| CONTENTS
X-ray picture
of a normal hip joint
X ray picture of an
arthritic hip
X ray picture of a
total hip prosthesis
Metal-backed cups -
hidden osteolysis
Computer tomography
- CT
helical CT for
detection of osteolysis
Magnetic resonance
imaging - MRI
Radioisotope imaging /
Bone scans
Ultrasound imaging
Laboratory tests
There are many diseases and accidents that may affect your
hip joint
To arrive at the right diagnosis of the hip joint disease
may be easy in some cases and it may involve several diagnostic procedures in other cases.
In a patient with idiopathic osteoarthritis of the hip
joint, for example, the plain X-ray picture, together with the physical examination
of the hip joint and the history may be all information needed to choose the appropriate
treatment.
In cases of secondary osteoarthritis after congenital hip
dislocation, on the other hand, the plain two-dimensional X-ray picture does
not inform the surgeon about the widespread changes in the skeleton of a
congenitally dislocated hip.
If the surgeon contemplates operative treatment of such
patient, he must order special X-ray examination to reveal the extent of the
anatomic changes. The knowledge of these changes then determines the choice of
treatment.
1
X-ray picture of the hip
joint
X-ray (roentgen)
picture corresponds to a negative photographic picture. The tissues with
much calcium, such as bone, are opaque for X-rays and appear as white on a X-ray picture.
Tissues with much water, as joint cartilage, are pervious for X-rays, and appear as black
on X-ray picture.
The X-ray picture of a healthy joint show the healthy joint
cartilage that separates the two bones, as a dark line in the middle of the joint - the
joint line.
X-ray picture of a normal hip joint.
Click on the icon for a full size picture.
The cushion of joint cartilage's on the surfaces of the hip
socket and femoral head is pervious for X-rays and reproduces as a dark band some 4 -5 mm
thick, called "joint line". This joint line, clearly visible, divides the
white "shadow" of the pelvic bone from the "shadow" of the femoral
head.
2
Arthritic hip joint
In many hip joint diseases, such as arthritis and
osteoarthritis, the joint cartilage is damaged, the thickness of the cartilage cushion
successively diminishes, and the cartilage may disappear altogether.
On a X-ray picture, the disappearance of joint cartilage is
represented by disappearance of the "joint line". The disappearance of
"joint line" is thus a diagnostic sign of arthritis or osteoarthritis of the hip
joint.
X-ray picture of an arthritic hip.
Click on the icon for a full size picture.
Note that in an arthritic hip joint the
femoral head and hip socket are in close contact (upper picture), because there is no
cartilage cushion between them.
On X-rays the disappearance of the joint
cartilage is represented by disappearance of the "joint line" (lower
picture); the shadows of the femoral head and the hip socket are also in close
contact, the joint line is lost.
This sign, however, is not absolute. Some patients with
idiopathic osteoarthritis of the hip have severe pain although their plain X-ray pictures
are almost normal. At the operation the surgeon is then surprised by the extent of the
osteoarthritic changes in the hip joint.
In these hips, the joint cartilage disappeared only
from a part of the joint surface, whereas it was retained on other parts of the joint
surface. The partial disappearance of joint cartilage caused severe pain and
stiffens, yet this localized area (focus) of destructed cartilage was not apparent on
ordinary plain X-ray picture.
3
X-ray pictures (Radiographs) of
total hip prostheses
Your surgeon usually orders a plain radiograph
of your total hip to assess the position of the total hip prosthesis and its anchor in the
skeleton. For this purpose plain radiographs are enough.
Picture: Conventional cemented total hip prosthesis
and its x-ray
(Click on the icon for full-size picture)
In patients with conventional total hip prostheses,
the X-ray picture demonstrates the white shadows of the metallic parts
of the prosthesis (shaft and ball components) in the thigh bone, these components are
surrounded by less white envelope, which represents the bone cement with added contrast
material (Barium salts).
