Knee arthrodesis

1. High-Yield Summary

• Primary Clinical Indication: Knee arthrodesis serves as the definitive limb-salvage procedure for catastrophic failure of total knee arthroplasty (TKA), most commonly recurrent, recalcitrant periprosthetic joint infection (PJI) failing repeated two-stage exchange arthroplasty, massive un-reconstructable metaphyseal bone loss (AORI Type 3), or complete, irreparable extensor mechanism disruption.
• Biomechanical Alignment Targets: To optimize metabolic energy expenditure and ground clearance during swing phase, the fused knee must be positioned in 5° to 7° of anatomical valgus, 10° to 15° of flexion, and 5° to 10° of external rotation (matching the contralateral foot progression angle).
• Limb-Length Discrepancy Strategy: An intentional limb shortening of 1.5 to 2.5 cm relative to the contralateral lower extremity is mandatory to facilitate swing-phase foot clearance and eliminate compensatory pelvic hiking, circumduction, or vaulting gait.
• Fixation Modality Gold Standard: Modular long intramedullary (IM) arthrodesis nails provide superior union rates (85% to 92%) and lower reoperation rates compared to external fixation or dual compression plating by offering load-sharing axial rigidity with independent femoral and tibial canal matching.
• The Critical Move: Meticulous subperiosteal posterior capsular debridement with broad blunt retractors directly protecting the popliteal neurovascular bundle, followed by applying active mechanical axial compression across broad bleeding flat-cut or step-cut cancellous surfaces prior to static distal and proximal interlocking screw placement.
• Catastrophic Pitfall: Fixation in full extension (0°) or hyperextension causes severe circumduction gait and debilitating lumbar spine fatigue; conversely, single-stage intramedullary nailing in the presence of persistent active infection contaminates the entire femoral and tibial medullary canals, producing intractable pan-medullary osteomyelitis.

2. Indications

Knee arthrodesis is a definitive limb-salvage procedure indicated when articular reconstruction is biologically or mechanically impossible, yet the patient possesses sufficient functional capacity and soft-tissue integrity to justify limb preservation over transfemoral amputation.

Absolute Indications

• Persistent, recalcitrant periprosthetic joint infection (PJI) following failed two-stage revision arthroplasty, particularly involving multi-drug resistant, polymicrobial, or fungal pathogens in a compromised host envelope.
• Complete disruption, loss, or irreparable deficiency of the extensor mechanism (quadriceps tendon, patella, patellar tendon) where primary repair, synthetic augmentation, or extensor allograft reconstruction has failed or is contraindicated.
• Catastrophic femoral and tibial metaphyseal bone loss (Anderson Orthopaedic Research Institute [AORI] Type 3) precluding stable purchase of revision hinged knee implants or modular endoprostheses.
• Severe neuropathic (Charcot) arthropathy of the knee with gross ligamentous instability, osseous fragmentation, and rapid joint destruction refractory to nonoperative bracing.
• Primary or metastatic periarticular malignant musculoskeletal neoplasms requiring radical en bloc resection where endoprosthetic reconstruction is contraindicated or technically unfeasible.

Relative Indications

• Younger, high-demand, heavy manual laborers with end-stage post-traumatic arthrosis or chronic septic arthritis who require joint stability and heavy axial loading over joint mobility.
• Permanent lower motor neuron deficit causing complete quadriceps paralysis (such as irreversible femoral nerve transection) where a stable, brace-free lower extremity is prioritized.
• Chronic recalcitrant patellofemoral and tibiofemoral instability with intractable pain following multiple failed soft-tissue stabilizations.

Contraindications

• Absolute: Active, uncontrolled systemic sepsis or acute necrotizing infection demanding immediate surgical source control.
• Absolute: Non-viable extremity with severe, un-reconstructable peripheral arterial disease, complete limb ischemia, or major sciatic/tibial motor and sensory loss (primary above-knee amputation indicated).
• Absolute: Bilateral knee disease requiring bilateral arthrodesis, which creates insurmountable functional impairment in sitting, toilet transfers, and ambulation.
• Absolute: Severe contralateral lower extremity impairment (such as contralateral transfemoral amputation, flail limb, or uncorrected end-stage joint destruction) that abolishes single-limb stability.
• Absolute: Total loss of the local soft-tissue envelope without options for regional rotational (gastrocnemius) or free microvascular tissue transfer.
• Relative: Severe symptomatic osteoarthritis or ankylosis of the ipsilateral hip, ipsilateral ankle, or subtalar joint, which prevents compensatory biomechanical motion and provokes early adjacent joint failure.
• Relative: Severe osteopenia, severe osteomalacia, or massive diaphyseal bone deficiency compromising cortical screw purchase or nail stability.

