Knee Arthrodesis

Primary Indications

Absolute / Common Indications

• Chronically infected total knee arthroplasty (TKA) after failed two-stage revision, where re-revision arthroplasty is not feasible
• Irreparable extensor mechanism deficiency (loss of quadriceps/patellar tendon) making a functional arthroplasty impossible
• Massive bone loss of the distal femur or proximal tibia not amenable to revision or megaprosthesis
• Post-tumour resection reconstruction where durable biological fusion is preferred over endoprosthesis (especially young, high-demand patients)

Relative Indications

• Neuropathic (Charcot) joint with recurrent instability and ulceration
• Failed septic arthritis with an unsalvageable, painful, unstable knee
• Young, heavy-labour or high-demand patient prioritising a durable, pain-free, weight-bearing limb over motion
• Failed multiple arthroplasties with a poor soft-tissue envelope but an intact, functional foot and ankle

Contraindications

• Bilateral knee disease requiring bilateral fusion - leaves the patient unable to sit, transfer or climb stairs
• Ipsilateral hip or ankle fusion / stiffness - a stiff knee plus a stiff hip or ankle is functionally disabling
• Contralateral above-knee amputation - the patient depends on the other limb's knee for mobility
• Active uncontrolled infection where eradication is impossible (consider amputation)
• Inadequate soft-tissue cover precluding fixation, or vascular insufficiency threatening healing

Goals of Surgery

• Eradicate infection (when present)
• Achieve a stable, painless, plantigrade, weight-bearing limb
• Restore acceptable limb length and alignment
• Achieve solid bony union in the optimal position

Pre-operative Assessment & Planning

Patient Factors

• Functional status of the rest of the limb chain: examine the ipsilateral hip and ankle and the contralateral limb - these determine whether a stiff knee will leave a usable limb
• Vascular status: palpate pulses, assess for peripheral vascular disease; a poorly perfused limb heals badly and may be better served by amputation
• Soft-tissue envelope: map previous incisions, sinuses and flaps; obtain a plastic-surgical opinion early if cover is marginal
• Comorbidities: diabetes, immunosuppression, smoking and malnutrition all impair fusion and infection control - optimise where possible

Infection Work-up (when applicable)

• Inflammatory markers (CRP, ESR), joint aspiration with culture and cell count
• Identify the organism and its sensitivities before definitive surgery; involve microbiology/infectious diseases
• Determine whether infection is active (mandates a staged approach) or quiescent/eradicated (permits single-stage definitive fixation)

Imaging & Templating

• Long-leg standing alignment films of both limbs for length and axis planning
• CT to define bone loss, canal patency and the feasibility of intramedullary nailing
• Template the expected defect, the construct, and the anticipated final limb length and shortening

Optimal Fusion Position

Evidence Base

Fixation and Fusion Rates

The intramedullary (IM) nail is the most commonly used construct and, as a load-sharing device, allows the earliest protected weight-bearing. Single-centre series report high union: Luyet et al. (2023) found an 89.6 percent fusion rate in 48 knees, with infection cured in 93 percent. However, pooled systematic-review data are more nuanced. Mercurio et al. (2024), pooling 787 patients, reported fusion in 71.9 percent after IM nail, 78.8 percent after external fixation, and 92.3 percent after compression plating, with no statistically significant difference between methods - and a higher conversion-to-amputation rate after compression plating (15.8 percent versus 5 percent external fixation, 4.3 percent IM nail). Goh et al. (2026), pooling 969 knees, found a low overall aseptic failure rate (6 percent) but a high complication rate (28 percent, recurrent infection 11 percent), and importantly showed that modern intercalary prosthetic and cement constructs failed less often than traditional bone-on-bone fusion (12 percent failure). The honest exam position is therefore: the IM nail is the workhorse for its load-sharing biomechanics and early mobilisation rather than a proven superior fusion rate, external fixation carries the highest pin-track burden, and infection eradication is the dominant determinant of success across all constructs.

Modular Arthrodesis Constructs

Gramlich et al. (2021) showed modular intramedullary arthrodesis secures the limb, restores mobility, improves quality of life and achieves high infection control in periprosthetic knee infection when revision arthroplasty is not an option - useful where bone loss is too great for a conventional nail to gain fixation.