The cup component made of plastic is less white, its shadow
is represents the bone cement envelope with added contrast material.
4 Hidden osteolysis behind metal backed cups
In patients with cementless cups, the cup has a
metallic backing, which casts a white shadow. At the same time the metallic shadow
completely may hide changes in the skeleton "behind the metallic cup". Changes
in femur are usually not so completely hidden.
It is important to know this fact. Patients with pain
symptoms may have apparently "normal" plain X-ray pictures. Yet they may
have more or less developed osteolysis (bone dissolving disease) "hidden" behind
the shadow of metallic components.
Picture: Osteolysis hidden behind the
metal backed cup
Click on the icon for a full size picture
Upper picture: Frontal view of metal backed cup. The
metallic cover of the cup may hide hide the osteolytic lesion that developed behind it.
Lower picture: Profile view of the same hip. In this view
the shadow was "projected away", and the osteolytic lesion is now visible on the
X-ray picture.
In these cases, the surgeon usually orders X-ray
pictures taken with different projections. You will be asked to turn your body (especially
pelvis) on the X-ray examination table, move your leg,etc, while the radiologist will take
the pictures. On "oblique" projections , the metallic shadow will be
projected "away" and the osteolytic lesion will appear on the
"oblique" X-ray picture.
5
CAT
CAT - computer assisted (
axial) tomography. (Also CT).
A special X-ray technique that investigates the organ with
many very thin "sprays" of X-rays. A computer then composes the definitive
picture from these small "spot" pictures. The examined organ appears as composed
of many thin slices. The surgeon can, for example, see a three-dimensional picture of the
hip joint with many details not seen on conventional X-ray pictures. The radiologist can
even "take out" the femoral head from the picture, so that the surgeon will see
the bottom of the hip cup (acetabulum).
For example in patients with secondary osteoarthritis after
congenital hip dysplasia, the skeleton is usually deformed and the dimensions are
distorted. The CAT shows for the surgeon a really three-dimensional picture
of the distorted anatomy of the hip joint, how much skeleton of the socket is still
preserved, how large is the marrow cavity, etc. Also for manufacturing of custom made
total hip prostheses, the manufacturer needs CAT pictures of the hip joint and thigh bone.
From these pictures the manufacturer gauges the dimensions of the custom made prosthesis.
6
CT scan and total
hip prosthesis /
helical CT
In the past, it has been impossible to use CT for
examination of patients with total hip prostheses. The metal in the prosthesis
caused so called scattering of X-rays, the image of the metal on the X-ray picture was
surrounded by small lightning-like spikes that concealed the changes in the skeleton
around the prosthesis.
Development in the computer software now allows successful
imaging of total the total joint prostheses and the soft tissues around them with CT
(Eustace 1998 ).
So called "helical computed tomography" (Puri
2002) makes it now possible to detect areas of "silent" osteolysis, hidden
behind the metal backed cup component of the total hip. Plain radiograms are not able to
detect this form of osteolysis, which is frequent in young patients operated on with
cementless acetabular cups.
Statistics demonstrated that 88% of all patients who had
silent osteolysis of total hips discovered by helical CT scans had
inaccurate plain radiograps. The plain radiographs either showed no osteolysis at all
(38%) or showed much smaller area of osteolysis than CT (50%).
The conventional X-ray pictures would
not only miss 20 % of all cases of osteolysis, the conventional radiographs
underestimated also the extent of the bone destruction.
The mean largest diameter of the bone destruction
discovered on plain X-rays measured 17 mm , whereas the helical CT scan revealed that the
diameter was 10 mm larger.
7
MRI
MRI- Magnetic Resonance
Imaging. It is a special technique that measures the amount of water
(hydrogen) atoms in the tissues. No X-rays are used, only very strong magnets. This
technique shows a very detailed picture of changes in the soft tissues, or areas in bone
with changes of water content. (Avascular necrosis, e.g.).
