IS Case 148: Prepatellar Bursitis
Imaging Sciences URMC 2008
Publication Date: 2009-05-21
The prepatellar bursa is a superficial bursa with a thin synovial lining located between the skin and the patella. The function of any bursa is to reduce friction and allow maximal range of motion. Prepatellar bursitis, also know as housemaid's knee or bricklayer's knee, is inflammation of the prepatellar bursa typically caused by chronic pressure on the knee in patients who have an occupation that involves kneeling. Other common etiologies include infection, crystal deposition diseases and rheumatoid arthritis. Septic bursitis is more common in children, and the most common organism is S. aureus entering through a break in the skin. Gout and pseudogout are more common in adults, and may involve any bursa. Patients with prepatellar bursitis present with chronic anterior knee pain, swelling, tenderness and fluctuant edema over the lower pole of the patella.
The prepatellar bursa is not normally evident on MR examination of the knee. Inflammation causes the bursa to fill with fluid giving its typical cystic appearance. It is important to distinguish prepatellar bursitis from other pathologies in the anterior knee. Prepatellar edema is a nonspecific finding that may be seen in trauma to the knee, and is fluid in the subcutaneous fat, lacking the smooth capsule of prepatellar bursitis. Prepatellar edema should be low-signal on T1-weighted sequences, high-signal is more suggestive or prepatellar hematoma. Increased signal intensity in the patella bone is suggestive of stress response or fracture of the patella. Increase T2-signal intensity in the distal pole of the patella with irregularity or fragmentation is suggestive of Sinding-Larsen-Johansson disease. Finally, patellar tendonitis may show increased T2-signal in the patellar peritendon (early) or tendon (late), or may show thickening with low T2-signal (chronic).
- Stoller DW, Tirman PFJ, Bredella MA. Patellar tendonitis. In: Diagnostic Imaging: Orthopaedics 1st Ed. Amirsys 2004. Sec.5: 98-101.