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The Case Files: Foreign Body in Hoffa's Fat Pad

Osgood, James Gale MD, MBA; Robison, Matthew MD; Siethel, Michelle PA

doi: 10.1097/01.EEM.0000450248.03982.f9
The Case Files

Dr. Osgood is an assistant professor of clinical emergency medicine, Dr. Robison is an associate professor of clinical emergency medicine, and Ms. Siethel a physician assistant, all at University Hospital in Columbia, MO.

A 19-year-old woman presents with right knee pain and a laceration after a fall. She states that she was drinking alcohol at a local bar, and fell and cut her knee on broken glass on the bathroom floor. She denies loss of consciousness or other injuries. The patient is able to bear weight, but has increased pain when moving her knee. She denied distal numbness or weakness. The patient also denied other medical problems, and her last tetanus was four years earlier.

Physical exam revealed a stable knee with several lacerations and abrasions with mild tenderness to palpation only near the laceration sites. ROM was mildly limited by pain. The sensation to the distal extremity was intact to light touch, and dorsalis pedis and posterior tibial pulses were 2+. X-rays of the knee were obtained. What is your diagnosis?



The x-ray demonstrates normal bony alignment without cortical disruption. A radiopaque foreign body was seen in Hoffa's fat pad, or the infrapatellar fat pad of the knee joint, which physically separates the antero-inferior synovial membrane of the knee from the patella. It is intraarticular but extrasynovial. Functionally, the infrapatellar fat pad may provide some cushioning to the articulating surfaces of the knee, but it also helps distribute synovial fluid during knee movement.

Orthopedics was consulted given the intraarticular position of the foreign body and a concern for possible violation of the synovium. The joint was injected with 160 mL of sterile saline without observed fluid extravasation, and the joint was thought to be intact. The wound was explored, but the foreign body was not found. The lacerations were left open. The orthopedist prescribed cephalexin for one week, and the patient was discharged with precautions to watch for signs of infection and follow-up.



Traumatic wounds are one of the most common reasons for an ED visit. Wound care accounts for five percent to 20 percent of all ED malpractice settlements against emergency physicians and for three percent to 11 percent of all claim dollars paid. A wound foreign body increases the risk of infection so any mechanism that suggests possible foreign body mandates judicious wound exploration, effective irrigation, and radiologic investigation, including the use of ultrasound, CT, or MRI for nonradiopaque material.

Studies found that retained glass was found in seven percent to 15 percent of wounds in patients injured by broken glass. Plain x-rays have 90% sensitivity in visualizing nonleaded glass with higher miss rates of small volume particles (15 mm3 or less). No randomized trials have examined the role of antibiotic prophylaxis, and its use is left to the discretion of the treating physician.

Warn the patient about an increased risk of infection before closing, and discuss signs and symptoms that warrant immediate reevaluation, with or without repair, if the mechanism suggests a possible retained foreign body. Consider delayed closure or leaving the wound open. Have a low threshold for specialty consultation and for early wound rechecks.

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