ACL Reconstruction Technique

Indication. ACL reconstruction aims to restore knee stability and allow return to pre-injury activity. The modern operation is an anatomic reconstruction that places the graft in the centre of the native ACL footprints, in contrast to historical non-anatomic (isometric) techniques that placed the femoral tunnel more anterior and proximal. Most surgeons perform single-bundle reconstruction; double-bundle (separate anteromedial and posterolateral bundles) aims to replicate anatomy more closely but has not shown clear superiority in outcomes. Decide who to operate on. Reconstruction is offered when instability is symptomatic or when protecting other structures:

Timing. The optimal window is 4 to 8 weeks post-injury, once full range of motion has been restored and the effusion has settled — operating too early (before regaining motion) raises the risk of arthrofibrosis. Not every acute tear needs early surgery: the KANON trial showed that a trial of structured rehabilitation, with delayed reconstruction reserved for ongoing instability, is a valid pathway in motivated patients. Who not to operate on. Low-demand patients, older sedentary individuals, those with no symptomatic instability who will modify activities, and partial tears with minimal laxity are managed non-operatively — RICE and protected weight-bearing in the acute phase (0 to 2 weeks), then progressive strengthening, proprioception and cycling through 2 to 12 weeks, with a functional brace and activity modification on return. Recurrent giving way despite a proper rehabilitation programme is the clearest signal to reconstruct. Graft selection — the one real choice. All autografts give comparable stability; the choice is individualised. Graft diameter greater than 8mm matters more than graft type.

Address associated pathology at the same sitting. Meniscal tears accompany 40 to 60 percent of ACL injuries — repair is preferred over meniscectomy and reconstruction improves healing rates. Isolated MCL injury is managed non-operatively and the ACL reconstruction staged; LCL or posterolateral corner injury may require reconstruction. Chondral damage is debrided or treated with microfracture or osteochondral grafting as indicated. A lateral extra-articular tenodesis (LET) is added in high-risk young patients (see the STABILITY evidence below).

Algorithm

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The goal is to place a tendon graft anatomically — in the centre of the native femoral and tibial ACL footprints — and fix it under correct tension so it restores anteroposterior and rotational stability. The exposure is arthroscopic, working through standard knee portals with the graft harvested through small separate incisions. The relevant anatomy is laid out first, because tunnel placement is the whole operation.

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Native anatomy you must reproduce. The ACL originates on the posteromedial aspect of the lateral femoral condyle and inserts on the anterior tibial plateau between the tibial spines. It has two functional bundles: - Anteromedial (AM) bundle — a more anterior and proximal femoral attachment; taut in flexion; the primary restraint to anterior tibial translation and the target that guides single-bundle reconstruction.

• Posterolateral (PL) bundle — a more posterior and distal femoral attachment; taut in extension; controls rotational stability and contributes to the pivot-shift phenomenon. The femoral footprint is semicircular and approximately 18 mm long. Its critical landmark is resident's ridge (the lateral intercondylar ridge), the bony ridge marking the anterior border of the footprint — the femoral tunnel is placed posterior to it. The tibial footprint is a broad oval depression (area approximately 120 to 150 mm²), sitting posterior to the anterior horn of the lateral meniscus and lateral to the medial tibial spine. The ACL's poor intrinsic healing — its blood supply is the middle genicular artery via the synovial membrane, and its mechanoreceptor-rich innervation is the posterior articular nerve — is why ruptures are reconstructed rather than repaired.

Rehabilitation progresses through four phases on a criteria-based pathway rather than a fixed calendar.

Return to sport is criteria-based, not time-based. The modern benchmarks are a quadriceps strength index greater than 90 percent of the contralateral side, a hop-test battery greater than 90 percent, an ACL-RSI psychological readiness score greater than 70, and completion of sport-specific training without symptoms. Around 85 to 90 percent of well-selected patients return to sport, with graft survival of about 85 to 90 percent at 10 years. Functional scores (IKDC, Lysholm) typically improve from around 50 to the mid-80s, though the Tegner activity level often sits one to two levels below pre-injury. Long-term, 50 to 70 percent develop radiographic osteoarthritis by 15 to 20 years (less often symptomatic); meniscal injury at the index event is the major driver.

Complications. Recognise them early — most late failures trace back to tunnel position, graft size or premature return to sport.

Revision reconstruction succeeds in 75 to 85 percent — lower than primary, with higher failure in revision-of-revision, often requiring staged procedures (bone grafting widened tunnels first) and consideration of lateral extra-articular augmentation.

Epidemiology. Population studies across high-income countries report roughly 30 to 80 ACL reconstructions per 100,000 person-years, with rates rising fastest in adolescents. The peak age is 15 to 25 years, and in the same pivoting sports females have a two- to three-fold higher rate than males (anatomical, hormonal and neuromuscular factors). High-risk sports include football (soccer), basketball, netball, handball, rugby, Australian rules football and alpine skiing. A second ACL injury — graft rupture or contralateral tear — occurs in 15 to 20 percent of athletes under 25 returning to pivoting sport. Neuromuscular warm-up programmes (FIFA 11+, PEP, netball KNEE programmes) reduce non-contact ACL injury by approximately 50 percent and are endorsed internationally. ACL injury classification guides who is reconstructed.

Clinical assessment. The Lachman test (20–30 degrees flexion) is the most sensitive (85–95 percent); the anterior drawer (90 degrees flexion) is less sensitive (40–50 percent); the pivot shift is the most specific for rotational instability (35–95 percent); and the Lever Sign is a useful adjunct (80–90 percent). Lachman is graded by translation: grade 1 (3–5 mm), grade 2 (5–10 mm), grade 3 (greater than 10 mm). A non-contact pivoting mechanism, a palpable pop (around 70 percent), and immediate haemarthrosis within 4–6 hours (contrast with the delayed effusion of a meniscal injury) are the hallmark history. Imaging. Plain radiographs (AP, lateral, skyline) are usually normal acutely, but a Segond fracture (avulsion of the lateral tibial plateau rim) is pathognomonic, as is a tibial spine avulsion in adolescents. Pre-operatively assess notch width (a narrow notch raises impingement risk), alignment and any established arthritis. MRI is the gold standard: primary signs are non-visualisation or discontinuity of the fibres and abnormal (horizontal) orientation; the classic secondary sign is the bone-bruise pattern of kissing contusions on the lateral femoral condyle and posterolateral tibial plateau. CT is reserved for revision planning (tunnel position and size), and stress radiographs (KT-1000/2000, side-to-side difference greater than 3 mm significant) provide objective translation. Associated injury patterns.

Global society guidance and registry evidence. There is broad international consensus on the principles:

Key evidence. The STABILITY trial (Getgood, 2020) showed that adding a lateral extra-articular tenodesis to hamstring ACL reconstruction in patients 25 years or younger cut graft rupture from 11 percent to 4 percent at two years (relative risk reduction approximately 67 percent; number-needed-to-treat 14) and reduced composite clinical failure from 40 percent to 25 percent — the basis for adding LET in high-risk young knees. The MOON cohort (Mariscalco, 2013) established graft diameter as a dominant failure risk: revision in 0 percent of grafts greater than 8 mm versus 7 percent at 8 mm or smaller. The KANON trial (Frobell, 2010) showed that structured rehabilitation with delayed reconstruction is a valid pathway, and the Chen meta-analysis (2020) confirmed BTB and hamstring give comparable stability with less anterior knee pain for hamstring. The MOON autograft risk calculator (Marmura, 2021) supports shared decision-making, favouring BTB or hamstring-plus-LET over isolated hamstring in high-risk young athletes.