The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 91, Issue Supplement 2 Part 1

Surgical Techniques | March 01, 2009

Use of Porous Tantalum Metaphyseal Cones for Severe Tibial Bone Loss During Revision Total Knee Replacement: Surgical Technique

R. Michael Meneghini, MD¹; David G. Lewallen, MD²; Arlen D. Hanssen, MD²

¹ New England Musculoskeletal Institute, University of Connecticut Health Center, MARB, 4th Floor, 263 Farmington Avenue, Farmington, CT 06034. E-mail address: meneghini@uchc.edu
² Department of Orthopedic Surgery, Mayo Clinic, 200 First Street S.W., Rochester, MN 55905

View Disclosures and Other Information

The original scientific article in which the surgical technique was presented was published in JBJS Vol. 90-A, pp. 78-84, January 2008

DISCLOSURE: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. One or more of the authors or a member of his or her immediate family received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from a commercial entity (Zimmer). Also, commercial entities (Zimmer and Stryker) paid or directed in any one year, or agreed to pay or direct, benefits in excess of $10,000 to a research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which one or more of the authors, or a member of his or her immediate family, is affiliated or associated.

Investigation performed at the Department of Orthopedic Surgery, Mayo Clinic, Rochester, Minnesota

The Journal of Bone and Joint Surgery, Incorporated

J Bone Joint Surg Am, 2009 Mar 01;91(Supplement 2 Part 1):131-138. doi: 10.2106/JBJS.H.01061

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Abstract

BACKGROUND: The best treatment method for large tibial bone defects during revision knee replacement has not been established. The purpose of this study was to determine the initial results obtained with a unique reconstructive implant, the porous tantalum metaphyseal cone, designed as an alternative treatment for severe tibial bone loss following total knee arthroplasty.

METHODS: Porous tantalum metaphyseal cones were implanted during fifteen revision total knee replacements in eight women and seven men who had an average age of 68.1 years at the time of the procedure. The patients had had an average of 3.5 prior total knee replacements. According to the Anderson Orthopaedic Research Institute bone defect classification, eight knees had a Type-3 defect and seven knees had a Type-2B bone defect. All patients were followed clinically and radiographically.

RESULTS: The patients were followed for an average of thirty-four months (range, twenty-four to forty-seven months). Overall, the average Knee Society clinical scores improved from 52 points preoperatively to 85 points at the time of the final follow-up. At the final follow-up evaluation, all fifteen porous metaphyseal cones showed evidence of osseointegration with reactive osseous trabeculation at points of contact with the tibia. There was no evidence of loosening or migration of any of these tibial reconstructions at the time of final follow-up.

CONCLUSIONS: At the time of short-term follow-up, the porous tantalum metaphyseal tibial cones effectively provided structural support for the tibial implants in this series. The potential for long-term biologic fixation may provide durability for these tibial reconstructions. Long-term follow-up and comparison with alternative reconstructive techniques will be required to evaluate the true effectiveness of this treatment approach.

LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.

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INTRODUCTION

INTRODUCTION | SURGICAL TECHNIQUE | References

Severe tibial bone loss remains a technical challenge for surgeons performing revision knee arthroplasty. Highly porous metals are relatively new biomaterials with advantages over conventional materials that include structural continuity, strength, low stiffness, high porosity, and high frictional coefficients. Porous tantalum metaphyseal cones were developed in an attempt to address the variable patterns of severe tibial bone loss encountered during revision knee arthroplasty. Conceptually, the advantage of these porous metal cones is the ability to achieve biologic fixation to native bone and concurrent cementation of the tibial baseplate and stem to the porous implant, effectively maximizing the biologic and structural integrity of the revision knee arthroplasty components. This is preferred over cementation of nonporous metal blocks or augments that do not obtain osseointegration and rely on tenuous cement fixation to the sclerotic and damaged bone in the proximal tibial metaphysis. An additional advantage of these implants is the ultimate achievement of long-term biologic fixation and avoidance of the nonunion, resorption, and collapse that can be associated with bulk allograft used in revision total knee arthroplasty.

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FIG. 1-A and FIG. 1-B: Anteroposterior (Fig. 1-A) and lateral (Fig. 1-B) radiographs of a patient with severe deficiency of the medial tibial plateau secondary to osteolysis and polyethylene wear. The osteolysis can be seen extending just past the tibial stem and has created a periprosthetic tibial fracture.

