Arthroscopic anatomic single-bundle reconstruction via an anterolateral viewing portal and anteromedial working portal, with a separate 3 to 4cm oblique incision over the pes anserinus for hamstring harvest.
- Anatomic single-bundle reconstruction via the trans-anteromedial (trans-AM) portal is the gold standard. Transtibial femoral drilling is obsolete - it forces a vertical, anterior tunnel (11 to 12 o'clock) that cannot restore rotational stability.
- A graft diameter of 8mm or greater is critical. Grafts smaller than 8mm carry a 2 to 3 times higher failure rate, especially in active males under 25 years.
- The femoral tunnel centre sits 1 to 2mm anterior to the over-the-top position, at 10:30 on a right knee (1:30 left knee), using resident's ridge as the anterior landmark with a minimum 2mm posterior wall.
- Tension and fix the graft at 20 to 30 degrees of flexion with an anterior drawer force after cycling it 20 to 30 times. Never fix in full extension (flexion contracture) or beyond 30 degrees (laxity).
- Suspensory cortical fixation (TightRope or Endobutton) gives greater than 1000N initial strength versus 400 to 600N for an interference screw; hybrid fixation is increasingly preferred.
- Return to sport is criteria-based, not time-based: a minimum of 9 months plus greater than 90 percent limb symmetry on strength and hop testing. Return before 9 months multiplies re-rupture risk about 7-fold.
- “Graft choice: hamstring is equivalent to bone-patellar-tendon-bone (BPTB) on objective stability with less anterior knee pain (10 versus 30 percent) and better cosmesis, but needs adequate diameter. BPTB gives bone-to-bone healing and consistent size but more kneeling pain and a 0.5 to 1 percent patella fracture risk. Quadriceps tendon is an emerging alternative with a large diameter and low donor morbidity.
- “Anatomic tunnel placement improves rotational stability - the trans-AM portal allows a proper 10:30 or 1:30 femoral position controlling both anterior translation and the pivot shift. Transtibial drilling places the tunnel too anterior and vertical (11 to 12 o'clock) with poor rotation control and higher failure.
- “Tension at 20 to 30 degrees of flexion is critical - fixing in full extension causes flexion contracture, fixing beyond 30 degrees causes laxity. Apply 20 to 30N with an anterior drawer force during tibial fixation after cycling the graft 20 to 30 times to eliminate creep.
- “Return to sport is criteria-based, not time-based - require a minimum of 9 months plus greater than 90 percent limb symmetry index on hop testing and isokinetic quadriceps and hamstring strength plus psychological readiness (ACL-RSI greater than 56). Early return before 9 months increases re-rupture risk 7-fold.
When & Why
Indication. Symptomatic ACL deficiency - a rupture with functional instability (a positive grade 2 to 3 pivot shift) affecting sport or work in an active patient, typically aged 15 to 55 years - that has failed or is unsuited to a structured rehabilitation trial. Specific scenarios: - Primary: ACL rupture with symptomatic instability (positive grade 2 to 3 pivot shift) in an active patient who wishes to return to pivoting or cutting sport.
- Combined ACL and meniscal injury requiring repair - concomitant meniscal repair improves outcomes but needs a modified rehabilitation protocol.
- Multi-ligamentous knee injury - staged management: address the collateral or posterolateral corner injury first, then reconstruct the ACL around 6 weeks later.
- Partial ACL tear with greater than 50 percent fibre disruption and demonstrable instability on examination (positive Lachman or pivot shift). Assess the whole knee, not just the ACL. Before committing, exclude or plan for associated injury - the reconstruction will fail if these are missed: - Meniscal tears in 40 to 50 percent of ACL-injured knees - identify and treat (repair where possible) at the same sitting.
- Collateral or posterolateral corner injury in 20 to 30 percent - test varus and valgus stability at 0 and 30 degrees (opening greater than 5mm indicates a grade III injury) and the posterolateral corner with the dial test.
- Cartilage damage and limb alignment (a varus malalignment with a posterolateral corner injury predicts failure and may need an associated osteotomy). The graft choice. All three autografts give equivalent objective stability in randomised trials, so selection turns on patient factors and the complications each graft carries:
Excellent initial strength (4090N), lower anterior knee pain (10 percent versus 30 percent for BPTB), better cosmesis. Main drawback: inadequate diameter (less than 8mm) in 5 to 10 percent, especially smaller patients, with a 2 to 3 times higher failure rate.
Bone-to-bone healing is faster (6 to 8 weeks versus 12 or more for soft tissue) and size is consistent; slightly lower revision rates in some registries. Costs: anterior knee pain (20 to 30 percent), persistent kneeling difficulty, patella fracture (0.5 to 1 percent).
Emerging alternative: a large reliable diameter (8 to 10mm), single-tendon harvest, low donor morbidity and excellent strength. Drawbacks: a more demanding harvest, a larger anterior incision, and less long-term outcome data.
