Medial Parapatellar Approach to Knee

The medial parapatellar approach to the knee is the most commonly performed surgical approach to any joint in orthopaedic surgery. With approximately 100,000 total knee arthroplasties performed annually in Australia, and 85% using this approach, it is an essential skill for all orthopaedic surgeons.

Historical Context:

• 1860s: Early attempts at knee arthrotomy for septic joints and tumors
• 1878: Von Langenbeck - first description of medial parapatellar approach
• 1950s-1970s: Refinement during development of modern TKA (Gunston, Freeman, Insall)
• 1980s: Standardization of technique by John Insall and others
• 1990s-2000s: Development of muscle-sparing alternatives (subvastus, midvastus)
• 2010s-present: Recognition that repair technique is more important than approach selection

Australian Epidemiology (AOANJRR 2023):

• Approximately 100,000 primary TKAs performed annually in Australia
• Medial parapatellar approach used in 85% of cases
• Subvastus approach: 5-10%
• Midvastus approach: 5-10%
• Median age at primary TKA: 69 years
• 15-year survival of modern TKA: 90% - excellent outcomes

Key Advantages:

• Versatile exposure - complete circumferential access to entire knee joint
• Familiar anatomy - most surgeons trained in this approach
• Extensile - can be extended proximally or distally without major complications
• Reproducible - reliable landmarks and tissue planes
• Proven track record - millions of successful procedures with excellent outcomes

Key Disadvantages:

• Violation of quadriceps mechanism (requires meticulous repair)
• Risk of extensor lag if poorly repaired (2-10% depending on technique)
• Patellar devascularization if excessive lateral release performed
• Cannot use in presence of previous vertical lateral incision

Comparison to Alternatives: The subvastus (Southern) and midvastus approaches attempt to preserve more quadriceps function by avoiding division of VMO fibers. However, they sacrifice exposure and are technically more demanding. Meta-analyses show minimal functional difference when medial parapatellar approach is properly repaired.

Quadriceps Mechanism Anatomy

The quadriceps mechanism is the critical anatomical structure for this approach:

Muscle Components (Proximal to Distal):

1. Rectus femoris - Central, two-joint muscle (hip and knee)
2. Vastus lateralis - Lateral, largest muscle mass
3. Vastus intermedius - Deep to rectus, anterior femur
4. Vastus medialis obliquus (VMO) - Distal-medial, critical for patellar tracking

Quadriceps Tendon:

• Three-layered structure (superficial: rectus, middle: vastus medialis and lateralis, deep: vastus intermedius)
• Inserts on superior pole of patella
• Medial arthrotomy divides medial layer (VMO and rectus contributions)

Patellar Blood Supply:

• Inferior genicular arteries (main supply) - preserved with this approach
• Superior genicular arteries - at risk if excessive proximal dissection
• Medial and lateral genicular anastomosis - rich network around patella
• Medial arthrotomy safer than lateral (preserves lateral superior genicular)

Innervation

Femoral Nerve (L2-L4): All quadriceps components receive branches from the femoral nerve:

• Motor branches enter muscles on deep surface
• VMO receives terminal branches - at risk with medial dissection
• No true internervous plane exists for medial approaches

Clinical Significance:

• Division of VMO fibers causes temporary denervation of those specific fibers
• Reinnervation occurs over 3-6 months with proper repair
• Complete quadriceps denervation does not occur (nerve enters on deep surface)

Medial Supporting Structures

Medial Retinaculum:

• Fascial layer from VMO to medial patella
• Critical for patellar tracking stability
• Must be repaired at closure to prevent lateral patellar maltracking

Medial Collateral Ligament (MCL):

• Superficial MCL - from medial femoral epicondyle to proximal medial tibia
• Stay 1cm anterior to superficial MCL during arthrotomy to avoid injury
• MCL injury causes medial instability and requires repair or constrained implant

Pes Anserinus:

• Sartorius, gracilis, semitendinosus tendons
• Insert on proximal medial tibia
• Remain posterior and safe with proper technique

Biomechanics of Extensor Mechanism

Quadriceps Force Requirements:

• Rising from chair: 3-4× body weight through quadriceps
• Stair climbing: 2-3× body weight
• Level walking: 1-2× body weight

Patella Function:

• Increases quadriceps moment arm by 30-50%
• Distributes force across femoral trochlea
• Protects underlying femur

Effect of Arthrotomy:

• Temporary 20-30% reduction in quadriceps strength post-operatively
• Returns to 90% of contralateral by 6 months with good repair
• Persistent lag (over 5°) indicates inadequate repair or quadriceps damage

The Medial Parapatellar Approach is NOT an Internervous Plane

This is a critical concept frequently tested in Orthopaedic examinations:

Key Examination Point: The medial parapatellar approach does NOT utilize an internervous plane. All quadriceps components are innervated by the femoral nerve (L2-L4).

