Anteromedial Approach to the Knee

Anteromedial Knee Approach Overview

The anteromedial approach to the knee provides versatile exposure for various knee procedures, from arthroscopic portals to open procedures including total knee arthroplasty.

Key Concepts:

• Standard approach for total knee arthroplasty (medial parapatellar variant)
• Not a true internervous plane - passes through or adjacent to vastus medialis
• Provides access to medial compartment, MCL, and medial meniscus
• Can be combined with other approaches for multiligament reconstruction
• Variations include subvastus and midvastus for TKA

Historical Context:

• Medial parapatellar arthrotomy described by Insall for TKA
• Subvastus approach developed to preserve extensor mechanism
• Midvastus represents compromise between exposure and muscle sparing

Indications

Advantages and Disadvantages

Advantages:

• Familiar, reproducible approach for most knee surgeons
• Excellent exposure of entire joint (femur, tibia, patella) for TKA
• Extensile - can extend proximally or distally as needed
• Direct access to medial structures (MCL, medial meniscus)
• Allows patellar eversion for TKA

Disadvantages:

• Disrupts VMO insertion (medial parapatellar variant)
• Risk to saphenous nerve with distal extension
• May affect patellar tracking if not closed properly
• Limited lateral compartment access
• Infrapatellar branch of saphenous nerve often transected

Surface Anatomy

Palpable Landmarks:

• Patella: Central reference point
• Patellar tendon: From inferior patella to tibial tubercle
• Tibial tubercle: Distal extent of incision
• Medial femoral condyle: Palpable medially
• Medial joint line: At level of inferior patella
• VMO muscle belly: Visible superomedially

Incision Planning:

Surgical Layers

Superficial Layer:

• Skin, subcutaneous tissue
• Prepatellar bursa (may require excision)
• Saphenous vein branches

Intermediate Layer:

• Quadriceps tendon and expansion
• Vastus medialis obliquus (VMO)
• Medial retinaculum
• Patellar tendon

Deep Layer:

• Joint capsule
• Synovial membrane
• Fat pad (may need partial excision)

Plane of Dissection:

• No true internervous plane
• Incision through/adjacent to VMO insertion
• Arthrotomy along medial patella border

Key Anatomical Structures

Pes Anserinus Order (superficial to deep):

• Sartorius - most superficial
• Gracilis - middle
• Semitendinosus - deepest

Anteromedial Approach Variations

Selection Criteria:

• Patient factors: obesity, ROM, deformity
• Procedure type: TKA vs UKA vs trauma
• Surgeon experience and preference
• Previous incisions on medial knee

Approach Comparison for TKA

Evidence Summary:

• No consistent difference in long-term outcomes
• Subvastus may have faster early recovery
• Medial parapatellar remains gold standard for most surgeons

Imaging Studies

Standard Preoperative Imaging:

Additional Imaging (Selected Cases):

• MRI: Soft tissue pathology, MCL injury, meniscal disease
• CT: Complex deformity, bone loss, previous hardware
• Vascular studies: If peripheral vascular disease suspected

Laboratory Investigations

Preoperative Labs (TKA):

• Full blood count
• Urea, electrolytes, creatinine
• Coagulation studies (if anticoagulated)
• HbA1c (diabetic patients, target below 8%)
• ESR/CRP (if infection concern)

Infection Workup (if concern):

• Joint aspiration for cell count, culture
• Synovial fluid WBC greater than 3000 concerning
• Alpha-defensin if available

Surgical Setup

Patient Positioning:

• Supine on standard operating table
• Knee flexed 90° over edge of bed
• Leg holder or foot of bed dropped
• Ensure hip and ankle freely mobile

Equipment:

Technical Tips

Key Steps:

1. Mark patella borders before incision
2. Full-thickness flaps to reduce devascularization
3. Protect patellar tendon during arthrotomy
4. Adequate proximal release for patella eversion
5. Flex knee to 90° after eversion

Exposure Enhancement:

• Partial fat pad excision
• Lateral retinacular release (if tight)
• Proximal quadriceps snip (revision)
• Tibial tubercle osteotomy (severe stiffness)

Avoid:

• Thin skin flaps
• Excessive traction on patella
• Forceful patella eversion (risk avulsion)
• Distal extension without protecting saphenous nerve

Wound Closure

Closure Technique:

Key Points:

• Repair VMO/quad tendon meticulously
• Test patella tracking with trial
• No lateral subluxation in extension
• Drain if significant ooze (optional)
• Sterile dressing, compression wrap

Incision: Midline skin incision or slightly medial (anterior midline for TKA). From 5cm above patella to tibial tuberosity.

Arthrotomy: Incise joint capsule along medial patellar border:

• Start proximally in quadriceps tendon (may split vastus medialis obliquus near its insertion)
• Continue along medial patella
• Then medial to patellar tendon

Patella Eversion: After releasing soft tissue attachments, evert patella laterally. May need lateral retinacular release if difficult to evert.

Exposure: Provides excellent exposure of entire joint (femur, tibia, patella) for TKA.

Subvastus Approach: Muscle-sparing.

Technique: Dissect beneath vastus medialis rather than through it. Lift VMO off intermuscular septum. Enter joint under VMO.

Advantages: Preserves quadriceps mechanism. May have faster recovery, less pain.

