title: Temperature changes during cortical bone drilling with a newly designed step drill and an internally cooled drill.
abstract: OBJECTIVE
  Bone drilling causes an increase in bone temperature, and a temperature above 47°C is critical because it causes thermal bone necrosis. Thermal osteonecrosis is common with the drill diameter of ≥4.5 mm without cooling. The aim of this study was to determine the increase of bone temperature during drilling using newly contructed two-step and internally cooled drills.
  
  
  METHODS
  An experiment was set up according to a central composite design. An internally cooled drill (3.4 mm and 4.5 mm) and a two-step drill (2.5/3.4 and 3.4/4.5 mm) were used in combination with feed rates of (0.02, 0.04, 0.10, 0.16 and 0.18 mm/rev) and cutting speeds (1.18, 10.68, 33.61, 56.55 and 66.05 m/min) with and without cooling with water of 24°C. Bone temperatures were measured with thermocouples. Drilling was performed on pig diaphyses with a three-axis mini milling machine.
  
  
  RESULTS
  Bone temperatures in all combinations of parameters with internal cooling were below the critical 47°C (p=0.05). The highest temperatures were detected using a 4.5-mm drill (40.5°C). A statistically significant effect other than cooling was found with the drill diameter and feed. A drill diameter of 3.4 mm with internal cooling developed a maximum temperature of 38.5°C and without cooling 46.3°C. For the same conditions a drill with diameter of 4.5 mm reached temperatures of 40.5°C and 55.7°C, respectively. The effect of feed rate is inversely proportional to the increase in bone temperature. With the feed rate 0.16 mm/rev, temperature was below critical even using the 4.5-mm drill (46.4°C, p=0.05). Using the 3.4-mm drill all temperatures were below critical (46.2°C, p=0.05). The two-step drill compared to a standard drill with the same diameter did not show statistical differences in maximum bone temperatures for all combinations of parameters (p=0.05).
  
  
  CONCLUSIONS
  A two-step drill does not have any advantages over a standard twist drill of the same diameter. An internally cooled drill causes a significantly smaller increase of bone temperature during drilling with water of 24°C. An internally cooled drill is currently the 'ideal' drill for traumatology/orthopaedics because it produces the smallest increase in bone drilling temperature. If internal cooling is used the regulation of other drilling parameters is of no importance.
authors.affiliation: Department of Surgery, University Hospital Center Zagreb and School of Medicine, University of Zagreb, Kišpatićeva 12, 10000 Zagreb, Croatia. augustin.goran@gmail.com
authors.forename: Goran
authors.initials: G
authors.lastname: Augustin
authors.forename: Slavko
authors.initials: S
authors.lastname: Davila
authors.forename: Toma
authors.initials: T
authors.lastname: Udilljak
authors.forename: Tomislav
authors.initials: T
authors.lastname: Staroveski
authors.forename: Danko
authors.initials: D
authors.lastname: Brezak
authors.forename: Slaven
authors.initials: S
authors.lastname: Babic
mesh_terms: D000818:Animals; D001831:Body Temperature; D002056:Burns / Q000209:etiology*; D004867:Equipment Design; D005269:Femur / Q000293:injuries* / Q000601:surgery; D006358:Hot Temperature / Q000009:adverse effects*; D008297:Male; D019637:Orthopedic Procedures / Q000009:adverse effects / Q000295:instrumentation; D010020:Osteonecrosis / Q000209:etiology / Q000517:prevention & control; D013552:Swine