ACL Reconstruction — Techniques

Anterior cruciate ligament (ACL) rupture is one of the most common and clinically significant sports injuries. ACL reconstruction (ACLR) restores knee stability to allow return to pivoting and cutting sports, and prevents secondary meniscal and chondral damage from chronic instability. The choice of graft, fixation method, and surgical technique significantly influences outcomes and long-term graft survival.

• Incidence: approximately 200,000–400,000 ACL injuries per year in the USA; approximately 30 per 100,000 population; females at 2–8× higher risk than males in equivalent sports due to neuromuscular and anatomical differences
• Mechanism: most commonly non-contact deceleration, cutting, or landing — valgus collapse mechanism is the classic biomechanical pattern; contact injuries account for approximately 30%
• Associated injuries at time of ACL rupture: medial meniscus tear (40–70%), lateral meniscus tear (24%), bone bruising (80%), chondral lesions (20–30%), MCL injury (20%)
• Natural history without reconstruction: ongoing instability, giving way episodes, secondary meniscal and chondral damage; 30% of ACL-deficient knees develop significant meniscal pathology within 2 years of injury if reconstruction is delayed
• ACLR is indicated for: young active patients wishing to return to pivoting sports, patients with functional instability affecting daily activities or sport, ACL deficiency with associated repairable meniscal tear

Graft selection is the most discussed and debated aspect of ACLR. No single graft is universally superior — each has distinct advantages and disadvantages, and selection should be individualised.

• BPTB vs hamstring: both are appropriate first-line graft choices; BPTB associated with lower re-rupture rate and higher laxity control in most systematic reviews; hamstring associated with less anterior knee pain; patient-specific factors (occupation, activity, existing knee pain) guide selection
• Graft diameter: hamstring graft diameter <8 mm associated with significantly higher re-rupture rate — if hamstring graft diameter is predicted to be <8 mm (based on patient height, sex, and MRI), switch to BPTB or QT
• Allograft in young athletes (<25 years): re-rupture rate 2–4× higher than autograft in most studies — avoid as primary graft in competitive young athletes; acceptable in older, recreational patients or revision setting

• Femoral tunnel: most critical technical factor — determines graft isometry and rotational control; anatomic femoral tunnel placement in the centre of the native ACL femoral footprint (approximately 11 o clock position in right knee, 1 o clock in left) is the goal; non-anatomic placement (vertical tunnel at roof) leads to rotational instability
• Transtibial vs anteromedial portal femoral tunnel drilling: transtibial technique creates more vertical (non-anatomic) femoral tunnel; anteromedial (AM) portal technique allows more anatomic, oblique femoral tunnel placement — superior rotational stability in biomechanical studies; AM portal now preferred in most centres
• Tibial tunnel: placed in the centre of the native ACL tibial footprint (anterior to PCL, posterior to medial intercondylar ridge — just medial to lateral tibial spine); too anterior = graft impinges on femoral notch in extension (notchplasty may be required); too posterior = vertical tunnel and risk of PCL impingement
• Tunnel aperture placement: ensure no graft-to-roof impingement in full extension by confirming clearance intraoperatively before final fixation
• Double-bundle ACLR: reconstructs both anteromedial (AM) and posterolateral (PL) bundles separately — theoretically superior rotational control; technically demanding; no definitive clinical superiority over single-bundle in large RCTs; not widely adopted

• Aperture fixation (interference screw, cross-pin) is biomechanically superior to suspensory fixation for initial stiffness — reduces "bungee cord" effect and windshield wiper motion; interference screw at both ends for BPTB provides optimal rigidity

