SECTION TWO
CHAPTER
23
Movement of the sacroiliac joint with special reference to the effect of load
Bengt Sturesson
Introduction Postmortem studies have been performed since the middle of the nineteenth century to analyze movements in the sacroiliac joints (SIJs). Miller et al (1987) and Vleeming et al (1992) have demonstrated load displacement behavior on cadavers. Weisl (1955) used lateral roentgenograms to perform studies on movements of living subjects. He noted 6-mm displacement between endpoints, but the error of measurement was calculated to be 3 mm. Colachis et al (1963) performed a study with rods in the iliac bones and reported 5 mm of translation but no other results. Selvik (1974) described a roentgen stereophotogrammetric analysis (RSA) by which it was possible to measure movements in all three dimensions. With this technique Egund et al (1978) demonstrated a maximal rotation of 2°. Grieve (1983) used a stereophotogrammetric method analyzing movements of skin markers positioned on the posterior superior iliac spines and the sacrum. She calculated the difference in millimeters of movement between standing and standing with one leg in flexion. The average movement was estimated to be about 10 mm between the positions. The error of measurement was not calculated but it was stated that ‘skin is not totally adherent to the underlying structures’.
Current in vivo studies Three different techniques for analyzing in vivo SIJ movements have been used. Sturesson et al (1989, 1999a, 2000a, 2000b) and Tullberg et al (1998)
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Movement, Stability and Lumbopelvic Pain used the RSA technique described by Selvik (1974). The investigations are discussed below. Kissling & Jacob (1995) performed a study with Kirschner rods in both ilia and sacrum on healthy volunteers. Measurements were made in standing, anteflexion, and retroflexion of the lumbar spine. The study showed an average total rotation in the SIJ between standing erect on both feet and onelegged stance of about 2° (range 0.4–4.3°) and no significant differences were observed with regard to sex, age, or parturition. Surprisingly, Smidt et al (1995) showed – with a stereophotogrammetric analysis of skin markers in the reciprocal straddle position – a movement much greater than any of the other modern studies reviewed: ‘The mean composite oblique–sagittal sacroiliac motion which occurred between the right and left straddle position was 9 degrees.’ The greatest error of measurement in this technique is the calculation of the bony landmarks. However, the authors rejected data with a difference of more than 5 mm compared to the neutral standing position. The error of the method is not quite clear.
Roentgen stereophotogrammetric analysis
allows for free movements of the object. In the setup used it is possible to make horizontal and vertical exposures, and the object can move freely in front of the roentgen films as long as it is positioned at the cross-over point of the roentgen beams (Fig. 23.1). In the studies by Sturesson et al (1989, 1999a, 2000a, 2000b) the patients were examined in eleven different positions in the different studies. The following positions were used: (1) supine; (2) prone with hyperextension of the left leg; (3) prone with hyperextension of the right leg; (4) standing; (5) sitting with straight knees; (6) standing with the left hip maximally flexed; (7) standing with the right hip maximally flexed; (8) standing in the straddle position with the left hip maximally flexed; (9) standing in the straddle position with the right hip maximally flexed; (10) supine with an external Hoffman–Slätis frame; (11) standing with an external Hoffman–Slätis frame. In Tullberg et al’s (1998) study the patients were examined in standing before and after treatment.
750 mm Focus 1
Focus 2
Selvik introduced RSA in Lund, Sweden, in 1972, and presented it further in his thesis entitled A roentgen stereophotogrammetric method for the study of the kinematics of the skeletal system (Lund 1974). RSA is a computerized system for exact radiographic localization of landmarks in the human body.
