Manual Therapy 19 (2014) 235e241
Contents lists available at ScienceDirect
Manual Therapy journal homepage: www.elsevier.com/math
Original article
Quantitative investigation of ligament strains during physical tests for sacroiliac joint pain using finite element analysis Yoon Hyuk Kim a, *, Zhidong Yao a, Kyungsoo Kim b, Won Man Park a a b
Department of Mechanical Engineering, Kyung Hee University, Yongin 446-701, South Korea Department of Applied Mathematics, Kyung Hee University, Yongin 446-701, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 May 2013 Received in revised form 3 November 2013 Accepted 11 November 2013
It may be assumed that the stability is affected when some ligaments are injured or loosened, and this joint instability causes sacroiliac joint pain. Several physical examinations have been used to diagnose sacroiliac pain and to isolate the source of the pain. However, more quantitative and objective information may be necessary to identify unstable or injured ligaments during these tests due to the lack of understanding of the quantitative relationship between the physical tests and the biomechanical parameters that may be related to pains in the sacroiliac joint and the surrounding ligaments. In this study, a three-dimensional finite element model of the sacroiliac joint was developed and the biomechanical conditions for six typical physical tests such as the compression test, distraction test, sacral apex pressure test, thigh thrust test, Patrick’s test, and Gaenslen’s test were modelled. The sacroiliac joint contact pressure and ligament strain were investigated for each test. The values of contact pressure and the combination of most highly strained ligaments differed markedly among the tests. Therefore, these findings in combination with the physical tests would be helpful to identify the pain source and to understand the pain mechanism. Moreover, the technology provided in this study might be a useful tool to evaluate the physical tests, to improve the present test protocols, or to develop a new physical test protocol. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Sacroiliac joint pain Physical test Finite element analysis Biomechanics
1. Introduction The sacroiliac joint is a firm joint that lies at the junction of the spine and the pelvis and transfers the load of the upper body to the lower body. The stability of the sacroiliac joint is maintained mainly through the combination of its bony structure with very strong intrinsic and extrinsic ligaments. Thus, it may be assumed that the stability is affected when some ligaments are injured or loosened, and this joint instability causes sacroiliac joint pain, though the instability is resulted from a trauma incident by high energetic impact, and inflammation is one reason for the pain (Ozgocmen et al., 2008). In addition, it has been reported that sacroiliac joint pain was a source of low back pain with a prevalence that varied from 0.4% (Cyriax, 1978) to 35% (Schwarzer et al, 1995). The diagnosis of sacroiliac joint pain has usually been based on intra-articular anaesthetic blocks and physical examinations which may include physical tests, a medical history, and imaging. There are various physical tests, such as the compression test, distraction test,
* Corresponding author. Tel.: þ82 31 201 2028; fax: þ82 31 202 8106. E-mail address: [email protected] (Y.H. Kim). 1356-689X/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.math.2013.11.003
sacral apex pressure test, thigh thrust test, Patrick’s test, and Gaenslen’s test, that can help to isolate the source of pain during the physical examination, as the sacroiliac joint can be moved or compressed by physicians while the hips and legs are placed in certain positions. The validity and reliability of these physical tests for the diagnosis of sacroiliac joint pain have been shown in previous clinical studies (van der Wurff et al., 2000a, 2000b; Laslett et al., 2003; Robinson et al., 2007; Laslett, 2008; Ozgocmen et al., 2008; Arab et al., 2009). The physical tests may stress ligaments in the sacroiliac joint differently, and the ligaments stretched during each test were qualitatively reported (Levin et al., 1998; Cattley et al., 2002; Laslett et al., 2003; Robinson et al., 2007; Magee, 2008). However, there is no research that quantitatively demonstrates which ligaments are stressed by which tests. In addition, information regarding the relationship between the physical tests and the biomechanical parameters such as intra-articular contact pressure as well as ligament stress and strain that may be related to pains in the sacroiliac joint and the surrounding ligaments is insufficient. In this study, a three-dimensional (3D) finite element (FE) model of the sacroiliac joint was developed and the biomechanical conditions for six typical physical tests were modelled. The sacroiliac joint contact pressure and ligament strain were investigated for each test.
