High Yield Overview

PRIMARY TOTAL KNEE REPLACEMENT (TKR)

Medial parapatellar arthrotomy - gold standard approach for primary TKR | intermediate

Critical Danger Structures - 5 Key Anatomical Zones

Popliteal Artery

Location: 10-15mm posterior to posterior capsule, risk during posterior osteophyte removal and PCL release

Protection: Maintain knee flexion when working posteriorly, avoid posterior capsule penetration, use retractors anteriorly, gentle soft tissue technique

Common Peroneal Nerve

Location: 15-20mm from lateral joint line at fibular neck, risk during valgus correction and lateral releases

Protection: Gradual correction of valgus deformity, avoid excessive lateral retraction, identify nerve in severe valgus (>20°), maintain knee flexion during releases

Patellar Tendon Insertion

Location: Tibial tubercle, risk during arthrotomy and patellar eversion

Protection: Stay 1cm medial to tubercle with arthrotomy, adequate medial release before eversion, gentle technique, avoid forced eversion with tight tissues

Medial Collateral Ligament

Location: 5-8mm from medial joint line, superficial and deep layers

Protection: Staged subperiosteal releases from tibia, avoid inadvertent cutting, preserve superficial MCL if possible, check stability after each release

Anterior Femoral Cortex

Location: 4-6mm anterior to distal femur, risk during femoral sizing and anterior cut

Protection: Avoid oversizing femoral component, correct flexion of cutting block, verify no anterior notching (causes supracondylar fracture risk)

Mnemonic

BALANCEBALANCE - Principles of Soft Tissue Balancing in TKR

Memory Hook:Examiners expect systematic gap assessment and staged releases - describe checking balance with spacers after EACH release, not releasing everything then checking

Mnemonic

ROTATIONROTATION - Establishing Correct Femoral Component Rotation

Memory Hook:Internal rotation is the most common error - causes 70% of patellar maltracking cases. Know all 3 landmarks and explain what to do if they disagree

Indications for Primary TKR

Primary Indications

Symptomatic tricompartmental knee osteoarthritis - Most common indication (90% of cases)
- Failed conservative management minimum 3-6 months (NSAIDs, physiotherapy, weight loss, injections, bracing)
- Kellgren-Lawrence Grade 3-4 radiographic changes
- Significant functional impairment (WOMAC, Oxford Knee Score)
- Pain affecting quality of life and activities of daily living
Inflammatory arthritis - 5-8% of cases
- Rheumatoid arthritis with end-stage destruction
- Psoriatic arthritis, ankylosing spondylitis
- Often younger patients, may require bilateral staged procedures
- Address medical optimization (DMARD management, steroid minimization)
Post-traumatic arthritis - 2-5% of cases
- Following tibial plateau fractures, distal femur fractures
- Significant cartilage loss and malalignment
- May have bone defects requiring augments or stems
- Higher complexity, increased revision rate
Avascular necrosis with collapse - 1-2% of cases
- Secondary arthritis from spontaneous osteonecrosis (SONK)
- Corticosteroid-induced AVN
- Sickle cell disease, Gaucher disease
- May have focal defects requiring augmentation
Failed osteotomy - 1-2% of cases
- Progressive arthritis after high tibial osteotomy (HTO) or distal femoral osteotomy (DFO)
- Technical challenges from altered anatomy
- May require custom cutting guides or computer navigation

Contraindications

Absolute:

Active infection (local or systemic)
Inadequate bone stock for fixation
Absent extensor mechanism
Neuropathic arthropathy (relative - may consider hinged TKR)
Severe peripheral vascular disease with ischaemia

Relative:

Previous septic arthritis (ensure eradicated, minimum 2 years post-treatment)
Psychiatric illness affecting compliance
Severe obesity (BMI >40 - increased complications, consider delay for weight loss)
Active malignancy
Immunosuppression (HIV, chemotherapy - increased infection risk)

Exam Pearl

Evidence-Based Thresholds: Know the Australian PBS criteria - age >55 years (or younger if inflammatory arthritis), severe symptoms >3 months despite conservative treatment, Kellgren-Lawrence Grade 3-4. AOANJRR 2023 shows 97.4% survivorship at 10 years for primary TKR, with best results in age 65-75 years.

