ACL Injury

History:

A non-contact pivoting, cutting, or landing injury, often with a felt or audible pop and immediate inability to continue play. Rapid haemarthrosis (within hours, often much sooner) strongly suggests ACL rupture; a slower effusion suggests meniscal tear. Subsequent giving way with pivoting is the functional hallmark.

Examination:

• •Lachman (knee at 20-30 degrees): most sensitive and specific. Soft end-point is the critical finding

• •Anterior drawer (90 degrees): less sensitive acutely

• •Pivot shift: most functionally relevant; often needs anaesthesia

• •Also assess menisci, MCL, PCL, and PLC (dial test - missed PLC is a graft-failure cause)

Red flags:

Knee dislocation with multi-ligament injury (popliteal artery risk). Inability to weight-bear (apply Ottawa Knee Rules). Segond fracture on X-ray (pathognomonic for ACL). Foot drop suggests common peroneal nerve injury.

ACL injury is a clinical diagnosis. MRI confirms and identifies associated injuries.

• •Plain radiographs (AP, lateral; Ottawa Knee Rules to guide): exclude tibial plateau fracture, fibular head fracture, Segond fracture (pathognomonic), tibial eminence avulsion, and lipohaemarthrosis on the lateral.

• •MRI: investigation of choice. Direct signs (ACL discontinuity, abnormal signal) plus indirect signs (kissing contusions at the lateral femoral condyle and posterolateral tibial plateau, anterior tibial translation, Segond fracture). Identifies repairable meniscal tears, root tears, osteochondral injury, PLC injury, and multi-ligament injury.

• •Per BOA, patients with haemarthrosis after acute knee injury should be assessed within a specialist pathway within 2 weeks with timely MRI access.

Per BOA, the prime indication for ACL reconstruction is symptomatic instability. Not all ruptures require surgery.

Acute:

PEACE & LOVE principles. Consider aspiration of a tense haemarthrosis. Early ROM, particularly regaining full extension. Quadriceps activation from day one. Per BOA, refer into a specialist acute knee injury pathway within 2 weeks with MRI access.

Indications for reconstruction:

Symptomatic instability (recurrent giving way), return to pivoting sport, young high-demand patient, repairable meniscal tear, multi-ligament injury.

Surgical options:

ACL reconstruction with autograft is the UK standard - hamstring, bone-patellar tendon-bone, or quadriceps tendon. Allograft is generally avoided in primary reconstruction in patients under 25-30 due to higher re-rupture rates. Lateral extra-articular tenodesis (LET) reduces re-rupture in young athletes, high-grade pivot shift, or generalised laxity. Early reconstruction (within 3 months) is favoured when a repairable meniscus is present; very early surgery (<3 weeks) on a swollen knee risks arthrofibrosis.

Non-operative:

Structured rehabilitation suits lower-demand patients and copers who achieve functional stability. Reconsider reconstruction if non-operative care fails.

Same core programme whether non-operative or post-reconstruction; typically 9-12 months before return to pivoting sport. Per BOA, structured rehab is the foundation.

Pre-hab (4-8 weeks pre-op):

• •Restore full ROM (full extension first), resolve effusion, restore quadriceps activation. The single most important pre-operative factor for outcome.

Phase 1 (0-6 weeks post-op):

• •Restore full extension - the number one early priority.

• •Progressive weight-bearing as tolerated.

• •Quadriceps activation: quad sets, straight leg raises.

• •ROM: 0 degrees by week 1, 90 degrees by week 2, full flexion by 6-8 weeks.

• •Effusion management.

Phase 2 (6-12 weeks):

• •Progressive open and closed kinetic chain strengthening.

• •Neuromuscular training: balance, proprioception, perturbation.

• •Normalise gait.

Phase 3 (3-6 months):

• •Progressive functional loading.

• •Running reintroduction (typically 3-4 months) when criteria met: no effusion, full ROM, quadriceps strength >70% of contralateral, good single-leg control.

Phase 4 (6-9 months):

• •Sport-specific training: cutting, pivoting, change of direction, agility.

• •Plyometric progression.

• •Address fear of re-injury (ACL-RSI).

Phase 5 (return to sport, 9-12+ months):

• •Criteria-based per BOA, not time-based.

• •Quadriceps strength and limb symmetry index >=90%.

• •No effusion, full ROM.

• •Psychological readiness (ACL-RSI score).

• •Return to pivoting sport rarely <9 months.

• •BOA Best Practice for ACL Injuries - Symptomatic instability is the prime indication for reconstruction. Specialist acute knee injury pathway within 2 weeks. Criteria-based return to pivoting sport (rarely <9 months).

• •ACL SNNAP trial (Beard et al., Lancet 2022) - Early ACL reconstruction produced better patient-reported outcomes than rehabilitation with optional delayed surgery in young active adults.

• •STABILITY trial (Getgood et al., AJSM 2020) - Adding lateral extra-articular tenodesis to hamstring autograft significantly reduced graft re-rupture rates in high-risk young athletes.

• •FIFA 11+ neuromuscular prevention programmes reduce ACL injury incidence by 50-70%. Previous ACL injury is the strongest single risk factor.

• •Cross bracing protocol (Filbay et al., BJSM 2023) - Prolonged bracing protocol promoting tear continuity; emerging non-operative option, not yet UK standard. Reported risks include re-injury, DVT, and flexion contracture.

• •Lachman is the most sensitive and specific test - a soft end-point is the critical finding. More reliable than anterior drawer acutely.

• •Rapid haemarthrosis after a pivoting injury strongly suggests ACL rupture; a delayed effusion suggests meniscal tear.

• •Segond fracture on X-ray is pathognomonic for ACL rupture. Tibial eminence avulsion is the bony equivalent in adolescents.

• •Per BOA, the prime indication for reconstruction is symptomatic instability. Return to pivoting sport should be criteria-based and rarely under 9 months.

• •The pivot shift is the most functionally relevant test; a high-grade pivot shift may favour adding LET to reduce re-rupture risk (STABILITY trial).

• •Females are 2-6x more likely to sustain non-contact ACL injury. FIFA 11+ programmes reduce incidence by 50-70%.