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Knee dislocation

Introduction 

Knee dislocations are an uncommon injury, but one that cannot be missed.  Any knee exam that reveals injuries to multiple ligaments (e.g. ACL/PCL) should raise the suspicion of a knee dislocation.  A significant number of knee dislocations spontaneously reduce, but the true incidence of that phenomenon is unknown.  Knees presenting dislocated should be reduced, and a thorough H&P should be performed.     Many knee dislocations are the result of high velocity injuries.  This group of dislocations has a high incidence of associated injuries, perhaps approaching 80%.  High velocity injuries are commonly caused by motor vehicle and motor cycle accidents, car vs. pedestrian injuries, industrial accidents, and falls from a height.  Low velocity injuries are often the result of athletic activities and minor falls.  Vascular injuries are relatively less common in this group (approximately 5%), and nerve injuries are present in about 20%.
 

Anatomy


Classification

General classification of knee dislocations is based upon the direction of the dislocation of the tibia in reference to the femur. Anterior (40%) - Usually involve a hyperextension mechanism.  20-50% present as spontaneously reduced (Wascher et al, J Trauma 1997).  Sequence of injuries involves ACL-PCL-capsule-neurovascular structures.  Often have both ACL and PCL tears.  The MCL and/or LCL can also be injured.  The popliteal artery is tethered at the adductor hiatus and arch of the soleus.
  Posterior (33%)  -- Typically higher energy injuries (e.g. dashboard).  Posterior dislocations often involve ACL and PCL injuries and are related to a direct blow on a flexed knee.  Can have associated extensor mechanism disruption.  Possible avulsion or complete disruption of popliteal artery.
 Lateral (18%) -
 Medial  (4%)
 Rotatory (4%) -- usually posterolateral.  THESE ARE OFTEN IRREDUCIBLE!  The medial femoral condyle can button-hole through the medial soft tissues resulting in a "dimple sign."  Interposed structures include the MCL and medial capsule (*OITE question!!!). 
 Wascher modification of the Schenck Classification: 
KD-I multiligamentous injury without injuring both cruciates
KD-II bicruciate injury only
KD-III  bicruciate injury + either posteromedial or posterolateral corner
KD-IV bicruciate injury + both posteromedial and posterolateral corners

KD-V multiligamentous injury with periarticular fracture

Diagnosis

Physical ExamLigamentous evaluation of cruciates, MCL, LCL, posterolateral, and posteromedial corners.  Exam under anesthesia is particularly helpful and should be performed at time of reduction if feasible.  Document pre and post-reduction pulses in all patients with knee dislocation or suspected knee dislocation.A thorough neurologic exam is a must, with special attention paid to peroneal nerve function.   
Imaging
 Can range from obvious dislocation to very subtle presentations.  Associated injuries seen on plain film can include tibial plateau fractures, proximal fibula fracture, intercondylar spine fracture, avulsion of Gerdy's tubercle, and avulsion of the fibular head.
 
MRI is used to characterize the soft tissue injury and to define occult osseous injuries (El-Khoury et al).  Can evaluate the menisci and articular surfaces with MRI.  MRI also helps with surgical planning - avulsed ligaments for repair and disruption to femoral or tibial origin. Can also assess extensor mechanism.

Treatment

 Non-operative treatment

Historically managed with a long period of immobilization.  Risk of arthrofibrosis or instability.  Relatively poor knee function with non-operative treatment in most series.

