Abstract
BackgroundAsymptomatic local bone resorption of the tibia under the baseplate can occasionally be observed after total knee arthroplasty (TKA). Its occurrence is not well documented, and so far no explanation is available. We report the incidence of this finding in our practice, and investigate whether it can be attributed to specific mechanical factors.MethodsThe postoperative radiographs of 500 consecutive TKA patients were analyzed to determine the occurrence of local medial bone resorption under the baseplate. Based on these cases, a 3D FE model was developed. Cemented and cementless technique, seven positions of the baseplate and eleven load sharing conditions were considered. The average VonMises stress was evaluated in the bone-baseplate interface, and the medial and lateral periprosthetic region.ResultsSixteen cases with local bone resorption were identified. In each, bone loss became apparent at 3 months post-op and did not increase after one year. None of these cases were symptomatic and infection screening was negative for all. The FE analysis demonstrated an influence of baseplate positioning, and also of load sharing, on stresses. The average stress in the medial periprosthetic region showed a non linear decrease when the prosthetic baseplate was shifted laterally. Shifting the component medially increased the stress on the medial periprosthetic region, but did not significantly unload the lateral side. The presence of a cement layer decreases the stresses.ConclusionLocal bone resorption of the proximal tibia can occur after TKA and might be attributed to a stress shielding effect. This FE study shows that the medial periprosthetic region of the tibia is more sensitive than the lateral region to mediolateral positioning of the baseplate. Medial cortical support of the tibial baseplate is important for normal stress transfer to the underlying bone. The absence of medial cortical support of the tibial baseplate may lead to local bone resorption at the proximal tibia, as a result of the stress shielding effect. The presence of a complete layer of cement can reduce stress shielding, though. Despite the fact that the local bone resorption is asymptomatic and non-progressive, surgeons should be aware of this phenomenon in their interpretation of follow-up radiographs.
Highlights
Asymptomatic local bone resorption of the tibia under the baseplate can occasionally be observed after total knee arthroplasty (TKA)
One of the major failure mechanisms in total knee arthroplasty (TKA) is aseptic loosening of the tibial component. In the past this has been attributed to the quality of the fixation as well as to the strength of the supporting bone, which is subject to a more or less pronounced stress shielding effect of the proximal tibial metaphyseal bone by the tibial baseplate [1-7]
In this study we report the incidence of this 'short term' local bone resorption, and we investigate whether it can be attributed to a stress shielding effect, which might lead to more generalized bone resorption in the long term and potential aseptic loosening
Summary
Asymptomatic local bone resorption of the tibia under the baseplate can occasionally be observed after total knee arthroplasty (TKA). One of the major failure mechanisms in total knee arthroplasty (TKA) is aseptic loosening of the tibial component. In the past this has been attributed to the quality of the fixation as well as to the strength of the supporting bone, which is subject to a more or less pronounced stress shielding effect of the proximal tibial metaphyseal bone by the tibial baseplate [1-7]. Asymptomatic local bone resorption of the proximal tibia under the prosthetic component can occasionally be observed after TKA (Figure 1). In literature two main reasons for bone resorption can be found:
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