Arthroscopic Portal Placement (Knee)

Knee arthroscopy is the MOST COMMONLY performed orthopaedic procedure worldwide, with over 4 million procedures annually (AAOS 2023). Understanding portal anatomy is CRITICAL for safe arthroscopy and minimizing neurovascular complications.

Standard Arthroscopic Portals

1. ANTEROLATERAL PORTAL (VIEWING PORTAL):

Location:

• 1cm proximal to joint line (superior to lateral tibial plateau)
• 1cm lateral to patellar tendon lateral border
• Level with inferior pole of patella when knee flexed 90°

Function:

• PRIMARY viewing portal for diagnostic arthroscopy
• Camera inserted through this portal for standard examination
• Provides view of medial compartment (medial meniscus, medial femoral condyle, ACL, PCL, intercondylar notch)

Structures at Risk:

• Lateral femoral cutaneous nerve (lateral thigh sensation) - runs 5-8cm lateral to portal (usually safe)
• Lateral superior geniculate artery - 2-3cm proximal to portal (safe with standard placement)
• Cartilage - lateral femoral condyle or lateral tibial plateau (avoid high/low placement)

Safe Zone:

• Soft tissue triangle bounded by: Patellar tendon medially, Joint line inferiorly, Inferior patella pole superiorly

2. ANTEROMEDIAL PORTAL (WORKING PORTAL):

Location:

• 1cm proximal to joint line (superior to medial tibial plateau)
• 1cm medial to patellar tendon medial border
• Level with inferior pole of patella when knee flexed 90°

Function:

• PRIMARY working portal for instruments (probes, shavers, graspers)
• Provides access to lateral compartment (lateral meniscus, lateral femoral condyle) when viewing from anterolateral
• Instrument portal for ACL tibial tunnel drilling (AM portal for tibial guide pin)

Structures at Risk (HIGHEST INJURY RISK):

• Saphenous nerve infrapatellar branch (medial knee/proximal leg sensation) - crosses DIRECTLY over portal site (2-7% injury rate - Mochizuki 2009)
• Medial superior geniculate artery - 2-3cm proximal to portal (usually safe)
• Saphenous vein - accompanies nerve (minor bleeding if injured)
• MCL superficial fibers - 1-2cm medial to portal (avoid excessive medial placement)

Safe Zone:

• Keep portal 1cm medial to patellar tendon (NOT more medial - increases saphenous nerve risk)
• Avoid extension inferior to joint line (risks tibial plateau cartilage)

3. SUPEROLATERAL (SUPRAPATELLAR) PORTAL:

Location:

• 2-3cm proximal to superior pole of patella
• 1cm lateral to lateral patellar border
• In line with anterolateral portal (straight proximal extension)

Function:

• Access to suprapatellar pouch (remove loose bodies, synovectomy)
• Outflow portal (continuous fluid drainage to maintain visualization)
• Accessory viewing portal for patellofemoral assessment (chondromalacia patellae, trochlear dysplasia)

Structures at Risk:

• Quadriceps tendon - portal enters THROUGH quadriceps tendon (use sharp trocar to penetrate tendon cleanly)
• Suprapatellar plica - may need to be released if thick/symptomatic

Safe Zone:

• Stay 1cm lateral to lateral patellar border (avoids vastus medialis muscle belly medially)

4. ACCESSORY ANTEROLATERAL PORTAL (MID-PATELLAR):

Location:

• At level of mid-patella (NOT inferior pole like standard anterolateral)
• 1cm lateral to patellar border
• 2-3cm proximal to standard anterolateral portal

Function:

• Trans-patellar tendon drilling for ACL tibial tunnel (avoids posterior cortex blowout)
• Access to posteromedial corner (posterior horn medial meniscus) when viewing from standard anterolateral
• Accessory working portal for meniscus repair (posterior horn lateral meniscus)

Structures at Risk:

