Accessing 3D Location of Standing Pelvis: Relative Position of Sacral Plateau and Acetabular Cavities versus Pelvis.

The goal of this paper is to access to pelvis position and morphology in standing posture and to determine the relative locations of their articular surfaces. This is obtained from coupling biplanar radiography and bone modeling. The technique involves different successive steps. Punctual landmarks are first reconstructed, in space, from their projected images, identified on two orthogonal standing X-rays. Geometric models, of global pelvis and articular surfaces, are determined from punctual landmarks. The global pelvis is represented as a triangle of summits: the two femoral head centers and the sacral plateau center. The two acetabular cavities are modeled as hemispheres. The anterior sacral plateau edge is represented by an hemi-ellipsis. The modeled articular surfaces are projected on each X-ray. Their optimal location is obtained when the projected contours of their models best fit real outlines identified from landmark images. Linear and angular parameters characterizing the position of global pelvis and articular surfaces are calculated from the corresponding sets of axis. Relative positions of sacral plateau, and acetabular cavities, are then calculated. Two hundred standing pelvis, of subjects and scoliotic patients, have been studied. Examples are presented. They focus upon pelvis orientations, relative positions of articular surfaces, and pelvis asymmetries.

Geometric Structure of 3D Spinal Curves: Plane Regions and Connecting Zones.

This paper presents a new study of the geometric structure of 3D spinal curves. The spine is considered as an heterogeneous beam, compound of vertebrae and intervertebral discs. The spine is modeled as a deformable wire along which vertebrae are beads rotating about the wire. 3D spinal curves are compound of plane regions connected together by zones of transition. The 3D spinal curve is uniquely flexed along the plane regions. The angular offsets between adjacent regions are concentrated at level of the middle zones of transition, so illustrating the heterogeneity of the spinal geometric structure. The plane regions along the 3D spinal curve must satisfy two criteria: (i) a criterion of minimum distance between the curve and the regional plane and (ii) a criterion controlling that the curve is continuously plane at the level of the region. The geometric structure of each 3D spinal curve is characterized by the sizes and orientations of regional planes, by the parameters representing flexed regions and by the sizes and functions of zones of transition. Spinal curves of asymptomatic subjects show three plane regions corresponding to spinal curvatures: lumbar, thoracic and cervical curvatures. In some scoliotic spines, four plane regions may be detected.

Spino-pelvic postural changes between the standing and sitting human position: proposal of a method for its systematic analysis.

This study presents numerical tools, based on biplanar radiography, allowing to analyze the 3D changes in position and length of the various spinal segments with respect to the pelvis which occur between the standing and sitting positions. Three asymptomatic adult subjects and twelve adult patients with low back pain or scoliosis had biplanar calibrated radiographs in the erect posture and sitting position. The 3D points of the spinal curve were then reconstructed from their plane projections using a standard photogrammetric technique. A technical data form has been formulated to present and summarize the complex 3D spino-pelvic changes occurring between both postures. The spine and pelvis are displayed as a chain of linear articulated segments, in their plane of maximum curvature, allowing users to compare both postures and to assess the global and local spinal mobility between the two fixed postures. Examples of asymptomatic volunteers and of subjects with low back pain or scoliosis demonstrate that different strategies can be adopted to perform this simple task and are presented to illustrate these new techniques and their clinical potential to discriminate between and within normal and pathological conditions.

Classification of pelvic and spinal postural patterns in upright position. Specific cases of scoliotic patients.

The 3D analyses of spinal shapes and postural features give a great number of data. The global patient posture includes his pelvic morphology and tilting, and his pelvic and spinal balance. In some scoliotic spines, the spinal curve belongs to a unique plane. In other scoliotic patients, the spinal curve shows several plane regions. The spinal structures are modeled from parameters locating the structural planes and by values of maximum curvatures. Some parameters have been introduced for describing the postural patterns and the spinal deformities. For each tested patient, each major parameter has been characterized by an index of class.

Personalized models of bones based on radiographic photogrammetry.

