High Yield Topics

Knee Dislocation

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Ovid: Handbook of Fractures

Authors: Koval, Kenneth J.; Zuckerman, Joseph D.
Title: Handbook of Fractures, 3rd Edition
> Table of Contents > IV – Lower Extremity Fractures and Dislocations > 34 – Knee Dislocation

34
Knee Dislocation
EPIDEMIOLOGY
  • Traumatic knee dislocation is an uncommon
    injury that may be limb-threatening; it should therefore be treated as
    an orthopaedic emergency.
  • True incidence is probably underreported.
    • From 20% to 50% spontaneously reduce.
  • It is rare: at the Mayo Clinic, only 14
    traumatic knee dislocations were observed in 2 million admissions. The
    largest series reported was from Los Angeles County Hospital, where
    over a 10-year period, 53 knee dislocations were seen.
ANATOMY
  • The ginglymoid (hinge joint) consists of
    three articulations: patellofemoral, tibiofemoral, and tibiofibular.
    Under normal cyclic loading, the knee may experience up to five times
    body weight per step. The normal range of motion is from 10 degrees of
    extension to 140 degrees of flexion with 8 to 12 degrees of rotation
    through the flexion-extension arc. The dynamic and static stability of
    the knee is conferred mainly by soft tissues (ligaments, muscles,
    tendons, menisci) in addition to the bony articulations.
  • Significant soft tissue injury is
    necessary for knee dislocation, including ruptures of at least three of
    four major ligamentous structures of the knee. The anterior and
    posterior cruciate ligaments (ACL and PCL) are disrupted in most cases,
    with a varying degree of injury to the collateral ligaments, capsular
    elements, and menisci.
  • The popliteal vascular bundle courses
    through a fibrous tunnel at the level of the adductor hiatus. Within
    the popliteal fossa, the five geniculate branches are given off, after
    which the vascular structures run deep to the soleus and through
    another fibrous canal. It is this tethering effect that leaves the
    popliteal vessels vulnerable to tenting and injury, especially at the
    moment of dislocation.
  • Associated fractures of the tibial
    eminence, tibial tubercle, fibular head or neck, and capsular avulsions
    are common and should be suspected.
MECHANISM OF INJURY
  • High-energy: A motor vehicle accident with a “dashboard” injury involves axial loading to a flexed knee.
  • Low-energy: This includes athletic injuries and falls.
  • Hyperextension with or without varus/valgus leads to anterior dislocation.
  • Flexion plus posterior force leads to posterior dislocation (dashboard injury).
    • Associated injuries include fractures of the femur, acetabulum, and tibial plateau.

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CLINICAL EVALUATION
  • Patients present with gross knee
    distortion unless the knee underwent spontaneous reduction. Immediate
    reduction should be undertaken without waiting for radiographs. Of
    paramount importance is the arterial supply, with secondary
    consideration given to neurologic status.
  • Patients who sustain a knee dislocation
    that spontaneously reduces may have a relatively normal-appearing knee.
    Subtle signs of injury such as mild abrasions, or a minimal effusion,
    or complaints of knee pain may be the only abnormalities.
  • The extent of ligamentous injury is
    related to the degree of displacement, with injury occurring with
    displacement greater than 10% to 25% of the resting length of the
    ligament. Gross instability may be realized after reduction.
  • Isolated Ligament Examination
    • ACL
      • Lachman at 30 degrees
    • PCL
      • Posterior drawer at 90 degrees
    • Lateral collateral ligament (LCL)/Posterolateral corner (PLC)
      • Varus stress at 30 degrees and full extension
      • Increased tibial external rotation at 30 degrees
      • Increased posterior tibial translation at 30 degrees
    • Medial collateral ligament (MCL)
      • Valgus stress at 30 degrees
  • Combined Ligament Examination
    • LCL/PLC and cruciate
      • Increased varus in full extension and at 30 degrees
    • MCL and cruciate
      • Increased valgus in full extension and at 30 degrees
    • PLC and PCL
      • Increased tibial external rotation at 30 and 90 degrees
      • Increased posterior tibial translation at 30 and 90 degrees
    • Stability in full extension
      • Excludes significant PCL or capsular injury.
  • A careful neurovascular examination is
    critical, both before and after reduction, and serially thereafter,
    because vasospasm or thrombosis resulting from an unsuspected intimal
    tear may cause delayed ischemia hours or even days after reduction.
    • Vascular injury—popliteal artery
      disruption (20% to 60%): The popliteal artery is at risk during
      traumatic dislocations of the knee owing to the bowstring effect across
      the popliteal fossa secondary to proximal and distal tethering. In a
      cadaveric study, hyperextension of the knee induced by anterior
      dislocation resulted in posterior capsular tearing at 30 degrees and
      popliteal artery tearing at 50 degrees. Although collateral circulation
      may result in the presence of distal pulses and capillary refill, it is
      inadequate to maintain limb viability.
    • The mechanism of arterial injury varies
      with the type of dislocation. When anterior dislocations injure the
      artery, it is usually by traction, resulting in an intimal tear. In
      contrast, vascular injuries associated with posterior dislocations are
      frequently complete arterial tears.

