High Yield Overview

KNEE ARTHRODESIS

Salvage Procedure | Failed TKA | PJI | Young Active Patient

90%Union rate

3-5cmLimb shortening

150°Optimal position

5-7°Valgus alignment

INDICATIONS

Primary

PatternFailed TKA with massive bone loss, extensor mechanism rupture

TreatmentIM nail or plate fixation

Infection

PatternRecurrent PJI, resistant organisms, failed 2-stage revision

Treatment2-stage fusion with antibiotic spacer

Salvage

PatternPost-traumatic arthritis with severe malalignment

TreatmentSingle stage if no infection

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

Examiner's 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

Mnemonic

FUSEKnee Arthrodesis Positioning

Flexion 0-15°

Allows both sitting and walking

Unrotated

Neutral rotation prevents toe-in/toe-out gait

Slight valgus 5-7°

Matches normal mechanical axis for gait

Equalize limbs

Shoe raise compensates for 3-5cm shortening

Memory Hook:FUSE the knee in the right position to allow the patient to sit and walk!

Mnemonic

FAILEDKnee Fusion Indications

Failed TKA revisions

Multiple failed attempts, no remaining options

Absent extensor mechanism

Irreparable quadriceps/patellar tendon rupture

Infection recurrent

PJI with resistant organisms

Ligament incompetence

Massive instability not correctable

Extreme bone loss

Cannot support revision implant

Desire to avoid amputation

Patient preference for limb salvage

Memory Hook:When TKA has FAILED beyond repair, fusion is the salvage answer!

Mnemonic

STOPContraindications to Knee Fusion

Same side hip/ankle fusion

Would create flail limb

Two-sided (bilateral)

Bilateral fusion devastating for function

Ongoing active sepsis

Must control infection first

Poor soft tissue envelope

Cannot achieve wound closure

Memory 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

LaboratoryBlood Tests

ESR, CRP, WBC - Infection markers. CRP should normalize before definitive fusion in 2-stage protocol. Albumin/prealbumin for nutritional status.

ImagingPlain Radiographs

AP/Lateral weight-bearing of entire limb. Assess bone loss, implant position, alignment. Long leg films for mechanical axis planning.

AdvancedCT Scan

3D reconstruction for bone stock assessment, canal patency, cement location. Essential for surgical planning.

NuclearBone Scan/WBC Scan

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

Intraoperative setup for knee arthrodesis with Charnley external fixator — Intraoperative photograph showing knee arthrodesis surgical setup. The knee is exposed through an anterior approach with the limb prepped and draped. Blue arrow indicates the extension block device used to maintain alignment during fusion. 'Proximal' label identifies femoral side. This demonstrates the Charnley compression arthrodesis technique which uses external fixation to achieve bone-to-bone compression for fusion.Credit: Goswami A et al. - Cureus 2024 via PMC11584295 - CC-BY 4.0

Immediate Postoperative Radiographs

Immediate postoperative AP and lateral radiographs showing Charnley external fixator for knee arthrodesis — Immediate postoperative radiographs (AP and Lateral views) demonstrating Charnley external fixator positioning. The bilateral frame consists of transfixing pins through the femur and tibia connected by compression bars. AP view shows the frame spanning the knee joint with bone surfaces apposed. Lateral view reveals additional tibial fixation with an intramedullary device. This configuration provides rigid compression across the fusion site while allowing controlled positioning.Credit: Goswami A et al. - Cureus 2024 via PMC11584295 - CC-BY 4.0

Radiological Evidence of Fusion

AP and lateral radiographs showing successful knee arthrodesis union with trabecular continuity — Follow-up radiographs (AP and Lateral views) demonstrating successful knee arthrodesis union. Blue arrows indicate trabecular continuity across the fusion site - the key radiological sign of solid bony union. Note the continuous trabecular pattern bridging from femur to tibia on both views. External fixator remains in situ during healing phase. Fusion is confirmed when there is visible bone bridging on two orthogonal views with absence of motion or pain clinically.Credit: Goswami A et al. - Cureus 2024 via PMC11584295 - CC-BY 4.0

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

Step 1Bone Preparation

Resect to bleeding cancellous bone. Remove sclerotic surfaces. Create flat, opposing surfaces for contact. Aim for maximum bone-to-bone contact.

Step 2Canal Preparation

Ream femoral and tibial canals sequentially. Start with narrow reamer, increase 0.5mm increments. Ream 1mm larger than planned nail diameter.

Step 3Provisional Reduction

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.

