Musculoskeletal infection by capt alauddin

1. Presented by: Capt Alauddin
MD, Ph-A, Radiology and Imaging

2. Infections of the musculoskeletal system
can be subdivided into 3 categories:
(a) those involving bones (osteomyelitis)
(b) those involving joints (infectious
arthritis) and
(c) those involving soft tissues (cellulitis).

3. Entry of infectious organism
into bones may be from:
• Hematogenous spread,
• From the contiguous soft
tissues or
• Direct implantation
secondary to trauma or
surgery.

4. Etiology : In children, the
etiology is typically
hematogenous
In infants, as diaphyseal
vessels extending through
the cartilaginous growth
plate reach the epiphysis,
so there is increased
frequency of epiphyseal
and joint infections.

5. In early childhood, these
diaphyseal vessels
terminate in the
metaphysis-forming
venous sinusoidal lakes
with a slow, turbulent
flow which allows blood
borne organisms to seed,
proliferate, and cause
metaphyseal infection.

6. In adults, the
hematogenous spread is
less common and the
bacterial access is usually
due to direct inoculation
from penetrating trauma,
surgery, or adjacent
contaminated soft tissue.

8. Different imaging techniques for
diagnosis of MSK infections include
• Radiographs
• Ultrasonography (USG)
• Computed tomography (CT)
• Magnetic resonance imaging (MRI)
and
• Functional Imaging( Bone
scintigraphy).

9. Soft-Tissue Infection :
Cellulitis: A spreading inflammatory
reaction of infectious origin
occurring along the skin,
subcutaneous and fascial planes with
edema and skin changes.
The common pathogens associated
with cellulitis are Streptococcus
pyogenes or Staphylococcus aureus.

10. Clinical presentations :
• Skin erythema without a well-defined border
• Increased skin temperature
• Swelling of the affected area
• Regional lymphadenopathy
• Systemic features such as fever and rigors may also be present.

11. Predisposing factors :
• Poor general health
• Skin laceration or ulceration
• Venepuncture
• Eczema and
• Immunosuppression

12. Radiographic features:
Ultrasound:
Diffuse swelling, hyperechogenicity of the skin, and
subcutaneous tissues to a variable degree and presence of
subcutaneous edema.

13. Cellulitis(Cont)
Transverse Ultrasound of the right
leg showing hyperechoic
subcutaneous fat lobules separated
by hypoechoic fluid-filled areas
which appears as branching,
anechoic striations typically known
as "cobblestone" appearance
This is suggestive of cellulitis.

14. Cellulitis(Cont)
In Doppler imaging
the presence of hyperemia
is the diagnostic of cellulitis.

15. Cellulitis(Cont)
CT of cellulitis shows
subcutaneous fat stranding with
thickening of overlying skin.

16. Cellulitis(Cont)
On MRI there is T2 hyperintensity of the affected area with diffuse
linear or ill-defined soft-tissue thickening with corresponding T1
hypointensity and postcontrast enhancement.

17. Necrotizing Fasciitis :
An aggressive infection of the skin
and soft tissue with necrosis of the
muscle, fascia, and subcutaneous
tissues. This infection typically
spreads rapidly along the fascial
plane, which has a poor blood
supply.

18. Necrotizing Fasciitis :
C/F: Pain, Fever, And Sepsis which are out of proportion.
Subtypes : Necrotizing fasciitis encompasses all soft-tissue infections
deep to the hypodermis,
2 subtypes depending upon the anatomical site,
• Fournier gangrene for the perineum and
• Ludwig angina for the submandibular region.

19. Necrotizing Fasciitis (cont):
Has an association with pre-existing
comorbidities, such as diabetes,
vascular disease, immunosuppression,
obesity, and drug abuse .
Etiology: Direct inoculation of bacteria
through a breach in the skin is seen in
the majority of cases, gram-positive
cocci such as Staph. aureus and
Streptococci are responsible in single
site infection.

20. Necrotizing Fasciitis :
Radiological features :
USG : Diffuse thickening of the
subcutaneous tissue, subcutaneous
hyperemia, perifascial fluid,
distorted appearance of the visual
field when there is presence of air
in soft tissue.