Anatomical Reality:

• VMO fibers are divided during arthrotomy
• Femoral nerve branches enter VMO on its deep (femoral) surface
• The arthrotomy divides muscle fibers but not the main nerve trunk
• Individual motor units are denervated and must regenerate

Comparison to Other Knee Approaches:

• Medial parapatellar: Divides VMO fibers (femoral nerve) - NO internervous plane
• Subvastus: Elevates VMO from capsule - attempts to preserve innervation
• Midvastus: Splits VMO muscle belly - partial denervation
• Lateral parapatellar: Divides vastus lateralis (femoral nerve) - NO internervous plane

Clinical Implications:

• Temporary quadriceps weakness expected post-operatively
• Reinnervation occurs over 3-6 months
• Meticulous repair allows proper healing and muscle fiber regeneration
• Functional outcomes are excellent despite lack of internervous plane

Examination Pearl: When asked "What is the internervous plane of the medial parapatellar approach?" the answer is: "There is NO true internervous plane. The approach divides VMO fibers which are all supplied by the femoral nerve. The muscle-sparing subvastus approach attempts to preserve VMO innervation by elevating rather than dividing the muscle."

Why the Medial Parapatellar Approach Works Despite This

The lack of internervous plane might seem like a disadvantage, but the approach has proven highly successful because:

1. Adequate repair allows fiber regeneration and reinnervation
2. Multiple quadriceps components provide redundancy
3. Patellar mechanics amplify remaining quadriceps force
4. Early mobilization stimulates recovery

Supine Position for Medial Parapatellar Approach

Standard Position: The patient is positioned supine on a standard operating table.

Key Positioning Elements:

1. Leg Holder vs Leg Post

   • Lateral leg holder (most common): Allows unrestricted access, easy removal
   • Leg post: Alternative for maintaining knee flexion during surgery
   • Ensure adequate padding to prevent peroneal nerve compression

2. Foot of Bed

   • Lower foot of bed (or use radiolucent triangle)
   • Allows knee to flex 90° during tibial preparation
   • Provides space for instruments

3. Tourniquet Placement

   • Upper thigh, as proximal as possible
   • Adequate padding underneath
   • Test before draping - ensure it inflates properly
   • Typical pressure: 250-300 mmHg (or systolic + 100-150 mmHg)

4. Limb Positioning Throughout Case

   • Femoral cuts: Knee flexed 90°, leg hanging over side
   • Tibial cuts: Knee flexed 90°, foot on sterile platform or held
   • Trial and closure: Full extension for proper soft tissue tensioning

Surgical Field Preparation:

• Prep: From mid-thigh to ankle, circumferential
• Drape: Four-corner drape with stockinette to thigh
• Foot: Include foot in sterile field or use impervious U-drape

Common Positioning Errors:

Examination Tip: Always mention tourniquet use and pressure when describing knee approach. Examiners expect awareness of compartment syndrome risk with prolonged tourniquet time (typically limit to 90-120 minutes).

Biomechanical Rationale for Medial Approach

Why Medial Rather Than Lateral? The medial parapatellar approach is strongly preferred over lateral for several biomechanical and anatomical reasons:

1. Patellar Blood Supply

   • Lateral superior genicular artery is the dominant blood supply to patella
   • Medial approach preserves this critical vessel
   • Lateral approach risks patellar avascular necrosis (AVN)

2. Patellar Tracking Biomechanics

   • Patella naturally tracks slightly lateral (Q-angle)
   • Lateral retinaculum is stronger than medial
   • Medial approach allows controlled lateral release if needed
   • Lateral approach cannot be balanced (cannot release medial structures)

