Pierre-Yves Lagacé

3D morphometric analysis of 43 scapulae

BackgroundAccurate knowledge of the scapular anatomy is fundamental for the preoperative evaluation but some bony landmarks are difficult to identify. Statistical approaches based on subject-specific parametric models could be used to overcome this difficulty. The aim of this study was to propose a quantitative parametric model of the scapula and to analyze correlations between descriptive morphologic parameters.Materials and methodsForty-three scapulae were scanned and reconstructed. Each 3D scapula was regionalized and a simple geometric element was best fitted on each region using least square method. Descriptive parameters of each region were obtained. Correlation and linear regression analyses were performed between all measurements in order to assess parameters that can be used as predictors of the other descriptive parameters.ResultsMorphometric scapular measurements from 3D reconstructions were obtained. Correlation and linear regression analyses assessed correlations between the glenoid width and both the glenoid height and the acromial width. Also, we obtained correlation between the orientation of the inferior part of the acromion on the A–P view and on the axillary view.DiscussionParametric models are widely used in biomechanics for identifying anatomical landmarks or rotations centers of these structures. For the scapula, no such model is available. We elaborated a first parametric model of scapula based on a large database of 43 scapulae. Our morphometric measurements are very close to others founded in literature. Correlations obtained should help to progress toward relevant subject-specific models of the scapula based on reduced information.

Analysis of humeral head displacements from sequences of biplanar X-rays: repeatability study and preliminary results in healthy subjects

This work presents an accurate method to measure gleno-humeral translations in a controlled pseudo-kinematic environment. Low-dose biplanar X-rays were acquired from nine healthy subjects at three elevations of the arm in the scapular plane. On each set of images, shoulder bony landmarks were manually located in 3D using a dedicated software. Intra-observer and inter-observer repeatability of landmark identification, as well as humeral head center (GH) translations, were studied. Repeatability for the identification of GH in the global coordinate system (CS) was good with 95% confidence intervals (CIs) ranging from 0.57 to 2.25 mm. Scapular landmark CIs ranged from 0.80 to 12 mm. Gleno-humeral translations of small amplitude ( < 6 mm) were detected in seven out of nine subjects. The results obtained here confirm that calibrated low-dose stereo-radiography is a promising tool for the functional analysis of the shoulder.

Investigation of 3D glenohumeral displacements from 3D reconstruction using biplane X-ray images: Accuracy and reproducibility of the technique and preliminary analysis in rotator cuff tear patients

Rotator cuff (RC) tears may be associated with increased glenohumeral instability; however, this instability is difficult to quantify using currently available diagnostic tools. Recently, the three-dimensional (3D) reconstruction and registration method of the scapula and humeral head, based on sequences of low-dose biplane X-ray images, has been proposed for glenohumeral displacement assessment. This research aimed to evaluate the accuracy and reproducibility of this technique and to investigate its potential with a preliminary application comparing RC tear patients and asymptomatic volunteers. Accuracy was assessed using CT scan model registration on biplane X-ray images for five cadaveric shoulder specimens and showed differences ranging from 0.6 to 1.4mm depending on the direction of interest. Intra- and interobserver reproducibility was assessed through two operators who repeated the reconstruction of five subjects three times, allowing defining 95% confidence interval ranging from ±1.8 to ±3.6mm. Intraclass correlation coefficient varied between 0.84 and 0.98. Comparison between RC tear patients and asymptomatic volunteers showed differences of glenohumeral displacements, especially in the superoinferior direction when shoulder was abducted at 20° and 45°. This study thus assessed the accuracy of the low-dose 3D biplane X-ray reconstruction technique for glenohumeral displacement assessment and showed potential in biomechanical and clinical research.

3D reconstruction of the scapula from biplanar radiographs

Access to 3D bone models is critical for applications ranging from pre-operative planning to biomechanics studies. This work presents a method for 3D reconstruction of the scapula from biplanar radiographs, which is based on the combination of a parametric model approach in conjunction with a Moving Least Squares (MLS) deformation technique. A parametric scapula model was created by fitting geometric primitives (with their descriptive parameters) to the CT reconstruction of a dry scapula. These geometric primitives were then used to define a set of handles which allow the user to control the as-rigid-as-possible deformation of the template model in real-time, until optimal correspondence between the actual X-ray images and the retro-projection of the deformed model. When applied to 10 dry scapulae, the presented method allowed obtaining reconstructions which were on average within 1mm of the CT-derived model at scapula regions of interest. Morphological parameters such as the glenoids dimensions and orientation were determined with errors of 1° and less than 1mm, on average. This is of great interest as the current methods used in clinical practice, which are based on 2D-CT, are subject to uncertainties of the order of 5° for glenoid version. This method is of particular interest as it further reduces our dependence to CT for 3D reconstruction of bones and clinical parameter estimation.

Does malpositioning of the arm influence radiographic range of motion measurement

Purpose: Radiographic range of motion measurement of the elbow has been shown to be both precise and reliable. For this method to be used routinely in research studies, it is important to describe its limits regarding: (1) rotation of the arm from the perfect lateral position and (2) the length of humerus and ulna visible on the radiograph. Material and Methods: A 3D bone reconstruction was performed from an upper limb CT scan. Planar radiographs were simulated for rotations of the elbow within a range of ±30o from the perfect lateral position. The field of view was modified, ranging from five visible centimeters of diaphysis on the radiograph to full visibility of the upper limb. Results: The disparity was less than 2.5° (mean=0.68°, SD=0.43°) when the flexed arm was rotated between -30.0° (external rotation, ER) and + 18.0° (internal rotation, IR). When considering the extended arm, measured angles differed by less than 2.5° (mean=0.79°, SD=0.57°) within a range of -15.0° (ER) to +30.0° (IR). When a minimum of 12 cm of humerus and ulna, from the capitellum, were visible on the radiograph measured angles varied very slightly (mean disparity of 0.71°, SD= 0.71°). Finally a qualitative description of the appearance of the radiographs was included to help surgeons estimate acceptable degrees of rotation. Conclusion: Range of motion (ROM) measurement shows consistent results, despite 15 to 30 degrees of internal or external rotation. The middle third of the humeral and ulnar diaphyses should be visible on the radiographs to ensure the validity of measurement. Radiographic ROM measurement is still recommended over the goniometer for research purposes because of its high reliability and precision. Moreover, malpositioning of the elbow should not jeopardize results since it will most likely be an angle measurement variation of less than 2.5°.