Imaging for Osteoarthritis: An Overview

Osteoarthritis: A Common Joint Disorder

Osteoarthritis is one of the most common disorders of joints. The joints most affected are the hip, knee, shoulder, the great toe and the base of the thumb. Degeneration of articular cartilage, leading to osteoarthritis, can occur without any predisposing factors or can be secondary to an associated condition, including a traumatic event or repetitive occupational-related trauma. Articular cartilage degeneration is a gradual process and the findings on radiographic imaging are dependent on the stage. The gradation of osteoarthritis (e.g. mild, moderate or severe and localized or diffuse) is used by the referring physician in determining appropriate treatment. Treatments include conservative therapy (e.g. physical therapy, alteration in precipitating event, oral medications, intraarticular steroid injections), or surgical treatment (e.g. osteotomies or joint replacement).

Various Imaging Examinations

Regardless of the joint, osteoarthritis has characteristic findings on conventional radiographs (x-rays) distinctive from other joint disorders such as rheumatoid arthritis. Osteoarthritis presents with localized nonuniform joint space narrowing. The joint narrows secondary to localized cartilage loss. Cysts or fluid-filled cavities can form in the bone secondary to chronic impaction of bone on bone contact. Osteoarthritis is the result of the body's response to cartilage destruction and the bodies attempt to stabilize the joint. In the absence of an effective cartilage buffer, there is chronic friction on the narrowed joint space. Sclerosis (increased bone density) results as the body lays down bone in response. The localized cartilage wear or loss results in incongruous joint surfaces and osteophytes (bone spurs) around the joint margins form in an attempt to stabilize the joint. There are basic routine x-ray views for imaging each joint an AP (anterio-posterior, or a frontal view), one or two oblique views, and a lateral view are standard. At Hospital for Special Surgery, special x-ray views that are designed to increase the sensitivity of the conventional radiographic study in detecting early changes are typically used in place of or in addition to the standard views.

Clinical signs of osteoarthritis may be evident before they are observed on conventional radiographic views. At Hospital for Special Surgery, MRI, CT, Ultrasound and Radionuclide Bone Scans are used in certain instances because they are more sensitive for the detection of early osteoarthritis.

• MRI (magnetic resonance imaging) is very sensitive to bony and soft tissue changes when dedicated protocols for the musculoskeletal system are used. MRI can demonstrate reactive bone edema or soft tissue swelling as well as small cartilage or bone fragments in the joint. At HSS, specific cartilage pulse sequences are used to identify early evidence of cartilage degeneration. When there is objective evidence of cartilage wear, appropriate treatment can be initiated to prevent or delay progression.
  
• CT (computed tomography) examinations are excellent for demonstrating the degree of osteophyte (bone spur) formation and its relationship to the adjacent soft tissues. CT examinations are also useful in providing guidance for therapeutic and diagnostic procedures.
  
• Ultrasound is extremely sensitive for identifying synovial cysts that can form in association with osteoarthritis. Ultrasound can also be used to image articular cartilage in patients who cannot tolerate an MRI examination because of claustrophobia or pacemakers. Ultrasound can also be used to provide guidance for diagnostic and therapeutic procedures.
  

The Faculty of the Department of Radiology & Imaging at HSS are Board Certified Radiologists with Fellowship specialty training in musculoskeletal imaging and cross section (CT/MR) imaging. While various subspecialty physicians perform these procedures, Radiologists are physicians trained in the use of all forms of imaging and have specific training in the physics behind imaging and the safe use of ionizing radiation (fluoroscopy/CT) as well as MR ultrasound safety.

Anesthetic and/or steroids injected into an osteoarthritic or painful joint can help reduce the pain. The advantage of having these injections performed using image guidance is that one can directly visualize the needle tip in the joint space. Direct visualization can be performed using fluoroscopy, CT or ultrasound guidance. A joint injection performed under fluoroscopy, which is real-time x-ray, or under CT guidance, is called an arthrogram. The radiologist will inject a small amount of contrast agent into the joint to confirm accurate needle placement. With ultrasound, the radiologist directly visualizes the needle in the joint, as well as neighboring muscles, arteries and veins.

Specific Joints

• Standard Conventional Radiographs
  • The standard conventional radiographic series obtained if a patient has hip pain from osteoarthritis, includes a frontal and lateral view of the hip. At Hospital for Special Surgery, a view of the pelvis is usually ordered as part of the initial examination to visualize other potential sources of hip pain, such as the low back or sacroiliac joints.
  • Positioning for these views is very specific as reproducability is invaluable to follow response to treatment and/or for preoperative planning.
    
• Optional Radiographs
  • Obtained fairly routinely by arthroplasty surgeons at Hospital for Special Surgery, optional radiographs include: Lowenstein lateral, cross table lateral, and false profile views. These views help to identify focal sites of early joint space narrowing/or bony changes secondary to osteoarthritis.
    
• Findings of Hip Osteoarthritis On Radiographs
  • Typically, joint space narrowing is focal either in the superolateral direction, although apical (up and into the pelvis) or medial (into the center of the body).
    
  • As the cartilage loss becomes severe, bone cysts and remodeling with sclerosis, or increased density is evident on the radiographs.
    
  • Gradually, osteophytes (bone spurs) form opposite to the direction of narrowing. This bone forms to stabilize the joints and compensate for the cartilage loss and narrowed joint space.

• Standard Conventional Radiographs
  • The standard x-ray examinations obtained to evaluate the knees in patients with osteoarthritis are an AP (frontal) and lateral view of the knee.

    At Hospital for Special Surgery, the frontal view is usually obtained with the patient weight bearing; a Merchant view of the patellofemoral joints (kneecaps at front of the knees) are also usually obtained.

• Optional Radiographs
  • Optional Radiographs are ordered commonly at Hospital for Special Surgery, in addition to the weight bearing (standing) frontal view of the knee is a weightbearing PA view of the knee, obtained with knee in slight flexion. This position helps evaluate if there is focal cartilage loss in the posterior aspect of the medial or lateral joint compartments. Positioning for these view is very specific.
• Findings of Knee In Osteoarthritis On Radiographs
  • Typically, the cartilage in one of the joint compartments, the medial, lateral, or anterior joint compartment is most severly 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 a cause or as a result of osteoarthritis. The patellofemoral joint (at the front of the knee) can be similarly affected. Lateral subluxation or patellar malalignment is very common.
    
  • As the disease progresses, osteophytes (bone spurs) form along the joint margins and bone cysts and sclerosis are also typically present. When small osteochondral or cartilage fragments are present in the joint they are referred to as loose bodies. Fluid can form in the joint secondary to the arthritis and is referred to as an effusion.