The influence of screw/hook insertion at apical vertebrae with rib head dislocation on degree of extraction of penetrated rib head from spinal canal in dystrophic scoliosis secondary to type 1 neurofibromatosis

English Keywords:Dystrophic scoliosis  Neurofibromatosis  Rib head penetration  Extraction  Posterior spinal correction and fusion surgery

English Abstract:

  【Abstract】 Objectives: To investigate the influence of screw/hook insertion at apical vertebrae with rib head dislocation on the degree of extraction of penetrated rib head from spinal canal in dystrophic scoliosis secondary to type 1 neurofibromatosis(NF1-DS). Methods: 18 NF1-DS patients with intraspinal rib head dislocation treated surgically from December 2007 to April 2014 were retrospectively reviewed. There were 9 males and 9 females, and the average age was 13.3±3.7 years. The surgical strategies were posterior spinal fusion on 7 patients, posterior spinal fusion(PSF) with preoperative halo traction on 4 patients, one-stage PSF with convex growth arrest(CGA) on 3 patients, staged supplemental anterior fusion following PSF on 2 patients, staged anterior release, CGA and PSF on 1 patient and staged growing rod technique with final PSF on 1 patient. The location of dislocated rib heads being categorized as apex accounted for the largest share in total (11, 45.8%), followed by apex+1(8, 33.3%) and apex-1(5, 20.9%), and no rib head excision was performed. The patients were stratified by the presence of screw/rod insertion at vertebrae with rib head dislocation. Comparisons were made to investigate whether the degree of extraction of penetrated rib head from spinal canal differed between two groups by using independent sample t test. It was explored whether correction of Cobb angle, vertebral rotation and translation(VT, VS) could contribute to the extraction of intra-canal rib head by linear regression analysis. Results: The spinal implant constructs were all pedicle screws on 8 patients and hybrid hook-screw constructs on 10 patients, the average number of fusion segments was 11.7, and the implant density averaged 63%. The thoracic Cobb angle and global kyphosis(GK) improved from 66.6°±15.4° and 56.4°±17.3° to 36.1°±16.7° and 35.1°±16.6°, respectively(P<0.001). Paired sample t-tests revealed significant reduction in intraspinal rib length(IRL) postoperatively(9.4±3.8mm vs. 5.1±3.8mm, P<0.001). The correction rates of IRL and Cobb angle were significantly larger for the 17 penetrated ribs with screw/rod insertion[(56.1±23.9)% vs. (32.6±8.0)%, P<0.05; (48.9±15.7)% vs. (33.5±16.3)%, P<0.05]. Moreover, the correction rates of VT and VR were also larger but didn not reach statistical significance[(31.6±27.6)% vs. (22.6±11.7)%, P>0.05; (13.8±23.4)% vs. (7.4±12.3)%, P>0.05]. Multiple linear regression analysis demonstrated that the correction rate of Cobb angle contributed significantly to correction of IRL(β=0.602, P=0.029). Conclusions: Screw/hook insertion at apical vertebrae with penetrated rib head contributes significantly to the degree of extraction of penetrated rib head from spinal canal. This effect can be strengthened by more correction of Cobb angle.