Overview & Indications
Knee arthroscopy is the most commonly performed orthopaedic surgical procedure in the world, with approximately 4 million procedures performed annually worldwide. Since its modern development by Masaki Watanabe in Tokyo in the 1950s and subsequent popularisation by Robert Jackson in North America in the 1970s, it has transformed the management of knee pathology — replacing open arthrotomy for the majority of intra-articular knee procedures and enabling minimally invasive diagnosis, biopsy, and treatment of meniscal, chondral, ligamentous, and synovial pathology. Despite its widespread use, knee arthroscopy requires a thorough understanding of intra-articular anatomy, systematic examination technique, portal placement principles, and the management of its recognised complications.
- Indications for diagnostic and therapeutic knee arthroscopy: (1) MENISCAL PATHOLOGY — meniscal tear repair, partial meniscectomy, meniscal root repair; (2) LIGAMENTOUS — ACL reconstruction (the most commonly performed therapeutic knee arthroscopy procedure), PCL reconstruction, posterolateral corner reconstruction (arthroscopic-assisted); (3) CHONDRAL PATHOLOGY — microfracture, chondral debridement, osteochondral autograft transfer (OATS), assessment of cartilage status before osteotomy or arthroplasty; (4) DIAGNOSTIC — when clinical and MRI findings are discordant; assessment of intra-articular pathology before definitive treatment decisions; (5) SYNOVIAL — synovectomy (RA, PVNS/TGCT, haemophilic arthropathy); synovial biopsy; (6) LOOSE BODIES — removal of loose bodies (osteochondritis dissecans fragments, degenerative loose bodies, synovial chondromatosis); (7) SEPTIC ARTHRITIS — washout and debridement; (8) PATELLOFEMORAL — lateral retinacular release, trochleoplasty-assisted; (9) FRACTURE — arthroscopic-assisted tibial spine fracture fixation, tibial plateau fracture assessment
- Contraindications: absolute — local skin infection at portal site (risk of septic arthritis); severe fibrous ankylosis preventing joint distension; relative — severe osteoporosis (risk of iatrogenic fracture with traction); coagulopathy (manageable with haematological optimisation pre-operatively); significant cardiac or pulmonary disease (anaesthetic risk); previous knee surgery with severe adhesions (relative — requires careful portal planning)
Patient Positioning & Theatre Setup
- Standard supine position: the patient is positioned supine on the operating table; the hip is slightly flexed and externally rotated (frog-leg position) to facilitate the figure-of-four position (external rotation of the hip with the foot resting on the opposite leg) for accessing the medial compartment; a lateral post (leg holder mounted to the table rail at the level of the mid-thigh) is used to hold the knee in the figure-of-four position and to apply a valgus stress when accessing the medial compartment; the lateral post is positioned at the lateral mid-thigh — NOT at the lateral knee (this would compress the common peroneal nerve); the foot is free to allow knee flexion and extension and for the figure-of-four position; the contralateral leg is positioned carefully (padded knee support to prevent peroneal nerve compression from the figure-of-four position of the operative leg resting against it)
- Alternative — leg holder (arthroscopic leg holder / cradle): an arthroscopic leg holder positions the thigh in a fixed position on the table, leaving the lower leg free to hang; the knee is flexed to 90° for portal placement and maintained at various angles during the procedure; the leg holder allows excellent access to the posterior compartments; the `hanging leg` technique relies on gravity to open the medial and lateral compartments rather than a lateral post
- Tourniquet: a pneumatic thigh tourniquet at 250–300 mmHg (or systolic + 100 mmHg) is routinely used for most knee arthroscopy procedures; provides a bloodless field; inflate AFTER limb exsanguination with an Esmarch bandage or limb elevation; tourniquet time should be minimised (generally kept below 90 minutes to reduce risk of tourniquet palsy and ischaemic muscle injury); for short diagnostic arthroscopies or procedures where visualisation is not significantly impaired by bleeding, some surgeons operate without a tourniquet
- Equipment: 30° arthroscope (standard; provides a wide field of view and is used for the majority of knee arthroscopy); 70° arthroscope (for viewing the posterior compartments and under the meniscus — particularly useful for posterior horn of the medial meniscus and posterior compartment loose body retrieval); standard 4.5 mm cannulated arthroscope for adult knees; light source and camera (4K or HD); shaver system (motorised resector with interchangeable blades — full-radius resector for meniscal debridement, burr for chondroplasty and microfracture, abrader); radiofrequency probe (for haemostasis, synovial debridement, and thermal shrinkage); pump system for joint distension (saline or water — saline preferred to reduce hyponatraemia risk with extravasation); standard and specialised instruments (basket forceps, graspers, probes, curettes)
Knee Arthroscopy Portals — Anatomy & Technique
Correct portal placement is the single most important technical determinant of successful knee arthroscopy. Poorly placed portals result in iatrogenic articular cartilage damage, inadequate visualisation, instrument crowding, and neurovascular injury. The standard portals are established with the knee at 90° of flexion, which maximises the joint space between the patella and the trochlear groove and defines the soft-spot anterior to the femoral condyles at the level of the joint line.
