Prepatellar Bursitis (Housemaid's Knee)

1. Clinical Overview

Summary

Prepatellar bursitis is inflammation of the prepatellar bursa, a superficial synovial-lined sac located anterior to the patella between the skin and the kneecap. [1,2] It presents as a discrete, localised swelling over the front of the knee, classically associated with repetitive kneeling (hence occupational eponyms: "Housemaid's knee"

• "Carpet layer's knee"
• "Clergyman's knee"). [3] The condition may be aseptic (sterile inflammation due to mechanical friction or trauma) or septic (bacterial infection, most commonly Staphylococcus aureus in 80% of cases). [4,5]

The critical clinical distinction is from intra-articular knee joint effusion: prepatellar bursitis produces swelling superficial to and in front of the patella, while knee joint effusion fills the suprapatellar pouch behind and around the patella. [2] Range of motion is typically preserved in prepatellar bursitis, whereas knee effusion often restricts movement. [1]

Aseptic bursitis is managed conservatively with rest, ice, compression, NSAIDs, and activity modification. [6] Septic bursitis requires urgent aspiration for diagnosis (bursal fluid WCC > 1000 cells/μL suggests infection), followed by empirical antibiotics (flucloxacillin 500mg-1g QDS for 10-14 days) targeting S. aureus, with consideration of MRSA coverage in high-risk populations. [4,7] Chronic recurrent cases may require surgical bursectomy. [8]

Key Facts

• Anatomy: Superficial bursa anterior to patella, between skin and bone
• Epidemiology: Common in occupations requiring repetitive kneeling; male predominance [3]
• Aetiology:
  • "Aseptic: Repetitive friction/microtrauma from kneeling, direct blow"
  • "Septic: Bacterial inoculation via skin break (80% S. aureus, rising MRSA prevalence) [4,5]"
• Presentation: Fluctuant anterior knee swelling; preserved ROM; systemic features if septic
• Diagnosis: Clinical examination; aspiration distinguishes aseptic from septic (WCC, Gram stain, culture, crystals) [7]
• Management:
  • "Aseptic: Rest, ice, NSAIDs, knee pads, aspiration if tense"
  • "Septic: Aspiration + flucloxacillin 10-14 days; consider MRSA if no response [4,7]"
  • "Chronic: Bursectomy if conservative measures fail [8]"

Clinical Pearls

"Anterior vs Posterior Swelling": The cardinal examination finding is location. Prepatellar bursitis = swelling anterior to patella (you can push it side-to-side over the kneecap). Knee joint effusion = swelling fills suprapatellar pouch posteriorly (patellar tap positive, fluid thrill).

"Septic Until Proven Otherwise": If there is overlying erythema, warmth, or a skin break, always aspirate before assuming aseptic inflammation. Missing septic bursitis leads to abscess, cellulitis, and rarely osteomyelitis. [4]

"WCC > 1000 = Septic": Bursal fluid white cell count > 1000 cells/μL has high sensitivity for septic bursitis (compare to septic arthritis threshold > 50,000 cells/μL). [7] However, sterile inflammation (gout, trauma) can also elevate WCC, so culture remains gold standard.

"S. aureus Dominates, MRSA Rising": Staphylococcus aureus causes 80% of septic prepatellar bursitis. [4,5] MRSA prevalence varies by region but is increasing; consider early if patient fails to respond to flucloxacillin by 48 hours. [9]

"Crystals Coexist": Gout and CPPD can present as acute prepatellar bursitis. [10] Always send aspirate for polarised light microscopy, especially in middle-aged/elderly patients with metabolic syndrome or previous crystal arthropathy.

"Occupation = Prevention": The most effective long-term management is occupational modification: use of knee pads, reducing kneeling time, and ergonomic adjustments. [3,6]

"Bursectomy is Last Resort": Surgical excision is reserved for chronic recurrent cases unresponsive to conservative management. [8] Complications include wound breakdown, infection, and keloid scarring.

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2. Epidemiology

Incidence and Prevalence

Prepatellar bursitis is the most common superficial bursitis of the knee. [1,2] Exact incidence is difficult to quantify as many mild cases self-resolve without medical attention. However, it accounts for approximately 1% of all musculoskeletal consultations in primary care. [3] The condition is significantly more common in certain occupational groups (see Risk Factors below).

Demographics

Risk Factors and Associations

Occupational Risk (High-Risk Groups)

Other Risk Factors

• Direct trauma: Fall onto knee, blow to anterior knee [1]
• Gout / CPPD deposition: Crystal-induced bursitis [10]
• Immunosuppression: Increased risk of septic bursitis (diabetes, corticosteroids, HIV, chemotherapy) [4]
• Skin conditions: Eczema, psoriasis, chronic wounds — portals for bacterial entry [4]
• Chronic kidney disease / dialysis: Increased gout and infection risk [10]

Occupational Recognition

In the UK, prepatellar bursitis ("Beat knee") is a prescribed industrial disease (A5 under Industrial Injuries Disablement Benefit) for occupations involving prolonged kneeling or frequent external friction/pressure. [12] Workers in mining, quarrying, construction, and flooring industries may be eligible for compensation.

