‘It’s like Chalk on a blackboard’ My Experiences Researching Patellofemoral Crepitus. By Claire Robertson

As a specialist in patellofemoral pain (PFP) 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!

In an attempt to answer questions I had on this topic I turned to the literature. My initial searching revealed the unexpected finding that crepitus is an alleged Roman God of flatulence. Looking to the mammalian veterinary 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 yes, but unhelpful in my quest to better understand the crepitus experienced by people I see in clinic!  Papers on joint crepitus in key medical journals dating back as far as 1885, (Heuter, 1885) starts to shed light on this intriguing topic. Blodgett, (1902), introduced the practice of joint auscultation, (listening with a stethoscope) 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). These studies, albeit interesting really don’t inform contemporary practice.

An absolute dearth of literature was seen for half a century until McCoy et al., (1987) investigated the prevalence of crepitus in normal subjects without pain. McCoy et al., (1987) investigated 247 symptomatic, and 250 normal knees and found that 99% of normal subjects had patellofemoral crepitus. This finding really fueled my desire researching this topic, and in particular to reach a better understand of why many people are really anxious about what, in essence is a normal finding.

I therefore firstly wrote an editorial where I posed my belief that patients were often very anxious regarding the noise in their knee, (Robertson, 2010). The response from this editorial was fascinating. Some were amused I should be discussing noisy knees, some thought it was a frivolous irrelevance, but most fed back that yes, they too had noted similar concerns about this phenomena amongst their patients.

The perception of some clinicians that this was an irrelevance to them, together with the overarching positive response of others, combined with my ongoing desire to start a line of enquiry led me to carry out the research I have published in Musculoskeletal Science and Practice, ‘People’s beliefs about the meaning of crepitus in patellofemoral pain and the impact of these beliefs on their behaviour: A qualitative study.’ I really wanted to explore what patients thought their joint cracking meant. I specifically looked at patients without osteoarthritis so that we knew the noise was not in response to joint pathology. In order to explore this previously unresearched topic I carried out semi-structured in-depth interviews, and the transcripts were then analysed for emerging themes. These, in essence were themes that came through again and again. The key themes were, belief about the noise, influence of others, and avoiding the noise .The answers to, ‘what do you think the noise means?’ were often alarming and frequently along the lines of, “my joint is wearing away”. The emergent theme of belief about the noise also revealed that for many it represented premature ageing and also brought about strong emotional responses. One 26-year-old gentleman voiced he was house hunting and he was so perturbed by the noise in his knee that he had decided to only look at ground floor properties. Just stop for a minute and reflect on that. He had a normal knee on MRI, but his belief about the noise had made him so fearful he was altering where he was going to live! The emotional response was very apparent and came through as a sub-theme of belief about the noise. One participant said, ‘It’s like chalk on a blackboard; it makes you feel a bit queasy really.’ In response to this research, in the clinical setting I now routinely ask, “What do you think it means?’ if a patient mentions their crepitus. It can be very revealing!

It is my belief that in the world of managing low back pain we are much better at exploring our patient’s beliefs and looking at fear avoidance. I would like to propose that this should be no difference in this instance just because we are looking at a symptom of noise, and in a different anatomical area.

My study also revealed that patients had tried to find a meaning for their crepitus, often through internet research, and often through asking health professionals. 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 Oxford dictionary define crepitus as, ” A grating sound or sensation produced by friction between bone and cartilage or the fractured parts of a bone.”, (Oxford dictionary). 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. It must also be noted that my research revealed patients felt unsatisfied with answers they had received from health professional regarding what the crepitus actually is. This led to patients feeling that it was dismissed as unimportant, or that the health professionals didn’t actually know themselves. Let’s just think about both of those issues. Firstly, and to be quite frank about it if something is important to the patient, it should be of importance to you as the health professional. Secondly, I think many health professionals are rather unclear about what exactly crepitus is, so I have summarized that here.

In the non-osteoarthritic knee crepitus will likely be either loud isolated cracks and pops which is either bubbles of gas releasing, (like knuckle cracking), or the patella clunking into the central portion of the trochlea, (it often feels better after this). But perhaps the noise that causes the greatest alarm is the fine grating often heard on the stairs. This was cited by many of the participants in my study as frequently commented on by family and friends, often reinforcing anxiety about the noise. It can be powerful to mention to patients the aforementioned work of McCoy et al., (1987) where 99% of normal subjects had some patellofemoral noise. It is my belief that many of the patients possibly had crepitus pre-dating their pain, but through the presence of pain have become hypervigilant to their knee and hence notice both the pain and swelling.

To return to the central issue of this blog is to inform regarding what is 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. To accurately inform and reduce anxiety is conversely likely to empower and reduce the risk of catastrophizing.

Claire Robertson MSc PGCE MCSP

Consultant Physiotherapist Wimbledon Clinics



Please find the link to Claire and colleagues article on patients experience of patellofemoral pain



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

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

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