Knee Arthrodesis

Knee arthrodesis fuses the femur and tibia into a single, rigid, weight-bearing lever. It is a salvage operation: it reliably relieves pain and eradicates infection, but it permanently sacrifices all knee motion. Reserve it for the joint that is genuinely unreconstructable, and confirm the patient understands and accepts a permanently stiff knee before proceeding. Goals of surgery. Eradicate infection where present; achieve a stable, painless, plantigrade, weight-bearing limb; restore acceptable limb length and alignment; and secure solid bony union in the optimal position. Primary indications - Chronically infected total knee arthroplasty (TKA) after failed two-stage revision, where re-revision arthroplasty is not feasible — the commonest indication

• Irreparable extensor mechanism deficiency (loss of quadriceps or 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 an endoprosthesis, especially in young, high-demand patients Relative indications - Neuropathic (Charcot) joint with recurrent instability and ulceration
• Failed septic arthritis leaving 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 — when a stiff knee leaves a non-functional limb - Bilateral knee disease requiring bilateral fusion — the patient cannot sit, transfer or climb stairs
• Ipsilateral hip or ankle fusion or 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, or inadequate soft-tissue cover and vascular insufficiency threatening healing — consider amputation Pre-operative assessment. Examine the whole limb chain: the ipsilateral hip and ankle and the contralateral limb determine whether a stiff knee leaves a usable limb. Palpate pulses and assess for peripheral vascular disease; a poorly perfused limb heals badly and may be better served by amputation. Map previous incisions, sinuses and flaps, and obtain a plastic-surgical opinion early if cover is marginal. Optimise diabetes, immunosuppression, smoking and malnutrition, which all impair fusion and infection control. Where infection is the indication, check inflammatory markers (CRP, ESR), aspirate for culture and cell count, identify the organism and its sensitivities, and decide whether infection is active (mandates a staged approach) or quiescent or eradicated (permits single-stage definitive fixation). Long-leg standing alignment films of both limbs plan length and axis; CT defines bone loss, canal patency and the feasibility of intramedullary nailing; template the defect, the construct and the expected final limb length. Arthrodesis versus above-knee amputation. These are the two end-stage options for the unreconstructable joint. Fusion preserves a longer, more energy-efficient, prosthesis-free, weight-bearing limb but leaves a stiff knee; amputation is a definitive single solution favoured for uncontrollable infection, severe pain, a non-viable limb or failed fusion. Frame the choice as a shared, honest decision.

Single-stage versus staged fusion. In active periprosthetic infection, separate infection eradication (radical debridement, removal of all hardware and cement, an antibiotic spacer, culture-directed antibiotics) from definitive fixation — passing an intramedullary nail through an actively infected canal risks disastrous proximal spread. Where infection is eradicated or quiescent, or the indication is non-infective (tumour, neuropathic joint, post-traumatic), a single-stage definitive fusion is appropriate and gives one operation and a faster path to union and weight-bearing.

The goal is to expose the knee through a midline approach, remove all failed hardware and devitalised tissue, appose flat vascular cancellous bone ends under compression in the correct position, and stabilise the construct — eradicating infection and protecting the popliteal neurovascular bundle and the common peroneal nerve throughout. The exposure is laid out in full below (and in depth on the medial parapatellar approach to the knee page).

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Weight-bearing depends on the construct. The IM nail is load-sharing and generally permits the earliest protected weight-bearing; plating and external fixation usually require a longer protected period until early union appears. Splint, cast or rely on frame stability per construct, with strict elevation and wound surveillance in this high-risk, often previously infected wound. Continue culture-directed antibiotics with microbiology and infectious-diseases input where infection was the indication, give multimodal analgesia, and provide VTE prophylaxis per local protocol given the prolonged immobility. Rehabilitation | Phase | Timing | Protection and weight-bearing | Therapy and milestones | |-------|--------|------------------------------|------------------------| | 1 | 0-6 weeks | Splint, cast or frame; IM nail permits earliest protected weight-bearing | Strict elevation and wound surveillance; toe and ankle range of motion; continue antibiotics if indicated | | 2 | 6 weeks to 3-6 months | Advance weight-bearing as radiographic union progresses | Gait re-education for the stiff-knee pattern; shoe raise for 2-5 cm shortening; pin-site care if framed | | 3 | 3-12+ months | Protected until solid union | Full functional retraining; union typically takes 3-12 months — longest with external fixation and in previously infected bone | Time to union and functional expectations. Union typically takes 3-12 months; do not permit unrestricted loading until solid bony union is confirmed clinically and radiographically (CT where union is in doubt). A solid fusion gives a stable, painless, weight-bearing limb but with a permanently stiff knee. The patient walks with a stiff-leg gait — pelvic hike, circumduction and vaulting of the contralateral limb — at increased metabolic 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.