| Portal | Location & Landmarks | Technique | Primary Use | Neurovascular Risk |
|---|---|---|---|---|
| Anterolateral (AL) portal — STANDARD VIEWING PORTAL | LATERAL to the patellar tendon, at the level of the INFERIOR POLE OF THE PATELLA, just above the joint line; the `soft spot` is palpated just lateral to the patellar tendon at the level of the joint line — a depression between the lateral femoral condyle, the patellar tendon, and the tibial plateau; the knee is at 90° flexion; the portal is 0.5–1 cm above the joint line laterally to avoid the anterior horn of the lateral meniscus | The joint is first DISTENDED with saline (30–50 mL injected through an 18-gauge needle in the superomedial portal position — just medial to and above the patella; the joint should fill easily and the needle should aspirate freely; if resistance is felt, the needle is not intra-articular); a STAB incision (longitudinal, parallel to the patellar tendon fibres — NOT transverse) is made with a No.11 blade through the skin and subcutaneous tissue down to but not through the capsule; a trocar and cannula are inserted through the incision angled slightly superiorly and medially; once the trocar enters the joint (a give is felt as it passes the capsule), it is angled inferiorly and posteriorly to advance into the joint; the trocar is replaced by the arthroscope | PRIMARY VIEWING PORTAL for the entire knee; provides access to the medial compartment (via valgus stress and figure-of-four position), lateral compartment, intercondylar notch, and suprapatellar pouch; the arthroscope spends the majority of the procedure in the AL portal | Infrapatellar branch of the saphenous nerve (IPBSN) — runs transversely across the front of the knee just below the joint line on the medial side; at risk with MEDIAL portals more than lateral; lateral portal is generally safe from major neurovascular structures; articular cartilage of the femoral condyle — risk if portal is placed too proximally (above the joint line) and the trocar impinges on the articular surface during insertion |
| Anteromedial (AM) portal — STANDARD WORKING PORTAL | MEDIAL to the patellar tendon, at the level of the joint line; the `soft spot` medial to the patellar tendon at the joint line is palpated; established UNDER DIRECT ARTHROSCOPIC VISUALISATION after the AL portal is established; a spinal needle (18-gauge) is inserted through the anticipated AM portal site under direct vision from the AL arthroscope — the needle should enter the joint in a clear space and should be visible in the medial compartment; the needle`s trajectory and angle within the joint should allow comfortable access to the medial meniscus, ACL, and intercondylar notch | ALWAYS establish the AM portal under direct arthroscopic visualisation (not blindly); use a spinal needle first to confirm the optimal angle and position before committing to a stab incision; the portal is placed just ABOVE the anterior horn of the medial meniscus (NOT through it — this would create a meniscal tear); the needle enters at 45° to the coronal plane, angled laterally — the trajectory must clear the medial wall of the lateral femoral condyle and the femoral attachment of the ACL | PRIMARY WORKING PORTAL — probing, meniscal surgery (partial meniscectomy, repair), ACL graft passage, loose body retrieval, medial compartment procedures; provides the complementary access point across the intercondylar notch from the AL viewing portal | Infrapatellar branch of the saphenous nerve (IPBSN) — the most commonly injured neurovascular structure in knee arthroscopy; crosses the anterior medial knee approximately 1–2 cm below the joint line; risk is highest with LOW medial portals; placing the AM portal AT or JUST ABOVE the joint line reduces IPBSN risk; injury causes numbness over the medial-anterior knee (usually temporary but can be permanent) |
| Superomedial (SM) portal | MEDIAL to the patella at the level of the SUPERIOR POLE of the patella; 1–2 cm above the superior pole of the patella, medial to the quadriceps tendon | A large-bore needle (14-gauge or specifically designed arthroscopy cannula) is inserted into the suprapatellar pouch for INFLOW of distension fluid; the portal can also accept the arthroscope for viewing the patellofemoral joint (particularly useful for assessing trochlear morphology and patellar tracking) | INFLOW portal (primary route for distension fluid); patellofemoral joint assessment (viewing portal when the arthroscope is placed here); evacuation of effusions; access for instruments working in the suprapatellar pouch (e.g. synovectomy, loose body removal from the pouch) | Generally safe; the saphenous vein and nerve are medial and inferior — the SM portal is above them; risk of quadriceps tendon penetration if placed too proximally |
