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Noise around the Knee

Song SJ, Park CH, Liang H, Kim SJ (2018) Noise around the knee. Clin Orthop Surg 10:1–8. doi.org/10.4055/cios.2018.10.1.1 - DOI - PubMed - PMC

In today’s letter

• Overview of what may be causing various noises around the knee

Rapid Results:

Non-harmful “crepitus” = Most likely caused by":

1. The buildup or bursting of tiny bubbles in the synovial fluid

2. Ligament snapping

3. Synovium or plica catching

4. Hypermobile or discoid meniscus

5. Emotional sensitivity to previous noise after knee surgery

“Crepitus” requiring further investigation:

1. Noise that is accompanied by pain and swelling

• 2 resources to check out to further you knowledge about knee noises

• Memem of the week: chatty patients, we all had them 😄 

Aim of the study?

• The authors examined the different types of knee noises based on their sound and when they occur, and explain how to distinguish between normal and abnormal noises.

Did you Know?

• Noise around the knee is commonly experienced during repetitive knee movements, such as extension, flexion, or squats.

• In most cases, the noise is physiological (non-harmful), and explaining its cause to patients can provide reassurance.

• Sometimes knee noise can indicate underlying pathological conditions, thus its important to understand when an onward referral is required

• Research by Crema et al. found a link between various knee structural pathologies and an increased risk of general crepitus in osteoarthritis.

• Schiphof et al. suggested that crepitus might be an early symptom of patello-femoral osteoarthritis.

• A study on people over 40 years old reported crepitus in 38.1% of women and 17.1% of men.

• Painful popping in the knee was observed in 96.5% of patients with posterior root tears of the medial meniscus, and patellar crepitus was found in up to 18% of patients with posterior-stabilised total knee arthroplasty

Differences of noises according to sound nature

• Various terms describe knee sounds, for example:

1. Popping

2. Snapping

3. Catching

4. Clunking

5. Clicking

6. Crunching

7. Cracking

8. Grinding

9. Grating

10. Clunking

• "Popping" refers to a sudden, sharp noise often associated with injuries, such as a root tear of the degenerative medial meniscus or ligament detachment.

• "Clunking" describes a loud, singular noise caused by resistance release, often seen in patellofemoral clunking after total knee arthroplasty

• "Clicking" is a small, singular noise occurring during one cycle of knee movement, frequently linked to meniscal tears.

• "Grinding" and "grating" describe continuous scratching noises, commonly found in degenerative osteoarthritis and patellofemoral pain syndrome.

Clinicians often use the term "crepitus" to describe joint sounds, as it is a familiar term used for lung sounds.

Differences of noises according to onset

• Patients are often unaware of when “crepitus” first begins.

• Pathological (non-harmful) knee noise can have either an acute or chronic onset.

• Acute noise accompanied by pain is often linked to meniscal or ligament injuries.

• Recurrent or chronic noise may result from old meniscal tears, cartilage damage, osteoarthritis, patello-femoral instability, or patello-femoral pain syndrome.

Differences between physiological (normal) and pathological (painful) noise

• The key to distinguishing between physiological and pathological knee noise is checking for pain and swelling/effusion in the knee joint.

Physiological noise is not linked to a history of injury, doesn’t worsen over time, and occurs sporadically due to air buildup in the joint fluid.

• Pathological noise is often accompanied by pain and swelling, indicating possible issues within the joint

• A loud "pop" with pain during an injury typically suggests ligament or meniscus damage.

• Research has been conducted to detect and compare physiological and pathological knee noise using acoustic emission techniques.

• Friction between articulating structures in the knee produces various vibrations, leading to acoustic energy that reaches the skin's surface.

• While most of this acoustic energy is reflected back into the tissue, a small portion pass through into the air, creating audible sounds.

• Studies have shown that knees with osteoarthritis produce acoustic emissions with greater frequency, higher peaks, and longer duration than healthy knees

Causes of physiological (normal) noise

• The origin of physiological knee noise can vary and may include:

1. The buildup or bursting of tiny bubbles in the synovial fluid

2. Ligament snapping

3. Synovium or plica catching

4. Hypermobile or discoid meniscus

5. Emotional sensitivity to previous noise after knee surgery.

• Repeated joint sounds during movement typically occur when anatomical structures rub against each other, but cracking sounds have a refractory period and cannot be repeated immediately, even with continuous movement.