SURGICAL TECHNIQUE

INTRODUCTION | SURGICAL TECHNIQUE | References

The patient is positioned and surgical exposure is performed with traditional techniques commonly utilized in revision knee replacement surgery. The surgeon must obtain sufficient exposure to perform an accurate assessment of the tibial defect. The quantity and location of remaining cortical and cancellous bone must be noted and considered in the final assessment of whether a porous metal metaphyseal cone is indicated to augment the reconstruction. The most common scenario encountered is a severe contained or uncontained osseous defect of the medial tibial plateau with varying amounts of the lateral tibial plateau remaining for structural support (Figs. 1-A, 1-B, 2-A, 2-B). In more severe cases, deficiency of both the medial and the lateral portion of the tibial metaphysis dictates that the interference fit of the cone taper engage sufficient remaining cortical bone to obtain stability (Figs. 3-A, 3-B, and 3-C). The assessment should include a determination of the size and shape that might be appropriate for the porous metaphyseal cone with respect to its fit within the tibial metaphysis as well as its tentative location and placement required to reconstitute the proximal tibial supporting surface.

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FIG. 2-A and FIG. 2-B: Close-up intraoperative photographs of the porous tantalum cone positioned with intimate contact against peripheral bone to obtain a stable frictional fit (Fig. 2-A) and with trial tibial components placed on the stable, reconstructed tibial platform with the trial insert (Fig. 2-B).

Once it has been determined that a porous metaphyseal cone is required for reconstitution of the metaphyseal defect, a trial intramedullary stem or a reamer may be used to create an appropriately aligned finishing cut and assess the correct alignment and position of the metaphyseal cone. The metaphyseal region and the associated defect are inspected visually to assess the fit of the trial tantalum metaphyseal cone, and a high-speed burr is used to contour the metaphyseal bone to accommodate the trial tantalum metaphyseal cone with the maximal bone contact and stability possible. The cone may achieve axial stability either by acting as a three-dimensional wedge within the tibial metaphysis or by resting on intact bone at the distal extent of the implant. The greatest implant height is 3 cm, which approximately equals the deepest tibial defect amenable to the use of these implants, as the superior portion of the cone should be positioned approximately at the level of the residual cortical rim if possible. However, because of the frequent loss of cortical rim, these implants were designed to be load-bearing for the tibial component and to load share with the available residual cortical tibial rim as necessary.

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FIG. 3-A, FIG. 3-B and FIG. 3-C: Figs. 3-A through 3-C Anteroposterior (Fig. 3-A) and lateral (Fig. 3-B) radiographs and intraoperative photograph (Fig. 3-C) of a patient with severe cavitary contained deficiency of the medial and lateral tibial plateaus secondary to osteolysis and polyethylene wear. The osteolysis can be seen extending past the tibial screws and keel, deep into the metaphysis.

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FIG. 3-D and FIG. 3-E: Fig 3-D Intraoperative photograph of the knee, demonstrating the porous tantalum cone positioned with intimate contact against peripheral tibial bone to obtain a stable frictional fit. Fig. 3-E Close-up intraoperative photograph of the stable porous tantalum cone with peripheral gaps between the bone and the porous tantalum cone. The gaps were filled with allograft putty to facilitate osseointegration and prevent intrusion of cement.

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FIG. 4: Intraoperative photograph of the final cemented tibial tray on the supporting porous tantalum metaphyseal cone. Note that a thin layer of cement was applied to the exposed exterior porous tantalum surface to avoid mechanical irritation of the collateral ligament.

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FIG. 5-A and FIG. 5-B: Anteroposterior (Fig. 5-A) and lateral (Fig. 5-B) radiographs of the patient shown in Figure 1-A, 1-B, demonstrating a stable reconstruction with a porous tantalum metaphyseal tibial cone and cemented stems to reconstitute the severe medial tibial osteolytic defect and cortical disruption.