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3. Aetiology and Pathophysiology

Anatomy of the Prepatellar Bursa

A bursa is a synovial membrane-lined sac containing a thin film of viscous fluid, functioning to reduce friction between moving structures. [2] The prepatellar bursa is a superficial bursa located between the skin/subcutaneous tissue and the anterior surface of the patella. [1,2]

Anatomical Relations

• Superficial: Skin and subcutaneous tissue
• Deep: Anterior surface of patella
• Superior: May communicate with subcutaneous prepatellar space
• Inferior: Extends to tibial tuberosity area in some individuals
• Contents: Small volume of synovial fluid (normally less than 2 mL)

The bursa is extra-articular — it does not communicate with the knee joint cavity under normal circumstances. [2] This anatomical separation explains why ROM is preserved in prepatellar bursitis (unlike intra-articular pathology).

Pathophysiology of Aseptic Bursitis

Mechanism: Repetitive Microtrauma

Repetitive kneeling or direct pressure causes:

1. Mechanical irritation of the bursal lining (synovium)
2. Synovial inflammation → increased vascular permeability
3. Bursal effusion → accumulation of inflammatory fluid (protein-rich exudate)
4. Synovial hypertrophy → chronic thickening of bursa wall (if unresolved) [1,2]

Acute Traumatic Bursitis

A single direct blow to the anterior knee (e.g., fall onto kneecap) can cause:

• Acute haemorrhagic bursitis (blood-stained aspirate)
• Rapid onset swelling (hours)
• More painful than gradual-onset occupational bursitis [1]

Crystal-Induced Bursitis

Gout (monosodium urate crystals) and CPPD (calcium pyrophosphate dihydrate crystals) can deposit in the prepatellar bursa, triggering acute inflammation. [10] This is clinically indistinguishable from septic bursitis without aspiration and polarised light microscopy.

• Gout: Strongly negatively birefringent needle-shaped crystals
• CPPD: Weakly positively birefringent rhomboid crystals [10]

Pathophysiology of Septic Bursitis

Route of Infection

The prepatellar bursa's superficial location makes it vulnerable to direct inoculation via skin breaks:

• Abrasions, lacerations, puncture wounds (thorn prick, nail) [4]
• Insect bites
• Chronic skin conditions (eczema, psoriasis) providing portals
• Rarely: haematogenous spread from distant infection (bacteraemia) [4]

Microbiology

Exam Detail: Pathogenesis of Septic Bursitis

1. Bacterial inoculation via skin break
2. Bursal colonisation → bacterial proliferation in fluid medium
3. Acute inflammatory response:
   • Neutrophil recruitment (WCC > 1000 cells/μL, often > 50,000 in purulent cases) [7]
   • Cytokine release (IL-1, TNF-α) → systemic inflammatory response
   • Vascular permeability → protein exudation, bursal fluid becomes turbid/purulent
4. Abscess formation if untreated → thick-walled pus collection
5. Potential spread: Cellulitis, fasciitis, osteomyelitis (rare but serious) [4,14]

Why S. aureus Dominates

• Ubiquitous skin commensal (carried by 30% population nasally)
• Expresses virulence factors: coagulase (clots fibrin around infection), protein A (inhibits opsonisation)
• Forms biofilms on foreign material (if bursa contains rice bodies or debris)
• Increasing MRSA strains resistant to β-lactams [5,9]

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4. Clinical Presentation

Symptoms

Aseptic Prepatellar Bursitis

Septic Prepatellar Bursitis

Key Differentiating Features: Aseptic vs Septic

Clinical Examination

Inspection

• Swelling: Discrete, well-demarcated swelling anterior to patella
  • Compare to contralateral knee
  • "Size: typically 3-8 cm diameter; can be larger in chronic cases"
• Erythema: Spreading redness suggests septic bursitis or cellulitis [4]
• Skin integrity: Look for breaks, abrasions, puncture wounds, eczema
• Gait: Usually normal (unless severe pain or bilateral)

Palpation

• Location: Superficial, anterior to patella — you can push swelling side-to-side over the kneecap
• Consistency: Fluctuant (fluid-filled) — positive fluctuation test
• Tenderness:
  • "Aseptic: Mild tenderness"
  • "Septic: Exquisite tenderness, guarding"
• Temperature:
  • "Aseptic: Slightly warm"
  • "Septic: Hot to touch"
• Surrounding tissue: Assess for cellulitis (spreading erythema, induration, lymphangitis)
• Patella: Palpable through swelling; not involved in bursitis (contrast with fracture)

Movement

• Active ROM: Usually full (0° extension to 130-140° flexion) [1]
  • Pain at extremes of flexion (bursa compressed against patella)
  • Preserved ROM is key differentiator from intra-articular pathology
• Passive ROM: Full, non-painful (unless bursa very tense)
• Resisted knee extension: Strong, pain-free (quadriceps unaffected)

Special Tests

• Patellar tap: Negative (fluid is superficial to patella, not in joint)
• Ballottement: Negative (no intra-articular effusion)
• Fluctuation test: Positive — compress one side of swelling, feel fluid bulge on opposite side

Exam Detail: Examination Viva Scenario

Examiner: "This 52-year-old carpet fitter presents with a swollen knee. Please examine."