3. Preoperative Planning

Imaging Review

• Full-Length Standing Alignment Radiographs: Bilateral 51-inch hip-to-ankle weight-bearing scanograms are mandatory to calculate baseline mechanical axes, evaluate contralateral limb alignment and foot progression angle, and measure pre-existing anatomical limb-length discrepancy.
• High-Quality Biplanar Views of Femur and Tibia: Dedicated full-length anteroposterior and lateral radiographs of the entire femur and tibia must be reviewed to assess medullary canal diameter, inner cortical dimensions, coronal and sagittal bowing, and the presence of retained hardware (such as ipsilateral total hip arthroplasty stems, proximal femoral plates, or retrograde ankle screws) that could obstruct intramedullary nail passage.
• Computed Tomography (CT) with Metal Artifact Reduction: Multiplanar thin-slice CT with metal artifact reduction software (MARS) provides three-dimensional evaluation of residual cortical rim thickness, AORI bone defect morphology, canal patency, occult bone cement fragments, and residual sequestra.
• Serologic and Synovial Infection Workup: Serum erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and D-dimer. Diagnostic knee arthrocentesis must be performed after a minimum 2 to 4-week antibiotic holiday, assessing synovial leukocyte count, polymorphonuclear percentage, alpha-defensin immunoassay, and extended aerobic, anaerobic, fungal, and mycobacterial cultures.

Equipment Checklist

• Modular Intramedullary Arthrodesis Nail System: Dedicated system providing independent femoral and tibial nails in multiple diameters (10 mm to 16 mm), varied lengths, anatomical sagittal bows, modular intercalary coupling sleeves (straight and angled for 5° valgus/10° flexion), internal mechanical compression bolts, and dynamic/static locking screws.
• Canal Preparation Instrumentation: Flexible intramedullary reamers (8.0 mm to 16.0 mm in 0.5 mm increments), ball-tipped guide wires (3.0 mm x 1000 mm), guide wire pusher, and entry reamers/awls.
• Retractor Inventory: Broad blunt Hohmann retractors, Bennett retractors, Meyerding retractors, and curved blunt posterior knee retractors designed to shield the popliteal neurovascular bundle during bone resection.
• Hardware and Cement Removal Tools: Ultrasonic cement extraction tools, high-speed carbide burrs, flexible osteotomes, reverse-cutting hooks, broken screw extractors, and endoscopes for medullary canal visualization.
• Dual Plating and External Fixation Backups: Heavy 4.5 mm dynamic compression or locking plates (distal femoral and proximal tibial contoured plates) and circular frame/external fixation components for salvage when medullary canal access is precluded.
• Biologics and Grafting: Morselized cancellous allograft chips, demineralized bone matrix (DBM), and harvesting systems for autologous reamer-irrigator-aspirator (RIA) bone graft.

Examination Under Anesthesia (EUA)

Prior to sterile scrubbing and draping, perform a rigorous clinical examination under anesthesia:

• True and Apparent Limb Length: Measure from the anterior superior iliac spine (ASIS) to the medial malleolus bilaterally using a rigid steel ruler or tape measure to quantify the exact deficit to be incorporated into surgical planning.
• Contralateral Rotational Profile: Assess the normal limb in the supine position by recording the thigh-foot angle, transmalleolar axis, and resting external rotation of the foot to replicate normal lower extremity kinematics.
• Adjacent Joint Mobility: Confirm passive motion of the ipsilateral hip (flexion, extension, abduction, adduction) and ankle/hindfoot (dorsiflexion, subtalar inversion/eversion). Substantial contractures must be recognized, as they impair post-fusion functional compensation.
• Integumentary Mobility: Palpate prior scars, identify tethered subcutaneous planes, and assess tissue turgor to verify that wound closure will be achievable without excessive tension.