• Pivot-shift phenomenon: rotational instability after standard ACLR remains in some patients — manifests as persistent pivot-shift despite anatomic graft; the anterolateral structures (anterolateral ligament, ALL; Kaplan fibres of ITB) are secondary rotational stabilisers
• LET (modified Lemaire technique): strip of ITB passed under the LCL and secured to the lateral femoral cortex — augments rotational control; simple and reproducible; evidence from STABILITY trial shows LET reduces re-rupture rate in high-risk patients
• STABILITY trial (Getgood, 2022): ACLR + LET vs ACLR alone in young active patients; ACL re-rupture rate significantly reduced with LET (10.6% vs 19.7% at 2 years) in high-risk patients; LET now recommended in high-risk patients (young, female, high-level sport, positive pivot shift Grade 2–3)
• ALL reconstruction: separate graft to reconstruct the ALL; more anatomic than LET; data accumulating; no definitive superiority over LET shown; technically more demanding
• High-risk criteria for adding LET/ALL: age <25, competitive pivoting sport, Grade 2–3 pivot-shift, anterior tibial slope >12°, hyperlaxity, revision setting

• Ligamentisation: graft undergoes avascular necrosis then vascularisation and remodelling (ligamentisation) over 12–24 months — weakest point is approximately 6–8 weeks post-operatively; this is the biologic basis for graduated return-to-sport protocols
• Return to sport: minimum 9 months post-ACLR before return to high-level pivoting sport is recommended by most guidelines; criteria-based return (not time-based alone): limb symmetry index >90% for quad/hamstring strength, hop tests, and Y-balance; psychological readiness assessed with ACL-RSI questionnaire
• Pre-operative rehabilitation (prehab): optimising pre-operative quad strength, ROM, and swelling reduces post-operative stiffness and improves outcomes; at least 3 weeks of prehab reduces post-operative stiffness risk
• Re-rupture rate: approximately 15–25% in athletes returning to high-level sport before 9 months; reduced to approximately 5–10% after 9 months; LET further reduces re-rupture in high-risk groups

• ACL repair (BEAR procedure, primary repair with augmentation): emerging evidence suggests selected proximal ACL tears (stump attached to femur) can be repaired with augmentation — BEAR (bridge-enhanced ACL repair) injects a biological scaffold to stimulate healing; early results comparable to reconstruction; not yet widely available; patient selection critical
• Revision ACLR: most common causes of failure — technical error (non-anatomic tunnel placement most common), biological failure, re-injury, missed concurrent pathology (posterolateral corner, ALL); assess tunnel position on CT before revision; if tunnels are malpositioned, stage the revision (allow tunnels to fill with bone graft before revision drilling)
• Steep posterior tibial slope and ACL graft failure: tibial slope >12° is an independent risk factor for ACL graft rupture — anterior tibial translation increases with increasing slope; address with slope-reducing osteotomy (posterior closing wedge proximal tibial osteotomy) in revision ACLR with steep slope to reduce re-rupture risk
• Growth plate considerations in skeletally immature: physeal-sparing and transphyseal techniques available; avoid damage to distal femoral and proximal tibial physes — use soft tissue grafts (hamstring) without bone plugs; physis-respecting tunnel placement; or physeal-sparing all-epiphyseal technique in young children

• BPTB: lower re-rupture rate, higher anterior knee pain; hamstring: less donor morbidity, quadrupled 4090 N; graft diameter <8 mm = switch graft
• Allograft: avoid in young (<25) competitive athletes — re-rupture rate 2–4× higher than autograft
• AM portal femoral drilling: more anatomic oblique tunnel vs transtibial vertical tunnel; superior rotational stability
• Too anterior tibial tunnel: notch impingement in extension; too posterior: PCL impingement and vertical tunnel
• LET (modified Lemaire): reduces re-rupture in high-risk patients; STABILITY trial 2022 — 10.6% vs 19.7% re-rupture at 2 years with LET
• Return to sport: minimum 9 months; criteria-based (quad LSI >90%, hop tests, psychological readiness); time-only approach insufficient
• Revision ACLR: most common cause = non-anatomic tunnel placement; CT tunnels before revision; stage if tunnels malpositioned
• Tibial slope >12°: risk factor for graft failure; consider slope-reducing osteotomy in revision ACLR
• High-risk for LET addition: age <25, competitive pivoting sport, Grade 2–3 pivot-shift, hyperlaxity, revision
• Ligamentisation: weakest at 6–8 weeks; remodelling 12–24 months; basis for graduated rehabilitation