The radiographic photogrammetry is applied, for locating anatomical landmarks in space, from their two projected images. The goal of this paper is to define a personalized geometric model of bones, based uniquely on photogrammetric reconstructions. The personalized models of bones are obtained from two successive steps: their functional frameworks are first determined experimentally, then, the 3D bone representation results from modeling techniques. Each bone functional framework is issued from direct measurements upon two radiographic images. These images may be obtained using either perpendicular (spine and sacrum) or oblique incidences (pelvis and lower limb). Frameworks link together their functional axes and punctual landmarks. Each global bone volume is decomposed in several elementary components. Each volumic component is represented by simple geometric shapes. Volumic shapes are articulated to the patient's bone structure. The volumic personalization is obtained by best fitting the geometric model projections to their real images, using adjustable articulations. Examples are presented to illustrating the technique of personalization of bone volumes, directly issued from the treatment of only two radiographic images. The chosen techniques for treating data are then discussed. The 3D representation of bones completes, for clinical users, the information brought by radiographic images.

[Testing of pronation and supination strength in the outpatient setting: a preliminary study]. / Evaluation de la force de pronosupination à la consultation: étude préliminaire.

Dynamometric studies of grip strength are widely used in clinics. We present a clinic dynamometer that can be used to measure pronation and supination moments while the subject being tested is holding a cylindrical handle in neutral pronosupination. One hundred volunteers without any previous history of upper extremity injury were tested in pronation and supination in order to provide a database of strength values and to study variations with respect to sex, age, dominance, weight and height.

Analysis of structural features of deformed spines in frontal and sagittal projections.

In the study of spine, two approaches exist. Clinicians still measure directly, either on X-ray films or on digitized images, a small number of angular values characterizing the profile of deformed spines. 3D software programs exist, but they describe the spinal features calculated from a large set number of inputs. An alternative approach is proposed for clinical applications. Frontal and sagittal radiographs are treated separately. Neutral curves are drawn from a small number of records in a small amount of time. Feature parameters accurately describe the spinal shape, and they are the basis for drawing the modeled curve of the spine. These parameters facilitate the follow up of evolutive back pathologies. Several examples display the new technique.

Three-dimensional in vivo displacements of the shoulder complex from biplanar radiography.

The goal of this study was to adapt roentgen photogrammetry to in vivo studies of shoulder skeletal motion during arm elevation in the scapular plane. Numerous in vitro and in vivo studies have been published describing shoulder bone movements. They involve plain radiographic measurements and utilize a three-dimensional (3D) approach. Measurements are either direct using pins implanted in bones, or indirect recording points on medical images. Roentgen photogrammetry locates points in space from two projections obtained from two different radiographic incidences. The technique has been applied in vivo by implanting metallic balls in bones. However, to be used as a standard clinical procedure, the technique must be adapted to be less invasive. In vivo photogrammetric reconstruction of known points in 3D space requires that the subject is strictly motionless between the successive radiographic exposures or that the exposures are obtained simultaneously. Methods used in this study were developed to allow subsequent exposures to be used for analysis. Numerical tools have been developed to align the two projections of a point in 3D space which have moved slightly between two successive exposures. The standard photogrammetric technique is completed by geometric modeling of the shoulder complex and humerus, and by the control of their mutual proximity at the level of joints. Bones are modeled as a set of simple volumes linked together using geometric shapes described by shape parameters. The coincidence between real bone contours and radiographic projections of the modeled bone gives the values of the shape parameters and the accurate location in space. Results focus on two different topics: errors related to the use of roentgen photogrammetry with successive exposures, and results obtained by applying roentgen photogrammetry to the in vivo shoulder complex. Results describing shoulder bone and joint displacements are presented for comparison with previously published results. The technique of roentgen photogrammetry can successfully be applied to patients. The radiographic protocol is simple, and data can be obtained easily and quickly from the digitized films. The data obtained from asymptomatic shoulders compared favorably with published values. Future research will focus on comparisons between kinematics of the symptomatic and asymptomatic contralateral limbs in volunteers.

A variability study of computerized sagittal spinopelvic radiologic measurements of trunk balance.

