43.internal fixation Flashcards
(46 cards)
type of implant used for complete anatomic reconstruction
when anatomic reconstruction (exact rebuilding) of a fracture is achieved, the rigid implant in place is a NEUTRALIZATION implant (shares or neutralized the forces being borne by the bone)bone supports fixation = fixation supports bone
type of implant for animals without anatomically reconstructed fractures in which you aim to achieve rigid fixation of implant > load on bone
Buttress/bridging carries all of the weight and resists all forces applied to the bone(ILN, plate rod, lengthening plates)
anatomic reconstruction vs biological osteosynthesis in terms of bone healing
anatomic recon –> primary healing (AO style)biological osteosynthesis –> secondary healing
fractures suitable for anatomic reconstruction
- ARTICULAR FRACTURES2. transverse3. short oblige4. long oblique5. minimally comminuted (lg frags)
principles of biological osteosynthesis
- indirect fracture reduction w limited surgical approach and disturbance of the fracture hematoma (OPEN BUT DO NOT TOUCH or CLOSED/MI)2. fracture stabilization using bridging osteosynthesis (less rigid)3. limited reliance on secondary implants4. limited use of bone grafts
Minimally invasive osteosynthesis main limitation
no direct observation of fracture segmentsmay need intraop fluoroscopically
tensile strength of orthopedic 316 L Stainless Steel Wire
tensile strength is related to cross sectional area = pi r squareddoubling radius, increases strength 4 fold
weakest point of a wire
weakest point of a wire is usually associated with the method used to secure it in generally, larger diameter wire has a higher knot strength
4 methods orthopedic wire is used
- tension band2. cerclage3. hemicerclage4. interfragmentary wire
relative strength of 18, 20, 22 gauge orthopedic wire
18 g 1.020 g 0.62 x22 g 0.36 x
twist, single loop and double loop knots and load resisted before loosening
twist–tension and secure at same time 260 Nsingle loop–wire tensioner used; wire is secured by bending 260 Ndouble loop– wire tensioner used; wire is secured by bending 666 N
twist, single loop and double loop knots—how do they loosen
twist–untwistsingle loop/double loop–unbend
based on mechanical studies, how many twists are necessary to maintain tension and produce a secure knot
1 (can cut it short)–generally recommend (AO) keeping 2-3 twistsdo not push down/flatten–will loosen
T/Fthe peak load resisted without regard to deformation is superior for twist knots
True (pg 579)
T/Fthe double loop cerclage generated more tension than both twist and single loop and was able to resist greater load before being classified as loose (30 N)
TRUEdouble initial 300-500 N resist 666 N before loosensingle initial 150-200 N resist 260 N before loosentwist initial 70-100 N resiss 260 N before loosen
T/Fresting tension of cerclage drops below 30 N (considered loose) with only 1% collapse of a diameter structure
TRUEcerclage cannot be placed in areas that may collapse
alternative material to routine orthopedic wire for cerclage
multifilament cable—strongnot flexible therefor can’t knot; need crimps or clamps to secure
fracture type that cerclage is MOST effective for
long oblique/spiral (fracture 2.5-3x diameter of bone)at LEAST 2 wires if not MOREspaced btwn half and the diameter of the bone apartperpendicular to fracture line (skewer pin if needed)
pins resist bending base on their area moment of inertia
area moment of inertia = radius to the fourth powerincrease radius by 2; increase AMI by 16
general recommendation for pin width of medullary cavity when used ALONE
70% medullary cavity aloneif plate rod decrease to 35-40% not to exceed 50%
dynamic vs cross pinning technique
some rotational stability can be achieved with pins placed separate from each other at the level of the fracturedynamic pins: Rush pins (do not penetrate opposite cortex)cross pins: penetrate opposite cortex (greater stability)
forces resisted with ILN system
bending, rotation and axialnot used in the radius
biomechanial advantage to ILN systems
–placed within neutral axis of the bone (experience direct axial compression during wt bearing, not bending)–locking (provides stability in torsion and compression)–large area moment inertia (radius to the fourth)
compare ILN systems vs plate biomechanically
plates are eccentrically placed compared to neutral axis of bone, prone to bending, AMI thickness to the third power–all predispose plate to fail at lower loads vs ILNILN placed within neutral axis of bone, resist compression, lock and hi AMI radius to the fourth power; risk of implant failure with ILN is lower than plate
