New technique promising to treat revision TKR bone loss

Intraoperative picture of the tantalum tibial cone.

By Elaine Fiedler

Using porous tantalum metaphyseal tibial cones may be an effective substitute for structural bone allografts when confronted with severe tibial bone loss during revision total knee replacements (TKR), according to the authors of Paper 405. This novel reconstruction method shows promising short-term results.

Although several methods can be used to address large bone defects during revision TKR, a "best" method has not yet been identified. However, the number of these defects are on the rise, partly because the patient population has become more active, which potentially leads to more polyethylene wear. Osteolytic lesions associated with particulate wear debris often result in an unpredictable pattern of extremely large bone defects.

Tibial metaphyseal bone defects are a formidable challenge in revision TKR. Treatment options include structural bone allografting, impaction cancellous bone grafting, specialized implants with metaphyseal augments, and custom prostheses.

The newly developed tibial cones use a relatively new biomaterial, tantalum trabecular metal, and are designed in different shapes and sizes to accommodate a variety of bone defects. The porous tantalum metaphyseal cones in this study were designed and developed by the two senior authors in conjunction with the Zimmer Corporation of Warsaw, Ind.

This IRB-approved study involved 15 patients with Type 2-B or Type 3 tibial bone defects, according to the Anderson Orthopaedic Research Institute (AORI) Classification. The 8 women and 7 men in the study had an average age of 68 years (range: 41 to 81 years) and an average of 3.5 prior TKR procedures (range: one to eight).

Preoperative radiograph showing tibial bone loss

Subsequent postoperative radiograph showing the use of the tantalum tibial cones. No

radiolucencies were observed between the cones and the adjacent tibial bone at the final follow-up.

Ten revisions were for aseptic failure; five were for a second stage reimplantation for infection. During the 15 revision knee replacements, the cones were implanted, and any voids between the cones and adjacent bone were filled with morselized cancellous bone or bone putty.

According to the authors, "The internal surface of these cones essentially reconstituted the proximal metaphyseal surface of the tibia to provide a receptive surface for cementation of the final tibial implant to the porous cone."

Prostheses included 7 rotating hinge, 3 semi-constrained and 5 posterior-stabilized implants. All components were stemmed (12 cemented, 3 uncemented).

All patients were followed for a minimum of two years (range: 24 to 38 months). The mean preoperative Knee Society Score of 52 points (range: 25-81) increased to 85.2 points (range, 49-100). The preoperative range of motion for the 15 patients averaged 6.2 degrees (range: 0 degrees to 35 degrees) of flexion contracture and 86.5 degrees (range: 30 degrees to 120 degrees) of flexion. By final follow-up, the flexion contracture had decreased to an average 1 degree (range: 0 degrees to 10 degrees) and the mean flexion had increased to 99.7 degrees (range: 80 degrees to 120 degrees).

At short-term follow-up, all cones demonstrated osseous integration with no evidence of implant migration or loosening. Two patients underwent debridement, component retention, and antibiotic suppression for recurrent infection and have fair functional results. One underwent revision 13 months postop for femoral aseptic loosening. The tibial component and cone were well fixed and were retained. There were no other reoperations or revisions.

The authors propose this novel method of bone defect reconstruction as a viable alternative to using structural allografts in revision TKR. The surgical technique is relatively simple; because these implants come in multiple sizes, the need to preoperatively size the patient is also eliminated. The study's results confirmed the excellent potential for successful bony ingrowth into these implants.

"The rapidity and ease of porous cone implantation, as compared with preparation of structural bone allograft prosthetic constructs, has resulted in shorter operative times, which provides significant potential for cost savings," they wrote.

One disadvantage, which the authors noted, however, may be potential problems in removing these implants, if necessary.

Although this study represents early follow-up, the authors concluded that the results are encouraging for patients and surgeons. They expressed the hope that biologically fixed porous cones will improve the long-term mechanical durability of difficult revision TKR.

The authors included Robert M. Meneghini, MD, of Indianapolis, and David G. Lewallen, MD, and Arlen D. Hanssen, MD, both of Rochester, Minn. Drs. Lewallen and Hanssen receive support and royalties from Zimmer, Inc.

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