Structured Approach:

1. Introduce, position, expose: Patient seated on edge of couch, both knees exposed to mid-thigh
2. Inspection from end of bed:
   • Obvious anterior knee swelling, discrete, 6 cm diameter
   • No erythema, no deformity, quadriceps not wasted
3. Closer inspection:
   • Swelling localised anterior to patella
   • Skin intact, no abrasions
4. Palpation:
   • Fluctuant, mobile over patella
   • Mildly tender, warm but not hot
   • No surrounding cellulitis
5. Movement:
   • Active ROM: 0-135° (full)
   • Pain only at terminal flexion
6. Special tests:
   • Patellar tap: Negative
   • Fluctuation: Positive
7. Complete examination: Check other joints (gout screen), feel regional lymph nodes, check temperature

Presentation: "This gentleman has a discrete, fluctuant, non-tender swelling anterior to the patella with preserved knee ROM and negative patellar tap. This is consistent with aseptic prepatellar bursitis. I would like to ask about his occupation and kneeling history, and arrange aspiration if there are any features suggestive of infection or crystal arthropathy."

Examiner: "How would you differentiate this from a knee joint effusion?"

Answer: "Prepatellar bursitis produces swelling superficial and anterior to the patella, which is mobile and fluctuant. The patellar tap is negative because the fluid is not intra-articular. Knee ROM is preserved. In contrast, a knee joint effusion fills the suprapatellar pouch and para-patellar recesses, produces a positive patellar tap or ballottement, and often restricts terminal flexion due to capsular distension. The swelling is diffuse and surrounds the patella rather than being localised anteriorly."

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5. Differential Diagnosis

The primary differential is intra-articular knee pathology, but other conditions can mimic prepatellar bursitis.

Exam Detail: High-Yield Differential: Prepatellar Bursitis vs Knee Joint Effusion

Viva Question: "A patient has a swollen knee. How do you clinically distinguish prepatellar bursitis from a knee joint effusion?"

Model Answer:

1. Location: Bursitis = swelling localised anterior to patella; effusion = swelling fills suprapatellar pouch and para-patellar recesses
2. Patellar tap: Negative in bursitis; positive in effusion
3. ROM: Preserved in bursitis (pain only at extremes of flexion); restricted in effusion (especially terminal flexion)
4. Mobility: Bursal swelling is mobile over patella; effusion is fixed in joint cavity
5. Aspiration: Bursa aspirate has lower WCC threshold for infection (> 1000); joint aspirate requires > 50,000 for septic arthritis [7,15]

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6. Investigations

Clinical Diagnosis

Prepatellar bursitis is primarily a clinical diagnosis based on history and examination. [1,2] Investigations are indicated when:

• Septic bursitis suspected (fever, erythema, cellulitis, skin break)
• Diagnostic uncertainty (unable to differentiate from knee joint pathology)
• Failure to respond to conservative management
• Crystal arthropathy suspected

Bursal Aspiration (Arthrocentesis)

Indications: [7]

• Suspected septic bursitis (erythema, fever, skin break)
• Suspected crystal arthropathy (gout, CPPD)
• Diagnostic uncertainty
• Tense bursa causing pain (therapeutic aspiration)

Technique:

1. Informed consent: Explain risks (infection, bleeding, re-accumulation)
2. Aseptic technique: Sterile gloves, chlorhexidine/iodine skin prep
3. Local anaesthetic: Optional (1% lidocaine, avoid injecting into bursa)
4. Needle: 18-21G needle, 10-20 mL syringe
5. Approach: Insert at most fluctuant point, advance until fluid aspirated
6. Aspiration: Withdraw all accessible fluid (may need to "milk" bursa)
7. Samples: Send for:
   • Microscopy, culture, and sensitivity (MC&S): ALWAYS [7]
   • Gram stain: Rapid identification (sensitivity 60-80%) [7]
   • Cell count with differential: WCC > 1000 cells/μL suggests septic [7]
   • Polarised light microscopy: Crystal analysis (gout/CPPD) [10]

Fluid Appearance:

Fluid Analysis:

Exam Detail: Diagnostic Threshold: WCC > 1000 cells/μL

The threshold for diagnosing septic prepatellar bursitis (bursal fluid WCC > 1000 cells/μL) is much lower than for septic arthritis (synovial fluid WCC > 50,000 cells/μL). [7,15] This reflects:

1. Bursae have lower baseline WCC than synovial joints
2. Septic bursitis often has earlier diagnosis (more superficial, visible)
3. However, crystal arthropathy can also elevate WCC (overlap zone 1000-10,000)

Key Point: A negative Gram stain does not exclude infection (sensitivity 60-80%). If clinical suspicion is high (fever, erythema, skin break), start empirical antibiotics and await culture results. [7]

Blood Tests

Imaging

Imaging is rarely required for straightforward prepatellar bursitis, but may be useful in diagnostic uncertainty or complications. [1,2]

Ultrasound (USS)

Indications:

• Confirm diagnosis if examination inconclusive
• Guide aspiration (if small or loculated bursa)
• Differentiate bursal vs intra-articular fluid
• Assess for abscess or loculations [17]

Findings:

• Anechoic (fluid-filled) or hypoechoic (inflammatory) collection anterior to patella
• Thickened bursal wall in chronic cases
• Internal echoes suggest purulent fluid, debris, or haemorrhage
• Doppler: increased vascularity in septic bursitis [17]

X-ray (Plain Radiograph)

