Snap Crackle and Pop – Why does my knee click? – by Claire Robertson

Snap Crackle and Pop – Why does my knee click? – by Claire Robertson
Claire Robertson joins us today to talk about creaky knees! Claire is a Consultant Physiotherapist, researcher and lecturer who runs a specialist patellofemoral pain service at Wimbledon Clinics. She’s kindly agreed to share some of the findings from her research and answer the question why does my knee click?…As a specialist in patellofemoral ...

Claire Robertson joins us today to talk about creaky knees! Claire is a Consultant Physiotherapist, researcher and lecturer who runs a specialist patellofemoral pain service at Wimbledon Clinics. She’s kindly agreed to share some of the findings from her research and answer the question why does my knee click?…

As a specialist in patellofemoral pain (PFP, sometimes called ‘Runners Knee‘) I have been increasingly aware of the importance placed by people on their knee joint noise, (crepitus). On asking about their presenting complaint it is often the first symptom mentioned, before pain or functional difficulties. For some people there is no pain, just noise! This has interested and led me to research this topic, asking people what they think their joint cracking means? The answers are often alarming and will frequently be along the lines of, “my joint is wearing away”. This is quite an extreme belief system to hold and may surely have significant impact on their behavioural response to their crepitus. The aim of this blog is to explore this topic further.

What exactly is joint crepitus? This is a question that I have heard posed by both patients and clinicians, and one that is surprisingly difficult to answer! I have heard various hypothesis from health and non-health care professionals, but have never been entirely convinced or aware of the level of evidence behind them. Most importantly does crepitus really matter? Crepitus is a major symptom in PFP, 25% of people will have PFP at some point in their life, (McConnell, 1996), and 2.5 million runners are diagnosed with PFP per year, (Crossley, 2010). I think the argument is strong for ensuring a good understanding of joint crepitus. We need to determine what this cracking, grinding, creaking, clicking, clunking, popping and other adjectives used for the phenomena of joint crepitus is.

Historical Perspective

An interest in crepitus is certainly nothing new. My initial searching revealed the unexpected finding that Crepitus is an alleged Roman God of flatulence! Looking to the mammalian vetinary literature also revealed the obscure finding that eland, (a type of African antelope) use knee crepitus in displays of dominance, (Bro-Jorgensen et al., 2008). Fascinating this may be, but unhelpful in my quest to better understand the crepitus I see in clinic! However, there are papers on joint crepitus in key medical journals dating back as far as 1885, (Heuter, 1885), which start to shed light on this intriguing topic. Blodgett, (1902), introduced the practice of joint auscultation, (listening with a stetoscope) with great interest in this technique persisting for several decades. Early studies focused on the intensity of joint crepitus volume, and this soon progressed in to more sophisticated studies, recording frequency, wavelength, sequencing, and quality of noise, (Steindler, 1937). Information on the type and location of pathology can now be readily found by imaging and or arthroscopy, and hence the literature on crepitus has evolved towards exploring the nature of crepitus, and how it is produced.

Loud isolated cracks and pops.

These are often seen during warm ups and activities involving crouching down. Some people even feel better after the knee has cracked. This will either be bubbles of gas popping, just like when someone cracks their knuckles, (which by the way does not lead to arthritis!), or the patella locating into the groove underneath as the muscles warm up. Neither are a case for any concern whatsoever, and should be seen as entirely normal.


People will very often associate their joint noise with a diagnosis of osteoarthritis (especially if someone in their family has osteoarthritis). A true osteoarthritic joint creak almost resembles a creaky door. This is indicative of bone on bone advanced osteoarthritis, and highly unlikely to be seen in runners. This noise is quite different from the fine grating that often originates from a non-arthritic patellofemoral joint. Ironically patients with advanced degenerative disease rarely complain of this as their pain, deformity and or functional loss is normally a much bigger problem.

