Salvage Procedure | Failed TKA | PJI | Young Active Patient
INDICATIONS
Critical Must-Knows
- Positioning critical: 0-15° flexion, 5-7° valgus, neutral rotation - allows sitting and walking
- IM nail preferred: Better biomechanics than external fixation, higher union rate (90% vs 75%)
- Limb shortening inevitable: 3-5cm average, requires shoe raise, compensates for stiff knee gait
- Infection control first: In PJI, use 2-stage with antibiotic spacer, minimum 6 weeks antibiotics
- Energy expenditure doubled: Walking requires 50-100% more energy than normal gait
Clinical Pearls
- "Knee arthrodesis is a SALVAGE procedure - last resort after multiple failed revisions
- "Position: 0-15° flexion for sitting, 5-7° valgus for gait, neutral rotation
- "IM nail (modular or long) provides superior fixation vs external fixator
- "Bone grafting essential for metaphyseal defects - allograft or autograft
Critical Knee Arthrodesis Exam Points
Position is Everything
0-15° flexion, 5-7° valgus, neutral rotation - Wrong position causes severe disability. Too much flexion = cannot walk. Too much extension = cannot sit. Varus = thrust and pain.
Bone Stock is Critical
Massive bone loss = poor union - Need adequate contact for healing. Bone graft all defects. Consider modular segmental replacement for extreme bone loss (over 10cm).
Infection Control First
Never fuse an infected knee - 2-stage approach mandatory for PJI. Antibiotic spacer 6-12 weeks. CRP normalization before fusion. Culture-guided antibiotics.
Patient Selection Key
Young, active, unilateral - Best candidates. Bilateral arthrodesis devastating. Consider amputation vs fusion discussion. Counsel extensively about permanent disability.
Knee Arthrodesis Quick Decision Guide
| Scenario | Approach | Fixation | Key Pearl |
|---|---|---|---|
| Failed TKA, adequate bone | Single stage | Long IM nail | Shortening 3-5cm expected |
| Failed TKA with PJI | 2-stage | Antibiotic spacer then nail | 6-12 week antibiotic holiday |
| Massive bone loss over 10cm | Segmental replacement | Modular prosthesis | Consider amputation |
| Young active patient | Primary fusion | IM nail or plate | Best functional outcomes |
FUSEKnee Arthrodesis Positioning
| F | Flexion 0-15° Allows both sitting and walking |
| U | Unrotated Neutral rotation prevents toe-in/toe-out gait |
| S | Slight valgus 5-7° Matches normal mechanical axis for gait |
| E | Equalize limbs Shoe raise compensates for 3-5cm shortening |
| F | Flexion 0-15° Allows both sitting and walking | S | Slight valgus 5-7° Matches normal mechanical axis for gait |
| U | Unrotated Neutral rotation prevents toe-in/toe-out gait | E | Equalize limbs Shoe raise compensates for 3-5cm shortening |
Hook:FUSE the knee in the right position to allow the patient to sit and walk!
FAILEDKnee Fusion Indications
| F | Failed TKA revisions Multiple failed attempts, no remaining options |
| A | Absent extensor mechanism Irreparable quadriceps/patellar tendon rupture |
| I | Infection recurrent PJI with resistant organisms |
| L | Ligament incompetence Massive instability not correctable |
| E | Extreme bone loss Cannot support revision implant |
| D | Desire to avoid amputation Patient preference for limb salvage |
| F | Failed TKA revisions Multiple failed attempts, no remaining options | I | Infection recurrent PJI with resistant organisms | E | Extreme bone loss Cannot support revision implant |
| A | Absent extensor mechanism Irreparable quadriceps/patellar tendon rupture | L | Ligament incompetence Massive instability not correctable | D | Desire to avoid amputation Patient preference for limb salvage |
Hook:When TKA has FAILED beyond repair, fusion is the salvage answer!
