OSTEOMYELITIS

TYPES

Non specific organisms (pyogenic) 
 
  - strep
  - staph

Specific organisms

  -  TB
  - Syphilis
  - Salmonella
 - fungal osteomyelitis, actino and madura mycosis
 - parasitic hydatid cyst

Spread of infection

- Haematogenous

• from a distant site in the body throat infection

- Direct

• Atmospheric air-open fracture 

- Neighbouring focus

Mastoiditis from middle ear infection
Dental root infection producing osteomyelitis of the mandible

- Iatrogenic

Following surgery on the bone for some other reason- ORIF

Osteomyelitis is comparatively more common  in children/ infants.
If it does occur in an adult, the commonest site is the thoracolumbar spine
Other bones can be affected  in diabetes mellitus, malnutrition, drug addiction, leukaemia and other immunocompromised situations

Clinical types of OM

Acute pyogenic OM
Chronic OM
Primary subacute OM
Acute flare up of chronic OM


Pyogenic OM

• Problem of childhood and adolescents
• undernourished children and debilitated adults
• common organisms- staph aureus and strep pyogenes
• In children <4 yrs old, haemophilus influenzae
• unusual organisms seen in drug addicts---
• in sickle cell anaemia, they have a predilection for salmonella OM
• Haematogenous spread is common. 
• Focus is usually from infectiosn like impetigo, septic tooth, throat infection, infected umbilical cord

Pathogenesis

Infection commonly starts in the metaphysis of a bone

This is due to the peculiar anatomy at this zone

- arteries tend to loop causing

- vascular stasis, which

- favours colonisation

Furthermore, there is less phagocytosis in the metaphysis

                       

Organisms colonises in the bone

Causes inflammation 

Phagocytic reaction, exudation of fluid, vascular congestion

Intraosseous pressure increases

Pain, obstruction to blood flow, vascular thrombosis

Pus forms in the bone and is forced out through the Volkmann;s canal with increased intraosseous pressure to the subperiosteal space

Subperiosteal abscess

The subperiosteal abscess bursts through the periosteum into the soft tissue, forming a sinus

It may also burst into a joint causing septic arthritis

Strips the periosteum--- periosteal blood supply is lost--- sequestrum

Intramedullary extension of the pus

Intraosseous blood supply cut off 

Dead bone- Sequestrum

Small dead bone absorbed by granulation tissue and osteoclastic activity

Large gradually separated from living bone destroyed and extruded

In certain situations like hip joint the metaphysis is intracapsular and infection can easily seep into the joint

In infants and adults, vascularity pattern--- intracapsular infected epi and metaphysis---- spread to the joint

Penetrates the periosteum---- track along soft tissue and penetrates the capsule


common vascularity between epiphysis/ metaphysis and synovium

Disruption of cartilage and spread

Pathological fracture


Healing takes place at any stage
- antibiotics
- natural persistence

Healing in early stage--- exudate is reabsorbed and new bony trabeculae formed

Organism, of lesser virulence or host demonstrates increased resistance--- result in formation of persistant abscess surrounded by fibrous membrane and walled by ring of dense bone called Brodie abscess.

When sequestrum has formed exudation continues til it is absorbed or extruded

Wall off area of infection may flare up again later---- chronic OM

Clinical features

antecedent infection
irritable, restless, vomiting, high grade fever with chills
pseudoparalysis of the limb
at first, no swelling later+ infdicates subperiosteal abscess formation
affected metaphysis is tender

Fluctuation present after abscess comes to soft tissue effusion in adjacent joint- sympathetic effusion
If infection continues unabated- septicaemia- fatal termination.

Laboratory findings

- Haemoglobin: low
- Total WBC: as high as 30 000 with leucocytosis
- ESR: high
- Blood culture: demonstrates presence of bacteraemia

Radiology of APOM

- initally, up to 10 days- normal
Later:  localised areas of destruction  in the metaphysis extending ti the diaphysis- moth- eaten appearance

Periosteal elevation: multiple laminations of bone deposition parallel to the bone- appears like the onion peel appearance- seen in Ewing;s sarcoma  .

Late sign: osteoporosis with a localised segment of apparently increase density eg femoral head.

Other Investigations

MRI
CT Radiography

Diagnosis and needle aided drainage of pus for culture and sensitivity from inaccessible parts- vertebra

Radionuclide examination

Technetium phosphate- Tc99m
Positive within hours to days
initially cold spot later hot spot
depends on vascularity to the part and in the presence of increased IOP may not reach the affected part.

