Master Techniques in Orthopedic Surgery Knee CH21

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21 Managing Bone Loss with Metaphyseal Cones

●● Although the debate regarding cemented and uncemented stem extensions in revision TKA per- sists, we favor the use of cemented stem extensions in most circumstances requiring the use of metaphyseal cones. 22-24 However, unless preoperative radiographs demonstrate a significant extra articular deformity, long stem trials (180-220 mm combined length) help optimize alignment by engaging the diaphysis. In most cases, it is not necessary to cement a stem of this length; and, therefore, before opening the real components, selection of a shorter, wider stem is appropriate. A stem that gives a combined length of 80 to 100 mm is usually adequate. ●● When cementing both femoral and tibial stems, it is preferable to cement the tibia first. To prevent malrotation during the cementing process, the tibial cement should be allowed to cure before proceeding with cementation of the femoral component. Use of a canal plug, cement gun, and pressurization for the tibia and femur helps achieve an optimal cement mantle. Antibiotic-impreg- nated cement is used in every revision case. POSTOPERATIVE MANAGEMENT When a stable construct has been created with the use of a metaphyseal cone, in conjunction with a cemented stem extension and cement about the core implant, the patient is allowed to weight-bear as tolerated on the operative extremity. Most patients require the use of a walker or crutches for ap- proximately 3 weeks and may then progress to a cane. The authors do not currently use continuous passive motion machines with any revision TKA, but do allow the majority of patients to participate in range of motion exercises in physical therapy. A brace or knee immobilizer is used when ambulating if a tubercle osteotomy was performed. COMPLICATIONS In revision TKAs, use of metaphyseal cones may be associated with all the usual complications that can occur in these difficult cases. These problems include mechanical failure of the prosthesis, insta- bility, infection, and aseptic loosening. Specific concerns regarding the metaphyseal cones include the potential for failure because of inadequate bone ingrowth or failure due to mechanical overload when the cones are used in uncontained defects where there is no potential for load sharing with surrounding host bone. At midterm follow-up, a deep periprosthetic infection rate of about 11% has been reported. 12,13 RESULTS Successful midterm results following revision total knee replacement have been reported using con- ventional block and wedge augments in cases with AORI type II defects. 25,26 In addition, growing data for tantalum cones has demonstrated reliable and rapid osseointegration with stable long-term fixation. 11-13,27 In an early report (24-38 months) on 15 tantalum tibial cones used in AORI type IIB or III bone defects, Meneghini et al 13 found that all tibial cones demonstrated bone ingrowth without evidence of loosening or migration. A midterm follow-up study completed by Kamath et al 12 at a mean of 70 months found a revision-free survival of the tibial cone component to be greater than 95%. Howard et al 11 also published an early report on 24 tantalum femoral cones used in type IIB or III bone defects. At a mean of 33 months, all reviewed femoral cones demonstrated osseointegration. In 2012, Lachiewicz et al 27 retrospectively reviewed 33 tantalum metaphyseal cones in a multicenter study (9 femoral and 24 tibial). At a mean of 40 months, the authors found that 26 of the 27 reviewed cones demonstrated osseointegration. Data is currently not available on the 3D printed titanium cones given their recent release. 1. Kelly MA, Clarke HD. Long-term results of posterior cruciate-substituting total knee arthroplasty. Clin Orthop Relat Res . 2002;(404):51-57. 2. Sierra RJ, Cooney WP IV, Pagnano MW, Trousdale RT, Rand JA. Reoperations after 3200 revision TKAs: rates, etiology, and lessons learned. Clin Orthop Relat Res . 2004;(425):200-206. 3. Bozic KJ, Kurtz SM, Lau E, et al. The epidemiology of revision total knee arthroplasty in the United States. Clin Orthop Relat Res . 2010;468(1):45-51. 4. Fehring TK, Odum S, Griffin WL, Mason JB, Nadaud M. Early failures in total knee arthroplasty. Clin Orthop Relat Res . 2001;(392):315-318. REFERENCES