Pre-operative Assessment and Planning

Clinical Assessment

Pain severity, location, mechanical vs inflammatory
Functional limitation (stairs, walking distance, night pain)
Previous surgery, infections, trauma
Medical comorbidities (cardiac, respiratory, renal, diabetes)
Medications (anticoagulants, immunosuppression, steroids)
Social factors (home setup, support, rehabilitation access)

Physical Examination

Gait pattern, walking aids requirement
Knee ROM (active and passive, document flexion contracture)
Coronal deformity (varus/valgus, correctability to neutral)
Ligament stability (MCL, LCL, PCL - affects implant choice)
Extensor mechanism integrity
Hip and ankle examination (exclude referred pain, assess overall limb alignment)
Vascular status (pulses, perfusion)
Skin condition (previous scars, infection risk)

Radiographic Assessment

Standard Views:

Standing AP - assess joint space narrowing, osteophytes, sclerosis, alignment
Lateral - assess patellofemoral joint, flexion contracture, tibial slope
Skyline patella - assess patellar tracking, arthritis
Long leg alignment (hip-knee-ankle) - measure mechanical axis deviation, plan correction

Templating:

Measure mechanical axis (normal 0° ± 3°)
Anatomic axis typically 5-7° valgus
Assess bone defects (may require augments, stems)
Plan component sizes (femur, tibia, patella)
Identify extra-articular deformity (may require osteotomy)

Special Investigations

CT scan if severe deformity, bone loss, or previous fracture (aids surgical planning, custom guides)
MRI if concern for osteonecrosis, infection
Joint aspiration if concern for infection (synovial WCC >3000, polymorphs >90%)
DEXA scan if osteoporosis concern (affects component fixation choice)

Medical Optimization

HbA1c <7% (ideally <6.5%) in diabetics
Smoking cessation minimum 6 weeks pre-op
Weight loss if BMI >35 (every 5 units BMI increases infection risk 10%)
Dental clearance (treat caries, periodontal disease)
Urology review if chronic UTI
Dermatology if psoriasis, eczema
MRSA screening and decolonization if positive
Cardiology clearance if significant CAD, valvular disease
Anemia correction (Hb >120 g/L, consider iron supplementation, EPO)

Pre-operative Red Flags

Active UTI (delay surgery, treat with culture-directed antibiotics)
Cellulitis, skin lesions (delay until resolved)
HbA1c >8% (defer for optimization)
Bacteremia from any source (identify and treat before proceeding)
Severe malnutrition (albumin <30 g/L, total lymphocyte count <1500)

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

EXAMINER

"A 68-year-old woman with end-stage tricompartmental knee osteoarthritis is listed for primary TKR. Walk me through your pre-operative assessment, surgical technique, and how you ensure optimal component positioning and soft tissue balance."

