Effect of tibial tray design on cement morphology in total knee arthroplasty
© Schlegel et al.; licensee BioMed Central Ltd. 2014
Received: 7 August 2014
Accepted: 18 November 2014
Published: 29 November 2014
Improvements to enforce primary fixation in cemented total knee arthroplasty have been suggested to be a key issue for long-term survival. In this context, it has been questioned whether specific implant design features influence bone cement morphology and hence primary interface strength. The purpose of this study was to investigate in vitro the influence of cement pockets on the tibial tray on cement penetration in the tibia.
Eight paired cadaveric, human tibiae were available for investigation. One side of a pair was implanted with a fixed bearing tibial tray (FB) featuring cement pockets on the undersurface, while in the other side, a mobile bearing platform (MB) without cement pockets was used. Specimens underwent computed tomography analysis of the cement morphology as well as BMD assessment.
While bone cement layer between implant and bone surface was thicker in the FB group (p = 0.032), bone cement penetration was not influenced by implant design (p = 0.529).
The present study suggests that cement pockets do not alter or enforce bone cement penetration under the tibial tray in an in vitro scenario.
KeywordsTotal knee arthroplasty Cementing technique Mobile bearing Cement pockets Bone cement penetration
Cemented total knee arthroplasty (TKA) is widely accepted as the most effective treatment for end-stage osteoarthritis of the knee. Although favorable clinical results have been reported, aseptic loosening of the tibial component remains troublesome -. As the need for revision surgery in total knee arthroplasty increases steadily, there is growing interest to improve initial fixation . Aseptic loosening can be attributed to continuous micromotion at the implant-cement or bone-cement interface . There is increasing evidence that the interface strength of the cemented fixation at the time of surgery is a major factor determining the long-term performance of the implant ,. However, there is little information regarding bone cement penetration characteristics with newer tray designs for alternative bearing philosophies such as mobile bearing platforms. There has been a higher prevalence of tibial failure with early component designs, which highlights the role of the implant itself in the loosening process . Implants featuring a peripheral lip on the undersurface have been suggested to enforce cement penetration, but the presence is depending on the manufacturer and the design . Another biomechanical study suggested likewise that surface preparation and type of metal substrate may influence the bonding of the tibial component to the cement . Thus, it can be questioned if cement mantle morphology differs among tibial trays of different designs. Design features on the undersurface of the component could influence bone cement penetration and likewise morphology in the trabecular bone, which could alter initial fixation strength. Hence, the aim of this study was to evaluate and compare bone cement penetration patterns in the tibial cancellous bone between different tibial tray designs by computed tomography (CT) scans and 3D imaging.
Specimen characteristics and results (F = female, M = male)
Cement layer (mm)
Differences in tibial component design and surgical technique influence the long-term performance of the implant regarding early aseptic loosening in TKA ; cementing techniques and choice of implant design still are controversial ,. It has been shown that a peripheral lip improves bone cement penetration into the osseous surface . The present study investigated in vitro whether cement pockets on the undersurface could likewise influence bone cement penetration characteristics. A cement pocket could possibly increase penetration by entrapment of bone cement in the undercutting area and directing it into the cancellous bone surface. However, the effect could not be observed in this in vitro scenario. Overall cement penetration was similar in the FB and MB group. The results from Vertullo and Davey on 177 consecutive TKA showed twice as deep cement penetration in lipped baseplates compared to unlipped ones . However, the data was derived from radiographs, which is questionable as the implants and the keels obscure some of the cemented area. In our experience, accuracy of discrimination between cement under the baseplate and real penetration is difficult and error-prone under those circumstances. Furthermore, the actual cement penetration depth into the bone could not be visualized by the cited study setup due to the interference of cement with flanges and stem and only the lateral part of the tray was studied. In our observation, the overall penetration depths were similar in both groups, as we could not observe a significant increase in cement penetration in the FB group. On the other hand, a cement pocket may enforce rotational stability. However, this issue was not investigated in the present study. Penetration depths in our setting ranged from 0.93 to 1.42 mm and match perfectly with the data retrieved in a preceding investigation . A mean cement penetration of 3 to 4 mm has been suggested to be the optimum for implant fixation -. Comparing the values to our data indicates that former studies could not differentiate between cement layer under the tray and actual penetration. Hence, cement penetration has probably been reported as a combination of both components, which might explain the observed differences. Further studies on bone cement penetration should focus on the “real” penetration into cancellous bone, as presented here. The thickness of the cement layer extending from the undersurface of the implant to the osseous surface was higher in the FB group (mean 2.32 mm) compared to the MB group (mean 1.47 mm). This effect is most likely related to the cement pockets of the FB implant and suggests that cement layer thickness is mainly influenced by implant design. Whether a thicker cement mantle is beneficial or detrimental is unclear and needs further research.
The small sample size is a limitation of the study. However, since the effects were similarly observed for each pair, the small sample size should not have biased the results. The transfer of in vitro testing to in vivo conditions remains limited, which has to be kept in mind when interpreting the presented results.
In summary, the present study suggests that cement pockets with undercuts do not alter or enforce bone cement penetration under a tibial tray in an in vitro scenario.
Financial support for this study was received from DePuy Orthopaedics. Furthermore, we acknowledge financial support by Deutsche Forschungsgemeinschaft and Ruprecht-Karls-Universität Heidelberg within the funding program Open Access Publishing.
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