| Superolateral (SL) portal | LATERAL to the patella at the level of the superior pole; 1–2 cm above the superior pole of the patella, lateral to the quadriceps tendon | Same technique as SM portal; inserted into the suprapatellar pouch | Inflow or outflow portal; viewing portal for the patellofemoral joint from the lateral side; access for instruments in the lateral suprapatellar pouch; some surgeons use the SL portal as the primary inflow and SM portal as the viewing portal for patellofemoral assessment | Generally safe; lateral femoral cutaneous nerve branches are lateral to the field |
| Posteromedial (PM) portal | The knee is FLEXED to 90°; the portal is placed in the POSTEROMEDIAL SOFT SPOT — a palpable depression just POSTERIOR to the medial femoral condyle and just ABOVE the posterior joint line; the saphenous vein and nerve are immediately adjacent medially; the portal is established by trans-illumination — the arthroscope is placed in the medial compartment and the light from the scope illuminates the posterior capsule from within; the illuminated soft spot posteriorly guides needle placement; a spinal needle is inserted under direct visualisation through the illuminated area into the posterior compartment | Established by trans-illumination or direct arthroscopic visualisation through the intercondylar notch; the needle must enter POSTERIOR to the posteromedial capsule and ANTERIOR to the posterior capsule — into the posteromedial compartment; the posteromedial compartment is entered by passing the arthroscope from the intercondylar notch through the posteromedial capsular `window` between the ACL and the medial femoral condyle | Posterior horn of medial meniscus assessment and repair (particularly for vertical longitudinal tears that extend into the posterior horn); posterior compartment loose body retrieval; posterior capsule procedures; all-inside meniscal repair devices are passed through the PM portal for posterior horn repairs | SAPHENOUS VEIN and SAPHENOUS NERVE — immediately posterior and medial to the PM portal; the most important neurovascular risk in the PM portal; use trans-illumination to identify the vein before portal establishment; a longitudinal stab incision reduces vein injury risk compared to a transverse incision; strict technique (posterior to the medial femoral condyle, not too inferior) reduces injury risk; popliteal artery risk is low but the artery is posterior — excess posteriorly directed force should be avoided |
| Posterolateral (PL) portal | POSTERIOR to the lateral femoral condyle, just ABOVE the posterior joint line; the common peroneal nerve passes around the fibular head — it is approximately 1.5–2 cm inferior to the PL portal; established by trans-illumination in the same manner as the PM portal | Trans-illumination technique; spinal needle under direct visualisation; the needle passes posterior to the iliotibial band and anterior to the biceps femoris tendon — between these two structures | Posterior horn of lateral meniscus; posterior compartment; posterolateral corner structures; loose bodies in the posterior compartment; PCL procedures; viewing posterior joint from the lateral side | COMMON PERONEAL NERVE — the most important risk with the PL portal; the nerve passes around the fibular neck approximately 1.5–2 cm below the PL portal; placing the portal TOO LOW risks the peroneal nerve; popliteal artery and vein are immediately posterior; strict attention to portal placement at the correct level and using trans-illumination reduces risk |
The 10-Point Systematic Diagnostic Examination
A systematic and complete examination of the entire knee joint is mandatory at every knee arthroscopy — even when the pre-operative diagnosis is clear. Unexpected pathology is found in a significant proportion of cases when a thorough systematic examination is performed. The 10-point examination described below covers all accessible intra-articular compartments and structures and should be performed in a consistent order so that no area is omitted.