EXCEPTIONAL ANSWER

I would approach this systematically through pre-operative assessment, surgical technique, and quality verification. Pre-operatively, I would assess her clinical presentation (pain severity, functional limitation, previous treatments), examine her knee (ROM, coronal deformity, ligament stability, extensor mechanism), and review radiographs (standing AP, lateral, skyline patella, long-leg alignment film). I would measure mechanical axis deviation, assess bone defects, and template component sizes. Medical optimization is critical - HbA1c <7% if diabetic, smoking cessation, weight loss if BMI >35, dental clearance, MRSA screening. For surgical technique, I use medial parapatellar arthrotomy as the gold standard approach. After tourniquet inflation and skin incision, I perform the arthrotomy 1cm medial to the patella and tibial tubercle to preserve lateral geniculate blood supply. I evert the patella, excise menisci and ACL, and remove osteophytes. For bone cuts, I start with distal femoral resection using IM guide at 5-7° valgus (0° to mechanical axis), resecting 9-10mm from the less worn condyle. Then proximal tibial resection using EM guide at 0° coronal plane with 5° posterior slope, resecting 10mm from lateral plateau in a varus knee. Component sizing and rotation are critical - I size the femur to match AP dimension and establish rotation using three landmarks: posterior condylar axis plus 3° external rotation, transepicondylar axis, and Whiteside's anteroposterior line. These should agree within 2-3°. I verify rotation with flexion gap assessment using laminar spreaders - should be rectangular, parallel to tibial cut, equal medial-lateral dimensions. Soft tissue balancing uses a staged release approach. For varus deformity I release: deep MCL, posteromedial capsule, semimembranosus, and POL, checking balance with spacers after each release. The goal is equal medial-lateral laxity of 1-2mm in both extension and flexion. After performing all femoral cuts (anterior, posterior, chamfers), I prepare the patella maintaining 15mm composite thickness with central peg placement. I trial all components with appropriate polyethylene thickness (typically 9-11mm) and assess: ROM should be 0-5° hyperextension to 110-120° flexion minimum, stability with equal laxity medially and laterally, central patellar tracking through full ROM without manual pressure, no anterior impingement. Once satisfied, I cement components sequentially - tibia first, then femur (careful to remove posterior cement before it sets), then patella. After inserting the polyethylene bearing, I perform final checks and deflate tourniquet for hemostasis. Quality verification throughout includes: mechanical axis 0° ± 3°, component positioning (femoral rotation 3° ER to PCA, tibial slope 5°), balanced gaps, and excellent patellar tracking without lateral subluxation.

VIVA SCENARIOStandard

EXAMINER

"You are 30 minutes into cementing the components of a primary TKR when you notice the patient's foot is pale, cold, and has no palpable dorsalis pedis or posterior tibial pulse. What do you do?"

EXCEPTIONAL ANSWER

This represents a vascular emergency - likely popliteal artery injury causing acute limb ischemia. I would immediately implement a systematic approach. First, I would inform the anesthetist and theatre team that we have a vascular emergency. Second, I would reassess the limb - check capillary refill (prolonged >3 seconds suggests arterial injury), check for Doppler signals with hand-held Doppler (absence confirms arterial occlusion), assess for compartment tension. Third, I would release the tourniquet immediately if still inflated - tourniquet alone could cause this picture, but timing suggests arterial injury. Fourth, I would urgently contact vascular surgery for immediate consultation - do not delay. While awaiting vascular surgery, I would assess the surgical field. If cement not yet polymerized, I would remove components to allow vascular exploration. If cement set, I would complete wound closure rapidly. I would expose the popliteal fossa through a medial approach (extend arthrotomy proximally, divide pes anserinus tendons, retract medial gastrocnemius, identify popliteal artery posterior to capsule). The mechanism of injury could be: (1) Direct laceration from saw or osteotome penetrating posterior capsule, (2) Intimal injury with thrombosis from hyperextension or retractor pressure, (3) Tourniquet-related ischemia (unlikely given no pulses after release). On-table assessment would include: inspection for obvious arterial bleeding (suggests laceration), palpation of popliteal artery (thrill suggests AV fistula, absent pulse suggests thrombosis), on-table angiography if available (defines level and nature of injury). Vascular surgery management options: (1) Primary repair if clean laceration <1cm, (2) Interposition vein graft using reversed saphenous vein if segmental loss >1cm, (3) Thrombectomy if acute thrombosis from intimal injury. I would perform prophylactic below-knee fasciotomies (four-compartment) if ischemia time exceeds 4-6 hours to prevent compartment syndrome. Post-operatively, the patient requires ICU monitoring with serial limb assessments, anticoagulation (heparin infusion), and may need second-look surgery at 24-48 hours. Prognosis: limb salvage 80-90% if recognized early and repaired within 6 hours, but amputation risk 10-20% if delayed diagnosis or failed repair. Long-term outcomes: successful revascularization allows TKR to function normally, but patient may have chronic venous insufficiency or neuropathy. This is a catastrophic complication and litigation risk - meticulous documentation is essential.