Disadvantages: More technically demanding. Limited exposure. May need to convert to MPP.

Distal Extension (for medial plateau, MCL):

Extend incision distally along subcutaneous border of tibia.

Saphenous Nerve and Vein: At risk. Runs with great saphenous vein which lies posteriorly. Stay anterior to avoid.

Pes Anserinus: Landmark for distal extent. Contains sartorius, gracilis, semitendinosus.

MCL Access: Expose MCL from epicondyle to tibial insertion.

Early Complications

Management Principles:

• Early recognition and intervention
• Wound issues: early wound care, may need debridement
• Haematoma: aspiration if tense, rule out bleeding disorder
• Infection: antibiotics, may need washout

Late Complications

Numbness Counselling:

• Infrapatellar branch injury almost universal in TKA
• Causes numbness lateral to incision
• Usually well-tolerated and not functionally significant

Approach-Specific Complications

Medial Parapatellar:

• VMO damage affecting patella tracking
• Risk of lateral subluxation if not closed well
• Usually heals without long-term sequelae

Subvastus:

• Higher conversion rate to standard approach
• May not achieve adequate exposure
• Potential VMO avulsion

Distal Extension:

• Saphenous nerve injury (numbness medial leg)
• Great saphenous vein injury (bleeding, haematoma)
• Pes anserinus damage

Prevention:

• Careful surgical technique
• Stay anterior when extending distally
• Identify and protect saphenous structures

Immediate Postoperative Care

Day 0-1:

• Compression dressing
• Ice therapy
• Elevation above heart level
• DVT prophylaxis (LMWH or other per protocol)
• Analgesia (multimodal approach)

Wound Management:

VTE Prophylaxis:

• Mechanical: TED stockings, foot pumps
• Chemical: LMWH or aspirin per protocol
• Duration: 2-6 weeks depending on risk

Rehabilitation Protocol

Phase 1 (Week 0-2):

• Weight bearing as tolerated (TKA)
• Quadriceps sets, straight leg raises
• CPM if used (controversial)
• ROM exercises

Phase 2 (Week 2-6):

• Progress ROM to 90° flexion
• Gait training without aids
• Progressive strengthening
• Stairs training

Phase 3 (Week 6-12):

• Full ROM goal (0-120°)
• Return to normal activities
• Low-impact exercise
• Avoid high-impact until 3-6 months

Follow-up Schedule

Red Flags:

• Increasing pain after initial improvement
• Wound breakdown, drainage
• Fever, systemic symptoms
• Sudden loss of ROM
• Calf pain, swelling (DVT concern)

Functional Outcomes

TKA Outcomes (Any Approach):

Factors Affecting Outcome:

• Preoperative function and ROM
• Patient expectations and motivation
• Surgical technique and alignment
• Implant design and fixation
• Rehabilitation compliance

Approach Comparison Outcomes

Evidence Summary:

• Meta-analyses show modest early benefit for subvastus
• No significant difference at 1 year or beyond
• Surgeon experience more important than approach
• Patient selection key for subvastus success

Implant Survival (TKA)

AOANJRR Data:

Revision Reasons:

• Loosening: 25-30%
• Infection: 20-25%
• Pain: 15-20%
• Instability: 10-15%
• Patellofemoral problems: 5-10%

Note: Approach type not independently associated with revision risk in registry data.

Key Studies

Approach Comparison RCTs:

Evidence Level:

• Multiple RCTs and meta-analyses available
• Level I evidence: No significant long-term difference between approaches
• Surgeon experience and patient selection more important

Infrapatellar Nerve:

• Mistry 2016: Nerve transection in 100% TKA
• Sensory deficit well-tolerated in most patients
• Does not correlate with functional outcomes

Guidelines and Recommendations

Approach Selection (Expert Consensus):

• No single approach superior for all patients
• Medial parapatellar: gold standard, most versatile
• Subvastus: consider in younger, thinner patients
• Midvastus: reasonable compromise

AAOS Guidelines (TKA):

• Strong evidence for TKA in OA
• No specific approach recommended
• Surgeon experience critical

NICE Guidelines:

• Standard TKA approach not specified
• Focus on outcomes, not approach
• Patient-centred decision making

Australian Guidelines:

• AOANJRR: monitors outcomes by implant, not approach
• No approach-specific recommendations

Australian Epidemiology

TKA Statistics (AOANJRR 2023):

• Approximately 70,000 TKAs performed annually
• Median age: 69 years
• Female predominance: 56%
• Primary indication: Osteoarthritis (97%)
• Most common approach: medial parapatellar (exact numbers not tracked)

Registry Monitoring:

• AOANJRR tracks implant survival, not surgical approach
• Overall revision rate: 5.6% at 10 years
• Best performing implants identified annually

Australian Practice Patterns

Approach Preferences:

• Medial parapatellar: Most common (estimated greater than 80%)
• Subvastus: Used by subset of surgeons
• Midvastus: Less common
• Lateral: Rare, selected valgus cases

Training:

• FRACS trainees learn medial parapatellar as standard
• Subvastus/midvastus exposure varies by training institution
• AOA courses include approach variations

Prosthesis Selection:

• Approach does not dictate prosthesis choice
• Most surgeons have preferred implant systems
• AOANJRR publishes best-performing combinations