4. Patient Positioning & Setup

Position the patient supine on a fully radiolucent carbon-fiber operating table to allow uninterrupted fluoroscopic imaging from the pelvis to the ankle. Place a firm radiolucent silicone or folded-sheet bump beneath the ipsilateral buttock to neutralize resting external rotation and maintain the patella directed toward the ceiling. The contralateral lower extremity is padded at all pressure areas (heel, sacrum, and fibular head) and secured flat or on an abducted leg board. Pad the ulnar nerves bilaterally at the elbows and secure the arms on padded armboards.

Apply a high-thigh sterile pneumatic tourniquet. The tourniquet may be inflated during the initial exposure, implant removal, and soft-tissue debridement, but it should be deflated prior to bony cuts, intramedullary reaming, and closure to monitor limb perfusion and achieve meticulous hemostasis. The entire surgical limb is prepped and draped freely from the iliac crest down to the toes using split sheets and an impermeable sterile stockinette, ensuring unrestricted limb manipulation throughout the procedure.

Safety Check

• Fluoroscopic Corridor Verification: Before surgical incision, bring the C-arm from the contralateral side and confirm clear, orthogonal anteroposterior and lateral visualization of four key anatomical checkpoints: the proximal femoral entry and hip, the distal femur, the arthrodesis docking interface, and the distal tibia down to the ankle joint.
• Vascular Baseline Confirmation: Palpate and mark the dorsalis pedis and posterior tibial arterial pulses. If pulses are not readily palpable, confirm distinct biphasic Doppler signals and communicate baseline acoustic parameters with the anesthesia team.

5. Approach

Surgical Approach and Intermuscular Interval

• Named Approach: Anterior midline approach with medial parapatellar arthrotomy. Whenever feasible, incorporate the most recent prior midline incision to prevent cutaneous necrosis. If multiple longitudinal scars are present, utilize the most lateral viable incision to preserve the dominant medial cutaneous vascular supply from the saphenous and descending genicular artery networks, ensuring a minimum 5 cm bridge between parallel incisions.
• Intermuscular Interval: The anterior midline knee approach represents an intermuscular corridor traversing the quadriceps tendon, medial patellar retinaculum, and patellar tendon. The rectus femoris and vastus lateralis (femoral nerve) are mobilized laterally, while the vastus medialis (femoral nerve) is reflected medially. A true internervous plane does not exist along the anterior extensor mechanism.

Neurovascular Danger Zones and Safe Retraction Corridors

• Popliteal Neurovascular Bundle: The popliteal artery, popliteal vein, and tibial nerve course directly posterior to the posterior capsule and posterior cruciate ligament insertion. In revision surgery, chronic post-infectious scarring fuses the posterior joint capsule directly to the adventitia of the popliteal vessels. Over-penetration of oscillating saw blades or posterior reamer excursion can lead to catastrophic arterial transection, pseudoaneurysm, or transection of the tibial nerve. Safe Retraction Corridor: Keep dissection strictly subperiosteal. Position broad, blunt Hohmann or Bennett retractors directly against the posterior femoral and tibial cortices inside the periosteal sleeve to shield the soft tissues during bone resection.
• Common Peroneal (Fibular) Nerve: The nerve travels along the medial border of the biceps femoris tendon before curving around the fibular neck into the lateral compartment. Acute correction of severe pre-existing fixed valgus deformities (greater than 15°) or severe fixed flexion contractures (greater than 20°) places the nerve under extreme traction, risking ischemic neurapraxia or complete foot drop. Safe Retraction Corridor: Maintain limb shortening of 1.5 to 2.5 cm to de-tension the sciatic and peroneal nerves, and avoid placing sharp retractors around the posterolateral tibial flare.
• Saphenous Nerve and Infrapatellar Branch: Exiting the adductor canal beneath the sartorius muscle, the saphenous nerve courses down the medial aspect of the knee, giving off transverse infrapatellar branches over the tibial tubercle. Medial exposure inevitably transects these sensory branches, resulting in lateral numbness over the proximal tibia. To prevent painful neuroma formation, identify transected nerve trunks, resect them sharply under tension, and allow them to retract into deep muscular tissue.