OBJECTIVE: The accurate measurement of spinal and pelvic alignment in the sagittal plane is of prime importance for various disorders. Pelvic incidence (PI) is a fundamental anatomic parameter that is specific and constant for each adult individual and is related to pelvic orientation as well as to the size of lumbar lordosis (LL). It is the summation of the sacral slope (SS) and pelvic tilt (PT), two position-dependent variables that determine pelvic orientation in the sagittal plane. The authors have proposed a computer software designed to measure PI, SS, PT, LL, and thoracic kyphosis (TK) on standardized standing lateral digitized x-rays of the spine and pelvis. The purpose of this study was to evaluate the inter- and intraobserver variability of measurements using this software, to determine if it can be used reliably in a clinical environment. METHODS: The standing lateral x-rays of 30 subjects were randomly selected from the database of two medical institutions. The normal population had standard radiographs on which the various pertinent landmarks were marked by one operator prior to digitization, whereas the scoliotic population had digital radiographs that obviated the need for prior marking of landmarks. Four individuals measured all variables on the 30 x-rays on two occasions, with a 15-day interval between the two sessions. Statistical analysis was done with intraclass correlation coefficients (ICCs). RESULTS: The ICC measured within observers was between 0.93 and 0.99, whereas the ICC between observers varied between 0.92 and 0.99. The variations observed were similar for normal and scoliotic subjects, and prior marking of the x-rays had no significant influence. CONCLUSION: We conclude that the variability of measurements with this method is lower than with similar radiologic measures done manually and that the use of this software can be recommended for future clinical and research studies of spinopelvic sagittal balance.

[Geometrical and mechanical analysis of lumbar lordosis in an asymptomatic population: proposed classification]. / Analyse géométrique et mécanique de la lordose lombaire dans une population de 160 adultes asymptomatiques: essai de classification.

PURPOSE OF THE STUDY: The main objective of this study was to describe the morphology and the mechanism underlying the organization of lumbar lordosis in terms of position and shape of the pelvis. A classification of lumbar lordosis was proposed based on the orientation of the sacral plane. MATERIAL AND METHODS: One hundred sixty asymptomatic young adult volunteers were x-rayed in a standardized standing position. A dedicated software was used for analysis of the spine and pelvis. The pelvic parameters were: pelvic incidence, sacral slope, pelvic tilt. The point separating thoracic kyphosis and lumbar lordosis was called the inflexion point. Lumbar lordosis was bounded by the sacral plate and the inflexion point. At the apex, the lumbar curve was divided into two tangent arcs of circle, quantified by an angle and the number of included vertebrae. The lower arc was geometrically equal to the sacral slope. Regarding the vertical line, a lordosis tilt angle was drawn between the inflexion point and the frontal limit of the sacral plate. RESULTS: The value of the lumbar lordosis was very variable. The best correlation was between lumbar lordosis and sacral slope, then between sacral slope and pelvic incidence. The upper arc of a circle remained constant while the lower arc changed with sacral slope. Good correlations were found between the sacral slope and the position of the apex and between sacral slope and lordosis tilt angle. DISCUSSION AND CONCLUSION: Regarding sacral slope, lumbar lordosis can be classified into four types. When the sacral slope is low, lumbar lordosis can either be both short and curved with a low apex and a backward tilt (type 1) or both long and flat with a higher position of the apex (type 2). When the sacral slope increases, lumbar lordosis increases in angle and number of vertebrae with an upper apex, with a progressively forward tilt (types 3 and 4). Depending on the shape and position of the pelvis, and because of the relation between sacral slope and pelvic tilt, the morphology of lumbar lordosis could be the main mechanical cause of degenerative diseases of the lumbar spine.

Sagittal morphology and equilibrium of pelvis and spine.

A prospective analysis of the sagittal profile of 100 healthy young adult volunteers was carried out in order to evaluate the relationship between the shape of the pelvis and lumbar lordosis and to create a databank of the morphologic and positional parameters of the pelvis and spine in a normal healthy population. Inclusion criteria were as follows: no previous spinal surgery, no low back pain, no lower limb length inequality, no scoliotic deviation. For each subject, a 30 x 90-cm sagittal radiograph including spine, pelvis and proximal femurs in standing position on a force plate was performed. The global axis of gravity was determined with the force plate. Each radiograph was digitized using dedicated software. The spinal parameters registered were values for thoracic kyphosis and lumbar lordosis. The pelvic angles measured were: pelvic incidence, sacral slope and pelvic tilt. The global axis of gravity was on average 9 mm anterior of the center of the femoral heads. The anatomic parameter of pelvic incidence angle varied from 33 degrees to 85 degrees (mean: 51.7 degrees, SD: 11 degrees). The average lumbar lordosis was 46.5 degrees. The average thoracic kyphosis was 47 degrees. We found a statistical correlation between incidence angle and lumbar lordosis (r=0.69, P<0.001) and between sacral slope angle and lumbar lordosis (r=0.75, P<0.001). Spine and pelvis balance around the hip axis in order to position the gravity line over the femoral heads. We propose a scheme of sagittal balance of the standing human body.

