- See:
Preparation for Proximal Tibial Cut:
- Discussion:
- intrameduallary & extrameduallary systems are available for aligning the
proximal tibial cut;
- IM system is less accurate, particularly when tibia has varus bow and may lead to excessive cement column;
- ref:
Extramedullary versus intramedullary tibial alignment guides for total knee arthroplasty.
- Application:
- knee is maximumly flexed w/ tibia distracted anteriorly & stabilized;
-
proximal jig application:
- proximal guide is affixed in center of interspinous eminence of plateau;
- proximal platform of tibial cutting guide conforms to the curved shape of the anterior cortex of the tibia;
- this allows the cutting platform to fit snugly up against the tibial cortex and improve the accuracy of the resection;
-
depth of tibial cut
- tibial stylus is used to determine the exact level of resection;
- removable stylus protrudes from top of platform and telescopes up & down in 2 mm increments to help the surgeon plan the level of resection;
- measurement off the lesser involved plateau:
- arms of platform are positioned against anterior tibial cortex at level 4-6 mm distal surface of the less involved tibial cortex;
- upper platform is adjusted so stylus rests in center of condyle;
- measurement off the more involved plateau:
- if resecting to 0 deg on deficient plateau results in > 10 mm of resection from opposite plateau, deficient side should be augmented
w/
bone grafts or modular metal wedge;
-
posterior slope
- both 0 deg and 5 deg cutting blocks are available in most systems;
- inaddition the cutting block assembly can be slanted posteriorly upto 5 deg, by moving the distal rod attachment anteriorly;
- Centering the Jig Assembly:
- because anatomic proximal tibia is generally in 3 deg of varus & because recommended resection angle is 0 deg, more bone is typically taken from lateral condyle;
-
centering the jig on the upper tibia:
- remember that jig systems fitted to anterior surface of proximal tibia will have a tendency to align in excessive
internal rotation because of
the everted patella tendon laterally;
- avoid tendency to internal rotation, center the jig between the intercondylar tibial spines and center it on the medial 1/3 of the tibial tubercle;
-
centering the jig on the tibial shaft:
- when properly oriented, guide is aligned w/ anatomic
mechanical axis of tibia,
and in almost all it parallels the anterior crest of the tibia;
- tibial alignment rod is inserted into distal femoral cuttng guide, and the knee brought into full extension;
-
centering the jig at the ankle:
- guides usually have centering device to localize distal portion of guide at center of ankle (point
slightly medial to intermalleolar axis;
- middle of tibia is approx 3-5 mm medial to the midpoint of ankle;
- mediolateral alignement is approx parallel to long
axis of tibia, but as lateral mallelous is more
prominent, bisecting trans-malleolar axis will prejudice the cut slightly into varus;
- compensation is made by translating lower assembly medially so as to align it w/ center of
talus, which at transmalleolar plane, is at interval between
EHL &
EDL or palpable anterior crest of distal tibia;
- at the ankle, adjustments to alignment can be made in two planes:
- by sliding device away from the ankle,
posterior slope can be applied to the tibial plateau resection;
- by sliding device medially & laterally at ankle, final adjustment can be made to centralize
distal alignment over center of talus & minimize chance for varus inclination of cut;
- Securing the Jig:
- a drill is inserted thru the proximal tibial cutting jig in preparation for insertion of fixation pegs;
- if fixation pins are inserted without prior drilling, then the pins will diverge instead of remaining parallell, which will prevent subsequent adjustment
of the cutting jig (if it is needed at the end of the case);
- Complications: Varus Positioning of Tibial Tray
Extramedullary versus intramedullary alignment guides in total knee arthroplasty.
Accuracy of intramedullary versus extramedullary tibial alignment cutting systems in total knee arthroplasty.
Extramedullary or intramedullary tibial alignment guides: a randomised, prospective trial of radiological alignment.
The extramedullary guide of the proximal tibia resection should be seen straight in front during total knee arthroplasty.
- Johnson and Johnson
