All the joints in the body have the capacity to make noises, some of which are a cause for concern, others are non sinister things happening within the body. One of the most common noises is the ‘pop’ sound generated with deliberate cracking of the finger knuckles. It is thought that this noise is created when the movement of the joint results in a sudden change in pressure in the liquid within a joint causing a small air bubble to form and then pop. Although this is the most common belief, other explanations of ‘pops’ are the sudden stretch of a ligament or adhesions being broken. It is not just the knuckles that can cavitate, the knees along with all the large joints in the body can produce sounds like this as well. These ‘pops’ are not to be worried about as they often occur regularly in people with lax ligaments. Although an old wives tale suggests that this can cause arthritis, there is no evidence to suggest this is the case, the only obvious detrimental effect is that they weaken the muscles around that joint transiently, and potentially this has a negative long term effect of strength.
One of the concerning noises that the knees can make is the grinding/grating noise that is generated by the patella-femoral joint (knee-cap joint). The back portion of the knee-cap is designed to glide up and down the centre of a groove situated in the lower part of the thigh bone (femur). With good knee function and correct activation of the supporting muscles around the knee, hip and ankle, the knee cap glides smoothly. With poor muscle support, or tight structures around the knee, the knee-cap moves poorly and creates high areas of pressure on these surfaces. This will particularly happen if the knee-cap tracks to one side of the groove in the femur. Over time, this leaves the joint surfaces rough and corrugated, and means that the once silent movement of a squat or getting down a step has now become a noisy grinding process.
Sometimes these tracking issues will only be evident through the noise that is produced, but it is likely that the will progress to develop sore, stiff and achey knees. With proper guidance this condition can be slowed in its progression, but if activity is continued or exercise done in a poor manner this can lead to significant issues that are far more difficult to manage.
Although there are other reasons that can create noises at the knee, these are the most common. The best way to distinguish between the two are by the length of time each noise happens for. A ‘pop’ caused by cavitation will tend to happen once and then is likely not to happen again in that burst of exercise. The grinding from the patella-femoral joint will happen again and again if the knee is moved in a way that causes pressure from the knee-cap onto the femur (eg; Squat, step-down).
Written by Mark Fotheringham – physiotherapist at Malvern Physiotherapy Clinic