Page 358 - Medicine and Surgery

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354 Chapter 8: Musculoskeletal system

Crystal arthropathies such as gout and pseudogout Aetiology
can be differentiated on examination of the crystals with Most infections result from haematogenous spread of
polarised light microscopy. The crystals of gout are neg- organisms. Local spread from a soft tissue infection
atively birefringent, whereas the crystals of pseudogout may also occur. Acute osteomyelitis is normally seen
are positively birefringent. in children but may also occur in malnourished or im-
munocompromised adults.
Haematogenous spread: Staphylococcus aureus and

Diagnostic imaging Streptococci are the common organisms. Previously
Haemophilus influenzae was seen in young children,
Many modalities of joint imaging and direct visualisa-
but it is now rare due to vaccination. Patients with
tion are used to diagnose and follow the course of mus-
sickle cell anaemia are prone to osteomyelitis due to
culoskeletaldisordersandareoftenusedincombination.
Salmonella.
The findings in individual conditions will be described Direct spread from local infection may occur with
later.
Streptococcus, Staphylococcus, anaerobes and gram-
X-ray: Many musculoskeletal disorders have charac-

negative organisms.
teristic X-ray findings. In acute inflammatory and
infectious disorders X-ray changes may be delayed.
Pathophysiology
Comparison of X-ray changes over time is especially
In children the long bones are most often involved; in
useful in monitoring disorders that have a degenera-
adults, vertebral, sternoclavicular and sacroiliac bones
tive course.
are more commonly involved than are long bones. In-
Ulrasound is of value in examining the joint and sur-

fections from a distant focus spread via the blood stream
rounding soft tissue. For example it may be useful in
and settle in the bone. In children the organisms usually
diagnosing the cause of a painful hip not amenable to
settle in the metaphysis because the growth disc (physis)
palpation. It may be coupled with diagnostic aspira-
acts as a barrier to further spread. In infants the infec-
tion or therapeutic joint injections.
tion tends to spread to the epiphysis and in adults the
Magnetic resonance imaging (MRI) is of increasing

infection may occur anywhere in the bone.
value in the diagnosis of musculoskeletal disorders.
Acute inflammation occurs accompanied by a rise in
It can demonstrate both bone and soft tissue disor-
pressure leading to pain and disruption of blood flow.
ders; in specialist centres dynamic MRI scanning can
Pus forms within the medulla of the bone and forces its
examine moving joints.
way to the surface along the Volkmann’s canals form-
Radioisotope bone scan shows the level of bone vascu-

ing a subperiosteal abscess. The infection then spreads
larityandremodelling.Itisofuseininflammatoryand
locally and in infants may enter the joint. In children
infectious conditions prior to X-ray changes, it is of
the physis acts as a physical barrier to intra-articular
great value in identifying malignant bone infiltration
spread. Necrosis of the bone due to pressure and dis-
and sites of infection.
ruptedbloodsupplymaycausepiecesofbonetoseparate
(sequestra).
Bone and joint infections Clinical features
Presentationrangesfromanacuteillnesswithpain,fever,
swelling and acute tenderness over the affected bone, to
Acute osteomyelitis an insidious onset of non-specific dull aching and vague
systemic illness. A history of preceding infection may
Definition
indicate the source and suggest the organism.
Acute bacterial infection of bone.
Complications
Age Asthebonehealsandnewboneisformed,infectedtis-
Normally seen in children and adults over 50 years. sueandsequestratedbonefragmentsmaybeenclosed.