| Step | Area Examined | Technique | Key Findings to Note |
|---|---|---|---|
| 1 | Suprapatellar pouch | Advance the arthroscope proximally from the AL portal into the suprapatellar pouch with the knee in extension; rotate the scope to view the walls and floor of the pouch | Synovitis (villous hypertrophy, hyperaemia — RA, infection, PVNS/TGCT, gout); loose bodies (free fragments of cartilage or bone in the pouch); plica (suprapatellar plica — a shelf of synovium across the pouch; the medial plica is more clinically significant — see Step 4); haemarthrosis (fat droplets visible in the distension fluid indicate osteochondral injury — `liphaemarthrosis`) |
| 2 | Patellofemoral joint | Flex the knee to about 30–45° and position the arthroscope to view the patella and trochlear groove; observe patellar tracking with passive knee extension and flexion | Patellar articular cartilage grading (Outerbridge/ICRS — Grade I softening/blistering; II partial thickness fissuring <50%; III deep fissuring >50%; IV full-thickness loss to bone); trochlear cartilage damage; lateral patellar tilt; patellar subluxation pattern; bipartite patella; MPFL injury assessment |
| 3 | Lateral gutter | The lateral recess between the lateral femoral condyle and the joint capsule; sweep the scope laterally and inferiorly | Loose bodies (the lateral gutter is a common collection point for loose fragments); synovitis; the popliteus tendon is visible in the lateral gutter as it enters the popliteal hiatus in the lateral meniscus — an important landmark and structure to preserve during lateral meniscal surgery |
| 4 | Medial gutter and medial plica | Sweep the scope medially to the medial recess; the medial plica is a shelf of synovium on the medial wall of the joint, running inferiorly from the suprapatellar pouch to the fat pad | Medial plica — assess its thickness, vascularity, and whether it is impinging on the medial femoral condyle articular cartilage; a pathological medial plica is thickened, fibrotic, and bowstrings across the medial femoral condyle, causing a characteristic cartilage wear track; medial gutter loose bodies; synovitis |
| 5 | Medial compartment — medial femoral condyle & medial tibial plateau | Apply valgus stress to the knee and position the leg in the figure-of-four position to open the medial compartment; advance the scope into the medial compartment | Articular cartilage of the medial femoral condyle (weight-bearing surface — most common site of medial compartment OA); medial tibial plateau cartilage; the medial femoral condyle — the posterior weight-bearing surface is assessed by flexing the knee beyond 90°; medial femoral condyle osteochondritis dissecans (OCD) — most common site (posterolateral aspect of medial femoral condyle — the `classic location`) |
| 6 | Medial meniscus — anterior horn, body, posterior horn | Systematic examination of the medial meniscus from anterior horn to posterior horn; probe the meniscus from the AM portal to assess its stability (normal meniscus should not be displaceable — it should be firm and immobile under probe pressure) | Medial meniscus tear classification (bucket-handle, radial, longitudinal, horizontal, complex); posterior horn tears are the most common site and must be assessed with care; probe the inferior surface (tibial side) which is the most common surface for horizontal tears; assess meniscal root attachment (anterior and posterior medial meniscal roots) — root tears cause extruded meniscus and behave like total meniscectomy; posterior horn — requires knee flexion beyond 90° and sometimes PM portal to assess fully |
| 7 | Intercondylar notch — ACL, PCL, fat pad | Withdraw the scope from the medial compartment into the intercondylar notch; examine the ACL, PCL, and the fat pad of Hoffa | ACL integrity — a normal ACL has a tight, glistening, well-tensioned appearance with visible longitudinal fibres; an ACL tear shows discontinuity, laxity (the `empty notch sign` — no taut fibres visible in the notch), or haemorrhage and swelling; assess both AM and PL bundles; PCL — the PCL is viewed posteriorly from the notch and is large, well-tensioned, and ribbon-like; fat pad of Hoffa — assess for impingement (Hoffa`s disease), loose bodies within the fat pad, and scarring; notch dimensions — a narrow notch (notch stenosis) is associated with ACL tear risk in some populations |
