RSA Suites

Figure 1 – Typical RSA setup for supine (lying down) position (hip, shoulder)

Figure 2 – Typical RSA setup for standing position (knee)

Figure 3 – Uni-planar calibration cage (usually for hip and shoulder exams)

Figure 4 – A biplanar RSA cage for knee joint replacement analysis

Figure 5 – Pair of RSA Images with analyses.

Radiostereometric Analysis (RSA) was developed by a Swedish researcher, Dr. Goran Selvik, in the mid 70’s as a method for determining an object’s three-dimensional location within a person’s body with extremely high accuracy, up to one tenth of a millimeter.

RSA uses two x-rays which converge on a person’s implant. Much like our vision, we see two individual images from our eyes which our brain combines into one picture, giving us depth perception. RSA is used for studying the migration and wear of many different joint replacements.

During a joint replacement surgery, the surgeon will insert a small number (usually < 10) of tantalum marker beads into the patient’s bone – femur, pelvis, or tibia. Tantalum is a metal that is highly radio-opaque (blocks all x-rays) and therefore appears bright white on an x-ray. These beads are smaller than 1 mm in diameter and are well known to be safe and have no effect on the patients’ implant. These markers are necessary to determine implant-bone motion, also known as loosening.

An RSA examination setup is shown in Figure 1.

The patient is placed above or in front of an RSA calibration cage (Figures 1 & 2). This cage provides the necessary markers to correctly locate the patients’ bone and implant markers in three dimensions. The type of cage depends on the location of the implant.

A uni-planar cage (Figure 3) is mainly used for hip and shoulder examinations but can also be used for knee examinations. A bi-planar cage (Figure 4) is sometimes used for knee examinations.

Two separate images are obtained from an RSA exam (Figure 5). These images are analyzed to determine the relative motion between the beads in the bone and the implant.

RSA is a longitudinal process, meaning that RSA examinations will be performed multiple times for a number of years, often 2 years but up to 10 years. The difference between the initial RSA examination and an examination at 1, 2, or 10 years down the road will determine the distance the implant has travelled into or out of the bone as well as any rotation or tilt of the implant. The amount of motion of the implant is important to be able to predict if the implant may become loose in the future and require a revision surgery.

The predictive ability of RSA is key to many new research studies being undertaken in North America and Europe. Because RSA is so accurate and can predict the outcome of implants (with a degree of certainty), clinical trials of new, untested implants can be performed on a small group of consenting patients with very short follow-up, and still provide the answers that researchers, surgeons, and clinicians need.

The Concordia Joint Replacement Group in partnership with the Orthopaedic Innovation Centre are spearheading the formation of a Canadian RSA Network. This network is made up of 5 Canadian orthopaedic centres with RSA capabilities and was initiated to unite and promote RSA research in Canada for the betterment of patient outcomes and safety in arthroplasty. For additional information, please visit CanadianRSANetwork.com.

There are a variety of non-surgical treatment options that should be considered before proceeding with a joint replacement.

Weight Loss

For both the hip and the knee, the forces acting across the joint are a combination of body weight pressing down on the joint and the muscles pulling up to stabilize the joint. As these values combine, the hip and knee experience 3-4 times the body weight in pressure with each step. Loosing excess weight reduces the pressure on damaged joints and can relieve pain.

Physical Therapy

By stretching, strengthening and re-balancing the muscle- forces across the joint, the movement and control of the joint can be improve. Pain can also be improved with therapy in addition to the mobility of the joint.

Acetaminophen

Acetaminophen (Tylenol) containing products can be very useful analgesics in arthritis. Given its low cost and good side effect profile, it is a good first-line drug for treating arthritis. It should be avoided in some patients with a history of liver disease and care should be taken not to exceed the total daily dose of 4gm per day. This is especially true when a patient takes multiple different medications that contain acetaminophen.

NSAIDs

Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) are medications that block the COX receptors on cells and reduce inflammation which can play a significant role in both osteoarthritis as well as other inflammatory arthridities such and rheumatoid arthritis and lupus. Different versions of this type of drug have different side-effect profiles, but, in general, NSAIDS, when taken for extended periods, can play a role in stomach irritation, ulcers, and bleeding and kidney problems with elevated blood pressure. While these can be very helpful medications, their prolonged use should be done under the guidance of a physician.

Steroid Injections

Steroid injection (often referred to as a “cortisone shot”) is generally performed with a depot version of a corticosteroid that remains within the joint. Once in the joint, the steroid blunts the inflammation within the joint and can reduce the pain of the arthritis. This effect can last from a few days to 6 months. There is a small risk of infection with an injection which can be very debilitating and destructive if it were to happen. The risk of infection is less than 1%. There is no agreed upon number as to how many times an injection can be repeated if the most recent injection had benefit for multiple months. Most agree that multiple injections can be offered, the whether a limit should exist or how high the limit may be is unknown.

Unloader Bracing

As arthritis progresses in the knee and joint space is lost, the leg becomes more bow-legged or knock-kneed. As this collapse occurs, increased load is applied to the already diseased and damaged section of the joint. By applying and unloader brace, the leg can be straightened and the load shifted back onto the more healthy area of cartilage remaining. This can reduce pain and suffering during activities such as walking, shopping and yard-work.

Viscosupplement Injection

Viscosupplement injections inject a purified, viscous fluid into the joint. The injection frequently includes components of normal healthy joint fluid known to be reduced in arthritis. While the exact mechanism of benefit is not known, many patients, especially with early arthritis, can benefit from these injections for a variable period of time.

Walking Aid

Many patients find the use of a cane, walking stick or walker to reduce their pain. By transferring weight to the walking aid, the effected joint can be off-loaded reducing the pain experienced and improving the distance that a patient can walk.

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