks 0 to 2)

• Dressing: A rigid cast or a semi-rigid dressing is applied in the operating theatre. This is crucial to prevent oedema, protect the wound from accidental trauma, and hold the heel pad in a precise central position.
• Weight-bearing: Strictly non-weight-bearing.
• Drain: The deep suction drain is typically removed at 48 hours or when output is minimal.
• Positioning: Elevate the limb to minimise swelling. Instruct the patient to avoid resting the stump directly on the bed, which can cause posterior pad migration.

Intermediate Phase (Weeks 2 to 6)

• Wound Check: The cast is changed at 10 to 14 days to inspect the wound and remove sutures. Diabetics may require sutures to remain longer (up to 3 weeks).
• Re-casting: A new snug-fitting cast is applied to continue shaping the stump and controlling oedema.
• Weight-bearing: The patient remains non-weight-bearing until 6 weeks post-operatively to ensure the heel pad anchors solidly to the distal tibia and the soft tissues heal comprehensively.

Late Phase (Weeks 6 and Beyond)

• Prosthetic Fitting: Once the wound is completely healed and the heel pad is stable (typically 6 to 8 weeks), the patient is referred to prosthetics for casting.
• Socket Design: A specific Syme prosthesis is used. It features a window or a flexible inner socket to allow the bulbous distal end to pass through the narrow ankle portion of the prosthesis.
• Rehabilitation: Gait training with the new prosthesis. The patient can often walk short distances (e.g., to the bathroom at night) without the prosthesis due to the end-bearing nature of the stump.

Prosthetic Considerations

• Bulbous Stump: The Syme stump is naturally bulbous at the end because the metaphyseal flare is preserved. This provides excellent suspension for the prosthesis (it won't slip off easily) but requires a specialized socket design (e.g., a medial window or an expandable wall) for donning and doffing.
• Leg Length Discrepancy: A Syme amputation shortens the limb by approximately 5 to 7 cm (the height of the calcaneus and talus combined). The prosthesis must make up this height. This limits the types of prosthetic feet that can be used, as there is less vertical clearance available compared to a transtibial amputation. Advanced high-energy-return feet may be difficult to fit.
• End-Bearing Advantage: Because the native heel pad is preserved and positioned directly under the tibia, the stump can bear direct axial load. This provides superior proprioception and allows limited barefoot ambulation, a massive functional advantage over transtibial amputations for nighttime mobility and showering.