Knee
Patellar Dislocation
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Patellar Dislocation
, Patellar Subluxation
See Also
Knee Dislocation
Definitions
Patellar Subluxation
Excessive
Patella
laxity in movement with typically lateral displacement
Patellar Dislocation
Severe subluxation with complete displacement of the
Patella
outside the trochlear groove
Patella
does not spontaneously relocate
Epidemiology
Most common
Knee Injury
seen in children
More common in teenage girls and young women
Associated with increased Q-Angle (see below)
Mechanism
Forceful deceleration with concurrent knee rotation or
Valgus force with strong quadriceps contraction
Results in lateral
Patella
displacement out of trochlear groove
Risk factors
Miserable Malalignment Syndrome
Tight lateral
Retina
culum
Patella
Alta
Patella
hypermobility
Vastus lateralis hypertrophy
Symptoms
Anterior knee ripping or tearing sensation at injury
Knee
flexes with dislocation
Patella
relocates with knee extension
Subluxation associated with giving way sensation
Dislocation is associated with severe pain
Signs
Knee
held in semi-flexed position
Palpable
Patella
deviated from normal position
Lateral Patellar Dislocation is more common than medial dislocation
Dislocation
Concurrent osteochondral
Fracture
in 28-52% patients
Associated with
Anterior Cruciate Ligament Tear
Subluxation
Instability and weakness
Reluctant to bear weight
Predisposing factors
Examine for predisposing factors listed above
J-Sign
Quadriceps angle (Q-Angle) >15 degrees
Imaging
Knee XRay
Views
Merchant and Infrapatellar views (knee flex 45)
Anteroposterior, Notch, and lateral views
Interpretation
Often normal
Medial
Patella
avulsion
Fracture
Osteochondral
Fracture
MRI
Knee
without Contrast
Indications
Osseous loose body on XRay
Large joint effusion (hemarthrosis)
Findings
Osteochondral defect
Medial Patellofemoral Ligament (MPFL) Tear
Differential Diagnosis
Knee Dislocation
Knee
spontaneous reduction prior to presentation may be misdiagnosed as
Patella
subluxation
Knee Dislocation
may occur with low energy mechanism (esp. in
Obesity
)
Knee Dislocation
is a risk for vascular injury, and missed dislocation risks limb loss
Management
Patella
reduction (if still dislocated)
Pre-reduction XRay not needed if isolated
Patella
dislocation (consider a post-reduction XRay)
Administer IV
Analgesic
s or
Anesthesia
Maneuver (two providers)
One provider gently extends knee
Second provider applies gentle pressure to relocate the
Patella
(medial pressure to relocate a laterally dislocated knee)
Bracing and taping
Alter aggravating activity
Physical Therapy and Rehabilitation
Soft tissue and
Patella
r mobilization
Muscle Strength
Vastus medialis oblique
Gluteus
Foot
and ankle
Consider immobilization
Indications
First
Patella
dislocation and
No significant Vastus Medialis disruption
Technique
Immobilize for 6 weeks
Knee
in full extension
Non-weight bearing
Foam pad protects Vastus Medialis
Lateral support holds
Patella
medially
Maintenance
Patella
r stability program after rehabilitation
Surgery Indications
Inadequate improvement in 6 months
Osteochondral
Fracture
Medial Patellofemoral Ligament (MPFL) Tear resulting in recurrent subluxation or dislocation
Complications
Osteochondral
Fracture
Medial Patellofemoral Ligament (MPFL) Tear
May result in recurrent
Patella
subluxation or dislocation
References
Rashidzada (2020) Crit Dec Emerg Med 34(11): 12-3
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