Knee Crepitus

Introduction

Knee crepitus is extremely common with 99% of knees making some sort of physiological noise (5). Noises experienced in the knee can be distressing and lead to fear avoidance behaviours due to catasrophisation and beliefs about the noises damaging the joints. (7). Knee crepitus is a poorly researched area but recent studies have shown that the majority of knee noises are physiological rather than pathological (1,2,3,4,5)

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 (6). Patients that 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. (6)

Physiological Noises Physiological noises of the knee are much more common than pathological noises. McCoy in 1990 measured sounds in participants knees using vibration arthrography and found that 99% of knees make some sort of noise.(5) People that 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 (1,2,3,4,6). People with knee crepitus often find the noises alarming and worrying and are reassured to know there is no pathology associated with the noise (7).

Cause of Physiological Knee Crepitus The exact cause of the crepitus is still unknown but there are a few theories around where the noise stems from.

Theories (all 6- except last one) 1. Build up and bursting of air bubbles in synovial fluid 2. Snapping of ligaments/ tendons over bony prominences (normally the bicep femoris over the lateral knee) 3. Catching of synovium or physiological plica 4. Hypermobile meniscus (6) 5. Discoid meniscus (6) 6. “Stick-Slip” phenomenon (Claires lecture notes) (8)

The loud, fine grating or gritty noise of a normal patella-femoral joint is a common type of knee crepitus. A new theory about where this noise is that the stick-slip phenomenon is occurring in the knee. Stick-slip is the result of friction when 2 surfaces move on one another. (9) The retropatellar cartilage can have an uneven surface, known as chondromalacia patellae and as such, the jerky movement of the patella on the femur could be the cause of the sound (8).

https://www.youtube.com/watch?v=TcebgBomjRs (stick-slip) https://www.youtube.com/watch?v=0hmWiDTA-xE(joint popping) https://www.youtube.com/watch?v=IjiKUmfaZr4(good video on joint popping bubbles)

Types of Noises experienced in the knee (6,8) Sound Characteristics Possible Cause Popping 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 trochlea notch of the femur Creaking Sounds like a creaky door Often in arthritic knees Cracking Spontaneous or during manipulation The build-up and bursting of gas bubbles within the synovial joint Tribonucleation (see video) 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) 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. Higher incidence in people with PFP and OA Various theories on the source of the noise

The relationship between Crepitus, Pain and Function in Patellofemoral Pain

There has been recent research conducted in knee crepitus and its link to pain and dysfunction. De Oliveira et al, 2018, (3) investigated 165 women with PFP and 158 pain-free subjects. They assessed the participants for the presence of knee crepitus, anterior knee pain as well as knee pain after 10 squats and 10 stairs climbed. Their results showed that while the incidence of crepitus is higher in women with PFP (68% of participants with PFP had crepitus and 33% of the asymptomatic knees had crepitus) there was no significant relationship between the presence if crepitus and self-reported function, physical activity level, worst pain level in the last month, pain on climbing stairs or pain squatting.

A different study by de Oliviera et al in 2018 (4) looked into the implication of knee crepitus in the clinical presentation of women with and without PFP. They found the same higher prevalence of crepitus in women with PFP at 50,7% versus only 33,3% of non-symptomatic women had crepitus. Their findings indicated the following

BULLET X Participants with PFP demonstrate higher Kinesiophobia, catasrophisation and lower self-reported function than participants with asymptomatic knees regardless of crepitus. Whether they had crepitus or not made no difference to the above variables X All the women that had PFP (with and without crepitus) and asymptomatic women 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 has been shown not to have a significant influence on strength or physical function and is common in people who have no pain.

Patients Beliefs of crepitus and impact on behaviour Claires article

A qualitative study conducted by Roberston et al in 2017 looked at peoples beliefs about knee crepitus and its 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 joints, the bones were grinding on each other. In general, the emotions around the origin of the noise were very negative and these were mainly due to not understanding where the noise was coming from 2. Influence of Others – Friend, Family and Health Professionals Most participants described how friend and family commented on their knee noises added to their distress. The family and friends body language and facial expressions eg wincing when they heard the knee also contributed to negative emotions around the knee crepitus. 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 it was. This again led to increased dissatisfaction. In participants where their knee crepitus had been discussed a much more positive view on the crepitus was reported. 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 from occurring. They would also avoid activities that they knew would cause crepitus. 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, where it is coming from.

Management of Crepitus

In patients that have crepitus linked to a pathology eg specific click indicating a meniscal tear, management for the pathological cause will be best care practice. Managing the pathology may also resolve the noise.

In the majority of patients, the crepitus in their knees is physiological and not linked to the pathology as such. These patients need education on the cause of the crepitus as well as the fact that the crepitus is not harmful, damaging and has no link in the development of OA of the knee.