Fracture fixation devices with threaded screwholes, which allow screws to thread to the plateand function as fixed angle device. Any plate that allows the insertion of fixed angle orangular stable screws or pegs can be used as alocking plate.
Follow the principle of ext.fixator INTERNAL FIXATOR Stability is maintained at angular stable screwplate interface. Single beam construct. Pullout strength of locking screws higher than thatof conv. screws
Has a combination hole wherebyconventional cortical screws can be appliedto achieve compression or locking headscrews can be applied for angular stability. No loss of primary or secondary #reduction. No necrosis (stress shielding) under theplate. Preservation of periosteal blood supply decrease in infection.
Increased stability, less soft tissue dissection enhanced # healing Strain at the # site is optimized so secondary bonehealing with callus formation. Allows the use of unicortical screws Higher resistance to infection, faster union andlower refractures.
More expansive More difficult to use to help achieve an adequatereduction.[speciality p] Do not improve reduction and cannot help apoorly reduced # fracture to heal.
Fractures associated with higher risk of loss ofreduction and plate or screw failure. Unsolved or problem fractures1. Comm. Intraarticular #2. Short segment periarticular #3. Osteopenic bone #.
According to mode of application of the plate. All indications are based on this four principles.1. Compression P2. Neutralisation P3. Bridging P4. Combination P
Mode of application compression or neutralizationprinciple.Compression P osteoporotic forearm #Neutralisation P osteoporotic ankle #. [first lagthen lock].
Mode of application bridging or combinationprinciple. Proximal & distal humerus, distal radius, proximaltibia.
.Applied , according to Combination principle.Lag screws for articular fixation, locking headscrews for metaphyseal bridging.Distal femur & tibia.
4. Comminuted shaft fracturesmode of application bridging principle [lockedinternal fixator].Shaft of femur, tibia, humerus.
Using locked internal fixator technique for simple #that requires interfragmental compression. Using minimally invasive percutaneous platefixation tech for simple fractures [violates conceptof # gap width in relation to strain nonunion.
Using locking internal fixator tech for fixingdisplaced intraarticular # [Malunion, arthritis]. Relatively C.I for # which can be satisfactorilyfixed with conventional plates.
Secondary loss of reduction with varus collapseas result of inadequate screw length andinappropriate fixation of locking head screws inplates.
Failure of interface between locking head screwsand threaded plate holes occurs if screws areinserted imperfect angle and torque limiting screwdrivers not used.
Increased strain in a construct with too muchstiffness and exposure to high rotational forces willlead either to breakage of plate in D.C part ofcombihole which is the weakest part of theconstruct or more rarely failure at screw plateinterface with breakage of screws.
Locking screws cannot recede back wards as aconventional screws can.So if longer screws areused in the head part of the periarticular # ,chanceof protrusion of the screws in to the Jt.
Formal preop planning is a must.1. Sequence of screw placement2. Length of screw3. Position of plate4. Surgical approach.• Help to reduce the guess work and increase thetechnical success
Correct positioning of the Pt esp, in MIPPOtechnique. Surgeon should also have preop plan for #reduction.
L.P offers minimal opportunity for screwangulation. [> 5* angulation failure. Screw should be perfectly lined lined up with theaxis of the screw threads in the plates. [otherwisecross threading or cold welding will occurs] Malaligned screw threads loose screws andloss of reduction.
In order to achieve a large area of stressdistribution on the plate ,at least three or fourholes should be left empty, at the level of the #.] Unicortical Screws should be of optimal length asshort s. failure, long s. push off from the farcortex thus destroying the tapped, near cortex.
Bicortical or unicortical self drilling / Self tapping or self taping Pullout resistance of unicortical locking screws isalmost identical to that of similar diameterbicortical conventional screws and about 70% ofbicortical L.S.
Locking screw heads are less likely to break sincedifference between core diameter of the screwshaft head is much smaller than conv.S. Nevertheless they can break in case of chronicinstability and increased strain as a result ofrotational forces.
Usage of torque limiting screw device so threadscannot be stripped or over-tightened. Even thenhappens in MIPPO due to difficulty in judging theorientation without direct visualization. Purchase of the screw in the bone cannot be felt,L.S always feel tight.
Two factors are essential in decision making;1. Quality of the cortical bone2. Extent of rotational forces applied to the corticalbone.
In a good quality cortical bone, the working lengthof a Unicortical screw provides sufficient pulloutstrength. In metaphyseal and osteoporotic ,due to thincortex always better to use bicortical screws.
As a general rule self drilling / self tapping screwsare used in a unicortical fashion , for MIPPOtechnique. Self drilling screws [sharp tips] can causeneurovascular damage or soft tissue damageacross the far cortex.
Bicortical screws should be used for # which areexposed to high rotational forces like SOH.
For long bone comminuted #, B.P used must be oflonger length with fewer screws to used. For periarticular # few screws are needed fordiaphysis and more screws are needed forarticular surface recon.
In general length of the plate should be two timesthe length of the fracture zone. Screws should be evenly spread and ideally thereshould be one empty hole between each pair ofholes filled with screws. To avoid local stress conc, 3 / 4 holes should beleft empty at the level of #.
Locking plates, particularly the specialized so-called all-locking plates, require an approach tofracture reduction that is completely different fromwhat is already practiced.• One should consider initially using combinationplates, that allows traditional reduction tech.