• Fat pad (Hoffa's fat pad) - portal traverses fat pad (risk of post-operative anterior knee pain 5-10% - Jacobson 1988)
• Patellar tendon - portal may nick lateral edge of tendon (usually no functional consequence)

Posterior Arthroscopic Portals

5. POSTEROMEDIAL PORTAL:

Location:

• 1cm proximal to joint line
• 1-2cm medial to medial border of patellar tendon (posteromedial to MCL)
• Anterior to posteromedial corner of knee

Function:

• Access to posterior horn medial meniscus (meniscus repair, meniscectomy)
• Viewing portal for posteromedial compartment (posterior capsule, PCL femoral attachment)
• Inside-out meniscus repair (needles exit through this portal - requires safety incision)

Structures at Risk (HIGH RISK):

• Saphenous nerve and vein - run 2-3cm medial to portal (2-7% injury risk - Mochizuki 2009)
• Medial head of gastrocnemius - portal passes between MCL and gastroc (stay anterior to avoid muscle)
• Popliteal vessels and tibial nerve - lie 15-20mm medial to portal (SAFE if portal kept anterior)

Safety Technique:

• Create portal with knee flexed 90° (posterior structures migrate posteriorly - increases safety clearance)
• Use spinal needle localization first (visualize intra-articular needle tip from anterolateral viewing portal)
• Direct portal anteriorly and laterally toward intercondylar notch (avoids posterior neurovascular structures)

6. POSTEROLATERAL PORTAL (SAFEST POSTERIOR PORTAL):

Location:

• 1cm proximal to joint line
• 1-2cm lateral to lateral border of patellar tendon (posterolateral to LCL)
• Anterior to popliteus hiatus

Function:

• Access to posterior horn lateral meniscus (meniscus repair, meniscectomy - MOST COMMON indication)
• Viewing portal for posterolateral compartment (posterior capsule, popliteus, arcuate ligament, PCL tibial attachment)
• PCL reconstruction (tibial tunnel drilling for transtibial technique)

Structures at Risk:

• Common peroneal nerve - runs 8-10mm lateral to portal (0.4% injury risk - Allardyce 2013) - SAFEST of posterior portals
• Inferior lateral geniculate artery - crosses portal site (1-3% injury causing hemarthrosis - Small 1985)
• Lateral head of gastrocnemius - portal passes lateral to gastroc (minimal risk)
• Popliteal vessels - lie 20-25mm medial to portal (SAFE)

Safety Technique:

• Posterolateral portal is PREFERRED posterior portal vs posteromedial (peroneal nerve 8-10mm lateral vs tibial nerve 5mm medial - Allardyce 2013)
• Create with knee flexed 90° and slight internal rotation (peroneal nerve migrates laterally - increases safety clearance)
• Use spinal needle localization + visualization from anterolateral portal
• Direct portal anteriorly and medially toward intercondylar notch

7. CENTRAL TRANSPATELLAR PORTAL (RARELY USED):

Location:

• Through center of patellar tendon
• 0.5-1cm proximal to tibial tubercle

Function:

• ACL femoral tunnel drilling (central portal gives BEST angle for anatomic femoral tunnel via transtibial technique)
• Access to intercondylar notch (notchplasty, ACL remnant debridement)

Structures at Risk:

• Patellar tendon - portal created THROUGH tendon (2-5% risk of patellar tendinopathy, anterior knee pain - Howell 1999)

Controversy:

• Most surgeons AVOID trans-patellar tendon portal (prefer accessory anterolateral for ACL femoral tunnel) due to patellar tendinopathy risk

Portal Triangulation Principles

Optimal Viewing and Working Relationship:

• Anterolateral (viewing) + Anteromedial (working): 60-70° angle for optimal instrument access to all compartments
• Anterolateral (viewing) + Posterolateral (working): 90-100° angle for posterior horn lateral meniscus repair
• Anteromedial (viewing) + Posterolateral (working): 120-130° angle for PCL femoral attachment visualization

Key Rule:

• Viewing and working portals should create 60-90° angle for optimal triangulation (less than 60° = instruments conflict, greater than 90° = difficult manipulation)

Patient Positioning

Setup:

• Supine position on operating table
• Leg holder or post at lateral thigh (allows knee flexion/extension and varus/valgus stress)
• Foot of bed dropped (allows knee to hang at 90° flexion for portal creation)
• Tourniquet on proximal thigh (250-280mmHg for 60-90 minutes) - optional (most surgeons use arthroscopic pump pressure for hemostasis without tourniquet)
• Arthroscopic pump pressure 40-50mmHg (higher pressure 50-60mmHg for posterior portal work or bleeding)

Portal Creation Technique

STEP 1: ANTEROLATERAL PORTAL (FIRST PORTAL - VIEWING):

Landmarks:

• Palpate patellar tendon medial and lateral borders
• Palpate joint line (soft tissue depression between patella and tibial plateau)
• Mark portal site: 1cm proximal to joint line, 1cm lateral to patellar tendon

Technique:

1. Skin incision: 5-7mm VERTICAL incision with #11 blade (vertical incision parallel to neurovascular structures)
2. Penetrate subcutaneous tissue with mosquito clamp or trocar (spread down to joint capsule)
3. Penetrate joint capsule: Use sharp trocar with 30° arthroscope inside (direct trocar anteriorly and slightly medially toward intercondylar notch)
4. Visual confirmation: Withdraw trocar, advance arthroscope - confirm intra-articular position (visualize fat pad, medial femoral condyle, or PCL)
5. Inflow: Connect arthroscopic pump to inflow port on camera sheath (40-50mmHg pressure)

STEP 2: ANTEROMEDIAL PORTAL (SECOND PORTAL - WORKING):

Inside-Out Technique (SAFEST):

1. Spinal needle localization: Insert 18G spinal needle through skin 1cm medial to patellar tendon, 1cm proximal to joint line
2. Visualize needle tip from anterolateral viewing portal (confirm needle enters joint in desired location - usually above medial tibial plateau, aimed at lateral compartment)
3. Adjust needle position if needed (too high/low/medial) until optimal position confirmed
4. Mark skin at needle entry site
5. Remove needle, make 5-7mm VERTICAL skin incision at mark
6. Penetrate joint capsule with blade or trocar under direct visualization from anterolateral portal (watch blade enter joint - avoid crossing to lateral compartment prematurely)

Outflow Portal (Optional):

• Create superolateral portal for outflow (continuous drainage maintains visualization)
• 2-3cm proximal to superior patella pole, 1cm lateral to lateral patellar border
• Use sharp trocar through quadriceps tendon into suprapatellar pouch

Systematic Diagnostic Arthroscopy (Order of Examination)

21-Point Examination (Outerbridge-Saunders Protocol):

SUPRAPATELLAR POUCH (from anterolateral viewing):

1. Suprapatellar plica (medial, lateral, central)
2. Suprapatellar synovium (synovitis, loose bodies)

MEDIAL COMPARTMENT (from anterolateral viewing, anteromedial working): 3. Medial gutter (synovitis, loose bodies) 4. Medial femoral condyle (chondral lesions - Outerbridge classification) 5. Medial meniscus anterior horn (tears, fraying) 6. Medial meniscus body (horizontal, vertical, radial tears) 7. Medial meniscus posterior horn (root tears, posterior horn tears) 8. Medial tibial plateau (chondral lesions, osteophytes)

INTERCONDYLAR NOTCH (from anterolateral viewing): 9. ACL (tear, degeneration, impingement) 10. PCL (tear, attenuation) 11. Intercondylar notch (notch stenosis, impingement lesions)

LATERAL COMPARTMENT (from anteromedial viewing, anterolateral working): 12. Lateral gutter (synovitis, loose bodies) 13. Lateral femoral condyle (chondral lesions) 14. Lateral meniscus anterior horn (tears, fraying) 15. Lateral meniscus body (tears, cysts) 16. Lateral meniscus posterior horn (tears, popliteus hiatus assessment) 17. Lateral tibial plateau (chondral lesions)