3. Valgus Deformity Correction

   • Most arthritic knees develop valgus malalignment over time
   • Medial approach allows release of contracted lateral structures
   • Easier to balance knee from medial side

4. Surgeon Positioning

   • Medial approach allows surgeon to stand on lateral side
   • Better access to both femur and tibia
   • More ergonomic positioning

Pathophysiology of Extensor Lag

Mechanism of Extensor Lag: Extensor lag (inability to fully extend knee actively, despite passive extension) occurs through several mechanisms after medial parapatellar approach:

1. Quadriceps Disruption

   • Surgical division of VMO fibers
   • Incomplete repair or repair under inadequate tension
   • Adhesions preventing gliding of quadriceps tendon

2. Pain Inhibition

   • Acute post-operative pain inhibits voluntary quadriceps contraction
   • Protective response reduces muscle activation
   • Typically resolves with pain control and physiotherapy

3. Muscle Atrophy

   • Rapid atrophy begins within 48 hours post-operatively
   • Can lose up to 30% quadriceps strength in first week
   • Recovery requires 3-6 months of rehabilitation

4. Patellar Complications

   • Patellar maltracking or subluxation
   • Patella baja (low-riding patella from adhesions)
   • Patellar tendon contracture

Prevention of Extensor Lag:

• Meticulous repair in layers (posterior capsule, VMO, retinaculum)
• Close in full extension to establish proper tension
• Interrupted absorbable sutures (not running)
• Gentle handling of quadriceps mechanism
• Avoid excessive lateral releases
• Early mobilization and physiotherapy

Pathophysiology of Stiffness

Knee Stiffness Post-TKA: Stiffness (loss of flexion and/or extension) is one of the most common complications after TKA:

Causes:

• Intra-articular adhesions: Scar between quad and femur (suprapatellar pouch)
• Component malposition: Femoral component flexed (limits flexion)
• Overstuffing: Patella too thick, joint too tight
• Infection: Low-grade infection causes pain and stiffness
• CRPS: Complex regional pain syndrome (type 1)

Prevention:

• Proper component positioning and soft tissue balancing
• Adequate patellar resurfacing (avoid overstuffing)
• Early mobilization and CPM (continuous passive motion)
• Aggressive physiotherapy from day 1 post-operatively

Pre-operative Assessment

History:

• Primary complaint: Knee pain (anteromedial, diffuse), stiffness, instability, deformity
• Duration and progression of symptoms
• Previous knee surgery (especially important - affects approach planning)
• Stiffness assessment: Can patient flex to 90° or more?
• Walking aids, functional limitations
• Medical comorbidities (especially vascular disease - assess pulses)

Physical Examination:

• Gait: Antalgic, varus/valgus thrust, flexed knee gait
• Alignment: Standing alignment (varus/valgus), patella position
• Range of motion:
  • Flexion (normal 135°, minimum 90° for standard TKA technique)
  • Extension (flexion contracture common in OA)
  • Measure and document - crucial for post-operative comparison
• Ligament stability: Varus/valgus stress, AP drawer
• Extensor mechanism: Patellar tracking, quadriceps strength, straight leg raise
• Limb alignment: Mechanical axis (weight-bearing line from hip to ankle)

Pre-operative Range of Motion Documentation: Critical for surgical planning and post-operative expectations:

• Flexion under 90°: Warn patient about stiffness risk, consider staged approach
• Flexion contracture over 20°: May need posterior capsular releases
• Stiff knee (under 70° arc): Plan for extensile options (quad snip, TTO)

Previous Surgery Considerations

Previous Knee Incisions:

• Vertical midline (most common): Use same incision for TKA
• Multiple incisions: Use most lateral incision (preserves medial blood supply)
• Previous lateral incision: Absolute contraindication to medial approach (vascular compromise risk)
• Oblique/transverse incisions: Plan carefully - may need plastic surgery consultation

Rule of Thumb: If previous incisions are present, use the most lateral viable incision to preserve medial blood supply to skin flaps.