| 8 | Lateral compartment — lateral femoral condyle & lateral tibial plateau | Apply varus stress and internally rotate the leg slightly to open the lateral compartment; the scope is advanced laterally from the intercondylar notch into the lateral compartment | Lateral femoral condyle articular cartilage; lateral tibial plateau; the `kissing contusion` pattern from ACL injury (lateral femoral condyle + posterolateral tibial plateau bone bruising on MRI corresponds to the arthroscopic finding of chondral abrasion at these locations); osteochondral defects; lateral compartment OA |
| 9 | Lateral meniscus — anterior horn, body, posterior horn, popliteal hiatus | Systematic examination of the lateral meniscus; identify the popliteus tendon at the popliteal hiatus (the gap in the lateral meniscus where the popliteus tendon enters the joint — a normal anatomical feature); probe the lateral meniscus | Lateral meniscal tears; discoid meniscus (the `smiling shelf` appearance instead of the normal thin crescent of lateral meniscus — the discoid meniscus covers the lateral tibial plateau extensively); popliteal hiatus — the popliteus tendon is identified here and must be recognised as normal anatomy (it is NOT a tear); lateral meniscal root tears; posterior horn lateral meniscal tears are common in ACL injuries (up to 60% lateral meniscal tears with ACL rupture) |
| 10 | Posterior compartments (PM and PL) | The arthroscope is passed from the intercondylar notch THROUGH THE POSTEROMEDIAL WINDOW — between the ACL and the medial femoral condyle — into the posteromedial compartment; this requires the 30° scope and careful negotiation through the tight capsular window; a PM portal instrument can then access the posterior compartment for examination or intervention | Posterior compartment loose bodies (a common location — loose bodies may be hidden in the posterior compartment and missed if it is not examined); posterior capsule integrity; posterior horn medial and lateral meniscus from behind; the PCL footprint and origin on the posterior tibia; posterior capsular scarring (arthrofibrosis); cyst communications (popliteal cyst communicating with the joint via the posteromedial capsule between the medial gastrocnemius and the semimembranosus) |
Operative Steps — Common Procedures
- Partial medial meniscectomy: (1) visualise the tear from the AL portal; (2) probe the tear from the AM portal to define its extent, morphology, and position; (3) determine resectability vs repairability (tears in the outer third red-red zone are repairable; white-white inner zone tears have no vascularity and are not repaired — meniscectomy only; red-white intermediate zone may be repaired in young patients); (4) for partial meniscectomy — resect the unstable torn fragment back to a stable rim using basket forceps or shaver; the aim is to leave a stable, smooth meniscal rim with no unstable flap; (5) use basket forceps for the initial bite then the shaver to smooth the remaining rim; probe the finished meniscus to confirm stability; the principle is `minimal meniscal resection` — leave as much stable meniscus as possible to preserve the load distribution and hoop stress function of the meniscus
- Meniscal repair (all-inside technique): (1) prepare the tear site — refresh the tear surfaces with a rasp or small shaver to create bleeding surfaces that will heal (fibrovascular clot forms in the tear and heals the surfaces); (2) introduce the all-inside repair device (FasT-Fix, MaxFire, etc.) through the appropriate portal — typically the ipsilateral anterior portal and/or the posteromedial portal for posterior horn tears; (3) the all-inside device deploys a suture anchor or implant on each side of the tear; the suture is tensioned and tied, approximating the tear surfaces; (4) multiple sutures are placed at approximately 5 mm intervals along the length of the tear; (5) probe the repair to confirm apposition and stability; post-operatively: non-weight-bearing for 6 weeks; no deep flexion for 4 months (to protect the meniscal repair from shear forces)
- Microfracture for chondral defects: (1) debride the chondral defect to a stable, vertical, well-defined margin — create a perpendicular `shoulder` at the defect edge using a curette or shaver; remove all loose cartilage to the calcified cartilage layer but do NOT penetrate the calcified cartilage (leave this as the base for MSC attachment); (2) remove the calcified cartilage layer with a curette to expose the subchondral bone; (3) using an arthroscopic awl, create perforations (microfractures) in the subchondral bone at 3–4 mm intervals and 2–4 mm depth across the entire defect base; the microfractures should bleed freely — the bleeding indicates penetration into the subchondral marrow space (which contains mesenchymal stem cells that will form the fibrocartilage repair tissue); (4) release tourniquet at the end of the procedure to confirm active bleeding from the microfractures; post-operatively: continuous passive motion (CPM) for 6–8 hours/day for 6 weeks; partial weight-bearing for 6–8 weeks; the fibrocartilage repair tissue (type I collagen-dominant) fills the defect over 3–6 months