Technique for sacroiliac motion analysis Tantalum balls with a diameter of 0.8 mm are implanted into the pelvic bones, using an instrument with a cannula and a spring-piston-release mechanism-striker system (Aronsen 1974) that presses the ball into place. At least three, but usually between four and six, tantalum balls are placed geometrically well spread into each ilium and into the sacrum. Two roentgen tubes are needed in the roentgen room. Optimal requirements are two ceilingsuspended telescopic units with exposure synchronization. The roentgen films are placed in parallel in a calibration cage with a frame containing tantalum balls. The relationship between the markers and the foci is established at the roentgen examination. This
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1100 mm
Object
300 mm
Film 2
Film 1
Fig. 23.1 The positions of roentgen tubes, object and roentgen films
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Movement of the sacroiliac joint with special reference to the effect of load Correct positioning of the patient is mandatory to achieve measurable radiographs. For example, if the lower limb is superimposed on the pelvis, the markers cannot be distinctly visualized. For this reason, only a few measurable examinations were made in the sitting position. When analyzing the position with the hip maximally flexed it was necessary to first maximally flex the hip and after that rotate the leg away from the radiation beams. A similar procedure was used when analyzing the films in the study of the effect of the external fixator. In some patients the steel rods of the Hoffmann– Slätis frame obscured the markers. The sacrum was defined as the fixed segment and the movements were described as rotation around and translation along the three orthogonal axes, as illustrated in Fig. 23.2. The rotation around the helical axis was also analyzed. The movements given are for the center of gravity of the markers in each iliac bone. The mean error for rotation and translation was 0.1–0.2° and 0.1 mm, respectively.
Patient population of the RSA studies In total, 41 patients (34 women 19–45 years of age, and 7 men aged 18–45 years) were included in the RSA studies by Sturesson et al (1989, 1999a, 2000a, 2000b). The studies were focused on various issues but the basic movement analysis was used in all studies to make the groups in the different studies Y
comparable in a wider perspective. In all, 21 patients had unilateral sacroiliac pain and 20 patients had bilateral symptoms. The studies by Tullberg et al (1998) comprised 10 patients.
Movement analysis Supine to standing In the supine position the load on the SIJ is less than in the standing position, when the weight of the upper body is transmitted through the SIJ. Consequently the sacrum was shown to rotate forwards relative to the ilia (nutation) when standing up from a supine position. As shown in Table 23.1, the rotation was equal on both sides, and the mean rotation was 1.3° around the helical axis. Although the rotation was rather small, more than 90% of the movement occurred around the X-axis. The mean rotation around the sagittal axis (Z) and the rotation around the longitudinal axis (Y) were close to zero. The range reflects in some cases a widening in the posterior part of the SIJ and in other cases a closing movement (Y-axis). The widening or closing pattern is also seen around the Z-axis, but to a lesser degree. Probably these movements around the Y- and Zaxes reflect the wide variation in the anatomy of the SIJ (Solonen 1957). The movements around the X-axis and the helical axis did not show statistical differences, thus it can be said that the innominates move around the sacrum as a unit or the sacrum moves symmetrically between the ilia.
Supine to sitting
X Z
345
Compared with the movement pattern from supine to standing, the movement from supine to sitting, both around the helical and the X-axis shows an increase of about 25%. However, the most interesting observation is a small but constant inward movement of the iliac crests, noted as positive values around the Z-axis for the left side and negative values for the right (Table 23.2).
Standing to prone with hyperextension
Fig. 23.2 The pelvis with the rotational axes.
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The largest movement in the SIJ was found between the ‘standing to prone with hyperextension’ positions (Tables 23.3 and 23.4). In the ‘prone position with hyperextension’ the load on the SIJ is low and in contrast to the other positions, the movement
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Table 23.1 Movements of the SIJs when changing from supine to standing (degrees and mm)
Rotation around the…
Joint
N
Mean
SD
Range
X-axis
Left Right
40 41
−1.1 –1.2
0.5 0.5
−2.3 to 0.0 –2.5 to –0.2
Y-axis
Left Right
37 38
0.1 0.3
0.6 0.3
–1.0 to 2.0 –0.2 to 0.9
Z-axis
Left Right
37 38
0.0 0.0
0.3 0.3
–1.0 to 0.5 –0.4 to 1.0
Helical axis
Left Right
36 37
1.3 1.3
0.5 0.6
0.2 to 2.3 0.4 to 2.6
Translation
Left Right
31 32
0.5 0.4
0.3 0.3
0.1 to 1.5 –0.1 to 1.3
N = number of joints.