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    • Vascular examination
      • Dorsalis pedis (DP) and posterior tibial (PT) artery pulses should be evaluated.
      • Pulse absent
        • Consider immediate closed reduction.
        • If still absent, proceed to the operating room for exploration.
        • If pulse returns, consider angiogram versus observation.
        • An 8-hour ischemic time is maximum.
      • Pulse present
        • If the ankle-brachial index (ABI) is >0.9, observe the patient.
        • If the ABI is <0.9, proceed with angiogram and/or exploration.
      • Vascular injuries: principles
        • Evaluate and document the vascular status
          (DP/PT pulses and capillary refill) in any patient with a proven or
          suspected knee dislocation.
        • Once the dislocation is reduced, the circulation should be reevaluated.
        • Revascularization should be performed within 8 hours.
        • Arteriography should not delay surgical reanastomosis.
        • It is unacceptable to suggest spasm as a cause for decreased or absent pulses in an attempt to justify observation.
        • If arterial insufficiency or abnormality is present, there is a vascular injury.
        • Arterial injury is treated with excision of the damaged segment and reanastomosis with a reverse saphenous vein graft.
        • An experienced vascular surgeon should be consulted to verify clinical findings and to interpret studies.
      • Vascular injuries: recommendations
        • Ischemic limb after reduction
          • Immediate surgical exploration is indicated.
          • Injury and location are predictable.
          • Arteriogram is indicated only if an additional associated proximal injury is present.
        • Abnormal vascular status: viable limb
          • Diminished pulses are noted.
          • Decreased capillary refill is seen.
          • The ABI is <0.9.
          • An “urgent” arteriogram is indicated.
        • Normal vascular status and no ligament or extremity surgery
          • PT/DP pulses and capillary refill are normal.
          • The ABI is >0.9.
          • Careful observation with serial examinations is warranted.
            • Vascular surgery and invasive radiology should be “available.”
          • Magnetic resonance angiography (MRA)/magnetic resonance imaging (MRI)
            • Evaluate for nonocclusive (intimal) injury.

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            • Sensitivity and specificity are uncertain.
            • Arteriogram is indicated if results are abnormal.
        • Normal vascular status: potential or planned ligament or extremity surgery
          • PT/DP pulses and capillary refill are normal.
          • The ABI is >0.9.
          • Careful observation with serial examinations is indicated.
            • Vascular surgery and invasive radiology should be “available.”
          • MRA/MRI are part of the preoperative evaluation.
          • Routine arteriography is performed within 24 to 48 hours.
          • Intimal injury
            • Anticoagulation is administered.
            • No tourniquet is used.
            • Consider limited and delayed surgery (10 to 14 days).
            • No endoscopic PCL (tibial tunnel) is performed.
      • Neurologic injury—peroneal nerve (10% to
        35%): This is commonly associated with posterolateral dislocations,
        with injury varying from neurapraxia (usual) to complete transaction
        (rare). Primary exploration with grafting or repair is not effective;
        secondary exploration at 3 months is associated with poor results.
        Bracing and/or tendon transfer may be necessary for treatment of
        muscular deficiencies.
RADIOGRAPHIC EVALUATION
  • A knee dislocation is a potentially
    limb-threatening condition. Because of the high incidence of
    neurovascular compromise, immediate reduction is recommended before
    radiographic evaluation. Following reduction, anteroposterior (AP) and
    lateral views of the knee should be obtained to assess the reduction
    and evaluate associated injuries. Widened knee joint spaces may
    indicate soft tissue interposition and the need for open reduction.
  • Plain radiographs
    • AP and lateral
    • 45-degree oblique
    • Patellar sunrise
    • Findings
      • Obvious dislocation
      • Irregular/asymmetric joint space
      • Lateral capsular sign (Segond)
      • Avulsions
      • Osteochondral defects
  • The use of angiography in every case of
    knee dislocation is controversial. Vascular compromise is an indication
    for operative intervention. Identifying intimal tears in a
    neurovascularly intact limb may be unnecessary because most do not
    result in thrombosis and vascular occlusion. Some authors advocate
    selective arteriography only if the ABI is <0.9. Regardless, the
    patient should be closely observed for evidence of vascular
    insufficiency.
  • MRI
    • Indications: all knee dislocations and equivalents