- ACL reconstruction (arthroscopic-assisted): (1) diagnostic arthroscopy and documentation of all associated pathology; (2) address any associated meniscal pathology (meniscal repair or partial meniscectomy before ACL reconstruction); (3) harvest the graft (quadrupled hamstring — ST/G, or BPTB, outside the joint through a separate incision); (4) notchplasty if required (remove the posterior wall of the intercondylar notch to create space for the graft and prevent notch impingement); (5) tibial tunnel drilling — guide pin and reamer through the AM portal or through a tibial tunnel guide, positioned in the footprint of the ACL on the tibial plateau (the centre of the ACL footprint — just anterior to the PCL, at the posterior aspect of the anterior horn of the lateral meniscus); (6) femoral tunnel drilling — through the AM portal (preferred — provides a more anatomical posterior wall position) or through the tibial tunnel (less anatomical but easier); the femoral footprint is on the posterior wall of the intercondylar notch at approximately the 10 o`clock (right knee) or 2 o`clock (left knee) position; (7) graft passage — the graft is passed through the tibial tunnel and pulled into the femoral tunnel using a passing wire or suture; (8) femoral fixation first (interference screw, cortical button, or aperture fix) then tibial fixation with the knee at 20–30° flexion under tension
Complications of Knee Arthroscopy
| Complication | Incidence | Mechanism / Risk Factors | Prevention & Management |
|---|---|---|---|
| Haemarthrosis | Most common complication — 0.5–1% requiring intervention; mild haemarthrosis is near-universal | Bleeding from synovial tissue, cut meniscal vessels, or subchondral bone (microfracture); inadequate haemostasis before closure; premature tourniquet deflation | Prevention: thorough radiofrequency haemostasis before closure; release tourniquet before wound closure to identify and address bleeding; compression bandage post-operatively; Management: aspiration for symptomatic haemarthrosis; re-arthroscopy for large or expanding haemarthrosis; the `haemarthrosis after knee arthroscopy` (HAKA) syndrome — severe haemarthrosis can cause significant pain, stiffness, and prolonged recovery |
| Infrapatellar branch of saphenous nerve (IPBSN) injury | 0.5–10% (most common nerve injury in knee arthroscopy); the most commonly reported nerve injury | The IPBSN crosses the anterior knee transversely, approximately 1–2 cm below the medial joint line; it is at risk with low medial portal placement or with transverse skin incisions at the medial portal; results in numbness, hypoaesthesia, or dysaesthesia over the medial-anterior knee, medial lower leg, and medial malleolus | Prevention: place medial portals AT or JUST ABOVE the joint line (not below); use LONGITUDINAL skin incisions (parallel to nerve fibres) rather than transverse incisions; blunt dissection to the capsule rather than sharp; Management: most recover spontaneously over 3–6 months; persistent dysaesthesia may be managed with desensitisation physiotherapy; surgical neurolysis is rarely required; permanent sensory deficit is a recognised outcome that should be included in pre-operative consent |
| Deep vein thrombosis (DVT) and pulmonary embolism (PE) | DVT 0.5–18% (most subclinical); symptomatic DVT ~1%; PE ~0.2% | Tourniquet use (venous stasis, endothelial injury from ischaemia-reperfusion); reduced mobility post-operatively; underlying thrombophilia; longer operative time; more complex procedures (ACL reconstruction higher risk than diagnostic arthroscopy); previous DVT | Prevention: graduated compression stockings; early mobilisation; LMWH for high-risk procedures (ACL reconstruction, complex procedures, high-risk patients with thrombophilia or previous DVT); consider aspirin for low-risk simple procedures; Management: confirmed DVT — anticoagulation (LMWH then DOAC); PE — anticoagulation ± vascular team depending on severity |
