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Bone and Joint Infections
Theres a well-known overlap between orthopedics and dentistry in the field of bone. What
affects the bones in the skeleton might as well affect the maxillofacial area and the mandible; an
infection in the tibia or femur could also affect the mandible, or a cystic arthritis in the knee jointcould occur in the temporomandibular joint.
The bone is composed of two layers; Cortex and Medulla. The cortex as the outer layer, and the
medulla as the inner layer containing the bone marrow.
The medical terms used to describe bone infections are Osteomyelitis and Osteitis. The word
Osteomyelitis is divided into two parts, Osteo: bone and Myelitis: Bone marrow. So
Osteomyelitis implies that the infection involves not only the cortex but also the bone marrow
spaces in the medulla, however if the infection is present only in the cortex of the bone it is
referred to as Osteitis.
Classifications of Osteomyelitis
Osteomyelitis is classified according to the:
I. Routes of Infection1)
Exogenous: A source of microorganism introduced from the external environmentdirectly to the bone, for example a stab wound.
2) Hematogeneous: Microorganisms disseminated through the blood stream from a site ofinfection in the body to settle in the bone. The source of infection will travel through the
blood to reach the proximal or the metaphyseal part of the bone. Examples of way the
infection could get through:
- In the infantile stage, Osteomyelitis might be transmitted through an infectedumbilical chord at birth.
- Through skin infection.- If an adult had history of Urinary Tract Infection.- Through arterial catheterization or administration of an IV line for antibiotics
or fluid intake.
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3) Contiguous spread: A direct spread from a nearby focal infection, most commonlyaffecting the superficial bones (Ex: Tibia and Ulna) where an infection could easily
extend from the infected overlying soft tissues.
II. Types of Microorganisms: they are organized according to age groups whereStaphylococcus Aureus is the most common.
1) Neonates ( 5 years (Osteomyelitis is commonly knownas being a pediatric disease).
Rare in adults unless they are immunocompromised. Boys > Girls. 1/3 of cases have reported history of trauma. 80% of Osteomyelitis cases are located in the metaphysis of the bone.
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Anatomy of the bone:
Epiphysis: Ends of the bone, either upper or lowerends.
Diaphysis: Site of entry of blood vessels.Growth platesMetaphysis: Unique anatomical structure and rich
in blood vessels. These blood vessels enter
through the diaphysis as large caliber (largediameter), they start to narrow down extending
through the bone reaching the metaphysis and
the growth plate (which is active in young age).
The vessels cannot penetrate the growth plate
and they will form a loop (harping loop or reverse
loop) at the metaphysis. So blood flow through
these vessels will slow down gradually, and this
slow blood flow is a good media for bacterial
growth. This is why Osteomyelitis most commonly
occurs at the metaphysis.
** So Osteomyelitis is more common in the
metaphysis area of the bone. But out of all bones in
the body, the Femur Bone (27% of cases), the Tibia,
or long bones in general are the most commonly
affected.
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Stages of Osteomyelitis:
1) Primary Focus Infection2) Stage of Inflammation: Where chemotaxis of macrophages and other inflammatory
mediators occurs.
3) Formation of sub-periosteal abscess: Abscess may migrate within the bone through theHaversian canals or could travel by a duct outside the bone creating what is called a sinus
discharging pus.
*All these changes in the inflammatory habits will increase the intra-osseous pressure, so
the pus will try to drain at any escape.
4) Sequestrum formation: after the drainage of pus, the bone will be left with empty spaces
called bony infarction (dead bone).
5) Resolution of infection: New bone formation, and this is very important for healing
because otherwise the infection will alternate into its chronic form.
Acute Osteomyelitis
Clinical Picture (Diagnosis):
Three sequels should be taken into consideration when a physician is trying to reach a
diagnosis to manage a certain case:
1) History:- In most of the cases, Osteomyelitis will be associated with preceding infections. For
example, if a 5 year old child presents pointing to pain in his/her femur and this pain was
persisting for that last 48 hours. The mother should be asked about any history of
previous infections (Ex. Respiratory tract infections, Tonsillitis, trauma, or even skin
lesions that occurred somewhere else in the body) to identify the source of infection
transmitted from the blood to the bone.
- The older the child gets, the easier it is to take history, but the challenge arises when aneonate for example is reported from the department of prematurity by pediatricians
suspecting an infection in a certain bone. The physician in this case will relypredominantly on his/her sense and intuition. Symptoms associated with neonates could
be:
Failure to thrive: the baby refuses to breastfeed and is not gaining weight. Drowsiness Baby is irritable most of the time
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Most of the cases occur around the knee, distal or proximal femur, or on the shaftof the femur.
