Knee Bursitis

Prepatellar bursitis presents with fluctuant well-circumscribed swelling directly over the anterior patella with preserved knee range of motion. The patellar tap is negative because the fluid is in the bursa, not the joint. Pain is provoked by direct kneeling. Infrapatellar bursitis produces tenderness and swelling below the patella over the patellar tendon and tibial tubercle and may coexist with patellar tendinopathy.

Pes anserine pain syndrome causes medial knee pain approximately 5 to 6 cm below the medial joint line over the proximal medial tibia. Tenderness sits below the joint line, distinguishing it from medial joint line tenderness in OA or meniscal tear. Resisted knee flexion and internal rotation typically reproduce pain.

Baker cysts produce posterior knee swelling in the posteromedial popliteal fossa and are typically painless or mildly uncomfortable, sometimes producing posterior tightness on full flexion. Rupture causes acute calf swelling, pain, and tenderness mimicking DVT. The crescent sign, ecchymosis around the medial malleolus from fluid tracking distally, is a classic finding. Venous duplex ultrasound is the investigation of choice to distinguish ruptured Baker cyst from DVT, since D-dimer is often elevated in either scenario.

Most aseptic knee bursitis is diagnosed clinically. Investigations are directed at excluding septic bursitis and identifying underlying causes. Aspiration is the key investigation when septic bursitis is suspected: send fluid for microscopy and Gram stain, culture and sensitivity, crystal analysis, cell count, and glucose. Aspiration is both diagnostic and therapeutic. Routine aspiration of uncomplicated aseptic bursitis is not always required.

Bloods (FBC, CRP, ESR) are indicated if septic bursitis is suspected, with blood cultures if febrile or systemically unwell. Serum urate is useful if gout is suspected. Ultrasound confirms bursal distension versus joint effusion, assesses Baker cysts, and guides aspiration. Venous duplex ultrasound is the investigation of choice for suspected ruptured Baker cyst, since D-dimer is not discriminatory. Plain radiographs and MRI are not first-line.

The critical distinction is septic versus aseptic.

Aseptic prepatellar or infrapatellar bursitis is managed conservatively per NICE CKS: activity modification (avoid kneeling, use kneeling pads), ice, compression, and oral NSAIDs. Aspiration is reserved for symptomatic relief of tense painful swellings unresponsive to conservative measures, followed by a compression bandage. Corticosteroid injection may be considered as second-line for recurrent or refractory cases once infection has been excluded. Most cases resolve conservatively; chronic recurrent disease rarely requires surgical bursectomy.

Septic bursitis requires mandatory aspiration both diagnostically and therapeutically. First-line oral antibiotic in UK practice is flucloxacillin, with clarithromycin or doxycycline if penicillin-allergic, typically for at least seven days and continued until erythema has resolved for 48 hours. IV antibiotics are needed if systemically unwell, immunocompromised, with spreading cellulitis, or after oral failure. Repeat aspiration may be required. Never inject corticosteroid into a suspected or confirmed septic bursa. Surgical drainage or bursectomy is reserved for refractory cases.

Pes anserine pain syndrome is managed within the framework of underlying knee OA per NICE NG226: optimise OA treatment, address obesity, prescribe quadriceps, hamstring, and hip strengthening, and consider local topical or oral NSAIDs. Corticosteroid injection may be used for refractory symptoms with limited supporting evidence.

Baker cyst management is directed at the underlying intra-articular pathology in adults. Ultrasound-guided aspiration provides short-term relief but recurrence is very common if the underlying cause is not addressed. Manage ruptured Baker cyst symptomatically after excluding DVT.

Prepatellar and infrapatellar bursitis: activity modification is the key intervention, particularly avoiding direct kneeling pressure. Use kneeling pads, foam mats, or alternative working postures. Maintain knee range of motion and quadriceps strength. Return to kneeling occupations with protective equipment once the bursa has settled. Address occupational risk factors and document under Prescribed Disease A11 where relevant.

Pes anserine pain syndrome: manage within the OA framework per NICE NG226. Quadriceps strengthening, hamstring strengthening and flexibility, hip abductor strengthening, aerobic conditioning, and weight management drive the gains. Address foot posture where contributory.

Baker cyst: rehabilitation is directed at the underlying joint pathology. Quadriceps and hamstring strengthening, range of motion exercises, and weight management are core. Aspiration without addressing the underlying joint typically leads to recurrence.

• •NICE CKS Pre-patellar bursitis: UK primary care framework recommending conservative management for aseptic bursitis and aspiration plus antibiotics for septic bursitis.
• •Lormeau et al. (2019): Around 80% of septic bursitis is caused by Staphylococcus aureus, supporting flucloxacillin as empirical first-line therapy in UK practice.
• •Baumbach et al. (2014): Approximately 30% of patients with septic bursitis are afebrile - absence of fever does not exclude infection.
• •NICE NG226 (Osteoarthritis): Framework for managing the underlying OA driving pes anserine pain syndrome and adult Baker cysts.
• •UK IIDB: Prepatellar bursitis (beat knee) is a Prescribed Disease A11 in occupational kneelers, recognised for compensation purposes.

• •Prepatellar bursitis sits anterior to the patella with a negative patellar tap and preserved knee range of motion. An intra-articular effusion is suprapatellar and patellar-tap positive. This anatomical distinction is the highest-yield exam point.
• •Septic versus aseptic is the critical decision. Around 30% of septic bursitis is afebrile; absence of fever does not exclude infection. Aspirate and send for microscopy, culture, and crystals.
• •Flucloxacillin is first-line oral antibiotic for septic bursitis in UK practice; S. aureus causes around 80%. Never inject steroid into a suspected septic bursa.
• •Baker cyst in adults is almost always secondary to intra-articular pathology. Treat the underlying joint disease.
• •Ruptured Baker cyst mimics DVT, with the crescent sign at the medial malleolus. Venous duplex ultrasound is the investigation of choice; D-dimer is not discriminatory.
• •Pes anserine tenderness sits 5 to 6 cm below the medial joint line. Medial joint line tenderness points to OA or meniscal pathology.