Advanced Imaging: MRI

Prior to now, we have discussed ways a doctor can get an image of your foot in the office.  However, as we discussed, there are times when a more advanced and detailed image is needed.  Magnetic Resonance Imaging (MRI) is a great tool to use in these situations.

In order to obtain an MRI, a patient is placed in a room with machine containing a giant magnet.  This magnet causes the hydrogen ions in your bones, muscle, and other soft tissue to give off a signal that can be detected by a computer.  Depending on the tissue, different signals will be given off.  The computer analyzes the signals and develops a picture.  Once the 1^st picture is taken, the machine moves a couple millimeters and takes the next picture. If you can imagine slicing up a tomato or onion, an MRI is like slicing the foot into many individual sections.  These individual slices are then grouped together so the doctor can get a good picture of the inside of the foot.

The major benefit to an MRI is that it can show bone, tendon, and cartilage in a very detailed image.  This can be used by the doctor as a surgical planning tool before he takes a patient to the operating room.  MRI can be helpful to diagnose a condition, but most problems can be diagnosed during a routine office visit without the help of an MRI.  Although there are exceptions to that rule, an MRI is not usually ordered until the doctor and patient have agreed that surgical treatment is needed.

Another benefit to MRI is that no radiation is received by the patient, and it does not require a dye or contrast to be injected into the patient.  MRI is a completely noninvasive imaging technique.  For these reasons, MRIs are very safe for the patient.

On the other hand, an MRI requires you to lie motionless for an extended period of time.  If you are moving when the slices are being taken, the image becomes distorted and impossible to interpret.  This can be somewhat uncomfortable.  In addition, if you have metal plates or screws in your body from previous surgery, the metal will distort the image, making it hard to see anything.  For that reason, some patients may not be able to get a useful MRI.  Lastly, MRIs are very expensive.  Most insurance providers will not pay for an MRI until multiple conservative measures have been exhausted with no improvement in treating the patient.

MRI is a valuable tool that has helped doctors see subtle problems that x-ray and ultrasound miss.  It is primarily a surgical planning tool to help surgeons be more prepared before surgery.  However, it must be used appropriately so not as to waste resources.

Podiatric Ultrasound

I’m sure many of you hear the word “ultrasound” and correlate it with pregnancy and gynecology, but ultrasound is a very safe and useful tool podiatrists have to visualize and diagnose the source of a patient’s pain.  Let’s discuss some of the pros and cons of ultrasound.

First and foremost, ultrasound is very safe to the patient.  Ultrasound is simply a machine that sends out sound waves at a certain frequency, which then forms an image from how the waves bounce back.  Most importantly, no radiation or tissue damage occurs from these sound waves.  This is supported by multiple studies and its long and continued use in visualizing babies in utero.  This long history of safety has led to the development of ultrasound machines specifically made to see bone, tendon, and ligament.

Secondly, ultrasound gives a real-time image.  X-rays, MRI, and CT scans are frozen images.  Ultrasound gives a “living image” so that as the patient moves the foot, the image reflects that movement.  This gives the doctor more information on how the foot is functioning as it moves.  Without this insight, the doctor might miss the true source of the pain.  Ultrasound can be used to visualize bone as well as soft tissue.  In addition, when giving an injection, the doctor can give it under the guidance of ultrasound.  This can help the doctor insure that the medicine is being placed in the area of inflammation.

Lastly, ultrasound is inexpensive and convenient.  Ultrasound machines for foot and ankle imaging are very small and can be moved from exam room to exam room very easily.  When compared to CT scans and MRI, ultrasound is much cheaper and therefore, insurances are more likely to cover the cost.  Ultrasound does not require a dye to be injected into your veins (often needed for CT scans), neither does it require you to lie motionless (as is needed with MRI).  All in all, is a very cost effective way to diagnose foot and ankle conditions.

The main disadvantage to ultrasound is that it requires a trained eye to both know the mechanics of the machine and to read the ultrasound image.  Only after much experience can a technician consistently read an ultrasound accurately.  Your podiatrist will be able to correctly interpret your ultrasound.

Now that we have covered the ways to image the foot and ankle in the office, we will discuss the more advanced imaging techniques of CT scans and MRIs in our next posts.