Arthrodesis versus Above-Knee Amputation

Low et al. (2024) systematically compared transfemoral amputation with knee arthrodesis for failed TKA: arthrodesis preserves a longer, energy-efficient, weight-bearing limb with generally better functional scores and prosthesis-free ambulation, whereas amputation may be preferred for uncontrollable infection, severe pain, or failed fusion. Hoveidaei et al. (2024) similarly framed knee fusion and above-knee amputation as the two end-stage options for unreconstructable periprosthetic infection, emphasising shared, honest decision-making.

Arthrodesis versus Amputation - Decision Summary

Choosing the Indication Wisely

• Fusion is a one-way salvage: once fused, motion is gone permanently, so reserve it for joints that are genuinely unreconstructable
• In tumour cases, weigh durable biological fusion (favoured in young, high-demand patients) against an endoprosthesis that preserves motion but carries long-term mechanical and infection risk
• Always confirm the patient understands and accepts a permanently stiff knee before proceeding

Key Evidence (Verified)

Relevant Anatomy for Knee Fusion

Posterior Neurovascular Structures

• Popliteal artery and vein run vertically in the popliteal fossa, immediately posterior to the joint capsule and posterior femoral cortex. Tethered proximally at the adductor hiatus and distally at the soleal (tendinous) arch - these tether points mean acute correction of a flexion contracture can stretch the artery.
• Tibial nerve lies most superficial in the fossa, then artery, then vein deepest against bone.
• Common peroneal nerve diverges laterally and wraps around the fibular neck - the structure most at risk during lateral plating and during correction of valgus/flexion deformity.

Bony Anatomy and Contact Surfaces

• Fusion relies on apposition of distal femur and proximal tibia cancellous surfaces. After implant removal there is often a large defect; flat, congruent, well-vascularised cancellous bone maximises contact area and compression.
• The patella is usually retained but plays no role in fusion; the patellofemoral joint is sacrificed.
• The medullary canals of femur and tibia must be co-axial for an IM nail to pass - canal sclerosis or deformity from prior surgery can prevent this.

Soft-Tissue Envelope

• Prior incisions, sinus tracts and the extensor mechanism status dictate the approach. A midline longitudinal incision through the most lateral usable previous scar protects the skin bridges.
• Compromised soft tissue may require plastic-surgical input (gastrocnemius/free flap) before or at fusion.

Mechanical Axis and Length

• The normal limb has roughly 5-7 degrees of anatomical valgus at the knee; fusion aims to reproduce this (5-8 degrees valgus) so the foot sits under the body's centre of gravity.
• Each removed centimetre of bone shortens the limb; total shortening of 2-5 cm is common and is preferable to tension on the neurovascular bundle from forced lengthening.

Vascular Considerations for Union

• Bone-end vascularity is the key determinant of union. Repeated surgery, infection and over-zealous debridement devascularise bone.
• Preserve periosteal blood supply where possible and consider bone graft (autograft/allograft) for defects to bridge gaps and improve the biological environment.

Surface Anatomy & Approach Landmarks

• The midline of the patella, tibial tubercle and anterior tibial crest guide the longitudinal incision and confirm rotation
• The fibular head and neck are palpated laterally to localise the common peroneal nerve before lateral dissection
• The adductor tubercle and medial/lateral epicondyles orient the coronal (valgus) plane during bone-end preparation
• The posterior joint line marks the danger plane - dissection and saw cuts must remain anterior to it to protect the popliteal contents

Biomechanics of the Fused Knee

• A fused knee converts the limb into a rigid lever; gait compensations include pelvic hike, circumduction and vaulting of the contralateral limb, all of which raise metabolic energy expenditure
• Correct coronal and rotational alignment keeps the ground-reaction force efficient and minimises moments at the ipsilateral hip and ankle
• Sitting requires the patient to extend the fused limb forward; excessive flexion at the fusion compounds this difficulty, which is why the sagittal target stays close to extension

Positioning and Preparation

Patient Position: Supine on a radiolucent table, sandbag/bump under the ipsilateral hip to control rotation, with image intensifier access for the whole limb. A tourniquet may be used if the soft tissues and vascular status allow, but is often avoided in revision/infected cases.