Selection algorithm. Choose hamstring for most primary reconstructions if an adequate diameter (8mm or greater) is achievable; choose BPTB in young high-risk males in cutting sports where registry data slightly favour BPTB, or where the hamstring diameter is inadequate; increasingly consider quadriceps tendon in larger patients, revision surgery, or when the hamstring is inadequate and you wish to avoid BPTB morbidity. Avoid allograft in young active patients (a 2 to 4 times higher failure rate). Timing of surgery. Operating in the acute phase (under 3 weeks) raises the risk of arthrofibrosis - wait for the effusion to resolve and range of motion (full extension, flexion over 120 degrees) to recover. The subacute window (3 to 6 weeks) is optimal in most cases. Chronic tears (over 6 weeks) carry a standard risk profile but may have secondary meniscal or cartilage damage. Consent specifically for: loss of extension (the most important preventable complication, 5 to 10 percent), graft failure or re-rupture (5 to 15 percent overall, higher in the young), saphenous nerve numbness from harvest (5 to 10 percent), anterior knee pain (10 to 20 percent), infection (0.3 to 1 percent), DVT or PE (0.1 to 1 percent), and the risk of a contralateral ACL tear over time. Setup. Supine with a commercial leg holder (or a lateral thigh post); thigh tourniquet optional (routine use is avoided to lower VTE risk and to preserve perfusion for visualisation). Confirm full range of motion before draping - passive extension to 0 degrees and flexion over 120 degrees. Flex and externally rotate the hip 30 to 45 degrees to relax the hamstrings for harvest, and drop the foot of the bed to allow knee hyperflexion (110 to 120 degrees) for femoral drilling. Standard kit: a 30-degree arthroscope (70-degree optional for the posterior compartment), a 4.5mm shaver, graspers, a 55-degree tibial guide, flexible reamers, a closed-end tendon stripper, a graft preparation board and sizing cylinders (6 to 12mm).
The Operation
The goal is to reproduce the centre of the native ACL footprint - controlling both anterior translation and rotation - using an arthroscopic anatomic single-bundle technique through the anterolateral viewing portal and anteromedial working portal, with a 4-strand hamstring autograft fixed at 20 to 30 degrees of flexion. The exposure (positioning, portals and the harvest incision) is laid out as the opening steps; the technique is the heart of the operation.
Operative sequence
- Perform a systematic bilateral examination: Lachman (most sensitive, about 85 percent), anterior drawer at 90 degrees (less sensitive), and pivot shift (most specific for functional instability).
- Test varus and valgus stability at 0 and 30 degrees to exclude collateral injury (opening greater than 5mm is grade III) and the posterior drawer to exclude PCL injury; run the dial test for the posterolateral corner.
- Document every measurement and grade for the operative note and medicolegal record, and compare with the contralateral knee (bilateral ACL injury occurs in 0.5 to 1 percent).
- Watch for: a missed multi-ligamentous injury changes the plan (staged treatment); excessive force during the pivot shift can worsen a chondral injury in an acute knee with bone bruising.
- Make a 3 to 4cm oblique incision over the pes anserinus (3cm distal and 2cm medial to the tibial tubercle) - centring it on the pes minimises saphenous nerve injury.
- Incise the sartorial fascia in line with its fibres; palpate the gracilis (superior, thin, ribbon-like) and semitendinosus (inferior, thicker, cord-like) at their tibial insertion and clear the origin with finger dissection.
- Pass a closed-end tendon stripper over each tendon sequentially; on any resistance, release accessory bands sharply with scissors - forced stripping causes premature amputation (10 to 15 percent).
- Aim for greater than 28cm of each tendon (allows about 7cm per limb after folding for whipstitch and tunnel length); confirm the tendon end is an intact muscle belly, not a torn mid-substance.
- Watch for: the saphenous nerve runs 2 to 3cm medial to the incision deep to the sartorius - stay superficial to the sartorial fascia; a semitendinosus artery branch (from the superior medial genicular) can avulse and bleed.
- Strip all muscle from the tendons with moist gauze or a scalpel, leaving pure tendon.
- Whipstitch each end with a number 2 high-strength non-absorbable suture (Ethibond or FiberWire) using a Krackow locking technique over a minimum 2.5cm; fold each tendon at its midpoint to create a 4-strand construct.
- Measure the diameter with sizing cylinders - target 8 to 10mm (8mm or greater is mandatory; smaller grafts fail 2 to 3 times more often in young males).
- Pretension on a graft board at 20 to 30 pounds for a minimum of 10 minutes to allow creep, keeping the graft moist throughout.
- Watch for: a diameter under 8mm (consider augmenting strands or switching to quadriceps or BPTB), whipstitch under 2.5cm (slippage on tensioning), and graft desiccation (reduced strength and viability).
- Distend the joint with 30 to 60ml saline via a superolateral patellar approach.
- Anterolateral viewing portal: 5mm incision 1cm lateral to the patellar tendon at the joint line; anteromedial working portal: created under direct vision adjacent to the patellar tendon (a high anteromedial portal about 1cm more proximal reduces saphenous nerve injury and must reach the lateral wall for femoral drilling).
- Run a systematic examination: suprapatellar pouch, patellofemoral joint, medial gutter and meniscus (posterior horn first), intercondylar notch and ACL remnant, lateral gutter and meniscus, PCL, and both chondral surfaces - probe both menisci completely.
- Watch for: a missed meniscal tear (probe the posterior horn of the medial meniscus) and iatrogenic chondral scoring; the infrapatellar branch of the saphenous nerve is injured in 50 to 70 percent with the anteromedial portal - counsel the patient.
