Pelvis and Hip X-rays




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Although we tend to talk of thepelvis.JPG (10065 bytes) pelvis as if it was one solid bone, in fact the pelvis, or pelvic girdle, is actually made up of four bones in the average adult.  These are: two hip bones (technically the Os coxae), the sacrum, and the coccyx (pronounced cocksicks which is more commonly called the tail bone).  It should be noted that the hip bone actually starts out as three separate bones separated by cartilage, but normally they have fused together to form one single bone by the time adulthood is reached.  You may also be interested to know that there is a difference between the pelvis of the average female and that of the average male.  A woman's pelvis tends to be lighter, broader, and have a larger hole, or inlet, in the center, thus making child birth easier.  This is one way that scientist and medical examiners can tell whether a skeleton came from a man or a woman.

The pelvis is different from just about any other part of the body in that when a plain pelvis x-ray is ordered, only a front view is obtained.   True, there is a side view that can be done, but except in certain unusual instances, it really does not give any additional information about the pelvic girdle in general.  It must be noted however that this does not hold true for any of the other x-rays series in which a certain part of the pelvis is being studied.  The one thing that is a little odd about x-rays of the pelvis is that the patient's legs must be rotated in towards each other so that the patients toes touch, almost as if the patient was pigeon toed.  The reason for this is that, more often than not, hip and pelvis problems are actually located in the section of the femur that connects to the hip, called the femoral neck.  Since this section of the femur is normally coming into the hips at an angle, the legs must be rolled if possible to place the femoral necks parallel to the film.  Otherwise some problems or defects may not be visible.

hipap.JPG (6496 bytes)With hip x-rays, we once again start taking a minimum of two films, a front or AP (short for Anterioposterior) view, and a side or Lateral view.   Technically, when doing a hip series, we are only interested in the affected, or hurt side, but if this is your first hip series within a reasonable period of time, we will most likely take a full pelvis shot for the front view, thus giving your doctor and the radiologist a way to compare the two hips.  If not, then the technologist will probably only do a front view of the side with the problem.  Occasionally, if for instance you've had a hip replacement or pining at some time in the past, then two front views will be done to give the comparison of the two hips and to make sure that the entire implanted piece is shown.  Still, these shots are fairly straight forward and simple.   It is when we get to the side views that things get a little strange.  Since you have two hips that lie within the same "plane", just rolling the patient up on his or her side will not give us the information we need about the hip that hurts as this would result in the uninjured hip being superimposed over the bad hip which would effectively hide any injury.  Instead the technologist will use one of two methods, a "frogleg" or a "crosstable".

The frogleg lateral, more properly name the Modified Cleaves Method, involves bending the patient's knee on the side of interest up until the patient's foot is even with his or her other knee, then letting the leg fall out to the side as far as the patient can.  While this x-ray will not show a true side view of the hip itself, it will show an excellent side view of the femoral neck, which is where most hip injuries occur anyway.  Plus, if the hip joint is displaced (moved out of position) towards either the front or back, it is extremely unlikely that the patient would be able to move his or her leg enough to do this particular picture anyway.

When a patient is unable to move his or her leg enough to do a cleaves x-ray, or the doctor needs to check for the alignment of the hip from front to back (such as after hip surgery), a crosstable lateral known as a Danelius-Miller View will be used.  For this x-ray, the technologist will place the film with a special filter called a grid attached to it beside the patient's hurt hip angling out from the patient at about the same angle as the angle of the femoral neck (that part of the femur that angles in from the main shaft to join with the pelvis to form the hip joint).  The x-ray tube is then turned so that it will shot across the table (thus giving us the name crosstable lateral) and angled so that the x-rays it produces will be perpendicular to the x-ray film.  The patient is then helped to raise the uninjured leg as high up in the air as they can and then the x-ray is quickly taken before the patient is forced to lower his or her leg.  Sometimes it is necessary to either provide the patient with something they can rest their foot on, or a helper will need to hold the patient's leg up.   You see, if the leg being held up in the air starts to tremble for any reason, this motion will be passed on to the hip we are trying to x-ray, resulting in a blurry film that is very hard to read.

Sometimes, though not often, a fracture of the hip will be in the hip socket, called the Acetabulum, instead of in the femoral neck.  When these fractures are suspected, a cat scan of the pelvis is the normal procedure in today's world to diagnose the problem.  However, while C.T. (the more correct name for cat scan) will show up these fractures with little trouble, it doesn't always show the orthopedist everything he or she needs to know.  Thus the technologist will normally be forced to use a set of angled shots, called obliques in order to give the doctor a better picture of just what he or she is dealing with.  Probably the most commonly used of these oblique x-rays developed for the hip are Judet Views.    In doing these x-rays, the patient is rolled up to a 45 degree angle one way, then the other, and x-rays are taken with the x-ray beam going straight down.  This, when done in conjunction with a regular pelvis x-ray, will demonstrate the entire socket or cup in the pelvis that the head of the femur fits into.

Another unusual but not that uncommon a problem that you may get x-rayed for is a separation of the Sacroiliac Joints, which are the joints between the hip bones themselves and the sacrum at the base of the spine.  These joints are fused together just like most of the joints between the twenty two bones that make up the skull, but if the right type of trauma occurs, such as certain car accidents, these joints can break partially or even completely free.  However, since these joints do not run straight back but rather at an angle, to adequately show them on an x-ray requires rolling the patient first to one side and then the other to an angle of about 20 to 30 degrees.   This will allow us a clear view straight down the joint, thus allowing the doctor and radiologist to see if the joint space is still closed as it should be, or opened up because of a fracture.

The final set of pelvic/hip x-rays commonly used are called Inlet-Outlet Views.  These x-rays were originally developed to help ob/gyn doctors to see if a woman's baby would fit through the pelvic opening during birth.  Now a days very view doctors would even consider ordering such x-rays during pregnancy due to the risk to the unborn child, but these views are still in use since they are invaluable in demonstrating various fractures of the pubis.  The pubis is a pair of relatively thin circles of bone at the front and bottom of the pelvis, and help form a fair amount of the support necessary to keep the pelvic "wings" in place.  In doing these x-rays, the technologist will have you lie on your back on the x-ray table just as if he or she was going to do a regular pelvis film, but the technologist will then do two shots, one with the tube angled up towards your head and the other with the tube angled down towards your feet.  The idea is to get one picture with the pubis parallel with the x-ray beam and another with the pubis perpendicular to the beam.  This allows the doctor to see just how badly displaced any fragments are, which in turn tells him whether he or she can safely allow the fracture to heal on it's on by way of a lengthy period of bed rest if that is the doctor's inclination, or whether surgery is an absolute must to repair the damage.

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