Bones II Flashcards
In situations of bone loss, ex: ostopenia, osteoporosis, bone lysis, what takes up the newly created space?
- existing tissue expands or loosens
- may include fluid ex: serous atrophy of fat
- replaced by fibrous tissue
Two concepts Allen likes:
- in order to diagnose a specific disease, you have to know that the specific disease exists
- the diagnosis of a bone disease requires the recognition of a pattern of bone loss, bone production, or both
Bone is susceptible to the same pathologic processes as ither tissues & organs, what are these?
- alterations of growth (aplasia, hypoplasia, atrophy, hyperplasia, neoplasia)
- circulatory disorders (hemorrhage & ischemia)
- inflammation & repair
- degeneration & necrosis
Sometimes in bone the pathologic processes like other tissues are overshadowed by underlying & more intuitive concepts concerning the pathogenesis of a lesion or disease: examples of this?
- trauma leading to a fracture
- nutritional or metabolic disorders leading to so-called metabolic bone disease
- like other organs, bone has a limited range of reactions to injury & mechanisms of repair
Which two processes that usually occur together are involved in the reaction of bone to injury?
- removal of damaged bone (resorption or lysis)
- production of new bone
- the proportion of these two reactions will vary
Injury to the periosteum (& endosteum) will usually be followed by?
formation of periosteal (& endosteal) new bone
Bone density will change in response to?
change in use
How is bone related to calcium & phosphorus?
- bone is a body’s main reservoir of calcium (~99%) & phosphorus (~85%) & is involved in plasma calcium & phosphorus homeostasis
- therefore, bone is affected by any disease involving abnormal calcium & phosphorus metabolism, including disorders of nutritional origin
What is a fracture?
- a break or rupture in a bone
- a common occurrence
- represents a physical discontinuity in a bone which results in instability & pain
- which may manifest as impaired movement (lameness, immobility, or recumbency)
What kind of fracture is this?
Greenstick
What kind of fracture is this?
spiral
What kind of fracture is this?
Comminuted
What kind of fracture is this?
Transverse
What kind of fracture is this?
compound
What is happening here?
vertebral compression
- What is the pathogenesis of fractures?
fractures occur under one of two circumstances:
1. either a normal bone fractures under excessive force - TRAUMATIC FRACTURE
2. or an abnormal bone fractures under normal force - PATHOLOGIC FRACTURE
What is fracture repair?
the healing of a fractured bone
What is the process of fracture repair?
- can be conveniently divided into 5 phases
- but important to appreciate that the divisions are arbitrary, they overlap & are concurrent, they may occur at different rates in different areas of a fracture, & they represent a summary of a complex & incompletely understood process
What are the 5 phases of fracture repair?
Phase I - Injury & Inflammation
Phase II - Organization of the Hematoma
Phase III - Callus formation: External & internal callus
Phase IV: Callus remodeling
Phase V: Callus modeling
What is phase I of fracture repair?
Injury & Inflammation
- when bone is fractured there is tearing of the periosteum & endosteum, rupture of blood vessels of the bone, & injury to surrounding soft tissue
- these events result in ischemic necrosis of bone at the fracture lines & associated marrow, formation of a hematoma, & inflammation
- these changes promote the immediate activation & recruitment of platelets, macrophages, & other leukocytes, all of which release growth factors
What is phase II of fracture repair?
Organization of the hematoma
- w/in 24-48 hrs, the hematoma btwn bone fragments begins to organize
- undifferentiated mesenchymal cells of the periosteum, endosteum, & bone marrow are activated, proliferate, & invade the hematoma
- similarly, endothelial cells proliferate to form new blood vessels, aka, neovascularization
What is phase III of fracture repair?
Callus formation: internal & external callus
- mass of exudate & CT that forms around a fracture during repair is called a callus or primary callus
- there is an external callus & an internal callus
- the external callus is usually more substantial (& easily noticed) w/ the periosteum making an important contribution
- where the blood supply is adequate & the oxygen tension is high (away from the fracture gap), undifferentiated mesenchymal cells become osteoblasts that produce (de novo) woven bone
- where the blood supply is poor & the oxygen tension is low (at or near the fracture gap), undifferentiated mesenchymal cells become fibroblasts & chondroblasts
- the cartilage produced by the chondroblasts is later REPLACED by woven bone via endochondral ossification
- the internal callus is produced by the endosteum & is formed in the same manner as the external callus
- it is usually smaller than the external callus & may temporarily occlude the medullary space
How quickly does callus formation occur?
