Technical Brief

The Effect of Stem Circumferential Grooves on the Stability at the Implant-Cement Interface

[+] Author and Article Information
Yara K. Hosein

Biomedical Engineering Graduate Program,
Western University,
London, ON N6A 5B9, Canada

Graham J. W. King

Department of Surgery,
Western University,
London, ON N6A 5B9, Canada

Cynthia E. Dunning

Biomedical Engineering Graduate Program,
Department of Surgery, and
Department of Materials & Mechanical Engineering,
Western University,
London, ON N6A 5B9, Canada
e-mail: cdunning@uwo.ca

1Corresponding author.

Manuscript received March 5, 2013; final manuscript received September 16, 2013; published online December 6, 2013. Assoc. Editor: Venketesh N. Dubey.

J. Med. Devices 8(1), 014504 (Dec 06, 2013) (5 pages) Paper No: MED-13-1022; doi: 10.1115/1.4025468 History: Received March 05, 2013; Revised September 16, 2013

The application of stem surface treatments and finishes are common methods for improving stem-cement interface stability in joint replacement systems; however, success of these surfaces has been variable. As opposed to applying a treatment or finish, altering stem design through changing the surface topography of the base stem material may offer some advantages. This study compared the effect of stem circumferential grooving on the torsional and axial stability of cemented stems. Fifteen metal stems were machined from cobalt chrome to have smooth (n = 5) or circumferential-grooved surfaces, where groove depth and spacing was either 0.6 mm (n = 5) or 1.1 mm (n = 5). Stems were potted in aluminum tubes using bone cement, left 24 h to cure, and placed in a materials testing machine for testing using a cyclic staircase loading protocol at 1.5 Hz. All stems were tested independently in compression and torsion on separate testing days, using the same stems repotted with new cement. Motion of the stem was tracked, and failure was defined either as rapid increase in stem motion, or completion of the loading protocol. Statistical analysis was used to compare interface strength and stem motion prior to failure. Grooved stems demonstrated increased interface strength (p < 0.001) and reduced motion (p < 0.01) compared to smooth stems under compression. In torsion, no significant difference was found in strength among the grooved and smooth stems (p = 0.10); however, grooved 1.1 mm demonstrated greatest interface motion prior to catastrophic failure (p < 0.01). Overall, circumferential-grooved stems offered improved stability under compression, and comparable stability in torsion, relative to the smooth stems.

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Fig. 1

Stem surface designs tested in both compression and torsion: (a) smooth, (b) 1.1 mm grooved, and (c) 0.6 mm grooved. All stems were cemented to fixed 20 mm depth, as indicated by the region highlighted by the double arrows.

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Fig. 2

Representative graphs of stem motion for smooth, grooved 0.6 mm and grooved 1.1 mm. (a) Relative stem motion under compression, and (b) relative stem rotation in torsion, was used to determine interface toggle prior to failure. (c) Global stem motion was used to determine the change in stem motion with increased number of cycles at the maximum load, as indicated by the starred region.

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Fig. 3

Interface stability offered by the smooth, grooved 0.6 mm, and grooved 1.1 mm stems under compression, as measured by (a) loads required to cause failure and, (b) interface toggle prior to failure. All stems failed at consistent loads, resulting in zero standard deviation for the measures of load at failure, as seen in part (a). Smooth stems showed the least stability (p < 0.01**) compared to the grooved surfaces.

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Fig. 4

Interface stability offered by the smooth, grooved 0.6 mm and grooved 1.1 mm stems under torsional loading, as measured by (a) torque required to cause failure and, (b) interface toggle prior to failure. No differences were found in the torque to failure among all stems (p = 0.1), however, grooved 1.1 mm stems showed greatest interface toggle prior to failure (p < 0.01*).

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Fig. 5

Stem motion with increased number of cycles at maximum compression load, for grooved 0.6 mm and grooved 1.1 mm stems. Grooved 1.1 mm stems showed increased stem motion compared to the grooved 0.6 mm (p = 0.03).




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