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- 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 patella tendon and MCL will not be injured;
- inadvertent transection of the lateral patellar tendon may occur w/ inadequate retraction during the proximal tibial cut;
- 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:
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- 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 tibial cut parallel to the tibial anatomic axis (and cutting distal femur at 5-7 deg to its anatomic axis);
- this 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 to have overall mech 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.
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Injury to the popliteal artery and its anatomic location in total knee arthroplasty