High-yield overview

Arthroscopic with possible open tunnel revision or staged bone grafting | advanced

Critical Danger Structures

Popliteal Artery

Location: Lies behind the posterior capsule in the popliteal fossa, separated from the posterior tibial cortex by only a few millimetres; the gap is smallest in extension and increases with knee flexion. Most at risk during tibial tunnel over-reaming, posterior debridement, and any deep femoral or transtibial drilling that breaches the posterior wall. Protection: Flex the knee to displace the artery posteriorly before posterior work. NEVER over-drill the femoral tunnel posteriorly - protect the posterior wall with a retractor and confirm an intact posterior cortical rim on fluoroscopy. Use a calibrated tibial guide and stop the reamer at the far cortex. If pulsatile bleeding occurs, inflate tourniquet and obtain immediate vascular surgery review. Document distal pulses and ankle-brachial index post-operatively.

Saphenous Nerve & Vein

Location: Posterior to sartorius tendon at medial joint line, 4-6mm from posteromedial capsule. At risk during hamstring harvest, medial portal placement, and tibial tunnel drilling. Protection: Oblique hamstring incision 3cm below joint line, blunt dissection to sartorius. Stay anterior to gracilis tendon insertion. Identify and protect during tibial tunnel reaming. Posteromedial portal with direct visualization.

Common Peroneal Nerve

Location: Wraps around fibular neck 1-2cm distal to joint line posterolaterally. Lateral portal and posterolateral corner reconstruction put it at risk. Only 10mm from posterolateral capsule. Protection: Avoid lateral portal more than 1cm below joint line. Knee flexion relaxes nerve. Palpate fibular neck during ALL procedures. If ALL reconstruction needed, identify nerve directly. Post-op foot drop = urgent EMG/exploration.

Lateral Femoral Condyle Posterior Wall

Location: Posterior cortex of lateral femoral condyle - at risk during femoral tunnel drilling, especially if drilling too posterior or with excessive reaming in revision setting with soft bone. Protection: Fluoroscopy to confirm tunnel position before reaming. Aim for 2mm posterior cortical rim. Use smaller reamer if tunnel widened. Anteromedial portal drilling allows better visualization than transtibial.

Tibial Plateau Posterior Cortex

Location: Posterior tibial cortex at risk if tibial tunnel angle too horizontal or over-drilled in revision with tunnel widening. Neurovascular structures directly posterior. Protection: Tibial guide at 55-60° angle. Fluoroscopy confirmation before over-reaming. If tunnel widened, use smaller graft or bone plug technique. Staged approach if massive widening.

Mnemonic

FAILUREFAILURE - Causes of ACL Reconstruction Failure

Mnemonic

STAGEDSTAGED - Two-Stage Revision Indications

Positioning and Preparation

Patient Position: Supine with leg holder, tourniquet high on thigh

Surgical Approach: Arthroscopic with possible open tunnel revision or staged bone grafting

Essential Equipment: CT scan for tunnel assessment, fluoroscopy, revision ACL instrumentation, bone grafting materials, backup graft options

Causes of ACL Reconstruction Failure (mechanistic framework)

Failure is usually multifactorial. Technical error (chiefly tunnel malposition) is repeatedly identified as the single largest contributor in revision series, followed by recurrent trauma and biological/unaddressed causes. Treat the figures below as approximate relative frequencies, not fixed values.

Category	Cause	Relative frequency	Key Features
Technical	Femoral tunnel malposition	Common (leading technical cause)	Too anterior, too vertical - leads to vertical graft, impingement
Technical	Tibial tunnel malposition	Moderate	Too anterior = extension impingement, too posterior = flexion loss
Technical	Inadequate notchplasty	Less common	Graft impingement in notch roof
Biological	Failed incorporation	Moderate	Graft intact but incompetent at 6-12 months
Traumatic	Re-injury	Common	New trauma to healed graft, contact sport
Unaddressed	Missed PLC injury	Moderate	Chronic posterolateral instability, varus thrust
Unaddressed	Untreated meniscal pathology	Moderate	Meniscal deficiency leads to increased graft load
Unaddressed	Uncorrected malalignment	Less common but high-impact	Varus alignment with PLC deficiency

Investigation Protocol:

CT scan: Tunnel position, widening, confluence assessment
MRI: Graft integrity, meniscal status, cartilage damage
Stress radiographs: Compare to contralateral, assess ligamentous laxity
Clinical: Pivot shift grade, varus/valgus opening, dial test for PLC

Key Evidence

Effect of graft choice on the outcome of revision ACL reconstruction in the MARS cohort

Level 2

MARS Group (Wright RW et al.) • American Journal of Sports Medicine

Clinical Implication: In revision ACL reconstruction, autograft is the default for young, active patients - allograft carries a materially higher early rerupture risk. This is the core evidence behind the revision graft hierarchy.

