WHAT CAUSES KNEE SNAPPING?
When you're working out, or playing your favorite sport, a snapping sensation within your knee
can cause pain and frustration, and can lead to buckling or giving way, falling, and eventually,
damage to the cartilage surfaces of the joint. The snap results when some structure within the
joint is momentarily caught between the moving bones, tension is applied and is then suddenly
released, much like plucking a guitar string.
The three most common causes for the painful snap are synovial flaps, torn menisci and loose
The most frequent source of snapping is a synovial flap or plica. The inside of every synovial
joint is lined by a normally thin and pliant membrane, called synovium. Synovium produces a
drop or two of joint fluid, which nourishes the articular cartilage and provides lubrication for the
joint surfaces. This membrane often has a few small thin folds, left over from embryonic
development, which can grow larger, thicker and stiffer to become larger structures, fibrous flaps
or shelves, that get can get caught and stretched between the moving parts. Pain is caused by
traction, pulling on the nerves of the surrounding tissues, and the snap is due to the sudden
release of tension, when it breaks free.
A torn meniscus can also cause a snap. The two tough, crescent-shaped meniscal fibrocartilages,
medial (inner side) and lateral (outer side), that cushion and guide the knee, are often torn in
athletic activities, especially the sudden twisting or cutting maneuvers in soccer, football, or
basketball. But tears can also occur by degeneration, just from getting older. Here, the substance
of the cartilage becomes softer and begins to shred and fragment, eventually evolving into a tear,
especially when repetitively crushed as with deep squatting. The meniscus tear fragment, like
the flap of synovium, can displace and get caught between the moving femur and tibia, causing
pain by traction, like a hangnail does, then snap when suddenly released.
Loose bodies are little pieces of cartilage and/or bone that are knocked out with trauma, fall out
from a joint surface due to disease (osteochondritis dessicans), or are actually grown, like pearls,
within the synovial membrane (synovial chondromatosis/osteochondromatosis), and then break
free inside the joint. Like the synovial flaps and meniscal tears, these fragments can get caught
between the moving parts.
Regardless of cause, significant snapping within the knee is always abnormal and needs to be
Above all, don't ignore it. You want to identify the source with an accurate diagnosis and
prevent permanent damage to the joint. But in the short term, you can try some conservative
measures to try to resolve the snapping.
Here's what to do:
1. If you notice recurrent snapping, especially if it's painful, STOP whatever activity is
causing the sensation.
2. Rest the knee, out straight. Every snap can damage the cartilage, so prevent that by
avoiding or minimizing joint motion.
3. Apply moist heat a few times a day, for 15-20 minutes each time. If the snapping is of
sudden onset, apply ICE for the first 48 hours, THEN begin to apply heat.
4. Try some OTC anti-inflammatory, like Advil (2 tabs, 4X/day) or Aleve (2 tabs,
2X/day), provided you have no stomach problems, like ulcers, or a history of GI
bleeding, and be sure to take it WITH FOOD OR MILK. If inflammation has caused a
synovial plica to swell and thicken, this regimen should shrink it by reducing
5. If you don't get relief within a few days to a week, then it's probably not from acute
inflammation and the snapping structure is fibrous tissue, or cartilage, which will not
shrink, even with reduced inflammation. Then, you need to see an orthopaedist for
definitive evaluation and treatment. If you don't, the repetitive snapping internal
derangement can damage the articular cartilage of joint and eventually result in arthritis.
To prevent this permanent damage, arthroscopic surgery to remove the source of the
snapping, is usually required.