Table 23.2 Movements of the SIJs when changing from supine to sitting with straight legs (degrees and mm)
Rotation around the…
Joint
N
Mean
SD
Range
X-axis
Left Right
11 11
–1.4 –1.4
0.6 0.6
–2.2 to 0.4 –2.5 to 0.6
Y-axis
Left Right
11 11
0.1 0.4
0.4 0.4
0.6 to 1.1 –0.4 to 1.1
Z-axis
Left Right
11 11
0.5 –0.3
0.2 0.2
0.2 to 0.8 –0.7 to 0
Helical axis
Left Right
11 11
1.5 1.6
0.6 0.6
0.7 to 2.3 0.8 to 2.6
Translation
Left Right
11 11
0.5 0.5
0.4 0.1
0.1 to 1.2 0.4 to 0.8
N = number of joints.
showed a significant difference between the provoked and the nonprovoked side. The difference (mean) was 0.34° around the helical axis (P < 0.0001, paired t-test). Although the mean was close to zero, the range of movement around the Y-axis on the provoked side was also greater compared to that on the non-provoked side. The asymmetry in the SIJ probably enlarges the magnitude of the movement around the Y-axis at the end of the physiologic movement although the force is put around the X-axis.
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Standing to standing with one hip maximally flexed The standing flexion test, or ‘rücklauf,’ was a commonly used diagnostic test for sacroiliac pain. However, it showed low reliability (Potter & Rothstein 1985, Sturesson et al 1999b) and low reproducibility (McCombe et al 1989). In all, 22 patients considered to have sacroiliac pain were analyzed with RSA (Sturesson et al 2000a). The results showed very small movements in the
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Table 23.3 Movement of the SIJ when changing position from standing to prone with the left leg hyperextended (degrees and mm)
Rotation around the…
Joint
N
Mean
SD
Range
X-axis
Left Right
30 30
1.9 1.7
0.9 0.7
–0.5 to 3.9 0.4 to 3.4
Y-axis
Left Right
30 29
–0.1 –0.1
0.7 0.6
–1.3 to 2.4 –2.0 to 1.2
Z-axis
Left Right
30 30
–0.2 –0.1
0.3 0.8
–0.9 to 0.3 –1.0 to 0.5
Helical axis
Left Right
30 29
2.1 1.8
0.7 0.5
0.9 to 3.9 0.6 to 4.0
Translation
Left Right
23 23
0.7 0.5
0.4 0.5
0.3 to 1.8 –0.5 to 1.6
N = number of joints.
Table 23.4 Movement of the SIJ when changing position from standing to prone with the right leg hyperextended (degrees and mm)
Rotation around the…
Joint
N
Mean
SD
Range
X-axis
Left Right
29 30
1.6 1.9
0.7 0.7
0.6 to 3.1 0.2 to 3.6
Y-axis
Left Right
29 30
–0.4 –0.3
0.5 0.7
–1.2 to 1.1 –1.2 to 2.0
Z-axis
Left Right
29 30
–0.1 0.1
0.3 0.4
–0.7 to 0.6 –0.8 to 0.8
Helical axis
Left Right
29 30
1.8 2.1
0.6 0.7
0.7 to 3.2 0.6 to 3.8
Translation
Left Right
23 25
0.6 0.6
0.3 0.5
0.2 to 1.6 –0.3 to 1.6
N = number of joints.
SIJ both on the provoked and the nonprovoked side (Tables 23.5 and 23.6). The small movements registered support the theory of form and force closure in the SIJ (Vleeming 1990a, 1990b). The selflocking mechanism when the pelvis is loaded in a one-leg standing position probably obstructs the movements in the sacroiliac joints.
