Introduction to Lower Extremity Arthrodesis

Despite the exponential advancements in total joint arthroplasty, arthrodesis of the major weight-bearing joints of the lower extremity—specifically the ankle and the knee—remains an indispensable procedure in the armamentarium of the orthopedic surgeon. Historically championed by pioneers such as Charnley and Brittain, the principles of compression arthrodesis have evolved into highly sophisticated techniques utilizing rigid internal fixation, intramedullary devices, and advanced external frames.

Arthrodesis is primarily a salvage operation. It is designed to provide a stable, painless, and plantigrade limb in the setting of end-stage osteoarthritis, inflammatory arthropathy (e.g., rheumatoid arthritis), post-traumatic destruction, neuropathic (Charcot) arthropathy, or catastrophic failure of a total joint arthroplasty. This masterclass delineates the evidence-based indications, biomechanical considerations, step-by-step surgical techniques, and postoperative protocols for arthrodesis of the ankle and knee.

Part I: Ankle Arthrodesis (Tibiotalar Fusion)

Ankle arthrodesis is the gold standard for end-stage tibiotalar arthritis. While total ankle replacement (TAR) has gained traction, arthrodesis remains the procedure of choice for young, active patients, those with severe deformity, or in cases of failed TAR.

Indications and Contraindications

Indications:
* Post-traumatic osteoarthritis (the most common indication).
* Primary osteoarthritis of the tibiotalar joint.
* Inflammatory arthritis (Rheumatoid arthritis, Ankylosing spondylitis).
* Neuropathic arthropathy (Charcot joint) with instability.
* Salvage of failed total ankle arthroplasty.
* Chronic instability with secondary degenerative changes.
* Paralytic deformities (e.g., post-polio syndrome, drop foot).

Contraindications:
* Absolute: Active untreated infection (unless using external fixation), severe peripheral vascular disease, medically unfit for surgery.
* Relative: Ipsilateral subtalar or transverse tarsal arthritis (consider pantalar or tibiotalocalcaneal fusion), severe osteopenia, active smoking (significantly increases nonunion rates).

Biomechanics and Optimal Positioning

The success of an ankle arthrodesis is entirely dependent on achieving the correct spatial orientation of the fused joint. Malpositioning leads to altered gait mechanics, increased energy expenditure, and accelerated degeneration of the adjacent subtalar and midfoot joints.

Clinical Pearl: The optimal position for ankle arthrodesis is:
* Neutral dorsiflexion/plantarflexion (0 degrees): Avoid plantarflexion at all costs, as it causes a vaulting gait, genu recurvatum, and midfoot breakdown.
* Valgus (0 to 5 degrees): Slight valgus unlocks the transverse tarsal joint, allowing for compensatory midfoot motion. Varus positioning locks the midfoot, leading to a rigid, painful gait.
* External Rotation (5 to 10 degrees): Must match the contralateral limb to ensure symmetric progression angle during the stance phase of gait.
* Posterior Translation: The talus should be translated slightly posterior relative to the tibia to decrease the lever arm on the midfoot and improve the cosmetic appearance of the ankle.

Surgical Approaches and Techniques

1. Arthroscopic Ankle Arthrodesis

Pioneered by Myerson and Glick, arthroscopic arthrodesis is ideal for patients with minimal deformity (<15 degrees of coronal/sagittal malalignment).

• Advantages: Lower morbidity, decreased blood loss, preservation of the extra-articular blood supply, and faster time to union (average 9 weeks compared to 14 weeks for open).
• Technique: Standard anteromedial and anterolateral portals are utilized. Aggressive debridement of the articular cartilage is performed using curettes, shavers, and burrs until bleeding subchondral bone is exposed. The medial and lateral gutters must be meticulously cleared. Fixation is typically achieved percutaneously with two or three large-diameter (6.5 mm or 7.3 mm) cannulated cancellous screws placed in a crossed configuration.