21. Necrotizing Fasciitis (Cont):
MRI :
T2 : high signal intensity,
T1 : low signal intensity and
Post Contrast: variable
enhancement.
Presence of low signal foci in
all sequences and blooming
artifact on the GRE in the
soft tissue is suggestive of
free air and is diagnostic of
necrotizing fasciitis

22. Pyomyositis :
Pyomyositis (also known as tropical myositis, pyogenic
myositis , suppurative myositis ) is a primary infection of skeletal
muscle and often associated with abscess formation.

23. Pyomyositis :
C/F : Pain localised to one or more muscles (although in most
cases it is in a single muscle),
variable degrees of systemic inflammatory manifestations
Predisposing conditions:
• Diabetes,
• Malnutrition,
• Human immunodeficiency virus (HIV) infection,
• Immunodeficiency,
• Drug abuse,
• Malignancy, or trauma

24. Pyomyositis :
stages: there are three stages-
a. invasive stage is characterized by nonspecific muscle edema
b. suppurative stage is characterized by intramuscular abscess
formation
c. late stage is characterized by septicemia and multiorgan failure
with a significantly high mortality rate

25. Pyomyositis :
Radiological features:
On USG, the affected muscle
shows low attenuation
changes and the collection
may have heterogeneous
contents with postacoustic
enhancement

26. Pyomyositis (cont):
(A) USG of the triceps
muscle, showing edema,
fusiform enlargement , and
ill-defined fluid collection
interspersed between the
muscle fibers.
(B) Ultrasonography image 2
weeks later after antibiotic
therapy shows complete
resolution.

27. Pyomyositis (cont):
MRI: shows only nonspecific muscle edema with high T2 and
isointense T1 signal change in the early stages.

28. Infectious Tenosynovitis :
Infection of the space between the
inner visceral layer adherent to the
tendon and an outer parietal layer
of tendon sheath with
inflammatory reaction and pus
formation
. Risk factors:
• Immunosuppression
• Diabetes
• Smoking

29. Infectious Tenosynovitis (cont) :
Most common pathogen is Staph.
aureus, less commonly by fungus
and MTB.
It commonly affects the flexor
tendons of the hands and wrist as
flexor tendon sheaths
communicate with adjacent bursae
and hence the direct spread of
infection is more common with
flexor tendons

30. Infectious Tenosynovitis :
Four physical exam signs are
collectively known as the Kanavel
signs:
• Fusiform swelling to the affected
digit
• Digit held in flexion at rest
• Tenderness with percussion
/palpation of flexor sheath
• Pain with passive extension of the
affected digit

31. Infectious Tenosynovitis (cont):
Radiological features:
USG demonstrate thickening of
the tendon and tendon sheath
with hyperemia on Doppler
imaging.

32. Infectious Tenosynovitis
(cont):
MRI: Shows tendon and
tendon sheath thickening
and the presence or
absence of fluid. It is
particularly useful to
depict the extent and
anatomical relations of
the tenosynovitis .

33. Septic Bursitis:
Inflammation of various
bursae due to chronic
repetitive strain or
mechanical reasons
characterized by sterile
inflammation of the bursal
wall with accumulation of
free fluid in the bursa.

34. Septic Bursitis:
Etiology: Staph. aureus is the most common
pathogen involved.
Superficial bursae are more commonly involved
due to the chance of direct inoculation due to
trauma, e. g: Olecranon bursa, prepatellar and
infrapatellar bursae.
Infection of deep bursae is uncommon and is a
result of either surgery, contiguous or
hematogenous spread, e. g trochanteric and
subacromial bursae.

35. Septic Bursitis(cont):
Radiological features: USG studies
show extensive inflammatory
changes of the bursa. Bursal wall
thickening with hyperemia on
Doppler imaging, peribursal
inflammation, and mixed
echogenic fluid with internal
debris are seen.

36. Septic Bursitis(cont):
MRI demonstrates thickened
bursae with fluid distention and
inflammatory edema of the
adjacent peribursal soft tissues

37. Osteomyelitis:
Osteomyelitis is defined as
inflammation of the bone &
medullary cavity due to infection
characterized by progressive
inflammatory destruction and new
apposition of bone.
Predisposing factors:
• Trauma,
• Bacteremia,
• Adjacent soft tissue infection,
• Surgery, or foreign bodies

38. Osteomyelitis:
Age of onset: Bone infections show a bimodal age distribution,
occurring most commonly in people younger than 20 or older
than 50 years of age.
Etiology: In children and adults, Staphylococcus is more common
and is seen in 90–95% of cases. In neonates and infants,
Streptococcus is more common. other microorganisms
responsible are Escherichia coli, Pseudomonas, and Klebsiella.