- Clear the ACL stump with a shaver and basket forceps, preserving the posterior fibres at the PCL; clear soft tissue from the lateral wall and roof to expose the bony landmarks.
- Identify the lateral intercondylar ridge (resident's ridge, the anterior border of the footprint), the over-the-top position (posterior border), and the bifurcate ridge between the AM and PL bundles if visible.
- Do not perform a routine notchplasty - only remove 2 to 3mm from the lateral wall with a burr if there is documented true bony impingement on an extension test; aggressive notchplasty removes footprint bone and enlarges the tunnel.
- Watch for: PCL injury (stay anterior to the posterior fibres), and poor visualisation of the landmarks (the whole anatomic plan depends on seeing them).
- Flex the knee 110 to 120 degrees and drop the foot of the bed to bring the lateral wall anteriorly; drill through the anteromedial portal (transtibial drilling is outdated and cannot reach this position).
- Target the centre of the femoral footprint: 1 to 2mm anterior to the over-the-top position, at 10:30 on a right knee (1:30 left knee) when viewed at 90 degrees, using resident's ridge as the anterior landmark.
- Place the guidewire first and confirm arthroscopically; ream sequentially with an offset guide and flexible reamers to 0.5 to 1mm larger than the graft, aiming for over 30mm of tunnel length.
- Confirm a minimum 2mm posterior wall by probing (a firm bone bridge, not soft tissue); record tunnel position and length.
- Watch for: posterior wall blowout (no cortical bone for the suspensory device to flip on), a non-anatomic anterior or vertical tunnel (poor rotation control), a short tunnel under 25mm, and medial femoral condyle cartilage damage from a medially divergent drill.
- Set the tibial guide at 55 degrees in the sagittal plane; the starting point is on the anterior tibia at the level of the pes incision, 1 to 2cm medial to the tibial tubercle.
- Drill the guide pin under direct arthroscopic vision; the intra-articular entry should sit at the centre of the tibial footprint - just anterior to the tibial spine, lateral to the medial spine, 7mm posterior to the anterior edge of the tibia, and posterior to the anterior horn of the lateral meniscus.
- Ream over the guidewire to 0.5 to 1mm larger than the graft.
- The critical check: in full extension, the tunnel (and so the graft) must run parallel to Blumensaat's line (the roof of the notch) on the lateral view - any divergence means roof impingement and the tunnel must be redrilled.
- Watch for: a tunnel too anterior (roof impingement, loss of extension, cyclops lesion, graft failure), too posterior (vertical graft, poor rotation control), too medial (PCL injury, medial wall blowout), and posterior cortex blowout from an uncontrolled guide pin.
- With the knee in full extension, arthroscopically confirm the graft trajectory will sit parallel to Blumensaat's line with no roof impingement.
- Probe the femoral posterior wall for a solid 2mm bone bridge; confirm both apertures are clearly visible and the tunnels are not convergent.
- If any position is suboptimal or impingement is demonstrated, redrill a correctly positioned tunnel now - it is always better to redrill than to proceed with a malpositioned tunnel.
- Pass a number 5 Ethibond passing suture retrograde from the anterior tibia through the joint and up into the femoral tunnel, exiting the far cortex.
- Secure it to the graft whipstitch and pull the graft into the tibial tunnel, through the joint, and into the femoral tunnel under arthroscopic vision with steady traction.
- Confirm the graft is not twisted (the whipstitches should be aligned - twisting cuts tensile strength by 30 to 50 percent), is fully seated at both apertures with no gap, and has no soft-tissue interposition between graft and bone.
- Preferred for hamstring graft: an adjustable cortical suspensory device (TightRope, ZipLOOP or adjustable Endobutton). Pass it through the femoral tunnel, flip the button on the far cortex (feel the click and see the confirmation mark at the skin), and seat it; tension the graft limb and lock per the manufacturer.
- Alternative: a bioabsorbable interference screw (PLLA or PDLA, 7 to 9mm by 25 to 30mm) inserted through the AM portal alongside - not through - the graft, parallel to the graft trajectory.
- Hybrid fixation (suspensory device plus interference screw) combines cortical strength with aperture fixation and is increasingly used.
- Watch for: a device not properly flipped (fixation failure on loading), screw divergence or graft laceration, and lateral cortex fracture from over-tension or an oversized screw.
- Before tibial fixation, manually cycle the graft through full range (0 degrees to over 120 degrees) 20 to 30 times with about 20 to 30N of tension to eliminate creep and precondition it.
- Position the knee at 20 to 30 degrees of flexion and apply an anterior drawer force to the proximal tibia to load the graft and restore normal tibial position.
- Hold firm manual tension (about 20 to 30N) on the tibial sutures and do not release it until tibial fixation is secured.
- Watch for: fixing in full extension (flexion contracture), fixing beyond 30 degrees (a lax graft), and inadequate cycling (early laxity from creep).
- While maintaining tension at 20 to 30 degrees with the anterior drawer force, insert a bioabsorbable interference screw (7 to 9mm by 25 to 30mm) alongside the graft, parallel to its trajectory (not divergent).
- Advance until flush with the bone or slightly countersunk (1 to 2mm) to prevent prominence; alternatives are a cortical button or a screw-and-spiked-washer post fixation as backup.
- Release tension slowly and retest range of motion and stability; pull on the graft to confirm solid fixation with no movement.
