What are the next steps for a patient with left knee pain and possible patellar dislocation after a fall, who had to manually reduce their knee joint?

Immediate Management of Suspected Patellar Dislocation After Fall

Obtain knee radiographs immediately (anteroposterior, lateral, and patellofemoral views) to rule out fractures and confirm reduction, followed by MRI to assess for medial patellofemoral ligament injury, osteochondral fractures, and anatomic risk factors for recurrent instability. 1

Initial Imaging Workup

Plain radiographs are mandatory as the first imaging study for any patient with acute knee trauma and a history suggesting patellar dislocation, even after spontaneous reduction. 1

• Obtain a minimum of three views: anteroposterior, lateral, and patellofemoral (sunrise/Merchant view) to evaluate for patellar fractures, osteochondral injuries, and confirm the patella is reduced. 1
• The patellofemoral view is specifically indicated when patellar dislocation is suspected, as it best visualizes patellar position and fracture patterns. 1
• Radiographs should be obtained regardless of Ottawa Knee Rule criteria when there is gross deformity or clinical suspicion of dislocation, as physician judgment supersedes clinical decision rules. 1

Advanced Imaging with MRI

MRI without contrast should be obtained as soon as possible after radiographs, ideally within days of injury. 2

• MRI is considered mandatory for evaluating predisposing anatomic factors (trochlear dysplasia, patella alta, tibial tuberosity lateralization) and detecting injuries that determine treatment. 2
• MRI identifies medial patellofemoral ligament (MPFL) tears, which occur in nearly all patellar dislocations and are critical for surgical planning. 3, 4
• MRI detects osteochondral fractures and "kissing contusions" (bone marrow edema on the medial patella and lateral femoral condyle), which are characteristic findings confirming the diagnosis even when dislocation was not witnessed. 3
• Half of patellar dislocations are clinically unsuspected because spontaneous reduction occurs before evaluation, making MRI findings diagnostic. 3

Assessment for Vascular Injury

In cases of significant trauma or knee dislocation (not just patellar dislocation), evaluate for vascular injury. 1

• Patellar dislocation alone rarely causes vascular injury, but true knee dislocation (tibiofemoral) carries approximately 30% risk of popliteal artery injury requiring urgent intervention. 1
• Assess for "hard signs" of vascular injury: absent pulses, pallor, neurological deficits, or palpable thrill. 1
• If vascular injury is suspected, obtain CT angiography of the lower extremity rather than conventional angiography as the initial study. 1
• Ankle-brachial index (ABI) <0.9 has 87% sensitivity and 97% specificity for vascular injury in limb trauma. 1

Risk Stratification for Treatment Planning

Evaluate specific anatomic and clinical factors that predict recurrent instability and guide surgical versus conservative management. 2, 4

High-Risk Features Favoring Early Surgical Consideration:

• Age: Younger patients (especially adolescents) have higher recurrence rates and more severe underlying anatomic abnormalities. 2, 4
• Low-energy mechanism: Minimal trauma causing dislocation indicates severe underlying pathoanatomy. 2
• Bilateral symptoms or family history: Suggests systemic predisposition to instability. 2
• MRI findings: MPFL rupture with multiple anatomic risk factors (trochlear dysplasia, patella alta, increased tibial tuberosity-trochlear groove distance). 2, 3
• Osteochondral fractures: Require surgical fixation or removal. 2, 3

Recurrence Risk Without Surgery:

• Approximately 25% of patients experience recurrent dislocation after first-time patellar dislocation treated conservatively. 2
• However, 50% of patients experience persistent symptoms (pain, swelling, giving way, functional limitations) even without frank redislocation. 2

Treatment Decision Algorithm

For first-time patellar dislocation:

1. If large osteochondral fracture present on imaging: Surgical fixation or fragment removal is indicated. 2, 3

2. If multiple high-risk anatomic factors present (trochlear dysplasia, patella alta, MPFL rupture, young age, low-energy mechanism): Consider acute MPFL reconstruction rather than conservative management, as recurrence risk approaches 40% and persistent symptoms affect 50% of patients. 5, 2, 4

3. If isolated MPFL injury without significant anatomic risk factors in older adolescent or adult: Initial conservative management with immobilization followed by rehabilitation is reasonable, though evidence certainty is very low. 5

4. If skeletal immaturity present: Avoid osseous procedures (tibial tuberosity transfer, trochleoplasty) to prevent physeal damage; MPFL reconstruction with soft-tissue techniques may be considered. 4

Common Pitfalls to Avoid

• Do not rely solely on clinical examination: Half of patellar dislocations are clinically unsuspected because spontaneous reduction occurs; MRI findings may be the only diagnostic evidence. 3
• Do not delay MRI: Obtain within days of injury while acute findings (bone marrow edema, soft tissue injury) are most apparent. 2
• Do not miss osteochondral fractures: These require surgical intervention and are best detected on MRI, though sometimes visible on radiographs as small bone fragments. 2, 3
• Do not confuse patellar dislocation with knee (tibiofemoral) dislocation: The latter is a limb-threatening emergency requiring immediate vascular assessment. 1
• Do not assume conservative management is always appropriate: With multiple risk factors, recurrence rates approach 40% and quality of life remains impaired in 50% of patients. 5, 2

Immediate Management Steps

• Immobilization: Place knee in extension with immobilizer or brace. 5
• Weight-bearing: Allow weight-bearing as tolerated with crutches for comfort. 5
• Referral: Arrange orthopedic follow-up within 1-2 weeks after MRI is obtained to discuss definitive treatment based on imaging findings and risk factors. 2