Posterolateral Instability of the Knee & Knee Dislocations

POSTEROLATERAL INSTABILITY

= when stress testing the lateral tibial plateau rotates posteriorly in relation to the femur with lateral opening of joint

associated with knee dislocation (see below)

Posterolateral injury components

1. popliteus tendon

2. arcuate ligament

3. LCL and lateral capsular ligaments

Tests:

• See Knee Examination

• Check common peroneal nerve function

Management:

• Surgery always required

Preop planning:

• X-Rays:

  • Segond fracture - avulsion fracture of lateral capsule off tibia - indicative of an associated ACL injury - seen on AP view.

• MRI

  • allows assessement of posterolateral corner injury as well as ACL & PCL

  • assess which structures of the posterolateral corner are injured and whether the injuries are mid-substance or whether they have been avulsed from the fibula or femur

Arthroscopic findings:

• "drive through sign" = >1cm of lateral opening and exceptional posterior visualization of the lateral meniscus

Procedure:

• Exposure: Identify the IT band, hamstrings, fibular head, peroneal nerve, and femoral attachment of the LCL

• Incision: - straight lateral incision centered over the lateral joint line; - proximally the subcutaneous flaps are mobilized to allow identification of the anterior and posterior borders of the IT band; - the anterior and posterior attachments of this band are freed to allow anterior and posteiror mobilization; - peroneal nerve is identified posterior to the biceps and is followed distally around the fibular neck (look for evidence of nerve injury

• Sequential assessment of injury: - look for avulsion of IT band off of Gerdy's tubercle, peroneal nerve injury, biceps avulsion off of the fibular head, LCL injury (proximal or distal), and popliteus avulsion

• Repair will procede from the deepest structures to the most superficial structures

  1. lateral meniscus repair

  2. Capsular repair

  3. Reattach popliteus to its femoral attachment (bone anchor) and to its fibular head attachment (pull thru sutures)

  4. Arcuate ligament: - reconstruction/repair of this structure is necessary to avoid excessive tibial rotation, especially as the knee moves from extension to flexion; - remember that the biceps tendon, LCL, and arcuate complex all insert on the fibular styloid, and that if there is a fibular styloid avulsion, osseous reattachement will restore all three structures; Achilles tendon allograft may be indicated; - main goal is to create a checkrein to external rotation;

  5. LCL repair / advancement on its femoral attachment

  6. Biceps Tendon

  7. IT Band: - note that the posterior 1/3 of the IT band attaches to the femoral epicondyle; - if this attachement is deficient, it should be repaired to help restore lateral stability

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KNEE DISLOCATIONS

Clinical Findings:

1. Popliteal artery & vein injury is common

   • note that knee dislocations that have spontaneously reduced may look benign but may lead to thrombosis of the popliteal artery

   • popliteal artery is usually tethered proximally at adductor hiatus & distally by arch of soleus

   • injury to the popliteal artery may initially manifest as an intimal tear or intraluminal thrombus.

2. Peroneal nerve injury:

   • in 20% to 40% (half of these palsies are permanent)

   • w/ peroneal nerve injury, be highly suspect for vascular injury; - even if pulse returns following reduction, consider need for arteriogram, since incidence of intimal injury is high w/ concomitant nerve injury

3. Both cruciates and least one collateral ligament are usually disrupted

Classification:

• Anterior (31%)

  • hyperextension of knee (may need > 30 deg of hyperextension to produce this injury)

  • often PCL & ACL torn

  • either the MCL or LCL or both will usually be injured

  • alternatively, hyper-extension injuries may cause disruption of the ACL and posterior capsule while the PCL is spared

  • Popliteal artery injury

• Posterior (25%)

  • disruption of both cruciate ligaments

  • possible extensor mechanism disruption

  • avulsion of or complete disruption of popliteal artery

• Lateral (13%)

• Medial ( 3%)

• Rotatory ( 4% - usually posterolateral)

Investigations:

1. X-Rays:

• Associated radiographic findings:

  1. Tibial plateau fracture

  2. Proximal fibula fracture

  3. Avulsion fracture of Gerdy's Tubercle

  4. Intercondylar spine fracture

  5. Avulsion of Fibular Head

2. Arteriogram - indications unclear

3. MRI - see above

Management:

• Reduction

  • may be complicated by interposed soft tissue

  • External fixation - it is important that the external fixator pin sites will not interfere with the ACL/PCL tunnel sites (during future ligament reconstruction)

• Vascular Inuries

  • the worst error to make is to underestimate the need to promptly treat these injuries

• Nerve injury:

  • the location of the nerve injury may be well above the knee joint

• Assessment of ligament injuries:

  • EUA

• Surgical Treatment of Ligament Injuries:

  • if vascular injury has been previously repair, get clearance from the vascular surgeon to utilize a tourniquet

  • Deep to superficial (as above)