Comprehensive guide to knee arthroscopy portal placement, technique, indications, complications and exam points for Orthopaedic - anterolateral, anteromedial, accessory portals
Reviewed by OrthoVellum Editorial Team
Orthopaedic clinicians and medical editors • Published by OrthoVellum Medical Education Team
Portal Placement | Minimally Invasive | Diagnostic and Therapeutic
Always AL portal FIRST. This is the viewing portal. Create it blind (but safely with spinal needle first). The AM portal is then created UNDER DIRECT VISION through the arthroscope. Never create AM portal blind.
The infrapatellar branch of saphenous nerve runs transversely across the anterior knee, typically 3-5mm below the joint line. It is commonly injured during portal placement, causing anterolateral knee numbness. This is similar to open surgery.
Portals must be at joint line level. Too proximal risks patellar surface damage; too distal risks meniscus or fat pad injury. Palpate the soft spot adjacent to the patellar tendon with the knee flexed 90 degrees.
Posterior portals risk neurovascular injury. The popliteal artery and tibial nerve are within 5mm of the posterior capsule. Use transillumination and accessory posterior portals only when essential.
Knee arthroscopy uses a standard two-portal technique with the anterolateral (AL) portal for viewing and anteromedial (AM) portal for working instruments. The AL portal is placed 1cm lateral to the patellar tendon at joint line level and is established first; the AM portal is then created under direct visualization 1cm medial to the patellar tendon. The infrapatellar branch of the saphenous nerve (IPBSN) runs transversely 3-5mm below the joint line and is commonly injured, causing anterolateral knee numbness. Portals must be at joint line level—too proximal damages the patella, too distal injures the meniscus or fat pad. Triangulation (working through AM while viewing through AL) is the fundamental skill. Posterior portals risk popliteal neurovascular structures and should only be used when essential.
Memory Hook:PORTALS reminds you of the systematic approach to knee arthroscopy portal creation
Memory Hook:SAFETY reminds you of what can go wrong in knee arthroscopy
Knee arthroscopy is one of the most commonly performed orthopedic procedures worldwide. It allows minimally invasive diagnostic and therapeutic access to all knee compartments.
Primary indications:
Evidence for Arthroscopy
Recent evidence (FIDELITY trial, MOSAIC trial) has questioned the role of arthroscopic partial meniscectomy in degenerative meniscal tears. For Exam, know that APM is NOT superior to sham surgery for degenerative tears but remains indicated for mechanical symptoms from acute traumatic tears and for meniscal repair in young patients.
Advantages:
Disadvantages:
Surface anatomy for portal placement:
Portal positions (standard two-portal technique):
| Portal | Position | Purpose |
|---|---|---|
| Anterolateral (AL) | 1cm lateral to patellar tendon, at joint line | Viewing portal |
| Anteromedial (AM) | 1cm medial to patellar tendon, at joint line | Working portal |
| Superolateral | 2cm above joint line, lateral | Outflow, visualization of patella |
| Superomedial | 2cm above joint line, medial | Rarely used - quadriceps in the way |
| Posteromedial | Posterior to MCL, at joint line | Posterior horn access, PCL surgery |
| Posterolateral | Posterior to LCL, at joint line | Popliteus access, posterolateral corner |
Structures at risk:
| Portal | Structure at Risk | Distance from Portal | Consequence of Injury |
|---|---|---|---|
| Anterolateral | Infrapatellar nerve | 3-5mm below | Lateral knee numbness (common) |
| Anteromedial | Infrapatellar nerve | 5-10mm below | Medial/anterior knee numbness |
| Posteromedial | Saphenous vein/nerve | 10-15mm anterior | Numbness, bleeding, thrombosis |
| Posterolateral | Common peroneal nerve | 25-30mm posterolateral | Foot drop (rare but devastating) |
| All posterior | Popliteal artery/vein | Variable (5-15mm) | Hemorrhage, pseudoaneurysm |
The popliteal artery lies within 5-15mm of the posterior capsule. When creating posterior portals: (1) Always use transillumination from the anterior scope, (2) Insert spinal needle under direct vision, (3) Make only skin incision with blade then use blunt trocar, (4) Stay in the plane superficial to the capsule until visualized arthroscopically.
Intra-articular anatomy (systematic examination):
Assessment:
Imaging review:
Consent points:
Essential equipment: Arthroscope (4mm, 30-degree), light source, camera, pump/gravity inflow, hand instruments (probes, shavers, graspers, cutters), tourniquet (optional).