39. The location of osteomyelitis within a bone varies with age, on
account of changes in vascularisation of different parts of the
bone
• Neonates: metaphysis and/or epiphysis
• Children: metaphysis
• Adults: epiphyses and subchondral regions

40. Osteomyelitis(cont):
Types : Waldvogel classification system based on pathogenesis
dividing the osteomyelitis into three separate groups
1. Hematogenous
2. Secondary to contiguous spread from a focus of infection
3. Associated with vascular insufficiency
Traditionally, it may be acute, subacute, or chronic, depending
on its clinical course, histologic findings, and disease duration

41. Acute osteomyelitis typically presents 2 weeks after bone
infection and chronic osteomyelitis 6 or more weeks after
bone infection. Some studies describe an additional
subacute phase, with 1–3 months of symptoms.

42. Osteomyelitis:
Radiological features :
Plain radiographs are usually the first technique of imaging. Destructive bone
changes do not occur until 7–10 days of onset of infection.
On radiographs taken after this time period, a number of changes may be
noted:
• Regional osteopenia
• Periosteal reaction/thickening (periostitis): variable; may appear
aggressive, including the formation of a codman's triangle
• Focal bony lysis or cortical loss
• Endosteal scalloping
• Loss of trabecular bone architecture
• New bone apposition
• Peripheral sclerosis

43. Acute Osteomyelitis:
Radiological features :
Plain X-ray of the proximal
humerus AP view showing ill-
defined bone lucency and
osseous destruction involving
the medial aspect of the
metaphysis in a child.

44. Osteomyelitis:
Radiological features :
Plain X-ray of the proximal
humerus AP view showing
proximal humeral metaphyseal
lucent focus with periosteal
reaction in diaphysis suggest
osteomyelitis.
Enlarged soft tissue shadow
around right shoulder joint with
increased density, that suggests
associated joint effusion.

45. Few radiological features
associated with osteomyelitis:
Periosteal Reaction : Periosteal
reaction is a nonspecific
radiographic finding that
indicates new bone formation in
reaction to the abnormal
stimulants. Periosteal reactions
may be broadly characterised as
benign or aggressive.

46. Periosteal Reaction (cont):
• nonaggressive types of
periosteal reaction include
noninterrupted, smooth, thick
or thin, and undulating
• aggressive types of periosteal
reaction include interrupted,
lamellated/onion skinning,
sunburst, Codman triangle,
and spiculated

47. Subperiosteal Abscess :
subperiosteal abscess is
most commonly found in
pediatric forms of
osteomyelitis, as these
patients are known to
have looser adherence of
the periosteum to the
underlying cortex.

48. Brodie’s Abscess : Intraosseous
abscess cavity filled with pus,
with a rim of granulation tissue.
First described by Brodie.
Intraosseous abscesses occur
most often in children, have a
predilection for the metaphysis
of long bones, and are observed
in the subacute or chronic stage
of osteomyelitis when the
organism has reduced
virulence.

49. Bony sequestrum:
piece of devitalized bone that
has become separated from the
surrounding bone during the
process of necrosis.
presence of a sequestrum is
definitive for chronic OM. The
presence of dead bone usually
with fistulous tracts secondary
to infection confirms the
presence of chronic
osteomyelitis.

50. Involucrum:
describes the formation of a
spherical capsule of viable new
bone around an area of
sequestered and necrotic bone.
The involucrum can be viewed
as a response to wall-off the
necrotic, infected sequestrum.

51. Involucrum:
The inner lining of the
involucrum faces the
sequestrum and consists of
granulation tissue
The outer layer of the
involucrum consists of
expansile, coarse, woven bone,
which is typically sclerotic in the
mature stage.

52. Cloaca: The term cloaca is used
to indicate an opening or
rupture of the bony cortex
overlying an area of
osteomyelitis that allows
granulation tissue and/or
intramedullary pus to be
discharged out of the bone.