Overview & Indications
Knee arthrodesis (fusion of the knee joint in a fixed position) sacrifices all knee movement but provides a stable, pain-free extremity capable of weight-bearing. It is generally considered a procedure of last resort — reserved for cases where arthroplasty has irretrievably failed, or where arthroplasty cannot be performed due to infection, oncological resection, or severe neuromuscular dysfunction. Despite its limitations, a well-performed arthrodesis can restore function and independence in a carefully selected patient.
- Primary indications for knee arthrodesis: (1) failed total knee arthroplasty (TKA) with chronic peri-prosthetic joint infection (PJI) not amenable to re-implantation (most common indication); (2) failed TKA with severe bone loss and inadequate soft tissue envelope precluding revision arthroplasty; (3) destructive septic arthritis of the native knee; (4) post-traumatic arthritis in a young heavy manual worker where TKA longevity is insufficient; (5) severe neuromuscular disease with inadequate quadriceps function to control a TKA; (6) oncological resection (distal femur or proximal tibia) where an endoprosthesis is not appropriate
- Failed TKA with PJI is now the most common indication — when a two-stage revision arthroplasty is not possible (persistent infection despite spacer, resistant organisms, inadequate bone and soft tissue, patient comorbidities), arthrodesis provides a reliable alternative to amputation
- Contraindications: ipsilateral hip or ankle arthritis (arthrodesis eliminates knee motion which increases compensatory stress at adjacent joints); contralateral limb problems; poor bone stock (fusion may fail); significant soft tissue deficiency
Optimal Position for Fusion
- Optimal fusion position: 0–10° of flexion (functional extension — avoids hyperextension which causes gait instability and increases energy consumption); 5–7° of valgus (neutral to slight valgus — mirrors normal anatomical alignment); neutral to slight external rotation (5–10°); functional limb length — the fused extremity should ideally be 1–2 cm shorter than the contralateral side to allow foot clearance during swing phase; positioning in these parameters produces the most efficient gait pattern and minimises energy expenditure
- Fusion in excessive flexion causes significant energy cost during gait (hip flexors must work harder to advance the limb) and poor cosmesis; fusion in varus creates medial thrust and accelerates ipsilateral hip and ankle OA
Surgical Techniques
| Technique | Description | Advantages / Disadvantages |
|---|---|---|
| Intramedullary nail (long stemmed) | A long intramedullary nail passes from the hip (through the greater trochanter) or the distal femur, through the knee joint, and into the tibia; the nail spans the entire femur-tibia unit and provides rigid fixation | Highest fusion rates (85–100%); allows early weight-bearing; gold standard for most cases; the nail must pass through the knee into the tibia — this is technically demanding when there is severe bone loss; the long nail distributes load along the entire limb, reducing stress shielding |
| External fixator (Ilizarov / circular frame) | A circular or monolateral external fixator spans the knee and applies compression across the fusion site; can be used with bone transport for significant bone defects | Preferred for infected cases (avoids internal implant in contaminated field); allows simultaneous bone transport for large defects; high pin site infection rate; bulky; prolonged treatment duration; lower fusion rate than IM nail if bone loss is not addressed |
| Dual compression plating | Two plates (one medial, one lateral or anterior) applied across the knee joint to achieve compression and rigid fixation | Good fixation; can address deformity; not appropriate in infected or contaminated cases; less commonly used as primary technique since IM nailing became standard |
- Infected TKA arthrodesis with bone loss: when PJI has caused significant distal femoral and proximal tibial bone loss (common after multiple revision surgeries), the IM nail alone may not achieve adequate bony contact for fusion; options include: (1) bulk structural allograft to fill the defect before nailing; (2) Ilizarov frame with bone transport (tibia or femur transported through the defect over weeks — the most reliable method for large segmental bone defects); (3) a custom modular IM nail spacer (megaprosthesis-type) bridging the defect and achieving fusion if viable bone is available at both ends
Outcomes & Complications
- Non-union: the most significant complication; rates vary from <5% with IM nailing and adequate bone contact to 20–30% in cases with significant bone loss or persistent infection; risk factors — active infection, poor bone stock, smoking, diabetes, steroid use, inadequate fixation
