Abstract
Implants without diaphyseal-fixed stems
The femoral component is removed first. Whether the implants are fixed with cement or osteointegration, the principles are the same. The interface between the metal implant and bone or cement is freed using both osteotome and saw. All interfaces are cut loose before the implant is driven off with either a hand-held driver and hammer or slap-hammer. Driving off the femoral component before it has been completely loosened removes excessive amounts of bone or causes major condylar fracture.
The polyethylene component is removed next, and then the tibial component. If the tibial component has no metaphyseal stem, the interfaces are separated directly with osteotome and saw until the tibial component is completely loose. If the tibial component has a metaphyseal stem, it usually requires a direct approach to the stem through a tibial osteotomy to loosen the stem from the cement mantle or bone attachment. If a tibial tubercle osteotomy is used to expose the knee, direct access can be obtained through the osteotomy to expose the attached interfaces. Several cuts with the osteotome will loosen the cement from the stem and allow the tibial component to be lifted from the tibial surface. Special care is taken to ensure that the posterior portion of the tibial surface is completely loosened from the bone before final removal is done. Driving tools and slap-hammers almost never are needed on the tibial component without a diaphyseal stem.
Implants with diaphyseal-fixed stems
Well-fixed diaphyseal stems are special challenges and often require bivalve osteotomy of the metaphysis and diaphysis to gain exposure. A sterile tourniquet is an important consideration for femoral stems that likely will require bivalve osteotomy. Preserving blood supply to both sides of the osteotomy can be achieved by maintaining a medial or lateral soft tissue hinge. A drill is used to penetrate the cortex and find the end of the stem, and then the oscillating saw is used to make a longitudinal cut along the medial side of the bone past the tip of the stem. A saw cut is made transversely at this level across the anterior surface of the diaphysis. Next the lateral side of the diaphysis and metaphysis is perforated multiple times with the drill bit and curved ¼-inch osteotome, leaving the periosteal attachment intact to the anterior bone flap. The bone flap then is carefully pried loose from the anterior surface of the stem. This exposes the stem in the posterior portion of the bone. The interfaces then can be carefully separated from the stem, allowing it to be lifted from the bone.
Repair of the femur and tibia requires cables that are passed around the bone and through the soft tissue hinges of the bone flaps. Revising with stems that bypass the osteotomy is a theoretical advantage, but this is not always possible.