It is much more likely that runners will have fine crepitus of a non-arthritic origin. However, they often feel anxious and hypervigilant regarding the meaning of their crepitus, and I think it is this group that often need reassuring. Some of these people may have chondromalacia patellae,(CMP) of the patellofemoral joint, an extremely common finding indicating fissuring of cartilage on the back of the patella but not a loss of vertical cartilage height. However, CMP with no pain is prevalent amongst runners, and we should therefore not be alarmed by the associated crepitus that comes from fluid passing through a slightly roughened surface. McCoy et al., (1987) investigated 247 symptomatic, and 250 normal knees and found that 99% of normal subjects had patellofemoral crepitus.

It is likely that in many cases the anxiety behind the meaning of crepitus is enhanced by inaccuracies and generalisations in the public domain. Internet sites such as the medical glossary for the government department of work and pensions define crepitus as, “A grating sound and sensation created when two rough surfaces in the human body come into contact-for example, in osteoarthritic joints or fractured bones rub together”, (Department of Work and Pensions website). Given the evidence presented in this editorial many of these Internet sites fail to discriminate between the unusual arthritic bone-on bone crepitus, and the common fine crepitus, leading many to wrongly self-diagnose their crepitus as a sign of severe degenerative disease.

Meaning to patients

To return to the central issue of this blog is to answer questions that can be meaningful to patients. It is my strong belief that if people voice anxiety regarding their joint crepitus, then it should firstly be taken seriously, and secondly addressed. Wolpert, (2007, p220) aptly states that, “It is the action based on beliefs that ultimately matters.” Hence to evade the belief system of people with crepitus through lack of interest or knowledge is to fail the person and leave them vulnerable to fear-avoidant behaviour, which may further compound their initial problem. In runners this can lead to reduction in mileage and at times complete cessation of running. If we advise our patients that crepitus is usually a normal knee noise and not a sign of damage, we can reduce anxiety and the risk of catastrophising, and keep runners running.


The body of literature on joint crepitus is mostly old and methodologically often out-dated. Clearly as imaging and arthroscopic surgery has advanced, so has the complex evaluation of joints, and the clinical need for assessment techniques such as joint auscultation and vibration arthrography has diminished, if not gone. However, this means that the interest in joint crepitus that has existed in the literature for a century has passed, and yet the relevance to patients remains current, and the understanding regarding belief systems and joint crepitus unexplored.

This blog has taken the viewpoint that even if crepitus doesn’t matter pathologically, if people are concerned by it, then it should be of interest to the practitioner/trainer. The author hopes that the reader now further understands this quirky topic, and as a result can inform and empower anyone whom it may concern.

Take home message for runners; noises from your knee such as clicking and creaking are very common and not a sign of joint damage. If you have any concern about your knees see a physiotherapist or health professional for an expert opinion.

For further information see our series of articles on patellofemoral pain.


Bro-Jorgensen J., Dabelsteen T. Knee clicks and visual traits indicate fighting ability in eland antelopes: multiple messages and back-up signals. BMC Biology 2008; 6:47. Available from: (10 July 2010)

Blodgett WE. Auscultation of the knee joint. Boston Med Surg J 1902; 146: 63-6.

Crossley KM, Barton CJ, Menz HB. Clinical predictors of foot orthoses efficacy in patellofemoral pain syndrome. Med Sci Sports Exerc; 42;5:687

Heuter C Grundriss der chirurgie. 3rd ed. Leipzig: FCW Vogel, 1885.

McConnell J., Management of patellofemoral problems. Manual Therapy 1996;1;2:60-66

McCoy G, McCrea JD, Beverland D, Kernohan G, Mollan RB. Vibration arthrography as a diagnostic aid in diseases of the knee. J Bone Joint Surg (Br) 1987; 69-B, 2: 288-293

Steindler A. Auscultation of joints. J Bone Joint Surg (Br) 1937; 19:121-36

Walter SCF. The value of joint auscultation. Lancet 1929; 1:92021

Wolpert L. Six Impossible things before breakfast. The evolutionary origins of belief. Chatham: Faber& Faber, 2007

Wikipedia (2010) (10 July 2010)