2. Open Transfibular Approach

The transfibular approach is the workhorse for open ankle arthrodesis, providing excellent exposure for deformity correction and joint preparation.

• Positioning: Lateral decubitus or supine with a large bump under the ipsilateral hip.
• Incision: A longitudinal incision over the distal fibula, curving slightly anteriorly toward the base of the fourth metatarsal.
• Fibular Osteotomy: The fibula is osteotomized 2 to 3 cm proximal to the joint line. The distal fibula is excised, morselized, and saved for autogenous bone graft. Alternatively, it can be split longitudinally and used as an onlay biological plate.
• Joint Preparation: The articular surfaces of the tibia and talus are resected using an oscillating saw or osteotomes. Flat cuts provide excellent apposition but limit adjustability. Contour-matching (cup and cone) reaming preserves bone stock and allows for multiplanar adjustment.
• Fixation: Rigid internal compression is paramount. The standard construct involves three 6.5 mm or 7.3 mm cannulated screws:
  1. Home Run Screw: From the posterior tibia into the talar neck.
  2. Medial Malleolar Screw: From the medial malleolus into the talar body.
  3. Lateral Screw: From the anterolateral tibia into the talar body.
• Bone Grafting: The morselized fibula and any local autograft are packed into the interstices and gutters to promote osteogenesis.

Surgical Warning: When placing the "home run" screw from the posterior tibia into the talar neck, extreme care must be taken to avoid penetrating the subtalar joint. Fluoroscopic confirmation in multiple planes is mandatory.

3. Tibiotalocalcaneal (TTC) Arthrodesis via Intramedullary Nailing

Utilized for combined ankle and subtalar arthritis, severe deformity, Charcot arthropathy, or salvage of failed TAR.

• Technique: A retrograde intramedullary nail is inserted through the plantar aspect of the calcaneus, traversing the subtalar and tibiotalar joints into the tibial diaphysis.
• Biomechanics: Provides a load-sharing construct with immense bending stiffness. Internal compression can be applied through the nail targeting guide.
• Pitfalls: Risk of injury to the lateral plantar nerve during calcaneal insertion. The entry point must be precisely at the junction of the middle and posterior thirds of the calcaneus, slightly lateral to the midline.

Postoperative Protocol

• 0-2 Weeks: Non-weight-bearing (NWB) in a well-padded short leg splint. Elevation is critical to manage edema.
• 2-6 Weeks: Sutures removed. Transition to a NWB short leg cast.
• 6-12 Weeks: Radiographic evaluation. If early consolidation is visible, transition to a controlled ankle motion (CAM) boot with progressive weight-bearing.
• 12+ Weeks: Full weight-bearing in regular footwear. Rocker-bottom shoe modifications can significantly improve gait kinematics.

Part II: Knee Arthrodesis

Knee arthrodesis is a formidable procedure, almost exclusively reserved as a salvage operation. The loss of knee flexion profoundly impacts sitting, stair climbing, and energy expenditure during gait (increasing energy cost by up to 25-30%). However, it provides a stable, durable limb that is vastly superior to above-knee amputation in terms of functional mobility.

Indications and Contraindications

Indications:
* Infected total knee arthroplasty (TKA) with massive bone loss or highly resistant organisms (the most common modern indication).
* Catastrophic failure of the extensor mechanism in the setting of TKA.
* Severe neuropathic (Charcot) arthropathy of the knee.
* Post-traumatic destruction of the joint with unreconstructible bone loss.
* Tumor resection requiring joint sacrifice.

Contraindications:
* Contralateral limb amputation (bilateral stiff knees or one stiff knee and one prosthesis make rising from a chair nearly impossible).
* Severe ipsilateral hip or ankle arthritis.
* Inadequate soft tissue coverage (requires plastic surgery consultation for flaps prior to bony fusion).

Biomechanics and Optimal Positioning

Unlike the ankle, the knee must be fused in a position that balances the demands of walking (which favors full extension) and sitting/clearance (which favors slight flexion).

