Clinical validation of a universal deformity correction strategy using direct incremental segmental translation (DIST)

2011

BACKGROUND

Both clinical reports and biomechanical computer modeling shows that excellent coronal, sagittal, and rotational deformity correction can be achieved using primarily translational forces.

PURPOSE

A common deformity reduction strategy using Direct Incremental Segmental Translation (DIST) was tested for correcting scoliosis (SC), kyphosis (KY), and spondylolisthesis (SP).

STUDY DESIGN

Retrospective review of prospectively collected data from a deformity database of consecutive surgical patients treated using the DIST strategy.

PATIENT SAMPLE

487 consecutive deformity patients (195 degenerative SP, 58 isthmic SP, 75 adult idiopathic SC, 25 adolescent idiopathic SC, 84 degenerative lumbar SC, 21 Scheuermann's KY, 29 other KY), age 58 years (range 12 - 90 years); prior surgery-52, smokers-56

OUTCOME

Measure Visual analog pain scores (VAS), Oswestry disability index (ODI), pain medication records were analyzed. Continuous data were compared with ANOVA or paired t-tests, as appropriate. Anderson-Darling was used to determine normalcy where sample sizes were sufficient. Discrete data were compared using Mann-Whitney or Sign Test, as appropriate. Frequencies were compared using chi-square.

METHODS

All underwent posterior fusion and instrumented deformity correction (except grade 1 SP) with DIST, using 3 universal steps: 1-release the spine to move, 2-bend the rods to desired spinal contour, 3-pull the spine to rods in a gradual, incremental, low-stress fashion. Releasing the spine to move occasionally required 3-column osteotomy (24), anterior release (113, average 4.8 levels), TLIF (294, average 1.7 levels). Clinical and radiographic data collected pre-op, 1 year, 2 years, latest follow-up.

RESULTS

At 5 years follow-up (range 24-108 months), complications: nonunion-17, adjacent degeneration-115 (degenerative lumbar SC-31, degenerative SP-50), adjacent fracture-31(14 in degenerative SC), infection-20, footdrop-9; Revision surgery was required to address these issues in 60 patients. Two osteoporotic patients had intraoperative loosening of a pedicle screw during reduction, both without consequence. Oswestry improved: SC pre-41, 4 year-23; KY pre-57, 3 years-32; SP pre-47, 3 year-26(P<0.01). VAS improved: SC pre-5.7, 4 year-2.7; KY pre-7.7, 3 year-2.4; SP pre-6.3, 2 year-2.9(P<0.01). Degenerative SC corrected from 31º pre to 11º, idiopathic SC corrected from 57º pre to 19º at 2 years. KY and SP were corrected in the sagittal plane using cantilever (KY) or direct translation.

CONCLUSIONS

The same universal translational correction strategy applies to mild and severe deformity of all types. Translational forces are effective in reducing all types of coronal, sagittal, and rotational deformity. Corrections are consistent with computer modeling predictions.