Abstract
Instruments are crucial to performing a knee replacement however they must be used properly.
Cutting guides may be solid blocks or slotted blocks. For the former the blade must be held on the surface of the block. A surgical peanut pressing the blade against the block helps. Slotted guides obviate this problem however the saw blade should be chosen so as not to bind in the slot, nor to be so thin that the blade wobbles in the slot. The most difficult resection is the posterior femoral resection. Because of the problem of holding a saw blade up against a cutting block, a slotted guide is best in this area. The cut should be checked twice since the hard bone in the posterior femoral condyles may cause the blade to deviate and result in an under-resection.
When blocks or guides are pinned to bone they should be inserted first through the convex side of the deformity (on the lateral side of a varus knee for instance). Often the bone on the concave side of a deformity is sclerotic and the pin may deviate changing the position of the block. A headed pin on the convex side will stabilise the block so that this will not occur.
Intramedullary femoral alignment rods should extend up to and slightly through the isthmus. The entrance point is NOT in the midline but slightly medial to this (it should be templated on the preoperative x-rays). Extramedullary guides for hip must be referenced from the femoral head; normal clinical evaluation for this is inaccurate and preoperative radiographic evaluation is usually necessary.
Intramedullary tibial alignment rods should enter at a point slightly anterior and medial to the midpoint of the tibia and should extend down to the level of the old distal tibial epiphyseal plate. The preoperative x-ray should be evaluated to ascertain the diameter of the canal. In some patients with a small intramedullary diameter a thinner rod may be necessary.
An extramedullary tibial alignment guide should be centred slightly medial to the mid malleolar point distally. In the lateral plane the reference landmark is the fibular shaft. A rod parallel to the fibular shaft will also be parallel to the midaxis of the tibia.
When any intramedullary guide is used the canal must be aspirated and washed to minimise the potential of fat embolisation. The rod should be fluted, the entrance hole large, and the insertion rate slow so as to avoid pressurisation of the medullary contents.
The abstracts were prepared by Mrs Dorothy L. Granchi, Course Coordinator. Correspondence should be addressed to her at PMB 295, 8000 Plaza Boulevard, Mentor, Ohio 44060, USA.
