Medical Specialty >> Orthopedics

Doctors Lounge - Orthopedics Answers

Back to Orthopedics Answers List

If you think you may have a medical emergency, call your doctor or 911 immediately. Doctors Lounge ( does not recommend or endorse any specific tests, physicians, products, procedures, opinions, or other information that may be mentioned on the Site.

DISCLAIMER: The information provided on is designed to support, not replace, the relationship that exists between a patient/site visitor and his/her physician. Please read our 'Terms and Conditions of Use' carefully before using this site.

Date of last update: 10/01/2017.

Forum Name: Bone trauma and fractures

Question: knee injury

 moomom - Thu Mar 31, 2005 10:29 pm

several months ago, my husband fell on a piece of wood. it left a bruise and a vertical indention through the center of his knee. recently he has noticed something strange. there is a pea sized ball on the surface of the knee just under the skin. when you manipulate this 'pea' it moves freely around his knee. it doesn't hurt unless you apply alot of pressure. when he moves it around it looks weird. to feel it is strange also. any thoughts on what ths could be? should he go to the doctor? thanks
 Dr. A. Saif - Thu Apr 07, 2005 4:04 pm

User avatar Hello again, Moomom,

Lots of causes for this mobile lump, after an injury. It could be "retention dermoid". This is an island of skin that gets embedded when there is an injury. It forms a tense lump, as the skin continues to shed squames (flakes of skin cells), but these squames are trapped buried undeer the surface. It is rare, and usually takes a few years to appear. It could be a bit of foreign matter trapped under the skin, embedded during the injury. This is perhaps more likely. It could be a feck of boneor osteophyte that was chipped off during the injury, and that has failed to get reattached. This is more likely within a joint, as there is space for the fragment to move around. In front of the knee however, it is conceivable that the fragment is now freely mobile within the "prepatellar bursa", a bag of fluid in front of the knee. Loose bodies can also develop spontaneously I gues, but rarely in the prepatellar bursa.



| Check a doctor's response to similar questions

Are you a Doctor, Pharmacist, PA or a Nurse?

Join the Doctors Lounge online medical community

  • Editorial activities: Publish, peer review, edit online articles.

  • Ask a Doctor Teams: Respond to patient questions and discuss challenging presentations with other members.

Doctors Lounge Membership Application

Tools & Services: Follow DoctorsLounge on Twitter Follow us on Twitter | RSS News | Newsletter | Contact us