A Belmont Report

Process Modeling

Case Study: Sequential Bone Drilling

Bone drilling is common in many orthopaedic procedures, including predrilling for screw placement, temporary bony fixation, and surface preparation for joint fusion. Significant heat is produced during drilling due to material removal and frictional resistance between the cortical bone and the drill. This heat dissipated from the drilling site can cause damage to the surrounding bone through thermal osteonecrosis, which is the result of the temporary or permanent loss of blood supplied to the bone that consequently leads to osteocyte and bone death. To suppress the heat, studies have shown that drill size, cutting speed, and irrigation have significant effects on bone temperature. Optimizing the sequence of holes drilled can also significantly reduce heat accumulation and thus associated thermal damage.

Experimental techniques (using a portion of ex vivo human shin bones) and finite element analysis (using a 3D axisymmetric advection inverse heat transfer model) were used to understand the process of heat spread during bone drilling.

Results of the techniques described below can be found in both the Journal of Orthopaedic Research (Heat accumulation during sequential cortical bone drilling) and Medical Engineering & Physics (Numerical evaluation of sequential bone drilling strategies based on thermal damage).

Schematic representation of the advection model for drilling heat transfer in finite element analysis.

 

Model configuration of 3D heat transfer FEA for bone drilling.

 

Sequential drilling in ankle surgery (left) and a simplified model in FEA (right).

 

Overall experimental setup (left) with a Stryker hand-drill attached to a linear stage, a bone sample with embedded themocouples, and a force dynamometer, a representative bone sample post sequential drilling (middle), and the cutting tools investigated: a twist drill (top right) and a Kirschner wire (bottom right).

 

Optimized drilling sequences for “corner” (top) and “middle” (bottom) starts. This is achieved by trying to place sequential holes as physically far apart as possible.

 

Temperature distribution (top) and predicted thermal damage (bottom) for(a) twist drill and (b) K-wire at 10 s after drilling Hole 9.