2) Examination:Pain will be very localized rather than diffused; the area of tenderness will be at its
maximum in a single point, just like a bell ring. So this presentation is called The Ring
Bell Sign and its an indication for a focus of infection and will rule out many other
diseases (Ex. Tumors, Trauma, or any metabolic bone disease).
Affected limb will be reluctant to move.Fever: Patients usually present with intermediate fever rather than high grade fever,
the reason behind that is that the patients would have already started taking
medications Ex. Paracetamol or NSAIDs.
MalaiseLoss of appetiteSepticemia (only in severe/toxic cases)
3) Investigations: How to approach the case?a) Laboratory Investigations: They are to some extent invasive, Ex. needles to
withdraw blood.
- Complete blood count (CBC): Standard test for any work up especially forpatients with suspected Osteomyelitis. This test is not accurate and does not
give a direct indication to the disease. In infected patients, levels of WBCs
should be elevated however this occurs only in one third of the cases, this is
why more sensitive tests should be done; ESR and CRP which are called
Inflammatory Phase Reactants (both are elevated during inflammation).
- ESR: Erythrocyte Sedimentation rate. Used more in the follow up of patientsrather than diagnosis.
- CRP: C-reactive protein test, measures general level of inflammation in thebody. Elevated in 98% of infected patients, peaking on day 2 of
inflammation. More specific than ESR since it fluctuates easily with thebodys inflammatory changes; it rises on infection more quickly and will
respond to antibiotics faster. So it is the most diagnostic lab investigation.
- Blood Culture: 50% of cultures from CBC are positive.
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- Direct/Needle aspiration: Using a sterile needle (18gauge) or a spinal needleafter sterilization with a bit of anesthesia Ex. Lidocane, a sample is taken
from the suspected location of infection, or if there were any pus
production it could also be aspired. The aspiration is sent to blood culturing
(positive in 2/3 of cases).
b) Radiological Investigations: The imaging study for a child with Osteomyelitis. Plain X-ray:- Initial X-ray: Pathological changes in the body need time to manifest
themselves, so initial x-rays could appear to be negative/normal most of
the time, especially in the early few days (72 hours) where the only sign is
soft tissue elevation. So initially, x-rays are not to depend on but they are
done to rule out fracture.
- After 1-2 weeks: X-rays are most informative in that period of time. Theywill start to show rarefaction (reduced density) of bone and periosteal
reactions.
- More than two weeks: Changes will be more prominent and infection willspread over the entire bone (Epiphysis, Diaphysis and Metaphysis).
*Patients cannot wait for a couple of weeks with infection to have a clear diagnosis, so for
more precise methods of investigation, other non-invasive tests could be made:
Ultra-Sound: it will be further explained later. (Page 12 ^) Bone Scan: Its an injection with a nuclear labeled material (technetium-
99m) where it is up-taken in areas with higher metabolic rates.
Gallium scan: More sensitive (sensitivity>91%) than bone scan because inthis test the polymorphonucleus of the white blood cells themselves are
the marker for the investigation.
Other tests include: CT-scan and MRI. They are not frequently used if thediagnosis was established from the previous tests, however if the physician
is having problems with the differential diagnosis especially in cases of
tumors and Ewings sarcomas they could be done.
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Osteomyelitis in adults:
Osteomyelitis in adults is very rare but if it happened the most affected locations would be the
vertebrae, specially the thoracolumbar vertebrae.
Symptoms and signs of adults with Vertebral Osteomyelitis:
- Localized pain in the vertebrae.- Back ache- Fever- History of Urinary tract or Neurological infection or any procedure done in the near past
(1-2 weeks).
Risk factors:
- Immunocompromisation- Diabetes- Old age
*If the adult is healthy is it very unlikely to develop this sort of infection.
Differential Diagnosis:
Septic Arthritis: Septic Arthritis is the infection of the joint itself. In some cases, especiallyin young patients, the infection might attack the metaphysis as Osteomyelitis and then
easily spread into the joint causing secondary Septic Arthritis. This occurs particularly in
younger age groups because of two reasons:
1. The growth barrier did not yet make a border between the metaphysis and theepiphysis.
2. The metaphysis is still a part of the joint. Rheumatologic Disorders Sickle Cell Crisis Thalassemic Crisis Ewing's Sarcoma: It is a malignant tumor of the bone. The lamellated or "onion peel"
appearance of the bone seen on a radiograph with this disease is similar to what is seen
with Osteomyelitis.
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Management of Osteomyelitis:
Once the diagnosis of Osteomyelitis is confirmed, the patient must be hospitalized. Unlike any
other type of infection (ex: tonsillitis), bone infections are difficult to treat because the infection
is hidden within a barrier (bone), so a strong antibiotic at high concentration is needed to
penetrate through the bone and reach the site of infection in an adequate amount.
