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Updated: Jul 1 2021

Posteromedial Corner Injury

  • summary
    • A posteromedial corner (PMC) injury is a traumatic knee injury that usually presents as a component of a multi-ligamentous knee injury and can can lead to chronic valgus knee instability.
    • Physical exam will demonstrate rotational instability and diagnosis is confirmed with MRI.
    • Treatment may be nonoperative for isolated PMC injuries. Operative management is indicated for PMC injuries that are associated with multi-ligamentous knee injury. 
  • Epidemiology
    • Incidence
      • compared to the posterolateral corner, considerably less literature has focused on the medial side of the knee, specifically, the posteromedial corner (PMC)
  • Etiology
    • Pathophysiology
      • mechanism of injury
        • a valgus force to the affected knee, most commonly occurring during athletic activity
        • anteromedial rotatory instability (AMRI) results from an injury that includes both the medial collateral ligament (MCL) and the posterior oblique ligament (POL).
      • pathoanatomy
        • POL is the most commonly injured structure.
        • may include sprains, partial tears, and complete tears and are best visualized on axial and coronal MR images.
        • 3 major injury patterns reported
          • POL injury and associated injury to the capsular arm of the semimembranosus
          • POL injury and complete peripheral meniscal detachment, and
          • POL injury and disruption of the semimembranosus and peripheral meniscal detachment.
    • Associated conditions
      • high prevalence of associated knee injuries (88%)
        • PMC injuries are most commonly found in association with other ligamentous knee injuries
        • almost all patients surgically treated for combined ACL and MCL injuries have POL tears or complete PMC ruptures
  • Anatomy
    • The anatomy of the medial side of the knee has been described by two different approaches
      • layered approach
        • layer 1 = deep fascia
        • layer 2 = superficial Medial Collateral Ligament (MCL)
        • layer 3 = joint capsule and the deep MCL
      • medial thirds approach
        • anterior third = from the medial border of the patellar tendon to the anterior border of the longitudinal fibers of the superficial MCL
        • middle third = comprised of the width of the longitudinal fibers of the MCL
        • posterior third = from the posterior border of the longitudinal fibers of the superficial MCL to the medial edge of the medial head of gastrocnemius
          • encompasses the contents of the Posteromedial Corner (PMC) of the knee.
    • Components of PMC
      • five major components that make up the PMC of the knee
        • posterior oblique ligament (POL).
        • semimembranosus tendon and its expansion
        • oblique popliteal ligament (OPL),
        • posteromedial joint capsule
        • posterior horn of the medial meniscussuperficial and deep portions of the MCL occupy the middle third of the medial side and are NOT typically considered part of the PMC.
          • superficial and deep portions of the MCL occupy the middle third of the medial side and are NOT typically considered part of the PMC.
  • Presentation
    • History
      • patients will typically describe a valgus force to the affected knee, most commonly occurring during athletic activity.
        • a pure valgus force often causes an isolated MCL injury
        • combined external rotation and valgus forces are likely to result in injury to the POL and other components of the PMC.
    • Symptoms
      • pain
        • medial knee pain
      • instability
        • subjective medial instability following a valgus mechanism of injury.
    • Physical exam
      • inspection
        • medial knee ecchymosis and bruising
      • motion
        • valgus stress testing should be performed at 0 and 30 degrees of knee flexion to assess the integrity of the MCL.
      • provocative tests
        • anteromedial rotatory instability (AMRI) on physical exam is the hallmark of PMC injury.
        • AMRI:
          • anterior subluxation of the anteromedial tibial plateau on the femoral condyle
          • tested by applying a valgus stress at 30 degrees of knee flexion while the foot is concomitantly externally rotated.
          • a positive test occurs with medial joint space gapping and anterior subluxation of the medial tibial plateau relative to the femur.
          • the positive exam correlates with a combined PMC and MCL injury.
        • anteromedial drawer test:
          • performed by flexing the knee to 90 degrees while externally rotating the foot 10-15 degrees and applying an anterior force to the knee.
          • anteromedial tibial plateau subluxation is a positive test
        • important to differentiate isolated MCL injury from AMRI, by assessing for valgus laxity associated with anterior rotatory subluxation of medial tibial plateau on the medial femoral condyle with the AMRI pattern.
  • Imaging
    • Radiographs
      • recommended views
        • AP and lateral plain films
        • may be augmented with valgus stress radiographs to assess medial gapping
    • MRI
      • views
        • MRI is the current imaging modality of choice for diagnosing complex injuries of the PMC
        • improved visualization of the structures with contrast-enhanced sequences and coronal oblique images
  • Treatment
    • Nonoperative
      • physical therapy
        • indications
          • isolated, low-grade medial knee injuries that involve the MCL and posteromedial corner can be treated non-operatively
    • Operative
      • PMC reconstruction
        • indications
          • multiligamentous injuries
          • knee dislocations
          • tibial-sided sleeve avulsions (sleeve of tissue encompassing both the MCL and posteromedial corner)
          • chronic injuries where patients have developed symptomatic AMRI
  • Techniques
    • PMC Reconstruction
      • goals
        • an anatomic reconstruction of the proximal and distal divisions of the superficial MCL and the POL using two separate grafts
      • approach
        • an anteromedial longitudinal incision beginning 4 centimeters medial to the patella and extending 8 centimeters distal to the joint line is utilized to expose both the femoral the distal tibial attachment sites of the superficial MCL.
        • sartorial fascia is incised to expose the gracilis and semitendinosus tendons
        • the semimembranosus tendon can be harvested for autograft based on surgeon preference
      • tibial tunnels
        • first, a reconstruction tunnel is created for the superficial MCL’s distal insertions
        • next, a reconstruction tunnel for the central arm of the POL is then placed just anterior to the direct arm attachment of the semimembranosus tendon.
      • femoral tunnels
        • superficial MCL tunnel is placed slightly proximal and anterior to the medial epicondyle.
        • femoral POL tunnel is placed approximately 8mm distal and 3mm anterior to the gastrocnemius tubercle
        • the femoral ends of the grafts are first fixed with interference screws.
        • POL graft is then placed into its tibial tunnel and tensioned in full extension and neutral rotation
        • the superficial MCL is weaved under the sartorial fascia and fixed in its tibia tunnel with the knee held in neutral rotation, 20 degrees of flexion, and a slight varus reduction force to ensure no medial compartment gapping
  • Complications
    • Chronic valgus instability or laxity
    • Post-operative stiffness
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