Anterior and posterior cruciate ligament injury — Rapid

Synopsis

Differentiate ACL and PCL mechanisms and examination patterns, recognise multiligament and vascular emergencies, use MRI after appropriate radiographs, begin criterion-led rehabilitation, and select reconstruction from instability and goals rather than imaging alone.

ACL injury typically follows pivot, deceleration or landing with a pop, rapid haemarthrosis and later giving way; PCL injury follows posterior tibial force or flexed-knee fall and may be subtler.
A spontaneously reduced knee dislocation can look normal. Document perfusion, ankle-brachial pressure and peroneal and tibial nerve function and use serial or vascular imaging pathways when multiligament injury is possible.
Obtain trauma radiographs first to identify fracture or avulsion. MRI maps ACL, PCL, menisci, cartilage and corners after immediate limb threats are addressed.
Use Lachman and pivot shift for ACL and posterior sag and drawer for PCL, comparing the other knee and recognising that pain and haemarthrosis reduce early accuracy.
Begin swelling control, full extension, quadriceps activation, gait and progressive strength before deciding from a quiet, examinable knee.
Non-operative care is credible for people without symptomatic instability who can meet activity goals through rehabilitation and modification; the MRI rupture alone is not an operative indication.
Reconstruction is considered for persistent functional instability, pivoting goals, repairable associated lesions or multiligament injury after shared discussion of rehabilitation, graft, failure and osteoarthritis risk.
In children, use an acute knee pathway, MRI within two weeks when examination is hard, document remaining growth and do not defer necessary surgery automatically until skeletal maturity.

Key red flags

Knee deformity, gross multidirectional instability, reduced pulse, cool foot or ankle-brachial pressure below the local normal threshold requires immediate vascular and orthopaedic escalation.

Progressive calf pain, tense swelling, pain on passive stretch or neurological loss suggests compartment syndrome and needs emergency assessment.

An acutely locked knee or large haemarthrosis may contain displaced meniscus or osteochondral fracture and requires an acute knee pathway.

Inability to straight-leg raise, patella alta or baja, or palpable tendon gap suggests extensor mechanism rupture rather than isolated cruciate injury.

Investigation priorities

Immediate neurovascular assessmentFirst step

Detect popliteal artery and peroneal or tibial nerve injury.

First-line trauma radiographsFirst line

Identify fracture, tibial-spine or PCL avulsion and alignment.

Management branches

ThreatTreat as knee dislocation

Deformity, multiligament laxity or abnormal perfusion suggests dislocation or vascular injury.

Reduce deformity, immobilise and document pulses, ankle-brachial pressure and nerve function before and after intervention.
Use urgent CT angiography and vascular consultation for abnormal or changing perfusion.
Image fractures and all ligament structures and admit for serial examination according to the local pathway.
Plan staged or definitive repair and reconstruction through a multiligament knee team.

RehabilitationCreate a quiet stable functional knee

Isolated injury is confirmed without a limb threat or urgent repairable block.

Restore full extension, swelling control, quadriceps activation and normal gait before high-load progression.
Build strength, neuromuscular control and activity-specific capacity with supervised review.
Assess whether instability persists during the person's actual work or pivoting goals.
Continue non-operative care when goals are met without giving way and protect secondary structures.

Key medicines

Short-term anti-inflammatory analgesiaUse a licensed topical NSAID or one oral NSAID at the lowest effective adult dose for the shortest period that supports motion and rehabilitation, adding gastroprotection when oral treatment and risk assessment indicate it.Assess ulcer, renal, cardiovascular and liver disease, pregnancy, anticoagulants and other NSAIDs; analgesia must not mask worsening compartment, vascular or fracture signs.

Post-reconstruction thromboprophylaxis when indicatedUse the exact mechanical and pharmacological regimen from the current local knee-ligament surgery pathway only after individual venous-thrombosis, bleeding, weight-bearing, travel, contraception and previous-event assessment.Routine medication is not identical for every arthroscopy; coordinate with neuraxial timing, renal function and existing anticoagulants and provide stop and urgent bleeding instructions.

Open full textbook →Answer 2 questions