Standing in the straddle position Smidt et al (1995, 1997) reported in their studies large movements, between 9° and 36° in the SIJ using the sustained reciprocal straddle position. To re-
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evaluate these results, six women with longstanding (3 to 9 years) lumbopelvic pain after pregnancy were analyzed with RSA in the reciprocal straddle position (Tables 23.7 and 23.8). The data show that a reciprocal movement could be demonstrated in the SIJ in the reciprocal straddle position. However, the movements are tenfold smaller than reported in the studies by Smidt et al (1995, 1997). These data also indicate that there could be a reciprocal movement in the sacroiliac joints in walking, even though this movement would be much less because a normal gait consists of much shorter steps than the test situation, and includes no sustained stance.
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Table 23.5 Movement of the SIJ when changing from standing on both feet to standing with the left hip maximally flexed (degrees and mm)
Rotation around the…
Joint
N
Mean
SD
Range
X-axis
Left Right
21 20
–0.2 –0.2
0.4 0.4
–1.0 to 0.5 –1.4 to 0.2
Y-axis
Left Right
21 20
0.2 –0.1
0.4 0.4
–0.7 to 0.8 –0.8 to 0.5
Z-axis
Left Right
21 20
0.2 0.1
0.3 0.3
–0.3 to 0.9 –0.4 to 0.8
Helical axis
Left Right
21 20
0.6 0.6
0.4 0.4
0.2 to 1.4 0.2 to 1.8
Translation along the helical axis
Left Right
21 20
0.3 0.3
0.2 0.4
0.1 to 1.0 0.0 to 2.2
N = number of joints.
Table 23.6 Movement of the SIJ when changing from standing on both feet to standing with the right hip maximally flexed (degrees and mm)
Rotation around the…
Joint
N
Mean
SD
Range
X-axis
Left Right
20 22
–0.1 –0.2
0.5 0.3
–1.0 to 0.7 –0.7 to 0.2
Y-axis
Left Right
20 22
0.0 –0.2
0.5 0.5
–1.1 to 1.8 –1.0 to 0.9
Z-axis
Left Right
20 22
0.1 –0.2
0.4 0.3
–0.3 to 1.2 –0.8 to 0.5
Helical axis
Left Right
20 22
0.7 0.7
0.5 0.3
0.1 to 1.8 0.2 to 1.2
Translation along helical axis
Left Right
20 22
0.3 0.3
0.2 0.2
0.0 to 0.7 0.0 to 0.8
N = number of joints.
This reciprocal movement could also explain the ‘catching’ of the leg in pregnant women (Sturesson et al 1997).
The effect of an external Hoffman–Slätis frame External fixation with a Hoffman–Slätis frame indeed reduces SIJ mobility (Table 23.9). The SIJ movements were analyzed (Sturesson et al 1999a) in ten patients with RSA in supine and standing positions, preoperatively and postoperatively with
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the external fixator applied. Eight patients could be used for the statistical analysis and the median reduction in rotation was 55% on the left side and 63% on the right side around the helical axes, and 74% around the X-axes on the left side and 66% on the right side. Already when the external frame was tightened, an anterior rotation of the sacrum was observed. Together with the reduction in movement in the SIJ, this anterior rotation of the sacrum into a more stable position corresponds well to the principles of form and force closure introduced by Vleeming et al (1990b).
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Table 23.7 Movements of the sacroiliac joints when alternating the straddle position from standing with the left hip maximally extended and the right hip maximally flexed, to standing with the right hip maximally extended and the left hip maximally flexed (the sacrum is the fixed segment) (degrees)
Rotation around the…
Joint
N
Mean
Range
X-axis
Left Right
6 6
–1.0 0.9
–0.3 to –1.6 0.8 to 1.1
Y-axis
Left Right
6 6
0.3 0.4
–0.8 to 1.0 0.2 to 0.8
Z-axis
Left Right
6 6
–0.5 –0.4
–1.4 to 0.0 –1.0 to 0.0
Helical axis
Left Right
6 6
1.3 1.2
0.7 to 2.1 0.9 to 1.3
N = number of joints.
