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.
(See also Bursitis Bursitis Bursitis is acute or chronic inflammation of a bursa. The cause is usually unknown, but trauma, repetitive or acute, may contribute, as may infection and crystal-induced disease. Symptoms include... read more 
.)
Indications
Aspiration of effusion to determine cause of bursitis
Rarely for injections of corticosteroid to treat 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 be sent to the laboratory for cell count, 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 reaccumulates.
Symptoms are not relieved by local measures such as ice, elevation, elastic bandage, and nonsteroidal and anti-inflammatory drugs.
When needed, bursal injection therapy provides rapid relief, which is particularly beneficial for large or painful effusions.
Contraindications
Absolute contraindications
Overlying cellulitis or skin ulcer, bacteremia, adjacent acute fracture or osteomyelitis, osteochondral fracture
Hypersensitivity to an injected substance
For corticosteroid injection, suspected septic bursitis
Relative contraindications
Poorly controlled diabetes: Any benefit of corticosteroids is weighed against risk of worsening glycemic control.
Previous corticosteroid injection into same site: Many experts advise waiting 3 to 4 months between injections and not exceeding a lifetime total of 4 injections.
Complications
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 (sometimes called steroid flare) occurring within a few hours of depot corticosteroid injection and usually lasting ≤ 48 hours (probably irritation due to crystals in the injection vehicle)
In diabetic patients, hyperglycemia that may persist for weeks after a depot corticosteroid injection
Equipment
Antiseptic solution (eg, chlorhexidine, povidone iodine, isopropyl alcohol)
Sterile drapes
Sterile gauze, sterile gloves, sterile adhesive bandage
20-mL syringe with 18- to 20-gauge needle for fluid withdrawal
Needle insertion site anesthesia (eg, topical freezing spray and/or injectable 1% lidocaine without epinephrine, in a 3-mL syringe)
Optional: For therapeutic injection, 5- to 10-mL syringe with 2 to 3 mL 1% lidocaine without epinephrine, rarely with injectable depot corticosteroid (eg, methylprednisolone acetate, 20 mg)
Hemostat
Some 3-, 5-, and 20-mL syringes with nonlocking hubs
For diagnostic aspiration, appropriate tubes for specimen collection, including blood culture bottles
Having an assistant is helpful.
Additional Considerations
For bursal injection therapy, local anesthetic and depot corticosteroid can be mixed in a single syringe (the anesthetic eliminates the pain of the corticosteroid).
Corticosteroid injection is rarely necessary in the prepatellar bursa.
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.
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
Fluid in the prepatellar bursa is often loculated, resulting in less fluid accessible for withdrawal than expected.
Positioning
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 Procedure
Do the procedure using sterile technique.
Prepare the site
Identify the bursa's point of maximum fullness and mark it on the skin for needle entry.
Prepare the area with antiseptic solution.
Apply sterile drapes that widely expose the needle insertion site and the patella.
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 sterile gloves.
Insert the needle (attached to the aspirating syringe) into the skin at the point of maximal fluctuance of the effusion from the lateral side.
Gently pull back 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 sterile dressing.
Transfer bursal effusion samples to tubes and other transport media for synovial fluid analysis Synovial fluid examination Some musculoskeletal disorders affect primarily the joints, causing arthritis. Others affect primarily the bones (eg, fractures, Paget disease of bone, tumors), muscles or other extra-articular... read more . Inspect the fluid for blood and fat.
Aftercare
A protective compression bandage may prevent reaccumulation of fluid in traumatic bursitis.
Prescribe limited activity, ice, elevation, and 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
Do not inject corticosteroids against resistance; if there is resistance, slightly withdraw the needle.
Tips and Tricks
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.
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
