Ligament Injuries

Knee ligament injuries: ACL (the big one), MCL/LCL, and the uncommon PCL. For fractures around the knee and true knee dislocation, see Knee Fractures & Dislocations. For patellar (kneecap) dislocation, a different injury with its own reduction technique, see Patellar Dislocation.

ACL rupture

• Demographics: young athletes in running/pivoting/contact sports (rugby, soccer, netball, basketball, skiing); non-contact pivoting injury accounts for most cases (67% in men, 90% in women). Females are ~4× more likely to tear an ACL, thought to relate to landing biomechanics (more valgus/extension on landing) as well as hormonal and anatomical factors.
• History: sudden change of direction — internal tibial rotation or valgus force; often a pop/crack; immediate pain with swelling within ~30 minutes (haemarthrosis, ~70%); then instability/giving way (72%) or locking (18%).
• Examination: effusion, diffuse joint-line tenderness.
  • Lachman test (anterior drawer at 20–30° flexion) — the most sensitive test (80–99% sensitivity, 95–96% specificity); positive if >2 mm more anterior translation than the uninjured knee, or no firm “end-feel”.
  • Lever/Lelli sign — heel on the bed, a fist under the proximal calf just distal to the tibial tuberosity, downward pressure over the quadriceps tendon; positive (ACL torn) if the heel stays on the bed. 63–100% sensitive, 90–100% specific, and easy to perform even with a tense effusion.
  • Anterior drawer (41–91% sensitive — less reliable than Lachman) and pivot-shift (18–48% sensitive but 97–99% specific — very reassuring if positive, but a negative test doesn’t rule it out).
  • Exam maneouvres are often difficult to perform acutely because of pain/swelling — a delayed outpatient exam once swelling settles can outperform MRI (one study: 88.7% sensitive/94.7% specific delayed exam vs 86.8%/73.7% for MRI).
• Investigations: X-ray may show a Segond fracture (lateral tibial plateau avulsion) — only seen in ~10% of ACL tears but pathognomonic when present. MRI grades the rupture and looks for associated meniscal tears.
• Management:
  • surgery is reserved for complete, symptomatic tears
  • early reconstruction for young/high-performance athletes; conservative treatment (structured rehab) is reasonable if there is no ongoing instability, with delayed reconstruction if instability develops — the KANON trial showed rehab-first with optional delayed reconstruction is not inferior to early surgery even in active adults
  • combined MCL+ACL injury: delayed ACL repair (early repair of both risks stiffness)
  • a knee immobilizer is only needed if the knee is unstable — don’t routinely immobilise a stable knee, as it just adds stiffness and atrophy.

PCL injury

Rare (isolated tears are only 4% of ligament tears); dashboard and hyperextension injuries, or a direct posterior blow to a flexed proximal tibia. Posterior knee pain.

• Examination: posterior sag sign (hips/knees flexed 90°, look for the tibia sagging posteriorly relative to the femur — 79% sensitive, 100% specific) and posterior drawer test (90% sensitive/99% specific for experienced examiners, but only ~70% sensitive for a grade I injury).
• Management: low-grade — protected weight-bearing and physiotherapy strengthening, return to sport in 1–2 weeks. High-grade with instability, combined-ligament injury, or a bony avulsion — surgical repair.

Collateral ligament injuries (MCL/LCL)

• MCL is the most common knee ligament injury (~42% of knee ligament injuries, likely under-counted since grade I tears are often missed) and rarely needs surgery; isolated LCL injury is rare (<2%) and commonly involves the PCL/posterolateral corner.
• History: direct varus/valgus blow (classically two soccer players kicking the ball simultaneously); immediate medial/lateral joint-line pain, worse with twisting; a “pop” may be reported.
• Examination: localised medial (or lateral) swelling; valgus stress test at 30° flexion for MCL (isolates the superficial MCL, 86–96% sensitive comparing side-to-side: grade I 1–4 mm laxity, grade II 5–9 mm, grade III ≥10 mm) — laxity at full extension instead suggests a multi-ligament injury or posteromedial capsule tear, not an isolated MCL sprain. Varus stress at 30° for LCL. An effusion suggests a concurrent ACL tear.
• Investigations: X-ray usually normal (rare avulsion signs: Stieda fracture at the medial femoral condyle for MCL, avulsion at the lateral femoral condyle for LCL); MRI is the investigation of choice and grades the injury.
• Management (MCL):
  • Grade I — NSAIDs, rest, progressive resistance/quad strengthening; return to sport in 5–7 days
  • Grade II/III (stable) — as above + hinged knee brace; return to sport 2–4 weeks (II), 4–8 weeks (III)
  • Grade III with instability or failed conservative care — operative repair.