• The exact cause of cracking sounds in the knee is still unclear, despite various proposed theories.

• Some researchers suggest that cracking is caused by the sudden collapse of a cavitation bubble.

• Others believe that the formation of a clear space or bubble is responsible for the cracking sound.

• Changes in joint pressure can lead to the slow formation of tiny gas bubbles within the joints.

• When these gas bubbles form quickly, they create a popping sound, which can also occur in other joints, such as the knuckles.

• Ligaments and tendons around the knee may stretch over a small bony prominence and then snap back, producing a clicking sound.

• Snapping syndrome of the knee joint is commonly caused by the biceps femoris tendon snapping over the lateral aspect of a normal knee joint.

Causes of pathological (painful) noise

Pathological knee noise can result from degenerative changes, pathological plica, patellofemoral instability, pathological snapping knee syndrome, and postsurgical crepitus.

Degenerative Changes in Knee Structure

• Osteoarthritis in the knee involves the gradual loss of cartilage, along with the formation of bony spurs and cysts at joint margins, which can lead to crepitus.

• Crepitus is also linked to medial collateral ligament issues in the medial tibiofemoral compartment but is less associated with cartilage damage in this area.

Clinical signs of degenerative changes include:

1. Pain around the patella

2. Tenderness in the quadriceps and patellar tendons

3. A positive compression test

4. A history of pain

All of which are significantly associated with MRI findings of patellofemoral osteoarthritis, such as cartilage lesions, osteophytes, cysts, and bone marrow lesions.

Pathological Plica

• The plica is a fold in the synovium, a remnant from the knee's embryological development.

• Pathological plica, which is inflamed, thickened, or less elastic, can cause pain and crepitus.

• Friction between the medial plica and the medial femoral condyle during daily activities can worsen the pathological condition, leading to symptoms like synovitis and pain.

Patellofemoral Instability

• Patellofemoral instability is a complex condition caused by multiple factors, including valgus or rotational deformities of the lower limb and structural abnormalities of the patella or femoral trochlea.

• This instability may also arise from issues such as defects in the medial patellofemoral ligament, dysplasia of the vastus medialis obliquus, hypertrophy of the vastus lateralis, and tightness in the lateral retinaculum.

• The instability leads to knee noise due to the hypermobility of the patella or the repositioning of a previously subluxated patella during knee movement.

• Research by Smith et al. showed that assessing crepitus is a more reliable physical examination for diagnosing patellofemoral instability than tests like palpation of the patellar retinaculum, patellar compression, Bassett’s sign, or evaluating the vastus medialis obliquus.

Pathological Snapping Knee Syndrome

• When snapping sounds around the knee are accompanied by pain, it's important to identify the underlying cause.

• Pathological snapping can originate from various extra-articular (outside of joint) and intra-articular (inside the joint) structures.

• Intra-articular causes can include conditions like ganglion cysts, lipomas, and synovial nodules.

• Extra-articular causes of snapping include the presence of a fabella, osteophytes, osteochondromas, and tendinopathies affecting the popliteus, biceps femoris, or pes anserinus tendons.

Postoperative Pathological Noise

• Knee surgeries can sometimes lead to postoperative noise, which may be pathological.

• Crepitus can occur in post meniscus removal

• Inflammation of Hoffa’s fat pad after arthroscopy have been identified as causes of postoperative crepitus.

• Patellofemoral crepitus or clunk after total knee arthroplasty is a significant concern following orthopedic surgery.

• Factors that may increase the risk of patellofemoral crepitus or clunk after total knee arthroplasty include previous knee surgeries, patella baja, and a higher postoperative flexion angle.

2 resources to check out

And further your knowledge about crepitus

1. A little overview of knee crepitus - LINK

2. Explanation & exercises for knee popping (video) - LINK

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