- Techique:
-
preparation and exposure for the proximal tibial cut:
- hyperflexion of the knee to allows the vessels to fall more posteriorly;
- curved knee retractors are positioned anterior to mid-coronal plane, so that the patella tendon and the MCL will not be injured;
- inadvertent transection of the lateral patellar tendon may occur w/ inadequate retraction during the proximal tibial cut;
- a blunt tipped curved Homan retractor may be placed behind posterior tibia and levered off of distal femur,
which allows tibia to be translated anteriorly;
-
extramedullary guides:
-
depth of the tibial cut (avoid
lowering of the joint line)
-
posterior slope:
-
rotation of tibial component:
- mechanisms can be used to avoid tendency to internal rotation;
- look down on tibial plateau & cutting jig w/ knee in flexion;
- face of jig should be parallel to plane of the femoral condyles;
-
plane of resection of the mechanical axis:
- after fixing tibial cutting jig in place, gentily flex and extend knee while watching that axis of cutting jig is parallel to axis of rotation of knee;
- current techniques involve making the tibial cut parallel to the tibial anatomic axis (and cutting distal femur at 5-7 deg to its
anatomic axis);
- advantage of this technique is that it reduces the probability of inadvertent excessively
varus
cut and thus the likihood of varus alignment of the limb;
- as its easier to cut right angles than 3 deg off right angle &
varus error in tibia is most common error w/
significant implicantions, most techniques call for resection of upper tibia at 90 deg to its long axis;
- valgus errors are well tolerated while varus errors are not;
- original PCA technique involved making the proximal tibia in 3 deg of varus in relation to its longitudinal axis;
- this means that distal femoral cut must be approx 9 deg of valgus in relation to
anatomic axis of femur
inorder to achieve an overall
mechanical axis of 0 deg;
-
hazards:
- peroneal nerve:
- at the level of tibial bone resection, the common peroneal nerve lies superficial to the lateral head of the gastrocnemius;
- mean distance from the bony posterolateral corner of the tibia to the nerve was 1.49 cm, with no distance less than 0.9 cm.
Analysis of the bone surface area in resected tibia. Implications in tibial component subsidence and fixation.
Effect of a cooled saw blade on prosthesis fixation. Randomized radiostereometry of 33 knee cases. S Toksvig-Larsen Acta Orthop. Scand Vol 65: 1994. p 533-537.
On the problem of heat generation in bone cutting. Studies on the effects on liquid cooling. S Toksvig-Larsen. JBJS. Vol 73-B.(1) 1991. p 13-15.
Arterial complications of total knee replacement. The Australian experience.
Injury to the popliteal artery and its anatomic location in total knee arthroplasty.
