Knee Crepitus

Original Editor - Mandy Roscher Top Contributors - Mandy Roscher, Jess Bell, Kim Jackson, Tarina van der Stockt and Robin Tacchetti

Introduction

"'My knees are noisy. What does this mean?' [...is a question] that, in my experience, patients worry about a lot" -- Claire Robertson

Knee crepitus is characterised as a grinding noise with a palpable vibration which may indicate cartilage damage in the patellofemoral joint. These noises tend to get louder in relation to increased damage. Pazzinatto note that the "presence of knee crepitus is possibly the first symptom of patellofemoral [osteoarthritis]." However, knee crepitus is extremely common - 99% of knees make some sort of physiological noise.

Noises in the knee can be distressing for patients, potentially leading to fear avoidance behaviours due to catastrophisation and beliefs that the noises are associated with damage in the joints. However, while there is limited research on knee crepitus, recent studies have shown that the majority of knee noises are physiological rather than pathological

Types of Crepitus

Crepitus can be subdivided into pathological noises and physiological noises.

Pathological Noises

Pathological noises are normally linked to a specific incident or injury, such as a popping sound heard with an ACL injury or a meniscal tear that clicks at a specific point in the knee movement cycle. Degenerative changes, pathological plica, patellofemoral instability, pathological snapping knee syndrome and post-surgical crepitus are all potential causes of pathological crepitus. Patients who have pathology associated with their crepitus will normally have additional symptoms of pain, swelling, joint effusions etc. The management of the initial injury should hopefully resolve the crepitus as well as additional symptoms.

Physiological Noises

Physiological noises of the knee are much more common than pathological noises. In 1987. McCoy et al. measured sounds in participants knees using vibration arthrography. They found that 99% of knees make some sort of noise:

"Normal subjects produced three signal types--physiological patellofemoral crepitus, patellar clicks, and the lateral band signal. In symptomatic subjects we identified and categorised many signal types and related them to pathology."

People who experience physiological knee crepitus often cannot accurately describe their knee noises and will not have a specific trauma related to their noises.

These noises are classified as physiological as they have no correlation to pain or function and are simply just a noise. People with knee crepitus often find the noises alarming and worrying and are reassured to know there is no pathology associated with the noise.

Cause of Physiological Knee Crepitus

"The origin of physiological noise varies and includes a buildup or bursting of tiny bubbles in the synovial fluid, snapping of ligaments, catching of the synovium or physiological plica, hypermobile meniscus or discoid meniscus, and perception of previous noise after knee surgery due to emotional concerns."

Theories

• It has been suggested that a build up and bursing of air bubbles causes cracking
  • More recent evidence from real-time magnetic resonance imaging (MRI) suggests that cracking sounds are related to cavity formation (not bubble collapse)
  • This theory is consistent with tribonucleation - i.e. "a process where opposing surfaces resist separation until a critical point, at which they separate rapidly creating a sustained gas cavity"
  • Please see the video on the left to see cavity formation on real-time MRI and the video on the right for more information on why joints "pop"

• Snapping of ligaments/ tendons over bony prominences (normally the bicep femoris over the lateral knee)
• Catching of synovium or physiological plica
• Hypermobile meniscus
• Discoid meniscus
• “Stick-Slip” phenomenon
  • One type of crepitus commonly heard in normal patellofemoral joints is a loud, fine grating or gritty noise
  • It has been suggested that this noise is caused by the stick-slip phenomenon occurring in the knee
  • Stick-slip occurs as a the result of friction when two surfaces move on one another
  • The retropatellar cartilage can have an uneven surface, which is known as chondromalacia patellae - the jerky movement of the patella on the femur could cause this loud, grating / gritty noise
  • The stick-slip phenomenon is illustrated in the following video

Types of Sounds Experienced in the Knee

Table 1 provides a summary of various types of sound that can occur in the knee and their possible causes.

Table 1. Types of sounds heard in the knee

Sound	Characteristics	Possible Cause
Pop	Heard during a trauma/ injury	Possible ACL / meniscal injury
Clicking	A single noise at a specific  part of the knee flexion-extension cycle	Possible meniscal damage / tear
Clunking	A single noise at a specific part of the knee flexion-extension cycle	Repositioning of the patella in the trochlea groove of the femur
Creaking	Sounds like a creaky door	Often in arthritic knees
Cracking / popping	Spontaneous or during manipulation	The build-up and bursting of gas bubbles within the synovial joint - tribonucleation
Snapping	A single noise at a specific  part of the knee flexion-extension cycle	Tendon snapping over bony prominence (normally bicep femoris tendon on lateral knee). This is normally physiological.
Fine gritty or grating sound, often quite loud	Can occur throughout knee flexion-extension, comes and goes, the volume of the sound can change	Found in asymptomatic and symptomatic people. There is a higher incidence in people with patellofemoral pain and osteoarthritis. There are various theories on the source of this noise.