6. Technique

Step 1: Exposure and Soft-Tissue Mobilization

• Incise the skin and subcutaneous tissue sharply through the previous anterior midline scar, creating full-thickness fasciocutaneous flaps without undermining to preserve dermal microvascular perfusion.
• Mobilize the medial parapatellar arthrotomy, entering the capsule along the medial border of the quadriceps tendon, continuing around the medial patella, and ending medial to the tibial tubercle.
• Excise the patella (patellectomy) or morselize the bony patella with a bone mill to serve as an abundant autologous cancellous bone graft source.
• Debride extensive fibrous pannus, pseudocapsule, and residual sinus tracts. Extract existing prosthetic components, antibiotic cement spacers, and all retained polymethylmethacrylate (PMMA) cement using flexible osteotomes, reverse chisels, and ultrasonic extraction tools without compromising cortical bone stock.

Step 2: Bone Preparation / Debridement

• Debride all non-viable, infected, and sclerotic bone margins until uniform punctate cortical and cancellous bleeding is visualized across the entire circumference of both the distal femur and proximal tibia (the paprika sign). Dense, avascular bone ends must not be retained.
• Resect the distal femoral articular surface perpendicular to the femoral anatomical axis in 5° to 7° of valgus, and resect the proximal tibial plateau perpendicular to the tibial mechanical axis in the coronal plane with 10° to 15° of sagittal flexion. Use an oscillating saw with copious saline irrigation to prevent thermal osteonecrosis.
• Sculpt matching docking surfaces. In the presence of substantial AORI Type 2 or 3 metaphyseal bone loss, shape the bone ends into a conical step-cut or chamfered geometry, allowing telescoping contact between the femoral and tibial cortices to maximize bone contact area and augment rotational resistance.

Step 3: Trialing and Provisional Fixation

• Cannulate the distal femoral canal through the intercondylar notch under fluoroscopic visualization using a starter awl. Pass a 3.0 mm ball-tipped guide wire retrograde up the femoral shaft past the isthmus. Sequentially ream the femoral canal in 0.5 mm increments using flexible reamers until distinct cortical chatter is encountered.
• Ream the tibial canal by creating an entry portal in the center of the proximal tibial surface (slightly anterior and medial to the tibial spine footprint). Pass the guide wire antegrade down the tibial shaft to the level of the distal tibial physeal scar, and sequentially ream the tibia.
• Trial modular intramedullary components. Insert trial femoral and tibial rods and connect them across the intercalary junction using the trial coupling sleeve.
• Verify anatomical alignment clinically and fluoroscopically: 5° to 7° of coronal valgus, 10° to 15° of sagittal flexion, 5° to 10° of external rotation (aligning the second metatarsal ray with the tibial tubercle and matching the contralateral foot progression angle), and 1.5 to 2.5 cm of deliberate limb shortening.

Step 4: Final Implant Placement or Suture Fixation

• Introduce the definitive retrograde modular femoral nail into the femur and advance it to the planned intercalary depth.
• Introduce the definitive antegrade modular tibial nail into the tibia.
• Couple the central modular junction across the intercalary joint gap, engaging the morse taper sleeve and securing the internal connection mechanism.
• Pack morselized autologous patellar bone graft, cancellous allograft, and demineralized bone matrix circumferentially around the docking site and within residual cortical voids.
• Compress the arthrodesis junction by activating the nail’s internal mechanical compression bolt while an assistant applies sustained manual longitudinal counter-pressure against the heel. Confirm rigid bone-on-bone coaptation without gap formation on biplanar fluoroscopy.
• Interlock the construct by inserting proximal static locking screws in the femur and distal static locking screws in the distal tibia through precision radiolucent guides or freehand fluoroscopy.
• Alternative Fixation: When medullary canals are obliterated or blocked by retained total hip stems, perform dual compression plating using heavy 4.5 mm dynamic compression or locking plates positioned at 90° angles (anterior and medial/lateral). In active, uncontrolled sepsis, apply a circular external frame (Ilizarov or Taylor Spatial Frame) with multiplanar tensioned wires and hydroxyapatite half-pins across the joint.

