Thermal analysis during bone drilling using rigid polyurethane foams: numerical and experimental methodologies

Osteotomy or bone cutting is a common procedure in orthopaedic surgery, mainly in the treatment of fractures and reconstructive surgery. However, the excessive heat produced during the bone drilling process is a problem that counters the benefits of this type of surgery, because it can result in thermal osteonecrosis, bone reabsorption and damage the osseointegration of implants. The analysis of different drilling parameters and materials can allow to decrease the temperature during the bone drilling process and contribute to a greater success of this kind of surgical interventions. The main goal of this study was to build a numerical three-dimensional model to simulate the drilling process considering the type of bone, the influence of cooling and the bone density of the different composite materials with similar mechanical properties to the human bone and generally used in experimental biomechanics. The numerical methodology was coupled with an experimental methodology. The use of cooling proved to be essential to decrease the material damage during the drilling process. It was concluded that the materials with less porosity and density present less damage in drilling process. The developed numerical model proved to be a great tool in this kind of analysis. © 2016, The Brazilian Society of Mechanical Sciences and Engineering.

Influence of drill speed and feed rate on bone damage

Implant failures and postoperative complications are often associated to the bone drilling. Estimation and control of drilling parameters are critical to prevent mechanical damage to the bone tissues. For better performance of the drilling procedures, it is essential to understand the mechanical behaviour of bones that leads to their failures and consequently to improve the cutting conditions. This paper investigates the effect of drill speed and feed-rate on mechanical damage during drilling of solid rigid foam materials, with similar mechanical properties to the human bone. Experimental tests were conducted on biomechanical blocks instrumented with strain gauges to assess the drill speed and feed-rate influence. A three-dimensional dynamic finite element model to predict the bone stresses, as a function of drilling conditions, drill geometry and bone model, was developed. These simulations incorporate the dynamic characteristics involved in the drilling process. The element removal scheme is taken into account and allows advanced simulations of tool penetration and material removal. Experimental and numerical results show that generated stresses in the material tend to increase with tool penetration. Higher drill speed leads to an increase of von-Mises stresses and strains in the solid rigid foams. However, when the feed-rate is higher, the stresses and strains are lower. The numerical normal stresses and strains are found to be in good agreement with experimental results. The models could be an accurate analysis tool to simulate the stresses distribution in the bone during the drilling process.

Thermal analysis in the drilling of solid rigid foam materials and ex-vivo bovine bones

Bone is a dynamic, highly vascularized tissue with a unique capacity to heal and regenerate without scarring. However, drilling remains a concern in several clinical procedures due to thermal damage of the bone and surrounding tissue. The success of this surgeries is dependent of many factors and also in temperature generation during the drilling bone. When an excessive heat is produced during the drilling, thermal necrosis can occur and the bone suffers injuries. Studies have shown that the increased temperature is directly related with the drilling parameters, particularly, the drill speed, feed-rate, applied force, the depth of cut, the geometry of the drill bit, the use or not of a cooling system and also the type of bone.