Distribution of coolant during drilling with open type internally cooled medical steel drill

Progress in Excision Methods of Bone Materials

Bone resection is a common technique in modern surgery, which can be divided into contact (such as mechanical osteotomy and ultrasonic osteotomy) and non-contact (such as laser osteotomy). Irrespective of the excision method, it causes processing damage to natural bone material, thus affecting bone healing. To reduce the machining damage in bone resection, different machining variables (cutting fluid temperature, feed rate, rotational speed, and ultrasonic frequency) were considered to explore the selection of various cutting conditions. This paper reviews the excision of natural bone materials including mechanical osteotomy, laser osteotomy, and ultrasonic osteotomy, especially traditional drilling and ultrasonic cutting, which represent the traditional and prospective methods of bone excision technology, respectively. Finally, the differences between methods are emphasized and the future trends in osteotomy technology and condition control during osteotomy are analyzed.

Study of the burr height at hole exit in bone drilling by twist drills

The burr at the hole exit is one of the key factors affecting bone drilling performances. In order to reduce burr height at hole exit during cortical bone drilling, the four key parameters in twist drilling of bones are analyzed based on the response surface method (RSM). The prediction model of the burr height is obtained via the analysis of variance. The influence trend and size of each factor on the height of the burr are further analyzed based on the RSM. Experimental results show that smaller point angle and diameter of the twist drill, smaller feed speed, and higher rotational speed can effectively reduce the burr height at hole exit. Then, the geometric variables of the twist drill and process parameters are optimized. When the point angle of the twist drill 2 Φ = 95°, the diameter D = 2.5 mm, the rotational speed n = 1500 rpm, and the feed speed vf  = 10 mm/min, the height of the burr at hole exit reaches the smallest. At the same time, the burr at the exit of the hole with different diameters of twist drills is studied. It is found to be beneficial to select a twist drill with a smaller diameter for drilling when the requirements of drilling are fulfilled.

Local heat generation during screw insertion into diaphyseal bone: a biomechanical study on different conditions (e.g. screw type, material, mode of insertion)

Background

The implantation of screws is a standard procedure in musculoskeletal surgery. Heat can induce thermal osteonecrosis, damage the bone and lead to secondary problems like implant loosening and secondary fractures. The aim of this study was to investigate whether screw insertion generates temperatures that can cause osteonecrosis.

Methods

We measured the temperature of twenty human femur diaphysis in a total of 120 measurements, while screws of different material (stainless steel and titanium alloy) and different design (locking and cortex screw) were inserted in three different screwing modes (manual vs. machine screwing at full and reduced rotational speed) with 6 thermocouples (3 cis and 3 trans cortex). Each was placed at a depth of 2 mm with a distance of 1.5 mm from the outer surface of the screw.

Results

The screw design (cortical > locking), the site of measurement (trans-cortex > cis-cortex) and the type of screw insertion (hand insertion > machine insertion) have an influence on the increase in bone temperature. The screw material (steel > titanium), the site of measurement (trans-cortex > cis-cortex) and the type of screw insertion (machine insertion > hand insertion) have an influence on the time needed to cool below critical temperature values. The combination of the two parameters (maximum temperature and cooling time), which is particularly critical for osteonecrosis, is found only at the trans-cortex.

Conclusion

Inserting a screw hast the potential to increase the temperature of the surrounding bone tissue above critical values and therefore can induce osteonecrosis. The trans-cortex is the critical area for the development of temperatures above the osteonecrosis threshold, making effective cooling by irrigation difficult. It would be conceivable to cool the borehole with cold saline solution before inserting the screw or to cool the screw in cold saline solution. If possible, insertion by hand should be considered.