Patellar dislocation
Patellar dislocation is an acute lateral displacement of the patella out of the femoral trochlear groove, usually from a twisting non-contact pivot or a direct blow, presenting with a hemarthrosis and a positive apprehension test, and confirmed by plain radiograph with MRI reserved to assess the medial patellofemoral ligament and cartilage before deciding on bracing versus surgical stabilization.
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What this article covers
- Overview
Patellar dislocation is an acute traumatic displacement of the patella out of the femoral trochlear groove, almost always laterally, most commonly from a non-contact twisting or pivoting movement on…
- Epidemiology
A common cause of acute traumatic knee hemarthrosis in adolescents and young adults, occurring during sport with the classic twisting or pivoting mechanism.
- Risk factors
A non-contact twisting or pivoting movement on a planted foot with the knee in valgus and external rotation, the classic mechanism, most often during sport.
- Pathophysiology
The medial patellofemoral ligament (MPFL) is the primary soft-tissue restraint against lateral translation of the patella out of the femoral trochlear groove during early knee flexion.
- Clinical features
Acute lateral knee pain and a rapidly developing effusion (hemarthrosis) after a twisting or pivoting injury or a direct blow to the medial patella is the hallmark and defining presentation, together…
- Differential diagnosis
Anterior cruciate ligament tear: an acute noncontact twisting injury with a popping sound and a large hemarthrosis, but without a history or exam finding of lateral patellar displacement, and with a…
- Diagnosis
Patellar dislocation is a clinical diagnosis established by the combination of a history of the kneecap displacing laterally (or a direct blow to the medial patella) with an acute hemarthrosis and a…
- Management
First, if the patella remains dislocated, perform closed reduction promptly by gently extending the knee while guiding the lateral patella medially with steady hand force, then reassess distal neurovascular status.
- Complications
Recurrent dislocation, the most common complication, particularly without adequate quadriceps rehabilitation or correction of an anatomic risk factor.
- Prognosis
Most first-time dislocations without a significant osteochondral fragment recover functional stability with bracing and physical therapy, without requiring surgery.
- Prevention
Complete a structured quadriceps, hip abductor, and core strengthening program of at least 6 to 12 weeks after any patellar dislocation, continuing beyond symptom resolution, since inadequate…
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Anterior cruciate ligament tear is a noncontact pivoting knee injury diagnosed clinically with the Lachman test and confirmed on MRI, and the central decision is surgical reconstruction versus supervised rehabilitation based on age, activity level, and knee instability.
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Overuse knee injuries, including patellofemoral pain syndrome, iliotibial band syndrome, pes anserine bursitis, and patellar or quadriceps tendinopathy, present with activity-related pain without a traumatic event and are diagnosed clinically by pain location, then managed with activity modification, cryotherapy, NSAIDs, and targeted physical therapy.