STOPContraindications to Knee Fusion
| S | Same side hip/ankle fusion Would create flail limb |
| T | Two-sided (bilateral) Bilateral fusion devastating for function |
| O | Ongoing active sepsis Must control infection first |
| P | Poor soft tissue envelope Cannot achieve wound closure |
| S | Same side hip/ankle fusion Would create flail limb | O | Ongoing active sepsis Must control infection first |
| T | Two-sided (bilateral) Bilateral fusion devastating for function | P | Poor soft tissue envelope Cannot achieve wound closure |
Hook:STOP and reconsider if these contraindications are present!
Overview and Epidemiology
Definition
Knee arthrodesis is the surgical fusion of the distal femur to the proximal tibia, eliminating the knee joint. It is a salvage procedure typically performed after multiple failed total knee arthroplasty revisions, recurrent periprosthetic joint infection, or in cases of massive bone or soft tissue loss where reconstruction is not possible.
Epidemiology:
- Incidence: 1-2% of failed TKA cases
- Increasing due to rising TKA revision rates
- Male predominance (PJI more common in males)
- Age: Variable (younger patients may prefer limb salvage)
Historical Context: Knee fusion was common before arthroplasty era. Modern indications are almost exclusively salvage after failed reconstruction. The procedure permanently sacrifices knee motion in exchange for a stable, pain-free limb.
Anatomy and Biomechanics
Critical Positioning Concept
The fused knee position determines functional outcome. 0-15° flexion allows sitting on chairs. 5-7° valgus matches normal mechanical axis for gait. Neutral rotation prevents abnormal foot progression angle.
Anatomical Considerations:
-
Bone stock: Often severely deficient after failed TKA/revisions
-
Femoral canal: May be damaged, sclerotic, or have cement
-
Tibial canal: Similar concerns; may have previous stem tracts
-
Soft tissue: Often compromised, previous incisions, extensor mechanism damage
Careful assessment of these anatomical factors is critical for successful fusion.
Biomechanical Principles:
-
Optimal position:
- Flexion: 0-15° (10-15° preferred for sitting)
- Valgus: 5-7° (matches mechanical axis)
- Rotation: Neutral (0-5° external rotation acceptable)
-
Limb shortening:
- Average 3-5cm after fusion
- Required for foot clearance (stiff knee cannot flex)
- Compensated with shoe raise
-
Energy expenditure:
- Walking requires 50-100% more energy
- Patients have significantly altered gait
- Hip and ankle compensate for lost knee motion
Position Effects on Function
| Position | Too Little | Optimal | Too Much |
|---|---|---|---|
| Flexion | Cannot sit comfortably | 0-15° | Cannot walk (over 30° = wheelchair) |
| Valgus | Varus thrust, pain | 5-7° | Excessive valgus, awkward gait |
| Rotation | Toe-out gait | Neutral | Toe-in gait, tripping |
Classification and Indications
Indications for Knee Arthrodesis
Absolute Indications:
- Recurrent PJI: Failed 2-stage revision, resistant organisms
- Massive bone loss: Cannot support revision implant
- Extensor mechanism loss: Irreparable quadriceps/patellar tendon rupture
- Failed allograft-prosthetic composite: No remaining reconstruction options
Relative Indications:
- Young, active patient preferring limb salvage over amputation
- Multiple failed revisions (over 2-3 revisions)
- Severe ligamentous instability not correctable with constrained implant
- Post-traumatic arthritis with severe bone/soft tissue damage
Key Decision Point
The decision between knee arthrodesis and above-knee amputation should be individualized. Younger, active patients often prefer fusion (limb salvage). Elderly or those with poor bone stock may do better with amputation (better prosthetic function).