Podiatric Imaging - X-rays

With the exception of dermatology, most doctors are treating conditions that they cannot see with the naked eye.  In order to overcome this hurdle, many different types of imaging techniques and instruments have been developed in order to allow the doctor direct visualization of the problem area.  Let’s discuss the imaging most often used in podiatry.

The most commonly used imaging technique in podiatry is radiographs, or x-rays.  Although there are many exceptions to this rule, most people who walk into a podiatrist’s office will get x-rays.  X-rays are the best to order when a patient’s main complaint could potentially involve the bones or joints.  X-rays give only two dimensional images, so it is necessary to take x-rays from multiple angles so that the doctor can mentally put the images together to form a three dimensional picture.  X-rays give the doctor important clues in figuring out the pain a person is experiencing.  Fractures, foot mal-alignment, and arthritis can be diagnosed with simple x-rays.  If a person has stepped on a foreign object, x-rays can help to locate the position of it.  X-rays also can help to push the doctor to order additional tests or refer out to a different specialist if certain signs are present suggesting disease like rheumatoid arthritis, peripheral arterial disease, or other systemic disease.  It may even be necessary to get an x-ray with a severely infected ingrown toenail to see if the infection has gotten into the bone.

 

A concern that some patients have is the radiation associated with x-rays.  This was a problem in past decades with more primitive x-ray machines.  However, modern x-ray machines minimize the scatter of x-rays by directing the beams directly at the target object and having a very short exposure time.  Lead is worn to protect against the small amount of scatter.  X-rays are avoided if the patient is currently pregnant.  You can be assured the amount of radiation received by the foot is very small.  In fact, an x-ray exposes you to the same amount of radiation you would receive by spending about 5 minutes in the sun.  When compared to tanning, sun-bathing, or going without sunscreen in the sun, the radiation of an x-ray is insignificant.

Even though x-rays show bones and joints very nicely, they do not show much in terms of muscles, tendons, ligaments, or blood flow.  In some complicated fractures, it may be hard to determine the extent of the fracture with only an x-ray.  In these cases, ultrasound, Magnetic Resonance Imaging (MRI), computed tomography (CT or CAT Scan), or bone scans may be used.  We will discuss each of these imaging techniques in the upcoming weeks.

Wound Debridement Continued

Let’s finish our discussion on the different types of debridement.

Mechanical debridement is another method to remove non-viable tissue. This is accomplished by applying wet to dry dressings. Normal gauze is soaked in some type of antibacterial solution and packed into the wound. Solutions may be simple saline, Dakin’s (a diluted version of bleach), or other antibacterial solutions. This wet gauze once packed into the wound is covered by dry gauze then wrapped. This dressing is changed every day. As the packed gauze is removed, dead tissue is removed with it. This is a very inexpensive way to keep a wound clean, ward off infection and allows for evaluation every day during dressing change. This dressing may be used prior to application of a Negative Pressure Wound VAC. However, dressing changes may be a very painful as they rip superficial tissue off.

Autolysis is another option for debridement. Autolysis means to let the body digest or get rid of bad tissue by its own means. The body produces digestive enzymes called MMP’s. MMP’s at the wound’s surface liquefy the dead tissue. In order to allow the MMP’s to work, an occlusive dressing is placed over the wound. Occlusive dressings are not permeable to air and they keep the wound isolated from the outside environment. Occlusive dressings are relatively controversial. Some feel that occluding a wound keeps fluid and possibly unknown pus in a wound. However, studies show occluding a wound keeps its pH low, which inhibits bacterial growth and promotes oxygen unloading from red blood cells. Autolytic debridement is a more advanced way to debride a wound and requires frequent evaluation and inspection.

All in all, each method of debridement has its place in wound therapy. Different physicians prefer different dressings depending on their experience and training. If you are currently working to heal a wound, work with your doctor to know which type of debridement is best for your situation.

Debridement of Diabetic Wounds

In light of our recent discussions on maggot therapy, I thought it would be wise to discuss different ways to debride diabetic wounds and their associated pros and cons. Wound care is continually being assessed for effectiveness and continues to evolve. This is a short review of some of the many options available.

