- Discussion:
- see:
-
tibial component
-
extra-medullary cutting guide;
-
preparation for proximal tibial cut
-
posterior slope
-
depth ofproximal tibial cut
- this cut is made at right angles to anatomcial axis of tibia;
- proximal tibial cut is made 2 mm below the anterior surface of the more involved side;
- in knee with fixed
varus deformity more bone is resected from lateral tibial plateau than off the medial tibial plateau;
- alternatively, the resection can be based off the less involved side;
- this cut should be < 5 mm below tibial plateau because tibial cancellous bone weakens rapidly as distance from the articular surface increases;
- due to complex geometries that may be present on degenerative tibial surface, it may be prudent to "eyeball" depth of proximal cut, rather than relying on stylus;
- reliance on the stylus alone may result in a inadvertently deep cut on the lesser involved side;
-
quick trial:
- if the femoral cuts have already been made (and the femoral trial is in place), insert a trial base plate
w/ an 8 mm spacer while the knee is in full extension;
- if the 8 mm spacer cannot be easily inserted (in full extension) then it is unlikely that a 10 or 12 mm spacer
will be able to be inserted (and therefore further proximal tibial resection is required);
-
consequences of excessive proximal tibial resection:
-
lowering of the joint line;
- loss of bone quality;
- quality of cancellous bone in the tibia is best in immediate subarticular area, and decreases rapidly w/ more distal resection;
- loss of surface area:
- surface area of the proximal tibia decreases w/ more distal cut;
- distal resection jeopardizes attachments of
IT band &
pes anserinus,
MCL and PCL;
-
PCL takes origin from posterior aspect of proximal tibia, so that its attachment is not lost when proximal tibia is resected just below the articular surface;
- valgus instability may result from an excessively deep resection along w/ an excessively steep
posterior slope (the later may remove the
posterior oblique ligament;
- resection more than 1 cm below original articular surface:
- cuts at this depth require
bone grafts or revision components;
- due to loss of
PCL, a
posterior stabilized prosthesis: will be required;
- in presence of severe deformity, proximal tip of fibula, normally located approx 1 cm below tibial articular surface, is good guide for the level of maximum resection;
Analysis of the bone surface area in resected tibia. Implications in tibial component subsidence and fixation.