- may begin w/in 24 hrs
- woven bone may be visible MICROSCOPICALLY as quickly as 36 hrs after fracture, but may not be visible RADIOGRAPHICALLY for 2 weeks
- under favourable conditions, it takes 4-6 wks for the primary callus to be replaced by a so-called bony callus
What causes the time for callus formation & remodeling to vary?
- animal’s age & health (including nutrition), the fracture type & location, associated injuries & infection, & the method & quality of fixation, if any
What is fixation?
- refers to fastening something firmly in position (holding something in a fixed position)
- in orthopedic surgery, fixation refers to the immobilization of the parts of a fractured bone
- fixation can be external (splint or cast), internal (various metal devices, or both
What is phase IV of fracture repair?
Callus remodeling
- w/ time, woven bone is replaced w/ lamellar bone, compact bone is formed in the cortex, & cancellous bone is formed in the metaphysis & diaphysis
- since resorption & formation are about equal, this represents remodeling
What is this and what does it do?
- cutting cones perform osteoclastic tunneling
- series of osteoclasts at the front of the cone & behind it are osteoblasts that lay down new bone
What is phase V of fracture repair?
Callus modeling
- final phase of fracture repair results in restoration of the fractured bone to its original form (size & shape) & function (or as close as possible)
- specifically, callus modelling involves the reduction in size of the callus & sculpting of the bone in response to the stresses of weight bearing & muscle pull
- this phase make take months to years
What does the end result of fracture repair look like?
What is the tissue & stability at the repair site at each of these times?
What are the complications of fracture repair?
nonunion, delayed union, malunion
What is nonunion?
failure of the fragments of a fractured bone to heal - to become fused bone
What causes nonunion?
- inadequate blood supply
- instability (movement)
- infection
- presence of necrotic fragments of bone or soft tissue w/in the fracture gap
- pathologic fractures rarely heal w/o intervention
What is a delayed union?
- describes a fracture that takes longer than normal to heal
- since the time required for fracture healing can be highly variable, the criteria for the diagnosis of a delayed union are also variable
When does a delayed union become a non-union?
- it is often difficult to differentiate btwn a nonunion & a delayed union
- some authorities define a nonunion as a fracture that fails to display any progressive changes - usually using radiography - for @ least 3 months after the time when normal fracture healing would have occurred
- others believe that a fracture that has not healed w/in 6 months of the injury will likely remain unhealed (w/o intervention) & is, therefore, defined as a nonunion
What is malunion?
- (mal is a prefix meaning ill or bad)
- refers to a fracture that has healed, but in an abnormal alignment (ex: results in a deformed limb or other structure)
- malunions can result in a shorter limb due to the fusion of overriding fragments; axial deformities (or crooked/bent limbs); & rotational deformities (or twisted limbs)
What is the physis?
- site of longitudinal growth (& sometimes growth in other directions) in endochondral bones
- it’s a temporary structure composed of hyaline cartilage
- it’s widest when growth is most rapid & becomes narrow as growth slows
- growth stops when the physis is entirely replaced by bone
- this is referred to as closure of the growth plate & marks skeletal maturity
What are 5 disorders associated w/ the physis?
- physeal/growth plate fractures (Salter-Harris fractures)
- growth retardation lattices
- growth arrest lines
- premature closure
- osteochondrosis/ osteochondritis
What are growth plate or physeal fractures?
- b/c the physis is composed of cartilage, it is physically weak compared to bone & can be more easily injured
- since the physis is the site of longitudinal growth, injury to the physis can affect longitudinal bone growth
what is the Salter-Harris classification?
- classifies growth plate injuries, including fractures, was 1st described for humans in 1963 & has been widely accepted & applied in both human & vet med
- classification groups physeal injuries into 1 of the original 5 types (or 4 additional types that are rare & have been added since)
- this classification system is useful in communicating the nature of an injury & predicting prognosis
- as the number associated with the type of injury increases, the prognosis for a return to a functional, straight, pain-free limb decreases
I - (S) - straight across (separated or slipped)
II - (A) - above (or away from joint)
III - (L) - lower (into joint)
IV - (TE) - through everything (both/all)
V - (R) - rammed (crushed)
What are capital femoral physeal fractures of Fe?