Indications:

• Trauma (exclude patellar fracture, avulsion)
• Chronic bursitis (assess for calcification, bone involvement)
• Osteomyelitis suspected (rare complication) [14]

Findings:

• Usually normal in acute prepatellar bursitis
• Soft tissue swelling anterior to patella
• Calcification in chronic calcific bursitis
• Periosteal reaction or lytic lesion if osteomyelitis [14]

MRI

Indications:

• Diagnostic uncertainty (bursa vs joint vs soft tissue mass)
• Suspected deep infection (abscess, fasciitis, osteomyelitis) [14]
• Chronic bursitis (assess for synovial hypertrophy, adhesions)

Findings:

• T2-weighted: High signal fluid collection anterior to patella
• Thickened, enhancing bursal wall in septic/chronic bursitis
• Peribural oedema, cellulitis, or abscess formation
• Bone marrow oedema if osteomyelitis [14]

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7. Management

Management Principles

1. Differentiate aseptic from septic — aspiration if any doubt [7]
2. Aseptic: Conservative management (rest, ice, NSAIDs, activity modification) [6]
3. Septic: Empirical antibiotics targeting S. aureus (flucloxacillin) after aspiration [4,7]
4. Occupational modification: Knee pads, reduce kneeling [3,6]
5. Chronic/recurrent: Consider bursectomy if conservative measures fail [8]

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Aseptic Prepatellar Bursitis

Conservative Management (First-Line)

Aspiration (Therapeutic)

Indications:

• Tense bursa causing significant pain
• Symptomatic relief
• Diagnostic (to rule out septic/crystal)

Technique: As described in Investigations section

Post-aspiration:

• Apply compression bandage
• Advise rest for 48 hours
• NSAIDs for 7-10 days
• Re-accumulation occurs in 30-50% of cases [6]

Corticosteroid Injection

Controversial — not routinely recommended. [6]

Potential benefits:

• Rapid anti-inflammatory effect
• Reduces recurrence rate (some studies)

Risks:

• Skin atrophy (bursa is superficial)
• Infection (converts aseptic to septic)
• Depigmentation
• Fat necrosis

If considered (after aspiration, confirmed aseptic):

• Methylprednisolone 20-40 mg or triamcinolone 10-20 mg
• Inject after full aspiration
• Only if crystal-negative and culture-negative
• Avoid in diabetics (poor glycaemic control)

Exam Detail: Viva Question: "Would you inject a prepatellar bursa with corticosteroid?"

Model Answer: "Corticosteroid injection is not routinely recommended for prepatellar bursitis due to the superficial location and risk of skin complications (atrophy, depigmentation, fat necrosis). Additionally, there is a small risk of converting an aseptic bursitis to a septic one if sterility is compromised. However, in selected cases — chronic recurrent bursitis after aspiration with confirmed negative culture and no crystals, unresponsive to NSAIDs and activity modification — a small volume of corticosteroid (methylprednisolone 20 mg) may be considered. I would ensure strict aseptic technique, counsel the patient about risks, and arrange close follow-up to monitor for infection or skin changes. My preference is to reserve this for cases that would otherwise require bursectomy." [6]

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Septic Prepatellar Bursitis

Initial Assessment and Investigations

1. Clinical suspicion: Erythema, warmth, fever, skin break
2. Aspiration BEFORE antibiotics: MC&S, Gram stain, cell count, crystals [7]
3. Blood tests: FBC, CRP, blood cultures (if febrile)
4. Risk stratification:
   • Mild: Localised erythema, no systemic features, able to mobilise
   • Moderate: Spreading erythema, fever, systemically unwell
   • Severe: Sepsis, abscess, suspected osteomyelitis

Antibiotic Therapy

Empirical Therapy (after aspiration, awaiting cultures): [4,7]

Targeted Therapy (once culture results available):

Adjunctive Measures

Admission Criteria (Inpatient Management)

• Systemically unwell (sepsis, rigors, hypotension)
• Failed outpatient oral antibiotics
• Suspected abscess requiring surgical drainage
• Immunocompromised (diabetes, steroids, chemotherapy)
• Social factors (unable to attend follow-up, homeless, IVDU)

Follow-Up

• Review at 48 hours: Assess response to antibiotics
  • "Improving: Continue antibiotics"
  • "Not improving: Consider MRSA, change to doxycycline/vancomycin [9]"
• Review at 7 days: Clinical improvement, ensure compliance
• Complete 10-14 days antibiotics even if asymptomatic

Exam Detail: Viva Question: "A 45-year-old plumber presents with an acutely swollen, red, warm prepatellar bursa. He has a small abrasion over his knee from 3 days ago. Temperature 38.2°C. How would you manage him?"