Clinical Assessment
History
- Previous surgeries: Number of revisions, infections, complications
- Current symptoms: Pain, instability, drainage
- Infection history: Organisms, antibiotic sensitivities
- Functional status: Ambulatory, walking aids, wheelchair
- Patient expectations: Understand permanent disability
Examination
- Skin: Scars, sinuses, soft tissue coverage
- Extensor mechanism: Quadriceps function, patellar tendon
- Stability: Gross instability, range of motion
- Neurovascular: Pulses, sensation, motor function
- Contralateral limb: Function, any abnormalities
Key Assessment Points:
-
Infection status:
- Active drainage/sinus = active infection
- ESR/CRP levels elevation
- Previous culture results and sensitivities
-
Bone stock assessment:
- Previous explant status
- Bone loss quantification
- Canal integrity
-
Soft tissue assessment:
- Multiple incisions
- Skin viability
- Muscle/fascia coverage
- May need plastic surgery consultation
-
Patient counseling:
- Permanent loss of knee motion
- Limb shortening (3-5cm)
- Shoe raise requirement
- Altered gait, increased energy expenditure
- 50% patient satisfaction rate
Investigations
Investigation Protocol
ESR, CRP, WBC - Infection markers. CRP should normalize before definitive fusion in 2-stage protocol. Albumin/prealbumin for nutritional status.
AP/Lateral weight-bearing of entire limb. Assess bone loss, implant position, alignment. Long leg films for mechanical axis planning.
3D reconstruction for bone stock assessment, canal patency, cement location. Essential for surgical planning.
If infection suspected but not confirmed. Tagged WBC scan most specific for PJI.
Aspiration:
- If any suspicion of infection, aspirate before surgery
- Send for cell count, culture (aerobic, anaerobic, fungal, AFB)
- Synovial fluid WBC over 3000 or PMN over 80% = infection
Clinical Imaging
Charnley External Fixator Technique
Immediate Postoperative Radiographs
Radiological Evidence of Fusion
Management Algorithm
2-Stage Knee Arthrodesis (For PJI)
Stage 1: Explant and Spacer
- Remove all implants and cement
- Aggressive debridement of infected tissue
- Multiple tissue cultures (5-6 samples)
- Antibiotic-loaded cement spacer placement
- IV antibiotics 6 weeks (culture-guided)
Antibiotic Holiday:
- Minimum 2 weeks off antibiotics before Stage 2
- Repeat aspiration to confirm eradication
- CRP should normalize (under 10 mg/L)
Stage 2: Definitive Fusion
- Remove spacer
- Intraoperative frozen section (over 5 PMN/hpf = abort)
- Bone preparation (remove sclerotic bone)
- Bone grafting if needed
- IM nail or plate fixation
- Continue oral antibiotics 3-6 months
When to Abort Stage 2
If frozen section shows over 5 PMN per high-power field, ABORT the fusion. Place new antibiotic spacer and extend antibiotic treatment. Proceeding with fusion in active infection = high failure rate.
Surgical Technique
Intramedullary Nail Technique (Preferred)
Positioning:
- Supine on radiolucent table
- Bump under ipsilateral hip
- Ensure C-arm access for both AP and lateral views
Approach:
- Previous midline incision (if present)
- Medial parapatellar arthrotomy
- Remove all implants and cement
IM Nail Steps
Resect to bleeding cancellous bone. Remove sclerotic surfaces. Create flat, opposing surfaces for contact. Aim for maximum bone-to-bone contact.
Ream femoral and tibial canals sequentially. Start with narrow reamer, increase 0.5mm increments. Ream 1mm larger than planned nail diameter.
Align femur to tibia with guide wire. Confirm position: 10-15° flexion, 5-7° valgus, neutral rotation. Use C-arm for AP and lateral confirmation.
Insert modular or long fusion nail. Confirm position fluoroscopically. Lock proximally and distally (2-3 screws each end).
Pack all defects with bone graft (autograft from resected bone, allograft, or combination). Ensure circumferential graft around fusion site.