- fracture through the physis of the head (caput) of the femur (ex of Salter-Harris type I fracture) is a surprisingly common lesion in Fe
- some believe this condition is a traumatic fracture
- most affected Fe are young (4-24 months), overweight, neutered males
- histologically, the fractured physis is thickened w/ irregularly arranged chondrocytes, which gives rise to the term physeal dysplasia
- pathogenesis of this condition is uncertain
- however, there is some evidence that certain physes of Fe that are neutered before 6 months of age - males more common than females - remain open longer than sexually intact Fe
- (the normal age at the time of closure of the proximal physis in Fe has reported to be about 9 months (or 270 days), w/ a range of 210 to 290 days)
- this has led some to believe that early neutering delays the closure of the proximal femoral physis, may lead to physeal dysplasia &, as these Fe become stronger & heavier, predisposes these Fe to a “slipped” capital femoral physis
- btwn 24% & 38% of affected Fe will develop bilateral fractures
What are growth retardation lattices (GRLs)?
- typically detected in aborted, stillborn, or neonatal animals
- thin lines to wide bands of increased bone density (osteosclerosis) in the metaphyses, parallel to the physes (but can also be seen w/in epiphyses)
- represent areas of impaired osteoclastic activity leading to the retention of LONGITUDINAL trabeculae of primary spongiosa
- GRLs is a poor term b/c growth need not be retarded for the lattices to appear
- THE LESION IS A FAILURE OF REMODELING
- GRLs are a nonspecific change (are lesions that can be caused by a variety of insults)
- a few known causes of GRLs include in utero infection of fetal calves w/ Bovine Viral Diarrhea (BVD) virus; canine distemper virus infection in growing puppies; & exposure to lead in any developing or growing animal
What are growth arrest lines (GALs)?
- are typically detected in young, growing animals
- GALs are also linear lesions in the metaphysis parallel to the physis
- however, they represent TRANSVERSE (vs. longitudinal) trabeculae of bone & are a result of a period of retarded or arrested longitudinal growth
- layer or layers of transverse trabeculae are carried into the metaphysis if growth resumes
- any debilitating disease of general malnutrition can retard growth & produce GALs
What is the importance of recognizing GRLs & GALs?
- these lesions are the consequence of a chronic, underlying disease condition, not an acute or spontaneous change
- need to go looking for underlying cause (pneumonia, starvation, parasitism)
What is premature closure of the physis?
- closure may be partial (focal) or complete (diffuse)
- if the closure is focal, it results in an altered shape of a growing bone
- if the closure is complete, it results in abnormally short bones
- trauma, vitamin A toxicity, manganese deficiency, & radiation injury known causes
- there may be others
- damage to epiphyseal vessels nourishing the proliferative zone of the physis can also cause localized physeal closure
- feeding moldy cereal straw to pregnant cows has produced this lesion & a disease known as congenital spinal stenosis in western Canada
- What is osteochondrosis or osteochondritis?
- THE FOCAL OR MULTIFOCAL FAILURE (OR DELAY) OF ENDOCHONDRAL OSSIFICATION RESULTING IN LOCALIZED THICKENING OF HYALINE CARTILAGE
- may occur at the physeal or articular areas of endochondral ossification
- pain & lameness may result b/c the retained cartilage is not as stable as bone & subject to injury
- clinically, osteochondrosis or osteochondritis are terms used to ID a variety of manifestations & sequelae of the presence of the thickened cartilage
What is the etiology of osteochondrosis?
- there appears to be multiple & interrelated factors which are associated w/ osteochondrosis & the factors at play may depend on the sp & location of the lesion
- genetic, hormonal, nutritional, metabolic, & mechanical factors are all thought to be involved
What are some examples of osteochondrosis that are treated like specific diseases?
Some forms of osteochondrosis, in certain spp, & at certain locations, are treated like specific diseases:
- ununited anconeal process of Ca - is the failure of the anconeal process (a secondary center of ossification) to fuse w/ the ulna
- epiphysitis or physitis (more accurate) in Eq - is a clinical term, but an inaccurate pathologic diagnosis, for a generalized disease of young horses characterized by thickening & dysplasia of physes of certain long bones
- osteochondrosis of swine - was relatively common at one time but is now rare. when used in relation to Sw, osteochondrosis is a generalized condition that is most common & easily diagnosed around joints
