Aseptic Failure of Tibial Components With Sleeves in Revision Total Knee Arthroplasty: A Novel Radiographic Assessment of Zonal Fixation.

BACKGROUND: Aseptic sleeve failure in revision total knee arthroplasty (TKA) is rare, and associated risk factors remain poorly understood. Shortcomings exist with current methods for assessing stem fill. We hypothesize that inadequate medial base plate support and undersized stems contribute to aseptic loosening and varus collapse of tibial components with sleeves. METHODS: This retrospective review evaluated TKA cases revised for aseptic loosening of tibial sleeves at a single academic center from 2011 to 2024. Stem-to-endosteal canal fill ratios of knee radiographs were measured using the Parsley method, with adequate fill defined >0.85. A novel area fill ratio was calculated along the sleeve and stem length using ImageJ software comparing implant area to total available area within the tibia. Medial base plate support was considered "unsupported" with gapping underneath the base plate >2 mm or with an excessive cement mantle. RESULTS: Eighteen patients were revised for aseptic loosening of tibial components with sleeves, the majority (55.6%) demonstrating an unsupported medial base plate. Diaphyseal stem AP and lateral fill ratios using traditional Parsley method were undersized at 0.81 ± 0.13 (avg ± SD) and 0.77 ± 0.14, respectively. Using the area fill ratio method, the AP and lateral diaphyseal stems were more undersized measuring 0.74 ± 0.1 and 0.68 ± 0.11, respectively. Sleeve AP and lateral area fill ratios were 0.55 ± 0.1 and 0.51 ± 0.07. CONCLUSIONS: Unsupported medial base plates and undersized tibial stems may contribute to aseptic loosening in revision TKA with sleeves. Current stem fill assessments have limitations, whereas the stem and sleeve area fill ratio represents a novel technique for comprehensive measurement of implant-to-endosteal contact.