12 - Bone II Flashcards
What are the 4 types of pathologic processes that bone is susceptible to? (similar to other tissues and organs)
- Alterations of growth
- Circulatory disorders
- Inflammation and repair
- Degeneration and necrosis
*limited range of reactions to injury and mechanisms of repair
What are the different types of alterations of growth?
- Aplasia
- Hypoplasia
- Atrophy
- Hyperplasia
- Neoplasia
What are the 2 types of circulatory disorders?
- Hemorrhage
- Ischemia
What are the 4 generalities about the reaction of bone to injury and disease?
- 2 processes: removal of damaged bone (lysis or resorption) AND production of new bone
- Injury to periosteum (and endosteum) will usually be followed by formation of periosteal (and endosteal) new bone
- Bone density will CHANGE in response to changes in use
- Bone is effected by any disease involving abnormal calcium and phosphorus metabolism
What is the definition of a fracture?
- Break or rupture in bone
- Common occurrence
- PHYSICAL discontinuity in a bone resulting in instability and pain
o May lead to impaired movement
What is the impaired movement ‘types’ that may occur due to a fracture?
- Lameness
- Immobility
- Recumbency
Descriptive terms used in radiology and surgery
- Incomplete (green stick, hairline) vs. comminuted
- Spiral vs. transverse vs spiral vs. oblique
- Compound: fractured bone being exposed to air! (possibility of infection)
When are 2 times that fractures occur? (EXAM!)
- Normal bone fractures due to excessive force=TRAUMATIC FRACTURE
- Abnormal bone fractures under normal force=PATHOLOGICAL FRACTURE
What is fractured repair?
- Healing of fractured bone
- Divided into 5 phases
- Arbitrary (how we explain it)
- OVERLAP and CONCURRENT
- Summary of COMPLEX events
Fracture repair is divided into 5 phases
- Injury and inflammation
- Organization of the hematoma
- Callus formation: external and internal callus
- Callus remodeling
- Callus modeling
First phase of fracture repair: injury and inflammation, ‘3 events’ that occur
- Tearing of periosteum and endosteum
- Rupture of blood vessels of the bone
- Surrounding soft tissue injury
What do the 3 ‘events’ of phase I of fracture repair result in?
- Ischemic necrosis of bone at fracture lines and associated marrow
- Formation of hematoma
- Inflammation
- *promote IMMEDIATE activation and recruitment of platelets, macrophages, and other leukocytes=all release growth factors
Second phase of fracture repair: organization of hematoma
- Hematoma between bone fragments begins to organize within 24-48hrs
- Activation of undifferentiated mesenchymal (stem) cells of periosteum, endosteum and bone marrow
o Invade hemostoma - Endothelial cells proliferate to form new blood vessels =neovascularization
- *’soft’ callus
What is a ‘callus’?
- Mass of exudate and connective tissue that forms around a fracture during repair
- *Internal and external
External callus
- More substantial (easily noticed) with the periosteum making an important contribution
Third phase of fracture repair: callus formation, distant from fracture gap
- Blood supply is adequate and oxygen tension is HIGH (favourable environment)
- Undifferentiated mesenchymal cells become osteoblasts that produce woven bone
Third phase of fracture repair: callus formation, near the fracture gap
- Blood supply is poor and oxygen tension is low (‘poor’ environment (low pH))
- Undifferentiated mesenchymal cells become fibroblasts and chondroblasts
- *Cartilage produced by chondroblasts is later REPLACED by woven bone via endochondral ossification
Internal callus
- Produced by endosteum
- Formed similar to external callus
- Smaller
- May temporarily occlude medullary space
Third phase of fracture repair: callus formation
- May begin within 24 hours
- Bone production begins within 36hrs
- Radiographic evidence possible by 2 weeks
- *under favorable conditions it takes 4-6 weeks for primary callus to be replaced by ‘bony callus’
Fourth phase of fracture repair: callus remodelling
- Woven bone is replaced by lamellar bone
- Compact bone formed in cortex
- Cancellous bone is formed in the metaphysis and diaphysis
- *resorption and formation are about equal=represents remodelling
- *cutting cones performs osteoclastic tunneling (points towards the fracture)
Time for callus formation and remodelling varies with
- Age
- Health and nutrition
- Fracture type and location
- Other injuries or infection
- Method and quality of fixation, if any (ex. internal or external fixation)
Fifth phase of fracture repair: callus modeling
- Restoration of fractured bone to its original form and function
- *reduction in size of callus
- *sculpting of bone in response to stresses of weight bearing and muscle pull
- Months to years!
What are the three common complications of fracture repair?
- Nonunion
- Delayed union
- Malunion
Nonunion fracture repair
- Failure of fragments of a fractured bone to heal (to become fused with bone)
What is nonunion fracture repair commonly caused by?
- Inadequate blood supply
- Instability
- Infection
- Fragments of necrotic bone or soft issue
- Other underlying disease (pathological fracture!)
Delayed union fracture repair
- Fracture that takes LONGER than normal to heal
- *time required to heal and criteria is VARIABLE
It can be difficult to differentiate between non-union and delayed union. What are ‘2 criteria’ used to decide on a non-union?