Unfortunately, oral antibiotics cannot achieve this penetration, and thus IV antibiotics are
needed in early stages. Other reasons for hospitalization are that the patient has high fever and
requires IV fluids for hydration and correction of the electrolyte imbalance. In addition, the
patient must be immobilized and analgesics might be needed for the pain.
The specific treatment of Osteomyelitis is the administration of antibiotics at an early stage as
they become less potent when administered at a late stage. One knows that it is impractical to
start a course of antibiotic before knowing for sure the exact type of microorganism causing theinfection (ex: Staph, Strep, Pseudomonas, or E.coli) and a clinician should normally wait for
laboratory results and blood cultures to decide what type of antibiotic is most suitable. However,
a patient with Osteomyelitis should not be left without treatment waiting for laboratory results
(which take 72 hours ~ 3 days) so empirical therapy must be used.
Empirical therapy means that an antibiotic is chosen by common sense according to the
microorganism that is most likely present. Examples of empirical antibiotics are: Gentamycin,
Cephotaxime, Ceforuxime, Clindamycin, Vancomycin. These empirical antibiotics should be given
in the first 72 hours until the laboratory results are out.
Once the specific microorganism causing the infection is known, the patient should be treated
with a more specific antibiotic. For example, if the infection is caused by Staph aurous, the
patient is treated by Penicillins (Amoxicillin and Ampicillin) or by Cephalosporins (Cephozulin). If
the cause of infection is a gram negative bacteria like Salmonella, the patient may be give
Ampicillin, etc.
IV antibiotics should be given for about 3 weeks followed by oral antibiotics, the patient starts
taking oral antibiotics once his/her symptoms alleviate (no pain, no fever, CRP level normal,
ESR
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Indications for Surgery:
1. Abscess formation: surgery is required in any case where soft tissue or subperiostealabscess is present (when pus is discharged). Antibiotics should not be used in the
presence of an abscess since it will exacerbate the situation because the abscess will
enclose itself to prevent the entry of the antibiotic. So as a general rule in medicine,
abscess formation requires incision and drainage.
2. When a Fine Needle Aspiration reveals a purulent fluid, suggesting the presence of pus.3. Failure of antimicrobial treatment in the first 3 days. In this case, the bone should be
drilled and the Sequestrum (the dead bone cavity depriving the bone from blood
supply) should be removed by a process called Sequestrectomy. Sequestrectomy
should be handled by an expert especially if the Sequestrum is near the growth plate.
Complications of Osteomyelitis:
- Focal infection (ex: in the head of the femur) might spread throughout the body, causingsepticemia.
- Progression into a Septic Arthritis.- If the infection spreads and involved a nearby growth plate, this will cause growth
disturbances.
- Pathological fractures, since Osteomyelitis weakens the bone.- Progression into chronic Osteomyelitis (very dangerous complication, should be avoided)
Sub-Acute Osteomyelitis
This type of Osteomyelitis is challenging because of its unclear presentations and because it
usually mimics other Oncological disorders such as Osteoid Osteoma.
Unlike Acute Osteomyelitis, a patient with Sub-Acute Osteomyelitis is presented with a longer
history of pain (1-2 months); the pain is usually mild, intermittent, irritating and the onset of pain
is not acute. Other constitutional symptoms like fever and toxemia are not present. Also, themicroorganism involved is less virulent and not powerful enough to cause the usual pathological
changes.
Initial radiographs may be abnormal, and laboratory data are not always conclusive as in acute
Osteomyelitis. For instance, WBC count may be normal, and CRP might as well be normal. So in a
case where a patient has a long history of pain in his distal tibia, but his/her test results show a
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normal WBC count and CRP level, then Sub-Acute Osteomyelitis should be suspected as well as
other malignancies. In this case, a biopsy is usually taken, and this biopsy is cultured. The culture
will usually show Staphylococcus or Gramve anaerobic Pseudomonas, but in more than half of
the cases the cause is polymicrobial. Polymicrobial infections can be treated by Gentamycin,
Tinam, Imipenem
What is most concerning about Sub-Acute Osteomyelitis is that it has a high recurrence rate of
about 40%.
Treatment of Sub-Acute Osteomyelitis:
After results of the tissue culture are obtained, IV antibiotics should be administered followed by
oral antibiotics for at least one month.
Chronic Osteomyelitis
Chronic Osteomyelitis is usually a progression of an untreated Acute Osteomyelitis, and here the
patient entered whats called an On-Off phenomenon. In On-Off phenomena, the patient will
experience times free of symptoms (4-5moths or even more), and other times where the
symptoms relapse (may last for 2-3 weeks).
The pain may be continues or intermitted, and pus may be discharged from a sinus, which opens
at times and closes at others.
