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Technical Briefs

Biomechanical Measurements of Surgical Drilling Force and Torque in Human Versus Artificial Femurs

[+] Author and Article Information
Meisam Salahi, Farrokh Janabi-Sharifi

Department of Mechanical and Industrial Engineering,
Ryerson University,
Toronto, ON, M5B 2K3, Canada

Emil H. Schemitsch

Martin Orthopaedic Biomechanics Laboratory,
St. Michael's Hospital,
Toronto, ON, M5B 1W8, Canada;
Department of Surgery,
University of Toronto,
Toronto, ON, M5G 1L5, Canada

Rad Zdero

Department of Mechanical and Industrial Engineering,
Ryerson University,
Toronto, ON, M5B 2K3, Canada;
Martin Orthopaedic Biomechanics Laboratory,
St. Michael's Hospital,
Toronto, ON, M5B 1W8, Canada
e-mail: zderor@smh.ca

1Corresponding author. Present address: Biomechanics Lab, St. Michael's Hospital, Li Ka Shing Building, West Basement, Room B114/B116, 38 Shuter Street, Toronto, ON, M5B 1W8, Canada.

Contributed by the Bioengineering Division of ASME for publication in the JOURNAL OF BIOMECHANICAL ENGINEERING Manuscript received June 8, 2012; final manuscript received October 10, 2012; accepted manuscript posted October 25, 2012; published online December 5, 2012. Assoc. Editor: Pasquale Vena.

J Biomech Eng 134(12), 124503 (Dec 05, 2012) (9 pages) doi:10.1115/1.4007953 History: Received June 08, 2012; Revised October 10, 2012; Accepted October 25, 2012

Few experimental studies have examined surgical drilling in human bone, and no studies have inquired into this aspect for a popular commercially-available artificial bone used in biomechanical studies. Sixteen fresh-frozen human femurs and five artificial femurs were obtained. Cortical specimens were mounted into a clamping system equipped with a thrust force and torque transducer. Using a CNC machine, unicortical holes were drilled in each specimen at 1000 rpm, 1250 rpm, and 1500 rpm with a 3.2 mm diameter surgical drill bit. Feed rate was 120 mm/min. Statistical significance was set at p < 0.05. Force at increasing spindle speed (1000 rpm, 1250 rpm, and 1500 rpm), respectively, showed a range for human femurs (198.4 ± 14.2 N, 180.6 ± 14.0 N, and 176.3 ± 11.2 N) and artificial femurs (87.2 ± 19.3 N, 82.2 ± 11.2 N, and 75.7 ± 8.8 N). For human femurs, force at 1000 rpm was greater than at other speeds (p ≤ 0.018). For artificial femurs, there was no speed effect on force (p ≥ 0.991). Torque at increasing spindle speed (1000 rpm, 1250 rpm, and 1500 rpm), respectively, showed a range for human femurs (186.3 ± 16.9 N·mm, 157.8 ± 16.1 N·mm, and 140.2 ± 16.4 N·mm) and artificial femurs (67.2 ± 8.4 N·mm, 61.0 ± 2.9 N·mm, and 53.3 ± 2.9 N·mm). For human femurs, torque at 1000 rpm was greater than at other speeds (p < 0.001). For artificial femurs, there was no difference in torque for 1000 rpm versus higher speeds (p ≥ 0.228), and there was only a borderline difference between the higher speeds (p = 0.046). Concerning human versus artificial femurs, their behavior was different at every speed (force, p ≤ 0.001; torque, p < 0.001). For human specimens at 1500 rpm, force and torque were linearly correlated with standardized bone mineral density (sBMD) and the T-score used to clinically categorize bone quality (R ≥ 0.56), but there was poor correlation with age at all speeds (R ≤ 0.37). These artificial bones fail to replicate force and torque in human cortical bone during surgical drilling. To date, this is the largest series of human long bones biomechanically tested for surgical drilling.

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References

Figures

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Fig. 1

Cross-sectional views of typical (a) human and (b) artificial femoral cortical specimens used for surgical drilling into the anterior cortex. White arrows show the approximate direction and location of drilling.

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Fig. 2

Experimental setup for surgical drilling into human and artificial femoral bone

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Fig. 6

Maximum torque results. Error bars are one standard deviation. SSD = statistically significant differences.

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Fig. 5

Maximum force results. Error bars are one standard deviation. SSD = statistically significant differences.

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Fig. 4

Typical smoothed data for drilling at 1000 rpm showing (a) force for a human femur, (b) torque for a human femur, (c) force for an artificial femur, and (d) torque for an artificial femur. Similar graphs were evident at other spindle speeds. Maximum force and torque were extracted from each graph. Measured unicortical thickness (MUT) was obtained only from the force graph using 1 N as the criterion for drill bit tip entry and exit and was then adjusted by subtracting the 1.6 mm length of the drill bit tip to obtain the true unicortical thickness. Torque beyond MUT was an artifact due to ongoing interfacial friction between the spinning drill bit and the hole, as the drill bit continued to be fed through the completed hole beyond its far wall. The human femur graphs are for specimen 11 (Table 1).

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Fig. 3

Typical raw unsmoothed data for drilling at 1000 rpm showing (a) force for a human femur, (b) torque for a human femur, (c) force for an artificial femur, and (d) torque for an artificial femur. Similar graphs were generated at other spindle speeds. Large arrows indicate the “step” in drilling load upon drill bit entry. The human femur graphs are for specimen 11 (Table 1).

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