X-ray Knee

[Libby Cowen]

TheX-ray image is black and white. Dense body parts, such as bones, block the passage of the X-ray beam through the body. These look white on the X-ray image. Softer body tissues, such as the skin and muscles, allow the X-ray beams to pass through them. They look darker on the image.

In a knee X-ray, an X-ray machine sends a beam of radiation through the knee, and an image is recorded on a computer or special film. This image shows parts of the bones of the knee, including the femur (the bone above the knee), the tibia and fibula (the lower leg bones), the patella (kneecap), and the soft tissues.

A knee X-ray can help find the cause of pain, tenderness, swelling, or deformity of the knee. It can show broken bones or a dislocated joint. After a broken bone has been set, an X-ray can show if the bones are aligned and if they have healed properly.

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Anterior-Posterior (AP) and Lateral. In the context of trauma the Lateral view is acquired with the patient lying supine and with a horizontal X-ray beam. This allows effusions to be visualised in the suprapatellar pouch.

A 'Skyline' or 'Sunrise' view is rarely indicated in the context of trauma. This view is only necessary if the standard views are normal and a patellar fracture is still suspected, or to assess patellar dislocation. A skyline view can only be acquired if the patient can tolerate knee flexion.

Fractures of the tibial plateau can be subtle with little displacement, or can be widely displaced, with varying degrees of comminution. There may be depression of the plateau surface, displacement of a fracture fragment, or a combination of both.

OA commonly affects the hip, knee, shoulder, the big toe, and the base of the thumb, and is commonly classified as primary or secondary OA. Primary OA is when the source of OA is unclear, and is commonly associated with age, sex, body mass index (BMI), or genetic factors. Secondary OA often has a clear source of joint degeneration and is commonly associated with joint injury, such as a trauma or repetitive-stress or occupational injury. Articular cartilage degeneration and other features of OA commonly occur as a gradual process.

Regardless of the joint that is affected, conventional radiographs (X-rays) are used to evaluate your joint for osteoarthritis. The presence of osteoarthritis is displayed on the radiograph as a narrowing or a reduction in space between the bones of the joint where the cartilage has worn away, as well as by the formation of osteophytes (bone spurs) on the margins of the joint.

When cartilage is lost, bone rubs against bone. This can cause cysts or fluid-filled cavities in the bone, which will also be visible in an X-ray. The bone also responds with sclerosis (increased bone density), in which more bone grows under where the cartilage used to be. If the joint surfaces become misaligned, then osteophytes may form. There are basic routine X-ray views for imaging each joint:

In order to detect early cartilage wear, HSS uses special X-ray views in place of or in addition to these standard views. These specialized views are designed to increase the sensitivity of a conventional radiographic study.

Symptoms of osteoarthritis may arise before the degeneration can be seen on standard X-rays. For this reason, radiologists at Hospital for Special Surgery often use the more sensitive MRI, CT and ultrasound forms of imaging, which are superior for detecting early osteoarthritis.

Magnetic resonance imaging is very sensitive imaging that can reveal subtle changes in bony and soft tissues. An MRI can show reactive bone edema (fluid build-up in the bone marrow), inflammation of soft tissues, as well as degenerated cartilage and damage to other soft tissues associated with OA. HSS uses a protocol of MRI pulse sequences with high sensitivity and accuracy to identify early evidence of cartilage degeneration. When evidence of cartilage generation is detected early, appropriate treatment can begin to minimize further degeneration, possibly postponing or eliminating the need for surgery.

Ultrasound is extremely sensitive for identifying synovial cysts that sometimes form in joints which have osteoarthritis. It is also excellent for evaluating the ligaments and tendons around the joint.

In addition to helping diagnose osteoarthritis, radiographic technologies can also be used to guide your doctor while applying treatments. For example, anesthetics and/or corticosteroids injected into a joint can help reduce the pain of osteoarthritis. It is helpful to perform such injection procedures using image guidance to aid in positioning the needle tip into the joint space. This kind of direct visualization can be performed using CT, ultrasound or fluoroscopy (a continuous real-time X-ray that works like an X-ray movie).