| Septic arthritis (post-arthroscopic) | 0.01–0.42% (rare); higher for complex procedures (ACL reconstruction ~0.3%); higher with prolonged operative time, allograft use, and immune compromise | Bacterial contamination at the time of surgery (most common — Staph aureus); haematogenous seeding; contaminated irrigation fluid; breach in sterile technique; portal site infection spreading intra-articularly | Prevention: pre-operative skin preparation; sterile technique; prophylactic antibiotics at induction (1g cefazolin IV); minimise operative time; Management: URGENT washout and debridement (re-arthroscopy or open arthrotomy for severe infection); IV antibiotics after joint fluid culture; joint cultures for organism identification; graft salvage vs removal in post-ACL reconstruction septic arthritis is debated — early washout within 2 weeks of infection can salvage the graft; delayed infection usually requires graft removal |
| Instrument breakage | 0.02–0.08%; rare but important when it occurs | Metallic fatigue of reusable instruments (particularly basket punches and graspers); applying excessive force to instruments (bending or torquing beyond instrument limits); using instruments for purposes for which they were not designed; poor maintenance of reusable instruments | Prevention: regular inspection and replacement of reusable instruments; avoid excessive force; use appropriately sized instruments; Management: ANY broken instrument fragment must be RETRIEVED before concluding the procedure; X-ray the knee before closure to confirm no metallic fragments remain; retain all instrument pieces to confirm complete retrieval; if retrieval is not possible arthroscopically — open arthrotomy for retrieval; a retained metallic fragment in a joint causes progressive articular cartilage damage |
| Fluid extravasation and compartment syndrome | Fluid extravasation is common and usually minor; compartment syndrome from extravasation is rare (<0.01%) but serious | Distension fluid (saline) extravasates through the portal wounds and capsular defects into the pericapsular soft tissues; large extravasation can cause massive soft tissue swelling of the leg and, rarely, compartment syndrome of the calf; risk factors: prolonged operative time; high pump pressures; complex procedures with large portal wounds; capsular damage | Prevention: minimise operative time; keep pump pressure at the lowest effective level (typically 40–60 mmHg); regular palpation of the thigh and calf for abnormal swelling; use outflow portals to reduce intra-articular pressure; Management: most extravasation resolves spontaneously; for concerning swelling — compartment pressure measurement; fasciotomy if compartment syndrome is confirmed; elevation, ice, and compression for mild extravasation |
| Articular cartilage damage (iatrogenic) | Varies widely; articular cartilage scuffing from trocar insertion is probably common but rarely documented | Trocar injury during portal establishment (particularly if the trocar impinges on the femoral condyle articular surface during insertion); instrument contact with articular cartilage during manipulation; shaver blade contact with articular surface | Prevention: careful, controlled portal establishment; angle the trocar away from articular surfaces during insertion; visualise the scope tip at all times; use a blunt-tipped obturator for scope insertion; Management: iatrogenic cartilage damage should be documented; if significant, treatment as for other chondral defects (microfracture, OATS depending on size) |
| Post-operative stiffness and arthrofibrosis | Clinically significant stiffness 2–10% after complex procedures; severe arthrofibrosis 1–3% after ACL reconstruction | Prolonged immobilisation post-operatively; inadequate early rehabilitation; cyclops lesion (a nodule of scar tissue forming anterior to the ACL graft in the intercondylar notch — causes a block to full extension — `extension loss`); haemarthrosis; infection; patient with tendency to hypertrophic scar formation (keloid tendency) | Prevention: early physiotherapy and ROM exercises post-operatively; avoid prolonged immobilisation; correct graft tunnel positioning (a tibial tunnel placed too anteriorly causes a cyclops lesion — the graft impinges in the notch in extension); Management: intensive physiotherapy; manipulation under anaesthesia (MUA) for early stiffness (<3 months); arthroscopic arthrolysis (scar tissue debridement and release of adhesions) for established arthrofibrosis; cyclops lesion — arthroscopic debridement restores extension |