Anatomical basis of latissimus dorsi and teres major transfers in rotator cuff tear surgery with particular reference to the neurovascular pedicles.

Musculotendinous transfers (MTT) of latissimus dorsi (LD) and teres major (TM), either in isolation or combination, have recently been advocated to treat irreparable rotator cuff tears. The purpose of this study was to (1) review the anatomy of the LD and TM neurovascular pedicles, and (2) undertake experimental MTT to humeral insertions of either supraspinatus or infraspinatus to evaluate tension on their nutrient arteries in six positions of the arm. Twenty-six shoulders were studied, 22 of which had previously been injected with red latex. Gross dissection, using 4.3 x magnification when necessary, was followed by one MTT for each shoulder (11 LD, 6 TM, 9 combined). The anatomy of the LD and TM neurovascular pedicles was consistent with classic descriptions in 85% of cases; "medialisation" of the thoracodorsal artery was observed in 4 specimens. Tension on the teres major artery was not observed in 15 isolated or combined MTTs, while tension on the thoracodorsal artery in at least one arm position was observed in 60% of 20 isolated or combined MTTs. Three factors were found to be associated with tension: medialisation of the thoracodorsal artery, fixation onto the supraspinatus insertion, and 90 degrees abduction combined with internal rotation. The results suggest that tension on the thoracodorsal artery is possible under certain circumstances when an isolated LD or combined MTT is performed to treat irreparable rotator cuff tear.

Potential excursion and relative tension of muscles in the shoulder girdle: relevance to tendon transfers.

Muscles used for transfer ought to have adequate structural properties. The purpose of this study was to provide a database of potential excursion (muscle excursion without reference to connective tissue restraints) and relative tension (muscle physiologic cross-sectional area in percentage among a group) in shoulder girdle muscles. Thirteen muscles in 13 human cadavers aged 17 to 89 years at death were studied. Potential excursion ranged from 6.7 cm (supraspinatus) to 33. 9 cm (latissimus dorsi). Relative tension ranged from 1.7% (levator scapulae) to 20.9% (deltoid). Significant discrepancies were found between the properties of some of the muscles used as transfers around the shoulder and the properties of the muscles for which they are commonly used as substitutes. Despite the limitations of cadaveric studies and the fact that many other factors are involved in muscle transfers, this database of structural properties of shoulder girdle muscles may help when planning tendon transfers around the shoulder.

A new radiographic method for evaluation of the position of the carpus in the coronal plane: results in normal subjects.

The methods used to quantify pathological variations of the position of the carpus in the coronal plane, mainly ulnar translation of the carpus from trauma or rheumatoid disease, are often difficult to use in arthritic or postsurgical wrists; moreover, they require the measurement of the whole length of the third metacarpal. The aim of this study was to determine a reliable and easy-to-use index to analyse the position of the carpus in the coronal plane. One hundred PA X-rays of normal wrists were studied, of which 56 presented with a medial hamate facet of the lunate. An index of position of the carpus in the coronal plane is defined as the ratio of orthogonal distances from [1] the most medial point of the distal radius and [2] the most medial point of the capitate to the long axis of the radius: its mean value being 1.06 (+/- 0.13) in this series of normal wrists. The index is influenced by the presence of a medial hamate facet of the lunate, but is not dependent on the ulnar head and radial styloid process, nor on the length of the third metacarpal. To help to define the usefulness of the index in quantifying the different types of ulnar carpal translations in clinical practice, further studies are required.

The weight-bearing knee after anterior cruciate ligament rupture. An in vitro biomechanical study.