Step 4Nail Insertion

Insert modular or long fusion nail. Confirm position fluoroscopically. Lock proximally and distally (2-3 screws each end).

Step 5Bone Grafting

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

Non-Weight BearingWeeks 0-6

Immobilization: Hinged knee brace locked in extension or long leg cast. NWB with crutches or walker. Wound care. DVT prophylaxis.

Progressive Weight BearingWeeks 6-12

TTWB to WBAT as tolerated once X-rays show early callus. Continue brace. Serial X-rays every 3-4 weeks.

Union AssessmentMonths 3-6

Full weight bearing when radiographic union achieved (bridging callus on 3/4 cortices). Wean brace. Shoe raise fitting.

Long-termBeyond 6 Months

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

Mabry TM, Jacofsky DJ, Haidukewych GJ, Hanssen AD • Clin Orthop Relat Res (2007)

Key Findings:

Retrospective comparison of fixation methods
IM nail union rate 87% vs Ex-fix 66%
IM nail fewer complications
IM nail shorter time to union

Clinical Implication: IM nail is the preferred fixation method for knee arthrodesis when infection is controlled, with higher union rates and fewer complications than external fixation.

Outcomes After Knee Arthrodesis

Conway JD, Mont MA, Bezwada HP • J Bone Joint Surg Am (2004)

Key Findings:

Multicenter review of 70 knee fusions
Overall union rate 78%
Infection main cause of failure
50% patient satisfaction rate

Clinical Implication: Knee arthrodesis achieves union in most cases but patient satisfaction is only moderate (50%). Extensive preoperative counseling about expectations is essential.

Knee Fusion for Failed TKA

Wiedel JD • J Am Acad Orthop Surg (2002)

Key Findings:

Comprehensive review of indications and technique
2-stage approach for PJI
Positioning critical for function
Patient selection determines outcomes

Clinical Implication: Proper patient selection, meticulous technique, and appropriate positioning are key determinants of successful knee arthrodesis outcomes.

Modular Fusion Nail

Puranen J, Kortelainen P, Jalovaara P • J Bone Joint Surg Br (1990)

Key Findings:

Purpose-built modular nail for knee fusion
High union rate (90%)
Adjustable length accommodates bone loss
Stable construct allows early mobilization

Clinical Implication: Modular IM nails designed specifically for knee fusion provide reliable fixation and high union rates, particularly valuable when significant bone loss is present.

Arthrodesis vs Amputation for Failed TKA

Sierra RJ, Trousdale RT, Pagnano MW • Clin Orthop Relat Res (2003)

Key Findings:

Comparative outcomes study
Similar energy expenditure
Amputation patients more satisfied with sitting
Arthrodesis patients preferred limb preservation
Decision should be individualized

Clinical Implication: Neither arthrodesis nor amputation is clearly superior - decision should be based on patient values, bone stock, infection status, and realistic expectations about outcomes.

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

Scenario 1: Failed 2-Stage Revision

EXAMINER

"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?"

EXCEPTIONAL ANSWER

This is a challenging case of recurrent PJI after multiple failed revisions. My management approach would be systematic. First, I would confirm the diagnosis with aspiration for cultures and sensitivities, and ensure the MRSA is characterized. Second, I would assess bone stock with CT scan to quantify defects. Third, I would have a detailed discussion with the patient about options: knee arthrodesis versus above-knee amputation, as further revision arthroplasty is not viable. Given his age, unilateral nature, and if he desires limb salvage, I would recommend a 2-stage knee arthrodesis. Stage 1 would involve explant, aggressive debridement, and antibiotic-loaded cement spacer with vancomycin for MRSA. He would receive IV vancomycin for 6 weeks culture-guided. After an antibiotic holiday, if CRP normalizes and aspiration is negative, Stage 2 would be IM nail fusion with extensive bone grafting for the defects. I would counsel him about 3-5cm shortening, need for shoe raise, altered gait, and only 50% chance of being satisfied with outcome.

KEY POINTS TO SCORE

Confirm MRSA and sensitivities

Patient options: fusion vs amputation (revision not viable)

2-stage approach mandatory for PJI

Extensive patient counseling about outcomes

COMMON TRAPS

✗Offering another revision arthroplasty (not appropriate after 2 failures)

✗Single-stage fusion in presence of active infection

✗Not discussing amputation as alternative

LIKELY FOLLOW-UPS

"What position would you fuse the knee in?"

"What if frozen section at Stage 2 shows 10 PMN per HPF?"

VIVA SCENARIOChallenging

Scenario 2: Extensor Mechanism Failure

EXAMINER

"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?"