Technical Points:

• Prep and drape the entire limb including the foot to assess rotation and length intra-operatively
• Have the contralateral limb available for length and rotation comparison
• Plan for general or regional anaesthesia; ensure cross-matched blood is available for revision/infected cases

Operative Steps

Step 1: Incision and Exposure

Approach: Use a midline longitudinal incision, incorporating the most appropriate previous scar (favour the lateral of parallel scars to protect skin bridges). Develop full-thickness fasciocutaneous flaps to avoid skin necrosis.

Technical Pearl: Excise sinus tracts and unhealthy scar en bloc; tissue handling determines wound healing in this compromised envelope.

Step 2: Implant Removal and Radical Debridement

Remove all hardware and cement: Extract the failed prosthesis, all cement, and any retained fixation. In infection, perform radical debridement of all non-viable bone and soft tissue.

Send Deep Samples: Take at least 3-5 separate deep tissue cultures and histology before antibiotics. The single most important determinant of success in the infected knee is the adequacy of debridement.

Step 3: Assess Bone Stock and Length

Evaluate Defect: Assess remaining distal femoral and proximal tibial bone, canal patency, and the resulting limb length.

Decision Point: The size of the defect and canal status drive the fixation choice - a contained defect with patent canals favours an IM nail; segmental loss or unusable canals favour dual plating, an external fixator/Ilizarov, or a modular arthrodesis nail.

Step 4: Prepare the Bone Ends

Create Congruent Surfaces: Make flat, parallel cancellous cuts on the distal femur and proximal tibia to maximise contact area and compression. Remove sclerotic, avascular bone to expose bleeding cancellous bone.

Set the Position: Provisionally appose the surfaces in 0-15 degrees flexion, 5-8 degrees valgus, and slight external rotation, checking against the contralateral limb. Use bone graft for contained defects to improve contact and biology.

Step 5A: Fixation Option - Intramedullary Nail

Technique: Ream and pass a long antegrade or retrograde IM nail spanning femur and tibia (modular/coupled nails are available for large defects). Compress across the fusion site and lock proximally and distally.

Advantages: Load-sharing construct allowing the earliest protected weight-bearing, no transarticular pins, most commonly used construct; single series report fusion around 80-90 percent (note pooled reviews show no significant fusion-rate advantage over external fixation).

Caution: Do not pass a nail through an actively infected canal in a single stage - it risks seeding the entire medullary canal. Reserve single-stage nailing for an eradicated/quiescent infection or use a staged approach.

Step 5B: Fixation Option - Dual (Compression) Plating

Technique: Apply two plates (commonly anterior and lateral, or medial and lateral) across the prepared bone ends under compression.

Advantages: Useful when the canal is unusable or deformed, allows precise positioning and compression, avoids spreading infection up the canal.

Disadvantages: Large soft-tissue exposure and stripping, extensive implant load in a compromised bed, generally lower union than IM nail and risk of plate-related wound problems.

Step 5C: Fixation Option - External Fixator / Ilizarov

Technique: Apply a uniplanar external fixator or a ring (Ilizarov) frame providing compression across the fusion; bifocal frames allow simultaneous bone transport for segmental defects or length restoration.

Advantages: Avoids internal hardware in an actively infected field, allows compression and correction, enables bone transport for defects/length.

Disadvantages: Lowest union rates, high pin-track infection and patient burden, prolonged frame time. Calif et al. (2004) described the Ilizarov frame as an option for compression arthrodesis of large weight-bearing joints, especially where internal fixation is contraindicated.

Step 6: Achieve and Confirm Compression

Compress the Site: Whatever the construct, apply axial compression across viable bone-on-bone contact - compression is the single biggest mechanical contributor to union.

Confirm Alignment: Verify position with the image intensifier and clinical comparison - recheck flexion, valgus and rotation before final tightening/locking. Correct now, not after closure.

Step 7: Bone Grafting and Defect Management

Graft Defects: Pack contained defects with autograft or allograft. For large segmental loss, plan bone transport (Ilizarov) or a modular arthrodesis implant rather than accepting a non-contact gap.