Arthrogram: A joint injection performed under fluoroscopic or CT guidance is called an arthrogram. The radiologist will inject a small amount of contrast agent into the joint to better visualize it. With ultrasound, the radiologist directly visualizes the needle inside the joint, as well as neighboring muscles, arteries and veins.

The faculty members of the HSS Department of Radiology and Imaging at HSS are board certified radiologists with specialized fellowship training in musculoskeletal imaging and cross-section imaging (MRI, CT, and ultrasound). Although other types of subspecialty physicians perform some of these procedures, radiologists are doctors who are trained in the use of all forms of imaging. HSS radiologists also have specific training in the physics behind the imaging, the safe use of ionizing radiation (fluoroscopy/CT), as well as in MRI and ultrasound safety.

Optional radiographs are obtained routinely by HSS joint replacement surgeons. They include the Lowenstein lateral, cross-table lateral, false-profile and elongated femoral neck views. All of these views help to identify the precise site of osteoarthritis.

Optional radiographs are routinely ordered at HSS. Most often, these will be a posteroanterior (back-to-front) X-ray, taken while the knee is weightbearing (standing position) and in slight flexion (knees slightly bent). This position helps the radiologist evaluate whether there is cartilage loss in the posterior (rear) portion of the of the medial (inside) or lateral (outer side) knee joint compartments. Positioning for these views is very specific.

Typically, the cartilage in one compartment of the joint (that is, the medial, lateral, or anterior patellofemoral joint compartment) is most severely affected. The standing X-rays may show narrowing of the involved joint space of the knee. Altered alignment of the knee joint is very common as either the cause or as a result of osteoarthritis. The patellofemoral joint (at the front of the knee) can be the focus of osteoarthritis of the knee or part of a more generalized condition. Lateral subluxation or patellar malalignment is very common.

As the disease progresses, osteophytes form along the joint margins and bone cysts and sclerosis are typically present. When osteochondral or cartilage fragments break off, they can remain in the joint or can get larger and are referred to as intra-articular loose bodies. Fluid can form in the joint secondary to the arthritis and is referred to as an effusion.

Reviewed by Matthew F. Koff, PhD

Assistant Scientist, Department of Radiology and Imaging, Hospital for Special Surgery

Assistant Professor of Biomedical Imaging in Orthopaedic Surgery, Weill Cornell Medical College

One of the most common reasons for a doctor's office visit is knee pain or injuries from osteoarthritis. While magnetic resonance imaging (MRI) is widely used by doctors to diagnose problems like torn knee ligaments and cartilage, a study in the September 2016 issue of the Journal of the American Academy of Orthopaedic Surgeons found that a simple x-ray may be a better diagnostic tool as it helps reduce time and cost.

The study looked at 100 MRI scans of knees from patients ages 40 and older and found that the most common diagnoses were osteoarthritis (39%) and meniscal tears (29%), which involve the tearing of the wedge-shaped pieces of cartilage in the knee joint. Almost 25% of MRI scans were taken before the patient first obtained an x-ray, and yet only one-half of those scans contributed to a patient's diagnosis and treatment for osteoarthritis.

Whether a patient needs surgery for knee problems depends on the amount of arthritis. If an x-ray shows that a person has significant arthritis, the MRI findings, like a meniscus tear, are less important because the amount of arthritis drives the treatment, according to lead researcher Dr. Muyibat Adelani of Washington University in St. Louis.

"X-rays are an appropriate screening test for knee pain in older patients, and often the results of an x-ray can tell whether an MRI would be even helpful," she says. In addition, an MRI costs about 12 times that of an x-ray (based on Medicare rates) and can take an hour to perform.

Normal AP and lateral knee radiographs in an adult male for reference. There mild or borderline patella alta. Nice example of the normal fat within the supra-patella recess region without a joint effusion evident.

A torn meniscus often can be identified during a physical exam. Your doctor might move your knee and leg into different positions, watch you walk, and ask you to squat to help pinpoint the cause of your signs and symptoms.

The device contains a light and a small camera, which transmits an enlarged image of the inside of your knee onto a monitor. If necessary, surgical instruments can be inserted through the arthroscope or through additional small incisions in your knee to trim or repair the tear.

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