ACL Tear

Rupture of the anterior cruciate ligament, usually non-contact, causing rotational instability of the knee.

Mechanism and risk

Non-contact (about 70%): deceleration, cutting or pivoting, or landing with the knee near extension. Classic pattern: dynamic valgus, tibial internal rotation, quadriceps-dominant landing.
Contact (about 30%): valgus or external rotation blow to the knee.
Sports: football, basketball, netball, handball, rugby, skiing, volleyball.
Female athletes in pivoting sports have 2 to 8 times the incidence.

Anatomical	Neuromuscular	Other
Narrow notch, steep tibial slope, small ACL, hypermobility	Knee valgus, stiff landing, poor core and hip control	Previous ACL injury, playing surface. Hormonal effects: evidence mixed

Presentation and diagnosis

Pop (about 70%), immediate pain, unable to continue
Haemarthrosis within about 2 hours
Lachman: most sensitive test (20 to 30° flexion, soft endpoint)
Pivot shift: most specific, hard to elicit acutely
Anterior drawer: less sensitive acutely (hamstring guarding)
Laxity grades: I (under 5 mm), II (5 to 10 mm), III (over 10 mm, no firm endpoint)

MRI

fibre discontinuity, abnormal signal. Secondary signs: bone bruises (lateral femoral condyle and posterolateral tibial plateau), Segond fracture, PCL buckling, meniscal tear. MRI is about 90 to 95% accurate for complete tears but does not replace the Lachman test, and partial-tear grade correlates poorly with instability.

Surgery or not

Favours reconstruction: functional instability despite rehab (clearest indication), young pivoting athletes, multiligament injury, repairable meniscal tear.
Reasonable to trial rehab: low-demand patients, “copers” who avoid pivoting, stable partial tears. Reconstruct if it fails.

Can it heal without surgery? Contested. Cross Bracing Protocol case series report about 90% healing on 3-month MRI, and KANON found 30% healed with rehab alone. But MRI continuity does not equal stability. Controlled data in pivoting athletes show about 70% recurrent instability versus 2.5% after surgery, and partial tears progress to complete rupture in up to 39%. RCTs are needed.

Return to play

Minimum 9 months, typically 9 to 12. Earlier return raises re-injury risk.
Around 80% return to any sport, but only about 55 to 65% reach pre-injury level.
Criteria, not time: limb symmetry at least 90% on strength and hop tests, no effusion, psychological readiness.

References

Filbay et al., Br J Sports Med 2023, doi:10.1136/bjsports-2023-106931
Ardern et al., Br J Sports Med 2011, doi:10.1136/bjsm.2010.076364
Boden et al., J Am Acad Orthop Surg 2010, doi:10.5435/00124635-201009000-00003

Medical disclaimer: this article is general information, not personal medical advice. Always consult a qualified doctor about your own situation.