Table 23.8 Movements of the innominates when alternating the straddle position from standing with the left hip maximally extended and the right hip maximally flexed, to standing with the right hip maximally extended and the left hip maximally flexed (the left ilium is selected as the fixed segment) (degrees)
Rotation around the…
N
Mean
Range
X-axis
6
1.9
1.3 to 2.4
Y-axis
6
0.2
–0.5 to 1.6
Z-axis
6
0.1
–0.2 to 0.4
The effect of manipulation Tullberg et al (1998) studied the effect of manipulation. The patients were examined both clinically and with RSA before and after the manipulation. In none of the 10 patients did manipulation alter the position of the sacrum in relation to the ileum, defined by RSA. Positional test results changed from positive before manipulation to normal after.
Men versus women The mean mobility of the SIJ for men is about 40% smaller than the movement registered for women between the positions ‘supine to standing’ (X-axis
N = number of joints.
Table 23.9 The difference in movement between supine and standing, with or without the external frame applied. The values around the transverse (X) and the helical (H) axes on the left and right side are presented. (Wilcoxon Sign rank test)
N
Median
Range
P-value
Without frame X left
8
–1.2
–0.5 to –2.3
0.02
With frame X left
8
–0.5
–0.2 to –1.6
Without frame H left
8
1.3
0.8 to 2.3
With frame H left
8
0.6
0.3 to 1.7
Without frame X right
8
–1.1
–0.4 to –2.4
With frame X right
8
–0.4
–0.1 to –0.7
Without frame H right
8
1.4
0.8 to 2.5
With frame H right
8
0.4
0.3 to 1.9
0.03 0.02 0.1
N = number of joints.
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Table 23.10 Movements of the sacroiliac joints around the X-axis and helical axis when changing from supine to standing position, split by sex (degrees)
Rotation around the…
Sex
N
Mean
Range
X-axis
Male Female
12 55
–0.7 –1.3
–0.1 to –1.2 0.0 to –2.4
Helical axis
Male Female
10 52
0.7 1.4
0.2 to 1.3 0.6 to 2.5
N = number of joints.
Table 23.11 Movements of the sacroiliac joints around the X-axis and helical axis when changing from supine to standing position, in patients with unilateral respectively bilateral symptoms (degrees)
Rotation around the…
N
Mean
Range
X-axis
Unilateral Bilateral
41 40
–1.0 –1.4
0 to –2.0 –0.6 to –2.5
Helical axis
Unilateral Bilateral
35 40
1.2 1.5
0.2 to 2.2 0.7 to 2.6
N = number of joints.
P = 0.0002; helical axis P < 0.0001 unpaired t-test; Table 23.10). Between the positions ‘standing’ and ‘prone with hyperextension’ the mean difference between men and women was about 30%.
Age With age, there was no decrease in total mobility. In fact, there was a statistically significant increase with age between ‘supine to sitting’ (r = 0.7, n = 11, P < 0.05) and ‘standing to prone with hyperextension’ (r = 0.6, n = 15, P < 0.01 regression analysis).
Hypermobility Interestingly, the movements in patients with bilateral symptoms (n = 20) were larger than those in the group with unilateral symptoms. In ‘supine to standing’ the mean rotation was 1.4° around the Xaxis and 1.5° around the helical axis in the group with bilateral symptoms, and 1.1° and 1.2°, respectively, in the group with unilateral symptoms (X-axis P = 0.0045; helical axis P = 0.0238 unpaired t-test; Table 23.11).
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Among the patients with unilateral symptoms, the mean mobility around both the X- and helical axes of the symptomatic joints was equal to the mobility of the asymptomatic joints. The standard deviations were about the same for symptomatic and asymptomatic joints.