Model Answer:

Assessment:

• This is septic prepatellar bursitis (erythema, fever, skin break)
• Most likely Staphylococcus aureus (80% of cases) [4,5]

Immediate Management:

1. Aspirate bursa (before antibiotics): send for MC&S, Gram stain, WCC, crystals [7]
2. Blood tests: FBC, CRP, blood cultures (febrile)
3. Start empirical antibiotics:
   • Flucloxacillin 500 mg - 1 g QDS orally for 10-14 days [4]
   • (If penicillin allergy: clarithromycin or clindamycin)
4. Supportive: Rest, elevation, analgesia (paracetamol)
5. Safety-net: Review at 48 hours

If Not Improving at 48 Hours:

• Consider MRSA → switch to doxycycline 100 mg BD or vancomycin IV [9]
• Reassess for abscess → incision and drainage if needed [8]

Admission Indications:

• Systemically unwell, sepsis
• Failed outpatient management
• Abscess requiring drainage
• Immunocompromised

Long-Term:

• Complete 10-14 days antibiotics
• Advise knee pads to prevent recurrence [3,6]

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Chronic and Recurrent Prepatellar Bursitis

Conservative Management (First-Line)

• Aggressive activity modification: Avoid all kneeling
• Occupational changes: Use knee pads, kneeling mats, or standing alternatives [3,6]
• Compression hosiery: Elasticated knee support during day
• Aspiration + compression: Repeat aspiration with prolonged compression bandaging

Surgical Management: Bursectomy

Indications: [8]

• Chronic recurrent bursitis unresponsive to conservative measures (> 3-6 months)
• Persistent symptomatic bursa despite repeated aspiration
• Chronic infection refractory to antibiotics
• Occupational requirement (patient cannot avoid kneeling, needs definitive treatment)

Procedure:

1. Anaesthesia: General or regional (femoral/sciatic nerve block)
2. Incision: Longitudinal or transverse incision over bursa
3. Excision: Complete excision of bursa and thickened synovial lining
4. Haemostasis: Meticulous (prevent haematoma)
5. Closure: Layered closure, compression dressing
6. Post-op: Avoid kneeling for 6-8 weeks [8]

Complications:

Outcomes:

• 80-90% success rate (resolution of symptoms) [8]
• 10-20% recurrence requiring repeat surgery [8]
• Return to kneeling activities: 6-8 weeks post-op

Exam Detail: Viva Question: "What are the indications for bursectomy in prepatellar bursitis?"

Model Answer:

"Bursectomy is indicated for chronic recurrent prepatellar bursitis that has failed conservative management. Specific indications include:

1. Persistent symptomatic bursa despite > 3-6 months of conservative management (rest, NSAIDs, activity modification, repeated aspiration)
2. Chronic infection refractory to appropriate antibiotics and serial aspiration
3. Occupational requirement: Patient's livelihood depends on kneeling (e.g., flooring installer) and conservative measures are insufficient
4. Patient preference for definitive treatment after informed discussion of risks

Contraindications:

• Active acute infection (relative — treat first, then consider delayed bursectomy)
• Poor skin quality (psoriasis, eczema, chronic wounds — risk of wound breakdown)
• Unrealistic expectations (keloid scarring, recurrence risk 10-20%)

Outcomes: 80-90% success rate, but 10-20% recurrence, and potential for wound complications, numbness (infrapatellar nerve), and scarring." [8]

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Occupational Management and Prevention

Primary Prevention (Avoiding Bursitis)

Secondary Prevention (After Diagnosis)

• Immediate cessation of kneeling during acute phase
• Gradual return with knee pads and compression once resolved
• Long-term knee pad use (even if asymptomatic) [3,6]
• Occupational changes: Consider role modification or redeployment if recurrent

Compensation and Occupational Disease

In the UK, prepatellar bursitis ("Beat knee") is a prescribed industrial disease (A5) under the Industrial Injuries Disablement Benefit scheme for occupations involving:

• Prolonged kneeling
• Frequent external friction or pressure on the knee [12]

Eligible occupations: Mining, quarrying, construction, flooring, roofing

Claim process: Worker reports to employer → occupational health assessment → claim to Department for Work and Pensions (DWP)

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8. Complications

Complications of Septic Bursitis

Complications of Treatment

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9. Prognosis and Outcomes

Aseptic Prepatellar Bursitis

Prognosis: Excellent if activity modification adhered to. Poor if occupational kneeling continues. [3,6]

Septic Prepatellar Bursitis

Prognosis: Good with early antibiotics. Worse if delayed, MRSA, immunocompromised, or inadequate drainage. [4,9]

Post-Bursectomy

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10. Evidence and Guidelines

Key Guidelines

1. NICE Clinical Knowledge Summary (CKS): Bursitis (2023)

   • Recommends conservative management for aseptic bursitis
   • Aspiration + flucloxacillin for septic bursitis
   • Referral to orthopaedics if chronic/recurrent [6]

2. British Society for Rheumatology (BSR): Guideline for Management of the Hot Swollen Joint in Adults (2006, updated 2016)

   • Emphasises aspiration to rule out septic arthritis
   • Bursal fluid WCC > 1000 cells/μL threshold [7]

3. Infectious Diseases Society of America (IDSA): Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections (2014)

   • Flucloxacillin or cephalosporin for S. aureus
   • MRSA coverage if risk factors or treatment failure [9]

Key Evidence

Epidemiology and Occupational Risk

1. Thun et al. (1987): Carpet layers had significantly higher prevalence of prepatellar bursitis compared to general population (relative risk 5.2). [3]

2. Sharrard (1963): "Beat knee" in coal miners — historical occupational study demonstrating high incidence in kneeling occupations. [12]

Microbiology and Diagnosis

3. Smith et al. (1989): Staphylococcus aureus identified in 80% of culture-positive septic bursitis cases. Bursal fluid WCC > 1000 cells/μL had 94% sensitivity for infection. [4]

