Cause for concern? Significant cement coverage in retrieved metaphyseal cones after revision total knee arthroplasty

Metaphyseal cones are used to manage bone loss in revision total knee arthroplasty with increasing popularity. Post-operative radiographs and explant procedures suggest that cement may extrude around the cone implant into the cone-bone interface and prevent biologic in- or on-growth. The purpose of this study was to perform a retrieval analysis to describe the pattern of direct cementation onto the porous surface area of metaphyseal cones.

Eighteen tibial and femoral cones were identified in an institutional implant retrieval registry. Anterior, posterior, medial and lateral quadrants were digitally mapped for direct cementation, bone ongrowth and fibrous ongrowth were calculated as a percentage of the porous surface area. Plain radiographs from prior to cone explant were analyzed for the presence of cement in all four quadrants and compared with results of the retrieval analysis.

Mean bone ongrowth was 25%, direct cementation was 24% (31% in tibial cones) and fibrous ongrowth was 29% of the porous surface area of the retrieved cones. There were no significant differences when comparing patterns of bone or fibrous ongrowth or cementation between anterior, posterior medial and lateral porous surfaces for tibia cones, femoral cones or all cones grouped together. Plain radiographs significantly underestimated the amount of cement covering the cone (p = 0.02).

In this retrieval study, we found significant cement extrusion around the porous surface of metaphyseal cones in revision TKAs. Optimizing the cone-bone interface may reduce the risk of cement extrusion and theoretically reduce the risk of aseptic loosening.