Sagittal spinal alignment helps distribute one's body weight through the pelvic girdle to minimize energy consumption when standing. Some authors have reported that the development of this spinal curvature was influenced by the pelvic incidence, and that spinal balance was determined by lumbosacral and pelvic alignment, including hip joint in the aging process [4,18
]. Some authors have also reported relationships between individual spinal SB and sagittal pelvic malrotation, which influences acetabular cup orientation [19
]. As well the relationships between spinal curvature and pelvic morphology, the relationships between hip joint and spine, and knee joint and spine have been studied. Parvizi et al. [13
] reported that the pain experienced by patients presenting hip arthritic and lower lumbar pain could often be resolved or improved after THA. Jackson and McManus [20
] found that the LL and the sacral inclination were related to the degree of extension of the hip. An abnormality in the hip joint has been shown to cause an abnormal curvature of the sagittal alignment of the spine and induce lumbago. This phenomenon has been referred to as the 'hip-spine syndrome' by Offierski and MacNab [12,21
]. Murata et al. [15
] also studied the relationship between knee joint and spine, and reported that symptoms arising from the lumbar spine might be caused by degenerative changes in the knee and this has been referred to as the 'knee-spine syndrome'.
In the current study, all the spinal parameters including the lumbosacral angle, the lumbar lordosis, and TK did not change significantly after TKA even in group A, in which a correction of over 10° was obtained. It was assumed that the results were caused by fixing the spinal curvature of the degenerated spinal column, including the intervertebral disc. The short follow-up period was also assumed to be another reason.
Murata et al. [15
] reported that knee angle did not correlate with the sacral inclination. However, in the current study there was a significant increase in the SS of group A when compared with group B (, ). This result indicates that the change of the knee joint angle had a greater affect on the nearest and most mobile segments, such as the hip and pelvis than the fixed degenerative spine.
The sacral slope and the pelvic tilt at preoperative (A) and 1 year postoperative (B) radiographies of the same patient, who had obtained over ten degrees of correction of the knee flexion contracture after total knee arthroplasty.
The sacral slope and the pelvic tilt in preoperative (A) and 1 year postoperative (B) radiographies of the same patient, who had obtained less than ten degrees correction of the knee flexion contracture after total knee arthroplasty.
The SS was influenced more by a change in the standing posture. So it seemed that correction of the flexion contracture of the knee joint induced an extension of the hip joint to place the gravity line along the hip axis by balance of the hamstring, quadriceps, torso and pelvic muscles [21-23
Consequently, this extension of the hip joint could induce an increase in the SS.
It has been reported that the PI tends to increase from 4 to 18 years of age, which is caused by an increase in the PT to place the center of gravity over the hips and lower limbs. Each individual has his or her constant PI after growth except when sacroiliac dissociation occurs.
The PI can be calculated by the summation of two parameters (SS and PT). So in adults, the increase of the SS induces a decrease in the PT [3
]. According to this hypothesis, the PT should have decreased significantly in the current study in group A, but this was not observed. We assumed that these results were not caused by errors in measuring the angle of the spine, pelvis and spinopelvic sagittal alignment, but by the error in taking correct lateral radiographs.
All the angles were measured twice by two observers and the results between the intraobserver and interobserver were highly reliable. But there was a different pelvic rotation in each occasion in the lateral standing whole spine radiography. In many cases, a different location of the two femoral heads was observed in the radiographs. The distance between centers of the two femoral heads was different for each radiograph. It is essential to completely overlap the femoral head. As the pelvis rotated, the midpoint of the upper endplate of the sacrum changed. So the PT could be changed ().
The radiographs, taken in different position [true lateral position (A) and slight oblique position (B)] of the same person at the same time. Pelvic tilt could be changed by rotation of the pelvis.
But even though there was no significant difference between group A and group B in the change of the PT (p=0.073), the opposite directional changes of the SS and the PT were noted in 11 out of 13 patients.
In the current study, there were no meaningful changes in the PI after TKR. The reason for this result was that the pelvis moved as a single unit unless there was dissociation between the ilium and the sacrum. That is, the PI did not change in the adult if there was no sacroiliac dissociation. Thus, in the current study the measured minimal postoperative change in PI was thought to be due to an error in measurement between the two groups. The sacroiliac joint become stiff after the age of fifty years or more and as a consequence the pelvis tilts as a unit.
Jackson and McManus [20
] reported that the vertical sagittal axis (VSA) was located within 2.5 cm centering as the most posterior superior corner of S1
, and was moved anteriorly with gradual stooping during the aging process. Kim et al. [18
] reported that there was about 15.4 mm of meaningful anterior movement of VSA between the ages of 55 and 66 in comparison with that between the ages of 20 and 30. The increase of the PT and the decrease in the SS induce anterior movement of the C7
vertebral body. In the current study, we anticipated posterior movement of the C7
vertebral body and a change of the SB into the negative direction. But there was no significant difference in the SB between two groups.
There are several possible reasons for these results; First, even though standardization of the subject posture was applied using the fist on the clavicle position, each individual posture was not constant. Slight forward bending of one's body changes the SB into the positive direction. On the contrary, a slight backward tilt changes that SB into the negative direction (). Particularly, some subjects preoperatively could hardly stand in a standardized posture due to pain in the the knee joint. The second reason was that the fixed curvature of the aged spine could not be compensated against the change in the flexed knee. Kim et al. [18
] reported that there was a limitation in the SB when evaluating the spinal balance due to the large standard deviation. In the current study, there was also a large standard deviation in the SB for each subject. So it is believed that the pelvic parameters are more useful factor to evaluate the spine than the SB and the SSA. There were some limitations to this study. First was the small number of material subjects, and the short follow-up period, which was 15 months. The second limitation was that the relationship between the clinical symptoms including lumbago and changes of the sagittal alignment parameters could not be estimated.
Variance of the spinal sagittal balance as a function of the positional change [flexion (A) and extension (B)] for the same person, at the same time.