VIVA SCENARIOStandard

EXAMINER

"A 55-year-old man with severe valgus deformity (20 degrees) and an incompetent PCL is scheduled for TKR. How would you manage the valgus deformity and what implant would you choose? Walk me through your soft tissue balancing technique."

EXCEPTIONAL ANSWER

This case presents two challenges: severe valgus deformity requiring extensive lateral releases and PCL incompetence requiring implant selection. I would approach this systematically. Pre-operatively, I would assess correctability of the valgus deformity with valgus stress radiographs - if deformity corrects to neutral, soft tissue balancing alone may suffice; if fixed deformity, bony correction may be needed. I would examine for common peroneal nerve symptoms (20-degree valgus puts nerve at risk during correction - warn patient pre-operatively that nerve palsy risk 2-5% vs 0.5% in neutral knee). For implant selection, PCL incompetence mandates posterior-stabilized (PS) design, not cruciate-retaining. The severe valgus deformity and likely bone loss may require constrained condylar knee (CCK) if extensive releases needed or significant lateral bone loss. I would template for component sizes and assess lateral bone loss (may need lateral femoral or tibial augments). Intra-operatively, I would use medial parapatellar arthrotomy (standard approach even for valgus). After exposing the joint, I would assess PCL integrity - if incompetent/attenuated, confirms PS design. I would perform standard bone cuts first: distal femur at 0 degrees to mechanical axis (5-7 degrees valgus to anatomic), proximal tibia at 0 degrees coronal. Then assess lateral tightness with laminar spreaders in extension and flexion. For valgus deformity, I perform staged lateral releases in sequence, checking balance after each: First, release iliotibial band (ITB) from Gerdy tubercle subperiosteally. Second, release popliteus tendon from femur. Third, release lateral capsule posteriorly in pie-crust fashion (multiple small punctures rather than complete release to avoid over-release). Fourth, release lateral collateral ligament (LCL) if needed, but this is rare and only if first three releases insufficient. Before extensive lateral release, I would identify and protect the common peroneal nerve - it is 15-20mm from lateral joint line at fibular neck, at high risk with valgus correction. I maintain knee flexion during lateral work to relax nerve. After each release, I reassess gaps with spacers - goal is rectangular extension and flexion gaps with equal medial-lateral laxity 1-2mm. If lateral releases achieve balance with standard PS implant, I would proceed with that. However, if after maximal safe lateral release there is still residual lateral laxity >3mm compared to medial side, or if lateral bone loss significant (>5mm lateral femoral or tibial loss), I would use CCK (constrained condylar knee) implant which provides varus-valgus constraint via tall tibial post and deep femoral box. CCK allows some lateral laxity to be accommodated without requiring complete lateral release and risking over-release or nerve injury. For femoral rotation in valgus knee, I would use transepicondylar axis as primary landmark (most reliable) rather than posterior condylar axis, as lateral condyle may be hypoplastic or dysplastic giving false reference. I verify rotation with rectangular flexion gap assessment. After trial reduction with appropriate poly thickness (may need thicker 11-13mm if residual laxity), I would test: ROM 0-120 degrees minimum, medial-lateral stability (1-2mm with standard PS, up to 3mm acceptable with CCK), central patellar tracking, no impingement. I would specifically assess common peroneal nerve function immediately post-operatively (dorsiflexion, sensation over first web space) given high-risk correction. Post-operative management includes warning patient about increased nerve palsy risk, observation for foot drop, early physiotherapy, and potentially ankle-foot orthosis (AFO) if nerve palsy develops. Most nerve palsies from valgus correction are neurapraxia and recover over 3-6 months with observation, but 20-30% may be permanent requiring tendon transfers.