Verify on PubMed (PMID 25274353)

Association between graft choice and 6-year outcomes of revision ACL reconstruction in the MARS cohort

Level 2

MARS Group • American Journal of Sports Medicine

Clinical Implication: The autograft survival advantage widens with longer follow-up, strengthening the case for autograft in revision - especially BTB autograft over BTB allograft in higher-demand patients.

Verify on PubMed (PMID 34260326)

Lateral extra-articular tenodesis reduces failure of hamstring autograft ACL reconstruction: 2-year STABILITY RCT

Level 1

Getgood AM et al. (STABILITY Study Group) • American Journal of Sports Medicine

Clinical Implication: Adding a lateral extra-articular procedure to soft-tissue ACL reconstruction substantially lowers rupture and residual rotatory laxity in young high-risk knees - a strong rationale for lateral augmentation in the revision setting.

Verify on PubMed (PMID 31940222)

Anterolateral ligament reconstruction is associated with significantly reduced ACL graft rupture rates at minimum 2-year follow-up (SANTI Study Group)

Level 2

Sonnery-Cottet B et al. • American Journal of Sports Medicine

Clinical Implication: Combined ACL plus anterolateral ligament reconstruction reduces graft failure in high-risk young athletes - supporting routine consideration of anterolateral augmentation in revision with rotatory instability.

Verify on PubMed (PMID 28151693)

Consistent indications and good outcomes despite high variability in techniques for two-stage revision ACL reconstruction: a systematic review

Level 4

Gopinatth V et al. • Arthroscopy

Clinical Implication: Two-stage revision is reserved for tunnel malposition or widening that precludes an acceptable new aperture (commonly cited threshold 10-14mm), bone-grafted with iliac crest autograft or allograft dowels, with good reported functional improvement.

Verify on PubMed (PMID 36863622)

Operative Technique

Step 1: PREOPERATIVE ASSESSMENT AND FAILURE ANALYSIS

PREOPERATIVE ASSESSMENT: CT scan MANDATORY to assess tunnel position, widening, and confluence risk. MRI for graft integrity, meniscal/cartilage status. Clinical exam: pivot shift grade, varus/valgus testing, dial test for PLC. IDENTIFY CAUSE OF FAILURE: technical (tunnel malposition), biological (incorporation), traumatic (re-injury), or unaddressed pathology (missed PLC, meniscal deficiency, malalignment).

Clinical Pearl

Technical Tip: EXAM KEY: MARS Study showed 80% of failures had identifiable technical cause. Femoral tunnel too ANTERIOR is most common error. CT is ESSENTIAL - correlate 3D position with failure mechanism. Check for hardware that needs removal.

Dangers at this step

Missed cause of failure leads to repeat failure
Inadequate imaging leads to intraoperative surprises

Step 2: STAGING DECISION

STAGING DECISION: One-stage if tunnels less than 14mm and non-confluent with proposed new position. Two-stage if: (1) tunnel widening more than 14-16mm, (2) confluence likely (less than 2mm between old and new tunnel), (3) active/recent infection, (4) massive bone loss requiring grafting. Document decision and communicate with patient regarding implications.

Clinical Pearl

Technical Tip: EXAM KEY: Two-stage adds 3-6 months but allows bone incorporation for better fixation. One-stage is preferred when possible for patient convenience. Use 3D CT reconstruction to plan new tunnel position relative to old.

Dangers at this step

One-stage with inadequate bone = fixation failure
Confluence creates communication between tunnels = instability

Step 3: GRAFT HARVEST

GRAFT SELECTION HIERARCHY: (1) Contralateral BPTB - gold standard autograft, bone-to-bone healing. (2) Ipsilateral quad tendon - thick, strong, low morbidity if previous hamstring used. (3) Allograft - for older/lower demand patients (MARS: 2x failure in under 25). Prepare graft on back table: size appropriately, mark orientation. Have backup plan if primary graft unavailable.