Pre-operative Imaging

Radiographs (mandatory):

• Standing AP both knees: Assess alignment (mechanical axis), joint space narrowing
• Lateral knee: Assess patellar height (Insall-Salvati ratio), posterior slope
• Skyline/sunrise view: Assess patellofemoral joint, trochlear dysplasia
• Long leg alignment films: If significant deformity (varus/valgus over 10°)

Radiographic Assessment:

CT Scan (selective indications):

• Significant bony deformity or malunion from previous trauma
• Extra-articular deformity (femoral or tibial)
• Assessment of femoral and tibial version
• Pre-operative planning for patient-specific instrumentation (PSI)

MRI (rarely indicated):

• Not routine for TKA planning
• May be useful if: diagnosis unclear (AVN vs OA), assessing meniscus/ligaments in younger patients considering alternative procedures

Pre-operative Templating

Modern TKA relies more on intra-operative assessment than templating, but basic planning is important:

Key Planning Points:

• Tibial resection level: 8-10mm from least-worn plateau
• Femoral sizing: Match anterior cortex (avoid notching) and posterior condyles
• Implant size estimate: Based on AP dimension of femur and tibia
• Soft tissue releases needed: Based on alignment and contractures

Laboratory Investigations

Standard Pre-operative Workup:

• FBC, U&E, coagulation studies
• Group and hold (or crossmatch if high bleeding risk)
• ECG (if over 50 years or cardiac history)

If Concern for Infection:

• ESR, CRP (elevated in infection but also in OA)
• Joint aspiration if red flags: rapid progression, systemic symptoms, night pain, fever
• Synovial fluid: cell count, differential, culture

Pre-operative Setup

1. Patient positioning: Supine, leg holder or post
2. Tourniquet: Upper thigh, test before draping
3. Prep and drape: Mid-thigh to ankle, circumferential
4. Time-out: Verify patient, side, procedure, antibiotics given

Skin Incision

Midline Vertical Incision:

• Landmarks: Center over patella, extend from 5cm above superior pole to 1cm medial to tibial tubercle
• Length: Typically 15-20cm (adjust based on patient size and adiposity)
• Rationale for midline: Equal distribution of blood supply, extensile, low wound complications

Incision Principles:

• Avoid undermining skin flaps (preserves blood supply)
• If previous scars: use most lateral viable incision
• Handle skin flaps gently (wrap in moist gauze)

Deep Dissection and Arthrotomy

Step 1: Identify Structures

• Palpate medial border of patella
• Palpate tibial tubercle distally
• Identify VMO muscle belly proximally

Step 2: Medial Parapatellar Arthrotomy

• Begin 2-3cm proximal to superior pole of patella in midline of quadriceps tendon
• Continue distally just medial to patella (5-10mm from edge)
• Curve medially at inferior pole toward tibial tubercle
• Stay 1cm anterior to MCL to avoid ligament injury
• Extend to level of tibial tubercle (preserves patellar tendon insertion)

Critical Technical Points:

• Anterior to MCL: Stay 1cm anterior to avoid MCL injury (causes instability)
• VMO fibers divided: This is intentional - creates surgical plane
• Preserve patellar tendon: Do not divide past tibial tubercle unless doing TTO
• Mark arthrotomy edges: Use markers or stay sutures for later repair

Patella Eversion

Technique:

1. Flex knee to 90° with gentle traction
2. External rotation of tibia
3. Sublux patella laterally and rotate to evert
4. Support everted patella with moistened gauze

If Cannot Evert Safely:

• Do NOT force eversion (risk patellar tendon avulsion)
• Perform quadriceps snip: proximal-lateral 45° release
• Alternative: sublux patella laterally without full eversion

Exposure of Joint

Suprapatellar Pouch:

• Release adhesions between quadriceps and femur
• Establish suprapatellar pouch for femoral component insertion

Medial and Lateral Gutters:

• Release medial gutter (easy, already divided)
• Release lateral gutter carefully (preserve lateral blood supply)
• Remove osteophytes from femoral condyles

Posterior Capsule:

• Release posterior capsule from tibia (for exposure and flexion gap balancing)
• Elevate medial meniscus and capsule as continuous sleeve

Cruciate Ligaments:

• PCL: Preserve (CR design) or excise (PS design)
• ACL: Excise (not functional in advanced OA)

Tibial Preparation

Step 1: Extramedullary Alignment Guide

• Entry point: Center of proximal tibia
• Distal reference: Ankle center (midpoint between malleoli)
• Varus/valgus: Align with mechanical axis (0° varus/valgus)
• Posterior slope: Match native (typically 3-7°)

