Multi-Ligament Knee Injuries

Multi-ligament knee injury (MLKI) refers to injury to two or more of the four major knee ligaments (ACL, PCL, MCL, LCL/PLC). Knee dislocation is defined as complete loss of tibiofemoral contact.

Mechanism of injury:

• High-energy trauma: Motor vehicle accidents, pedestrian vs car, motorcycle
• Low-energy trauma: Sports injuries, falls in obese patients (ultra-low velocity)
• Direction of force: Anterior, posterior, lateral, medial, rotational

Knee stability structures:

The knee relies on four major ligaments working in concert:

Posterolateral Corner (PLC):

The PLC is a complex of structures providing varus and rotational stability:

• Fibular collateral ligament (FCL/LCL): Primary varus restraint
• Popliteus tendon: Primary restraint to external rotation at 30 degrees flexion
• Popliteofibular ligament: Links popliteus to fibular head
• Lateral capsule: Secondary stabilizer
• Arcuate ligament: Variable importance

Popliteal artery anatomy:

The popliteal artery is at risk because:

• Tethered at two points: Adductor hiatus (proximal) and soleal arch (distal)
• Travels close to the posterior capsule
• Cannot move away from displacing tibia
• Intimal tears may not be immediately evident

Common peroneal nerve:

• Wraps around fibular neck
• At risk in lateral dislocations and PLC injuries
• Injury in 25-40% of MLKI
• Recovery variable (50% partial recovery)

History:

• Mechanism of injury (crucial for understanding pattern)
• Direction of force if witnessed
• Any sensation of knee "going out" or "snapping back"
• Presence of gross deformity initially
• Time since injury

Physical examination priorities:

Vascular assessment protocol:

1. Palpate pulses: Popliteal, dorsalis pedis, posterior tibial
2. Calculate ABI: Ankle-Brachial Index (normal more than 0.9)
3. If ABI less than 0.9: Angiography (CT-angio or conventional)
4. If pulses absent: Immediate vascular surgery consult
5. Serial exams: Every 6 hours for 48 hours (intimal tears can progress)

Ligament examination (once vascular status confirmed):

Nerve examination:

• Common peroneal: Ankle dorsiflexion, toe extension, lateral leg sensation
• Tibial nerve: Ankle plantarflexion, toe flexion, plantar sensation
• Saphenous: Medial leg and ankle sensation

Differential diagnosis:

The acutely unstable or grossly swollen knee after trauma has several mimics. The cardinal point is that a multiligament injury or spontaneously reduced dislocation must be actively excluded, because the others do not carry the same limb-threatening vascular risk.

MRI imaging:

MRI is essential for surgical planning:

• Defines which ligaments are injured
• Identifies repairable vs reconstructable injuries
• Assesses meniscal tears (common)
• Evaluates cartilage injury
• Determines PLC involvement

Timing of MRI:

• Once patient stable and vascular status confirmed
• Usually within first week
• May be limited by swelling initially

Key MRI findings:

Vascular assessment algorithm:

Persistent instability:

• Usually due to missed PLC injury
• Or inadequate PCL reconstruction
• Revision surgery required
• Address all structures and consider alignment

Postoperative protocol:

Key rehabilitation principles:

• Slower progression than isolated ACL
• Protect PCL graft (no active hamstrings early)
• Balance motion restoration with stability
• Patient-specific based on tissue quality and compliance
• Return to sport later than isolated ligament injuries

Outcomes by pattern:

Prognostic factors:

• Positive: Early surgery, complete reconstruction, good compliance
• Negative: Vascular injury, nerve injury, delayed surgery, missed PLC

Long-term concerns:

• Post-traumatic osteoarthritis (20-50%)
• Residual laxity (often acceptable if functional)
• Stiffness (10-20% require intervention)
• Chronic pain (10-15%)
• Return to high-level sport is often not achieved

Global epidemiology. Knee dislocation is rare. In a US national all-payer dataset of 99,688 coded knee dislocations (2010-2022), associated vascular injury occurred in only 1.1%, of which one quarter required repair (Dubin et al, J Orthop 2024). This contrasts sharply with the historical 30% figure derived from high-energy true dislocations, and the gap reflects case mix rather than contradiction. Prospective national series confirm a young, male-predominant population (mean age around 37, roughly 80% male) with common peroneal nerve injury in the order of 18% (Lustig et al, Orthop Traumatol Surg Res 2009). Obesity, including ultra-low velocity dislocation, is an independent risk factor for vascular injury and for missed diagnosis worldwide.

Major guidance, side by side. No single high-level society guideline governs the multiligament knee; practice is driven by expert consensus and systematic-review evidence, which is remarkably consistent across regions:

The areas of genuine international agreement are: vascular assessment first with ABI 0.90 as the action threshold; early surgery (within roughly 3 weeks) beats delayed surgery; and the posterolateral corner should be reconstructed rather than repaired in isolation (Levy et al, Arthroscopy 2009).

Registry evidence. There is no dedicated multiligament knee registry; this is a ligament-reconstruction rather than an implant-arthroplasty problem, so the major joint registries (NJR, AJRR, AOANJRR, Swedish/SHAR, Norwegian, NZJR) do not capture it. The relevant population-level data come instead from national administrative datasets and prospective multicentre cohorts (e.g. the French Society of Orthopaedic Surgery series and US national database studies cited above). Where end-stage post-traumatic arthritis later requires arthroplasty, those joint registries become relevant for implant selection and survivorship.

Global practice variation.

• High-resource settings favour MRI-planned, single-stage anatomic reconstruction of all torn ligaments at 1-3 weeks, often with allograft.
• Limited-resource settings more often rely on staged surgery, autograft (allograft and graft banks may be unavailable), bracing of selected collateral injuries, and acceptance of non-operative management in older or comorbid patients.
• Allograft availability is the single largest driver of technique differences worldwide; autograft-only strategies (hamstrings, quadriceps, contralateral grafts) are well described where banks are limited.