Prepatellar Bursa Injection

Indications and Clinical Considerations

Bursae are formed from synovial sacs that allow easy sliding of muscles and tendons across one another at areas of repeated movement. These synovial sacs are lined with a synovial membrane invested with a network of blood vessels that secrete synovial fluid. Inflammation of the bursa results in an increase in the production of synovial fluid with swelling of the bursal sac. With overuse or misuse, these bursae may become inflamed, enlarged, and on rare occasions infected. Although there is significant intrapatient variability as to the number, size, and location of bursae, anatomists have identified a number of clinically relevant bursae, including the prepatellar bursa, which lies between the subcutaneous tissues and the patella ( Fig. 158.1 ). This bursa may exist as a single bursal sac or in some patients as a multisegmented series of sacs that may be loculated.

The prepatellar bursa is vulnerable to injury from both acute trauma and repeated microtrauma. Acute injuries frequently take the form of direct trauma to the bursa via falls directly onto the knee or from patellar fractures, as well as from overuse injuries, including running on soft or uneven surfaces. Prepatellar bursitis also may result from jobs that require crawling or kneeling, such as carpet laying or scrubbing floors; the other name for prepatellar bursitis is housemaid’s knee . If the inflammation of the prepatellar bursa becomes chronic, calcification of the bursa may occur.

The patient with prepatellar bursitis frequently notes pain and swelling in the anterior knee over the patella that can radiate superiorly and inferiorly into the area surrounding the knee ( Fig. 158.2 ). Often the patient is unable to kneel or walk down stairs. The patient also may report a sharp, “catching” sensation with range of motion of the knee, especially on first rising. Prepatellar bursitis often coexists with arthritis and tendinitis of the knee joint, and these other pathologic processes may confuse the clinical picture.

Physical examination may reveal point tenderness in the anterior knee just above the patella. Swelling and fluid accumulation surrounding the patella often are present. Passive flexion and active resisted extension of the knee reproduce the pain. Sudden release of resistance during this maneuver markedly increases the pain. The prepatellar bursa may become infected, with systemic symptoms, including fever and malaise, as well as local symptoms, with rubor, color, and dolor present ( Fig. 158.3 ).

Plain radiographs of the knee may reveal calcification of the bursa and associated structures, including the quadriceps tendon, consistent with chronic inflammation ( Fig. 158.4 ). Magnetic resonance imaging and/or ultrasound imaging is indicated if bursitis, internal derangement, occult mass, or tumor of the knee is suggested ( Figs. 158.5 and 158.6 ). Electromyography helps distinguish prepatellar bursitis from femoral neuropathy, lumbar radiculopathy, and plexopathy. The injection technique described later serves as both a diagnostic and a therapeutic maneuver.

Clinically Relevant Anatomy

The prepatellar bursa lies between the subcutaneous tissues and the patella (see Fig. 158.1 ). The bursa is held in place by the ligamentum patellae. Both the quadriceps tendon and the prepatellar bursa are subject to the development of inflammation caused by overuse, misuse, or direct trauma. The quadriceps tendon is made up of fibers from the 4 muscles that constitute the quadriceps muscle: the vastus lateralis, the vastus intermedius, the vastus medialis, and the rectus femoris. These muscles are the primary extensors of the lower extremity at the knee. The tendons of these muscles converge and unite to form a single, exceedingly strong tendon. The patella functions as a sesamoid bone within the quadriceps tendon, with fibers of the tendon expanding around the patella and forming the medial and lateral patellar retinacula, which help strengthen the knee joint ( Fig. 158.7 ). These fibers are called expansions and are subject to strain; the tendon proper is subject to the development of tendinitis. The prepatellar, infrapatellar, and prepatellar bursae also may concurrently become inflamed with dysfunction of the quadriceps tendon.