What is the appropriate management for a patient with swelling superior to the patella (kneecap) without pain?

Management of Painless Suprapatellar Swelling

Begin with plain radiographs (AP, lateral at 25-30° flexion, and tangential patellar view) as the mandatory first imaging study, followed by clinical assessment to distinguish between benign effusion, occult fracture, or soft tissue pathology. 1, 2

Initial Diagnostic Approach

Obtain standard three-view knee radiographs immediately to exclude fracture, loose bodies, or chronic joint pathology before considering the swelling benign. 1, 2 The absence of pain does not eliminate serious pathology—small osseous avulsion fragments at the superior pole may indicate sleeve fracture or prior patellar subluxation events that require surgical intervention. 3, 4

Key Clinical Features to Assess

• Ability to perform active straight leg raise: Inability indicates quadriceps mechanism disruption (sleeve avulsion, quadriceps tendon rupture) requiring urgent surgical repair, even without significant pain. 4
• Palpable defect or gap superior to patella: Suggests complete tendon disruption. 4
• History of recent fall, direct trauma, or eccentric loading: Raises concern for occult fracture or tendon injury. 4
• Fever, systemic symptoms, or immunosuppression: Mandates immediate arthrocentesis to exclude septic arthritis, which can present with minimal pain in immunocompromised patients. 1, 5

Imaging Algorithm

If Radiographs Show Small Bony Fragment or Abnormality

Order MRI without IV contrast to evaluate for sleeve avulsion fracture, quadriceps tendon integrity, cartilage injury, and loose bodies. 3, 1 MRI is essential because sleeve avulsions in adults are extremely rare and easily missed on plain films alone. 4

If Radiographs Are Normal But Clinical Concern Persists

• Ultrasound may confirm effusion and guide aspiration if infection or crystal disease is suspected. 6, 1
• MRI without contrast is appropriate if mechanical symptoms develop (locking, catching), inability to bear weight persists beyond 5-7 days, or there is clinical suspicion for internal derangement despite normal radiographs. 1

Management Based on Etiology

Benign Effusion (Normal Radiographs, Negative Red Flags)

• Conservative management with close observation is appropriate if the patient can bear weight fully and perform straight leg raise without difficulty. 1
• Avoid corticosteroid injection until infection is definitively excluded—injecting infected joints or supporting structures causes catastrophic outcomes including tendon rupture and septic spread. 3, 5
• Aspiration is indicated if the effusion is atraumatic and etiology remains unclear after initial assessment, to exclude crystal disease or low-grade infection. 1

Sleeve Avulsion or Quadriceps Mechanism Injury

• Surgical repair using Krakow pullout sutures through transosseous patellar tunnels provides secure fixation and excellent functional outcomes when sleeve avulsion is confirmed. 4
• Do not delay surgery if extensor mechanism disruption is identified—these injuries require anatomic repair for restoration of function. 4

Suspected Infection Despite Minimal Pain

• Perform arthrocentesis immediately with synovial fluid analysis (cell count, Gram stain, culture, crystal analysis) and obtain blood cultures if fever is present. 1
• Obtain ESR and CRP, as the combination provides optimal sensitivity and specificity for joint infection. 1
• Never inject corticosteroids into any joint until infection is completely excluded—this is an absolute contraindication. 3, 5

Critical Pitfalls to Avoid

• Never skip radiographs even when swelling appears clinically benign—approximately 20% of patients inappropriately receive advanced imaging without baseline radiographs. 1, 2
• Never assume painless swelling is benign: Sleeve avulsions, bipartite patella variants, and even septic arthritis in immunocompromised patients can present with minimal pain. 5, 4, 7
• Never inject corticosteroids into the suprapatellar region or any knee structure until infection and structural injury are definitively excluded—this causes tendon weakening, spontaneous rupture, and inhibits healing. 3
• Do not delay aspiration if infection is suspected based on patient risk factors (immunosuppression, malignancy, bacteremia, prosthetic joint)—septic arthritis is an orthopedic emergency even without classic inflammatory signs. 1, 5

Follow-Up Strategy

If initial workup is negative and conservative management is chosen, reassess at 5-7 days for development of mechanical symptoms, inability to bear weight, or progression of swelling. 1 If symptoms persist or worsen, proceed to MRI without contrast to identify occult pathology. 1