Technical Pearl: Avoid leaving a non-contact gap bridged only by hardware - bone must touch bone under compression for biological union. A modular arthrodesis nail or bone transport restores contact when the defect is too large for simple apposition.

Step 8: Protect the Soft-Tissue Envelope

Tension-free Cover: Reassess skin tension after fixation; in a compromised, previously infected or irradiated envelope, plan gastrocnemius or free-flap cover with the plastic surgeons rather than closing under tension.

Avoid Wound Catastrophe: A breakdown over the construct in a previously infected bed can lead to deep infection and loss of the fusion - the soft-tissue plan is as important as the bony plan.

Step 9: Closure and Drainage

Layered Closure: Achieve meticulous haemostasis, place deep drains, and close in layers over the construct. Involve plastic surgery for flap cover if the envelope is inadequate.

Dressing/Splint: Apply a bulky dressing; protect with a splint/cast or rely on frame stability depending on the construct.

Single-Stage versus Staged Fusion

Single-Stage Fusion

• Appropriate where infection is eradicated or quiescent, or where the indication is non-infective (tumour, neuropathic joint, post-traumatic)
• Definitive fixation (usually an IM nail) is performed at the same sitting as bone preparation
• Advantages: one operation, faster path to union and weight-bearing

Staged Fusion

• Mandatory in active periprosthetic infection - the first stage is radical debridement, removal of all hardware/cement, an antibiotic spacer and culture-directed antibiotics
• Definitive fixation follows once inflammatory markers normalise and the wound is quiescent
• Avoids the catastrophic complication of seeding the medullary canal with an intramedullary nail through infected bone

Technical Pearls

• Maximise bone contact: the single biggest biological lever for union after infection control - flat, parallel, vascular cancellous surfaces
• Compression, compression, compression: every construct must deliver axial compression across viable bone
• Check rotation last and against the other leg: rotational malposition is the easiest error to make and the hardest to tolerate
• Plan for shortening early: accept a few centimetres and a shoe raise rather than tensioning the popliteal vessels

Specific Management Pearls

When Fusion Fails

• A failed fusion forces the same end-stage decision as the original problem: re-fusion with a better construct (usually conversion to a compressive IM nail once infection is quiescent) versus above-knee amputation.
• Repeated failed surgery, intractable pain or uncontrollable infection shifts the balance towards amputation - counsel the patient that amputation is a definitive, reliable solution, not simply a failure.

Staged Strategy in Active Infection

• In active periprosthetic infection, separate infection eradication (debridement, antibiotic spacer, culture-directed antibiotics) from definitive fixation. Passing an IM nail through an infected canal is a recognised cause of disastrous proximal spread.

Stiff-Knee Gait and Adjacent-Joint Overload

• Every fused knee produces a stiff-leg gait; counsel patients pre-operatively so the result is not perceived as a failure
• Watch for ipsilateral hip, ipsilateral ankle and lumbar spine pain from the compensatory gait - manage with physiotherapy, analgesia and orthotics, and reserve further surgery for refractory cases
• Correct fusion position is the best prophylaxis against adjacent-joint overload

Managing Limb-Length Discrepancy

• Most discrepancies (2-5 cm) are managed simply with a shoe raise
• Large, symptomatic discrepancies in motivated patients can be addressed with Ilizarov distraction osteogenesis (bone transport), accepting the frame burden
• Never restore length by forcibly distracting the fusion site acutely - this risks neurovascular injury and non-union

Guidelines, Registries & Global Practice

Evidence Synthesis

• Pooled systematic reviews of arthrodesis for periprosthetic joint infection (Mercurio et al., 2024; Goh et al., 2026) show no significant difference in fusion rate between intramedullary nailing and external fixation, while consistently emphasising that infection eradication is the dominant determinant of success; the IM nail is favoured mainly for its load-sharing biomechanics and earliest weight-bearing rather than a proven fusion-rate advantage.
• Goh et al. (2026) further found that modern intercalary prosthetic and cement constructs fail less often than traditional bone-on-bone fusion, supporting construct selection as a key modifiable factor.
• Comparative reviews of fusion versus above-knee amputation (Low et al., 2024) report that knee arthrodesis patients are significantly more likely to achieve independent bipedal ambulation than transfemoral-amputation patients (86 percent versus 46 percent), with arthrodesis favoured where the limb is salvageable and amputation favoured for an uncontrollable infection or a non-viable limb.