Nail Options:
- Long TKA revision nail (shortest option, need cement or modular)
- Modular fusion nail (purpose-built, adjustable length)
- Two nails technique (femoral + tibial retrograde/antegrade)
Complications
| Complication | Incidence | Risk Factors | Management |
|---|---|---|---|
| Nonunion | 10-25% | Infection, bone loss, external fixation | Revision surgery, bone graft, change fixation |
| Infection | 5-15% | Previous PJI, diabetes, immunosuppression | Debridement, antibiotics, may need amputation |
| Malposition | 5-10% | Technical error, bone loss | Corrective osteotomy (rarely) |
| Limb length discrepancy | 100% | Inherent to procedure | Shoe raise (3-5cm) |
| Adjacent joint OA | 30-50% | Altered biomechanics | Hip/ankle arthritis treatment |
Specific Complications:
-
Nonunion: Most common complication. Risk factors include infection, inadequate bone contact, poor fixation. Management: Revision surgery with bone graft and improved fixation.
-
Persistent infection: May require amputation if cannot be controlled. Continuous suppressive antibiotics may be option in some cases.
-
Hardware failure: Nail breakage can occur at fusion site. Usually indicates nonunion.
-
Periprosthetic fracture: Stress riser at nail tip. May need revision fixation.
Postoperative Care
Rehabilitation Protocol
Immobilization: Hinged knee brace locked in extension or long leg cast. NWB with crutches or walker. Wound care. DVT prophylaxis.
TTWB to WBAT as tolerated once X-rays show early callus. Continue brace. Serial X-rays every 3-4 weeks.
Full weight bearing when radiographic union achieved (bridging callus on 3/4 cortices). Wean brace. Shoe raise fitting.
Annual follow-up. Monitor for adjacent joint arthritis. Gait training. Activity modification counseling.
Weight-Bearing Protocol:
- Non-weight bearing 6 weeks minimum
- Progress based on radiographic healing
- Average time to union: 4-6 months
- Some patients require up to 12 months
Outcomes and Prognosis
Union Rates:
- IM nail: 85-95%
- External fixation: 65-75%
- Plate fixation: 75-85%
Functional Outcomes:
- Walking with aid: 75-80%
- Community ambulator: 60-70%
- Return to work (sedentary): 50-60%
- High satisfaction: 40-50%
Factors Affecting Outcome:
- Bone stock quality
- Infection control
- Patient compliance
- Fixation method
- Comorbidities (diabetes, vascular disease)
Realistic Expectations
Counsel patients that knee arthrodesis is a salvage procedure, not a reconstructive one. Expectations should be: pain relief (80-90%), stable limb for ambulation (70-80%), but permanent disability (100%), altered gait (100%), and only moderate satisfaction (50%).
Arthrodesis vs Amputation:
| Factor | Knee Arthrodesis | Above-Knee Amputation |
|---|---|---|
| Limb preservation | Yes | No |
| Energy expenditure | Increased 50-100% | Increased 40-60% |
| Gait quality | Stiff-legged, asymmetric | Smoother with prosthesis |
| Sitting comfort | Difficult (leg straight) | Better (prosthesis off) |
| Phantom pain | N/A | 30-50% |
| Revision surgery rate | 20-30% | 10-15% |
Evidence Base
IM Nail vs External Fixation for Infected TKA
- 85 consecutive arthrodeses for infected TKR; retrospective comparison
- IM nail union 23/24 (96%) vs external fixation 41/61 (67%)
- Deep infection recurrence higher with IM nail (8.3%) than ex-fix (4.9%)
- Major complications in 34 patients (40%) irrespective of technique
Arthrodesis of the Knee (Instructional Review)
- Comprehensive instructional review of indications and technique
- Infected TKA is the most common modern indication
- Deficient bone stock and poor apposition reduce fusion success
- Function after arthrodesis is superior to above-knee amputation
Salvage of Infected Total Knee Fusion
- Review of fusion techniques for failed infected TKA
- Compression external fixators least successful when severe bone loss present
- Ilizarov technique achieves rigid fixation despite bone loss
- Internal fixation (IM nail, plate) best for fusion when severe bone loss present
Arthrodesis With Long Intramedullary Nail
