Deep Infrapatellar 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 superficial and deep infrapatellar bursae. The superficial infrapatellar bursa lies between the subcutaneous tissues and the upper part of the ligamentum patellae. The deep infrapatellar bursa lies between the ligamentum patellae and the tibia ( Fig. 160.1 ). These bursae may exist as single bursal sacs or in some patients as a multisegmented series of sacs that may be loculated.

The infrapatellar bursa is vulnerable to injury from both acute trauma and repeated microtrauma. Acute injuries frequently take the form of direct trauma to the bursae via falls directly onto the knee or patellar fractures, as well as overuse injuries, such as from long-distance running. Infrapatellar bursitis also may result from jobs that require crawling or kneeling, such as laying carpet or scrubbing floors. If the inflammation of the infrapatellar bursae becomes chronic, calcification of the bursae may occur.

The patient with deep infrapatellar bursitis frequently reports pain and swelling in the anterior knee below the patella that can radiate inferiorly into the area surrounding the knee. 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. Infrapatellar bursitis often coexists with arthritis and tendinitis of the knee joint, and these other pathologic processes may confuse the clinical picture ( Box 160.1 ).

Physical examination may reveal point tenderness in the anterior knee just below the patella. Swelling and fluid accumulation often surround the lower patella. Passive flexion as well as active resisted extension of the knee reproduce the pain. Sudden release of resistance during this maneuver markedly increases the pain. The deep infrapatellar bursa is not as susceptible to infection as the superficial infrapatellar bursa.

Plain radiographs of the knee may reveal calcification of the bursa and associated structures, including the quadriceps tendon, consistent with chronic inflammation. Magnetic resonance imaging and/or ultrasound imaging is indicated if bursitis, internal derangement, occult mass, or tumor of the knee is suggested ( Fig. 160.2 ). Electromyography helps distinguish infrapatellar bursitis from neuropathy, lumbar radiculopathy, and plexopathy. The injection technique described later serves as both a diagnostic and a therapeutic maneuver.

Clinically Relevant Anatomy

The deep infrapatellar bursa lies between the ligamentum patellae and the tibia (see Fig. 160.1 ). The bursa is held in place by the ligamentum patellae. Both the ligamentum patellae and the deep infrapatellar bursa are subject to the development of inflammation after overuse, misuse, or direct trauma ( Fig. 160.3 ). The ligamentum patella attaches above to the lower patella and below to the tibia. The fibers that make up the ligamentum patellae are continuations of the tendon of the quadriceps femoris muscle. 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. These fibers are called expansions and are subject to strain; the tendon proper is subject to the development of tendinitis.