Critical Move

The irreversible procedural step is the execution of subperiosteal posterior joint debridement under direct visualization with blunt bone retractors shielding the popliteal artery and tibial nerve, followed by applying active mechanical axial compression across bleeding bone surfaces prior to distal locking. Achieving intimate cancellous coaptation in 10° to 15° of sagittal flexion eliminates junctional micro-motion and provides the load-sharing stability required for primary bridging osseous union.

7. Pearls and Pitfalls

Pearls

• The Paprika Sign as Viability Indicator: Continue debriding sclerotic bone ends until uniform punctate bleeding is visible across 100% of both cut surfaces. Retaining dense avascular bone inevitably results in delayed union or pseudoarthrosis.
• Planned 1.5 to 2.5 cm Shortening: Deliberate shortening of 1.5 to 2.5 cm provides natural foot clearance during the swing phase, eliminating the need for exhausting compensatory pelvic hiking, circumduction, or vaulting gait.
• Autologous Patellar Bone Slurry: Never discard the excised patella. Morselize it into an autologous cancellous bone slurry and pack it circumferentially around the docking site to bridge residual cortical gaps.
• Independent Canal Optimization: Because femoral and tibial canal diameters and anatomical bows differ substantially, modular dual-radius nail systems allow independent diameter and length optimization for each bone segment.
• Heel-Strike Compression Maneuver: Apply continuous manual axial force against the plantar aspect of the heel while tightening the nail’s internal compression bolt to ensure intimate bone-to-bone coaptation before placing static locking screws.

Pitfalls

• Fixation in Full Extension (0°) or Hyperextension: Fixing the knee in extension produces severe circumduction and contralateral vaulting gait, markedly increasing energy expenditure and provoking chronic lumbar back pain. Always secure 10° to 15° of sagittal flexion.
• Single-Stage Nailing in Active Sepsis: Driving a long intramedullary nail across an actively infected joint contaminates the entire medullary canals of both femur and tibia, converting a local joint infection into pan-femoral and pan-tibial osteomyelitis. Always perform a staged protocol with interim antibiotic spacer for active sepsis.
• Peroneal Nerve Traction Injury: Acute correction of long-standing severe valgus or flexion contractures stretches the tethered common peroneal nerve around the fibular neck. Maintain planned limb shortening of 1.5 to 2.5 cm to de-tension the nerve, and perform prophylactic peroneal nerve release if severe valgus is corrected.
• Eccentric Reaming and Cortical Perforation: In osteopenic or scarred bone, rigid reamers can easily breach the anterior femoral or posterior tibial cortex. Use flexible reamers over centered guide wires with frequent biplanar fluoroscopic verification, and neutralize breaches with auxiliary cerclage cabling or plates.

8. Postoperative Care

Immediate

• Weight-Bearing Status: Patients with rigid modular intramedullary nail constructs begin partial weight-bearing (30 to 50 lbs) with crutches or a walker on postoperative day 1, advancing to weight-bearing as tolerated (WBAT) by 2 to 4 weeks, as controlled axial loading accelerates bone healing. If dual compression plating or external fixation is used, touch-down weight-bearing (TDWB) is maintained for 6 to 8 weeks.
• Immobilization: A soft compressive dressing is applied. No external knee splint or cast is required for rigid intramedullary nails. For plating or compromised bone stock, a hinged knee brace locked in extension or cylinder splint is utilized for 6 weeks.
• Venous Thromboembolism Prophylaxis: Pharmacologic thromboprophylaxis (such as low-molecular-weight heparin or direct oral factor Xa inhibitors) is maintained for 35 days postoperatively, coupled with mechanical calf compression devices.
• Incisional Wound Management: Closed-incision negative pressure wound therapy (ciNPWT) is applied for 5 to 7 days in high-risk soft-tissue envelopes to minimize edema and prevent wound dehiscence.

