Prepatellar Bursitis
Prepatellar bursitis (PPB), sometimes termed ‘housemaid’s knee’ or ‘carpenter’s knee’, refers to inflammation of the bursa in the prepatellar soft tissue above the patella. Overall, it is relatively poorly described in the literature and the epidemiology is not well understood. It is most common in middle aged males. The prepatellar bursa is located between the patella and overlying subcutaneous tissue. The purpose of the bursa is to separate the patellar tendon from the skin and reduce friction.
Case Introduction
You are evaluating a 41 year old plumber with insidious onset of anterior knee pain. He denies trauma or fever. On exam, there is obvious swelling of the prepatellar space with a tender, fluctuant mass without erythema. Range of motion is intact. Which of the following ultrasound findings will help confirm your suspected diagnosis?
A) Cobblestoning of the anterior knee
B) Heterogeneous appearance of patellar tendon
C) Large joint effusion
D) Hypoechoic fluid collection anterior to patella
Image 1: Illustration of prepatellar bursitis (courtesy of orthoinfo.aaos.org)
The majority of cases of prepatellar bursitis are non-infectious or aseptic. Of these, the majority are due to chronic repetitive microtrauma such as occupational (housekeeping, plumbing, carpet installation, etc) or sports such as wrestling, baseball (catchers) and volleyball. Occasionally, acute blunt trauma can also also cause PPB. Other diseases such as gout, pseudogout, rheumatoid arthritis, systemic lupus erythematosus are also associated with increased risk (Diering 2017).
Prepatellar bursitis can also be due to infectious causes, mostly commonly from skin lesions but can also occur due to primary cellulitis or, more rarely, hematogenous spread. Staphylococcus aureus (#1) is most commonly implicated, followed by Brucella sp. The prepatellar bursa is the second most common location for septic bursitis behind the olecranon bursa, which is 4x more common (Ho 1978). Rarely, hemorrhagic prepatellar bursa can occur due to trauma or in patients on anticoagulation.
Image 2: Clinical example of prepatellar bursa (courtesy of wikipedia.org)
By history, patients most commonly report some form of acute or repetitive microtrauma. They will endorse knee pain, swelling and trouble ambulating. On exam, they will have obvious prepatellar swelling with overlying erythema, warmth. The prepatellar space will be fluctuant, tender with or without crepitus. Range of motion is restricted. Note that clinically, it can be difficult to distinguish septic from aseptic PPB. Patients typically do not have a joint effusion.
Image 3: Lateral knee radiograph demonstrating soft tissue swelling in the prepatellar space (courtesy of radiopaedia.org)
Image 4: Ultrasound of the patella (at the bottom in white) with layered soft tissue edema, a small fluid collection (in black) and some cobblestoning near the surface. Most consistent with septic prepatallar bursitis.
Standard radiographs of the knee are typically normal but can show prepatellar soft tissue swelling. Ultrasound is likely the best imaging modality as it will show a hypoechoic fluid collection anterior to the patella (Draghi 2015). Evidence of infection such as cobblestoning may be present. Ultrasound can also be used for aspiration if indicated. MRI is typically not needed. If there is a need to exclude septic bursitis, aspirate should be sent for analysis. Septic bursitis typically will have a purulent appearance, high white blood cell count with a polymorphonuclear cell predominance, positive gram stain 70% of the time and positive cultures.
Most patients will have improvement and resolution of symptoms if treated promptly. Non-infectious PPB can be treated with activity modification, compression sleeve, and NSAIDS and in many cases this will be definitive. Recalcitrant cases may require corticosteroid injection or physical therapy. Knee pads should be considered in patients with repetitive microtrauma. In the case of septic bursitis, antibiotics should be initiated with broad coverage which can be tapered to the culture. Orthopedic surgery should be consulted to discuss bursectomy vs irrigation and debridement. In chronic, refractory aseptic cases bursectomy may also be an option.
There are no evidence based guidelines for rehabilitation or return to play. Most athletes can return to sport when symptoms and swelling has resolved. Care should be taken by the athlete, athletic trainer and other medical staff to prevent recurrence by properly padding the knees and/or modifying playstyle where possible. Complications are few and far between. Some folks may have trouble returning to their sport or occupation for recurrent cases. If septic bursitis is diagnosed, need for hospitalization and surgery are the most common issues.
Case Conclusion
Answer is D. The described patient is most likely to have prepatellar bursitis. Most cases are aseptic and will show a large hypoechoic fluid collection anterior to the patella. In septic cases, there may be cobblestoning but he has no fever or erythema. A joint effusion is unlikely in this vignette given his range of motion is intact. A heterogenous patellar tendon could be possible in the case of patellar tendonitis but doesnt fit the case in question.
Draghi F, Corti R, Urciuoli L, Alessandrino F, Rotondo A. Knee bursitis: a sonographic evaluation. (2015) Journal of ultrasound. 18 (3): 251-7. doi:10.1007/s40477-015-0168-z – Pubmed
– More Knee Pain from Sports Medicine Review: https://www.sportsmedreview.com/by-joint/knee/
– Read More @ Wiki Sports Medicine: https://wikism.org/Prepatellar_Bursitis
References
- Ho G, Tice AD, Kaplan SR (1978) Septic bursitis in the prepatellar and olecranon bursae: an analysis of 25 cases. Ann Intern Med 89(1):21–27
- Diering, Nina, et al. “Calcific prepatellar bursitis in a patient with limited cutaneous systemic sclerosis.” JDDG: Journal der Deutschen Dermatologischen Gesellschaft 15.12 (2017): 1248-1250.
- Draghi F, Corti R, Urciuoli L, Alessandrino F, Rotondo A. Knee bursitis: a sonographic evaluation. (2015) Journal of ultrasound. 18 (3): 251-7. doi:10.1007/s40477-015-0168-z – Pubmed