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    • Valuable diagnostic tool
      • Preoperative planning
      • Identification of ligament avulsions
      • MCL: injury location
      • Lateral structures: popliteus, LCL, biceps
      • Meniscal pathology
        • Displaced in notch an indication for early surgery
        • Limited arthroscopy secondary to extravasation
      • Articular cartilage lesions
CLASSIFICATION
Descriptive
This is based on displacement of the proximal tibia in
relation to the distal femur. It also should include open versus
closed, reducible versus irreducible. It may be classified as occult,
indicating a knee dislocation with spontaneous reduction.

Anterior: Forceful knee hyperextension
beyond -30 degrees; most common (30% to 50%); associated with posterior
(and possibly anterior) cruciate ligament tear, with increasing
incidence of popliteal artery disruption with increasing degree of
hyperextension
Posterior: Posteriorly directed force
against proximal tibia of flexed knee (25%); “dashboard” injury;
accompanied by anterior and posterior ligament disruption as well as
popliteal artery compromise with increasing proximal tibial displacement
Lateral: Valgus force (13%); medial supporting structures disrupted, often with tears of both cruciate ligaments
Medial: Varus force (3%); lateral and posterolateral structures disrupted
Rotational: Varus/valgus with rotatory component (4%); usually results in buttonholing of the femoral condyle through the articular capsule
Anatomic Classification (Schenck, 1992)

I Single cruciate + collateral ACL + collateral
PCL + collateral
II ACL/PCL Collaterals intact
IIIM ACL/PCL/MCL LCL + PLC intact
IIIL ACL/PCL/LCL + PLC MCL intact
IV ACL/PCL/MCL/LCL + PLC  
V           Fracture-dislocation
C           Arterial injury
N           Nerve injury
Utility of Anatomic Classification
  • It requires the surgeon to focus on what is torn.
  • It directs treatment to what is injured.
  • It leads to accurate discussion of injuries among clinicians.
  • Comparison of similar injuries can be made within the wide spectrum of knee dislocations.

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TREATMENT
  • Immediate closed reduction is essential,
    even in the field and especially in the compromised limb. Direct
    pressure on the popliteal space should be avoided during or after
    reduction. Reduction maneuvers for specific dislocations:
    • Anterior: Axial limb traction is combined with lifting of the distal femur.
    • Posterior: Axial limb traction is combined with extension and lifting of the proximal tibia.
    • Medial/lateral: Axial limb traction is combined with lateral/medial translation of the tibia.
    • Rotatory: Axial limb traction is combined with derotation of the tibia.
  • The posterolateral dislocation is
    believed to be “irreducible” owing to buttonholing of the medial
    femoral condyle through the medial capsule, resulting in a dimple sign
    over the medial aspect of the limb; it requires open reduction
  • The knee should be splinted at 20 to 30 degrees of flexion. The knee must be perfectly reduced in the splint.
  • External fixation
    • This approach is better for the grossly unstable knee.
    • Protects vascular repair.
    • Permits skin care for open injuries.
General Treatment Considerations
  • Most authors recommend repair of the torn structures.
  • Nonoperative treatment has been associated with poor results.
  • Period of immobilization
    • A shorter period leads to improved motion and residual laxity.
    • A longer period leads to improved stability and limited motion.
  • Recent clinical series have reported better results with operative treatment.
  • No prospective, controlled, randomized trials of comparable injuries have been reported.
  • Once stiffness occurs, it is very difficult to treat.
  • Complete PLC disruption is best treated with early open repair.
    • Late reconstruction is difficult.
  • Reconstitution of the PCL is important.
    • It allows tibiofemoral positioning.
    • Collateral and ACL surgery evolves around PCL reconstitution.
    • ACL reconstruction before PCL treatment is never indicated.
Nonoperative
  • Immobilization in extension for 6 weeks
  • External fixation
    • “Unstable” or subluxation in brace
    • Obese patient
    • Multitrauma patient
    • Head injury
    • Vascular repair
    • Fasciotomy or open wounds
    • Removal of fixator under anesthesia
  • Arthroscopy