The Relationship Between Crepitus, Pain and Function in Patellofemoral Pain

Recent research has explored the relationship between knee crepitus and pain and dysfunction. In 2018, De Oliveira et al. assessed study participants for the presence of knee crepitus, anterior knee pain, and knee pain after ten squats and ten stairs climbed. The study participants included:

• 165 women with patellofemoral pain
• 158 pain-free subjects

De Oliveira et al. found that even though the incidence of crepitus is higher in women with patellofemoral pain (68% of participants with patellofemoral pain had crepitus and 33% of the asymptomatic knees had crepitus), there was no significant relationship between the presence of crepitus and self-reported function, physical activity level, worst pain level in the last month, pain on climbing stairs or pain squatting.

Another study by De Oliviera et al. explored the impact of knee crepitus on the clinical presentation of women with and without patellofemoral pain.

• Again, they found a higher prevalence of crepitus in women with patellofemoral pain (50.7%) compared to non-symptomatic women (only 33.3% had crepitus)

• Participants with patellofemoral pain had higher levels of kinesiophobia, catastrophisation and knee stiffness than participants with asymptomatic knees regardless of crepitus

• All participants who had patellofemoral pain (with and without crepitus) and asymptomatic participants WITH crepitus had lower functional performance than women with no crepitus and symptomatic knees

An important take away from this study is that knee crepitus alone does not have a significant influence on strength or physical function and is common in people who have no pain. But "[i]n pain-free women, crepitus was associated with poorer objective function."

Knee Crepitus and Osteoarthritis of the Knee

Individuals with osteoarthritis of the knee will commonly present with crepitus. Research has shown that crepitus can be an indicator of structural changes and the development of osteoarthritis.

A 2018 study by Pazzinatto et al. investigated the clinical implications of crepitus in individuals with knee osteoarthritis. They found that individuals who had osteoarthritis of the knee and crepitus had lower self-reported function compared to individuals with osteoarthritis and no knee crepitus. However, there was no difference in the objective function (knee strength and performance) between groups. Pazzinatto et al. concluded that knee crepitus does not impact knee strength, objective function and pain in individuals with osteoarthritis. However, a patient's beliefs and anxiety around the noises, may cause knee crepitus to have a negative effect on their health-related perception.

Patients Beliefs of Crepitus and the Impact on Behaviour

A qualitative study conducted by Roberston et al. examined people's beliefs about knee crepitus and their influence on their behaviours. Three major themes were identified in this study.

1.   Belief about the Noise

The study participants expressed that knowing what the noise meant and where it was coming from was very important to them. Most had tried to find out what the origin of the noise was through googling and asking their healthcare professional but had not come up with any answers. Some beliefs were that is symbolised ageing and that the bones were grinding on each other. In general, the emotions around the origin of the noise were very negative and these negative emotions were mainly caused by a lack of understanding about where the noise was coming from.

"The patients were really frustrated. They didn't really know what it meant. They found that anxiety meant that they were doing the good old Google trying to find out on the Internet [...] So, [the] search for meaning and the lack of clarity actually, probably [increased] anxiety." -- Claire Robertson

2.   Influence of Others – Friend, Family and Health Professionals

Most participants described how friends and family commented on their knee noises and how this added to their distress. The body language of family and friends and their facial expressions (e.g. wincing when they heard the noises) also contributed to negative emotions around the knee crepitus.

"So, there were lots of comments from patients around things like friends and family would say, 'Ooh, that you want to get that checked out'" -- Claire Robertson

Participants in the study reported a dissatisfaction with healthcare professionals when it came to knee crepitus stating that they often felt that the crepitus was disregarded and some even felt the health professional didn’t even know what the noise was. This again led to increased dissatisfaction. Participants who had been able to discuss their knee crepitus with a health professional had a much more positive view on the crepitus.

"And a lot of the patients felt, they thought it meant they had arthritis and that the knee was wearing away, the noise was bone on bone. [They] quite often felt angry towards the health professionals because they hadn't had any decent answers" -- Claire Robertson

3.   Avoiding the Noise

Because most participants believed that the noise in their knee was dangerous or damaging to the joint, several ended up altering movements to avoid the noise. They would also avoid activities that they knew would cause crepitus.

"Every single patient said, 'I would avoid doing physio exercises if they made my knee make its noise'." -- Claire Robertson

Implications for practice

This study shows that education from healthcare practitioners around knee crepitus is extremely important. Patients need to understand what the noise is and where it is coming from.

Management of Crepitus

In patients where crepitus is linked to a pathology (e.g. a specific click indicating a meniscal tear), management for the pathological cause will be best care practice. Managing the pathology may also resolve the noise.

However, in the majority of patients, the crepitus in their knees is physiological and not linked to the pathology. These patients need education on the cause of the crepitus as well as the fact that the crepitus is not harmful or damaging.