Effect of stem length on prosthetic radial head micromotion

Dave R. Shukla, James S. Fitzsimmons, Kai Nan An, Shawn W. O'Driscoll

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

Background: Osteointegration of press-fit radial head implants is achieved by limiting micromotion between the stem and bone. Aspects of stem design that contribute to the enhancement of initial stability (ie, stem diameter and surface coating) have been investigated. The importance of total prosthesis length and level of the neck cut has not been examined. Methods: Cadaveric radii were implanted with cementless, porous-coated radial head stems. We resected 10, 12, 15, 20, and 25 mm of radial neck in each specimen. Stem-bone micromotion was measured after each cut. Values were expressed in terms of quotients (cantilever quotient). Results: A threshold effect was observed at 15 mm of neck resection (cantilever quotient, 0.4), with a significant increase in micromotion observed between 12 mm (40 ± 10 μm) and 15 mm (80 ± 25 μm). A cantilever quotient of 0.35 or less predicted implant stability, whereas implants with a cantilever quotient of 0.6 or more were unstable. In between, the stems were "at risk" of instability. Conclusion: Initial stem stability of a porous-coated, cementless radial head implant is dependent on length of the implant stem within bone and the level of the cut (amount of bone resected). Stability may be compromised by an implant with a combined head and neck length that is too long compared with the stem length within the canal. We found a critical ratio of exposed prosthesis to total implant length (cantilever quotient of 0.4), which puts the prosthesis at risk of inadequate initial stability. These data carry important implications for implant design and use.

Original languageEnglish (US)
Pages (from-to)1559-1564
Number of pages6
JournalJournal of Shoulder and Elbow Surgery
Volume21
Issue number11
DOIs
StatePublished - Nov 2012

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Neck
Prostheses and Implants
Bone and Bones
Head

Keywords

  • Basic Science Study
  • Biomechanical Study
  • Implant geometry
  • Implant micromotion
  • Radial head arthroplasty
  • Radial head implant
  • Radial head stability
  • Stem length

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine
  • Surgery

Cite this

Shukla, D. R., Fitzsimmons, J. S., An, K. N., & O'Driscoll, S. W. (2012). Effect of stem length on prosthetic radial head micromotion. Journal of Shoulder and Elbow Surgery, 21(11), 1559-1564. https://doi.org/10.1016/j.jse.2011.11.025

Effect of stem length on prosthetic radial head micromotion. / Shukla, Dave R.; Fitzsimmons, James S.; An, Kai Nan; O'Driscoll, Shawn W.

In: Journal of Shoulder and Elbow Surgery, Vol. 21, No. 11, 11.2012, p. 1559-1564.

Research output: Contribution to journalArticle

Shukla, DR, Fitzsimmons, JS, An, KN & O'Driscoll, SW 2012, 'Effect of stem length on prosthetic radial head micromotion', Journal of Shoulder and Elbow Surgery, vol. 21, no. 11, pp. 1559-1564. https://doi.org/10.1016/j.jse.2011.11.025
Shukla, Dave R. ; Fitzsimmons, James S. ; An, Kai Nan ; O'Driscoll, Shawn W. / Effect of stem length on prosthetic radial head micromotion. In: Journal of Shoulder and Elbow Surgery. 2012 ; Vol. 21, No. 11. pp. 1559-1564.
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AB - Background: Osteointegration of press-fit radial head implants is achieved by limiting micromotion between the stem and bone. Aspects of stem design that contribute to the enhancement of initial stability (ie, stem diameter and surface coating) have been investigated. The importance of total prosthesis length and level of the neck cut has not been examined. Methods: Cadaveric radii were implanted with cementless, porous-coated radial head stems. We resected 10, 12, 15, 20, and 25 mm of radial neck in each specimen. Stem-bone micromotion was measured after each cut. Values were expressed in terms of quotients (cantilever quotient). Results: A threshold effect was observed at 15 mm of neck resection (cantilever quotient, 0.4), with a significant increase in micromotion observed between 12 mm (40 ± 10 μm) and 15 mm (80 ± 25 μm). A cantilever quotient of 0.35 or less predicted implant stability, whereas implants with a cantilever quotient of 0.6 or more were unstable. In between, the stems were "at risk" of instability. Conclusion: Initial stem stability of a porous-coated, cementless radial head implant is dependent on length of the implant stem within bone and the level of the cut (amount of bone resected). Stability may be compromised by an implant with a combined head and neck length that is too long compared with the stem length within the canal. We found a critical ratio of exposed prosthesis to total implant length (cantilever quotient of 0.4), which puts the prosthesis at risk of inadequate initial stability. These data carry important implications for implant design and use.

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