Clinical Pearl: The optimal position for knee arthrodesis is:
* Flexion (0 to 10 degrees): Slight flexion assists with foot clearance during the swing phase of gait and makes sitting slightly more comfortable. Fusing in >15 degrees of flexion causes excessive limb shortening and quadriceps fatigue.
* Valgus (5 to 7 degrees): Restores the normal mechanical axis of the lower extremity.
* Rotation (Neutral to 5 degrees external): Matches the normal tibial torsion.

Surgical Approaches and Fixation Strategies

1. Intramedullary Nailing (The Gold Standard)

For failed TKA, intramedullary (IM) nailing provides the highest union rates (85-95%) and the most rigid biomechanical construct.

• Preparation: The previous midline incision is utilized. The failed prosthesis and all cement/debris are meticulously removed. If active infection is present, a staged approach is mandatory: Stage 1 involves explantation and placement of an articulating or static antibiotic spacer; Stage 2 (after normalization of inflammatory markers) involves definitive arthrodesis.
• Bone Cuts: The distal femur and proximal tibia are prepared. Cylindrical reaming or flat cuts can be used. Flat cuts provide excellent compression but shorten the limb. If bone loss is massive, structural allografts or custom titanium trabecular metal cones may be required.
• Nail Insertion:
  • Long Antegrade/Retrograde Nails: A long, modular nail is passed from the greater trochanter (or retrograde from the knee) down to the distal tibia. This spans the entire mechanical axis.
  • Short Modular Nails: Inserted through the knee, locking into the femoral and tibial diaphyses.
• Compression: Dynamic compression is applied across the arthrodesis site before final distal locking.

2. Dual Plating

Advocated by Lucas and Murray, and later Nichols, dual plating is utilized when the medullary canal is deformed, obliterated, or when an IM nail is contraindicated.

• Technique: Two heavy-duty, broad dynamic compression plates (or modern locking plates) are applied. Typically, one plate is placed anteriorly and the other medially or laterally to provide orthogonal fixation.
• Drawbacks: Requires extensive soft tissue stripping, increasing the risk of wound breakdown and devascularization of the bone ends. It is a load-bearing construct, making it more susceptible to fatigue failure before union occurs.

3. External Fixation (Ilizarov / Monolateral Frames)

External fixation is the treatment of choice in the presence of active, recalcitrant infection or massive soft tissue defects.

• Technique: Circular (Ilizarov/Taylor Spatial Frame) or robust monolateral frames are applied.
• Advantages: Allows for compression across the fusion site without placing hardware in the infected bed. It also permits simultaneous limb lengthening via distraction osteogenesis (bone transport) if limb shortening is severe (>3-4 cm).
• Disadvantages: Pin tract infections, bulky apparatus, and significant psychological burden on the patient.

Postoperative Protocol and Complications

• Weight-Bearing: With a long IM nail, patients can often begin partial weight-bearing immediately, progressing to full weight-bearing by 6 weeks. Plating and external fixation require delayed weight-bearing.
• Complications:
  • Nonunion: Occurs in 10-15% of cases, heavily dependent on bone quality and eradication of infection.
  • Infection: Recurrence of infection is a devastating complication, often necessitating above-knee amputation.
  • Limb Length Discrepancy: Shortening of 2-3 cm is common and actually beneficial for swing-phase clearance. Shortening >3 cm requires a shoe lift.
  • Stress Fractures: Can occur at the tip of the IM nail or plates due to stress shielding and altered modulus of elasticity.

Conclusion

Arthrodesis of the ankle and knee are technically demanding procedures that require a profound understanding of lower extremity biomechanics, meticulous soft tissue handling, and rigid fixation principles. While joint-sacrificing, a well-executed arthrodesis provides a durable, functional, and pain-free limb, rescuing patients from the debilitating consequences of end-stage arthritis, infection, or failed arthroplasty. Mastery of these techniques—ranging from arthroscopic minimal-incision approaches to complex intramedullary reconstructions—is an essential competency for the advanced orthopedic surgeon.