7th CL Davis Diagnostic Pathology Symposium Diagnostic Orthopaedic Pathology Reno, NV October 19, 2007

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1 7th CL Davis Diagnostic Pathology Symposium Diagnostic Orthopaedic Pathology Reno, NV October 19, 2007 Roy R. Pool, DVM, PhD Professor of Pathology, Texas A&M Department Veterinary Pathobiology Director of Surgical and Osteopathology Services

2 Pathogenesis of Bone, Joint & Tendon Sheath Infection

3 Vascular Role in the Formation of Morphologic Patterns in Inflammatory Bone and Joint Disease

4 Two Patterns of Skeletal Infection Hematogenous vs Implantation Patterns in Immature Animals Reflect: Portal of entry of microbial agents Age of animal: : newborn, juvenile, adult Species of animal: : Contaminated environment; placentation/colostrum colostrum Local vascular anatomy at site where agent localizes in capillary bed of the bone

5 Vascular Supply to Epiphysis and Metaphysis of Foals and Calves Articular cartilage: : Vessels located in vascular canals and originating in the subchondral spongiosa of the epiphysis nourish the deep 2/3 of articular cartilage. Transphyseal blood vessels bridge the metaphyseal physis and act as conduits for passage of infectious exudate in osteomyelitis of neonates

6 Blood Supply to a Long Bone Nutrient vessels: Diaphysis Diaphysis,, Metaphysis, Epiphysis Medullary vessels: Medullary cavity Cortical vessels: Centrifugal Flow & Centripetal Flow

7 Hematogenous Osteomyelitis in Adult Animals Hematogenous localization in the skeletons of adult animals is uncommon Rare monostotic lesions: : Adults are generally resistant to hematogenous spread of most microbial agents Sites of monostotic lesion: : May occur at sites of chronic injury and repair,, e.g. hip dysplasia, spondylosis. Rare polyostotic lesions: Hematogenous spread from chronic sites of infection often located in internal organs, e.g. liver, lungs, uterus, etc. or in immunocompromised or debilitated individuals

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9 Histopathology of a Biofilm Protecting Bacteria from Inflammatory Cell Exudate

10 Histological Appearance of Osteomyelitis Acute (left): Necrotic bone and bone marrow, neutrophilic exudate and bacteria in biofilm. Biofilm hides bacteria within cavities within in bone. Chronic (right): Osteoclasts remove dead bone, chronic exudate that also contains neutrophils and poorly vascularized dense fibrous tissue.

11 Importance of Curettage in Treatment of Osteomyelitis Must remove necrotic bone and adipose tissue containing bacteria or fungi that are being protected by biofilm from antibiotics and from f host inflammatory cells and antibodies

12 Osteomyelitis in a Foal

13 Polyostotic Osteomyelitis in a Foal Skeletal pattern of lesion distribution Subchondral bone sites of multiple epiphyses Metaphyseal physes of multiple long bones

14 Extension of Septic Epiphysis to Joint

15 Extension of Inflammation in Septic Epiphysis Through Articular Cartilage to Opposing Joint Surface

16 Extension of Septic Epiphysitis to Opposing Joint Surface

17 Pathogeneis of Sequestrum Formation

18 Osteomyelitis of Distal Tibia of a Young Horse Note: Sequestrum, Involucrum and Cloaca

19 Osteomyelitis in Juvenile Dog Due to Bite Wound from Cat Original ulnar cortex has become a sequestrum Thick dense reactive cuff of bone has become the involucrum Small cloaca is present near midshaft Observe growth of distal ulna since onset of infection.

20 Osteomyelitis and Joint Infection in Old Dog with Chronic Hip Dysplasia This 10 yr-old dog with hip dysplasia was chronically lame for several years but over a 4-day 4 period progressed to a nonweight- bearing lameness without any history of trauma.

21 Hematogenous Osteomyelitis in the Adult Horse (Rare focal lesions are more common than polyostotic lesions)

22 Street Nail Puncture Wound This horse who had received a digital neurectomy as treatment for chronic pain of navicular disease stepped on a nail, developed osteomyelitis but didn t exhibit pain until infection extended into i the coffin joint.

23 Nail Puncture in Heel of Nerved Horse

24 Subchondral Bone Infected by Extension from Infected Joint Through a Complete Thickness Defect in Articular Cartilage

25 Via Articular Defect from Infected Joint

26 Via Articular Defect from Infected Joint

27 Lumpy Jaw of Cattle (Mandibular( Actinomycosis) Agent: Actinomycosis bovis (Gram+ anaerobe) Pathogenesis: : Common soil contaminant on plant awn penetrates peridontal ligament> alveolitis> > osteomyelitis Site: : Cheek teeth (molars) of mandible/maxilla Lesion: Bony-walled pyogranulomas contain sulfur granules

28 Hematogenous Infectious Inflammatory Joint Disease (Left): Radial blood supply enters joint to supply synovium as well w as epiphyseal spongiosa and subchondral bone (Right): Acute synovitis with neutrophils emerging from capillaries and migrating into the joint cavity

29 Synovial Pannus A flat sheet of granulation tissue Synovial Pannus: Arises from synovium at joint capsule insertion line May arise from subchondral capillary bed beneath ulcerated articular surface

30 Histological Appearance of a Pannus

31 Severe Articular Damage Left: Chronic Strep. zooepidemicus infection in the tibiotarsal joint of a horse. Note: Severe ulcerations and erosions and thickened joint capsule Right: Macerated specimen of same lesion

32 Tendon Sheath Infection (Note: Tendons and ligaments are generally resistant to infection n unless there is a laceration) Tendon sheath infection Puncture wound or deep skin laceration-most often Extension from infected skin lesion or adjacent joint Infection of the tendon/ligament itself usually requires a laceration or puncture wound because of the dense connective tissue covering of the tendon (epitenon)) or ligament (epiligamentum( epiligamentum)

33 Extension into Surface of a Tendon by Exudate from Chronic Suppurative Tensosynovitis Border of SDF tendon of a race horse that had a contaminated corticosteroid injection into the digital sheath 2 months earlier. r. Drainage and antibiotic treatment were unsuccessful.

34 Sequela to Inflammation: Adhesions

35 Digital Sheath Infection with Bilateral Osteomyelitis of the Proximal Sesamoid Bones of the Horse

36 Digital Sheath-Proximal Sesamoid Infection Number: 7 lame horses having 8 paired lesions Breed: Age: Site: TB-3; QH-3; Pinto-1 3yr-3 7yr-2 10yr-1 15yr-1 Forelegs: RF-4; LF-2 Hindlegs: : RH-6; LH-4 Signs: 2/5-5/5 5/5 (mean= 4/5) lameness

37 Digital Sheath+/-Proximal Sesamoid Infection

38 Digital Sheath-Proximal Sesamoid Infection

39 Digital Sheath-Proximal Sesamoid Infection Idiopathic etiology. Vascular supply to axial surface is an insignificant one Possible that chronic microdamage to the insertion line of the intersesamoidean ligament of some horses stimulates repair and new vessels that predispose to localization of bacterial emboli?

40 Digital Sheath-Proximal Sesamoid Infection

41 End Topic 5