- Lack of progress for 3 months after you expect the bone to heal (radiographically)
- Lack of healing after 6 months will likely remain unhealed
Malunion fracture repair
- Healing of fracture bone that results in abnormal alignment (DEFORMITY!)
What can malunions result in? (3)
- Shorter limb due to fusion of overriding fragments
- Axial deformities (or crooked/bent limbs)
- Rotational deformities (twisted limbs)
What is the physis a site of?
- Longitudinal growth in endochondral bones
o Injury can affect longitudinal bone growth - *Temporary structure composed of hyaline cartilage
o Weaker and more easily injured
When is the physis the widest or narrowest?
- Widest: when growth is most RAPID
- Narrowest: when growth SLOWS
When does growth at the physis stop?
- When it is entirely replaced by bone
- *closure of growth plate=MARKS SKELETAL MATRUITY
What are some of the disorders associated with the physis (5)?
- Physeal/growth plate fractures
- Growth retardation lattices
- Growth arrest lines
- Premature closure
- Osteochondrosis/osteochondritis
What can be used to classify growth plate injuries?
- SALTER-Haris classification
- 5 types
- lower the number=better the prognosis
- *useful to communicate the nature of injury and PREDICTING PROGNOSIS
SALTER-Harris classification
- S: straight across (separated or slipped)
- A: above (or away from the joint)
- L: lower (into the joint)
- TE: through everything
- R: rammed (ruined or crushed)
What is an example of a Salter-Harris type I fracture?
- capital femoral physeal fractures in cats
Capital femoral physeal fractures of cats
- Fairly common
- Trauma? But sometimes without trauma?
o UNCERTAIN PATHOGENESIS - *histologically: fracture physis is thickened with irregularly arranged chondrocytes=physeal dysplasia
Which cats are most affected with capital femoral physeal fractures?
- Young (4-24 months), overweight, neutered males (delayed physeal closure times)
o May lead to physeal dysplasia
o Open longer than normal (ex. after 7-9 months)
o 24-38% of affected cats develop BILATERAL disease
What are growth retardation lattices (GRLs) typically detected in?
- Aborted, still born or neonatal animals
What are growth retardation lattices?
- Thin to wide bands of increased bone density (osteosclerosis) in the metaphyses, PARALLEL to the physes (also within epiphyses)
What do GRLs represent?
- Areas of impaired osteoclastic activity leading to retention of LONGITUDINAL trabeculae of primary spongiosa
- *FAILURE OF REMODELLING
GRLs are a nonspecific change and can caused by a WIDE variety of insults. What are some examples?
- utero infection of fetal calves with BVD
- canine distemper virus infection in growing puppies
- exposure to LEAD in any developing or growing animal
Where are growth arrest lines (GALs) typically detected?
- Young, growing animals
- *debilitating disease OR general malnutrition can retard growth and produce GALs
What are GALs?
- Linear lesions of osteosclerosis in metaphysis parallel to the physis
o Line is because they are at RIGHT ANGLES to normal bone - Represent TRANSVERSE (vs. longitudinal) trabeculae of bone
What are GALs a result of?
- Period of retarded or arrested longitudinal growth
- *layers of transverse trabeculae are carried into the metaphysis if growth resumes
What is the importance of recognizing GRLs and GALs?
- Consequence of a CHRONIC, UNDERLYING DISEASE CONDITION
o NOT scute or spontaneous change - No ‘direct significance’ to the animal
Grossly what do GALs and GRLs look like?
*alternating patterns of increased and decreased bone lattices
If the premature closure of the physis is focal, what will it result in?
- Altered shape of growing bone
If the premature closure of the physis is complete, what will it result in?
- Abnormally SHORT bones
What are some known causes of premature closure of growth plates?
- Trauma
- Vit A toxicity
- Manganese deficiency
- Radiation
- *multiple and interrelated factors, may depend on species and location of lesion
What else may cause localized physeal closure?
- Damage to epiphyseal vessels nourishing the proliferative zone of the physis
- Feeding moldy cereal straw to pregnant cows: congenital spinal stenosis in western Canada
Osteochondrosis or osteochondritis (EXAM): definition
- Focal or multifocal failure (or delay) of endochondral ossification resulting in LOCALIZED thickening of hyaline cartilage
Where might osteochondrosis occur?
- Physeal or articular areas of endochondral ossification
o Articular-epiphyseal (AE) complex
AE complex
- At end of bone (epiphysis) there is still some growth
o Should have endocardial ossification
o When failed=chondrolysis
What might result in osteochondrosis?
- Pain and lameness
o Retained cartilage is not as stable as bone=subject to injury
What are osteochondrosis and osteochondritis used to identify clinically?
- Variety of manifestations and sequelae of presence of thickened cartilage
What is an example of osteochondrosis in dogs?
- Ununited anconeal process
o Failure of anconeal process (secondary center of ossification) to fuse with the ulna
What is an example of osteochondrosis in pigs?
- Relatively common, but now rare
- GENERALIZED condition that is most common and easily diagnosed around joints
- Ex. Toxic amounts of Vit A=full closure of growth plate in humerus
o Ex. mixing error at feed supply, polar bear liver
What is an example of osteochondrosis in horses?
- Physitis
o Inaccurate pathological diagnosis
o Generalized disease of YOUNG horses characterized by thickening an dysplasia of physes of certain long bones
