Surgical technique of metaphyseal sleeves and cones

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In Part 1 of this newsletter we outlined how metaphyseal fixation of revision TKA can be performed with structural allograft, cones, or sleeves. Nowadays, most surgeons prefer cones or sleeves over allograft, so we have focused on these two treatment techniques here. In addition to describing the surgical techniques, we also interviewed one advocate for cone and one for sleeve technique with the aim of providing a balanced overview of each technique.

Surgical technique using cones

After removing the previous components, the remaining bone is thoroughly cleaned of residual cement, fibrous, and nonviable tissue. This facilitates a correct assessment of the actual bone loss to properly prepare the bone for the correct cone size. While residual tissue may hinder osseointegration of the ingrowth surface, residual cement may even damage or deflect the instruments used to prepare for the cone during bone preparation creating excess bone loss or even fracture.

The position of the bony defect in relation to the intramedullary canal can be estimated with trial cones. The trial cones can be placed upside down on the bone surface over the reamer to assess the size and orientation of the defect and correct placement of the cone.

Various manufacturers provide different methods to guide alignment. All systems have in common that they use the medullary canal as the reference point to fix the guide. Depending on the manufacturer, fixed templates or variable dials are attached to the initial guide (Figure 1), which then allow exact placement of the instrumentation.

Figure 1. In this cone system a cannulated tibial cone reamer, calibrated by cone size, is inserted over an intramedullary reamer which is used for medullary canal referencing. Redrawn from Surgical Protocol of the Triathlon Revision Knee System, Stryker Corporation, Mahwah, New Jersey.

Once the guide and the template are in place, the cavity is prepared by cutting at a trajectory that mills or reams the bone to exactly match the shape of the implant. Since cones achieve their stability through press-fit, a good seating of the cone in the bone (Figure 2) is paramount for primary stability, which is the basis for osseointegration (Figure 3).

Figure 2. Central, porous titanium metaphyseal tibial cone, with intimate and circumferential host bone contact. Image courtesy of Bryan Springer.

Figure 3. Tibial metaphyseal cone osseointegration demonstrated by a “spot weld” (arrow) 5 years after revision TKA using a tibial metaphyseal cone and short-cemented stem construct. X-ray courtesy of Bryan Springer.

This is done with sequentially sized reamers, broaches, rasps, or burrs in a stepwise manner. It is important to pay particular attention to the amount of bone that is being removed. Enough bone should be removed to create a circumferential fit of the cone, however, one must ensure that bone is not removed excessively, because this may increase the risk of fracture.

While there is considerable variation in the techniques between the individual manufacturers, the instruments possess marks, which delineate the size and depth of the corresponding cone.

There may be cases in which the shape of the defect makes it impossible to create a perfect circumferential press fit on all sides of the cone due to bone loss being more prominent on one side compared to the other. In such situations, voids may be filled with morselized graft, demineralized bone matrix, or a suitable synthetic bone substitute. This is tightly packed around the cone until maximal stability is ascertained. This maneuver is not only to enhance the primary stability but also to prevent cement from flowing into the interface between cone and host bone when the final component is cemented into position.