- Confirm full passive extension to 0 degrees (any deficit is unacceptable and must be corrected now) and flexion over 120 degrees.
- Arthroscopically check graft clearance from the roof in full extension (no impingement); perform a Lachman and pivot shift to confirm a firm endpoint and negative pivot shift.
- Confirm the graft is firm but not over-constrained, the tibial screw is flush, haemostasis is achieved, no loose bodies remain, and recheck the menisci for missed pathology.
- Irrigate copiously with 3 to 4 litres of saline to reduce post-operative synovitis and haemarthrosis.
- Inject a local anaesthetic mixture (20ml of 0.25 percent marcaine with 1:200,000 epinephrine; some add 4mg morphine) into the joint and portals for multimodal analgesia.
- Close the portals with a single 3-0 or 4-0 nylon suture each (poor closure risks a synovial fistula); close the harvest site in layers - repair the sartorial fascia with 2-0 vicryl, subcutaneous 3-0 vicryl, and a 3-0 monocryl subcuticular skin closure.
- Confirm haemostasis at the harvest site (a haematoma may become infected); apply a sterile dressing, a compression bandage to the upper thigh, and cryotherapy.
- Cryotherapy and elevation for 24 to 48 hours; multimodal analgesia (paracetamol 1g four times daily, NSAIDs unless contraindicated, opioids as needed and minimised).
- Mobilise weight-bearing as tolerated with crutches in a hinged brace (the brace is for comfort and fall protection and is not mandatory in all).
- VTE prophylaxis is primarily mechanical (TED stockings, early mobilisation, ankle pumps); chemical prophylaxis (LMWH or a NOAC) only for high-risk patients (previous VTE, thrombophilia).
- Start range-of-motion exercises on day 1 - quadriceps sets hourly, heel slides for flexion, prone hangs for extension - with the goal of full extension (0 degrees) by 2 weeks; refer to physiotherapy on day 1.
Lies about 1cm posterior to the posterior capsule and PCL at the joint line, exiting the popliteal fossa through the soleus arch. Never drill blindly posteriorly; keep the guide pin controlled during femoral and tibial drilling, maintain hyperflexion during femoral reaming, and place a finger posterior to the tibia during tibial reaming to feel for penetration.
Exits the subsartorial canal 8 to 10cm proximal to the medial joint line and runs 2 to 3cm medial to the pes insertion deep to the sartorius, alongside the great saphenous vein. Centre the incision on the pes anserinus, stay superficial to the sartorial fascia, and avoid medial retraction; injury causes medial leg numbness in 5 to 10 percent.
Crosses superficially 1 to 2cm below the medial joint line from posterior to anterior, supplying the anterior knee. Injury is largely unavoidable with the anteromedial portal (occurs in 50 to 70 percent) - counsel the patient, make the smallest portal possible, and consider a high anteromedial portal to reduce the area of numbness.
Forms the posterior wall of the intercondylar notch, inserting on the posterior tibia about 1cm distal to the joint line. During notch debridement stay anterior to the PCL fibres; during tibial reaming keep the guide pin lateral to the medial tibial spine and avoid an overly posterior tunnel - injury causes posterior laxity.
The hyaline cartilage of the medial femoral condyle adjacent to the notch is at risk during trans-AM portal femoral drilling. Maintain 110 to 120 degrees of flexion so the lateral wall comes anteriorly, keep the drill from diverging medially, and insert the reamer carefully to avoid iatrogenic chondral damage.
A femoral tunnel placed too posteriorly or reamed too shallowly blows out the posterior wall, leaving no cortical bone for the suspensory button to flip on - the fixation fails and the tunnel must be revised to a more anterior position. Probe the wall before reaming and confirm a solid 2mm bone bridge. Equally, a tibial tunnel that is not parallel to Blumensaat's line in full extension will impinge the graft on the roof, causing loss of extension, a cyclops lesion and eventual graft failure. Both positions must be verified before the graft is passed; redrill rather than accept malposition.
The native ACL controls anterior translation AND rotation. An anatomic tunnel at 10:30 or 1:30 restores both and abolishes the pivot shift; a transtibial tunnel is forced into a vertical 11 to 12 o'clock position that controls translation but not rotation, leaving a residual pivot shift and higher failure rates. Drilling through the anteromedial portal at 110 to 120 degrees of flexion is what allows you to reach the anatomic position - transtibial drilling simply cannot.
Cycle the graft 20 to 30 times through full range to eliminate creep, then tension and fix at 20 to 30 degrees of flexion with an anterior drawer force. Fixing in full extension risks a flexion contracture (hard to treat, a major cause of anterior knee pain); fixing beyond 30 degrees leaves a lax graft when the knee extends. Achieve 0 degrees of extension before leaving theatre and by 2 weeks post-operatively.