A porous tantalum cone of the appropriate size and shape is chosen, and that implant is impacted into the tibial or femoral metaphysis with size-specific impactors. Once the porous metal cone is in its final and stable position (Figs. 2-A and 3-D), the trial tibial tray and stem can be inserted to allow assessment of joint alignment, stability, and motion and thus determination of the final implant, as is routinely performed in revision total knee arthroplasty (Fig. 2-B). Any areas or voids between the periphery of the porous tantalum cone and the adjacent bone of the proximal part of the tibia are filled with morselized cancellous bone graft or putty to prevent any egress of bone cement between the cone and the host bone during cementation of the stemmed component (Fig. 3-E). The internal surface of the cone essentially reconstitutes the proximal metaphyseal surface to provide a receptive surface for cementation of the final tibial implant to the porous cone. While it is optimal for the tibial tray to be in direct contact with the porous metal cone circumferentially, the reality of these complex bone deficiencies creates variable degrees of alignment mismatch. This mismatch frequently results in contact between the tibial tray and the porous metal cone at only one location, which is an acceptable construct that was associated with no adverse consequences in our initial clinical series.

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FIG. 6-A and FIG 6-B: Postoperative anteroposterior (Fig. 6-A) and lateral (Fig. 6-B) radiographs of the patient shown in Figure 3-A, 3-B, 3-C, 3-D, 3-E, demonstrating a stable reconstruction with a porous tantalum metaphyseal tibial cone and cemented stems to reconstitute the severe medial and lateral tibial osteolytic defect.

The tibial revision implant is inserted through the cone in the correct rotational alignment with use of either cementless or cemented stem extensions. With either type of stem fixation, polymethyl-methacrylate is placed between the porous cone and the tray and the proximal keel of the tibial component. This is analogous to metaphyseal cementation, to unite the prosthetic stemmed implants to the porous cone (Figs. 4, 5-A, 5-B, 6-A, 6-B). Once the cement has hardened, the remainder of the surgical procedure is carried out in a standard fashion, with insertion of the appropriate polyethylene insert and meticulous wound closure.

CRITICAL CONCEPTSINDICATIONS:Large contained or uncontained tibial osseous defects in a patient with a failed total knee replacement due to instability, osteolysis, infection, or aseptic loosening.A defect that is larger than what is appropriately reconstructed with traditional modular blocks or wedges.Typically, Type-2 and Type-3 (moderate-to-severe cancellous and/or cortical) defects as rated with the Anderson Orthopaedic Research Institute bone defect classification¹.RELATIVE CONTRAINDICATIONS:Completely contained defects with a substantial supportive cortical rim may be more appropriately treated with impaction grafting in younger patients.Small uncontained defects that are less than 5 to 10 mm in depth and isolated to one tibial plateau will likely be more amenable to treatment with standard metal blocks.Reconstruction of large tibial defects in young patients may be more appropriately performed with a bulk allograft in an attempt to reconstitute bone stock for future revision surgery.The most severe tibial deficiencies that do not have any proximal supportive rim for interference fit of even a portion of the porous tantalum metaphyseal cone are more appropriately reconstructed with a whole tibial allograft or a tumor megaprosthesis.PITFALLS:Removal of the metaphyseal cones has not been required to date but likely will be technically challenging. Therefore, the surgeon should consider this potential problem when considering the use of these implants for a particular patient and revision total knee arthroplasty.Failure to remove all fibrous and osteolytic tissue from the tibial metaphyseal cavities will create difficulty with accurate determination of the correct size and shape for the porous metal cone.Excessive removal of viable cancellous and/or cortical bone should be avoided as the need for excessive removal may indicate that the porous metal cone is not necessary.Overly aggressive impaction of the final implant should also be avoided. Tibial metaphyseal bone in the revision setting is typically sclerotic, mechanically weak, and prone to inadvertent fracture. The frictional coefficient of the porous tantalum implant will create greater resistance to insertion.Tibial component systems with a wide proximal keel will have less rotational freedom within the porous metal metaphyseal cone. This may limit the surgeon's ability to restore the proper rotation of the tibial component independent of the metaphyseal defect.AUTHOR UPDATE:There have been no substantive changes in the technique or outcomes since the time that our original article was published.

CRITICAL CONCEPTS

INDICATIONS:

Large contained or uncontained tibial osseous defects in a patient with a failed total knee replacement due to instability, osteolysis, infection, or aseptic loosening.A defect that is larger than what is appropriately reconstructed with traditional modular blocks or wedges.Typically, Type-2 and Type-3 (moderate-to-severe cancellous and/or cortical) defects as rated with the Anderson Orthopaedic Research Institute bone defect classification¹.

