Week 4 Flashcards
Explain the theory from Frost about mechanostat theory.
Mechanostat is a term describing the way in which mechanical loading influences bone structure by changing the mass and architecture. Bone turnover is depending on the amount of strain.
It has phases:
- Disuse: < 800μStrain: Remodeling (bone adaptation and bone repair) Bone mass and bone strength is reduced.
- Adapted State: 800 - 1500μStrain: Remodeling (bone repair) Bone mass and bone strength stays constant (homeostasis: bone resorption=bone formation).
- Overload: > 1500μStrain: Modeling (bone growth): bone mass and bone strength is increased.
- Fracture: > circa 15000μStrain: Maximum elastic deformation exceeded, causing bone fracture.
What is the effect of:
- Overloading
- Unloading
- Normal loading
What is the effect of:
- Overloading: bone formation
- Unloading: bone loss
- Normal loading: mechanically induced bone formation + loss
To keep bone, we need to load it dynamically. Both the amount of strain & the loading cycles is important.
What are the 3 types of animal experiments that are carried out often?
- Overloading: Turkey ulna (forearm) loading, sheep ulnar osteotomy (remove a part of the bone), rat ulna/tibia loading, rat exercise backpack.
- Unloading: tail suspension, rat neurectomy (nerve is blocked).
- High-frequency loading: Turkey ulna high frequency loading, turkey whole-body vibration, sheep whole-body vibration, human whole-body vibration.
Bone fractures=
Can be the result of … or …
Bone fractures= medical condition in which there is a damage in the continuity of bone.
Can be the result of high force impact/stress, or a minimal trauma injury as a result of certain medical conditions that weaken bone.
What are 4 signs/symptoms of bone fractures?
- Deformation
- Painful
- Swelling/bruising
- Loss of function
What are the 4 categories to classify bone fractures?
- Mechanism: traumatic, pathologic, periprosthetic.
- Soft tissue involvement: closed (skin intact), open (wound), clean vs contaminated.
- Displacement: translated, angulated, rotated, shortened.
- Fracture pattern: comminuted, impacted, greenstick, oblique.
What are the two types of fracture healing?
What are the two types of fracture healing?
- Primary/ direct healing
- Secondary/ indirect healing
What are the 3 phases in fracture healing and their duration?
- Inflammatory phase; hours-days
- Reparative phase; days-weeks
- Remodeling phase; months-years
External fixation=
Internal fixation=
External fixation= surgical treatment used to stabilize bone and soft tissues at a distance from the operative or injury focus.
Internal fixation= operation in orthopedics that involves surgical implementation of implants for the purpose of repairing a bone (stainless steel, titanium).
Explain primary/direct healing
if the healing can happen internally, by the normal bone healing process (osteonal/ internal bone healing remodeling). Only with absolute stability of the fracture!
Explain secondary/ indirect healing
with callus formation, similar to embryological bone development (includes intramembranous and endochondral bone formation). With relative stability (flexible fixation methods).
Explain the first phase of fracture healing
- Inflammatory phase: Starts with fracture and granulation tissue formation.
Fracture > blood vessels rupture > blood cells in tissue > blood vessels constrict (bleeding stops in minutes) > hematoma formation (hours) > cells die winning the clot (h-days) > fibrobraslts survive and proliferate > form granulation tissue.
Granulation tissue forms on the surface of wounds and acts as a wound filler. Fibroblasts produce matrix that consist of loose connective tissue (collagen). Tiny blood vessels grow in and bring in cells of the immune tissue (which clean up any remaining damage).
Explain the 2nd phase of fracture healing
- Reparative phase: soft and hard callus formation.
Soft callus formation:
Via intramembranous ossification (woven bone, collagen is not well orientated). Granulation tissue is replaced by fibrous tissue and fibrocartilage. Ingrowth of blood vessels (from periphery towards center).
Hard callus formation:
Starts when the fracture ends are linked by soft callus. Intramembranous ossification continues. Soft tissue undergoes endochondral ossification (begins at pheriphert, where strain is lowest > reduction of strain centrally > turns into bony callus). Initial bone brigde away from original cortex. By endochondral ossification, the soft tissue gap is replaced by woven bone and joins the original cortex.
Explain the 3rd phase of fracture healing
Remodling phase: remodeling to original bone contour (incl. the medullary canal).
Woven bone is replaced by lamellar bone (via surface erosion and osteonal remodeling). Can a few months up to several years. Often, patients can use their bone again after the reparative phase. But ‘real’ bone is only back after the remodeling phase.