- 33 knee arthrodeses with a long trochanteric-entry IM nail
- 29/33 united at first attempt; 32/33 eventually united after correction
- Fusion achieved even in the presence of prior infection; no new infections
- Good bone-to-bone contact between resected surfaces was critical to union
Modular Arthrodesis vs Above-Knee Amputation (Septic TKA)
- Cohort of 113 patients (81 modular arthrodesis, 32 amputation) after septic TKA failure
- Major complication in over one-third of both groups; reinfection 22% (arthrodesis) vs 35% (amputation)
- Functional outcome (LEFS) and physical SF-12 comparable between groups
- Amputees fitted with microprocessor-controlled knees scored significantly higher (LEFS 56)
Above-Knee Amputation vs Arthrodesis (Recurrent PJI)
- Case-control study of 43 patients (20 amputation, 23 arthrodesis) for recurrent knee PJI
- Recurrent infection 10% (amputation) vs 21.7% (arthrodesis); difference not significant
- Amputation group had less pain, better mobility and better SF-36 quality of life
- Mean follow-up 6.7 years
Exam Viva Scenarios
Use these scenarios to practise clinical reasoning and management decisions
Scenario 1: Failed 2-Stage Revision
"A 65-year-old male presents with recurrent MRSA PJI following two failed 2-stage revisions for infected TKA. His CRP is elevated at 45 mg/L, he has a draining sinus, and he walks with a frame. His contralateral knee has a well-functioning TKA. X-rays show massive bone loss in the distal femur and proximal tibia. How would you manage this patient?"
Scenario 2: Extensor Mechanism Failure
"A 58-year-old female had a TKA 3 years ago complicated by patellar tendon rupture. She had two attempts at reconstruction with allograft, both of which failed. She now has no functional extensor mechanism, walks with a locked knee brace, and has valgus instability. There is no evidence of infection. What are your options?"
Scenario 3: Massive Bone Loss
"A 70-year-old male had multiple revision TKAs, the last being explant for infection with antibiotic spacer in situ. Infection is now controlled (CRP normal, aspiration negative). CT shows greater than 15cm combined bone loss (8cm distal femur, 7cm proximal tibia). His femoral and tibial canals are patent but widened. What are your options for limb salvage?"
MCQ Practice Points
Positioning
Q: What is the optimal position for knee arthrodesis? A: 10-15° flexion, 5-7° valgus, neutral rotation. This allows sitting (flexion), matches mechanical axis (valgus), and prevents gait abnormalities (neutral rotation).
Union Rates
Q: Which fixation method has the highest union rate for knee arthrodesis? A: IM nail (85-95%) has superior union rates compared to external fixation (65-75%) or plate fixation (75-85%).
Contraindications
Q: What is an absolute contraindication to knee arthrodesis? A: Ipsilateral hip or ankle fusion. This would create a "flail limb" with no functional joints. Bilateral knee fusion is also a relative contraindication.
Limb Shortening
Q: How much limb shortening is expected after knee arthrodesis? A: 3-5cm. This is intentional to allow foot clearance during swing phase (stiff knee cannot flex). Compensated with shoe raise.
Stage 2 Abort
Q: When should Stage 2 of a 2-stage knee fusion be aborted? A: If intraoperative frozen section shows over 5 PMN per high-power field. This indicates persistent infection. Place new spacer and extend antibiotics.
Guidelines, Registries & Global Practice
Global Epidemiology:
- Arthrodesis is performed in roughly 1-2% of failed/infected TKA, but absolute numbers are rising worldwide as primary TKA volume and revision burden grow.
- The dominant modern indication everywhere is unsalvageable periprosthetic joint infection (PJI), followed by extensor mechanism loss and massive bone loss.
- Major joint registries (NJR, AJRR, AOANJRR, SHAR, Norwegian, NZJR) do not track arthrodesis as a distinct procedure; it is captured indirectly within revision/removal codes, so registry data quantify the upstream revision burden rather than fusion outcomes.
