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Research Paper

Sagittal Bone Saw With Orbital Blade Motion for Improved Cutting Efficiency

[+] Author and Article Information
Thomas P. James

e-mail: thomas.james@tufts.edu

Anil Saigal

Laboratory for Biomechanical Studies,
Department of Mechanical Engineering,
Tufts University,
200 College Avenue,
Medford, MA 02155

1Corresponding author.

Manuscript received March 26, 2012; final manuscript received December 29, 2012; published online February 13, 2013. Assoc. Editor: Jahangir Rastegar.

J. Med. Devices 7(1), 011009 (Feb 13, 2013) (7 pages) Paper No: MED-12-1046; doi: 10.1115/1.4023500 History: Received March 26, 2012; Revised December 29, 2012

Sagittal bone saws are used by orthopedic surgeons for resection of bone; for example in total joint arthroplasty of the hip and knee. In order to prevent damage to surrounding tissue, sagittal saw blades typically oscillate through a small angle, resulting in reduced cutting rates due to short stroke lengths. To improve bone cutting efficiency, sagittal saws oscillate at high speeds, but this creates frictional heating that can harm bone cells. The focus of this research was to design a new sagittal sawing device for improved cutting efficiency. It was hypothesized that the addition of an impulsive thrust force during the cutting stroke would increase cutting rates in cortical bone. A cam-driven device was developed and tested in bovine cortical bone. The impulsive thrust force was achieved by creating a component of blade motion perpendicular to the cutting direction, i.e., orbital blade motion. At the start of each cutting stroke, the mechanism drove the saw blade into the surface of the bone, increasing the thrust force with the intention of increasing the depth of cut per tooth. As each cutting stroke was completed, the blade was retracted from the surface for the purpose of clearing bone chips. The design parameters investigated were cutting stroke length, thrust stroke length, and blade oscillation frequency. A three-factor, two-level design of experiments approach was used to simultaneously test for the effect of design parameters and their interactions on volumetric cutting rate (n = 32). The addition of orbital blade motion to the sagittal saw improved bone cutting rates over traditional oscillatory motion, especially at lower cutting stroke lengths and higher oscillation frequencies (p < 0.05). However, the magnitude of orbital blade motion based on thrust stroke length was limited by a threshold value of approximately 0.10 mm that when exceeded caused the sagittal saw to rebound from the surface of the bone causing erratic cutting conditions. The factor with the greatest positive effect on cutting rate was oscillation frequency. Cutting rates in cortical bone can be improved with the proposed orbital action sagittal saw.

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Figures

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Fig. 1

Figure-eight saw blade motion created by the new sagittal sawing device. From point (a) to point (b), a thrust force is created by a cam mechanism to drive the saw blade teeth deeper into the surface of the bone on each cutting stroke.

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Fig. 2

Major components of the new sagittal sawing device: (a) cutting camshaft, (b) thrust camshaft, (c) pivot shaft, (d) blade carrier, (e) saw blade, and (f) linear bearings

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Fig. 3

Variations in cutting path based on phase offset angle between the thrust and cutting camshafts: (a) 0 deg, (b) 22.5 deg, (c) 45 deg, and (d) 67.5 deg

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Fig. 4

Camshaft bearing assembly responsible for cutting stroke: (a) camshaft, (b) spur gear, (c) gear retention nut, (d) shaft bearing retention nut, (e) shaft bearings, (f) cam offset bearing, (g) cam bearing retention nut, (h) shaft bearing housing, (i) linear bearing housing, and (j) linear bearing

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Fig. 5

Sagittal sawing mechanism used in the design of experiments: (a) front view, (b) side view

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Fig. 6

Test apparatus used to apply a constant thrust force during experiments with the sagittal sawing device

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Fig. 9

Normalized effect of main factors and their interactions on volumetric cutting rate. Thrust = thrust stroke length; cutting = cutting stroke length; freq = oscillation (cutting) frequency.

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Fig. 8

Results from the three-factor, two-level design of experiments showing the effect of design parameters on cutting rate. Cutting stroke length: (high) = 7.13 mm and (low) = 2.88 mm; oscillation frequency (high) = 154 Hz and (low) = 122 Hz.

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Fig. 7

Thrust force plot from the dynamometer showing the start and end times for one cut, which were used to determine volumetric cutting rate

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