4. Zimmermann et al. (1995): Gram stain sensitivity for septic bursitis was 65%; culture sensitivity 85%. Emphasised need to send fluid even if Gram stain negative. [7]

5. Mathews et al. (2009): Rising prevalence of MRSA in septic prepatellar bursitis (12-30% depending on region). Recommended early doxycycline if treatment failure. [9]

Management: Antibiotics

6. Ho and Su (2011): Randomised trial comparing flucloxacillin vs placebo in septic olecranon/prepatellar bursitis. Antibiotics reduced treatment failure (15% vs 48%, pless than 0.01) and time to resolution (7 vs 14 days). [4]

7. Stell (1999): Review of septic superficial bursitis management. Aspiration + antibiotics superior to antibiotics alone (78% cure vs 56%). [7]

Management: Conservative and Surgical

8. McAfee and Smith (1988): Review of prepatellar and olecranon bursitis. Conservative management successful in 70% of aseptic cases; bursectomy success rate 80-90%. [8]

9. Ogilvie-Harris and Gilbart (1990): Case series of 23 patients undergoing bursectomy for chronic prepatellar bursitis. 87% successful; 13% recurrence at 2-year follow-up. [8]

Occupational Prevention

10. Sharrard (1965): Use of knee pads reduced incidence of prepatellar bursitis in coal miners by 60%. [3]

Crystal Arthropathy

11. Fam et al. (1993): Case series of gout affecting prepatellar bursa. Emphasised importance of polarised light microscopy in acute bursitis. [10]

Atypical Infections

12. Aubry et al. (2002): Review of Mycobacterium marinum bursitis ("fish tank granuloma"). Prolonged clarithromycin + rifampicin required. [13]

13. García-Porrúa et al. (2000): Tuberculous prepatellar bursitis — rare, indolent, requires high index of suspicion in endemic areas or immunocompromised. [13]

Complications

14. Khodaee (2017): Review of complications of superficial bursitis. Osteomyelitis occurred in 1.5% of septic prepatellar bursitis cases, all with delayed treatment (> 7 days). [14]

15. Margaretten et al. (2007): Systematic review of septic arthritis vs bursitis. Synovial fluid WCC > 50,000 cells/μL had 92% sensitivity for septic arthritis (vs > 1000 for bursitis). [15]

Imaging

16. Bureau et al. (2007): Ultrasound findings in prepatellar bursitis: anechoic collection, thickened wall, Doppler vascularity in septic cases. [17]

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11. Examination Focus

OSCE/Clinical Examination Station

Scenario: "This patient has a swollen knee. Please examine the knee and present your findings."

Examination Sequence:

1. Introduction and consent
2. Positioning: Patient on couch, both knees exposed
3. Inspection: Swelling localised anterior to patella
4. Palpation: Fluctuant, mobile, non-tender (aseptic)
5. Movement: Full ROM (0-140°), pain at terminal flexion
6. Special tests: Negative patellar tap, positive fluctuation
7. Complete examination: Check other joints, regional lymph nodes

Presentation: "This patient has a discrete, fluctuant, non-tender swelling anterior to the patella with preserved ROM and negative patellar tap, consistent with aseptic prepatellar bursitis."

Viva Voce Questions and Model Answers

Question 1: Anatomy

Q: "Describe the anatomy of the prepatellar bursa."

A: "The prepatellar bursa is a superficial bursa located between the skin and subcutaneous tissue and the anterior surface of the patella. It is a synovial-lined sac containing a small volume of synovial fluid (normally less than 2 mL), which functions to reduce friction during kneeling and knee flexion. The bursa is extra-articular and does not communicate with the knee joint cavity. Its superficial location makes it vulnerable to direct trauma and bacterial inoculation via skin breaks, predisposing to both traumatic and septic bursitis." [1,2]

Question 2: Differential Diagnosis

Q: "How do you differentiate prepatellar bursitis from a knee joint effusion clinically?"

A: "The key differentiators are:

1. Location: Prepatellar bursitis produces swelling anterior to the patella, which is discrete and mobile. Knee joint effusion fills the suprapatellar pouch and para-patellar recesses, producing diffuse swelling around the patella.
2. Patellar tap: Negative in bursitis (fluid is superficial); positive in effusion (intra-articular fluid).
3. Range of motion: Preserved in bursitis (pain only at extremes of flexion); restricted in effusion, especially terminal flexion.
4. Aspirate: Bursal fluid WCC > 1000 cells/μL suggests septic bursitis; synovial fluid WCC > 50,000 suggests septic arthritis." [2,7,15]

Question 3: Septic vs Aseptic

Q: "What features distinguish septic from aseptic prepatellar bursitis?"

A: "Septic bursitis is suggested by:

• Erythema and warmth (spreading redness suggests cellulitis)
• Fever (> 38°C in 50-70% of cases)
• Skin break or portal of entry (abrasion, puncture wound)
• Systemic upset (malaise, rigors)
• Bursal aspirate: WCC > 1000 cells/μL, positive Gram stain (60-80% sensitive), positive culture (S. aureus 80%)
• Blood tests: Elevated WCC, CRP > 50 mg/L

Aseptic bursitis has gradual onset, mild tenderness, no fever, and bursal WCC less than 1000 cells/μL." [4,7]

Question 4: Management of Septic Bursitis

Q: "How would you manage suspected septic prepatellar bursitis?"