Aftercare & Complications
Rehabilitation Modern management uses an accelerated protocol - immediate weight-bearing as tolerated, early range of motion and no routine bracing - which multiple randomised trials show is equivalent or superior to traditional restricted protocols with lower stiffness rates. | Phase | Timing | Goals | Key programme | |-------|--------|-------|---------------| | 1 | 0 to 2 weeks | Control swelling; full extension (0 degrees); 90 degrees flexion; quad activation | WBAT with crutches, brace for comfort; quad sets hourly, heel slides, prone hangs, cryotherapy; no active hamstring work | | 2 | 2 to 6 weeks | Full ROM 0 to 130 degrees; normal gait; progress strengthening | Wean aids; closed-chain (wall sits, mini squats 0 to 60 degrees, step-ups); cycling high seat; pool walking from week 4; proprioception | | 3 | 6 to 12 weeks | Normalise strength; functional activities | Squats to 90 degrees, lunges, step-downs; open-chain quads from week 8 to 12; hamstring strengthening from week 8; perturbation training | | 4 | 12 to 24 weeks | Running program; sport-specific training | Straight-line running from week 12 to 16; plyometrics (double then single leg); agility (cutting, figure-8); isokinetic testing at 4 months | | 5 | 6 to 12 months | Return to sport (all criteria met) | Minimum 9 months; quad and hamstring greater than 90 percent LSI; hop testing greater than 90 percent LSI; full ROM; no effusion; ACL-RSI greater than 56; progressive non-contact to full competition | Most patients return to desk work around 6 weeks; elite athletes should aim for 12 months. At 2 years roughly 65 to 80 percent return to pre-injury activity level and 85 to 90 percent are satisfied, with a negative Lachman in 85 to 95 percent. Complications
- Recognition
- Acute pop and swelling, or gradual instability; positive Lachman and pivot shift; MRI shows graft disruption
- Prevention
- Anatomic tunnel placement, graft diameter 8mm or greater, proper tensioning and fixation, criteria-based RTS at a minimum of 9 months with greater than 90 percent LSI
- Management
- Revision reconstruction; evaluate tunnel malposition or bone loss; consider allograft or alternative autograft; address associated injuries
- Recognition
- Extension deficit over 5 degrees (most problematic); firm endpoint; may be a cyclops lesion or anterior interval scarring
- Prevention
- Achieve full extension by 2 weeks; do not fix in full extension; ensure no impingement; aggressive early ROM; avoid the acute inflammatory phase
- Management
- Physiotherapy first; arthroscopic adhesiolysis if no improvement by 3 months; excise a cyclops lesion; manipulation under anaesthesia rarely needed
- Recognition
- Progressive stiffness with a hard endpoint; patella infera on X-ray; generalised scarring at arthroscopy
- Prevention
- Wait for acute inflammation to resolve pre-op; early ROM, especially extension; avoid immobilisation; treat meniscal injury to reduce inflammation
- Management
- Intensive physiotherapy for 3 to 6 months; arthroscopic debridement and manipulation; some cases are refractory
- Recognition
- Pain over the anterior knee, worse with kneeling or prolonged sitting; rule out cyclops or hardware prominence
- Prevention
- Hamstring graft has a lower rate than BPTB; avoid impingement; early patellofemoral mobilisation and strengthening
- Management
- Most resolve with time and physiotherapy; quadriceps and patellar mobilisation; rarely hardware removal or PFJ arthroscopy
- Recognition
- Numbness or dysaesthesia over the medial leg; positive Tinel at the harvest site
- Prevention
- Centre the incision on the pes anserinus; stay superficial to the sartorial fascia; avoid medial dissection; counsel pre-op
- Management
- Usually a neuropraxia resolving over 6 to 12 months; permanent numbness in 2 to 5 percent but rarely symptomatic
- Recognition
- Superficial: wound erythema, drainage; deep: effusion, pain, raised inflammatory markers; higher with allograft
- Prevention
- Perioperative antibiotics; meticulous sterile technique; no intra-articular steroid within 3 months; vancomycin graft pre-soak
- Management
- Superficial: antibiotics and wound care; deep: urgent arthroscopic washout with graft retention if under 3 weeks and stable, else graft removal and staged revision with 6 weeks IV antibiotics
- Recognition
- Loss of extension with a palpable nodule in the anterior interval; terminal extension pain or a clunk; MRI shows a soft-tissue mass
- Prevention
- Anatomic tunnels avoiding impingement; remove graft debris; achieve full extension early; avoid over-constraint
- Management
- Arthroscopic excision of the fibrous nodule with debridement of the anterior interval; excellent outcome if treated early
- Recognition
- Painful prominence (especially the tibial screw); inflammatory reaction to a bioabsorbable screw; breakage
- Prevention
- Countersink screws; bioabsorbable preferred to avoid MRI artifact; insert parallel to the graft; size appropriately
- Management
- Prominent or reactive hardware: removal after 6 months when the graft has healed; breakage is usually asymptomatic
- Recognition
- Residual laxity, impingement or pain; graft not parallel to Blumensaat's line on the lateral X-ray; CT confirms position
- Prevention
- Anatomic trans-AM technique; use resident's ridge and the bifurcate ridge; verify position before graft passage
- Management
- Mild: compensate with rehabilitation; significant symptomatic malposition: single-stage or staged revision with bone grafting of the tunnels
- Recognition
- Leg swelling, pain, warmth; SOB and chest pain if PE; duplex for DVT, CTPA for PE
- Prevention
- Early mobilisation; mechanical compression; chemical prophylaxis only if high risk; avoid prolonged tourniquet
- Management
- Anticoagulation for 3 to 6 months; proximal DVT carries higher risk; an IVC filter only if anticoagulation is contraindicated
Viva & Exam Focus
HARVESTHARVEST - hamstring graft technique
TUNNELTUNNEL - anatomic tunnel positioning
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A 22-year-old male footballer presents with an ACL rupture. Walk me through your management and discuss the key complications of ACL reconstruction and how you prevent them.”
