How to Remove a Well-Fixed Porous Tantalum Cone

As the demand for primary TKA continues to increase, usage of revision TKA will closely follow with more than 268,000 revision TKA procedures expected in the United States alone by 2030 [2]. Porous tantalum cones were introduced more than a decade ago as a strategy to manage some of the larger femoral and tibial bone defects encountered at the time of revision TKA [1, 3], and have been widely adopted because they osteointegrate reliably even in compromised metaphyseal bone. Surgeons who perform revision TKA sometimes need to remove these cones, which is challenging because of the limited surgical access to the metaphyseal bone of the proximal tibia and distal femur.

Unlike titanium metaphyseal sleeves such as Metaphyseal-Filling Sleeves (DePuy Inc, Warsaw, IN, USA), which can be disengaged from their taper connection [4], the tantalum cone (Zimmer Inc, Warsaw, IN, USA) is a separate implant from the stemmed revision component [6]. The external surface is designed to achieve osteointegration within the surrounding metaphyseal bone, while the internal surface serves as an interface for cemented fixation of the stemmed revision component. The femoral or tibial component typically blocks access to the intramedullary canal and tantalum cone. Therefore, surgeons attempting to remove the cone should debond the stemmed revision component from the cement interface within the cone. To do this, the femoral or tibial component should be freed from the metaphyseal bone using the surgeon’s preferred technique of a saw, high-speed burr, or flexible osteotomes as is done routinely in the removal of primary TKA components. After this initial interface is disrupted, a bone tamp can be placed either on the anterior flange of the femoral component or under the tibial baseplate, and several firm mallet blows delivered in-line with the intramedullary canal. In my experience, the stemmed component will often debond and come free. If this occurs, the surgeon will be left with easy access to the osteointegrated cone that can then be removed with a high-speed burr.

The more-challenging scenario occurs when the stemmed revision component does not debond from the metaphyseal cone. In this case, the construct will need to be removed as a single unit, which is best done using an osteotomy in order to access the intramedullary canal. For a well-fixed femoral cone, I believe that an anterior distal femoral osteotomy (Fig. 1A-F) is the safest option, as it does not disrupt the medial or lateral collateral ligaments. The surgeon can perform this osteotomy with a microsagittal saw and flexible osteotome, allowing direct access to the cone. At this point, the surgeon can use his or her preferred technique to carefully disrupt the osteointegrated interface between the tantalum cone and surrounding bone. To avoid scarring to the overlying extensor mechanism, I do not replace this osteotomy fragment and instead leave the anterior defect uncontained. Because the defect is bypassed by a long intramedullary stem, it is typically not necessary to restrict weightbearing or alter normal postoperative protocols.

Fig. 1A-F.

This image shows a 62-year-old woman with an infected revision TKA requiring removal of the femoral cone which is osteointegrated on both anteroposterior (A) and lateral (B) radiographs. An anterior distal femoral osteotomy (C) allows a window for direct access to the tantalum cone, which can then be easily removed with acceptable bone loss (D). The osteotomy fragment was not replaced, and the anterior cortical defect remains at the time of reimplantation and can be seen on anteroposterior (E) and lateral (F) radiographs. (Published with permission from H. John Cooper MD).

For a well-fixed tibial cone, two osteotomy options seem reasonable. The first option is a tibial tubercle osteotomy, which has been well-described [5] and allows excellent access to the tantalum cone while improving exposure. Another option is to create medial tibial osteotomy (Fig. 2A-C), which begins just medial to the tibial tubercle, extends distal enough to allow access to the bottom of the tantalum cone, and extends medially approximately 1.5 cm to 2.5 cm. I prefer this option because it does not interfere with the extensor mechanism or affect the patient’s rehabilitation. Unlike the tibial tubercle osteotomy, the medial tibial osteotomy does not have a soft-tissue hinge, therefore the osteotomy fragment should be removed from the patient while the cone is removed. The surgeon can then choose to replace the osteotomy fragment at the end of the case or to leave an uncontained medial tibial defect if (s)he does not wish to replace the osteotomy fragment. The overlying superficial MCL and medial soft tissue sleeve typically hold this fragment in place without supplementary fixation, and as long as the osteotomy fragment is not excessively thin or necrotic, I have had good success with healing whenever it can be replaced in a near-anatomic position. Similar to the anterior distal femoral osteotomy described above, the medial tibial osteotomy is bypassed by a long intramedullary stem, and therefore it is not necessary to restrict weightbearing or alter normal postoperative protocols.

Fig. 2A-C.

A schematic of the medial tibial osteotomy is shown. The medial cortical window is created with a microsagittal saw just medial to the tibial tubercle (A). This fragment is removed from the field (B), allowing direct access to the well-fixed tantalum cone (C). (Published with permission from H. John Cooper MD).