New Review of Metaphyseal Cones and Sleeves in Revision Total Knee Replacement Published in JAAOS® – Journal of the American Academy of Orthopedic Surgeons

September 17, 2021

Article explores approaches for managing bone loss during revision total knee replacement, including versatility and interchangeability of cones and sleeves with different systems

Ahmed Siddiqi, D.O., M.B.A.
Lead Author, Orthopedic Surgeon, Hackensack Meridian Jersey Shore University Medical Center and assistant professor at Hackensack Meridian School of Medicine, Hackensack, NJ

A new comprehensive review article by orthopedic surgeons from Hackensack Meridian Jersey Shore University Medical Center, Hackensack University Medical Center, Hackensack Meridian School of Medicine, Brigham and Women’s Hospital, and the Cleveland Clinic, “The Use of Metaphyseal Cones and Sleeves in Revision Total Knee Arthroplasty,”1 was published in the September 2021 edition of JAAOS®, the Journal of the American Academy of Orthopedic Surgeons. The article presents different design philosophies, types of manufacturing, clinical outcomes, and the versatility and interchangeability of varying cones and sleeves with different total knee arthroplasty systems.

Total knee replacement or total knee arthroplasty is a common orthopedic procedure and one of the most successful procedures in all of medicine. According to the Agency for Healthcare Research and Quality, in 2017 more than 754,000 knee replacements were performed in the United States. With new implant designs and innovative surgical techniques, knee replacements can function well for 15 to 20 years in the majority of patients.

A knee revision is the replacement of prosthetic implants in a person who previously had total knee replacement. In this surgery, the original prosthesis is removed and a new prosthesis is put in place. Metaphyseal cones and sleeves, made of porous metal, are unique solutions for bone defects, substituting for bone loss in these surgeries. Metaphyseal refers to the trumpet-shaped end of long bones. Much bone remodeling occurs in the metaphyseal region of a bone after fracture.

“The projected burden of revision total knee arthroplasties (rTKA) is expected to continue to increase with the rising number of primary TKAs performed each year,” said Ahmed Siddiqi, D.O., MBA, lead author and an orthopedic surgeon at Jersey Shore University Medical Center in Neptune, NJ and assistant professor at Hackensack Meridian School of Medicine, Hackensack, NJ. “This is a particularly relevant article as the management of femoral and tibial bone loss encountered in rTKA can be challenging, and it necessitates appropriate surgical planning.” Michael Kelly, M.D., Chairman, Orthopedic Surgery, Hackensack University Medical Center, was also part of the research team.

The article states that metaphyseal cones and sleeves have emerged as an increasingly popular option of addressing metaphyseal femoral and tibial bone loss in rTKA. “Understanding what cones and sleeves are available and when to use them are critical parts of preoperative evaluation and planning,” Dr. Siddiqi added. ”Cones and sleeves have been designed to replace bone loss during rTKA by increasing the contact area between the femoral and tibial metaphyseal bone and the implant and providing a porous surface for biologic implant fixation,” he said.

The comprehensive review article includes a section on bone-loss classification, exploring various bone-defect classification systems primarily based on defect size, severity, and location that guide both surgical management and outcomes.

It also provides a complete background on cones and sleeves and states that bone loss encountered during rTKA is a challenging problem because little consensus exists on optimal management. Bone grafts, metal augments, metaphyseal sleeves, and more recently, ultra-porous cones all have been reported as viable options.

A section of the article outlines the materials and manufacturing of metaphyseal cones and sleeves, explaining that ultra-porous metals offer a three-dimensional cellular metal structure with interconnected pores, and that ultra-porous metal exhibits lower but sufficient stiffness compared with solid metal. The article elaborates on other substances used for the cones and sleeves, including tantalum, tritanium, StikTite, InteGrip, 3DMetal, and Porocoat.

The article provides the history of metaphyseal cones. Porous tantalum cones were the first metaphyseal cones introduced for commercial use with the potential advantage of improved biologic fixation from high porosity, interconnected pores, low modulus of elasticity and the ability to fill bone deficits while withstanding physiological loads. It further explains the genesis of second-generation designs from different vendors that have evolved to include improved cones. It also discusses classification to guide the development of metaphyseal cone geometrics, explaining that both first-generation and second-generation metaphyseal cones offer different geometric designs to provide options for best fit within the host bone.

The article provides a similar section on the background and history of metaphyseal sleeves. It explains that structural allografts (tissue graft from a donor) and metal augments are viable options for uncontained metaphyseal defects but may undergo stress shielding, resorption, and late plateau or fractures. Similar to nonporous augments and ultra-porous cones, metaphyseal sleeves are another option for the management of large bone defects in rTKA.

The authors advise that although there are no absolute guidelines for the use of metaphyseal fixation in rTKA, sleeves are most often used when addressing contained and uncontained metaphyseal defects. The article further provides an overview of the design philosophy and surgical technique of metaphyseal sleeves.

In addition, the article includes a section on clinical outcomes, reporting that since initial short-term tantalum cone studies, several authors have reported continued success at midterm follow up, and that most literature on the first-generation metaphyseal cones has reported survivorship of tibial cones with limited data on femoral cones. Similar to metaphyseal cones, metaphyseal sleeves have demonstrated excellent short-term and midterm radiographic and clinical outcomes.

The authors state that metaphyseal cones and sleeves are both viable and effective options for addressing femoral/tibial bone defects in rTKA, and that both techniques allow for appropriate bone defect management and metaphyseal bone fixation with comparable clinical and radiological results and survival rates.

A discussion of interchangeability states that the independent preparation of metaphyseal cones and revision TKA allows for seamless interchangeability of cones and rTKA platforms from different vendors. The authors advise, however, that it is important to be mindful of each vendor’s cone specifications and sizing to be able to appropriately use the different cones and stems associated with revision systems, and that interchangeability of femoral cones with different systems may be more limited compared with tibial cones.

The authors also state that contraindications for metaphyseal cones/sleeves include acute or chronic infections, patients with allergies to implant materials and metals, prominent muscular, nerve, vascular or other comorbidities that significantly affects the viability of the limb, and inadequate bone stock to accommodate a cone or sleeve that prevents a stable anchor of the implant.

The authors conclude that the burden of rTKA is expected to increase with the rise in the number of TKA procedures being performed yearly. Management of bone loss during rTKA is challenging and necessitates appropriate surgical planning using allografts or metal substitutes. Metaphyseal cones and sleeves have emerged as increasingly popular options for addressing metaphyseal femoral and tibial bone loss.

“Understanding what cones and sleeves are available is a critical part of the preoperative evaluation and planning,” said Dr. Siddiqi. “Metaphyseal cones allow for interchangeability of different revision TKA systems the independent implant preparation. Both metaphyseal cones and sleeves have demonstrated excellent radiographic survivorship and clinical functional outcomes at mid-term follow up.”

The authors, however, advise that further research is needed to continue to prove the efficacy of second-generation metaphyseal cones and the utility of metaphyseal sleeves without stems.