Survival of primary total knee arthroplasty in a modern anatomic implant with and without a short stem extension.

introductionIn primary conventional TKA, the tibial fixation is achieved by the epiphyseal and metaphyseal zone. One of those two zones of fixation, can be compromised by the local bone quality (bone micro-architecture and resistance), previous surgery or decreased surface of contact, leading to micro-mobility of the implant and potentially leading to aseptic loosening (AL). It was our hypothesis that the addition of a short fully cemented stem would improve the metaphyseal and epiphyseal fixation of the implant. To verify this hypothesis, the goals of this retrospective study were therefore to compare if (1) The presence of a short, stubby stem will dissipate stress and decrease micro-mobility at the epiphyseal level resulting in less radiolucent lines around the tibial component. (2) Short stem primary TKA may improve survivorship of the implant in patients potentially at risk for aseptic loosening. MATERIALS AND

methodsRetrospective cohort study of 326 patients operated with a morphometric implant between 2013 and 2018. A short stubby stem was added to the tibial implant, if at the time of the tibial cut, the surgeon judged the epiphyseal bone quality to be poor or a smaller tibial size was necessary. All primary TKA were radiographically evaluated. RLLs were recorded and described according to their radiological aspect, localization, time of appearance and their progression over time. Survivorship was compared in the 2 groups using the national joint registry.

results71 TKAs out of 326 (22%) were stemmed. Of the 255 TKAs without stem, 53 (21%) showed RLLs under the tibial base plate and 1 case (0.4%) was revised for potential AL of the tibial implant. No RLLs were observed in the group of stemmed implants and no revisions for aseptic loosening were needed. Patients with stubby stems were elderly women with risk factors for osteoporosis or young men in need for correction of big coronal deformities.

conclusionA short stubby stem extension can reduce the rate of RLLs and AL in primary TKA, probably by adding metaphyseal fixation to the classic epiphyseal fixation of the tibia and by a reduction in micro- and macro-motion of the tibial component. Based on the results of our study, the addition of a short cemented stubby stem decreased the rate of RLL with no revision observed in the stemmed group during the study period. The used knee system allows this option. Intra-operative decision can be made easily when risk factors such as osteoporosis, female gender, big deformities, obesity can be identified. LEVEL OF EVIDENCE: III.