Spinal Osteotomy for Sagittal Deformities using “Posterior Only Approach”: A Novel Classification System

Abstract

Introduction

Numerous types of posterior approach based osteotomies have been described but often there is a loss of clarity on the best osteotomy for each patient. We have proposed a morphological classification of sagittal deformities based on the status of the anterior and posterior column, the extent of column deficiency and the flexibility of the deformity. This classification will be useful as guideline for osteotomy selection and for comparing the practice preferences and outcomes between different institutions.

Methods

We analyzed retrospectively collected data for 187 posterior based osteotomies for sagittal deformity. A morphological classification of sagittal deformity was created on basis of collected data. The deformities with intact anterior and posterior column was Type I, where 1A had mobile disc spaces and 1B ankylosed segments. Type II had deficiency of any one column with IIA having a deficiency of posterior column only and Type IIB of anterior column only. Type III had an insufficiency of both columns with Type IIIA being less than 60°, IIIB > 60° and IIIC having buckling collapse. We then prospectively analyzed this morphological classifcation in seventy-five patients with sagittal deformity who underwent various osteotomy procedures for different pathologies. We matched all the cases for six types of anatomical spinal osteotomies and one salvage procedure (anterior strut fusion). The osteotomy procedures considered were partial facetectomy, Ponte's osteotomy, pedicle substraction osteotomy, disc bone osteotomy, single vertebrectomy, multilevel vertebrectomy and salvage procedure in the form of anterior strut grafting.

Results

The mean age was 20.1years and mean sagittal deformity was 67.70°(28–129°). An average correction of 41% (11 to 78%) was achieved and an association of more complex osteotomies for higher class of deformities was noted. The inter-observer agreement for four spine surgeons classifying the 75 deformities was noted to be high (agreement rate K-0.83) using the above morphological classification. A chi-square analysis performed to test the association between the classification and the type of osteotomy, which showed an observable trend with a highly significant association (p < 0.001) showing that the type of osteotomy to be performed could be predicted by the classification.

Conclusion

The proposed classification of the sagittal deformity had a high inter-observer agreement and was useful in predicting the type of osteotomy. The classification would be valuable in training and teaching purposes. This classification could also be used for comparing the osteotomy selection and outcomes between different institutions.