Step 2: Tibial Resection

• Resection level: 8-10mm from least-worn plateau
• Verify: Should preserve joint line height
• Use oscillating saw for smooth cut

Femoral Preparation

Step 1: Intramedullary Alignment Guide

• Entry point: Anterior to PCL insertion (roof of intercondylar notch)
• Advance rod into femoral canal
• Set valgus angle (typically 5-7°)

Step 2: Distal Femoral Resection

• Resection: 9-10mm from most-worn condyle
• Equal medial and lateral resection (balanced in extension)

Step 3: Anterior/Posterior Femoral Cuts

• Size femur based on AP dimension
• Set rotation: parallel to epicondylar axis or 3° external rotation from posterior condyles
• Make anterior and posterior cuts

Step 4: Chamfer Cuts

• Complete femoral preparation with chamfer cuts

Patellar Preparation (if resurfacing)

Technique:

• Resect to 15mm total thickness (bone + implant)
• Use free-hand or saw guide technique
• Ensure three-point fixation of patellar component
• Avoid over-resection (increases fracture risk)

Trial and Balancing

Trial Components:

• Insert tibial trial and polyethylene insert
• Insert femoral trial
• Reduce patella and assess tracking

Soft Tissue Balancing:

• Extension gap: Should be balanced (equal medial and lateral tension)
• Flexion gap: Should match extension gap
• Release contracted structures as needed:
  • Varus deformity: Release deep MCL, posteromedial capsule
  • Valgus deformity: Release lateral structures (ITB, popliteus, LCL)

Patellar Tracking Assessment:

• No thumb test: Patella should track centrally without manual pressure
• If lateral tracking: consider lateral release (last resort)

Final Implant Insertion

Cementing Technique:

• Clean and dry bone surfaces
• Apply cement to bone (not implant)
• Insert implants in sequence: femur → tibia → patella
• Hold in position until cement fully polymerized
• Remove excess cement (especially posterior)

Closure

Critical Repair Steps:

1. Reduce patella to anatomic position
2. Extend knee fully for proper tension
3. Close in layers:
   • Posterior capsule (absorbable 1-0 interrupted)
   • VMO and quadriceps tendon (absorbable 1-0 interrupted) - CRITICAL LAYER
   • Medial retinaculum (absorbable 2-0 interrupted or running)
4. Check ROM: Should achieve 90° flexion minimum, full extension
5. Subcutaneous layer (absorbable 2-0 or 3-0)
6. Skin (staples, absorbable subcuticular, or monofilament)

Dressings and Immobilization

• Apply compressive dressing
• Place knee immobilizer or brace in extension (first 24 hours)
• Drain optional (surgeon preference)

Extensor Mechanism Complications

1. Extensor Lag

Definition: Inability to actively fully extend the knee despite passive full extension

Incidence:

• With good repair: 2%
• With poor repair: 10%

Causes:

• Inadequate arthrotomy repair (most common)
• Quadriceps damage during surgery
• Pain inhibition (acute post-operative)
• Adhesions in suprapatellar pouch

Management:

• Acute (under 6 weeks): Intensive physiotherapy, quadriceps strengthening
• Chronic (over 6 weeks): If lag over 10° and functional impairment → consider reoperation (repair revision, adhesiolysis, V-Y advancement)

Prevention:

• Meticulous repair in layers
• Close in full extension
• Use interrupted (not running) sutures
• Early mobilization and physiotherapy

2. Patellar Maltracking

Definition: Abnormal patellar tracking (lateral subluxation or tilt)

Incidence: 1-5%

Causes:

• Component malposition: Femoral component internally rotated, tibial component internally rotated
• Inadequate lateral release: Tight lateral retinaculum
• Excessive medial release: Over-release of medial structures
• Patella baja: Low-riding patella from adhesions

Clinical Presentation:

• Anterior knee pain
• Catching or grinding sensation
• Visible lateral tracking or J-sign (patella jumps laterally into trochlea with flexion)

Management:

• Non-operative: Physiotherapy, patellar taping, quadriceps strengthening (especially VMO)
• Operative: Lateral release (if not done), tibial tubercle osteotomy (if severe), component revision (if malpositioned)