 Operative treatment


Goals of surgery:  anatomic repair and reconstruction of all associated ligamentous and meniscal injujries, allow for relatively early ROM, provide long-term stability to knee without stiffness.  Timing, graft selection, and technique remain controversial.  Allografts are gaining popularity due to availability, lack of donor site morbidity, and the reduced operating time that is associated with their use.
 Emergent Treatment:  Criteria - irreducibility, open dislocation, compartment syndrome, vascular repair (should do prophylactic fasciotomies).  Treatment in these cases involves a spanning external fixator that allows for stability and access to the limb.
 Non-Emergent Surgery:  Need to ensure adequate perfusion of the limb.  Should generally wait for resolution of the acute inflammation and soft tissue edema (may decrease the risk of arthrofibrosis).  A "capsular seal" is needed for arthroscropic techniques, and requires about 10 days of soft tissue healing for this to be present.  Surgical planning should involve imaging studies and planning of allograft tissue.  Recommended that surgery occur in window between weeks 2 and 3.  If reconstruction is done beyond 3 weeks, patients tend to have more scarring in collateral structures and the posterolateral corner.  This makes the repair difficult or impossible.


Complications

Vascular injuries "Vascular injuries in knee dislocations:  The role of physical examination in determining the need for arteriography." Stannard et al, JBJS (86), 2004.

           

126 dislocated knees at average 19-month follow up.  Physical exam of vascular status was used to determine the need for arteriography.  Physical findings in the first 48 hours that led to angiography:  Change in pulses

Expanding hematoma around the knee

Extremity pallorExtremity coolness
Study found a strong correlation between physical exam and the need for arteriography.  100% sensitive and 99% specific.  One false positive.  No false negatives. Especially recommended watching KD-IV dislocations for 48 hours.  17 additional limbs received arteriography because of "attending preference."  All of these limbs were without vascular injury.
 Journal of Trauma. 2004.  Mills et al Harborview

            38 patients with knee dislocation underwent ABI and clnical exam to determine the need for arteriography.  ABI of 0.90 used as cutoff.  11 patients met criteria of having ABI of less than 0.90, and all had vascular injury on arteriography.  In 27 patients with ABI greater than 0.90, none had a vascular injury.  100% sensitivity, 100% specificity, 100% positive predictive value.  Shock Trauma has data that supports this with a retrospective study of 57 knees.
  
Neurologic Injury 
Neurologic Injuries occur in 20-40%.  Usually involve common peroneal nerve.  Can be neuropraxia or neuronotmesis.  Neurologic injuries are most common after a posterolateral dislocation.  Need to document a neurologic exam prior to manipulation or reduction.  About 50% of these neurologic injuries will recover.
 Compartment Syndrome
 Fluid extravasation
 Wound Problems
 Arthrofibrosis
 Residual Laxity
 Arthritis
 Heterotopic Ossification
 

Red Flags and Controversies

Graft Choice

Timing of Surgery

Vascular Exam Modalities 

Outcomes

Outcome studies are problematic with this injury as they tend to be small retrospective series with significant heterogeneity in injury patterns and treatment methodology.
Richter et al OKO 2004 -  38% require an additional surgical intervention due to motion problems.  Post-op instability of one or more ligaments is present in 37% of patients.  25-75% have significant residual pain.
 "Arthroscopically assisted combined anterior and posterior cruciate ligament reconstruction in the Multiple Ligament Injured Knee: 2 to 10 Year Follow-up."  Fanelli et al, AJSM 2002
            Case series of 35 multiligament knees
            Endoscopic techniques (very heterogenous) - used allograft, autograft, did repairs and reconstructions, variability in bracing and treatment of the MCL
            Results - looked at objective tests, knee ligament rating scales, stress radiographs, and arthrometric testing
            Found no difference between acute/chronic repairs (8weeks)
            Patients essentially had functionally stable, but not normal knees
 "Surgical Management of Knee Dislocations" Harner, et al JBJS 2004
            Case series of 31 knees with 2-6 year f/u
Anatomic repair/reconstruction using allograft tissues (heterogenous)
Results:  Acute repairs better than chronic using subjective rating scales (3 week cut-off)
ROM the same - 1 deg loss of ext, 12 deg loss of flexion
More predictable results in the acutely reconstructed knee
Functional stability restored, but don't expect a return to high demand activities
  

Miscellaneous

References

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