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. Watch for ipsilateral hip, ipsilateral ankle and lumbar spine pain from the compensatory stiff-knee gait; manage with physiotherapy, analgesia and orthotics, and reserve further surgery for refractory cases. Adapting to a fused knee. Sitting requires the limb to be extended forward — aisle seats, raised chairs and car-seat adjustment help. A left-sided fusion is generally compatible with an automatic vehicle; a right-sided fusion may need vehicle adaptation. A contralateral shoe raise or ipsilateral build-up offsets shortening and smooths gait. Most patients return to community ambulation and many to light work; high-impact and kneeling activities are limited. 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); and wound breakdown or flap compromise.

Role and epidemiology. Knee arthrodesis is a salvage procedure whose commonest indication is the chronically infected TKA after failed two-stage revision, frequently compounded by extensor mechanism loss, massive bone loss or a poor soft-tissue envelope. Its use has declined somewhat as megaprosthesis and modular revision options have matured, but it remains the durable biological answer for the truly unreconstructable joint, and the benchmark against which amputation is compared. Biomechanics of the fused knee. A fused knee converts the limb into a rigid lever. Gait compensations — pelvic hike, circumduction and vaulting of the contralateral limb — all raise metabolic energy expenditure, which is why sitting, driving and stair-climbing with an extended limb must be discussed before surgery. The normal limb has roughly 5-7 degrees of anatomical valgus at the knee, so fusion aims for 5-8 degrees of valgus to keep the foot beneath the body's centre of gravity. Each removed centimetre of bone shortens the limb; total shortening of 2-5 cm is common and preferable to tension on the neurovascular bundle from forced lengthening. Bone-end vascularity is the key determinant of union — repeated surgery, infection and over-zealous debridement devascularise bone, so preserve periosteal blood supply where possible and graft defects to bridge gaps. Evidence on fixation and fusion rates. The intramedullary 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, 89.6 percent in 48 knees, infection cured in 93 percent). Pooled systematic-review data are more nuanced: Mercurio (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 and 4.3 percent IM nail). Goh (969 knees) found a low overall aseptic failure rate (6 percent) but a high complication rate (28 percent, recurrent infection 11 percent), and showed that modern intercalary prosthetic and cement constructs failed less often than traditional bone-on-bone fusion (12 percent versus 2 and 0 percent). The honest exam position: 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. Arthrodesis versus above-knee amputation. Low (44 papers, 470 amputation and 1034 arthrodesis patients) found knee arthrodesis patients significantly more likely to achieve independent bipedal ambulation than amputees (86.4 percent versus 45.6 percent), with similar revision-surgery rates between groups and the caveat of substantial selection bias. Hoveidaei framed fusion and above-knee amputation as the two end-stage options for unreconstructable periprosthetic infection, emphasising shared, honest decision-making. The consistent message: where the limb is salvageable, arthrodesis preserves better walking function; amputation is reserved for uncontrollable infection, a non-viable limb or failed fusion. 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 for the highest union and earliest mobilisation. Where modular implants are unavailable or the infection burden is high, the Ilizarov or ring fixator remains an important, cost-effective option that also enables bone transport for segmental loss and deformity. Tumour-resection arthrodesis is more commonly chosen in young, high-demand patients in units that prioritise a durable biological reconstruction over an endoprosthesis. 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.

Further reading 1. Gramlich Y, Steinkohl D, Kremer M, et al. Modular knee arthrodesis secures limb, mobility, improves quality of life, and leads to high infection control in periprosthetic knee infection when revision knee arthroplasty is not an option. Arch Orthop Trauma Surg. 2021;141(8):1349-1360. Evidence for modular intramedullary arthrodesis with large bone loss. 2. White SP, Porteous AJ, Newman JH, et al. Arthrodesis of the knee using a custom-made intramedullary coupled device. J Bone Joint Surg Br. 2003;85(1):57-61. Technique and outcomes of coupled intramedullary knee arthrodesis. 3. Klinger HM, Spahn G, Schultz W, et al. Arthrodesis of the knee after failed infected total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc. 2006;14(5):447-453. Outcomes of fusion as salvage for the infected failed TKA. 4. Yeoh D, Goddard R, Macnamara P, et al. A comparison of two techniques for knee arthrodesis: the custom made intramedullary Mayday nail versus the double Huckstep nail. Knee. 2008;15(4):263-267. Comparative series of intramedullary arthrodesis constructs. 5. Calif E, Stein H, Lerner A. The Ilizarov external fixation frame in compression arthrodesis of large, weight bearing joints. Acta Orthop Belg. 2004;70(1):51-56. Description of Ilizarov compression arthrodesis where internal fixation is contraindicated.