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Objective Guidelines for Removing an External Fixator after Tibial Lengthening Using Pixel Value Ratio: A Pilot Study

  • Basic Research
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Clinical Orthopaedics and Related Research®

Abstract

During limb lengthening over an intramedullary nail, decisions regarding external fixator removal and weightbearing depend on the amount of callus seen at the lengthening area on radiographs. However, this method is subjective and objective evaluation of the amount of callus likely would minimize nail or interlocking screw breakage and refracture after fixator removal. We asked how many cortices with full corticalization of the newly formed bone at the lengthening area are needed to allow fixator removal and full weightbearing and how to radiographically determine the stage of corticalization. We retrospectively reviewed 17 patients (34 lengthenings) who underwent bilateral tibial lengthenings over an intramedullary nail. The average gain in length was 7.2 ± 3.4 cm. We determined the pixel value ratio (ratio of pixel value of regenerate versus the mean pixel value of adjacent bone) of the lengthened area on radiographs. There were no nail or screw breakage and refracture. Partial weightbearing with crutches was permitted when the pixel value ratio was 1 in two cortices and full weightbearing without crutches was permitted when the pixel value ratio was 1 in three cortices. The pixel value ratio on radiographs can be an objective parameter for callus measurement and may provide guidelines for the timing of external fixator removal. We cannot determine from our limited data the minimum pixel value in how many cortices would suggest safe removal, but we can say our criteria were not associated with subsequent refracture.

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Author information

Authors and Affiliations

  1. Department of Pediatric Orthopaedics, Xin-Hua Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China

    Li Zhao MD, PhD & Qing Fan MD

  2. Institute for Rare Diseases and the Department of Orthopedic Surgery, Korea University Medical College, Guro Hospital, # 80, Guro-Dong, Guro-Gu, Seoul, 152-703, Korea

    K. P. Venkatesh MS & Hae Ryong Song MD, PhD

  3. Department of Biostatistics, Korea University Medical College, Guro Hospital, Seoul, Korea

    Man S. Park

Authors
  1. Li Zhao MD, PhD
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  2. Qing Fan MD
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  3. K. P. Venkatesh MS
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  4. Man S. Park
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  5. Hae Ryong Song MD, PhD
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Corresponding author

Correspondence to Hae Ryong Song MD, PhD.

Additional information

This study was supported by a grant from the Korea Healthcare Technology R&D Project, Ministry for Health, Welfare and Family Affairs, Republic of Korea (A080588).

Each author certifies that his or her institute has approved or waived approval for the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research.

This study was performed at Korea University School of Medicine.

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Zhao, L., Fan, Q., Venkatesh, K.P. et al. Objective Guidelines for Removing an External Fixator after Tibial Lengthening Using Pixel Value Ratio: A Pilot Study. Clin Orthop Relat Res 467, 3321–3326 (2009). https://doi.org/10.1007/s11999-009-1011-7

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  • DOI: https://doi.org/10.1007/s11999-009-1011-7

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