EXCEPTIONAL ANSWER

This is a case of irrepairable extensor mechanism failure, which is one of the absolute indications for knee arthrodesis. My management would be: First, confirm no infection with normal inflammatory markers and aspiration. Second, assess bone stock and soft tissue coverage with imaging. Third, discuss options with the patient. Her options are: (1) Knee arthrodesis - would provide a stable, pain-free limb but permanent loss of flexion, (2) Above-knee amputation with prosthesis, (3) Continued brace use (unlikely to be acceptable). Given her young age and likely desire for limb salvage, I would recommend single-stage knee arthrodesis using an IM nail. She has no infection, so 2-stage is not required. Positioning would be 10-15° flexion for sitting, 5-7° valgus, neutral rotation. I would address the valgus instability with appropriate bone cuts. She needs extensive counseling about 3-5cm shortening, shoe raise, energy expenditure increase, and functional limitations.

KEY POINTS TO SCORE

Irrepairable extensor mechanism = indication for fusion

Confirm no infection first

Single-stage appropriate if no infection

Position and patient counseling critical

COMMON TRAPS

✗Offering another extensor mechanism reconstruction

✗Excessive flexion position (over 15°)

✗Fusing in the existing valgus position

LIKELY FOLLOW-UPS

"How would you manage the valgus during fusion?"

"What if she refuses fusion and wants more reconstruction attempts?"

VIVA SCENARIOCritical

Scenario 3: Massive Bone Loss

EXAMINER

"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?"

EXCEPTIONAL ANSWER

This is an extremely challenging case of massive bone loss after multiple revisions. With over 15cm combined bone loss, standard fusion techniques will be difficult. My approach: First, I would confirm infection eradication with repeat inflammatory markers and intraoperative cultures/frozen section. Second, options for this degree of bone loss include: (1) Fusion with modular segmental prosthesis - this uses a tumor prosthesis concept with stems into remaining diaphyseal bone, creating a spacer-like fusion. (2) Fusion with structural allograft-prosthetic composite - femoral and tibial allografts with IM nail through both. (3) Above-knee amputation - may be the most functional option given the severity of bone loss. Third, I would have an honest discussion with this patient. Given his age (70), the magnitude of surgery, high complication rates with massive reconstruction, and rehabilitation demands, amputation with prosthesis may offer better functional outcomes with lower risk. However, if he strongly desires limb salvage, I would proceed with modular fusion prosthesis, counseling him about high revision rates (30-40%) and potential for eventual amputation.

KEY POINTS TO SCORE

Over 15cm bone loss = extreme case

Modular segmental prosthesis or allograft-prosthetic composite options

Honestly discuss amputation as potentially better option

High complication rates with massive reconstruction

COMMON TRAPS

✗Attempting standard IM nail fusion (inadequate bone contact)

✗Not discussing amputation option

✗Underestimating complexity and complication rates

LIKELY FOLLOW-UPS

"What is a modular fusion prosthesis?"

"How do you obtain consent for this magnitude of surgery?"

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.

Australian Context

AOANJRR Data:

Knee arthrodesis not specifically tracked (salvage procedure)
Failed TKA outcomes tracked
Revision rates provide context for when fusion considered

Australian Practice:

Most knee fusions performed in tertiary referral centers
Multidisciplinary approach: orthopaedic surgeon, infectious disease, plastic surgery
PBS-listed antibiotics for PJI treatment
Extended antibiotic courses (6-12 weeks IV + oral) standard

Consent Considerations:

Detailed documentation of alternatives (amputation, continued non-operative)
Permanent disability discussions
Failure rates and potential for amputation
QOL impact counseling

Medicolegal:

Informed consent critical given permanent disability
Document patient expectations
Ensure understanding of alternatives

High-Yield Exam 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%

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

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

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

Step 1Bone Preparation

Resect to bleeding cancellous bone. Remove sclerotic surfaces. Create flat, opposing surfaces for contact. Aim for maximum bone-to-bone contact.

Step 2Canal Preparation

Ream femoral and tibial canals sequentially. Start with narrow reamer, increase 0.5mm increments. Ream 1mm larger than planned nail diameter.

Step 3Provisional Reduction

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.

Step 4Nail Insertion

Insert modular or long fusion nail. Confirm position fluoroscopically. Lock proximally and distally (2-3 screws each end).

Step 5Bone Grafting

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)

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

Factor

Knee Arthrodesis

Above-Knee Amputation

Limb preservation

Yes

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%