Mechanical evaluation of a 4-mm cancellous "rescue" screw in osteoporotic cortical bone: A cadaveric study

Simon J. Wall, Sandeep P. Soin, Trevor A. Knight, Simon C. Mears, Stephen M Belkoff

Research output: Contribution to journalArticle

Abstract

OBJECTIVES: Obtaining sufficient fracture fixation in osteoporotic bone is challenging. The purposes of the current study were (1) to compare the pullout strength of a 4-mm cancellous screw (cancellous screw group) with that of a 3.5-mm cortical screw (cortical screw group), and (2) to measure the pullout strength of a 4-mm cancellous screw placed as a rescue screw (rescue screw group) in a stripped 3.5-mm cortical screw (stripped screw group) hole while controlling for bone density and cortical thickness. METHODS: We inserted 4 screws, one from each experimental group, into 11 osteoporotic cadaveric radii, while recording the insertion torque. Radii were mounted on a servohydraulic testing machine, and each screw was pulled out at a rate of 5 mm/min. Pullout strength was recorded. The effects of cortical thickness (near, far, and total), bone density, insertion torque, and the experimental screw group (cortical, cancellous, stripped, and rescue screw groups) on pullout strength were analyzed using multiple linear regression with random effects. Statistical significance was set at P <0.05. RESULTS: There was no significant difference in pullout strength between the cortical and cancellous screw groups. The rescue screw group had significantly less pullout strength than did the cortical and cancellous screws, and only partly increased pullout strength compared with stripped screws. Bone density significantly affected pullout strength, but insertion torque and cortical thickness were not significant covariates. CONCLUSIONS: There seems to be no advantage in using a cancellous screw over a cortical screw in bicortical fixation in osteoporotic bone. Although the rescue screw provided greater pullout strength than the stripped screw, it is unknown if the purchase it provides is clinically sufficient.

Original languageEnglish (US)
Pages (from-to)379-382
Number of pages4
JournalJournal of Orthopaedic Trauma
Volume24
Issue number6
DOIs
StatePublished - 2010

Fingerprint

Torque
Bone Density
Bone and Bones
Fracture Fixation
Linear Models
Cortical Bone

Keywords

  • Osteoporosis
  • Pullout strength
  • Rescue screw
  • Screw purchase
  • Stripping

ASJC Scopus subject areas

  • Surgery
  • Orthopedics and Sports Medicine
  • Medicine(all)

Cite this

Mechanical evaluation of a 4-mm cancellous "rescue" screw in osteoporotic cortical bone : A cadaveric study. / Wall, Simon J.; Soin, Sandeep P.; Knight, Trevor A.; Mears, Simon C.; Belkoff, Stephen M.

In: Journal of Orthopaedic Trauma, Vol. 24, No. 6, 2010, p. 379-382.

Research output: Contribution to journalArticle

Wall, Simon J. ; Soin, Sandeep P. ; Knight, Trevor A. ; Mears, Simon C. ; Belkoff, Stephen M. / Mechanical evaluation of a 4-mm cancellous "rescue" screw in osteoporotic cortical bone : A cadaveric study. In: Journal of Orthopaedic Trauma. 2010 ; Vol. 24, No. 6. pp. 379-382.
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N2 - OBJECTIVES: Obtaining sufficient fracture fixation in osteoporotic bone is challenging. The purposes of the current study were (1) to compare the pullout strength of a 4-mm cancellous screw (cancellous screw group) with that of a 3.5-mm cortical screw (cortical screw group), and (2) to measure the pullout strength of a 4-mm cancellous screw placed as a rescue screw (rescue screw group) in a stripped 3.5-mm cortical screw (stripped screw group) hole while controlling for bone density and cortical thickness. METHODS: We inserted 4 screws, one from each experimental group, into 11 osteoporotic cadaveric radii, while recording the insertion torque. Radii were mounted on a servohydraulic testing machine, and each screw was pulled out at a rate of 5 mm/min. Pullout strength was recorded. The effects of cortical thickness (near, far, and total), bone density, insertion torque, and the experimental screw group (cortical, cancellous, stripped, and rescue screw groups) on pullout strength were analyzed using multiple linear regression with random effects. Statistical significance was set at P <0.05. RESULTS: There was no significant difference in pullout strength between the cortical and cancellous screw groups. The rescue screw group had significantly less pullout strength than did the cortical and cancellous screws, and only partly increased pullout strength compared with stripped screws. Bone density significantly affected pullout strength, but insertion torque and cortical thickness were not significant covariates. CONCLUSIONS: There seems to be no advantage in using a cancellous screw over a cortical screw in bicortical fixation in osteoporotic bone. Although the rescue screw provided greater pullout strength than the stripped screw, it is unknown if the purchase it provides is clinically sufficient.

AB - OBJECTIVES: Obtaining sufficient fracture fixation in osteoporotic bone is challenging. The purposes of the current study were (1) to compare the pullout strength of a 4-mm cancellous screw (cancellous screw group) with that of a 3.5-mm cortical screw (cortical screw group), and (2) to measure the pullout strength of a 4-mm cancellous screw placed as a rescue screw (rescue screw group) in a stripped 3.5-mm cortical screw (stripped screw group) hole while controlling for bone density and cortical thickness. METHODS: We inserted 4 screws, one from each experimental group, into 11 osteoporotic cadaveric radii, while recording the insertion torque. Radii were mounted on a servohydraulic testing machine, and each screw was pulled out at a rate of 5 mm/min. Pullout strength was recorded. The effects of cortical thickness (near, far, and total), bone density, insertion torque, and the experimental screw group (cortical, cancellous, stripped, and rescue screw groups) on pullout strength were analyzed using multiple linear regression with random effects. Statistical significance was set at P <0.05. RESULTS: There was no significant difference in pullout strength between the cortical and cancellous screw groups. The rescue screw group had significantly less pullout strength than did the cortical and cancellous screws, and only partly increased pullout strength compared with stripped screws. Bone density significantly affected pullout strength, but insertion torque and cortical thickness were not significant covariates. CONCLUSIONS: There seems to be no advantage in using a cancellous screw over a cortical screw in bicortical fixation in osteoporotic bone. Although the rescue screw provided greater pullout strength than the stripped screw, it is unknown if the purchase it provides is clinically sufficient.

KW - Osteoporosis

KW - Pullout strength

KW - Rescue screw

KW - Screw purchase

KW - Stripping

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