Thoracic Curve Correction Ratio: An Objective Measure to Guide against Overcorrection of a Main Thoracic Curve in the Setting of a Structural Proximal Thoracic Curve.

Matthew R Landrum,Stefan Parent,Anthony C Capraro,Amer F Samdani,John M Flynn,Joshua M Pahys,Patrick J Cahill,Andrew H Milby,Burt Yaszay,Susan E Nelson

doi:10.3390/jcm11061545

Abstract

Purpose: The correction of double thoracic (Lenke 2) curves has been associated with higher rates of postoperative shoulder imbalance that may compromise long-term outcomes following spinal deformity correction. A number of methods have been proposed to mitigate this risk, though no accepted standard measurement exists. The purpose of this study is to validate a novel quantitative method of determining the relative curve correction magnitude in double thoracic curves. Methods: Retrospective data from a multi-center database of patients undergoing surgical correction of left-proximal thoracic, right-main thoracic Lenke 2 curves were analyzed. A novel measurement tool, the Thoracic Curve Correction Ratio (TCCR), was applied for the purposes of validation against historical data. Results: A total of 305 patients with complete two-year follow-up data were included. The TCCR, or the ratio of postoperative percent correction of the thoracic curves divided by the ratio of the preoperative curve magnitudes, displayed a significant negative correlation (Pearson R = −0.66; p < 0.001) with T1 tilt at two years postoperatively. Conclusions: The TCCR could be added as an important factor in the preoperative planning process and intraoperative assessment in order to reduce postoperative T1 tilt. While T1 tilt remains an imperfect surrogate measure for clinical shoulder balance, it serves as one of many potential measures that the surgeon may evaluate quantitatively and radiographically.

Highlights

The clinical significance of the proximal thoracic curve with regard to shoulder balance was first highlighted in the literature by Ponseti [1] and has been subsequently recognized as an important consideration in the prevention of postoperative shoulder imbalance following surgical correction [2–4]
There exists a paucity of reliable, reproducible measures that can be used for quantitative preoperative planning and intraoperative assessment
The Preoperative Thoracic Curve Ratio (PreTCR) measurement demonstrated a significant positive correlation with T1 tilt in our series. This correlation suggests that this measure may be of use in determining whether a proximal thoracic curve is structural and merits inclusion in the correction and fusion construct

Summary

Introduction

Modern spinal instrumentation and fusion techniques have allowed for the application of increasingly powerful correction maneuvers during spinal deformity surgery. As these techniques have evolved, so too has the planning process for such procedures. Persistent shoulder imbalance following posterior spinal fusion (PSF) for deformity correction may have a significant negative impact on clinical outcomes and has led to a number of proposed measures for quantifying its presence and impact. Kuklo et al sought to improve upon the historically used T1 tilt by studying the correlation of numerous radiographic surrogates with clinical shoulder balance and concluded that the clavicle angle was the most useful [5]. Yagi et al proposed a variation on this technique, instead examining the clavicle chest cage angle difference (CCAD) [6].

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