Clinical Pearl

Technical Tip: EXAM KEY: MARS Study Level I evidence: autograft SUPERIOR to allograft in patients younger than 25. Quad tendon graft 9-10mm thick, comparable strength to BPTB. If contralateral knee, counsel about bilateral morbidity.

Dangers at this step

Saphenous nerve injury with hamstring harvest
Patellar fracture with BPTB harvest
Inadequate graft size

Step 4: DIAGNOSTIC ARTHROSCOPY AND GRAFT REMOVAL

DIAGNOSTIC ARTHROSCOPY: Standard portals, may need modified placement if scar tissue. Systematic evaluation: graft remnant (probe for competence), meniscal status, cartilage grade, PCL integrity. REMOVE FAILED GRAFT: use shaver, careful debridement of scar tissue. Preserve notch roof. Identify existing tunnel apertures and assess for sclerosis.

Clinical Pearl

Technical Tip: EXAM KEY: Probe the graft remnant - if it's intact but incompetent (soft, stretched), this is BIOLOGICAL failure. May retain some fibers if well-positioned to augment new graft. Document meniscal status - will you repair or transplant?

Dangers at this step

Popliteal injury if aggressive posterior debridement
Chondral damage from instruments
Incomplete graft removal causing impingement

Step 5: HARDWARE REMOVAL

HARDWARE REMOVAL: Remove interference screws if protruding into tunnel or if new tunnel position requires it. Bioabsorbable screws may be expanded/fragmented - curette out debris. Metal screws may require trephine or reverse threader. Document: bone quality after removal, any bone loss, tunnel dimensions after debridement.

Clinical Pearl

Technical Tip: EXAM KEY: Have multiple extraction tools available: trephines, reverse threaders, bone tamps. Femoral screw may require outside-in or mini-open lateral approach for access. Leave well-positioned screws if not interfering.

Dangers at this step

Femoral condyle fracture with aggressive extraction
Stripped screw head requiring trephine
Posterior wall blowout

Step 6: TUNNEL PREPARATION

TUNNEL MANAGEMENT OPTIONS: (1) Use existing tunnels if well-positioned and less than 12mm. (2) New tunnels if malpositioned but less than 14mm and non-confluent - drill new anatomic position. (3) Bone graft if more than 14-16mm or confluence - pack with autograft/allograft, stage 3-6 months. Confirm new position with fluoroscopy before reaming.

Clinical Pearl

Technical Tip: EXAM KEY: Anatomic femoral tunnel at 1:30-2:00 (right knee) or 10:00-10:30 (left knee), low on lateral wall. Tibial tunnel in posterior half of native ACL footprint. Use fluoroscopy to confirm 2mm posterior cortical rim before reaming femoral tunnel.

Dangers at this step

Posterior wall blowout with over-reaming
Tunnel confluence creating instability
Popliteal injury with deep femoral drilling

Step 7: NEW TUNNEL CREATION

NEW TUNNEL DRILLING: Femoral tunnel via anteromedial portal (preferred) or outside-in for difficult cases. Tibial tunnel with standard ACL guide at 55-60°. Use smaller reamers if bone quality poor or tunnels expanded. Confirm tunnel position and length with measurements and fluoroscopy. Avoid posterior wall blowout on femur, anterior plateau fracture on tibia.

Clinical Pearl

Technical Tip: EXAM KEY: Anteromedial portal drilling allows independent femoral tunnel in anatomic position. Knee at 110-120° flexion for AM portal drilling. If concerned about posterior wall, start smaller reamer or use outside-in technique with fluoroscopy guidance.

Dangers at this step

Posterior wall blowout - protect the posterior cortical rim
Popliteal artery injury - lies just behind the posterior capsule; avoid posterior wall breach and deep over-reaming
Peroneal nerve with lateral drilling

Step 8: GRAFT PASSAGE AND FIXATION

GRAFT PASSAGE: Pass graft with appropriate tension, confirm orientation. FIXATION: Start with femoral side - interference screw, suspensory button, or hybrid. Cycle graft 20-30 times to remove creep. Fix tibial side at 20-30° flexion with appropriate tension. Avoid over-tensioning which limits ROM.

