Is it safe to back out pedicle screws after augmentation with polymethyl methacrylate or calcium phosphate cement? A biomechanical study

Woojin Cho, Chunhui Wu, Xiujun Zheng, Serkan Erkan, Sanjeev J. Suratwala, Amir A. Mehbod, Ensor E. Transfeldt

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

STUDY DESIGN: Biomechanical cadaveric study. OBJECTIVE: To determine the torque required to remove pedicle screws augmented with polymethyl methacrylate (PMMA) or calcium phosphate cement (CPC); thus, proving the safety of back out of augmented screws in the osteopotoric model, which would be a more dangerous setting than the nonosteoporotic model. SUMMARY OF BACKGROUND DATA: To our knowledge, no earlier study has characterized the safety of backing out pedicle screw augmented with PMMA or CPC. METHODS: Pedicle screws were inserted in 24 osteoporotic vertebrae (48 pedicles). The maximal insertion torque and pullout strength of each screw were recorded. After pullout of the pedicle screws, the vertebrae were then randomized into 2 groups of 12 (24 pedicles) each. PMMA was injected into the pedicles in the first group and CPC was injected into the second group after which the pedicle screws were inserted. The pedicle screws were inserted into the pedicle holes augmented with PMMA or CPC, respectively. Finally, all augmented screws were backed out and the maximal removal torque was recorded using a digital torque wrench. RESULTS: Throughout the study, no incidence of pedicle or lamina fractures was observed. The average insertion torque was 0.5±0.27 and 0.45±0.29 N•m for groups 1 and 2, respectively (P=0.724). The average pullout strength was 723.1±391.7 and 671.2±383.0 N (P=0.950). After cement augmentation, the average removal torque was 0.77±0.31 and 0.81±0.26 N•m for PMMA and CPC, respectively (P=0.494). CONCLUSIONS: The results of this study showed that pedicle screws can be easily and safely backed out after augmentation with PMMA or CPC. The result of CPC, however, may only be valid before any bony ingrowth.

Original languageEnglish (US)
Pages (from-to)276-279
Number of pages4
JournalJournal of Spinal Disorders and Techniques
Volume24
Issue number4
DOIs
StatePublished - Jun 2011
Externally publishedYes

Fingerprint

Polymethyl Methacrylate
Torque
Spine
Safety
calcium phosphate
Pedicle Screws
Cohort Studies

Keywords

  • calcium phosphate cement
  • cement augmentation
  • maximum insertional torque
  • maximum removal torque
  • osteoporosis
  • pedicle screw
  • polymethyl methacrylate
  • revision

ASJC Scopus subject areas

  • Clinical Neurology
  • Surgery
  • Orthopedics and Sports Medicine

Cite this

Is it safe to back out pedicle screws after augmentation with polymethyl methacrylate or calcium phosphate cement? A biomechanical study. / Cho, Woojin; Wu, Chunhui; Zheng, Xiujun; Erkan, Serkan; Suratwala, Sanjeev J.; Mehbod, Amir A.; Transfeldt, Ensor E.

In: Journal of Spinal Disorders and Techniques, Vol. 24, No. 4, 06.2011, p. 276-279.

Research output: Contribution to journalArticle

Cho, Woojin ; Wu, Chunhui ; Zheng, Xiujun ; Erkan, Serkan ; Suratwala, Sanjeev J. ; Mehbod, Amir A. ; Transfeldt, Ensor E. / Is it safe to back out pedicle screws after augmentation with polymethyl methacrylate or calcium phosphate cement? A biomechanical study. In: Journal of Spinal Disorders and Techniques. 2011 ; Vol. 24, No. 4. pp. 276-279.
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abstract = "STUDY DESIGN: Biomechanical cadaveric study. OBJECTIVE: To determine the torque required to remove pedicle screws augmented with polymethyl methacrylate (PMMA) or calcium phosphate cement (CPC); thus, proving the safety of back out of augmented screws in the osteopotoric model, which would be a more dangerous setting than the nonosteoporotic model. SUMMARY OF BACKGROUND DATA: To our knowledge, no earlier study has characterized the safety of backing out pedicle screw augmented with PMMA or CPC. METHODS: Pedicle screws were inserted in 24 osteoporotic vertebrae (48 pedicles). The maximal insertion torque and pullout strength of each screw were recorded. After pullout of the pedicle screws, the vertebrae were then randomized into 2 groups of 12 (24 pedicles) each. PMMA was injected into the pedicles in the first group and CPC was injected into the second group after which the pedicle screws were inserted. The pedicle screws were inserted into the pedicle holes augmented with PMMA or CPC, respectively. Finally, all augmented screws were backed out and the maximal removal torque was recorded using a digital torque wrench. RESULTS: Throughout the study, no incidence of pedicle or lamina fractures was observed. The average insertion torque was 0.5±0.27 and 0.45±0.29 N•m for groups 1 and 2, respectively (P=0.724). The average pullout strength was 723.1±391.7 and 671.2±383.0 N (P=0.950). After cement augmentation, the average removal torque was 0.77±0.31 and 0.81±0.26 N•m for PMMA and CPC, respectively (P=0.494). CONCLUSIONS: The results of this study showed that pedicle screws can be easily and safely backed out after augmentation with PMMA or CPC. The result of CPC, however, may only be valid before any bony ingrowth.",
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T1 - Is it safe to back out pedicle screws after augmentation with polymethyl methacrylate or calcium phosphate cement?