“Why do you use hamstring autograft and what are the alternatives? Compare the graft choices and justify your selection for different patient populations.”
“Explain your femoral tunnel positioning technique and why you use the trans-anteromedial portal approach. What are the consequences of non-anatomic tunnel placement?”
Indications
- ACL rupture with symptomatic instability (positive grade 2 to 3 pivot shift) in active patients aged 15 to 55
- Combined ACL and meniscal injury requiring repair (modified rehab)
- Multi-ligamentous injury - staged: address collateral or posterolateral corner first, then ACL at 6 weeks
- Partial tear with greater than 50 percent fibre disruption and demonstrable instability
Key anatomy
- AM bundle (60 to 70 percent, taut in flexion, controls anterior translation and internal rotation); PL bundle (30 to 40 percent, taut in extension)
- Femoral footprint: lateral wall of the lateral femoral condyle, centre 1 to 2mm anterior to over-the-top, 10:30 right or 1:30 left; landmarks are resident's ridge and the bifurcate ridge
- Tibial footprint: 7mm posterior to the anterior edge, lateral to the medial spine, posterior to the anterior horn of the lateral meniscus
- Danger structures: popliteal artery 1cm posterior to the PCL; saphenous nerve 2 to 3cm medial to the pes; infrapatellar branch at the AM portal (unavoidable, 50 to 70 percent); PCL forms the posterior wall
Critical steps
- EUA: Lachman (most sensitive), pivot shift (most specific), collaterals at 0 and 30 degrees (greater than 5mm opening is grade III), document and compare bilaterally
- Harvest: 3 to 4cm oblique incision 3cm distal and 2cm medial to the tubercle; gracilis superior and thin, ST inferior and thick; release accessory bands sharply; target greater than 28cm
- Graft prep: 4-strand by folding; Krackow whipstitch minimum 2.5cm; pretension 20 to 30 pounds for at least 10 minutes; diameter 8 to 10mm (8mm or greater mandatory)
- Femoral tunnel: trans-AM portal at 110 to 120 degrees; centre 10:30 right or 1:30 left using resident's ridge; depth over 30mm; posterior wall at least 2mm (probe)
- Tibial tunnel: 55-degree guide; entry 7mm posterior to the anterior edge, lateral to the medial spine; must be parallel to Blumensaat's line in extension
- Femoral fixation: suspensory cortical device preferred (greater than 1000N), confirm the flip by click and mark; hybrid adds an interference screw
- Tensioning: cycle 20 to 30 times through full ROM; fix at 20 to 30 degrees with an anterior drawer; maintain 20 to 30N
- Tibial fixation: bioabsorbable interference screw 7 to 9mm, parallel to the graft, flush or countersunk, tension maintained throughout
Danger zones
- Popliteal artery: 1cm posterior to the PCL; never drill blindly posteriorly; hyperflexion for femoral reaming; finger behind the tibia for tibial reaming
- Saphenous nerve: 2 to 3cm medial to the pes, deep to the sartorius; incision centred on the pes, stay superficial, avoid medial dissection
- Infrapatellar branch: unavoidable with the AM portal (50 to 70 percent) - counsel, minimise portal size, consider a high AM portal
- PCL: stay anterior during notch debridement, avoid an overly posterior tibial tunnel
- Medial femoral condyle cartilage: maintain 110 to 120 degrees for femoral drilling, keep the drill from diverging medially
Technique pearls
- Graft diameter 8mm or greater is critical (less than 8mm fails 2 to 3 times more often in young males)
- Trans-AM portal anatomic technique is the standard; transtibial is outdated and cannot reach the anatomic position
- Parallel to Blumensaat's in extension is mandatory - divergence means impingement, redrill before graft passage
- Suspensory femoral fixation preferred (greater than 1000N versus 400 to 600N for an interference screw); hybrid adds aperture fixation
- Fix at 20 to 30 degrees, never full extension or past 30; cycle 20 to 30 times first
- Achieve 0 degrees of extension before leaving theatre and by 2 weeks post-op
- Return to sport is criteria-based: minimum 9 months plus greater than 90 percent LSI on strength and hop testing and ACL-RSI greater than 56
- Accelerated rehab: immediate WBAT, early ROM, no prolonged bracing - lower stiffness than restricted protocols
Complications
- Graft failure 5 to 15 percent: higher under age 20 (RR 2 to 3), males, diameter less than 8mm (RR 2 to 3), RTS before 9 months (RR 7), non-anatomic tunnel
- Loss of extension 5 to 10 percent: the most important preventable complication; prevent with parallel tunnels, fixing at 20 to 30 degrees, early ROM to 0 degrees by 2 weeks
- Arthrofibrosis 2 to 5 percent: prevent by avoiding the acute phase and ensuring no impingement; treat with intensive PT then arthroscopic adhesiolysis
- Anterior knee pain 10 to 20 percent: lower with hamstring; prevent with proper technique; most resolve with time and PT
- Saphenous nerve injury 5 to 10 percent: prevent with incision centred on the pes and staying superficial to the sartorius; usually a neuropraxia
- Infection 0.3 to 1 percent: higher with allograft; deep infection needs urgent washout with graft retention if under 3 weeks
- Cyclops lesion 2 to 5 percent: focal anterior arthrofibrosis with extension loss; arthroscopic excision gives an excellent result
- DVT or PE 0.1 to 1 percent: prevent with early mobilisation and mechanical compression; chemical prophylaxis only if high risk
Numbers examiners want
- Graft diameter less than 8mm: 2 to 3 times failure
- RTS before 9 months: 7 times re-rupture risk
- Anterior knee pain: hamstring 10 percent versus BPTB 30 percent
- Saphenous nerve injury 5 to 10 percent; overall failure 5 to 15 percent; arthrofibrosis 2 to 5 percent; infection 0.3 to 1 percent
- Age under 20: 2 to 3 times failure risk
- Hamstring revision hazard about twice that of BPTB (Norwegian registry, adjusted HR 2.3), driven by young age
Background & Evidence
