Knee Ultrasound

The knee joint is a complex structure. The stability of the knee heavily relies on strong internal ligaments (the cruciate ligaments) and ligaments around the knee (the medial and lateral collateral ligament complex). The patella (kneecap) lies in front of the knee and is part of the extensor mechanism with the quadriceps and patellar tendons, all of which function as one unit.

In young patients, knee pain is often caused by acute injuries, repetitive overuse, or patellar maltracking. In middle-aged and older patients, a common cause is osteoarthritis, which is “wear and tear” of the knee joint whereby the knee becomes painful and stiff.

Ultrasound performs well when evaluating the external structures around the knee. It is most useful to assess localised pain or lumps and bumps around the knee.  It is used to look for joint effusions (build-up of joint fluid) and active inflammation in patients with rheumatoid arthritis and other inflammatory conditions. Evaluation of the internal structures of the knee, including the cruciate ligaments, menisci, and cartilage requires MR imaging.

Ultrasound-guided interventions, such as steroid injections into the knee joint or aspirations of cysts, such as a large Baker’s cyst are successful and safe.

Knee Arthritis

Osteoarthritis is a common degenerative joint disease, affecting middle-aged to elderly patients. Osteoarthritis is characterized by degeneration of the cartilage, gradually leading to the narrowing of the joint space.

This process is typically diagnosed and monitored using radiographs (x-rays). However, ultrasound can add valuable information about structures not visible on radiographs. Ultrasound can show morphological changes in bone, the menisci, and the femoral cartilage. It can show joint effusions and synovitis (inflammation of the inner joint membrane) as secondary signs of a derangement within the knee joint [1], [2]. 

In patients with inflammatory conditions such as rheumatoid arthritis, the main role of ultrasound is to identify active inflammation in the joint.

Ultrasound is used to perform injections into the knee joint safely.

Jumper’s Knee: Quadriceps and Patellar Tendinitis

The quadriceps and patellar tendons are located directly under the skin at the front of the knee. These are very strong tendons required to straighten the knee, such as when standing up from a squatting position.

“Jumper’s knee” is a chronic overuse injury of these tendons. The patellar tendon is more often affected than the quadriceps tendon.

This condition is also called patellar tendinitis or tendons. Athletes who play sports with a lot of jumping and running are at higher risk.

 On ultrasound of patellar tendonitis, the tendon appears swollen with loss of the typical brightness and fibrillar architecture of healthy tendons. The high resolution of ultrasound easily detects small tears in the tendons.  Doppler ultrasound can demonstrate increased blood flow in the tendon, confirming the presence of inflammation.

 A specialist clinician should guide the treatment of Jumper’s knee. If steroid injections are required, this can be safely performed under direct ultrasound guidance [1]. “Dry needling” is a specific intervention for tendinosis that aims to disrupt the chronic degenerative process and promote localised bleeding and the tendon’s healing [3].

After anesthetizing the skin, the affected portion of the tendon is fenestrated using a needle. This process is performed controlled and targeted manner under the direct vision of the needle sewing ultrasound.

Prepatellar Bursitis

There are several bursae around the knee at increased pressure or tissue friction sites. At the front, there are three different bursae. 

The prepatellar bursa is the largest and most affected bursa. It lies between the skin and the patella (kneecap). Repetitive or prolonged kneeling can cause it to become inflamed, causing swelling and pain called bursitis. Acute trauma can also lead to bursitis, such as a fall or direct blow to the kneecap. Because of its location, the prepatellar bursa is also at risk of penetrating injuries, resulting in injections.

Prepatellar bursitis is clinically obvious, but ultrasound can confirm the diagnosis. While this should usually settle with rest, anti-inflammatory pain killers and icing, ultrasound-guided aspiration and steroid injection can be performed in selected cases [4].

Baker’s Cyst

A Baker’s cyst, also called a popliteal cyst, is fluid distension of the medial gastrocnemius-semimembranosus bursa in the back of the knee. While this bursa contains a small trace of fluid in many asymptomatic patients, the bursa can fill significantly with fluid, causing local symptoms such as pain, pressure, or limited range of motion.

Baker’s cysts can occur spontaneously in young patients, but they are often associated with injuries to the knee or indicate an underlying condition, such as osteoarthritis or rheumatoid arthritis. In most cases Baker’s cyst do not require any treatment other than addressing any potential underlying condition of the knee. In some cases, ultrasound-guided drainage of the cyst may be feasible to elevate local symptoms [5].

Iliotibial Band Syndrome

The iliotibial band (ITB) is a tendinous band that runs down the outer side of the thigh from the pelvis to the knee. The ITB is a dynamic structure that moves when the knee is bent. ITB syndrome is where increased friction occurs between the ITB and the underlying knee bone. This leads to painful irritation and inflammation of the ITB and surrounding soft tissues.  It is an overuse disorder commonly occurs in runners, cyclists, and basketball athletes.

Ps usually complain of pain during activities and tenderness on the outer side of the knee. The diagnosis of ITB syndrome is mainly based on clinical examination. Ultrasound can demonstrate soft tissue inflammation or bursa formation at the site of increased friction. Ultrasound is also used if a steroid injection is required to reduce the inflammation and the pain [6].

Referrences

[1]        S. Nuhmani et al., “Patellar Tendinopathy-Does Injection Therapy Have a Role? A Systematic Review of Randomised Control Trials,” J Clin Med, vol. 11, no. 7, Apr. 2022, doi: 10.3390/JCM11072006.

[2]        W.-T. Wu, K.-V. Chang, C.-P. Lin, C.-C. Yeh, and L. Ozcakar, “Ultrasound imaging for inguinal hernia: a pictorial review,” Ultrasonography, vol. 41, no. 3, Jul. 2022, doi: 10.14366/USG.21192.

[3]        M. P. López-Royo, M. Ortiz-Lucas, E. M. Gómez-Trullén, and P. Herrero, “The Effectiveness of Minimally Invasive Techniques in the Treatment of Patellar Tendinopathy: A Systematic Review and Meta-Analysis of Randomized Controlled Trials,” Evidence-based Complementary and Alternative Medicine : eCAM, vol. 2020, 2020, doi: 10.1155/2020/8706283.

[4]        “Pre-patellar bursitis | Health topics A to Z | CKS | NICE.” https://cks.nice.org.uk/topics/pre-patellar-bursitis/ (accessed Aug. 16, 2022).

[5]        “Baker’s cyst – NHS.” https://www.nhs.uk/conditions/bakers-cyst/ (accessed Aug. 16, 2022).

[6]        F. Jiménez Díaz, S. Gitto, L. M. Sconfienza, and F. Draghi, “Ultrasound of iliotibial band syndrome,” Journal of Ultrasound, vol. 23, no. 3, p. 379, Sep. 2020, doi: 10.1007/S40477-020-00478-3.