Clinical Pearl

Technical Tip: EXAM KEY: Suspensory fixation (EndoButton, TightRope) useful in revision with poor bone stock. Interference screw requires adequate bone rim. Hybrid fixation (interference + backup) for maximum security. Test tension: should allow 1-2mm laxity at full extension.

Dangers at this step

Over-tensioning = loss of extension (flexion contracture)
Under-tensioning = persistent laxity
Graft twist reducing strength

Step 9: ADJUNCT PROCEDURES

ADJUNCT PROCEDURES: Meniscal repair/transplant if deficient - PRESERVE MENISCUS. High tibial osteotomy if chronic PLC with varus thrust (can be staged or concurrent). Anterolateral ligament reconstruction if: high-grade pivot shift (Grade 3), young high-risk athlete, revision setting. Address all pathology to maximize success.

Clinical Pearl

Technical Tip: EXAM KEY: STABILITY RCT - adding a lateral extra-articular tenodesis cut graft rupture from 11% to 4% in high-risk young patients (NNT 14.3). Consider lateral augmentation in all high-risk revisions. Triple varus knee (bone varus + PLC + thrust) MUST have HTO before or with ACL. Meniscal MAT for symptomatic deficiency.

Dangers at this step

Missed PLC = ongoing instability despite ACL revision
Uncorrected varus = graft overload and failure
Nerve injury with ALL reconstruction

Step 10: FINAL ASSESSMENT AND CLOSURE

FINAL ASSESSMENT: Arthroscopic confirmation of graft position, tension, and absence of impingement. Full ROM check - should achieve full extension and at least 120° flexion. Lachman and pivot shift testing - should be negative. Document findings. Standard closure with portal sites. Brace in extension.

Clinical Pearl

Technical Tip: EXAM KEY: Full extension is CRITICAL - flexion contracture severely limits function. If impingement on notch, perform notchplasty. Photo-document graft position for records. Aggressive early extension exercises post-op.

Dangers at this step

Unrecognized impingement → graft failure
Inadequate hemostasis → hemarthrosis
Flexion contracture if not achieving extension

Complications

Complications: Recognition, Prevention, and Management

Clinical Decision Scenarios

Use these scenarios to practise clinical reasoning and management decisions

CLINICAL SCENARIOStandard

CLINICAL PROMPT

"A 22-year-old male professional footballer presents 18 months after primary ACL reconstruction with hamstring autograft. He describes persistent instability with pivoting movements. Clinical exam shows Grade 2 Lachman and Grade 2 pivot shift. How would you investigate and manage this patient?"

PRACTICAL APPROACH

This young athlete with persistent instability after primary ACL reconstruction requires systematic evaluation for cause of failure and comprehensive preoperative planning. My INVESTIGATION would include: (1) CT scan - MANDATORY for tunnel assessment including position, widening, and confluence risk with proposed new tunnel position; (2) MRI - to assess graft integrity (competent vs failed), meniscal status, cartilage damage, and associated ligament injuries; (3) Stress radiographs - compare to contralateral side for objective laxity; (4) Clinical examination - pivot shift grade, varus/valgus stress testing, dial test for posterolateral corner. CAUSE IDENTIFICATION is critical: Technical failure (tunnel malposition - most common), biological failure (graft intact but incompetent at 6-12 months), traumatic re-injury, or unaddressed pathology (missed PLC, meniscal deficiency, malalignment). For MANAGEMENT, assuming CT shows malpositioned femoral tunnel (too anterior - most common error), tunnels less than 14mm, and non-confluent with proposed new position: I would recommend ONE-STAGE revision with CONTRALATERAL BPTB (gold standard autograft for young athlete based on MARS study showing 2x failure rate with allograft in under-25s). Given his high-risk profile (young, professional athlete, Grade 2 pivot shift), I would add a LATERAL EXTRA-ARTICULAR PROCEDURE - lateral extra-articular tenodesis or anterolateral ligament reconstruction (STABILITY RCT showed graft rupture fell from 11% to 4% with LET in high-risk young patients; SANTI cohort showed HT+ALL rupture 4.13% vs 16.77% for BPTB). Operative technique: Diagnostic arthroscopy to confirm graft failure and assess meniscal/cartilage status, remove failed graft, drill new anatomic femoral tunnel via anteromedial portal (position 1:30-2:00 for right knee, low on lateral wall), tibial tunnel in posterior half of footprint, pass graft with appropriate tension, suspensory femoral fixation, interference screw tibial fixation.

