KNEE DISLOCATION

(FEMOROTIBIAL)

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% are spontaneously reduced.

Most knee dislocations are the result of high-energy injuries, such as motor vehicle or industrial accidents. They can also occur with low-energy injuries, such as those that occur in sports.

ANATOMY

The ginglymoid (hinge joint) consists of three articulations: (1) patellofemoral, (2) tibiofemoral, and (3) tibiofibular. Under normal cyclic loading, the knee may experience up to five times body weight per step. The normal range of motion is from 0 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 the tibia of a flexed knee.

Low-energy: This includes athletic injuries and falls in an obese patient.

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.

   

  CLINICAL EVALUATION

Patients present with gross knee distortion unless the knee underwent spontaneous reduction. Immediate reduction should be undertaken without waiting for radiographs. The arterial supply is of paramount importance. Secondary consideration should be 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. These injuries may be difficult to assess acutely.

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 (PT) 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 PT 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.

• 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.

    • The maximum ischemic time should be 6 to 8 hours.

  • 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:

      • 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) should be considered.

      • Evaluate for nonocclusive (intimal) injury.

      • Sensitivity and specificity are uncertain.

      • Arteriogram is indicated if results are abnormal.

  • Neurologic injury—peroneal nerve (10% to 35%): This is commonly associated with posterolateral dislocations, with injury varying from neurapraxia (usual) to complete transection (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

• Forty-five–degree oblique and/or plateau views if an associated fracture is suspected

• Findings

  • Obvious dislocation

  • Irregular/asymmetric joint space

  • Lateral capsular sign (Second)

  • 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

• Valuable diagnostic tool

  • Preoperative planning

  • Identification of ligament avulsions

  • MCL: injury location (femur, tibia, midsubstance)

  • Lateral structures: popliteus, LCL, biceps

  • Meniscal pathology

    • Displaced in notch, an indication for early surgery

    • Limited arthroscopy secondary to extravasation

  • Articular cartilage lesions

     

    CLASSIFICATION (FIG. 34.1)

     

     

     

    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.

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.

• It protects vascular repair.

• It 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. There are high rates of heterotopic ossification.

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

• 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 of the limb. A fasciotomy should be performed at the 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 or knee 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)

• 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.