Global Practice Variation

• In high-resource settings, a single-stage or staged intramedullary nail (including modular arthrodesis nails for large defects) is the predominant approach owing to the highest union rates and earliest mobilisation.
• In settings where modular implants are unavailable or where infection burden is high, the Ilizarov/ring fixator remains an important and cost-effective option, also enabling bone transport for segmental loss and deformity.
• Tumour-resection arthrodesis is more commonly chosen in young, high-demand patients in regions and units that prioritise a durable biological reconstruction over an endoprosthesis.

Decision-Making Principle

• Across all settings the principle is constant: eradicate infection, maximise vascular bone contact under compression, fuse in the optimal position, and reserve amputation for the unsalvageable limb or patient.

Immediate Post-operative Phase (0-6 Weeks)

Protection and Weight-Bearing

• Weight-bearing depends on the construct: IM nail generally permits earlier protected weight-bearing as a load-sharing device; plating and external fixation often require a longer protected period until early union signs appear
• Splint, cast or rely on frame stability per construct
• Strict elevation and wound surveillance in this high-risk (often previously infected) wound

Infection Management

• Continue culture-directed antibiotics with microbiology/infectious-diseases input where infection was the indication
• Monitor wound, inflammatory markers and clinical signs for recurrent infection
• Plastic-surgical follow-up if a flap was used

Pain and Thromboprophylaxis

• Multimodal analgesia; expect significant early pain in this major salvage procedure
• VTE prophylaxis per local protocol given prolonged immobility

Intermediate Phase (6 Weeks to 3-6 Months)

Progressive Loading

• Advance weight-bearing as radiographic union progresses, guided by serial radiographs (CT if union is in doubt)
• Gait re-education with a physiotherapist for the stiff-knee gait pattern
• Provide a shoe raise to accommodate the expected 2-5 cm shortening

Frame Care (if external fixator/Ilizarov)

• Pin-site care and surveillance for pin-track infection
• Adjust compression/transport as planned; counsel on prolonged frame time and burden

Recovery and Rehabilitation (3-12+ Months)

Time to Union

• Union typically takes 3-12 months, longest with external fixation and in previously infected bone
• Do not permit unrestricted loading until solid bony union is confirmed clinically and radiographically

Functional Expectations

• A solid fusion gives a stable, painless, weight-bearing limb but with a permanently stiff knee
• The patient walks with a stiff-leg (vaulting/circumduction) gait at increased energy cost and must learn to sit, drive and transfer with an extended limb
• Counsel that fusion preserves a longer, more energy-efficient limb than above-knee amputation, but at the cost of knee motion

Long-term Monitoring

• Surveillance for late non-union, hardware failure and recurrent infection
• Watch for adjacent-joint (ipsilateral hip/ankle, lumbar spine) overload symptoms from the stiff knee
• Address limb-length and alignment issues with orthotics; reserve revision/osteotomy for symptomatic malunion

Adapting to a Fused Knee - Practical Advice

• Sitting: the limb must be extended forward; aisle seats, raised chairs and car-seat adjustment help
• Driving: a left-sided fusion is generally compatible with an automatic vehicle; a right-sided fusion may need vehicle adaptation
• Footwear: a contralateral shoe raise or ipsilateral build-up offsets shortening and smooths gait
• Activity: most patients return to community ambulation and many to light work; high-impact and kneeling activities are limited

Outcome Assessment

• Patient-reported outcome measures and gait/walking-distance assessment
• Serial radiographs (and CT where union is uncertain) until solid fusion is confirmed
• Inflammatory markers if recurrent infection is suspected

Warning Signs Requiring Urgent Evaluation

• New or worsening discharge, erythema or rising inflammatory markers (recurrent infection)
• Acute pain and deformity (hardware failure or fracture through the fusion)
• New foot drop or distal ischaemia (neurovascular complication)
• Wound breakdown or flap compromise