Rehabilitation Protocol

9. Outcome

• Bony Union Rates: Modular intramedullary arthrodesis nails achieve radiographic union rates of 85% to 92%, with a mean time to solid union ranging from 4 to 8 months. In contrast, dual compression plating yields union rates of 70% to 80%, and circular external fixators achieve union rates of 65% to 75%.
• Infection Eradication: Staged debridement followed by modular intramedullary nailing successfully eradicates infection in 88% to 94% of patients presenting with chronic recalcitrant PJI, avoiding the high pin-track infection rates (40% to 50%) characteristic of external fixators.
• Functional Capacity and Ambulatory Independence: Over 80% to 85% of patients achieve pain-free independent community or household ambulation without assistive devices. While navigating stairs and sitting in tight spaces (such as airplanes or automobiles) remain challenging, patient satisfaction exceeds 80% when compared to transfemoral amputation.
• Metabolic Efficiency vs. Transfemoral Amputation: Patients with an arthrodesed knee expend significantly less metabolic energy during ambulation than transfemoral amputees utilizing a prosthetic limb, particularly in elderly cohorts where fewer than 40% of above-knee amputees achieve functional prosthetic ambulation.
• Leg-Length Discrepancy Compensation: The planned 1.5 to 2.5 cm of shortening is well tolerated and, when addressed with custom footwear modifications, normalizes pelvic symmetry, prevents lumbar back strain, and facilitates smooth forward progression.

10. Complications

Given the compromised biological host status, previous extensive surgical trauma, and scarred tissue envelopes, complication rates following knee arthrodesis range from 25% to 45%.

11. Evidence-Based Synthesis

Modern clinical decision-making is grounded in high-quality randomized controlled trials and prospective registry analyses, corroborated by seminal biomechanical and anatomical descriptions.

12. References

• Mercurio M, Gasparini G, Cofano E et al. Knee Arthrodesis for Periprosthetic Knee Infection: Fusion Rate, Complications, and Limb Salvage-A Systematic Review. Healthcare (Basel). 2024. doi:10.3390/healthcare12070804 [Level I: Systematic Review & Meta-Analysis]
• Rajasekaran RB, Ponniah HS, Palanisami DR et al. A comparative analysis of three knee arthrodesis techniques to manage failed total knee arthroplasty due to infection: intramedullary nailing, LRS external fixator, and compression plating. Arch Orthop Trauma Surg. 2026. doi:10.1007/s00402-026-06469-z [Level II: Comparative Cohort Study]
• Kamboj AS, Das A, Thorat BS et al. Two-Stage Modular Intramedullary Knee Arthrodesis for Persistent Periprosthetic Joint Infection After Failed Total Knee Arthroplasty: Mid-Term to Long-Term Outcomes. JB JS Open Access. 2026. doi:10.2106/JBJS.OA.26.00203 [Level IV: Clinical Case Series]
• Hetto P, Geisbüsch A, Lehner B. Results of Knee Arthrodesis Using an Intramedullary Modular Arthrodesis System After Failed Total Knee Arthroplasty After Up to 17 Years. J Arthroplasty. 2026. doi:10.1016/j.arth.2025.08.052 [Level IV: Clinical Case Series]
• Schlossmacher B, Tietje C, Lallinger V et al. High failure rates and poor quality of life after modular non-fusion knee arthrodesis following failed total knee arthroplasty: a multicenter retrospective study of 85 patients. Arthroplasty. 2026. doi:10.1186/s42836-026-00415-5 [Level IV: Multicenter Cohort Study]

13. Master Class Pro-Tip

When addressing severe metaphyseal bone defects during modular intramedullary knee arthrodesis, flat transverse saw cuts often fail to provide adequate mechanical coaptation. Sculpting a conical step-cut docking geometry, allowing the distal femoral cortex to telescope into or interlock with the proximal tibial metaphysis, dramatically increases the contact surface area and enhances rotational resistance. Before placing the distal tibial interlocking screws, apply sustained manual axial load from the plantar aspect of the foot while engaging the nail’s internal mechanical compression bolt. This preloads the bone-implant interface, closes microscopic gaps, and eliminates interface micro-motion, which is the single most critical biomechanical determinant of rapid trabecular bridging.

Master Class Surgical Pearl: Knee Arthrodesis