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Posterolateral corner injuries of the knee

Background

Isolated injuries of the posterolateral corner of the knee are uncommon, accounting for <2% of all acute knee ligamentous injuries. However, 43% to 83% of ACL and PCL injures may have a concomitant injury of the PLC {ref: 18768708 ).

Anatomy and Function

Structures of posterolateral corner (PLC) [1]:

  1. lateral collateral ligament (LCL)
  2. popliteus muscle
  3. popliteofibular ligament
  4. popliteomeniscal ligament
  5. iliotibial tract
  6. arcuate ligament
  7. fabellofibular ligament
  8. biceps femoris

Layers of the lateral knee *:*

  1. Superficial
    1. Iiliobibial tract
    2. superficial biceps
  2. Middle
    1. patellar retinaculm (anterior)
    2. lateral patellofemoral ligaments (two-proximal and distal)
    3. patellomeiscal ligament
  3. Deep (two portions):
    1. Superficial
      1. LCL
      2. fabellofibular ligament
    2. Deep
      1. coronary ligament
      2. popliteal hiatus
      3. arcuate ligament
      4. popliteofibular ligament

The posterolateral corner structures provides:

  • resistance to varus stress
  • external tibial rotation
  • posterior tibial translation (maximum at early knee flexion)

Diagnosis

Mechanisms:

  • blow to anteromedial knee, contact and noncontact hyperextension injuries, and varus blow to flexed knee [1]

Associated injuries

  • One must rule out injury of the cruciates, particularly PCL injury, as isolated PLC injuries are rare. In cases of combined injury, a knee dislocation which has spontaneously reduced should be considered.
  • The LCL has been reported to be injured in PLC injuries only 23% of the time, therefore increased varus laxity should not be used solely to determine diagnosis/treatment [1].
  • Common peroneal nerve injury: 15% [1]
  • Vascular injury: 33% [1]

Physical exam:

Varus stress test: This should be done in full extension and 30 degrees of flexion. Instability at 30 degrees is indicative of LCL injury, while instability in full extension represents associated injuries to the cruciates and posterior capsule. Lateral-sided opening is graded as I, II, or III (0-5mm, 6-10, >10mm opening respectively) [1]. It should be noted that posterolateral corner injury patterns do exist in which there is minimal lateral opening yet significant rotatory instablility (popliteal/PFL injury) .

Anterior drawer at 90 with intrnal tibial rotation: Positive test will reveal increased translation compared to when the tibia is in neutral rotation. Tibia will also tend to internally rotate while test is being performed [1].

Posterolateral drawer:knee is flexed to 80 degrees, foot is externally rotated while a posterior load is applied. A positive result is seen when the lateral tibial plateau rotates posteriorly and externally relative to the medial plateau .

Hyperextension recurvatum sign: With patient lying supine and both knees extended, both of the legs are passively lifted off the table by the great toe. In patients with a PCL and posterolateral capsule injury the knee hyperextends and the tibia rotates externally [1].

Reverse pivot-shift test: Start position: tibia rotated externally and the knee flexed while under a valgus stress. As the knee is extended the posterioly subluxed tibia reduces at 20 - 30 degrees of flexion as the it band changes from a flexor to an extensor of the knee [1] .

Dial test: This test is based on studies by Gollehon et al and Grood et al who published studies reporting that isolated sectioning of the PLC resulted in a maximal average inrease of 13 degrees of rotation at 30 degrees of knee flexion and 5.3 degrees and 90 degrees of flexion. Isolated sectioning of the PCL had no effect on rotation. Combined sectioning of the PCL and PLC produced greater increases in external rotation, particlularly at 90 degrees of flexion where and average of 20.9 degrees of external rotation was observed. Therefore, testing external rotation at the knee in both 30 and 90 degrees of knee flexion can aid in the diagnosis of PLC vs. combined PLC, PCL injuries .

Radiography:

Plain x-rays: may reveal fractures of fibula (arcuate sign) , avulsions of the popliteus tendon from the lateral femoral epicondyle, Gerdy tubercle avulsion, as well as avulsion fractures of the lateral tibia plateau, (e.g. Segond Fracture) [1]. Long leg standing x-rays are useful in cases of chronic tears in order to quantify potential bony malalignment.

MRI: 90-95% accurate in the diagnosis of LCL, popliteus, and biceps tend injuries using thing-slice coronal oblique T1-weighted images (68% accurate for diagnosis of popliteofibular ligament injuies) [1]

Diagnostic arthroscopy: popliteofibular ligament can be seen as vertically oriented fibiers descending from intraarticular portion of popliteus tendon. Avulsion of femoral insertion of popliteus tendon can often be seen in lateral gutter. Positive "drive-through" sign is suggestive of PLC injury [1].

Classification

Duration

  • Acute: < 3-6 weeks
  • Chronic: > 3-6 weeks

Varus Instability:

  • Grade I: sprains without tensile failure and little or no varus instability (0-5mm)
  • Grade II: Partial injuries with minimal abnormal laxity (6-10mm)
  • Grade III: complete disruptions with significant laxity (>10mm)

Rotational instability: Defined by dial test with instability present when an increase of 10 degrees in external rotation compared to the contralateral knee.

  • Grade I: 0-5 degrees increase in external rotation
  • Grade I: 5-10 degrees increase in external rotation
  • Grade I: >10 degrees increase in external rotation

Treatment:

Grade I: Treat nonoperatively with crutches and a hinged knee brace for 4-6 weeks. Immobilize in full extension early, followed by progressive motion, weight bearing, and strengthening. Return to full activity in 3 to 4 months .

Grade II: Treat surgically with internal fixation or suture repair in high-demand patients or those with avulsion injuries.

Grade III: Avulsion injuries with significant bony fragments should be repaired primarily with screws. Acute, isolated midsubstance injuries should be repaired and augmented with a graft reconstruction.

Acute Grade III with associated multiligament injuries:

When compared to repair alone, reconstruction of the PLC leads to more reliable outcomes. A level 3 cohort study of multiligament-injured knees treated by a single surgeon has reported a 40% failure rate for LCL/PLC injuries which were repaired and followed by a delayed reconstruction of the cruciates versus a 6% failure rate for LCL/PLC injuries which underwent a single-stage multiligament knee reconstruction (p=0.04). The authors concluded that reconstruction of the PLC/LCL is a more reliable option than repair alone in the setting of a multiligament knee injury . Another level II cohort study has reported similar results with a 37% repair failure rate for multiligament injured knees that  underwent repair of the PLC vs. a 9% reconstruction failure rate for knees that underwent PLC (LCL, popliteus, popliteofibular ligament) reconstruction using a modified 2-tailed technique .

Instability of the PLC is also associated with failure of ACL and PCL reconstructions. In the setting of the multiligament-injured knee that has undergone reconstruction of the injured cruciate ligament,  PLC-deficient knees place increased loads on ACL graft when subject to varus and coupled varus-internal rotation forces . Likewise, PLC-deficient knees place 22% to 150% increased forces on the PCL graft under all loading conditions .

Surgical Technique

Repairs performed within three weeks of injury typically lead to improved results (before capsular scarring and soft-tissue stretching occur). Additionally, there has been an increased trend toward more anatomic reconstruction of the three most critical biomechanical structures that provide stability to varus and external rotation forces (i.e. the LCL, popliteus tendon and the PFL).

Modified Two-Tailed Technique

References:

[1] Garrick, J. G. (Ed.). (2004). Orthopaedic Knowledge Update: Sports Medicine (3rd ed.). Rosemont, IL: American Academy of Orthopaedic Surgeons.

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