The whole body MRI camera is a large machine and the
patient is placed inside it for 10 -15 minutes inside it. Claustrophobic patients may
become anxious once in the small tunnel. The machine is also noisy, not because it will
break in pieces, but because the changing magnetic fields are noisy.
The technique must not be used in patients with pacemakers.
Also patients with other objects inside body, which are manufactured from magnetic (
ferromagnetic) metallic alloys, cannot have MRI examination.
All artificial joints are made from
non-magnetic metal alloys, and thus the MRI examination may be done in
patients with artificial joints.
It is very important that before any MRI examination you
tell to the radiologist about all your previous operation, especially operations that
might implant foreign objects in your body. Most radiologic Departments have a special
routine for asking the patients
In the past, it was difficult to provide MRI image of total
hips. A new computer technique called MARS (Metal Artifact Reduction Sequence) now
provides MRI images of total hips of "diagnostic quality". Still, the MRI of the
acetabular component and the skeleton around it is of diagnostic quality in only about 40%
of all cases, whereas the MRI of the femoral component is of diagnostic quality in 100% of
all cases (White 2000).
The precision of the MRI may be increased when one injects
the rare metal Gadolinium together with MRI. Gadolinium concentrates in areas of scar
tissues that may be distinguished by this technique, for example scars after surgery
around the total hip.
This technique has been used for detecting changes in the
soft tissues around the total hip prosthesis, but also to detect the blood clots in large
veins.
There are situations, when patients with artificial joints
need MRI of other body organs (abdominal or chest cavity or extremities).
These patients may be anxious that their total joints may
be damaged by the MRI examination.
They can be not. Here are the reasons:
Basically, MRI or rather its strong magnetic field produces
three effects on the metallic implants / total joints in the body.
1) If the implant is fabricated from ferromagnetic
material, the MRI apparatus attracts or deflects the object. Such patients must not be
examined with MRI.
Modern orthopedic devices are fabricated of NON
FERROMAGNETIC IMPLANTS and experiments demonstrated that their position is not influenced
by the electromagnetic field produced by the MRI apparatus. (Clerc 1997). Even the one
contemporary total hip model which is manufactured from stainless steel (Furlong'
total hip) dos not contain ferromagnetic material and according to the manufacturer there
are no objections to MRI examination of the patients with these prostheses.
2) The strong magnetic field might produce electric (eddy)
currents in the metallic implant. These currents might heat up the material. Experiments
showed that heating of the metallic implants ranged from 0 to 0,5 degrees Celsius,
depending on the form and the implant material, and on the length of the examination. Thus
the heat effect is negligible. (Buchli 1988, Ho 2001).
3) The implants produce a "shadow area" around
the pictures of themselves. The size of this area depends on the character of the
material, the largest shadow is produced by stainless steel, titanium produces the
smallest shadow. Modern techniques can reduce this shadow area if the implant is oblong
(femoral shaft) and parallel with the magnetic field (femoral shaft again).
8
Radioisotope Bone scan
Bone scan.
Some metals when injected into circulation will concentrate in areas with high turnover of
newly formed bone tissue, such as in areas of bone fracture or bone infection. The
isotopes of these metals emit a radiation and when taken up in the tissues, the radiation
may be detected with special scanning techniques. Such metals are Technetium,
Gallium, Indium. The Technetium bone scan can reveal hair-line bone fractures,
which do not show on conventional X-rays, can detect activity in early stages of
osteoarthritis, not apparent on conventional X-ray pictures, or it can detect bone tumors.
It is still not sure how accurate is this technique to detect early stages of total hip
loosening.
The Indium scan is used to
identify the areas of infection, for example the "indolent" infections of total
hips. This test is conducted in two steps. In the first step, the laboratory removes a
sample of your blood, isolates your white blood cells and labels them with Indium-isotope.
This will take some time. You will return some days later, and the labeled white
cells will be injected back into your blood circulation. These labeled white cells
will travel in the circulation, seek the spots in the body where infection is ongoing and
be taken up there in increasing amounts. The white cells labeled with Indium will thus
label the infection spot.