Epidemiology. ACL injury is among the most common and significant sports knee injuries, with the highest rates in pivoting and cutting sports - soccer, basketball, skiing and football. The Prodromos meta-analysis showed a higher incidence in female than male athletes in comparable sports. Reconstruction is one of the most frequently performed orthopaedic procedures, and revision burden (around 5 to 10 percent at 10 years) is a major driver of registry research. Pathoanatomy and biomechanics. The ACL originates from the posteromedial aspect of the lateral femoral condyle and inserts on the anterior tibia between the spines. It is 30 to 35mm long and 10 to 12mm wide, with a cross-sectional area of 30 to 50mm-squared, and is supplied by the middle genicular artery with limited intrinsic healing capacity. Its two functional bundles - the anteromedial (60 to 70 percent, taut in flexion, controlling anterior translation and internal rotation) and the posterolateral (30 to 40 percent, taut in extension, controlling hyperextension) - are the basis of anatomic single-bundle reconstruction, which reproduces the centre of both footprints. The ACL is the primary restraint to anterior tibial translation (85 percent of restraining force at 30 degrees, 90 percent at 90 degrees) and a secondary restraint to internal rotation, with proprioceptive mechanoreceptors aiding neuromuscular control.
- Native ACL
- 2160 N
- 4-strand hamstring
- 4090 N
- BPTB
- 2900 N
- Native ACL
- 242 N/mm
- 4-strand hamstring
- 807 N/mm
- BPTB
- Higher (bone blocks)
- Native ACL
- Native
- 4-strand hamstring
- Soft tissue, 12 or more weeks
- BPTB
- Bone-to-bone, 6 to 8 weeks
- Native ACL
- 100 percent
- 4-strand hamstring
- 75 to 80 percent of native
- BPTB
- Restored with bone-block healing
- Native ACL
- Reference standard
- 4-strand hamstring
- Never returns to 100 percent of native properties (ligamentisation)
- BPTB
- Faster biological incorporation
- Key points
- Lower anterior knee pain (10 percent), better cosmesis; risk of inadequate diameter (less than 8mm)
- Key points
- Bone-to-bone healing, consistent size; more anterior knee pain (30 percent) and kneeling pain; patella fracture 0.5 to 1 percent
- Key points
- Large reliable diameter (8 to 10mm), single tendon, low morbidity; less long-term data
- Key points
- No donor morbidity, but higher failure in the young (RR 2 to 4), infection risk, slower incorporation
- Key points
- Historical interest only - unacceptable failure rates, not recommended
Technique variations. Graft harvest variations include the standard 4-strand (both tendons, gold standard), a 5-strand (a longer semitendinosus folded to preserve the gracilis) and a tripled semitendinosus (often under 8mm, higher failure). Femoral drilling variations are the trans-AM portal (gold standard, anatomic), the transtibial technique (obsolete, non-anatomic), the outside-in technique (excellent femoral control, separate lateral incision) and the all-inside technique (retrodrilled sockets, less bone removal). Outcomes. At 2 years the Lachman is negative in 85 to 95 percent and the pivot shift in 80 to 90 percent, with a side-to-side KT-1000 difference under 3mm in 85 to 90 percent; 65 to 80 percent return to pre-injury activity and 85 to 90 percent are satisfied. Stability is maintained in 80 to 85 percent at 10 years. Long-term osteoarthritis is common and largely reflects the initial injury (40 to 60 percent radiographic changes at 10 years, 70 to 80 percent at 20 years) - the OA rate is similar whether the ACL is reconstructed or not. Failure rates and risk factors. Revision runs at 2 to 5 percent at 2 years, 4 to 8 percent at 5 years and 5 to 10 percent at 10 years:
- Relative risk
- RR 2 to 3 times (strongest factor)
- Relative risk
- RR 1.5 to 2 times
- Relative risk
- RR 2 to 3 times
- Relative risk
- RR 2 times
- Relative risk
- RR 7 times
- Relative risk
- RR 2 to 3 times
- Relative risk
- RR 2 to 4 times
Registries, guidelines and global practice. National ligament registries (Norwegian, Swedish, Danish, Kaiser Permanente US, New Zealand) provide the strongest revision-rate data and converge on the same signals - young age, hamstring graft, small diameter and return to pivoting sport. The Norwegian Knee Ligament Registry found hamstring grafts carry roughly twice the revision hazard of BPTB (adjusted HR 2.3), with the youngest group (15 to 19 years) the dominant risk factor (HR 4.0) and sex having no effect. The MOON consortium (US, prospective) identifies graft diameter, younger age and activity level as the principal predictors of failure. NICE (UK), AAOS (US) and ESSKA (Europe) all support individualised decision-making - early reconstruction for patients with functional instability or who wish to return to pivoting sport, and structured rehabilitation as a legitimate first-line strategy in many patients - reflecting the KANON-trial evidence. Antibiotic prophylaxis follows local or named-society guidance (a single pre-incision IV dose of a first-generation cephalosporin in most settings), with vancomycin pre-soaking of the graft increasingly used to reduce septic arthritis risk. Key evidence. The Cochrane review (Mohtadi, 2011) of 19 RCTs (1597 patients) found no significant difference in functional outcome or re-rupture between hamstring and BPTB, though BPTB gave a more statically stable knee with more anterior knee and kneeling problems while hamstring showed a trend to flexion-strength loss. The KANON trial (Frobell, 2013) showed that structured rehabilitation with optional delayed reconstruction was a legitimate first-line strategy - by 5 years 51 percent of the optional-delayed group had undergone reconstruction with no difference in KOOS or radiographic osteoarthritis. The Delaware-Oslo cohort (Grindem, 2016) showed that passing return-to-sport criteria (over 90 percent strength and hop symmetry) and delaying return to at least 9 months reduced reinjury from 38.2 percent to 5.6 percent.