Large contained or uncontained tibial osseous defects in a patient with a failed total knee replacement due to instability, osteolysis, infection, or aseptic loosening.

A defect that is larger than what is appropriately reconstructed with traditional modular blocks or wedges.

Typically, Type-2 and Type-3 (moderate-to-severe cancellous and/or cortical) defects as rated with the Anderson Orthopaedic Research Institute bone defect classification¹.

RELATIVE CONTRAINDICATIONS:

Completely contained defects with a substantial supportive cortical rim may be more appropriately treated with impaction grafting in younger patients.Small uncontained defects that are less than 5 to 10 mm in depth and isolated to one tibial plateau will likely be more amenable to treatment with standard metal blocks.Reconstruction of large tibial defects in young patients may be more appropriately performed with a bulk allograft in an attempt to reconstitute bone stock for future revision surgery.The most severe tibial deficiencies that do not have any proximal supportive rim for interference fit of even a portion of the porous tantalum metaphyseal cone are more appropriately reconstructed with a whole tibial allograft or a tumor megaprosthesis.

Completely contained defects with a substantial supportive cortical rim may be more appropriately treated with impaction grafting in younger patients.

Small uncontained defects that are less than 5 to 10 mm in depth and isolated to one tibial plateau will likely be more amenable to treatment with standard metal blocks.

Reconstruction of large tibial defects in young patients may be more appropriately performed with a bulk allograft in an attempt to reconstitute bone stock for future revision surgery.

The most severe tibial deficiencies that do not have any proximal supportive rim for interference fit of even a portion of the porous tantalum metaphyseal cone are more appropriately reconstructed with a whole tibial allograft or a tumor megaprosthesis.

PITFALLS:

Removal of the metaphyseal cones has not been required to date but likely will be technically challenging. Therefore, the surgeon should consider this potential problem when considering the use of these implants for a particular patient and revision total knee arthroplasty.Failure to remove all fibrous and osteolytic tissue from the tibial metaphyseal cavities will create difficulty with accurate determination of the correct size and shape for the porous metal cone.Excessive removal of viable cancellous and/or cortical bone should be avoided as the need for excessive removal may indicate that the porous metal cone is not necessary.Overly aggressive impaction of the final implant should also be avoided. Tibial metaphyseal bone in the revision setting is typically sclerotic, mechanically weak, and prone to inadvertent fracture. The frictional coefficient of the porous tantalum implant will create greater resistance to insertion.Tibial component systems with a wide proximal keel will have less rotational freedom within the porous metal metaphyseal cone. This may limit the surgeon's ability to restore the proper rotation of the tibial component independent of the metaphyseal defect.

Failure to remove all fibrous and osteolytic tissue from the tibial metaphyseal cavities will create difficulty with accurate determination of the correct size and shape for the porous metal cone.

Excessive removal of viable cancellous and/or cortical bone should be avoided as the need for excessive removal may indicate that the porous metal cone is not necessary.

Overly aggressive impaction of the final implant should also be avoided. Tibial metaphyseal bone in the revision setting is typically sclerotic, mechanically weak, and prone to inadvertent fracture. The frictional coefficient of the porous tantalum implant will create greater resistance to insertion.

Tibial component systems with a wide proximal keel will have less rotational freedom within the porous metal metaphyseal cone. This may limit the surgeon's ability to restore the proper rotation of the tibial component independent of the metaphyseal defect.

AUTHOR UPDATE:

There have been no substantive changes in the technique or outcomes since the time that our original article was published.

References

INTRODUCTION | SURGICAL TECHNIQUE | References

Engh GA, Ammeen DJ. Bone loss with revision total knee arthroplasty: defect classification and alternatives for reconstruction. Instr Course Lect. 1999;48: 167-75.48167 1999 [PubMed]

Topics

retinal cone ; metals ; reconstructive surgical procedures ; tantalum ; tibia ; knee replacement arthroplasty ; osteopenia

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R. Michael Meneghini, David G. Lewallen, Arlen D. Hanssen; Use of Porous Tantalum Metaphyseal Cones for Severe Tibial Bone Loss During Revision Total Knee ReplacementSurgical Technique. The Journal of Bone & Joint Surgery. 2009 Mar;91(Supplement_2_Part_1):131-138.

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