title: Load sharing mechanism across graft-bone interface in static cervical locking plate fixation.
abstract: OBJECTIVE
  This study is a retrospective clinical study over more than 4 years of follow up to understand the mechanism of load sharing across the graft-bone interface in the static locking plate (SLP) fixation compared with non-locking plate (NLP).
  
  
  METHODS
  Orion locking plates and Top non-locking plates were used for SLP fixation in 29 patients and NLP fixation in 24 patients, respectively. Successful interbody fusion was estimated by dynamic X-ray films. The checking parameters were as follows : screw angle (SA) between upper and lower screw, anterior and posterior height of fusion segment between upper and lower endplate (AH & PH), and upper and lower distance from vertebral endplate to the end of plate (UD & LD). Each follow-up value of AH and PH were compared to initial values. Contributions of upper and lower collapse to whole segment collapse were estimated.
  
  
  RESULTS
  Successful intervertebral bone fusion rate was 100% in the SLP group and 92% in the NLP group. The follow-up mean value of SA in SLP group was not significantly changed compared with initial value, but follow-up mean value of SA in NLP group decreased more than those in SLP group (p=0.0067). Statistical analysis did not show a significant difference in the change in AH and PH between SLP and NLP groups (p>0.05). Follow-up AH of NLP group showed more collapse than PH of same group (p=0.04). The upper portion of the vertebral body collapsed more than the lower portion in the SLP fixation (p=0.00058).
  
  
  CONCLUSIONS
  The fused segments with SLP had successful bone fusion without change in initial screw angle, which was not observed in NLP fixation. It suggests that there was enough load sharing across bone-graft interface in SLP fixation.
authors.affiliation: Department of Neurosurgery, Spine and Spinal Cord Institute, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: In Ho
authors.initials: IH
authors.lastname: Han
authors.forename: Sung Uk
authors.initials: SU
authors.lastname: Kuh
authors.forename: Dong Kyu
authors.initials: DK
authors.lastname: Chin
authors.forename: Byung Ho
authors.initials: BH
authors.lastname: Jin
authors.forename: Yong Eun
authors.initials: YE
authors.lastname: Cho
authors.forename: Keun Su
authors.initials: KS
authors.lastname: Kim