References
Graft size and patient age are predictors of early revision after ACL reconstruction with hamstring autograft
- 256 primary hamstring-autograft reconstructions; overall revision 7.0 percent at mean 14-month follow-up
- Revision 1.7 percent for grafts over 8mm, 6.5 percent for 7.5 to 8mm, and 13.6 percent for grafts 7mm or less (p equals 0.027)
- Revision 0.7 percent in patients aged 20 or older versus 14.3 percent in those under 20 years
- Age under 20 (OR about 19) and decreased graft diameter (OR about 2.2) independently predicted early revision
Increased risk of revision with hamstring tendon grafts compared with patellar tendon grafts after ACL reconstruction (Norwegian Cruciate Ligament Registry, 2004 to 2012)
- 12,643 primary reconstructions (9,215 hamstring, 3,428 patellar tendon); overall 5-year revision 4.2 percent
- Adjusted hazard ratio for revision 2.3 (95 percent CI 1.8 to 3.0) for hamstring versus patellar tendon grafts
- The youngest age group (15 to 19 years) had HR 4.0 versus the oldest group - age was the dominant risk factor
- Sex had no significant effect on revision rate
Patellar tendon versus hamstring tendon autograft for anterior cruciate ligament rupture in adults (Cochrane systematic review)
- 19 randomised or quasi-randomised trials, 1,597 young-to-middle-aged adults, minimum 2-year follow-up
- No significant difference between grafts for functional outcome, return to activity, IKDC or re-rupture
- Patellar tendon reconstructions were more statically stable (Lachman, pivot shift, instrumented testing)
- Patellar tendon had more anterior knee and kneeling problems and a loss of extension; hamstring showed a trend to flexion-strength loss
Treatment for acute anterior cruciate ligament tear: five year outcome of randomised trial (KANON)
- 121 young active adults randomised to early ACL reconstruction plus rehab versus rehab with optional delayed reconstruction
- By 5 years, 51 percent of the optional-delayed group had undergone reconstruction (30 of 59 patients)
- No significant between-group difference in KOOS, SF-36, Tegner activity, or incident radiographic osteoarthritis
- Meniscal surgery rates did not differ between strategies
Simple decision rules can reduce reinjury risk by 84 percent after ACL reconstruction: the Delaware-Oslo ACL cohort study
- 106 patients in pivoting sports, prospective 2-year follow-up of reinjury
- Return to level I sport increased reinjury rate 4.3-fold versus not returning
- Reinjury rate fell 51 percent for each month return to sport was delayed up to 9 months, with no further reduction afterwards
- Passing return-to-sport criteria (over 90 percent on strength and hop symmetry) markedly reduced reinjury (5.6 percent versus 38.2 percent)
Further key references 1. Webster KE, Feller JA, Leigh WB, Richmond AK. Younger patients are at increased risk for graft rupture and contralateral injury after ACL reconstruction. Am J Sports Med. 2014;42(3):641-647. 2. Leys T, Salmon L, Waller A, Linklater J, Pinczewski L. Clinical results and risk factors for reinjury 15 years after ACL reconstruction: hamstring and patellar tendon grafts. Am J Sports Med. 2012;40(3):595-605. 3. Prodromos CC, Han Y, Rogowski J, Joyce B, Shi K. A meta-analysis of the incidence of anterior cruciate ligament tears as a function of gender, sport, and a knee injury-reduction regimen. Arthroscopy. 2007;23(12):1320-1325.e6. 4. Spindler KP, Wright RW. Clinical practice. Anterior cruciate ligament tear. N Engl J Med. 2008;359(20):2135-2142. 5. Kyung HS, Kim HJ, Yoo JD, Seo JH, Kim YB. Factors influencing graft rupture after primary ACL reconstruction. Knee Surg Sports Traumatol Arthrosc. 2014;22(9):2046-2052.