Aspiration of the prepatellar bursa is done for diagnostic purposes (eg, particularly to exclude septic bursitis).
The prepatellar bursa lies just below the skin, increasing the risk of skin damage and infection from corticosteroid injection therapy.
Prepatellar bursitis typically manifests with obvious swelling and erythema; thus, ultrasonography for evaluation and needle guidance is usually unnecessary. Extension of erythema beyond the patellar bursa suggests infection.
(See also Bursitis.)
Indications for Aspirating or Injecting a Prepatellar Bursa
Aspiration of effusion to determine cause of bursitis
Occasionally for injections of corticosteroid to treat recalcitrant or recurrent noninfectious inflammation
Prepatellar bursal puncture is usually done diagnostically (eg, to diagnose septic or crystal-induced bursitis). Because the prepatellar bursa is the second most common site of septic bursitis, effusion fluid should routinely be sent to the laboratory for cell count and differential, crystal analysis, Gram stain, culture, and sensitivity tests.
Corticosteroid injection is rarely necessary in the prepatellar bursa. Therapeutic injection should be done only if all of the following criteria are satisfied:
Infection has been excluded by bursal fluid analysis.
Bursal fluid repeatedly reaccumulates.
Symptoms are not relieved by local measures such as ice, elevation, elastic bandage, and nonsteroidal and anti-inflammatory drugs.
When needed, bursal injection may provide rapid relief, which is particularly beneficial for large or painful recurrent effusions.
Contraindications to Aspirating or Injecting a Prepatellar Bursa
Absolute contraindications
Hypersensitivity to an injected substance
For corticosteroid injection, suspected septic bursitis
Inserting a needle through obviously infected skin should be avoided when possible, but if septic bursitis is suspected, fluid should be aspirated.
Relative contraindications
Poorly controlled diabetes: Any benefit of corticosteroids is weighed against risk of worsening glycemic control and risk of infection.
Recent (ie, within the last 3 months) corticosteroid injection into same site (although no evidence has evaluated this practice).
Coagulopathy is not a contraindication (1).
Complications of Aspirating or Injecting a Prepatellar Bursa
Complications are uncommon and include
Subcutaneous fat atrophy, skin atrophy and sinus tracts, temporary skin depigmentation, and infection due to superficial (< 0.5 cm deep) corticosteroid injection
Painful local reaction thought to result from a chemical synovitis in response to the crystals in the corticosteroid solution (sometimes called postinjection flare) occurring within a few hours of depot corticosteroid injection and usually lasting ≤ 48 hours
In diabetic patients, hyperglycemia after a depot corticosteroid injection
Equipment for Aspirating or Injecting a Prepatellar Bursa
Sterile gauze, gloves, adhesive bandage
20-mL syringe with 18- to 20-gauge needle for fluid withdrawal
Hemostat, if switching of syringe while the needle remains inserted is anticipated
Some 3-, 5-, and 10-mL syringes
For diagnostic aspiration, appropriate tubes for specimen collection, including blood culture bottles
Having an assistant is helpful.
Additional Considerations for Aspirating or Injecting a Prepatellar Bursa
For bursal injection, local anesthetic and depot corticosteroid can be mixed in a single syringe. Adding the anesthetic helps confirm good needle placement when injection immediately relieves pain. Adding anesthetic also may decrease the risk of the corticosteroid causing subcutaneous fat atrophy and the risk of postinjection flare.
Corticosteroid injection is rarely necessary in the prepatellar bursa (based on an increased risk of infection and skin atrophy and a paucity of data showing improved long-term outcomes).
Septic bursitis cannot be ruled out by the initial gross and microscopic examination of the aspirated effusion. Infected fluids (even from Staphylococcus aureus, the most common organism) tend to show a minimal fluid leukocytosis (although the neutrophil percentage is generally high). If the history or physical examination suggests septic bursitis, withhold bursal corticosteroid injection. Septic bursitis requires drainage or sometimes bursal excision in addition to systemic antibiotics.
Immediate analgesia after injection of local anesthetic helps confirm correct needle placement and that the prepatellar bursa is the source of pain.
Relevant Anatomy for Aspirating or Injecting a Prepatellar Bursa
Fluid in the prepatellar bursa is often loculated, resulting in less fluid accessible for withdrawal than expected. In such cases, ultrasound-guidance for aspiration may be helpful.
Positioning for Aspirating or Injecting a Prepatellar Bursa
Position the patient reclined or supine. Comfortably rest the knee, slightly flexed, on a pillow.
To avoid vasovagal episodes, avert the patient's head and orient your work area so that the patient does not see the needles.
Step-by-Step Description of Aspirating or Injecting a Prepatellar Bursa
Prepare the site
Aspirate at the base of the effusion; avoid an injection trajectory that risks piercing the patella.
Prepare the area with antiseptic solution.
Spray freezing spray at the needle insertion site until it just blanches and/or inject a skin wheal of local anesthetic (eg, ≤ 1 mL).
Puncture the bursa
Wear gloves.
Insert the needle (attached to the aspirating syringe) into the skin at the base (bottom) of the effusion.
Gently pull back periodically on the plunger as you advance the needle. If the needle hits bone, retract and then readvance it at a different angle.
Fluid will enter the syringe when the bursa is entered.
Drain all fluid from the bursa. Use your fingertips to apply gentle pressure to the bursal periphery to milk the fluid toward the needle tip.
If injecting the bursa, stabilize the needle hub with your hand and switch syringes. If the needle is on too tight, hold the hub of the needle with a hemostat.
Inject any drugs and withdraw the needle.
Apply an adhesive bandage or dressing.
Transfer bursal effusion samples to tubes and other transport media for synovial fluid analysis. Inspect the fluid for blood and fat.
Aftercare for Aspirating or Injecting a Prepatellar Bursa
A protective compression bandage may prevent reaccumulation of fluid in traumatic bursitis.
Prescribe limited activity, ice, elevation, and, if not contraindicated, oral nonsteroidal anti-inflammatory drugs (NSAIDs) until pain subsides.
Instruct the patient to return for reassessment to exclude infection if pain is continuously and progressively increasing after several hours or persists for > 48 hours.
Warnings and Common Errors for Aspirating or Injecting a Prepatellar Bursa
Do not inject corticosteroids against resistance; if there is resistance, slightly withdraw the needle.
Tips and Tricks for Aspirating or Injecting a Prepatellar Bursa
Consider doing ultrasonography if there is no obvious large effusion.
When inspecting bursal fluid, consider the following: The blood due to a traumatic needle insertion tends to be nonuniformly bloody and tends to clot. Nontraumatic fluid should be evaluated by polarized light microscopy for the presence of crystals.
Reference
1. Yui JC, Preskill C, Greenlund LS: Arthrocentesis and joint injection in patients receiving direct oral anticoagulants. Mayo Clin Proc 92(8):1223–1226, 2017. doi: 10.1016/j.mayocp.2017.04.007