Gallium 67
Taken up by leucocytes
independent of vascular tree
also taken up by inflamed soft tissue and hence difficult to differentiate between cellulitis and osteomyelitis

Indium 11 labelled leucocytes
taken up by leucocytes
most suitable more sensitive
requires technical expertise and is time consuming.

MRI

Useful in early detection of osteomyelitis and soft tissue extension


DDX

Rheumatic fever: onset more gradual, consitutional symptoms less, acute and confined to the joint, polyarticular, response to salicylates and ACTH is dramatic. Antibiotics have no effect.

Ewings sarcoma: fever, leucocytosis, subperiosteal reaction- onion peel appearance, destruction confined to the diaphysis, responds to radiotherapy, biopsy shows tumour cells.

Acute septic arthritis:  fluid accumulation in the joint occurs earlier, pain and inflammation limited to the joint, joint movements grossly restricted, aspiration reveals purulent synovial fluid

Treatment: Early diagnosis with a high degree of suspicion is beneficial and necessary
Blood for investigations are collected and high doses of antibiotics are started as early as possible.

Antibiotics are changed later if necessary as per culture and sensitivity  reports

Immediate drainage is of paramount importance and is done before signs of subperiosteal infection is seen.

To wait is to invite trouble and disaster. Maximum waiting period allowed is 24 hours SOS to improve general condition patient.
Immediate drainage by opening a cortical window at the suspected site.

Closed continuous drainage for 24-48 hours.
Or leave the wound open and allow secondary healing

Prolonged antibiotics as per culture and sensitivity report for minimum period of 6 weeks with initial 2 weeks of parenteral antibiotics.

COMPLICATIONS

Acute osteomyelitis invariably ends up as chronic osteomyelitis
Septicaemia and fatal end
Multifocal osteomyelitis in debilitated individuals- rare

After an attack of acute osteomyelitis recurrence of infection is a rule- the interval may vary.
Once an osteomyelitis always an osteomyelitis

Acute OM leading to chronic OM
Haematogenous infection with a low virulence organism may be chronic from the beginning
Infection from an external wound usually causes chronic osteomyelitis

Pathology

Repair when incomplete persistance of infection
Repair process- hyperaemia formation of granulation tissue and aborption of necrotic cancellous ad cortical bone.

When sequestrum is small and infection is controlled sequestrum gets resorbed
When large and infection persists- it separates out and lies in a cavity
The surrounding tissue attempts to wall off infection--- forms thick bony wall--- called the involucrum

Pathology

Involucrum has multiple openings called cloacae, openings for exudate, debris and sequestra to drain though the sinus.
Once sequestrum  is extruded- infection is better controlled and settles down.

TYPES OF SEQUESTRUM

STIR BCD

Sandy   ------    tuberculur OM of the vertebra
Tubular ------   tubercular OM of the long bone
Ivory ---------   syphilitic osteomyelitis
Ring ----------  stump/ skeletal traction
Black ---------  prolonged exposure of bone
Cortical ------   pyogenic OM adults
Diaphyseal ---  pyogenic OM- children


Clinical features

In the period of inactivity no symptoms
Fever, pain, swelling and tenderness of bone
Sinuses discharging pus and bony spicules- sequestrum
Bone is thick, irregular or may be deformed
Skin dusky thin and scarred.

Muscles are scarred and contracted- produce deformities of adjoining joints

Radiology

Moth eaten appearance
Osteoporotic bone
Sequestrum
Involucrum
Bone thick and irregular
Bone may be deformed
Pathological fracture

Other Investigations

Sinogram

Traces the sinus tract and helps planning of surgery and removal of entire tract to prevent recurrence.

Sequestrectomy and saucerisation
Scondary healing of wound
Prolonged antibiotic- minimum of 6 weeks to 3 months according to culture and sensitivity report with initial parental antibiotics.

COMPLICATIONS
Acute flare up chronic osteomyelitis
Squamous cell carcnima of chronic discharging sinus
Contracture of muscle producing deformity of joints

Stimulation/ destruction of growth plate leading to discrepancy of limb length or deformities
Pathologic Fracture
Septic arthritis of adjacent joint- deformity and ankylosis
Amyloidosis

Brodie's abscess

Described by brodie in the tibial metaphysis in 1832
Indicates subacute pyogenic osteomyelitis usually of staphylococcal origin
Commonly seen in children- boys

Commonly affects the ends of the tibial bone
ABscess varies from 1cm-4cm in diameter
Radiologically seen as cavity surrounded by dense ring of bone.

Appropriate antibiotics may decrease the size of the lesion
If pain persists- may require surgical decompression of the abscess.