Guideline & Society Positions on the Failed/Infected Knee
| Body | Region | Position relevant to arthrodesis |
|---|---|---|
| MSIS / ICM consensus | International | Defines PJI and staged management; arthrodesis/amputation reserved for unreconstructable or uncontrollable infection |
| AAOS | US | PJI diagnosis/management guidance; salvage (fusion or amputation) after failed staged revision |
| BOA / BOAST + NICE | UK | Joint infection pathways through specialist centres; fusion as limb-salvage when revision not viable |
| AO Foundation | International | Technical principles of IM nail / plate fusion and compression |
| EFORT / EBJIS | Europe | Bone & joint infection consensus underpinning staged eradication before fusion |
High- vs Limited-Resource Practice Variation:
- High-resource settings: MDT care (arthroplasty surgeon, infectious diseases, plastic surgery, microbiology); modular fusion nails and segmental endoprostheses available; microprocessor-controlled prosthetic knees make amputation a competitive functional alternative.
- Limited-resource settings: External fixation (compression frames, Ilizarov) remains a mainstay where implant cost or supply limits modular nails; longer treatment in-frame is accepted in exchange for low hardware cost and the ability to manage active infection.
Consent & Medicolegal (universal):
- Document the permanent loss of knee motion, 3-5 cm shortening with shoe raise, altered high-energy gait, and only moderate satisfaction.
- Record that amputation and continued non-operative management were discussed as genuine alternatives, with realistic union and reinfection figures.
Differential: Choosing the Salvage Option
When standard revision arthroplasty is no longer viable, the decision is between competing salvage strategies. Distinguishing them on the right grounds is a classic viva test.
Salvage Options for the Unreconstructable Knee
| Option | Best suited to | Key advantage | Key drawback / discriminator |
|---|---|---|---|
| Knee arthrodesis | Young, active, unilateral; good bone for apposition | Stable painless weight-bearing limb; function better than AKA in ambulators | Permanent loss of flexion; difficult sitting; shortening |
| Above-knee amputation | Poor bone stock, uncontrollable infection, fit prosthesis users | Definitive sepsis control; smoother gait with MPK prosthesis | Limb loss; phantom pain; energy cost |
| Resection/spacer arthroplasty | Low-demand, comorbid, non-ambulatory | Less surgery; controls infection | Unstable, often painful flail knee |
| Chronic antibiotic suppression | Unfit for surgery; well-fixed implant | Avoids major surgery | Does not eradicate infection; not curative |
| Repeat staged revision | Reconstructable bone, sensitive organism, intact extensor | Preserves a mobile knee | Not viable after repeated failure or major bone/extensor loss |
Controversies & Areas of Uncertainty
Arthrodesis vs Amputation
Comparative cohorts (Hungerer 2017; Trouillez 2021) show similar reinfection and overall function, but amputees with microprocessor knees may report less pain and better quality of life. No randomised data exist; the choice remains values-based.
IM Nail vs External Fixation
IM nailing gives higher union but, in infected cases, a higher recurrent-infection risk than external fixation (Mabry 2007). The trade-off, not a single "best" device, drives selection.
Single- vs Two-Stage in PJI
Two-stage remains the default for established PJI, but single-stage fusion is debated for sensitive organisms and good soft tissues, mirroring the single- vs two-stage revision debate. Evidence is low-level.
Optimal Position
Most authors fuse in slight flexion (0-15°) and 5-7° valgus, but the ideal flexion for balancing sitting against gait energy cost is not standardised and varies with patient height and contralateral limb.
Clinical summary
Indications
- •Failed multiple TKA revisions
- •Recurrent PJI (resistant organisms)
- •Extensor mechanism loss
- •Massive bone loss
Positioning
- •Flexion: 10-15° (allows sitting)
- •Valgus: 5-7° (matches MA)
- •Rotation: Neutral
- •Shortening: 3-5cm expected
Fixation
- •IM nail preferred (90% union)
- •External fix for active infection
- •Modular nail for bone loss
- •Bone graft all defects
2-Stage Protocol
- •Stage 1: Explant + spacer
- •IV antibiotics 6 weeks
- •Antibiotic holiday 2 weeks
- •Stage 2: Fusion if CRP normal
Complications
- •Nonunion 10-25%
- •Infection 5-15%
- •Malposition 5-10%
- •Adjacent joint OA 30-50%