Tourniquet use is surgeon-dependent. Benefits: bloodless field, faster surgery. Risks: tourniquet pain, potential nerve compression. Many surgeons use tourniquet only if bleeding obscures vision.
Key Concept: There is NO true internervous plane in knee arthroscopy portals.
Unlike open surgical approaches that exploit intervals between muscles supplied by different nerves, arthroscopy uses small stab incisions through skin and capsule. The concept of "internervous plane" is not applicable to portal-based approaches.
Definition: A surgical plane between muscles supplied by different nerves, allowing separation without denervation.
Applies to: Open surgical approaches (medial parapatellar, posterior hip approach, etc.)
No internervous plane: Portals are small stab incisions (5-10mm) through skin and capsule directly into the joint.
Key principle: Minimize tissue trauma by staying at joint line, using spinal needle localization, and avoiding major neurovascular structures.
Nerve considerations for portal placement:
The infrapatellar branch of saphenous nerve (IPBSN) is the main nerve at risk. It emerges from beneath the sartorius muscle and runs horizontally across the anterior knee, typically passing 3-5mm below the standard portal sites.
Viva Answer
When asked about internervous planes in knee arthroscopy, state: "The concept of internervous plane is not applicable to arthroscopic portals. These are small stab incisions directly through skin and capsule. The main nerve at risk is the infrapatellar branch of the saphenous nerve, which runs horizontally across the anterior knee. This is avoided by staying at joint line level and using horizontal skin incisions. Injury causes anterolateral numbness but typically resolves or is well-tolerated."
Standard Patient Position:
Key Setup Considerations:
Knee Position:
Access Requirements:
Draping:
Advantages: Gravity assists flexion, easy to apply varus/valgus stress, simple setup.
Disadvantages: Surgeon must stabilize leg, may be awkward for prolonged cases.
Advantages: Hands-free stabilization, consistent positioning, easier for long cases.
Disadvantages: Cost, setup time, may limit positioning options for some procedures.
Positioning for Specific Procedures:
Step 1: Joint Distension (optional)
Step 2: Anterolateral Portal (Viewing)
Palpate the soft spot 1cm lateral to the patellar tendon at the level of the inferior pole of the patella. The knee should be flexed 70-90 degrees.
Insert 18g spinal needle through the soft spot, aiming for the intercondylar notch. Confirm intra-articular position by aspirating fluid if joint distended.
Make horizontal stab incision with 11-blade, 5-10mm long, centered on the needle entry point. Horizontal incision is parallel to IPBSN.
Insert blunt trocar with sheath, aiming toward intercondylar notch. Feel the capsule give way as you enter the joint. Do NOT force.
Remove trocar, insert 4mm 30-degree arthroscope. Connect camera, light source, and inflow. Confirm intra-articular position.
Step 3: Anteromedial Portal (Working) - UNDER DIRECT VISION
From AL portal, look toward the medial compartment. Identify the medial femoral condyle, anterior horn of medial meniscus, and fat pad.
Insert spinal needle under direct visualization 1cm medial to the patellar tendon at joint line level. Watch the needle enter the joint on screen.
The needle should enter above the anterior horn of medial meniscus, avoiding fat pad entrapment. Adjust entry point if needed before skin incision.
Make horizontal stab incision over needle, 5-10mm long. Remove needle and keep incision open.
Insert blunt trocar through the portal under direct vision. Can use portal cannula or work with instruments directly.
The AM portal must be created under direct arthroscopic vision. Blind AM portal placement risks injury to the anterior horn of the medial meniscus, articular cartilage, or fat pad. Always localize with spinal needle first and visualize the needle entering the joint.
The working portal position is confirmed, and instruments can now be triangulated.
