Influence of varying stem and metaphyseal sleeve size on the primary stability of cementless revision tibial trays used to reconstruct AORI IIA defects. A simulation study

Abstract

Traditionally, diaphyseal stems have been utilized to augment the stability of revision total knee replacement (rTKR) implants. More recently metaphyseal augments, such as sleeves, have been introduced to further augment component fixation. The effect of augments such as stems and sleeves have on the primary stability of a rTKR implant is poorly understood, however it has important implications on the complexity, costs and survivorship of the procedure. Finite element analysis was used to investigate the primary stability and strain distribution of various size stems and sleeves used in conjunction with a cementless revision tibial tray. The model was built from computer tomography images of a single healthy tibia obtained from an 81-year-old patient to which an Anderson Orthopaedic Research Institute (AORI) IIA defect was virtually added. The influences of varying body mass index (BMI) and bone modulus were also investigated. Stemless sleeves were found to provided adequate primary implant stability (average implant micro-motion <50 μm) for the studied defect. Addition of a stem did not enhance the primary stability. Furthermore, this study found that varying BMI and bone modulus had a considerable effect on strain distribution but negligible effect on micro-motion in the sleeve area. In conclusion, the addition of diaphyseal stem to a metaphyseal sleeve had little benefit in enhancing the primary stability of tibial trays augmented when simulating reconstructions of AORI IIA tibial defects. Additional studies are required to determine the relative benefit of the diaphyseal stem when using metaphyseal sleeves defects with more extensive bone loss. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1876-1886, 2018.

Influence of stems and metaphyseal sleeve on primary stability of cementless revision tibial trays used to reconstruct AORI IIB defects

“…The gait cycle was discretized into 2% intervals, with a total of 51 increments. The forces were applied at four points on the proximal surface of the tibial tray . The distal 30% of the tibia was rigidly constrained in all subjects.…”

“…Material properties were derived from the CT scans (ScanIP, Simpleware Ltd.) in a similar method to Awadalla et al, using a linear empirical relationship . The relationship were used to relate Hounsfield units to apparent density (Equation ) and then density to Young's modulus (Equation ).…”

“…Micromotion and strain were only evaluated in the metaphysis, adjacent to the sleeve. Micromotion was obtained by finding the initial correspondence between neighboring implant and bone nodes prior to the simulation Using an in‐house Matlab code (MathWorks, Natick, MA), the initial correspondent node pairs (CNP) were used to calculate the resultant displacement between the current frame CNP and the previous frame CNP (entire load cycle is 51 frames).…”

“…Since the authors investigated multiple activities, using a standard method to compare the effect of the loading condition and the bone defect on the implant primary stability. The authors used an established method of CPS and CPM to report on the worst case scenario throughout all the gait cycles . This study reports the mean and 95 percentile value of the CPM and CPS.…”

“…Computational studies also suggest that sleeved tibial implants with no stems can be used to manage AORI IIA defects. Awadalla et al used finite element analysis (FEA) to investigate the primary stability of a revision tibial tray augmented with a sleeve with and without a stem when reconstructing a type IIA defect. The authors reported that adequate primary stability could be achieved with a metaphyseal sleeve alone.…”