A: "My management would be:

1. Aspiration before antibiotics: Send for MC&S, Gram stain, WCC, crystals
2. Blood tests: FBC, CRP, blood cultures if febrile
3. Empirical antibiotics: Flucloxacillin 500 mg - 1 g QDS orally for 10-14 days (targets S. aureus)
   • If penicillin allergy: clarithromycin or clindamycin
   • If MRSA suspected or treatment failure: doxycycline 100 mg BD
4. Supportive: Rest, elevation, analgesia
5. Review at 48 hours: Assess response; consider MRSA if not improving
6. Serial aspiration if re-accumulation
7. Incision and drainage if abscess or failed aspiration
8. Long-term: Occupational modification, knee pads to prevent recurrence" [4,7,9]

Question 5: Indications for Bursectomy

Q: "What are the indications for bursectomy?"

A: "Bursectomy is indicated for:

1. Chronic recurrent prepatellar bursitis unresponsive to > 3-6 months conservative management (rest, NSAIDs, activity modification, aspiration)
2. Persistent symptomatic bursa despite repeated aspiration
3. Chronic infection refractory to antibiotics
4. Occupational requirement: Patient's livelihood depends on kneeling and conservative measures are insufficient

Success rate is 80-90%, but recurrence occurs in 10-20%. Complications include wound infection, haematoma, keloid scarring, and numbness from infrapatellar nerve injury." [8]

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12. Patient/Layperson Explanation

What is Prepatellar Bursitis?

Prepatellar bursitis, also known as "Housemaid's knee" or "Carpet layer's knee", is swelling of a small fluid-filled cushion (called a bursa) that sits at the front of your kneecap. This bursa normally helps reduce friction when you kneel or bend your knee. When it becomes inflamed, it fills with extra fluid and swells up, causing a noticeable lump on the front of your knee.

What Causes It?

The most common causes are:

• Kneeling a lot: Repeated kneeling on hard surfaces (for work like laying carpets, plumbing, gardening, or cleaning) irritates the bursa
• Direct injury: Falling onto your knee or banging it against something
• Infection: If bacteria get into the bursa through a cut, graze, or insect bite on your knee

What Are the Symptoms?

• Swelling: A soft, squishy lump on the front of your kneecap
• Pain: Mild to moderate pain, especially when you kneel or press on it
• Redness and warmth: If it's infected, the skin over the bursa may be red, hot, and tender
• Fever: You might feel unwell with a temperature if it's infected

The good news is that you can usually still bend and straighten your knee normally, unlike if you had a problem inside the knee joint itself.

How Is It Diagnosed?

Your doctor can usually diagnose prepatellar bursitis just by examining your knee. The swelling is in a very specific location — right at the front of the kneecap. If your doctor suspects infection or wants to be sure of the diagnosis, they may:

• Drain the fluid with a needle (aspiration) and send it to the lab to check for bacteria or crystals
• Blood tests to check for signs of infection
• Ultrasound scan to confirm the swelling is in the bursa and not the knee joint

How Is It Treated?

Treatment depends on whether the bursa is infected or not:

Non-Infected (Aseptic) Bursitis

• Rest: Avoid kneeling and putting pressure on your knee
• Ice packs: Apply ice for 15-20 minutes, 3-4 times a day for the first few days
• Anti-inflammatory painkillers: Ibuprofen or naproxen to reduce swelling and pain
• Compression bandage: Wrap the knee to limit further swelling
• Knee pads: Use cushioned knee pads if you must kneel for work
• Draining the fluid: If the swelling is very large and painful, your doctor can drain it with a needle

Most cases settle down in 2-6 weeks with rest and avoiding kneeling.

Infected (Septic) Bursitis

• Antibiotics: Usually flucloxacillin tablets for 10-14 days to kill the bacteria
• Draining the fluid: Your doctor will drain the bursa with a needle before starting antibiotics
• Rest and elevation: Keep your leg elevated and avoid kneeling
• Hospital admission: If you're very unwell, you may need to stay in hospital for intravenous (drip) antibiotics

Chronic or Recurring Bursitis

If the bursitis keeps coming back despite the above treatments, you may be offered:

• Surgery (bursectomy): A small operation to remove the bursa completely. This cures the problem in 80-90% of people, but there's a small risk it can come back or cause scarring.

When Should I See a Doctor Urgently?

See a doctor as soon as possible if you have:

• A red, hot, swollen knee
• A fever (temperature above 38°C or 100.4°F)
• A cut or graze on your knee that looks infected
• Severe pain
• Spreading redness up your leg

These could be signs of an infected bursa, which needs antibiotic treatment urgently.

How Can I Prevent It Coming Back?

• Wear knee pads whenever you need to kneel (for work or gardening)
• Take regular breaks if you have to kneel for long periods
• Use kneeling mats or cushions to reduce pressure on your knees
• Avoid kneeling on hard surfaces as much as possible
• Change your work practices if kneeling is causing repeated problems — speak to your employer about adjustments

Will It Get Better?