When standard two-portal arthroscopy provides insufficient access, several options exist:
1. Additional Anterior Portals
2. Posterior Portals (see above)
3. Inside-Out and Outside-In Techniques
4. Mini-Open Conversion
5. Pump Pressure Optimization
| Procedure | Viewing Portal | Working Portal | Accessory Portals |
|---|---|---|---|
| Meniscal repair (medial) | Anterolateral | Anteromedial | Posteromedial (suture retrieval) |
| ACL reconstruction | Anterolateral | Far AM (accessory) | Anteromedial, sometimes superolateral |
| PCL reconstruction | Anterolateral | Anteromedial | Posteromedial essential |
| Posterior loose body | Anterolateral | Posteromedial | Posterolateral may be needed |
| Complication | Incidence | Prevention | Management |
|---|---|---|---|
| IPBSN injury/numbness | 10-30% | Horizontal incisions, stay at joint line | Counseling, typically well-tolerated |
| Infection | Less than 1% | Sterile technique, prophylactic antibiotics | Arthroscopic washout, IV antibiotics |
| DVT/PE | Less than 1% | Early mobilization, chemical prophylaxis if high risk | Anticoagulation, IVC filter if indicated |
| Hemarthrosis | 2-5% | Meticulous hemostasis, drain suprapatellar pouch | Aspiration, compression, rarely re-arthroscopy |
| Stiffness/arthrofibrosis | 1-2% | Early ROM, avoid excessive synovitis | Physical therapy, MUA, arthroscopic lysis |
| Compartment syndrome | Rare | Monitor pump pressure, recognize extravasation | Immediate decompression, fasciotomies |
| Neurovascular injury | Rare | Proper portal technique, avoid posterior structures | Vascular surgery consult, nerve exploration |
Compartment Syndrome - Key Points:
During knee arthroscopy, periodically palpate the calf and thigh for swelling. If significant extravasation is detected, lower pump pressure, consider switching to gravity inflow, and expedite the procedure. Postoperatively, monitor for compartment syndrome symptoms.
Instrument Breakage:
Practice these scenarios to excel in your viva examination
"The examiner asks: 'Describe your technique for establishing portals for knee arthroscopy.'"
"A patient develops severe calf pain and swelling 4 hours after knee arthroscopy. The calf is tense to palpation. What is your concern and management?"
"You are performing an ACL reconstruction. What portals do you need and why?"
"A 52-year-old presents with a degenerative medial meniscal tear on MRI. They ask whether arthroscopy will help. How do you counsel them?"
Portal Order Question
Q: Which portal should be established first during knee arthroscopy? A: The anterolateral portal is always established first as the viewing portal. The anteromedial portal is then created under direct arthroscopic vision. Never create the AM portal blind.
IPBSN Question
Q: What nerve is most commonly injured during knee arthroscopy, and what is the consequence? A: The infrapatellar branch of the saphenous nerve (IPBSN) is injured in 10-30% of cases, causing anterolateral knee numbness. Prevention: horizontal skin incisions, staying at joint line level.
Evidence Question
Q: According to the FIDELITY trial, what is the role of arthroscopic partial meniscectomy for degenerative meniscal tears? A: The FIDELITY trial showed APM is no better than sham surgery for degenerative meniscal tears. Non-operative management with physiotherapy is recommended first-line.
Compartment Syndrome Question
Q: How is compartment syndrome prevented during knee arthroscopy? A: Monitor pump pressure (keep less than 60mmHg), periodically palpate leg compartments for swelling, limit operative time, and recognize capsular tears that increase extravasation risk.
Meniscal Repair Zone Question
Q: Which zone of the meniscus has the best healing potential and why? A: The red-red (peripheral) zone has the best healing potential due to its blood supply from the perimeniscal capillary plexus. The red-white (middle) zone has intermediate potential, while the white-white (central) zone has poor healing due to avascularity.
Patient Positioning Question
Q: What are the two main positioning options for knee arthroscopy, and when is each preferred? A: Supine with leg hanging (60-90° flexion) is preferred for most procedures - allows gravity to open joint. Supine with leg support is used for ACL reconstruction when tibial tunnel drilling requires stable position. Both options should maintain thigh support.
Knee arthroscopy is one of the most common orthopedic procedures in Australia with over 100,000 procedures performed annually. However, rates have declined significantly following publication of high-quality RCTs (FIDELITY, METEOR) demonstrating limited benefit for degenerative meniscal tears compared to sham surgery or physiotherapy. Australian practice has shifted toward meniscal repair over resection in younger patients with traumatic tears, aligned with international guidelines.
The Australian orthopaedic community has been at the forefront of implementing evidence-based practice changes, with many surgeons now offering structured rehabilitation as first-line treatment for degenerative tears. This represents a significant shift from historical practice patterns and aligns with recommendations from the Royal Australasian College of Surgeons regarding informed consent for procedures with limited evidence of efficacy.
Consent considerations in Australia must include explicit discussion of evidence regarding degenerative tears, documentation that non-operative management was offered and declined, and realistic expectation setting regarding outcomes given the natural history of osteoarthritis progression.
Orthopaedic Relevance
For Orthopaedic Operative Surgery station, you must be able to describe portal placement in detail: patient positioning, AL portal first (landmarks, technique), AM portal under direct vision, systematic joint examination sequence, and common complications. Know the evidence regarding APM for degenerative tears and be prepared to discuss non-operative alternatives.
High-Yield Exam Summary