T2 - A biomechanical study

AU - Cho, Woojin

AU - Wu, Chunhui

AU - Zheng, Xiujun

AU - Erkan, Serkan

AU - Suratwala, Sanjeev J.

AU - Mehbod, Amir A.

AU - Transfeldt, Ensor E.

PY - 2011/6

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N2 - STUDY DESIGN: Biomechanical cadaveric study. OBJECTIVE: To determine the torque required to remove pedicle screws augmented with polymethyl methacrylate (PMMA) or calcium phosphate cement (CPC); thus, proving the safety of back out of augmented screws in the osteopotoric model, which would be a more dangerous setting than the nonosteoporotic model. SUMMARY OF BACKGROUND DATA: To our knowledge, no earlier study has characterized the safety of backing out pedicle screw augmented with PMMA or CPC. METHODS: Pedicle screws were inserted in 24 osteoporotic vertebrae (48 pedicles). The maximal insertion torque and pullout strength of each screw were recorded. After pullout of the pedicle screws, the vertebrae were then randomized into 2 groups of 12 (24 pedicles) each. PMMA was injected into the pedicles in the first group and CPC was injected into the second group after which the pedicle screws were inserted. The pedicle screws were inserted into the pedicle holes augmented with PMMA or CPC, respectively. Finally, all augmented screws were backed out and the maximal removal torque was recorded using a digital torque wrench. RESULTS: Throughout the study, no incidence of pedicle or lamina fractures was observed. The average insertion torque was 0.5±0.27 and 0.45±0.29 N•m for groups 1 and 2, respectively (P=0.724). The average pullout strength was 723.1±391.7 and 671.2±383.0 N (P=0.950). After cement augmentation, the average removal torque was 0.77±0.31 and 0.81±0.26 N•m for PMMA and CPC, respectively (P=0.494). CONCLUSIONS: The results of this study showed that pedicle screws can be easily and safely backed out after augmentation with PMMA or CPC. The result of CPC, however, may only be valid before any bony ingrowth.

AB - STUDY DESIGN: Biomechanical cadaveric study. OBJECTIVE: To determine the torque required to remove pedicle screws augmented with polymethyl methacrylate (PMMA) or calcium phosphate cement (CPC); thus, proving the safety of back out of augmented screws in the osteopotoric model, which would be a more dangerous setting than the nonosteoporotic model. SUMMARY OF BACKGROUND DATA: To our knowledge, no earlier study has characterized the safety of backing out pedicle screw augmented with PMMA or CPC. METHODS: Pedicle screws were inserted in 24 osteoporotic vertebrae (48 pedicles). The maximal insertion torque and pullout strength of each screw were recorded. After pullout of the pedicle screws, the vertebrae were then randomized into 2 groups of 12 (24 pedicles) each. PMMA was injected into the pedicles in the first group and CPC was injected into the second group after which the pedicle screws were inserted. The pedicle screws were inserted into the pedicle holes augmented with PMMA or CPC, respectively. Finally, all augmented screws were backed out and the maximal removal torque was recorded using a digital torque wrench. RESULTS: Throughout the study, no incidence of pedicle or lamina fractures was observed. The average insertion torque was 0.5±0.27 and 0.45±0.29 N•m for groups 1 and 2, respectively (P=0.724). The average pullout strength was 723.1±391.7 and 671.2±383.0 N (P=0.950). After cement augmentation, the average removal torque was 0.77±0.31 and 0.81±0.26 N•m for PMMA and CPC, respectively (P=0.494). CONCLUSIONS: The results of this study showed that pedicle screws can be easily and safely backed out after augmentation with PMMA or CPC. The result of CPC, however, may only be valid before any bony ingrowth.

KW - calcium phosphate cement

KW - cement augmentation

KW - maximum insertional torque

KW - maximum removal torque

KW - osteoporosis

KW - pedicle screw

KW - polymethyl methacrylate

KW - revision

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