The most obvious way to debride a wound is manually with a curette or scalpel blade. This is the mainstay of wound debridement due to its practicality and ease. This type of debridement can be done quickly in an office visit or bedside without any major equipment. It is cheap and fast and allows for evaluation immediately after. In more recent times, debridement using a machine producing sound waves has been used bedside to remove dead tissue. However, there is no evidence showing that it is more effective than a scalpel blade.

Surgical methods are another way to debride wounds. This is usually reserved for unusually large or chronic wounds that need deeper or more radical debridement. Instruments like the VersaJet combine manual debridement with highly pressurized water to remove non-viable tissue. The benefit of surgical debridement is that the patient is sedated so the doctor can be more aggressive and insure all dead is tissue removed. However, taking the patient to the operating room, needing medical clearance and the assistance of an anesthesiologist makes surgical debridement less practical and is only used if medically necessary.

Another type of debridement is use of ointments that contain enzymes that breakdown dead tissue. This is especially useful in situations where a patient has full sensation to the wound. Manual debridement may prove to be too painful for the patient to go through. In contrast, enzymatic ointments slowly dissolve making it painless for the patient. The downside of enzyme ointments is that they take longer to work. In addition, enzymes are very sensitive to small changes in pH, making it possible for them to be inactivated if the wound is too acidic or basic.

We’ll discuss mechanical debridement, autolytic debridement, as well as how wound care dressings can effect debridement in our next post.

Medical Maggots continued

As more and more patients have difficult wounds to heal, we have looked to the past and brought back more primitive yet effective ways to clean and close wounds. One of these techniques is putting maggots into wounds.

Maggots are simply baby or immature flies. There are many species of flies, some of which are not beneficial for wounds. So it is not a good idea to go diving into dumpsters trying to find a nice batch of them. Special pharmacies have them available for wound care clinics and hospitals. Once ordered, they can be shipped overnight and ready the next day for application.

Once the maggots are placed in a wound, precautions need to be taken so that they do not escape. A mesh net is put over the wound, and the wound is surrounded by a very adherent material. This keeps them in the wound so that they can deliver maximum benefit. The maggots will then secrete enzymes that dissolve the dead and non-viable tissue at the wound’s surface over a couple days’ time. Once dissolved, the maggots consume the components of the dissolved material. After a couple days in the wound, the maggots can become much larger then when they were put in. They are removed from the wound to assess if they did their job well. It may take a couple of treatments of maggot therapy to remove all the dead tissue.

Another great benefit of maggot therapy is that it can be combined with other wound treatments without caution. Antibiotics, hyperbaric oxygen, and even wound VACs (vacuum assisted closure) can be used after maggots to increase the chance of healing.

Although putting eventual flies into a wound may not seem very cutting edge or fancy, some treatments stand the test of time. Maggot therapy can help wounds to heal and prevent amputations of the foot and leg. Ask your podiatrist if he feels that maggot therapy may be beneficial for the healing of your wound.

Medical Maggots

We have discussed extensively on this blog the devastating effects of diabetes on wound healing.  It can make sores that normally heal in days take months to heal.  The longer a wound stays unhealed and open, the greater chance of it getting infected and needing IV antibiotics at the hospital. 

Although the majority of wounds seen today are results of diseases like diabetes or venous insufficiency, that has not always been the case.  In past decades, the majority of wounds were related to war injuries.  In times of war, wounds were primarily results of bullets, explosions and shrapnel.  Back then, antibiotics has not been discovered and doctors were limited on how to clean wounds to prevent infection.  Most available treatments were harmful to both dead tissue and good tissue.  Many people lost limbs or even their lives from what would be considered today as minor wounds. 

Although there is documentation of maggots being used throughout history to help heal wounds, the first modern day use of them came during the American Civil War in the 1860s.  Doctors noticed that fly larvae seemed to leave good tissue alone and clean out only the bad.  Wounds treated with maggots seemed to heal faster and allow soldiers to keep their injured limbs.  Once antibiotics were discovered around the time of World War II, the combination of these two therapies proved to be a huge advancement in wound care.

In recent decades, maggot therapy has been used less and less as it seemed to be a very primitive form of treatment.  Obviously, the suggestion of using maggots to heal a wound has not been openly accepted by patients.   But when we remember that a diabetic’s immune system isn’t functioning properly, something has to be done to heal their wounds.  Maggots are now being used more and more to heal chronic wounds.  We’ll discuss how exactly maggots clean wounds in the next post.