Surgical saw blades are medical devices that are used with surgical power tool systems and that enable the bones to be shaped by cutting (osteotomy). Today, surgical saw blades are disposable medical devices. So how important is surgical saw blade tooth geometry in osteotomy?
During cutting, a heat is generated due to friction between the surgical saw blade and the bone. It is known that this heat on the bone negatively affects the healing process after the operation. Obvious side effects of increases in the temperature of the bone during cutting or drilling; impaired bone regeneration (Eriksson AR, Albrektsson T, 1984), bone infection, decreased bone mechanical strength (Christie, 1981) and delayed postoperative recovery. (Pallan, 1960)
Toksvig-Larsen et al. (1992) compared different saw blades (Figure 1) with different designs and showed that the saw geometry is not decreasing the temperature to below the critical level (47 – 50 ° C). Table 1 shows the results for cutting bovine bone using different saw blades.
Regardless of the extensive usage of saw blades and surgical power tools in surgeries, there are few researchers investigating saw blade performance in experimental models (Krause et al., 1982; Wevers et al., 1987; Toksvig-Larsen et al., 1990; 1992; Ark et al., 1997a; 1997b; 1997c). For any orthopedic operation, the durability of the blade has been a major concern for all surgeons (Ark ve diğerleri, 1997b). In addition, blunt blades require the application of extra force, which can contribute to excessive friction heat (Allan et al., 2005). The abrasion of the saw blade has been linked to two different criteria. Firstly, it is assumed that the reuse of the blade blunts the blade, and secondly, it is assumed that the accidental contact of the blade with a metal jig or cutting guide during surgery may be the main cause of the blunt blade. Wevers et al. (1987) found that half of the saw blades taken from the operating room were seriously damaged. They stated that reuse of saw blades may decrease cutting efficiency. They also found that the force required to cut the cortical bone using a blunt saw blade (32.08 N) was about five times higher than the force required with new blades (6.75 N). This result is consistent with the findings of Matthews and Hirsch (1972) investigating the in vitro drilling process in the human cortical femoral bone. (Worn drill bits cause huge temperature increases compared to new drill bits)
Ehlinger et al. in 2019 investigated whether surgical saw blade tooth geometry influences crack initiation or progression on the hinge for high tibial osteotomy.
They divided the saw blade tooth geometry into 3 shapes as shown in Figure 2 below. These are “Rectangular, U-shaped and V-shaped”.
They measured the local stress concentration and energy release rate for these three shapes. They found that the U-shaped surgical saw blade tooth geometry had the lowest local stress concentration and lowest energy release rate. That is, the rate of crack formation or propagation of the U-shaped geometry was the lowest.
As a result, the surgical saw blade tooth geometry is not very effective in reducing the temperature on the bone below the critical level. The more important part here is the use of a new (sharp-toothed) blade and the way the surgeon uses the blade. It is recommended that surgeons wait 5 seconds every 10 seconds while cutting. Interruption in cutting processes will significantly reduce cortical bone temperature elevation. This is a very important procedure in very dense bone types. (Sharawy et al., 2002; Wachter and Stoll, 1991).
In contrast, surgical saw blade tooth geometry is important for crack initiation or propagation in cortical bone. As seen above, a U-shaped surgical saw blade has a lower rate of crack initiation or propagation than others.
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