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Session: Medical Instruments - Surgery I
Session starts: Friday 25 January, 10:30
Presentation starts: 11:00
Room: Lecture room 557

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Sanaz Berahmani ()
Dennis Janssen ()
David Wolfson ()
Maarten de Waal Maelfijt ()
Nico Verdonschot ()

Abstract:
To achieve desirable outcomes in cementless total knee arthroplasty (TKA), sufficient primary stability is essential. The primary stability inhibits excessive motions at the bone-implant interface, hence providing the necessary condition for osseointegration [1]. Primary stability for cementless TKA is provided by press-fit forces between the bone and implant. The press-fit forces depend on several factors including interference fit, friction between bone and implant surface, and the bone material properties. It is expected that bone mineral density (BMD) will affect the stability of cementless TKA [2]. However, the effect of BMD on the primary stability of cementless femoral knee component has not been investigated in vitro. Calibrated CT-scans of 9 distal femora were obtained after the surgical cuts were made by an experienced surgeon. Since the press-fit forces of the femoral component mainly occur in the AP-direction, the BMD was measured in the anterior and posterior faces for a depth of 5mm; this depth was based on stress distributions from a Finite Element Analysis of the same implant design. In addition, four strain gauges were connected to different locations on the implant’s outer surface to measure strain as representative of bone relaxation. A cementless Sigma CR femoral component (DePuy International, Leeds, UK) was then implanted using an MTS machine. In order to simulate a ‘normal’ bone condition, the implanted bone was pre conditioned for one hour at a cyclic load of 300-1500 N, and a rate of 1Hz. In addition, two waiting periods of 30 minutes were included before and after the dynamic loading. Finally, the implants were pushed-off from the bone in a high-flex position. Forces and displacements were recorded both during insertion and push-off tests. Strong correlations were found for insertion and push-off forces with BMD (R2=0.82 and R2=0.88, respectively). A strong linear correlation was also found between final strain and push-off forces (R2=0.90). BMD also showed strong correlation with final strain corrected for maximum strain measured during insertion (R2=0.80). There is no consensus on the best fixation method for the TKA but some surgeons prefer a cementless design for young and active patients. The results of our study showed that the primary stability of a cementless femoral component depends on the bone mineral density. Therefore, patient selection based on bone quality may increase the likelihood of good osseointegration and adequate long-term fixation for cementless femoral knee components.