Cement Bonds Screw Implants into Bone

Implant failure is a well acknowledged complication both in human and veterinary orthopedic surgery. Various biomaterials and coating methods have been designed to increase bone-implant interface stability. Wear debris formation and subsequent implant loosening are downsides of the non-resorbable bone cements such as PMMA, whereas both Ca- and Mg-cement can increase the biomechanical strength of the bone-implant interface and yet be resorbed during bone remodeling. A potential advantage of Mg-cement is the adhesive properties, demonstrated to increase extraction torque of screws in canine bones. If these biomechanical properties could be sustained, implant failure may be reduced.

In this study cortical bone screws were placed into horse cannon bones. Each screw hole was injected with either Calcium(Ca)-cement (Norian SRS, Synthes Inc.), Magnesium(Mg)-cement (Ostecrete, Bone Solutions, Inc.), polymethylmethacrylate (PMMA; Simplex, Synthes Inc.) or left untreated as a control. Cements were allowed to set. Torque necessary to extract the screw were analyzed among the groups to determine the biomechanical stability of the bone-screw interface. Histomorphometry was used to evaluate bone activity and characteristics of the bone-implant interface. Computed tomography was used to quantify material location and presence next to the screw. Mg-cement significantly increased the extraction torque compared to control (p=0.019) and Ca-cement (p=0.012) and interface toughness (energy absorbed to failure) compared to control (p=0.007), Ca-cement (p=0.012) and PMMA (p=0.027). Histologically all cements distributed well around the screw. These results suggested that the Mg-cement can improve the biomechanical strength of the bone-implant interface. Use of this cement may increase the strength of our fracture repairs. orthopedic surgical procedures.

Graph 1 – Extraction torque (Nmm) and energy absorbed to failure (Nmm°) for screws inserted to equine cannon bones with or without a cement. a, b- significant difference between control and Ca-cement. a, b, c- significant difference between control, Ca-cement and PMMA (p<0.05).
Extraction Torque Energy Absorbed to Failure
Figure 2 – Computed tomography 3D reconstruction images of bone-screw interface. Note boxes where density was measured within and adjacent to the threads confirming the presence of cement.
Computed tomography 3D reconstruction images of bone-screw interface Computed tomography 3D reconstruction images of bone-screw interface Computed tomography 3D reconstruction images of bone-screw interface

Histomorphometry

All threads were filled with cement indicating consistent distribution of material.

Figure 1 – Photomicrographs of longitudinal sections of cortical screws with cement in equine cannon bones. Figures A-F. A and D) Ca-cement B and E) Mg-
Photomicrographs of longitudinal sections of cortical screws with cement in equine cannon bones Photomicrographs of longitudinal sections of cortical screws with cement in equine cannon bones Photomicrographs of longitudinal sections of cortical screws with cement in equine cannon bonesPhotomicrographs of longitudinal sections of cortical screws with cement in equine cannon bones
Photomicrographs of longitudinal sections of cortical screws with cement in equine cannon bones Photomicrographs of longitudinal sections of cortical screws with cement in equine cannon bones Photomicrographs of longitudinal sections of cortical screws with cement in equine cannon bones

Conclusions

This study suggests that Mg-cement can safely and effectively improve the biomechanical strength of the bone-implant interface. When clinically available, Mg-cement may be beneficial in reducing the likelihood of implant failure.