Validation of a new computer-assisted tool to measure spino-pelvic parameters

Abstract

Background Context

Evaluation of sagittal alignment is essential in the operative treatment of spine pathology, particularly adult spinal deformity (ASD). However, software applications for detailed spino-pelvic analysis are usually complex and not applicable to routine clinical use.

Purpose

This study aimed to validate new clinician-friendly software (Surgimap) in the setting of ASD.

Study Design/Setting

Accuracy and inter- and intra-rater reliability of spine measurement software were tested. Five users (two experienced spine surgeons, three novice spine research fellows) independently performed each part of the study in two rounds with 1 week between measurements.

Patient Sample

Fifty ASD patients drawn from a prospective database were used as the study sample.

Outcome Measures

Spinal, pelvic, and cervical measurement parameters (including pelvic tilt [PT], pelvic incidence [PI], lumbar-pelvic mismatch [PI-LL], lumbar lordosis [LL], thoracic kyphosis [TK], T1 spino-pelvic inclination [T1SPI], sagittal vertical axis [SVA], and cervical lordosis [CL]) were the outcome measures.

Methods

For the accuracy evaluation, 30 ASD patient radiographs were pre-marked for anatomic landmarks. Each radiograph was measured twice with the new software (Surgimap); measurements were compared to those from previously validated software. For the reliability and reproducibility evaluation, users measured 50 unmarked ASD radiographs in two rounds. Intra-class correlation (ICC) and International Organization for Standardization (ISO) reproducibility values were calculated. Measurement time was recorded.

Results

Surgimap demonstrated excellent accuracy as assessed by the mean absolute difference from validated measurements: PT: 0.12°, PI: 0.35°, LL: 0.58°, PI-LL: 0.46°, TK: 5.25°, T1SPI: 0.53°, and SVA: 2.04 mm. The inter- and intra-observer reliability analysis revealed good to excellent agreement for all parameters. The mean difference between rounds was <0.4° for PT, PI, LL, PI-LL, and T1SPI, and <0.3 mm for SVA. For PT, PI, LL, PI-LL, TK, T1SPI, and SVA, the intra-observer ICC values were all >0.93 and the inter-observer ICC values were all >0.87. Parameters based on point landmarks rather than end plate orientation had a better reliability (ICC≥0.95 vs. ICC≥0.84). The average time needed to perform a full spino-pelvic analysis with Surgimap was 75 seconds (+25).

Conclusions

Using this new software tool, a simple method for full spine analysis can be performed quickly, accurately, and reliably. The proposed list of parameters offers quantitative values of the spine and pelvis, setting the stage for proper preoperative planning. The new software tool provides an important bridge between clinical and research needs.

Introduction

The importance of sagittal alignment analysis in adult spinal deformity (ASD) has long been emphasized [1], and numerous studies have reported the deleterious impact of spino-pelvic malalignment on patient-reported outcomes [2], [3]. Accurate sagittal alignment analysis has become an essential tool in treatment planning for ASD and can be used to calculate the correction needed [4], [5], [6]; inadequate treatment can result in poor postoperative alignment and patient-reported outcomes [7], [8].

Despite its importance, analysis of the sagittal plane and individualized surgical planning can be an arduous practice. In response, dedicated software has emerged to simplify sagittal plane assessment. Multiple forms of digital measurement software have been shown to be faster, more accurate, more precise, and less variable than manual techniques [9], [10]. These computer-based measurements provide a step forward in sagittal spino-pelvic evaluation, but their application remains largely limited to research: although nearly 90% of spine surgeons recognize the importance of such software, less than half regularly use software to analyze and plan sagittal realignment procedures [11].

Even with computerized software, the process of spino-pelvic analysis on radiographs has until recently involved several complex steps, and many current software applications are considered time-consuming, technically demanding, and unpractical. Most existing dedicated spine software programs require extensive measurements to generate spino-pelvic parameter values [12], [13]. In one such case, the user must identify the femoral heads and the superior and inferior end plates of every single vertebra in the spine to generate measurements; in addition, such programs have complicated interfaces and are often limited to the computers in which they are installed. As a result, these programs are used primarily in the research realm, but are difficult to implement for routine clinical use.

Surgimap (Nemaris Inc, New York, NY, USA) is a dedicated spine measurement and surgical planning software that was developed to be applicable in both the research and the clinical realms [14]. Within one application, users can upload images and use a variety of tools for measuring coronal and sagittal radiographs. By identifying key parameters on the radiograph with 11 cursor clicks, an entire collection of spino-pelvic parameters can be automatically and instantaneously generated. Parameters can be modified, shown to patients, and saved by the clinician for future analysis. Finally, Surgimap can be run from either a desktop or a portable storage device (such as a universal serial bus [USB]), allowing the entire database of images and measurements to be carried by the physician to the office, the operating room, or any other location, without the need for additional software or specific operating systems. Authors have advocated the use of this platform based on its effective and clinically useful osteotomy simulations and surgical planning [14]. The reliability of this software has been established in a recent study [15], but since that publication, a more sophisticated, yet user-friendly sagittal alignment tool has been incorporated into the software.

The current study validates the accuracy and reliability of this specialized sagittal alignment tool. By simplifying the sagittal plane analysis, the software can provide a more efficacious and applicable method to routine clinical evaluation of important spino-pelvic parameters.