CLINICAL SCENARIOStandard

CLINICAL PROMPT

"The CT scan shows tunnel widening greater than 16mm on both tibial and femoral sides, with significant bone loss. What is your two-stage revision strategy?"

PRACTICAL APPROACH

With tunnel widening greater than 16mm bilaterally, the patient requires TWO-STAGE revision as one-stage would result in inadequate bone stock for fixation and high risk of tunnel confluence. STAGE 1 includes: (1) Arthroscopic debridement of failed graft remnant and scar tissue; (2) Hardware removal - extract interference screws using trephines or reverse threaders, curette any bioabsorbable screw fragments; (3) Bone grafting of both tunnels - options include iliac crest autograft (gold standard for incorporation), femoral head allograft, or synthetic bone graft substitute. Pack tunnels densely with morselized graft, confirm fill on fluoroscopy; (4) Temporary stabilization with hinged knee brace; (5) Rehabilitation: Protected weight bearing, ROM exercises, maintain quadriceps strength. BETWEEN STAGES: Wait 3-6 months for bone graft incorporation. Monitor with CT at 3 months to confirm solid incorporation before proceeding. Assess clinical status - ROM, quadriceps function, any signs of infection. STAGE 2: Once CT confirms solid bone incorporation with normalized tunnel diameter, proceed with revision ACL reconstruction using contralateral BPTB autograft (preferred in young athlete). Drill new anatomic tunnels through incorporated bone graft. Consider ALL augmentation given revision setting and prior failure. Standard fixation with interference screws now feasible with restored bone stock. POST-OPERATIVE rehabilitation follows standard ACL protocol with return to sport criteria including isokinetic testing (greater than 90% LSI), hop testing, and psychological readiness - typically 9-12 months minimum.

CLINICAL SCENARIOStandard

CLINICAL PROMPT

"A 28-year-old female presents 3 years after ACL reconstruction. She has Grade 3 pivot shift, varus thrust gait, and dial test positive at 30 degrees. MRI shows intact but incompetent ACL graft. What is your comprehensive management plan?"

PRACTICAL APPROACH

This patient has the TRIPLE VARUS KNEE: (1) constitutional bone varus, (2) posterolateral corner (PLC) deficiency (positive dial test at 30°), and (3) varus thrust gait. This is a complex multiligament failure that requires comprehensive reconstruction and alignment correction. CLINICAL ASSESSMENT: Confirm PLC deficiency with dial test at 30° and 90° (positive at 30° only = isolated PLC), varus stress testing, reverse pivot shift. Assess ACL graft with Lachman, anterior drawer, pivot shift. Full limb alignment with standing long leg radiographs - measure mechanical axis deviation and weight-bearing line. CT for tunnel assessment. MRI for graft status, meniscal/cartilage assessment, PLC structures (LCL, popliteus, popliteofibular ligament). SURGICAL PLAN - This requires STAGED or CONCURRENT approach: STAGE 1/CONCURRENT: HIGH TIBIAL OSTEOTOMY (HTO) - Correct mechanical axis to neutral or slight overcorrection (62-65% of tibial width). Medial opening wedge technique preferred - allows concurrent procedures. This is ESSENTIAL because uncorrected varus will overload any ligament reconstruction. LIGAMENT RECONSTRUCTION: ACL revision with contralateral BPTB autograft. PLC reconstruction using Larson technique or modified LaPrade (reconstruct LCL, popliteus, popliteofibular ligament). Anterolateral ligament reconstruction given high-grade pivot shift and revision setting. TECHNICAL CONSIDERATIONS: If HTO concurrent, fix osteotomy first then perform arthroscopic ACL through same incision. PLC reconstruction through posterolateral approach - identify and protect peroneal nerve. Rehabilitation is prolonged - protect osteotomy and all reconstructions, brace 6 weeks, progressive weight bearing once osteotomy healed (8-12 weeks).