title: Objective guidelines for removing an external fixator after tibial lengthening using pixel value ratio: a pilot study.
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.
authors: Department of Pediatric Orthopaedics, Xin-Hua Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors: Li
authors: L
authors: Zhao
authors: Qing
authors: Q
authors: Fan
authors: K P
authors: KP
authors: Venkatesh
authors: Man S
authors: MS
authors: Park
authors: Hae Ryong
authors: HR
authors: Song
mesh_terms: D000293:Adolescent; D000328:Adult; D001852:Bone Lengthening / Q000009:adverse effects / Q000295:instrumentation*; D001858:Bone Nails; D002146:Bony Callus / Q000000981:diagnostic imaging* / Q000503:physiopathology; D002113:Calcification, Physiologic; D003446:Crutches; D020878:Device Removal; D016267:External Fixators; D005260:Female; D050723:Fractures, Bone / Q000209:etiology / Q000517:prevention & control; D006801:Humans; D008297:Male; D010865:Pilot Projects; D017410:Practice Guidelines as Topic; D011237:Predictive Value of Tests; D011857:Radiographic Image Interpretation, Computer-Assisted; D020127:Recovery of Function; D012189:Retrospective Studies; D013977:Tibia / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery*; D013997:Time Factors; D016896:Treatment Outcome; D016474:Weight-Bearing; D055815:Young Adult