The radiation from the isotopic agents is weak, the amount
of radiation is generally not much more than the radiation from a single X-ray picture.
Computerized bone scanning shows a three-dimensional
picture of the places with high uptake of isotopes.
Doctors often use bone scan in patients with pain in the
total hip. Studies demonstrated that (Technetium) bone scan is not reliable during the
first year after the total hip surgery. Later on, a patient with a negative bone scan is
unlikely to have loosening of the total hip, although about 5% of patients with loose
total hips have negative bone scans. This (Technetium) bone scan cannot distinguish
between loosening caused by bacterial infection and other forms of loosening.
PET - Positrone Emission Tomography, is now experimentally used to
detect the inflammation and infection around the total joints. The compound injected is a
labeled glucose - blood sugar derivate. This compound concentrates in areas of great
cellular activity. Inflammatory cells around infected total joints need much glucose to
keep going. The labeled compound thus concentrates in these cells an emits positrons which
are detected and imagined with special cameras.
8A
ULTRASOUND
is a technique used to
detect changes in the soft tissues around the total hip such as
haematomas (collections of
blood)
ossifications in the muscles
(forming of the bone tissue)
ruptures of the tendons (such
as in the gluteus medius muscle).
The technique is also used to
detect
blood clots (deep vein
thrombosis),
pieces of bone marrow
wandering in the veins during the operation
9
Laboratory tests (some of
them)
Erythrocyte sedimentation
rate (ESR), more familiarly "sed", measures the speed at which
clumps of red blood cells falls through blood serum to the bottom of a long thin tube. If
the cells fall faster than normal (usually the normal speed limit is up to 20 mm for men
to 28 mm/hour for women), then the test is interpreted as a sign of active
inflammation. This test is non specific, the "sed" may be higher both in
an innocent flu and in a widespread cancer tumor. Very high "sed" usually
is found in severe infections and in some blood tumors.
It is important to know that in about 5 % of
all total hip infections the patients may still have normal / borderline values of ESR.
These patients have usually been on long, intensive treatment with antibiotics
(suppressive treatment).
CRP - C reactive protein.
This test measures the concentration of a substance called C reactive protein in
blood. With high concentrations the test is considered positive. The test is positive in
infections, also in patients treated with antibiotics. It follows the intensity of
infection more quickly than "sed".
White blood cells.
The concentration of white blood cells in the blood is increased in infections. The upper
limit for normalcy varies in different laboratories. It is, however, known that the late,
slowly developing infections of the total hip prosthesis seldom have high counts of white
blood cells.
Rheumatoid Factor (RF)
is a compound (antibody) secreted by certain tissue cells (B cells). It is found in the
blood of up to 85 % people with R.A. (Rheumatoid Arthritis). Its occurrence is associated
with the more progressive and aggressive form of R.A. The diagnostic value of this test
is, however, diminished by the fact that about 7% of people aged 70+ also bear this factor
although they have no signs of R.A.
Genetic markers typing.
This is as yet not a standard procedure. Researchers have been able to correlate fairly
accurately the different types of R.A. with variable sub-types of genetic markers, such as
HLA-DR1. Such genetic information allows the rheumatologist to gauge the severity of the
inflammation and fine-tune the treatment.
See also (www.arthritis.ca/can)
References:
Buchli R et al Magn Res Med 1988, 7:255 -61
Clerc CO et al. J Biomed Mater Res
1997; 38: 229-34
Eustace S et al. Orthop Clin North Am 1998; 29: 67-84
Ho WS J Magn Reson Imaging 2001; 14:
472-7
Puri L et al. J Bone Joint Surg-Am,
2002;84-A: 609 -14
White L et al Radiology 2000; 215: 254 -62
Before you take any decision, please read carefully
the Disclaimer
BACK to
Total hip Index
NEXT to Are
you a candidate?
|