Metabolic Bone Disease 3 - Radiology of Bone Disease
Anil Chopra
1. Explain the descriptive radiographic signs as they relate to metabolic bone
diseases
2. Describe the role and limitations of plain radiographs in osteoporosis
3. Describe the correlation of the fundamental differences between osteomalacia ,
osteoporosis and rickets with their radiographic appearances
4. Explain how to recognize the radiographic appearances of hyperparathyroidism
and correlate it with the basic patho-physiology
5. List and briefly describe the imaging modalities available to image bone in
general
The main radiological changes identified in MBDs are a decrease in bone density
(osteopaenia, which occurs in osteoporosis, osteomalacia, and primary
hyperparathyroidism), an increase in bone density (osteosclerosis, which occurs in
Paget’s disease and secondary and tertiary hyperparathyroidism), and co-existing
osteopaenia and osteosclerosis.
Limitations in Radiography
Osteoporosis is the decreased quantity of bone overall (i.e. bone mass is reduced), but
the microstructure of the bone is normal. In osteoporosis, calcium ion levels,
phosphate levels, vitamin D levels, and PTH levels are all normal so only radiography
can be used to diagnose it.
In diagnosing osteoporosis, plain x-rays films are of limited use as they only really
can be used to view fractures due to osteoporosis. Bone mineral density
measurements are of importance in diagnosing osteoporosis.
Differences between osteomalacia, osteoporosis and rickets.
Osteomalacia and rickets are the same disease but rickets is in children and
osteomalacia in adults. It is caused by a failure to, or insufficient mineralisation of the
osteoid and the growth plate. In x-rays there are clear defective mineralisation,
especially at long bones, with looser zones. These looser zones are regions where too
much osteoid has been laid down by the osteoblasts due to the action of PTH. These
appear as linear areas of low density surrounded by sclerotic borders. They are
translucent. There is also bowing of the long bones of the lower limbs and blurring of
the epiphyseal plate in rickets.
Osteoporosis cannot really be seen on x-rays. Only fractures caused by osteoporosis
can be seen.
Hyperparathyroidism
There are three types of hyperparathyroidism:
1. Primary hyperparathyroidism – this is most commonly caused by a parathyroid
adenoma (normally of a single gland) inducing the excess secretion of PTH from
the pituitary. It is associated with osteopaenia (or increased bone resorption).
In primary hyperparathyroidism, a key feature is bone resorption and this occurs
in many regions:
 Subperiosteal resorption – most noticeable on the radical aspect of the middle and
ring fingers’ phalanges.
 Subchondral resorption – most noticeable in the distal clavicle and the pubis.
 Intracortical resorption – osteoclasts are found around haversian canals and small
lucencies are seen (such as pepper pots in the skull).
2. Secondary hyperparathyroidism – this is normally caused by parathyroid
hyperplasia due to long term or persistent hypocalcaemia. It is linked to being a
causative factor in rickets, osteomalacia, and chronic renal failure.
3. Tertiary hyperparathyroidism – this is where a patient has a chronically low
plasma Ca2+ concentration and so the parathyroid glands become autonomous in
its activity and are unregulated.
The radiological changes in secondary and tertiary hyperparathyroidism are
loosers zones, sclerosis in the axial skeleton and vertebral end plates, arteries and
cartilage show calcification.
Imaging
Radiology – is a primary diagnostic tool and can easily identify most fractures ad
breaks. However, a reduction in bone density will only be seen when around 50% of
the bone mass has already been lost.
QCT (Quantitative CT scan) – is a conventional scanner, measuring the bone
mineral content by looking at the change in the x-rays as they pass through the bone.
It is used to assess high risk patients and their fracture risk, and to monitor the
progress of treatment. It can provide a very good measurement of bone volume. QCT
is confined to done only on the spine, pelvis, and hip and involves a high radiation
dose.
Ultrasound – good in the peripheries e.g. heel. It is a quick test that is cheaper than
DEXA scanning, but is the least accurate of all techniques, as changes in places like
the heel take place slower than in the central areas.
DEXA – involves a complicated x-ray scan and compares the scanned patient’s bone
mineral density (mineral per surface area) with a sex matched young adult. It is used
in the diagnosis and fracture risk assessment. It has a short scanning time and so
relatively small radiation dose. It accuracy is high ad usually offers reproducible
results. It assesses the area of bone and not the volume of bone. It stands for dual
energy x-ray absorptiometry.