3. Patellar Tendon Rupture

Definition: Complete disruption of patellar tendon from tibial tubercle

Incidence: 0.1-0.5% (rare but catastrophic)

Risk Factors:

• Revision TKA (highest risk)
• Rheumatoid arthritis
• Chronic steroid use
• Multiple previous surgeries
• Patellar tendon injury during surgery

Clinical Presentation:

• Sudden pain and inability to extend knee
• Palpable gap inferior to patella
• Patella alta (high-riding patella) on X-ray
• Cannot straight leg raise

Management:

• Always operative: Primary repair with augmentation (mesh, allograft, or extensor mechanism allograft)
• Poor outcomes even with surgery - warn patients
• Some require ambulatory brace long-term

Prevention:

• Minimize patellar tendon manipulation
• Avoid excessive eversion force
• Preserve infrapatellar fat pad if possible
• Consider extensile options early (quad snip, TTO) rather than forceful eversion

Immediate Post-operative Period (Day 0-2)

Day of Surgery:

• Remove knee immobilizer once recovered from anesthesia
• Mobilization: Weight-bearing as tolerated with walking frame (same day)
• ROM exercises: Begin gentle flexion/extension exercises
• DVT prophylaxis: Rivaroxaban 10mg daily × 5 weeks OR enoxaparin OR aspirin
• Pain management: Multimodal (paracetamol + NSAID + opioid PRN)
• Ice and elevation

Day 1-2:

• Continue mobilization with physiotherapy
• ROM goals: 90° flexion, 0° extension by discharge
• Drain removal (if used): Typically 24 hours
• Ensure adequate pain control (patient-controlled analgesia or oral regimen)

DVT Prophylaxis (Australian Guidelines):

• Chemical: Rivaroxaban 10mg daily × 35 days (most common) OR Enoxaparin 40mg daily OR Aspirin 100mg daily
• Mechanical: TED stockings, foot pumps intra-operatively
• Early mobilization: Most important prophylaxis

Week 1-6 (Early Recovery Phase)

Mobilization:

• Progress from walking frame → crutches → single stick → unaided
• Typical timeline: Frame for 1-2 weeks, crutches/stick for 2-4 weeks, independent by 6 weeks
• Weight-bearing: Full weight-bearing as tolerated from day 0

Range of Motion:

• Flexion goal at 2 weeks: 90°
• Flexion goal at 6 weeks: 110-120°
• Extension goal: 0° (full extension) by 2 weeks

Physiotherapy:

• Quadriceps strengthening: Straight leg raises, quad sets, short-arc quads
• ROM exercises: Stationary bike, wall slides, active-assisted flexion
• Gait training: Normalize gait pattern, reduce antalgic limp

Wound Care:

• Dressing: Remove at 48 hours, apply waterproof dressing
• Suture/staple removal: 10-14 days (or absorbable sutures left in place)
• Showering: Allowed after 48 hours with waterproof dressing

Follow-up:

• 2 weeks: Wound check, ROM assessment, radiographs
• 6 weeks: Clinical and radiographic assessment

Week 6-12 (Intermediate Recovery Phase)

Functional Progression:

• Driving: Typically allowed at 6 weeks (if right knee: able to emergency stop)
• Return to work: Sedentary work 4-6 weeks, manual labor 3-6 months
• Activities: Swimming, cycling encouraged; impact activities avoided until 3 months

Physiotherapy:

• Progress to resistance training
• Balance and proprioception exercises
• Functional activities (stairs, sit-to-stand)

ROM Goals:

• Flexion: 120° by 12 weeks (near maximum expected)
• Extension: Maintain 0° (any loss of extension is significant problem)

Month 3-12 (Late Recovery Phase)

Functional Recovery:

• Most functional improvement by 6 months
• Continued improvement until 12 months
• Return to sport: Low-impact activities (golf, doubles tennis, swimming) at 3-6 months
• Avoid: High-impact activities (running, singles tennis, jumping sports)

Monitoring:

• 3 months: Clinical assessment, radiographs
• 12 months: Final clinical and radiographic assessment
• Annual: Lifelong monitoring (clinical ± radiographs)

Expected Outcomes at 12 Months:

• Satisfaction: 80-85% very satisfied, 10-15% satisfied, 5-10% dissatisfied
• ROM: 0-120° average (sufficient for most activities)
• Pain: Minimal or no pain (VAS less than 2/10)
• Function: Independent with ADLs, community ambulation

Short-term Outcomes (0-2 years)

Function:

• ROM: Average 0-120° (sufficient for most activities - stair climbing requires 90°, getting out of chair requires 100°)
• Pain relief: 90-95% report significant pain improvement
• Walking distance: Unlimited by 6 months in majority
• Return to work: 80% return to work if employed pre-operatively

Complications:

• Infection: 0.5-1% (acute), 0.5-1% (chronic)
• Stiffness: 5-10% require MUA
• Instability: 0.5-1%
• Extensor lag: 2% (with good repair)
• DVT/PE: Under 1% (with prophylaxis)
• Peroneal nerve palsy: 0.5-1% (related to valgus correction and tourniquet)

Long-term Outcomes (AOANJRR Data - Australian Context)

Implant Survival:

• 5 years: 96-97% survival
• 10 years: 93-94% survival
• 15 years: 90-91% survival
• 20 years: 85-87% survival

Modern TKA has excellent long-term survival comparable to or better than THA.

Causes of Revision (AOANJRR):

Patient Satisfaction

Satisfaction Rates:

• Very satisfied: 65-75%
• Satisfied: 15-20%
• Neutral: 5-10%
• Dissatisfied: 5-10%

Reasons for Dissatisfaction:

• Persistent pain (most common - anterior knee pain)
• Stiffness (inability to kneel, squat, or participate in activities)
• Unmet expectations (unrealistic expectations about return to high-impact activities)
• Instability or feeling of "giving way"
• Noise (clicking, clunking from patellofemoral joint)

Prognostic Factors

Good Prognosis (Low Revision Risk):

• Age over 65 (lower activity demands)
• Primary osteoarthritis (better bone quality than inflammatory arthritis)
• BMI under 30
• Normal alignment (varus under 10°, no severe deformity)
• Good pre-operative ROM (over 90° flexion)
• No comorbidities (diabetes, vascular disease increase infection risk)

Poorer Prognosis (Higher Revision Risk):

• Age under 55 (higher activity levels, longer expected lifespan)
• Inflammatory arthritis (RA, psoriatic - bone quality issues)
• BMI over 35 (higher infection risk, implant stresses)
• Severe deformity (varus over 15°, flexion contracture over 20°)
• Stiff knee (pre-operative flexion under 70°)
• Neuropathic joint (Charcot) - contraindication

AOANJRR Data (Australian Orthopaedic Association National Joint Replacement Registry):

• Approximately 100,000 primary TKAs performed annually in Australia
• Medial parapatellar approach: 85% of primary TKAs
• 15-year survival: 90% (excellent outcomes)
• Main causes of revision: Infection (26%), loosening (28%), instability (14%)

Australian Healthcare Context:

• TKA is a high-volume procedure in both public and private sectors
• Enhanced recovery protocols (ERAS) increasingly adopted across Australian hospitals
• Medial parapatellar approach fully compatible with ERAS
• Same-day discharge and 23-hour stay programs expanding in selected patients

Training Implications:

• Essential skill for FRACS Orthopaedic examination (clinical and viva)
• All candidates expected to describe approach in detail
• Understanding of alternatives (subvastus, midvastus) expected
• Complication management (extensor lag, stiffness, patellar maltracking) critical

DVT Prophylaxis - Australian Guidelines: The Australian and New Zealand Working Party on the Management and Prevention of Venous Thromboembolism recommends:

• Rivaroxaban 10mg once daily for 35 days (most commonly used)
• OR Enoxaparin 40mg subcutaneous once daily for 35 days
• OR Aspirin 100-150mg once daily for 35 days (in selected low-risk patients)
• Plus mechanical prophylaxis (TED stockings, foot pumps) and early mobilization

Antibiotic Prophylaxis: Therapeutic Guidelines (eTG) recommendations:

• Cefazolin 2g IV at induction (or cefuroxime 1.5g IV)
• Vancomycin 25-30mg/kg IV if penicillin allergy or MRSA risk
• Redose if surgery over 4 hours
• No post-operative antibiotics routinely (cease within 24 hours)