Real time noninvasive assessment of external trunk geometry during surgical correction of adolescent idiopathic scoliosis

Trunk deformity evaluation based on 3D measurements of front body surface landmarks in people with severe physical disabilities

PURPOSE

To assess reliability and validity of a trunk deformity evaluation method expressed as rotational and lateral lean angles between the upper and the lower trunk and between the lower trunk and the pelvis using 3D positions of six front body surface landmarks.

METHODS

Inter- and intra-rater reliabilities of the proposed method in adults with typical development (n = 22) were assessed, and its validity was also assessed through correlations between the Cobb angle and the analyzed trunk deformity parameters in adults with severe physical disabilities (n = 22).

RESULTS

The mean differences between two raters and between the initial and second measures were within 2°. Moderate correlations were found between the Cobb angle and both the upper and the lower trunk lateral lean angle and the upper trunk rotation angle.

CONCLUSIONS

The proposed trunk deformity evaluation appears to be a reliable and valid approach for bedridden people with physical disabilities.

Intraoperative implant rod three-dimensional geometry measured by dual camera system during scoliosis surgery

Treatment for severe scoliosis is usually attained when the scoliotic spine is deformed and fixed by implant rods. Investigation of the intraoperative changes of implant rod shape in three-dimensions is necessary to understand the biomechanics of scoliosis correction, establish consensus of the treatment, and achieve the optimal outcome. The objective of this study was to measure the intraoperative three-dimensional geometry and deformation of implant rod during scoliosis corrective surgery.A pair of images was obtained intraoperatively by the dual camera system before rotation and after rotation of rods during scoliosis surgery. The three-dimensional implant rod geometry before implantation was measured directly by the surgeon and after surgery using a CT scanner. The images of rods were reconstructed in three-dimensions using quintic polynomial functions. The implant rod deformation was evaluated using the angle between the two three-dimensional tangent vectors measured at the ends of the implant rod.The implant rods at the concave side were significantly deformed during surgery. The highest rod deformation was found after the rotation of rods. The implant curvature regained after the surgical treatment.Careful intraoperative rod maneuver is important to achieve a safe clinical outcome because the intraoperative forces could be higher than the postoperative forces. Continuous scoliosis correction was observed as indicated by the regain of the implant rod curvature after surgery.

Do Current Recommendations for Upper Instrumented Vertebra Predict Shoulder Imbalance? An Attempted Validation of Level Selection for Adolescent Idiopathic Scoliosis

BACKGROUND

Shoulder balance for adolescent idiopathic scoliosis (AIS) patients is associated with patient satisfaction and self-image. However, few validated systems exist for selecting the upper instrumented vertebra (UIV) post-surgical shoulder balance.

QUESTIONS/PURPOSES

The purpose is to examine the existing UIV selection criteria and correlate with post-surgical shoulder balance in AIS patients.

METHODS

Patients who underwent spinal fusion at age 10-18 years for AIS over a 6-year period were reviewed. All patients with a minimum of 1-year radiographic follow-up were included. Imbalance was determined to be radiographic shoulder height |RSH| ≥ 15 mm at latest follow-up. Three UIV selection methods were considered: Lenke, Ilharreborde, and Trobisch. A recommended UIV was determined using each method from pre-surgical radiographs. The recommended UIV for each method was compared to the actual UIV instrumented for all three methods; concordance between these levels was defined as "Correct" UIV selection, and discordance was defined as "Incorrect" selection.

RESULTS

One hundred seventy-one patients were included with 2.3 ± 1.1 year follow-up. For all methods, "Correct" UIV selection resulted in more shoulder imbalance than "Incorrect" UIV selection. Overall shoulder imbalance incidence was improved from 31.0% (53/171) to 15.2% (26/171). New shoulder imbalance incidence for patients with previously level shoulders was 8.8%.

CONCLUSIONS

We could not identify a set of UIV selection criteria that accurately predicted post-surgical shoulder balance. Further validated measures are needed in this area. The complexity of proximal thoracic curve correction is underscored in a case example, where shoulder imbalance occurred despite "Correct" UIV selection by all methods.

The quality of evidence of psychometric properties of three-dimensional spinal posture-measuring instruments

BACKGROUND

Psychometric properties include validity, reliability and sensitivity to change. Establishing the psychometric properties of an instrument which measures three-dimensional human posture are essential prior to applying it in clinical practice or research.

METHODS

This paper reports the findings of a systematic literature review which aimed to 1) identify non-invasive three-dimensional (3D) human posture-measuring instruments; and 2) assess the quality of reporting of the methodological procedures undertaken to establish their psychometric properties, using a purpose-build critical appraisal tool.

RESULTS

Seventeen instruments were identified, of which nine were supported by research into psychometric properties. Eleven and six papers respectively, reported on validity and reliability testing. Rater qualification and reference standards were generally poorly addressed, and there was variable quality reporting of rater blinding and statistical analysis.

CONCLUSIONS

There is a lack of current research to establish the psychometric properties of non-invasive 3D human posture-measuring instruments.

A review of the trunk surface metrics used as Scoliosis and other deformities evaluation indices

BACKGROUND

Although scoliosis is characterized by lateral deviation of the spine, a 3D deformation actually is responsible for geometric and morphologic changes in the trunk and rib cage. In a vast related medical literature, one can find quite a few scoliosis evaluation indices, which are based on back surface data and are generally measured along three planes. Regardless the large number of such indices, the literature is lacking a coherent presentation of the underlying metrics, the involved anatomic surface landmarks, the definition of planes and the definition of the related body axes. In addition, the long list of proposed scoliotic indices is rarely presented in cross-reference to each other. This creates a possibility of misunderstandings and sometimes irrational or even wrong use of these indices by the medical society.

MATERIALS AND METHODS

It is hoped that the current work contributes in clearing up the issue and gives rise to innovative ideas on how to assess the surface metrics in scoliosis. In particular, this paper presents a thorough study on the scoliosis evaluation indices, proposed by the medical society.

RESULTS

More specifically, the referred indices are classified, according to the type of asymmetry they measure, according to the plane they refer to, according to the importance, and relevance or the level of scientific consensus they enjoy.

CONCLUSIONS

Surface metrics have very little correlation to Cobb angle measurements. Indices measured on different planes do not correlate to each other. Different indices exhibit quite diverging characteristics in terms of observer-induced errors, accuracy, sensitivity and specificity. Complicated positioning of the patient and ambiguous anatomical landmarks are the major error sources, which cause observer variations. Principles that should be followed when an index is proposed are presented.