Abstract
BackgroundGiven the increasing number of osteoporotic fractures of the distal femur, screw augmentation with bone cement is an option to enhance implant anchorage. However, in implant removal or revision surgeries, the cement cannot be removed from the distal femur without an extended surgical procedure. Therefore, the aims of this study were to investigate (1) whether cement augmentation has any influence on screw removal and removal torque, and (2) whether the implantation of a femoral component of a knee arthroplasty and its initial interface stability are affected by the remaining screws/cement.Material and methodsEight pairs of fresh-frozen human female cadaveric distal femurs (mean age, 86 years) with a simulated AO/OTA 33 A3 fracture were randomized in paired fashion to two groups and fixed with a distal femoral locking plate using cannulated perforated locking screws. Screw augmentation with bone cement was performed in one of the groups, while the other group received no screw augmentation. Following biomechanical testing until failure (results published separately), the screws were removed and the removal torque was measured. A femoral component of a knee arthroplasty was then implanted, and pull-out tests were performed after cement curing. Interference from broken screws/cement was assessed, and the maximum pull-out force was measured.ResultsThe mean screw removal torque was not significantly different between the augmented (4.9 Nm, SD 0.9) and nonaugmented (4.6 Nm, SD 1.3, p = 0.65) screw groups. However, there were significantly more broken screws in in the augmented screw group (17 versus 9; p < 0.001). There was no significant difference in the pull-out force of the femoral component between the augmented (2625 N, SD 603) and nonaugmented (2653 N, SD 542, p = 0.94) screw groups.ConclusionThe screw removal torque during implant removal surgery does not significantly differ between augmented and nonaugmented screws. In the augmented screw group, significantly more screws failed. To overcome this, the use of solid screws in holes B, C, and G can be considered. Additionally, it is possible to implant a femoral component for knee arthroplasty that retains the initial anchorage and does not suffer from interference with broken screws and/or residual cement.Level of Evidence 5
Highlights
6% of all femoral fractures occur at the distal femur, so they are relatively rare [1]
The aims of this study were to investigate whether (1) screw removal is possible following augmentation, (2) the screw removal torque is affected by the augmentation, and (3) there is interface instability in cases when knee arthroplasty is required after screw augmentation
In the augmented screw group, 7 broken screws were located in hole B, 6 broken screws were in hole C, and 4 broken screws were in hole G
Summary
6% of all femoral fractures occur at the distal femur, so they are relatively rare [1]. Approximately 50% of all distal femoral fractures occur in elderly patients, implying that the number of osteoporotic fractures is rising. Supracondylar fractures are the most common type in the elderly due to attenuated bone quality, especially within the metaphyseal part of the distal femur [3, 4]. The osteosynthesis of such fractures is challenging due to reduced implant anchoring [5, 6]. Given the increasing number of osteoporotic fractures of the distal femur, screw augmentation with bone cement is an option to enhance implant anchorage. The aims of this study were to investigate (1) whether cement augmentation has any influence on screw removal and removal torque, and (2) whether the implantation of a femoral component of a knee arthroplasty and its initial interface stability are affected by the remaining screws/cement
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