PATH 20 MUSCULOSKEL DS

• Mechanical: protection for brain / spinal cord / chest organs, rigid internal support for limbs. Mechanical properties relate to specific construction and internal architecture. Although extremely light, bone has high tensile strength. The combination of strength and light wt is a result of hollow tubular shape, layering of bone tissue, and
• internal buttressing of matrix.

• Metabolic/ Mineral Storage: principal
• resovoir for Ca, other ions (P, Na, Mg)

Haematopoietic: bone is a host for haematopoietic BM   

• Multinucleate giant cells responsible for removal of bone matrix, and are found in surface depressions at bone surfaces referred to as Howship’s lacunae.

• (osteoBlast = osteoBuilder)
• - produce bone matrix and control its mineralisation

• The non-mineralised matrix synthesised by osteoblasts is osteoid.
• When osteoblasts incorpd into bone = osteocytes, and occupy lacunar spaces.

 = non-mineralised matrix synthd by osteoblasts

• immature and disorgd precursor of lamellar bone
• (collagen fibres in the matrix are irregularly arranged)

has an organised and layered structure (collagen fibres aligned to form lamellae), and represents mature bone

an external shell or cortex and an internal medullary cavity comprising cancellous bone and marrow

'trabeculae'

dense compact cylindrical units (osteons or haversian systems)

• Infection of bone and marrow
• Virtually any pathogen
• Pyogenic bacteria, mycobacteria

• Classification
• Aetiological
• Acute / chronic
• Routes of infection

1) Blood borne (haematogenous)

2) Secondary to a contiguous focus of extra-osseus infection (Diabetic foot infections, dental)

3) Direct implantation(trauma, surgery, e.g. joint prosthesis)

Virtually any bone

• Site / location dependent on:
• Route of infection
• Nature of vascular supply

and there are Age related differences

• Paediatric
• Staph. aureus most common > 3 yrs
• Metaphyseal regions (high vascular flow)
• Femur, proximal tibia and humerus, distal radius

• Neonatal
• Often also involves adjacent joint
• Staph. aureus, group B strep., E.coli.

• Adults
• Spread probably via periosteal vessels cortex long bones / flat bones, eg vertebra

• IV drug users
• spine or pelvis, unusual sites

Most commonly affects bones prone to injury (least covering): phalanges, tibia and forearm bones

Often polymicrobial

Compound / comminuted fractures, puncture wounds iatrogenic infection (after internal fixation, joint replacement)

• Bacteria lodge in marrow
• Trauma - ?
• predisposing factor(with stasis / thrombosis)
• Acute inflammatory response
• Increased intracompartmental pressure

bact in bone...divide & prolif.....inflam response.....swell....no where to go....pressre increases......vasc flow decreases......death of bone and marrow

• Paediatric : local pain and fever
• Plain X-rays : often initially normal
• Intense uptake isotope scans
• MRI detects abnormality quicker
• Conclusive diagnosis : identification of organism
• Blood cultures +/- from lesion itself

Determined by:

• anatomic location
• host response / “resistance”
• the number / virulence of pathogens
• effectiveness of therapy

• Resolution and repair
• Sequestrum resolved
• Organisms dealt with
• Defect fills with granulation tissue
• Ossification + healing

• Inadequate host response
• Inadequate antibiotic therapy
• Inadequate removal of sequestrum

• Sequestrum, bacteria persist within non-healing cavity. 
• Infection may gradually spread beyond involucrum into soft tissues: sinuses

• Rare complications:
• Malignant Transformation (SCC)
• Amyloid

Brodies abscess

• = clinical entity distinct from bacterial osteomyelitis.
• -Autoinflam disorder, bactl culture usu negative
• -Kids and adolescents
• - bone pain and fever prolonged, fluctuating course
• - often multifocal, most often in tubular bones, clavicle
• - less frequently the spine and pelvis

• X-ray appearance suggests subacute or chronic osteomyelitis
• Biopsy and laboratory findings are nonspecific
• Aetiology is largely unknown

• Spread from focus of active visceral disease (usu lungs)
• Sites : spine, hip and knee (immunocompromised: often multifocal)
• Chronic granulomatous reaction
• No raised intracompartmental pressure
• Little reactive new bone
• Extension through bone + periosteum into soft tissue and joints

• = Tuberculous Osteomyelitis in Spine
• Collapsed vertebrae, angulation, often kyphosis, extension across and destruction of discs, cord compression, meningitis, thoracic, lumbar psoas frequently affected, ‘cold’ abscess

• Tuberculous Osteomyelitis can also occur in:
• Hip / knee destruction of subchondral bone, narrowing of joint space, ankylosis

• Spinal TB
• Anterior vertebral elements
• Destruction vertebral end plate
• Spread across intervertebral discs
• Involvement of adjoining vertebral bodies
• Cold abscesses paravertebral tissues / psoas

• - Blood borne infection of synovium
• - Extension of an adjoining focus of infection e.g. osteomyelitis
• - Direct inoculation(trauma/operative)

• Acute septic arthritis is a medcl emergncy

• Acute non-gonococcal septic arthritis = medical emergency Early diagnosis, rapid and aggressive therapy
• Dx - Aspiration and appropriate culture
• Can lead to significant morbidity (stuffed joints) and mortality
• Even with prompt diagnosis and treatment, high morbidity rates

• Febrile illness
• Hip, knee and ankle - usually monoarticular
• Cartilage readily destroyed
• Staph aureus, strep, H. influenzae, Gram negative rods

Traumatic chronic inflammatory arthritides(+/-) immunocompromised

Iatrogenic joint injection / aspiration / prosthetic joint replacements

• Swollen, red, warm, painful joint
• Fever, raised WCC
• Acute inflammatory reaction
• joint capsule and synovium = swelling + effusion
• histol, looks same as other inflam/infxn..eg pimple.

• Normal: 
• small volume
• clear
• 200 WBC/mL
• <25 PM's
• culture negative

• Septic/bacterial
• small volume
• turbid/ yellow/green
• 100,000 WBC/mL
• >90 PM's
• culture positive

• Large joints
• Haematogenous spread to synovium
• Chronic granulomatous inflammatory process
• Destroys articular cartilage and subchondral bone
• Joint destruction - fibrous ankylosis

• Chronic swelling and effusion
• Few acute signs of inflammation
• Loss of range of motion
• Formation of draining sinuses

• = a discontinuity. 
• Types:

• Complete
• Incomplete (greenstick)
• Simple / closed
• Open / Compound
• Comminuted
• Stress

• The principal factors that affect healing are:
• 1) Wound immobilisation
• 2) Vascular supply
• 3) Presence of infection
• 4) Physical stress

• Good vascular supply
• Minimal necrosis
• Precise anatomical reduction
• Immobilisation
• Absence of infection

• Infection
• Vascular compromise
• Malignancy
• Systemic disease
• Persistent/excessive motion
• Cleft / non-union
• ‘pseudoarthrosis’ forms
• Excessive gap / poor reduction - Fibrous union