Unilateral weight bearing was simulated on 12 cadaver knees to quantitate anterior tibial translation (ATT) after anterior cruciate ligament (ACL) transection and to asses the role of the posteromedial structure and the hamstrings in controlling laxity. With the ACL intact, ATT was 3.5 +/- 2.8 mm in extension and 4.3 +/- 3.6 mm at 60 degrees flexion. After sectioning the ACL, ATT was 6.5 +/- 4.7 mm in extension and 17.5 +/- 10 mm at 60 degrees flexion (P = 0.001). Applying a force in the hamstrings was unable to correct the pathological ATT observed after ACL section. Partial medial meniscectomy did not increase ATT after the ACL section. Disinsertion of the posterior horn of the medial meniscus and total medial meniscectomy increased ATT significantly compared to isolated ACL section. After ACL transection, sectioning the meniscotibial fibers or posteromedial capsule significantly increased ATT (6.5 +/- 0.5 mm in extension). Section of the postero-oblique ligament or popliteus tendon had no effect on ATT.

A solidification procedure to facilitate kinematic analyses based on video system data.

When video-based motion analysis systems are used to measure segmental kinematics, the major source of error is the displacement of skin-fixed markers relative to the underlying skeletal structure. Such displacements cause the marker representation of the segment to deform, thereby decreasing the accuracy of subsequent three-dimensional kinematic calculations. We have developed a two-step solidification procedure to address this problem. First, the mean rigid shape is computed which best represents the time-varying marker configuration of each segment. Second, a least-squares minimization is used to replace the measured marker coordinates with those corresponding to the best-fit mean rigid shape. Rigid body theory can then be applied unambiguously to perform kinematic analyses. To evaluate this approach, we defined an unperturbed three-dimensional reference movement using kinematic data from the swing phase of gait. After perturbing the marker coordinates with artificial noise, the rotation matrix and translation vector (absolute and relative movement) between each pair of successive images were computed using (1) reference frames fixed directly to the perturbed marker coordinates, (2) a least-squares minimization procedure found in the literature, and (3) the proposed solidification procedure. The least-squares and solidification procedures produced extremely similar results which, relative to the direct calculation, reduced kinematic errors on average by 20-25% when the maximum distance between markers was small (e.g. < 15 cm). The solidification methodology therefore combines the numerical benefits of the least-squares method with the conceptual benefits of a rigid body method.

Modeling the moving skeleton of walking subjects.

The proposed study consists in moving several bones such as pelvis, femur and tibia in conditions as similar as possible to those obtained in a walking subject, to evidence the functioning of this hip and knee joints. The analysis is performed during the stance phase when the joints are loaded. This study is the first phase of a research consisting in: (i) the visualization of the motion of joints in both normal and pathologic subjects; and (ii) the calculation in real time of articular loading caused by muscular forces when sustaining both the external and inertial loads. This research will provide the kinematic and dynamic boundary conditions applied to both a knee and a hip prosthesis of the patient in movement.

The balance point of the intervertebral motion segment: an experimental study.

A loading or "balance" point was sought that could serve as a functional reference for mechanically testing spinal motion segments. This point is located above the in-vitro motion segment where, when an axial compressive load is applied, the segment exhibits minimal coupled rotation. The balance point is a reliable indicator of the mechanical characteristics of the segment. Segments exhibited increasing rotation as axial compressive loads were applied further and further away from the balance point. The location of the balance point was significantly affected by sustained static or cyclic flexion-compression loading and by brief flexion-compression overloads.

[The Armstrong procedure in scoliosis surgery. Clinical, biomechanical and tridimensional study]. / Le montage de Armstrong dans la chirurgie de la scoliose. Etude clinique, biomécanique et tridimentionnelle.

The Armstrong procedure combines the use of a conventional Harrington rod in the concavity of a curve, together with a distracting force on the convex side, this force being applied one vertebra lower. Workers have used this procedure in 35 cases. It is concluded that there are three advantages: A better horizontal disposition of the lower vertebra. Greatly diminished stress on the two rods shown by a biomechanical study. Derotation is more easily obtained and the spine is better balanced as a whole, as shown by a three-dimensional study comparing this method and conventional Harrington rodding.