Screw-blade fixation systems for implant anchorage in the femoral head: Horizontal blade orientation provides superior stability. Issue 7 (July 2021) - Schopper, Clemens
Highlights: Novel biomechanical investigation of two recent screw-blade implant systems utilized for fixation of proximal femoral fractures. Human cadaveric biomechanical testing using both paired and BMD-matched group assignments. BMD evaluation by means of CT scanning with use of calibration phantom. Large sample size featuring forty specimens assigned to four study groups. Novel test setup investigating sensitivity towards accuracy of implantation via precise and deviant implant positioning scenarios. Precise, innovative protocol for progressively increasing cyclic loading with implementation of electrical interface for failure detection. Abstract: Objectives: Despite continual improvement in the methods and devices used for treatment of proximal femoral fractures, unacceptably high failure rates remain. Novel screw-blade implant systems, combining a lag screw with a blade – the latter adding rotational stability to the femoral head – offer improvement of osseous purchase, especially in osteoporotic bone. The aim of this study was to compare biomechanically the head element (HE) anchorage of two screw-blade implant systems differing in blade orientation in the femoral head – vertical versus horizontal. Methods: Twenty paired human cadaveric femoral heads were assigned to four groups ( n = 10), implanted with either Rotationally Stable Screw-Anchor HE (RoSA-HE, vertical blade orientation) or Gamma3 Rotation Control Lag Screw (Gamma-RC, horizontal blade orientation) in center or off-center position, and biomechanically tested until failure under progressively increasing cyclic loading at 2 Hz. Results: Cycles to failure and failure load were significantly higher for Gamma-RC versus RoSA-HE in center position and not significantly different between them in off-center position, p = 0.03 and p = 0.22, respectively. In center position, the progression of both rotation around implant axis and varus deformation over time demonstrated superiority of the implant with horizontal versus vertical blade orientation. Compared with center positioning, off-center implant placement led to a significant decrease in stiffness, cycles to failure and failure load for Gamma-RC, but not for RoSA-HE, p < 0.01 and p = 0.99, respectively. Conclusion: Horizontal blade orientation of screw-blade implant systems demonstrates better anchorage in the femoral head versus vertical blade orientation in center position. As the stability of the implant system with horizontal blade orientation drops sharply in off-center position, central insertion is its placement of choice.