Prepatellar Bursitis

Inflammation of the prepatellar bursa, located in the subcutaneous tissue in front of the patella and the proximal patellar tendon. Also called housemaid's knee, carpet layer's knee or kneeler's knee.

• It results from repeated or prolonged kneeling and pressure (carpet layers, plumbers, roofers, tile setters, cleaners, gardeners, miners, wrestlers and volleyball players), from a direct blow or fall onto the knee, or from other causes such as gout, rheumatoid arthritis, pseudogout, and infection.
• Septic prepatellar bursitis accounts for about 20 to 30% of cases of bursitis here, and is caused mostly by Staphylococcus aureus (about 80%, including MRSA), then streptococci. Skin breaks (abrasion, laceration, insect bite, injection, tattoo, or dermatitis) over the bursa are the usual portal. Risk factors: manual work involving kneeling, diabetes, alcohol misuse, immunosuppression and corticosteroid use, and chronic kidney disease.
• The bursa is separate from the knee joint, so the knee joint is normally unaffected.
• It affects men more than women, mostly of working age.

• Swelling in front of the patella, which can be a localised, fluctuant "egg like" mass, with or without redness, usually painless in chronic aseptic cases, and painful when kneeling.
• Full range of knee motion, including full active flexion (though flexion is limited by the swelling and tenderness), with no joint line tenderness and no intra articular effusion. Straight leg raise is intact.
• Septic bursitis: warmth, erythema extending beyond the bursa, marked tenderness, fever and malaise, a break in the overlying skin, regional lymphadenopathy, and cellulitis of the anterior knee.
• Chronic bursitis: a thickened, nodular bursal wall, with intermittent flares and loose bodies (rice bodies).
• Differential diagnosis: septic arthritis of the knee (diffuse joint swelling, effusion, painful and limited motion in all directions), infrapatellar bursitis (below the patella), superficial infrapatellar bursitis, pes anserine bursitis, patellar tendinopathy, patellar fracture, Osgood-Schlatter disease, Baker cyst (behind the knee), prepatellar haematoma, cellulitis, rheumatoid nodule, gouty tophus, and tumour (synovial sarcoma, metastasis).
• Complications: recurrent or chronic bursitis, abscess, septic knee arthritis (rare), osteomyelitis of the patella, sepsis, cutaneous fistula, and scarring.

• Clinical. The key points are the position of the swelling in front of the patella, a full range of movement of the knee joint, and the absence of a joint effusion.
• Aspirate the bursa for fluid analysis when infection is suspected or the diagnosis is unclear (use an 18 to 21 gauge needle, inserted through uninfected skin at the side, and with an oblique track). Send for cell count and differential, Gram stain, aerobic and anaerobic culture (with mycobacterial and fungal cultures when chronic), and crystals. Turbid or purulent fluid and a white cell count above 10,000 cells/mm3 favour infection, though counts can be lower in septic bursitis.
• Blood tests: full blood count, CRP, ESR, urate, glucose, creatinine, and blood cultures in febrile patients.
• X-ray of the knee for fracture, foreign body, calcification, osteomyelitis or osteoarthritis. Ultrasound confirms the superficial fluid collection, differentiates it from an intra articular effusion, and guides aspiration. MRI for deeper extension, osteomyelitis or a suspected mass.

• Aseptic traumatic or occupational bursitis:
  • Stop kneeling or use knee pads with a wide soft base, kneeling mats or a kneeling stool.
  • Ice 10 to 15 minutes 3 times daily, compression bandage and elevation.
  • NSAIDs for 1 to 2 weeks: ibuprofen 400 mg orally 8 hourly with food, naproxen 500 mg 12 hourly, or topical diclofenac 1% gel 2 to 4 g 3 to 4 times daily. Add paracetamol 1 g 6 hourly.
  • Most settle in 2 to 8 weeks. Aspiration of a large, tense, painful, non-infected bursa gives quick relief, followed by a compression wrap and knee pad. Recurrence of fluid is common.
  • Corticosteroid injection is not routinely recommended because of risks of skin atrophy and infection. If needed for a persistent aseptic, non-gouty bursa after infection is excluded: methylprednisolone acetate 20 to 40 mg (or triamcinolone 20 mg) with lidocaine 1% 2 mL, using strict asepsis.
  • Gout: colchicine 500 micrograms orally 8 to 12 hourly (maximum 1.5 mg per day in a flare, with dose reduction in renal impairment) or prednisolone 30 to 40 mg daily for 5 days, then allopurinol 100 mg daily titrated to a serum urate below 360 micromol/L, with colchicine prophylaxis for 3 to 6 months.
• Septic bursitis:
  • Outpatient (mild, no systemic features, reliable patient): flucloxacillin 500 mg to 1 g orally 6 hourly, or cefalexin 500 mg orally 6 hourly, for 10 to 14 days (longer in immunosuppression or slow response). Penicillin allergy: clindamycin 300 to 450 mg orally 8 hourly. MRSA risk: co-trimoxazole 160/800 mg, 2 tablets 12 hourly, or doxycycline 100 mg 12 hourly.
  • Inpatient (fever, spreading cellulitis, immunosuppression, diabetes, or failure of oral therapy): flucloxacillin 2 g IV 6 hourly or cefazolin 2 g IV 8 hourly, with vancomycin 15 to 20 mg/kg IV 8 to 12 hourly (adjusted to levels) if MRSA is possible. Convert to oral therapy after 3 to 5 days of improvement, for a total of 2 to 3 weeks.
  • Daily or alternate day needle aspiration until fluid stops, or incision and drainage (with drain placement) for purulent loculated collections.
  • Surgical bursectomy (open or endoscopic) for failure after 5 to 7 days of correct treatment, chronic thickened bursa, recurrent infection, a draining sinus, or necrosis. Healing takes 2 to 4 weeks, with a compression dressing, and early gentle knee mobilisation.
  • Tetanus prophylaxis if there is a skin wound, according to immunisation status.
• Chronic bursitis: elective bursectomy for persistent symptoms or recurrent flares (after 3 to 6 months of failure of conservative care), with about 90% good outcomes, and risk of wound complications and a tender scar.
• Prevention: protective kneepads, frequent breaks and changes of position, soft kneeling surfaces, and prompt cleaning and covering of abrasions on the knee.
• Special groups:
  • Diabetes and alcohol misuse: lower threshold for admission, tight glucose control, and early IV antibiotics.
  • Immunosuppression: prolong therapy, and cover MRSA early.
  • Renal impairment: adjust colchicine, allopurinol and vancomycin doses, and avoid NSAIDs.
  • Pregnancy: rest, ice and compression, and paracetamol. Avoid NSAIDs after 20 weeks. Cefalexin or flucloxacillin for infection, and avoid doxycycline and co-trimoxazole.
  • Anticoagulation: aspirate with a fine needle and apply firm compression for 10 minutes.
• Follow up: review at 48 to 72 hours for septic bursitis, and weekly until healed. Refer to orthopaedics for bursectomy, suspected knee joint involvement, persistent or recurrent disease, and to rheumatology for inflammatory arthritis or gout needing long term therapy.