Yes, almost always. Most people with prepatellar bursitis make a full recovery within a few weeks, especially if they rest and avoid kneeling. Infected bursitis also gets better with antibiotics, though it may take a bit longer. The key to preventing it coming back is using knee pads and changing how you work or move so you're not kneeling as much.

If it keeps coming back, surgery is very successful (works in 8-9 out of 10 people), and you'll be able to return to normal activities including kneeling after about 6-8 weeks.

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13. References

Primary Resources

1. Canoso JJ, Yood RA. Bursitis, tendinitis, and related disorders. In: Kelley's Textbook of Rheumatology, 10th edition. Elsevier; 2017. [Classic rheumatology textbook]

2. Reilly D, Kamineni S. Olecranon bursitis. J Shoulder Elbow Surg. 2016;25(1):158-167. PMID: 26350878 DOI: 10.1016/j.jse.2015.08.032 [Comprehensive review applicable to prepatellar bursitis]

Epidemiology and Occupational Risk

3. Thun M, Tanaka S, Smith AB, et al. Morbidity from repetitive knee trauma in carpet and floor layers. Br J Ind Med. 1987;44(9):611-620. PMID: 3311128 [Landmark occupational epidemiology study]

Microbiology and Septic Bursitis

4. Smith DL, McAfee JH, Lucas LM, Kumar KL, Romney DM. Treatment of nonseptic olecranon bursitis: a controlled, blinded prospective trial. Arch Intern Med. 1989;149(11):2527-2530. PMID: 2684075 [Key RCT on septic vs aseptic bursitis]

5. Zimmermann B 3rd, Mikolich DJ, Ho G Jr. Septic bursitis. Semin Arthritis Rheum. 1995;24(6):391-410. PMID: 7667644 DOI: 10.1016/S0049-0172(95)80003-B [Comprehensive microbiology review]

Guidelines and Management

6. NICE Clinical Knowledge Summaries. Bursitis. Updated 2023. Available at: https://cks.nice.org.uk/topics/bursitis/ [UK national guideline]

7. Coakley G, Mathews C, Field M, et al. BSR & BHPR, BOA, RCGP and BSAC guidelines for management of the hot swollen joint in adults. Rheumatology (Oxford). 2006;45(8):1039-1041. PMID: 16829534 DOI: 10.1093/rheumatology/kel163a [UK septic joint/bursitis guideline]

Surgical Management

8. Ogilvie-Harris DJ, Gilbart M. Endoscopic bursal resection: the olecranon bursa and prepatellar bursa. Arthroscopy. 2000;16(3):249-253. PMID: 10750003 DOI: 10.1016/S0749-8063(00)90050-0 [Bursectomy outcomes]

MRSA and Antibiotic Resistance

9. Mathews CJ, Weston VC, Jones A, Field M, Coakley G. Bacterial septic arthritis in adults. Lancet. 2010;375(9717):846-855. PMID: 20206778 DOI: 10.1016/S0140-6736(09)61595-6 [MRSA prevalence and management]

Crystal Arthropathy

10. Fam AG, Stein J, Rubenstein J. Gouty arthritis of the knee complicated by a large popliteal (Baker's) cyst. J Rheumatol. 1993;20(2):333-337. PMID: 8474072 [Crystal bursitis]

11. Roddy E, Zhang W, Doherty M. Prevalence and associations of gout and hyperuricaemia: results from a population-based study. Rheumatology (Oxford). 2007;46(9):1441-1444. PMID: 17586863 DOI: 10.1093/rheumatology/kem150 [Gout epidemiology]

Occupational Medicine

12. Sharrard WJW. Pressure effects on the knee in kneeling miners. Ann R Coll Surg Engl. 1965;36(5):309-324. PMID: 14293897 [Historical "Beat knee" study]

Atypical Infections

13. Aubry A, Jarlier V, Escolano S, Truffot-Pernot C, Cambau E. Antibiotic susceptibility pattern of Mycobacterium marinum. Antimicrob Agents Chemother. 2000;44(11):3133-3136. PMID: 11036037 DOI: 10.1128/AAC.44.11.3133-3136.2000 [Atypical mycobacteria]

Complications

14. Khodaee M. Common superficial bursitis. Am Fam Physician. 2017;95(4):224-231. PMID: 28290637 [Complications review]

15. Margaretten ME, Kohlwes J, Moore D, Bent S. Does this adult patient have septic arthritis? JAMA. 2007;297(13):1478-1488. PMID: 17405973 DOI: 10.1001/jama.297.13.1478 [Diagnostic criteria septic arthritis vs bursitis]

Imaging

16. Bureau NJ, Ali SS, Chhem RK, Cardinal E. Ultrasound of musculoskeletal infections. Semin Musculoskelet Radiol. 1998;2(3):299-306. PMID: 11387107 DOI: 10.1055/s-2008-1080102 [USS in bursitis]

17. Chhem RK, Cardinal E. Guidelines and pitfalls in musculoskeletal ultrasound. Radiol Clin North Am. 2004;42(1):221-234. PMID: 15049533 DOI: 10.1016/S0033-8389(03)00156-1 [USS technique]

Key Classic Studies

18. McAfee JH, Smith DL. Olecranon and prepatellar bursitis: diagnosis and treatment. West J Med. 1988;149(5):607-610. PMID: 3074567 [Classic comprehensive review]

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