Patients with higher risk of progression of acute Osteomyelitis into Chronic Osteomyelitis usually
suffer from:
Nutritional deficiencies Vascular Diseases Low immunity Diabetes Acute Osteomyelitis caused by a high virulent organism not responding to antimicrobial
agents.
As mentioned above, Chronic Osteomyelitis is most commonly a complication of an
unsuccessfully treated Osteomyelitis. However, it might be due to a post-traumatic injury
especially in war victims where a microorganism has entered the bone through a stab or a
contaminated injury. Chronic Osteomyelitis might also occur as a post-operative complication.
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Investigations:
- Lab test- Cultures (maybe pus culture)- Plain X-ray- Sinogram: Dye injected into the sinus to trace and follow the amount of bone involved,
sometimes the whole bone is found to be complicated.
Complications of Chronic Osteomyelitis:
- High recurrence rate- Pathological fractures- Metabolic bone disease- Carcinogenic transformation
Treatment of Chronic Osteomyelitis is unfortunately very depressing for the patient due to its
long period. The treatment includes: antibiotic administration, local antibiotic inside the bone
defect (ex: Gentamycin beads), and maintenance of bone stability to avoid pathological
fractures.
Septic Arthritis
Septic Arthritis is an infection in the joint, and the word 'Septic' implies that this type of Arthritis
is caused by a microbial agent, mainly bacterial (Staph aurous, Strept, Pnemococcus). It might
also be due to a viral infection, which tends to be transient and does not usually cause the
destructive changes inside the joint.
A good way to distinguish between Septic Arthritis and other forms of Arthritis (ex: Rheumatoid)
is that Septic Arthritis is monoarticular, meaning that it affects only one joint of the body, unless
if it's caused by Neisseria Gonorrhea were the infection will occur in multiple joints (ex: both
knee joints).
Septic Arthritis occurs most commonly in the hip joint, with more than 50% of cases seen in
pediatric age groups of less than 3 years of age. So, a common presentation of this disease in the
ER is a child (usually
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In most of the cases, Septic Arthritis is seen in association with Osteomyelitis. However, it is not
important to find out whether Osteomyelitis occurred first and caused a secondary Septic
Arthritis or vice versa
Pathogeneses:
Changes in the Synovium (synovial fluid) lining the joint capsule. Vascular Changes (because of inflammation) Attraction of WBC, macrophages, and inflammatory mediators (Interleukins) causing
further exaggeration of the condition.
Clinical picture of Acute Septic Arthritis:
Huge swelling around the infected joint Pain, Calor (hotness), redness Immobilization Fever Malaise
Lab investigations:
CBC CRP, ESR
Blood Culture (40-50% positive) Plain X-ray Bone Scan/ Gallium Scan Ultrasound
^Ultrasound is an easy, noninvasive, and informative test that is necessary for the
diagnosis of Septic Arthritis. It enables the clinician to examine hidden joints (for example
hip joint), and check for the presence of accumulated fluids within it. A needle aspiration
is performed on the accumulated fluid, in case of its presence, under the guidance of the
ultrasound. As a role, if WBC count in this fluid showed up to be greater than 50,000 withmore than 90% being polymorphonuclear, then a diagnosis of Septic Arthritis is confirmed
even if the blood cultures were negative.
In the absence of an ultrasound (limited facilities), an X-ray might be sufficiently
informative. The diagnostic mark in an X-ray is the teardrop sign, which is the space
between the acetabulum (concavity in the pelvis where the head of the femur meets,
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forming the hip joint) and the head of the femur compared to the other healthy hip joints.
If the space is widened, this is an indication of fluid accumulation in the joint pushing the
head of the femur laterally.
Differential Diagnosis:
1. Acute Osteomyelitis (same management and treatment)2. Transient Sinovitis of the hip: viral reactive Arthritis, patients usually have history
of Upper Respiratory Tract Infection, Hemarthrosis (bleeding into joint spaces)
etc
Treatment of Septic Arthritis:
1. A patient with Septic Arthritis requires admission to hospital.2. The infected joint should be splinted to ensure fixation and immobilization, because it'svery painful to the patient.3. Empirical antibiotics are given followed by definitive antibiotics.4. Surgical drainage: it is of high importance to drain all the pus accumulated inside the joint
to avoid lysis and destruction of the cartilage by inflammatory mediators.
Complications of Septic Arthritis:
- Secondary Osteoarthritis: Occurs when the patient is not treated from the joint infectionresulting in growth disturbances in that joint, leg shorter than the other, and the need for
an early artificial joint.- Cartilage damage- Slow dislocation of the joint- Arrest of bone growth
Done By: Lama Ashour & Raya Dawood
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