**6. Conclusions**

Comprehensive analysis of the pelvic and subpelvic sectors as part of the sagittal, frontal and cross-sectional balance of the trunk sheds new light on some spinal diseases and their relation to the pelvis. Stiffness in the lumbar spine and lumbosacral fusion, both seen in everyday practice, are significant risk factors for THA subluxation and dislocation due to the lack of variation in the acetabular anteversion from a standing to a sitting position. This concept is not yet well defined, but our data suggest that taking spinal flexibility into account is important when planning a THA implantation, or at least identifying the unusual patients who have an abnormal pelvic (i.e. acetabular) posture.

Knowledge of the biomechanics of the lumbosacral joint is relevant for the hip surgeon performing hip replacements in elderly subjects or in those with abnormal sagittal, frontal or rotational posture and/or a large reduction in functional range of motion. Analysis of sagittal balance must therefore be individual and integrated into the comprehensive evolution of the subject over time, because the phenomenon of an aging spine is frequently associated with the process of aging hips.

The analysis of acetabular orientation cannot be limited to the frontal orientation of the acetabular cup on the AP view and the lateral view of the hip should be considered: standing, sitting, and squatting positions correspond to changes in spinal orientation and acetabular sagittal tilt. The relation between the position of the spine and the acetabulum has a direct influence on the real functional range of motion of the hips. Anterior pelvic plane, pelvic tilt and sacral slope variations are relevant parameters for planning and navigation.

The mobility of the lumbosacral junction is a crucial parameter in the mechanical function and the stability of THAs, especially in elderly populations. With the increase of the survival of THA, spinal aging and progressive pelvic posterior version must now to be taken into account. Late dislocations of mechanical origin have been reported: modifications of the biomechanics of the spine, transmitted to the hip, may be responsible. The standard measurement of anatomic acetabular anteversion on CT scan images in a supine position should be carefully interpreted as it can induce a false or approximate analysis of the acetabular cup position from a functional standpoint. The analysis of pelvic morphology based on the incidence angle may provide new information about THR dysfunction and abnormal wear, especially in patients with unusual postures.

### **7. References**

90 Recent Advances in Arthroplasty

The impact of pelvic rotation and of the pelvic tilt on acetabular orientation raises the question of the choices of guidelines for pre- and postoperative evaluation in cases of hip replacement surgery. The use of guidelines depending on the pelvic bone (anterior pelvic plane, sacral transverse plane, axis through the femoral heads) neglects these two essential phenomena (Lazennec et al., 2007; Tannast et al., 2005). The use of the horizontal transverse plane (or the horizontal plane in space) makes it possible to integrate pelvic tilt into the assessment of acetabular anteversion, which can thus be envisioned "functionally" and not only restrictively as a simple fixed morphologic parameter. Pelvic rotation must be considered and assessed just like vertebral rotation, as analyzed by spine surgeons, compared with a vertical plane of reference perpendicular to the horizontal transverse

Fig. 22. Pelvic rotation is pushed to extremes in cases of scoliosis with the pelvic vertebrae

Comprehensive analysis of the pelvic and subpelvic sectors as part of the sagittal, frontal and cross-sectional balance of the trunk sheds new light on some spinal diseases and their relation to the pelvis. Stiffness in the lumbar spine and lumbosacral fusion, both seen in everyday practice, are significant risk factors for THA subluxation and dislocation due to the lack of variation in the acetabular anteversion from a standing to a sitting position. This

plane.

included in the deformity

**6. Conclusions** 


Hip-Spine Relations: An Innovative Paradigm in THR Surgery 93

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**6** 

*Japan* 

**X-Ray Digital Linear Tomosynthesis** 

Tsutomu Gomi1, Hiroshi Hirano2 and Masahiro Nakajima3

Interest in tomosynthesis and its clinical applications has been revived by recent advances in digital X-ray detector technology. Conventional tomography technology provides planar information of an object from its projection images. In tomography, an X-ray tube and X-ray film receptor are positioned on either side of the object. The relative motion of the tube and film is predetermined based on the location of the in-focus plane (Ziedses des plate 1932). A single image plane is generated by a scan, and multi-slice computed tomography (CT) scans are required to provide a sufficient number of planes to cover the selected structure in the object. Tomosynthesis acquires only one set of discrete X-ray projections that can be used to reconstruct any plane of the object retrospectively (Grant 1972). This technique has been investigated in angiography and imaging of the chest, hand joints, lungs, teeth, and breasts (Stiel et al 1993 , Duryea et al 2003 , Sone et al 1995 , Niklason et al 1997 , Dobbins et al 2003).

Existing tomosynthesis algorithms can be divided into three categories: (1) backprojection algorithms, (2) filtered backprojection (FBP) algorithms, and (3) iterative algorithms. The Fig.1 view shown here highlights the difficulty in visualizing three-dimensional (3D) information in X-ray radiography. In the Fig.2 view it turns an acquisition direction to avoid superimposition of an object. The three resulting projection images may be shifted and added (SAA) so as to bring either the circles or triangles to coincide (i.e., focus), with the complementary object smeared out. The basis for FBP is the backprojection of data acquired in projections acquired over all angles. This procedure is performed for each pixel in a projection, and for all possible angles of the projected data, then one has created a simple backprojection image of the object (Fig.3). The backprojection algorithm is referred to as "SAA", whereby projection images taken at different angles are electronically SAA to generate an image plane focused at a certain depth below the surface. The projection shift is adjusted so that the visibility of features in the selected plane is enhanced while that in other planes is blurred. Using a digital detector, image planes at all depths can be retrospectively

**1. Introduction** 

**2. Performance of tomosynthesis** 

**2.1 General tomosynthesis reconstruction methods** 

*3Department of Radiology, Dokkyo Medical University Hospital* 

**Imaging of Arthoroplasty** 

*1School of Allied Health Sciences, Kitasato University 2Department of Radiology, Shinshu University Hospital* 

