title: Is there an Increase in Valgus Deviation in Tibial Distraction Using the Lengthening Over Nail Technique?
abstract: BACKGROUND
  During tibial lengthening, the soft tissues of the posterolateral compartment produce distraction-resisting forces causing valgus angulation. Although this occurs with the classic Ilizarov method, whether a valgus deformity develops with the lengthening over nail (LON) technique is questioned, because the intramedullary nail is thought to resist deforming forces and adequately maintain alignment of the distracted bone.
  
  
  OBJECTIVE
  The purposes of this study were to (1) determine the amount of valgus deviation during tibial lengthening with the LON technique; and (2) analyze the factors that may be associated with valgus deviation with the LON technique.
  
  
  METHODS
  Between June 2009 and September 2013, we performed 346 tibial lengthenings using the LON technique, lengthening and then nail technique, or lengthening with an intramedullary lengthening device. Sixty patients (120 tibias) who underwent bilateral lower leg lengthening with the LON technique were enrolled in this retrospective study. To limit the number of variables, we analyzed only the right tibia in all patients (60 tibias). The mean followup was 42 months (range, 26-71 months). The mean age of the patients was 25 years (range, 18-40 years). There were 36 male and 24 female patients. The mean final length gain was 67 ± 9 mm. The mean time for distraction was 100 ± 25 days. The overall valgus deviation was assessed by measuring the change in the medial proximal tibial angle and mechanical femorotibial angle on radiographs obtained before and after surgery and after completion of lengthening. Several demographic, surgical, and distraction-related variables were considered possible factors to prevent valgus deviation: proximal fixation method; presence of a blocking screw; diameter and length of the intramedullary nail; degree of nail insertion; length of the nail in the distal segment after completion of distraction; final length gain; and patient's BMI. During the period studied, the blocking screw was to maintain the mechanical axis in patients who had neutral or valgus alignment preoperatively, or to prevent more valgus change in patients who underwent acute correction of varus deformity intraoperatively. Uni- and multivariate analyses were conducted.
  
  
  RESULTS
  Valgus deviation occurred during the tibial LON. The medial proximal tibial angle increased from 86° (95% CI, 85°-86°) to 90° (95% CI, 89°-91°) (p < 0.001). The mechanical femorotibial angle changed from 2.2° varus (95% CI, 3°-1.4° varus) to 2.6° valgus (95% CI, 1.8°-3.4° valgus) (p < 0.001). Valgus deviation was evident in proximal and distal segments. In the multivariate regression model, use of a blocking screw was the only factor that was associated with decreased valgus deviation, and its effect size, although detectable, was small (-2.62; 95% CI, -4.65 to -0.59; p = 0.013).
  
  
  CONCLUSIONS
  We found that valgus deviation does occur during tibial lengthening using the LON technique, but that blocking screw placement may help to minimize the likelihood that severe valgus deviation will occur. Future prospective studies should be conducted to confirm this preliminary finding.
  
  
  METHODS
  Level III, therapeutic study.
authors.affiliation: Department of Orthopedic Surgery, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Hoon
authors.initials: H
authors.lastname: Park
authors.affiliation: Division of Orthopedic Surgery, Severance Children's Hospital, Yonsei University College of Medicine, Seoul, 03722, Korea.
authors.forename: Keun Jung
authors.initials: KJ
authors.lastname: Ryu
authors.affiliation: Division of Orthopedic Surgery, Severance Children's Hospital, Yonsei University College of Medicine, Seoul, 03722, Korea.
authors.forename: Hyun Woo
authors.initials: HW
authors.lastname: Kim
authors.affiliation: Division of Orthopedic Surgery, Severance Children's Hospital, Yonsei University College of Medicine, Seoul, 03722, Korea.
authors.forename: Jin Ho
authors.initials: JH
authors.lastname: Hwang
authors.affiliation: Division of Orthopedic Surgery, Severance Children's Hospital, Yonsei University College of Medicine, Seoul, 03722, Korea.
authors.forename: Joon Woo
authors.initials: JW
authors.lastname: Han
authors.affiliation: Division of Orthopedic Surgery, Severance Children's Hospital, Yonsei University College of Medicine, Seoul, 03722, Korea. orthopaedee@naver.com.
authors.forename: Dong Hoon
authors.initials: DH
authors.lastname: Lee
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D001858:Bone Nails; D016723:Bone Remodeling; D060906:Coxa Valga / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D015999:Multivariate Analysis; D019857:Osteogenesis, Distraction / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods; D011859:Radiography; D012189:Retrospective Studies; D012307:Risk Factors; D013977:Tibia / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D013997:Time Factors; D016896:Treatment Outcome; D055815:Young Adult
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