PATELLOFEMORAL JOINT (from inferolateral or superomedial viewing): 18. Patella (chondromalacia - Outerbridge grade, facet lesions) 19. Trochlea (trochlear dysplasia, chondral lesions) 20. Patellar tracking (assess with knee flexion/extension)

POSTERIOR COMPARTMENT (from posterolateral portal if indicated): 21. Posterior horn menisci (medial/lateral), posterior capsule, PCL attachments

Indications for Knee Arthroscopy

DIAGNOSTIC ARTHROSCOPY (Decreasing Indication):

• MRI has largely REPLACED diagnostic arthroscopy (90-95% accuracy for meniscus tears, ACL tears, chondral lesions - Ryzewicz 2007)
• Reserved for: Equivocal MRI findings, mechanical symptoms (locking, catching) without clear diagnosis, acute traumatic hemarthrosis with suspected meniscus/cartilage injury

THERAPEUTIC ARTHROSCOPY (PRIMARY INDICATIONS):

1. Meniscus Pathology:

• Meniscus tears with mechanical symptoms (locking, catching) or persistent pain - partial meniscectomy (resect unstable tear only, preserve stable rim)
• Meniscus root tears (medial meniscus posterior root most common) - consider root repair vs meniscectomy (root repair better outcomes if repairable - LaPrade 2015)
• Meniscus repair (inside-out, outside-in, all-inside techniques) for peripheral tears in vascular zone (outer 1/3 "red-red zone") in patients less than 40 years

2. Ligament Reconstruction:

• ACL reconstruction (primary, revision) - arthroscopic-assisted tunnel drilling, graft passage, fixation
• PCL reconstruction (transtibial, tibial inlay) - less common, complex arthroscopic technique
• Multi-ligament reconstruction (ACL + PCL, ACL + LCL, etc.) - usually arthroscopic-assisted with open component

3. Cartilage Procedures:

• Chondral loose body removal (osteochondritis dissecans, post-traumatic fragmentation)
• Microfracture for focal chondral defects (less than 2cm²) - Outerbridge grade IV (bone exposed)
• Autologous chondrocyte implantation (ACI) - arthroscopic-assisted membrane fixation
• Osteochondral autograft transfer (OATS/Mosaicplasty) - arthroscopic harvest and implantation

4. Synovial Pathology:

• Synovectomy for inflammatory arthritis (rheumatoid arthritis, pigmented villonodular synovitis)
• Plica resection (symptomatic medial plica causing medial knee pain and clicking)

5. Fracture Fixation:

• Tibial plateau fractures (Schatzker I-III) - arthroscopic-assisted reduction and percutaneous fixation
• Tibial eminence fractures (ACL avulsion) - arthroscopic reduction and suture fixation

CONTRAINDICATIONS:

Absolute:

• Active infection (septic arthritis, overlying cellulitis) - risk of seeding joint
• Severe arthrofibrosis with inability to flex knee to 90° (inadequate working space)

Relative:

• Advanced osteoarthritis (Kellgren-Lawrence grade 3-4) - arthroscopic debridement NOT effective (Moseley 2002 - placebo-controlled trial showed no benefit)
• Unrealistic patient expectations (expecting arthroscopy to 'cure' arthritis)
• Medical comorbidities increasing anesthesia risk (optimize first)

Outcomes by Procedure

Meniscectomy:

• Symptom relief: 80-85% patients have good-excellent outcomes at 2 years (reduced locking, catching, pain)
• Long-term: 50-60% develop radiographic OA by 10-15 years (meniscectomy accelerates OA - Englund 2003)
• Extent of resection: Greater resection = faster OA progression (preserve as much stable meniscus as possible)

Meniscus Repair:

• Healing rate: 70-85% for peripheral "red-red" zone tears (outer 1/3 with vascular supply)
• Failure rate: 15-30% require revision meniscectomy (most failures within 2 years)
• Better outcomes: Young age (less than 30 years), acute tears (less than 6 weeks), peripheral location, concomitant ACL reconstruction (ACL reconstruction increases meniscus repair healing by 10-15% - Wasserstein 2013)

ACL Reconstruction:

• Graft survival: 85-90% at 10 years for primary reconstruction (Barret 2011)
• Revision rate: 8-12% (higher in young athletes less than 20 years - 15-20% revision rate)
• Return to sport: 65-75% return to pre-injury sport level, 90% return to some sport activity

Chondral Procedures:

• Microfracture: 60-70% good-excellent outcomes at 2 years, deteriorates by 5 years (fibrocartilage vs hyaline cartilage)
• ACI/MACI: 70-80% good-excellent outcomes sustained to 5-10 years (superior to microfracture for lesions greater than 2cm²)

Portal-Related Complications

1. SAPHENOUS NERVE INJURY (2-7% - MOST COMMON):

Clinical Manifestation:

• Numbness over medial knee and proximal medial leg (saphenous nerve distribution)
• Dysesthesia (tingling, burning sensation) in 30-40% of cases
• Painful neuroma (10-15%) at portal site - tender nodule palpable at anteromedial portal

Natural History:

• Transient (60-70% cases): Resolves by 6-12 months
• Permanent (30-40% cases): Persistent numbness (usually well-tolerated if no neuroma pain)

Prevention:

• Keep anteromedial portal 10mm (NOT MORE) medial to patellar tendon medial border
• Vertical skin incisions (parallel to nerve course) - reduces transection risk vs horizontal incisions
• Small portal size (5-7mm) - large incisions (greater than 10mm) increase nerve exposure area
• Sharp capsule penetration (clean cut vs blunt tearing which avulses nerve branches)

Management:

• Observation for 6-12 months (60-70% resolve spontaneously)
• Desensitization therapy (massage with graded textures) for dysesthesia
• Neuropathic pain medications: Gabapentin 300mg TDS (titrate to 900mg TDS), amitriptyline 25mg nocte
• Neuroma excision if symptomatic beyond 12 months (painful tender nodule) - 70% symptom improvement

2. HEMARTHROSIS (1-3%):

Mechanism:

• Inferior lateral geniculate artery injury during posterolateral or inferolateral portal creation (most common - Small 1985)
• Synovial bleeding from aggressive synovectomy or fat pad resection
• Inadequate hemostasis before tourniquet release

Clinical Manifestation:

• Progressive knee swelling in first 24-48 hours post-op
• Tense effusion (50-150mL blood)
• Pain, limited ROM

Prevention:

• Spinal needle localization for posterior portals
• Direct portals ANTERIORLY toward intercondylar notch (avoids posterior dissection into geniculate arteries)
• Cauterize bleeding vessels with radiofrequency ablation BEFORE completing procedure
• Release tourniquet BEFORE wound closure, ensure hemostasis

Management:

• Aspiration (50-150mL blood typical) - provides symptom relief
• Re-arthroscopy if persistent bleeding (greater than 200mL aspirated or re-accumulates rapidly) - identify and cauterize bleeding vessel
• Observation if small volume (less than 50mL) - spontaneous resolution by 1-2 weeks

Outcome:

• 95% resolve with aspiration ± observation
• Rarely requires open ligation or angiographic embolization

3. INFECTION (0.1-0.5%):

Risk Factors:

• Diabetes (3× increased risk)
• Obesity (BMI greater than 30)
• Smoking
• Prolonged procedure time (greater than 90 minutes)
• Intra-articular corticosteroid injection within 3 months

Clinical Manifestation:

• Septic arthritis (acute infection): Fever, severe pain, tense effusion, warmth, erythema (onset 2-7 days post-op)
• Portal cellulitis (superficial infection): Erythema around portal site, no systemic symptoms

Prevention:

• Pre-operative antibiotic prophylaxis (cephazolin 2g IV) within 60 minutes of incision
• Strict sterile technique (draping, gown, gloves)
• Minimize procedure time (complete diagnostic + therapeutic arthroscopy within 60-90 minutes)
• Avoid intra-articular corticosteroid injection close to surgery date (delay 3 months if possible)

Management:

• Septic arthritis:
  • Arthroscopic irrigation and debridement (URGENT within 24 hours) - remove fibrinous debris, copious lavage (6-9L saline)
  • Aspiration for Gram stain and culture (obtain BEFORE starting antibiotics if possible)
  • IV antibiotics (empiric: flucloxacillin 2g QDS + gentamicin 4-6mg/kg daily, adjust based on culture results)
  • Duration: 2 weeks IV + 4 weeks PO (total 6 weeks)
• Portal cellulitis:
  • Oral antibiotics (flucloxacillin 500mg QDS or cephalexin 500mg QDS for 7-10 days)
  • Local wound care (daily dressings)

Outcome:

• With early I&D (within 24-48 hours): 90-95% infection clearance, full recovery
• Delayed treatment (greater than 3 days): 20-30% risk of chronic infection, chondral damage, reduced ROM

4. PERONEAL OR TIBIAL NERVE INJURY (0.4-1.2%):

Mechanism:

• Direct trauma during posterior portal creation (posterolateral: peroneal nerve, posteromedial: tibial nerve)
• Excessive posterior dissection beyond joint capsule into neurovascular structures

Clinical Manifestation:

• Peroneal nerve palsy (posterolateral portal injury 0.4% - Allardyce 2013):
  • Foot drop (ankle/toe dorsiflexion weakness - tibialis anterior, EHL, EDL)
  • Steppage gait (high stepping to clear foot)
  • Sensory loss over dorsum of foot and lateral leg
• Tibial nerve palsy (posteromedial portal injury 1.2%):
  • Calf weakness (gastrocnemius, soleus - ankle/toe plantarflexion weakness)
  • Intrinsic foot weakness (FHL, FDL, lumbricals/interossei)
  • Sensory loss over plantar foot

Prevention:

• Posterolateral portal PREFERRED over posteromedial (peroneal nerve 8mm lateral vs tibial nerve 5mm medial - Allardyce 2013)
• Knee flexed 90° + slight internal rotation for posterolateral portal (peroneal nerve migrates laterally)
• Spinal needle localization MANDATORY - visualize needle tip intra-articularly BEFORE creating portal with blade
• Blunt trocar or switching stick after initial capsule penetration (avoid sharp blade deep to capsule)
• Direct portal ANTERIORLY toward intercondylar notch (avoid posterior dissection)

Management:

• Immediate post-operative palsy (recognized in PACU):
  • Urgent MRI to assess for hematoma compressing nerve (rare - less than 5% of cases)
  • If hematoma: Urgent decompression (evacuate hematoma, achieve hemostasis)
  • If NO hematoma: Observation (likely neurapraxia from direct trauma - 70-80% spontaneous recovery by 4-6 months)
• Dynamic splinting:
  • Peroneal palsy: AFO (ankle-foot orthosis) to prevent foot drop, protect from tripping
  • Tibial palsy: Solid AFO for ankle stability (less common - tibial palsy usually less disabling than peroneal)
• Serial EMG at 6-8 weeks (signs of reinnervation indicate recovery)
• Nerve exploration if NO recovery by 6 months (neurolysis vs nerve grafting)
• Tendon transfers if no recovery by 12 months:
  • Peroneal palsy: Tibialis posterior transfer to dorsum of foot (restores dorsiflexion)
  • Tibial palsy: Usually do NOT require transfer (compensatory mechanisms adequate)

Outcome:

• Neurapraxia (mild contusion): 90-95% complete recovery by 6 months
• Axonotmesis (moderate crush): 60-70% recovery by 12 months
• Neurotmesis (complete transection): Requires nerve repair or grafting (40-50% functional recovery)