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    • Manipulation for flexion
    • Assessment of residual laxity
Operative
  • Indications for operative treatment of knee dislocation include:
    • Unsuccessful closed reduction.
    • Residual soft issue interposition.
    • Open injuries.
    • Vascular injuries.
  • Vascular injuries require external
    fixation and vascular repair with a reverse saphenous vein graft from
    the contralateral leg; amputation rates as high as 86% have been
    reported when there is a delay beyond 8 hours with documented vascular
    compromise to limb. A fasciotomy should be performed at time of
    vascular repair for limb ischemia times longer than 6 hours.
  • Ligamentous repair is controversial: The
    current literature favors acute repair of lateral ligaments followed by
    early motion and functional bracing. Timing of surgical repair depends
    on the condition of both the patient and the limb. Meniscal injuries
    should also be addressed at the time of surgery.
Treatment Recommendations of Specific Patterns
  • ACL + MCL (class I knee dislocation)
    • MCL: predictable healing
    • Cylinder cast immobilization in extension for 2 weeks
    • Hinged brace permitting to range of motion
    • Delayed ACL reconstruction
      • Motion restored
      • Residual laxity and desired activity level
  • ACL + LCL/PLC (class I knee dislocation)
    • Delayed surgery at 14 days
      • Capsular healing
      • Identification of lateral structures
    • Arthroscopic ACL: femoral fixation
      • Instruments and experience with open techniques
      • Femoral fixation
    • Tibial fixation/ACL tensioned after LCL/PLC
    • Open posterolateral repair/reconstruction
  • ACL + PLC (class II knee dislocation)
    • Collateral ligaments intact
    • Hinged brace and early range of motion
      • Extension stop at 0 degrees
    • Arthroscopic reconstruction after 6 weeks
      • PCL only in most cases
      • ACL/PCL limited to high-demand patient
    • Sedentary individuals: no surgery
  • ACL + PLC + MCL (class IIIM knee dislocation)
    • Immobilization in extension
    • Early surgery (2 weeks)
      • Examination under anesthesia and limited diagnostic arthroscopy (MRI)
      • Single straight medial parapatellar incision
      • Open PCL reconstruction or repair
      • MCL repair
  • ACL + PLC + LCL/PLC (class IIIL knee dislocation)

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    • Immobilization in extension
    • Delayed surgery at 14 days
      • Diagnostic arthroscopy
      • Arthroscopic or open PCL
      • Open LCL/PLC
    • Incisions critical: avoidance of the midline
      • PCL: medial (open or arthroscopic)
      • Straight posterolateral
COMPLICATIONS
  • Limited range of motion: This is most
    common, related to scar formation and capsular tightness. This reflects
    the balance between sufficient immobilization to achieve stability
    versus mobilization to restore motion. If it is severely limiting,
    lysis of adhesions may be undertaken to restore range of motion.
  • Ligamentous laxity and instability:
    Redislocation is uncommon, especially after ligamentous reconstruction
    and adequate immobilization.
  • Vascular compromise: This may result in
    atrophic skin changes, hyperalgesia, claudication, and muscle
    contracture. Recognition of popliteal artery injury is of paramount
    importance, particularly 24 to 72 hours after the initial injury, when
    late thrombosis related to intimal injury may be overlooked.
  • Nerve traction injury: Injury resulting
    in sensory and motor disturbances portends a poor prognosis, because
    exploration in the acute (<24 hours), subacute (1 to 2 weeks), and
    long-term settings (3 months) has yielded poor results. Bracing or
    muscle tendon transfers may be necessary to improve function.

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