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Technical Briefs

Adjustable Slot Cutting Guide for Improved Accuracy During Bone Resection in Total Knee Arthroplasty

[+] Author and Article Information
Thomas P. James

Associate Professor
Department of Mechanical Engineering,
Tufts University,
200 College Avenue,
Medford, MA 02155
e-mail: thomas.james@tufts.edu

Owen P. McGonigle

Orthopaedic Resident
Tufts Medical Center,
Department of Orthopaedics,
800 Washington Street,
Boston, MA 02111

Imran S. Hasan

Internal Medicine Resident
Kaiser Permanente Santa Clara,
710 Lawrence Expressway,
Santa Clara, CA 95051

Eric L. Smith

Chief of Arthroplasty
Tufts Medical Center,
Department of Orthopaedics,
800 Washington Street,
Boston, MA 02111

1Corresponding author.

Manuscript received August 18, 2012; final manuscript received August 1, 2013; published online December 5, 2013. Assoc. Editor: William K. Durfee.

J. Med. Devices 7(4), 044502 (Dec 05, 2013) (6 pages) Paper No: MED-12-1104; doi: 10.1115/1.4025341 History: Received August 18, 2012; Revised August 01, 2013

Slotted cutting guides are used by orthopaedic surgeons to improve the accuracy of bone resection during total knee replacement. Accuracy of the saw cuts has an effect on patient mobility and on implant survival time. While computer navigation systems have improved the accuracy of cutting guide placement, the contribution to cutting error from blade toggle within the slots of the cutting guide persists. In this research, equations were derived to quantify angular cutting error based on the parameters affecting blade and cutting guide geometry. Analytically, the relationship between cutting plane error and blade thickness was determined to be linear. A smaller gap, due to thicker blades with minimal tooth offset, results in less cutting error. From an experimental standpoint, six commercially available cutting guides were tested for femoral plane cutting accuracy by resection of synthetic bone under the guidance of computer navigation. The results indicate an average flexion/extension error of 3.8 deg for a 0.89 mm thick blade and 2.0 deg for a 1.27 mm blade. Varus/valgus error due to twisting of the blade within the slot was less than 1.0 deg, regardless of blade thickness. To improve upon cutting accuracy, an adjustable slot cutting guide was designed and tested. From more closely matching slot width to blade thickness, the results indicate that cutting plane error can be reduced to less than 1.0 deg in both the flexion/extension and varus/valgus planes.

FIGURES IN THIS ARTICLE
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Copyright © 2013 by ASME
Topics: Blades , Cutting , Errors , Bone
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References

Figures

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Fig. 1

Bone cutting error on the distal end of the femur. Flexion/extension error, defined here by the angle θ, is rotation of the planar cut about an axis formed by the intersection of the transverse and coronal (frontal) planes. Varus/valgus error, defined here by the angle ϕ, is rotation of the planar cut about an axis formed by the intersection of the transverse and sagittal planes.

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Fig. 2

Cross-section of the cutting guide (side view) showing the parameters involved in determining angular flexion/extension error, defined by θ

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Fig. 3

Cross-section of the cutting guide (front view), perpendicular to the length of the blade, showing the parameters involved in determining angular varus/valgus error, defined by ϕ

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Fig. 4

Prototype of the proposed cutting guide with an adjustable slot width to improve cutting accuracy (constant cutting guide length = 19.0 mm)

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Fig. 5

(a) Using the computer navigation system to establish the initial location of the prototype cutting guide on the distal end of the femur and (b) measurement of varus/valgus and flexion/extension angles relative to initial cutting guide placement

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