Discussion The first implantation of tantalum markers in patients occurred in 1973. In 1990 it was calculated that 2000 patients had been investigated using about 20 000 tantalum balls. Nowadays, about 50 000 tantalum balls have been implanted in 5000 patients, mostly in Sweden but also in the Netherlands and USA. RSA has taken the role as the gold standard in determining mobility in orthopedic research concerning growth, small movements in joints and tendons, and in micromotion of arthroplasties. The error of the method is so small that hardly any other technique can compete in terms of precision. As with all methods, it has its drawbacks, for example, the procedure is time-consuming. Furthermore, there is a need for technical skill in all the different
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Movement of the sacroiliac joint with special reference to the effect of load steps, and for the support of an engineer with knowledge of kinematic analysis (KINLAB, KINERR, X-RAY 90). Because of the radiation dose, RSA cannot be used on volunteers. The doseequivalent of radiation in patients examined with 8 to 10 double exposures on the pelvic bones varied between 2.3 and 7.2 mSv (Sturesson et al 1989). This is equal to the radiation dose of an ordinary plain roentgenogram of the lower back and pelvis. As far as the SIJ is concerned, the identical movements of symptomatic and asymptomatic joints show that RSA cannot identify a SIJ dysfunction. However, we have shown that there are probably small differences in mobility between patients with unilateral and with bilateral symptoms (see Table 23.11). It might be that patients with unilateral symptoms and those with bilateral symptoms reflect groups with a different etiology. Good evidence is lacking but it can be postulated that pain in patients with unilateral symptoms primarily is caused by trauma or reactive arthritis. In patients with bilateral symptoms the cause could be overload, for example after pregnancy, especially among women with relatively larger SIJ mobility. The SIJs are probably comparable with other joints and hypermobility is likely to involve a subgroup of individuals in the upper range of the normal distribution of mobility. Standing on both legs as well as standing on one leg with the other leg flexed implies load on the SIJ. When standing on one leg not only does the load of the body weight act on the SIJ but so too do the stabilizing muscles around the pelvis. Thus the load is more than doubled as compared to standing on both legs. That means that the lateral forces on the SIJ must increase to withstand the increased load and to balance the entire pelvis as well as to stabilize the SIJ. Kissling & Jacob (1995), using Kirschner wires in both ilia and sacrum, obtained similar results with stereophotogrammetry as were found with the RSA. The main advantage of their technique is the lack of radiation. However, the procedures and analyzing technique appear to be more complicated for the patients. Furthermore, the sacral bone is rather thin in the central part and it is difficult to get a good grip for the Kirschner wires. They can be placed in the lateral part of the sacrum but there they will be influenced by the large dorsal sacroiliac ligaments, thus affecting the accuracy. Noninvasive techniques using different types of skin marker probably measure a complex motion, involving also the connective tissue and skin. In themselves, they cannot reflect real SIJ motion, but if compared with data obtained with the RSA or
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‘Kirschner wire technique’ they can be of value in showing for example reduced mobility.
Summary • RSA is a technique for measuring small
SIJ movements with a high accuracy and specificity. The results probably reflect real SIJ movements. Another invasive technique using Kirschner wires shows a similar pattern of movement in the SIJ. • The SIJ movements are small and normally
distributed. • SIJ mobility in men is on average 30–40% less
than in women. • Small differences in SIJ movements occur
between patients with unilateral and patients with bilateral pain. • No significant differences occur in mobility
between symptomatic and asymptomatic joints in patients with unilateral symptoms. • The RSA studies reveal no indications of
hypo- or hypermobility. • Manipulation does not alter the position of the
SIJ. • The movements of the SIJ are reduced by
muscular force. • The movements of the SIJ are reduced by
increased load. • The movements in the SIJ can be reduced by
an external Hoffman–Slätis frame. • The movements in the SIJ in the straddle
position show a reciprocal pattern. • The movements in the SIJ are greater in the
less loaded situation compared to the loaded situation. • For clinical use as yet no technique measuring
mobility can be recommended because it cannot reveal a SIJ disorder. RSA and other mobility measuring techniques can be recommended for further research concerning SIJ biomechanics.
References Aronson AS, Holst L, Selvik G 1974 An instrument for insertion of radiopaque bone markers. Radiology 113:733–734
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