| Popliteal vessel injury | <0.01%; rare but potentially limb-threatening | The popliteal artery and vein are posterior to the posterior capsule; risk with: posterior portal procedures (PM and PL portals); excessive posterior force with instruments; complex posterior compartment work; distension-related injury (the fluid separates the posterior capsule from the popliteal vessels by only a few mm) | Prevention: strict portal placement technique; trans-illumination for posterior portals; avoid excessive posterior force; Management: suspected vascular injury — urgent vascular surgical assessment; CT angiography; vascular repair; limb-threatening — damage control with temporary vascular shunt if available |
Outerbridge & ICRS Chondral Grading
| Grade | Outerbridge (1961) | ICRS (2000) | Appearance on Arthroscopy |
|---|---|---|---|
| Grade I | Softening and swelling of the cartilage; no surface disruption | Nearly normal — superficial softening or blistering; partial-thickness fissures or cracks not exceeding <50% cartilage depth | Soft, boggy feel on probe; slight pallor or discolouration; no visible fissuring; `blister` appearance (focal softening) |
| Grade II | Fragmentation and fissuring of the cartilage in an area of ½ inch or less | Abnormal — partial-thickness fissures or cracks; depth <50% cartilage thickness; small defects | Visible fissuring, fibrillation (`crab meat` or `velvet` surface texture); partial-thickness loss; soft on probing but surface is disrupted |
| Grade III | Fragmentation and fissuring of the cartilage in an area greater than ½ inch; fissuring to bone | Severely abnormal — cartilage defect >50% depth but NOT down to bone; deep fissuring | Deep fissuring to near-bone level; `crab meat` texture; subchondral bone may be partially visible through the cartilage; fibrillated flaps of cartilage may be loose |
| Grade IV | Erosion of the cartilage to subchondral bone | Severely abnormal — full-thickness cartilage loss to bone; `bone on bone` | Exposed subchondral bone visible; may have eburnation (polished ivory appearance of bone rubbing against bone); surrounding fibrillated cartilage; indicates end-stage compartment arthritis |
Exam Pearls
- Standard portals: AL (lateral to patellar tendon, inferior pole of patella — PRIMARY VIEWING); AM (medial to patellar tendon, joint line — PRIMARY WORKING; established under direct vision using spinal needle first); SM or SL (above patella — INFLOW); PM and PL (posterior portals — via trans-illumination technique)
- IPBSN injury — most common nerve complication: crosses anterior knee medially ~1–2 cm below joint line; at risk with low medial portals and transverse incisions; prevent by placing AM portal AT the joint line and using LONGITUDINAL incisions; usually temporary; include in consent
- Systematic 10-point examination: suprapatellar pouch → patellofemoral → lateral gutter → medial gutter/plica → medial compartment → medial meniscus → intercondylar notch (ACL/PCL) → lateral compartment → lateral meniscus → posterior compartments; NEVER skip steps — unexpected pathology is found when a systematic approach is used
- Meniscal vascularity zones: red-red (outer third — vascular, good healing — repair); red-white (middle third — some vascularity — repair in young patients); white-white (inner third — avascular, no healing — meniscectomy only); meniscal repair aims to leave as much stable meniscus as possible (hoop stress function)
- Instrument breakage: ANY broken fragment MUST be retrieved before closing; X-ray the knee before closure; open arthrotomy if arthroscopic retrieval fails; document all instrument counts and conditions; retained metallic fragments cause progressive articular damage
- Outerbridge/ICRS grading: I (softening — no surface disruption); II (fissuring <50% depth); III (fissuring >50% depth, near-bone); IV (full-thickness loss — bone exposed); Grade IV = indication for articular cartilage restoration or arthroplasty consideration
- Cyclops lesion after ACL reconstruction: a nodule of scar tissue forming anterior to the graft in the notch; causes EXTENSION LOSS (the patient cannot fully extend the knee); caused by tibial tunnel placement too far ANTERIOR; treatment — arthroscopic debridement; prevention — correct tibial tunnel placement (centre of ACL footprint, posterior to anterior horn of lateral meniscus)
- Post-arthroscopic septic arthritis: rare but serious (0.01–0.42%); prophylactic antibiotics at induction; URGENT washout if diagnosed; graft salvage possible with early washout (<2 weeks); later infection usually requires graft removal