- Gait after arthrodesis: patients with a well-positioned knee arthrodesis ambulate with a characteristic gait — circumduction of the stiff limb during swing phase (to achieve foot clearance); energy expenditure during walking is increased by approximately 30–40% compared to normal; most patients achieve independent community ambulation with or without an aid; a shoe raise on the fused side (1–2 cm) improves foot clearance and reduces circumduction
- Ipsilateral hip and ankle OA: long-term complication; the loss of knee motion transfers stress to adjacent joints; particularly significant if the contralateral hip or knee also has arthritis
- Infection: persistent or recurrent PJI after arthrodesis; managed with prolonged antibiotics; rarely requires amputation
- Implant failure: nail fracture or backing out in long IM nails; more common in non-union cases with continued motion at the fusion site
- Amputation vs arthrodesis: in cases of failed TKA with chronic PJI where arthrodesis is not feasible (inadequate bone stock for fusion, persistent virulent infection, uncontrolled sepsis), above-knee amputation (AKA) may be the only option; AKA has a higher mortality in this patient population and a very poor functional outcome (rehabilitation with a prosthetic limb in an elderly comorbid patient is limited); arthrodesis is strongly preferred over amputation when technically achievable
Consultant-Level Considerations
- Two-stage revision vs arthrodesis for infected TKA: the decision between attempting a two-stage revision (resection arthroplasty spacer, antibiotic treatment, then re-implantation of a new TKA) and arthrodesis depends on: organism virulence (highly resistant organisms — MRSA, fungal PJI — favour arthrodesis); number of prior revision attempts; bone and soft tissue quality; patient age, functional demand, and medical comorbidities; patient preference (mobility vs stability); a successful two-stage revision preserves movement and function but carries the risk of re-infection and further procedures; arthrodesis provides a definitive infection-free result with no further implant but at the cost of knee movement
- Ilizarov frame for bone transport after knee arthrodesis: when large segmental bone loss is present (e.g., after removing an infected distal femoral or proximal tibial component), the Ilizarov technique can transport a regenerate segment across the defect; corticotomy is performed at a well-vascularised metaphyseal site, and the segment is slowly transported (1 mm per day) to fill the defect; this process takes many months but can fill defects of 5–15 cm without the need for bulk allograft; the reconstructed limb is then fused with an IM nail
- Knee arthrodesis in oncology: resection of the distal femur or proximal tibia for bone tumours (osteosarcoma, giant cell tumour) can be reconstructed with an endoprosthesis (megaprosthesis), osteoarticular allograft, or arthrodesis; arthrodesis is reserved for cases where endoprosthesis is not appropriate (prior infection, very young child with significant growth remaining, failed endoprosthesis); provides excellent durability but sacrifices knee motion; discussed in conjunction with the limb salvage article
- Functional outcomes and patient satisfaction: patient satisfaction after knee arthrodesis is generally high in the context of long-standing PJI — relief from infection and pain outweighs the loss of movement in most patients; quality of life scores improve significantly after arthrodesis compared to the pre-operative state of chronic infection; careful pre-operative counselling about the permanent nature of the procedure and the expected gait pattern is essential
Exam Pearls
- Most common indication: failed TKA with chronic PJI not amenable to revision arthroplasty; procedure of last resort before amputation
- Optimal fusion position: 0–10° flexion; 5–7° valgus; neutral rotation; 1–2 cm shortening for foot clearance during swing phase
- Long IM nail: gold standard technique; highest fusion rates (85–100%); spans entire femur-tibia unit; allows early weight-bearing
- External fixator: preferred for infected cases — avoids internal implant in contaminated field; Ilizarov for large bone defects with transport
- Gait after arthrodesis: circumduction during swing phase; ~30–40% increased energy expenditure; shoe raise 1–2 cm on fused side; most achieve independent community ambulation
- Non-union: most significant complication; higher with bone loss, active infection, smoking, diabetes; IM nail reduces risk vs external fixation
- Amputation vs arthrodesis: arthrodesis strongly preferred; AKA has higher mortality and poor functional outcomes in the elderly comorbid patient
- Two-stage revision vs arthrodesis: virulent/resistant organisms (MRSA, fungal PJI), multiple prior failed revisions, poor bone/soft tissue = favour arthrodesis
- Ilizarov bone transport: fills large segmental defects (5–15 cm) after infected implant removal; 1 mm/day; months of treatment; avoids bulk allograft
- Contraindications: ipsilateral hip or ankle arthritis; contralateral limb problems; poor bone stock