236
Y.H. Kim et al. / Manual Therapy 19 (2014) 235e241
2. Materials and methods A 3D FE model of the sacroiliac joint was developed (Fig. 1). First, 3D CAD models of the fourth lumbar vertebra (L4), the fifth lumbar vertebra (L5), the sacrum, and the ilium were reconstructed from computed tomography (CT) images of a male subject (25 years old, 175 cm of height, and 66 kg of weight) using the 3D-DOCTOR (Able Software, MA, USA) and the RapidformÒ 2004Ô (INUS Technology, Inc., Seoul, Korea), where the cortical and cancellous regions of the bones were distinguished. Two intervertebral discs between L4 and L5 and between L5 and the sacrum were also modelled based on the CT images. The FE models of the bones and discs were developed from the CAD models using the FEMAP (MSC.Software Co., Santa Ana, CA, USA). The cartilages in the sacroiliac joint were developed with a uniform thickness, where the regions of the articular surfaces were chosen from CT images, and the thicknesses of the cartilages were obtained from the literature. The sacral and iliac cartilages had 2 mm and 1 mm of thicknesses, respectively. The
bone end-plate thicknesses of the sacral and iliac parts of the cartilage were 0.23 mm and 0.36 mm, respectively. The gap between two cartilages was assumed to be 0.3 mm (McLauchlan and Gardner, 2002). The material properties drawn from previous studies (Oonishi et al., 1983; Dalstra et al., 1995; Kim et al., 2010) were summarized in Table 1. Seven kinds of ligaments, the anterior sacroiliac ligament (ASL), interosseous sacroiliac ligament (ISL), long posterior sacroiliac ligament (LPSL), short posterior sacroiliac ligament (SPSL), sacrospinous ligament (SS), sacrotuberous ligament (ST), and iliolumbar ligament (IL), were modelled as 3D tension-only truss elements. The attachment regions were determined based on the literature (Gray, 2000). The ASL consisted of numerous thin bands connecting the anterior surface of the lateral part of the sacrum to the margin of the auricular surface of the ilium and to the preauricular sulcus. The ISL consisted of a series of short strong fibres connecting the tuberosities of the sacrum and ilium. The LPSL was attached by one extremity to the third transverse tubercle of the back of the sacrum,
Fig. 1. Loading and boundary conditions for six physical tests.
Y.H. Kim et al. / Manual Therapy 19 (2014) 235e241 Table 1 Material properties of the sacrum, ilium, lumbar spine, disc, and endplate.
Sacrum Ilium Lumbar spine
Disc
Cortical Cancellous Cortical Cancellous Cortical Cancellous Post Annulus ground substance Nucleus
Endplate
Young’s modulus (MPa)
Poisson’s ratio
17,000 100 17,000 100 12,000 100 3500 4.2
0.3 0.2 0.3 0.2 0.3 0.2 0.3 0.45
0.2 1000
0.4999 0.4
237
2) Distraction test The patient lies supine while the examiner applies pressure to the anterior superior iliac spines. Then, the examiner pushes down and out with the arms. In this study, the ideally simplified pressure in a dorsal direction was considered because it is difficult to define the dorsal and lateral direction dependent on the examiner. Thus, the most posterior regions of the ilia were fixed in the z-direction, the most posterior regions of sacrum were fixed in the supine position, and two compressive (downward) forces of 125 N along the anterioreposterior direction were simultaneously applied on both the left and right anterior superior iliac spines (Fig. 1(b)). 3) Sacral apex pressure test
and by the other to the posterior superior spine of the ilium. The SPSL passed from the first and second transverse tubercles on the back of the sacrum to the tuberosity of the ilium. The SS was a thin triangular ligament attached by its apex to the ischial spine, and medially, by its broad base, to the lateral margins of the sacrum and coccyx, in front of the sacrotuberous ligament with which its fibres are intermingled. The ST connected the sacrum (the lower transverse sacral tubercles, the inferior margins of the sacrum and the upper coccyx) to the tuberosity of the ischium. The IL was a strong ligament passing from the tip of the transverse process of the L5 to the posterior part of the inner lip of the iliac crest (the upper margin of the ilium). The material properties (Young’s modulus according to the strain level) of each ligament were obtained from the literature (Ivanov et al., 2009). To validate the developed models, three tests were performed. For the pelvis model, the distribution of maximum principal strain on the cortical bone of the pelvis in the hip joint was compared to that in a previous study (Zhang et al., 2010) under the same loading and boundary conditions for the single-legged stance. For the sacrum model, the loadedisplacement relationship was compared to that in previous studies (Miller et al., 1987; Eichenseer et al., 2011), where the ilia were fixed and the displacements of a node lying in the mid-sagittal plane between the inferior S1 and superior S2 vertebral endplates were estimated under five translational forces (anterior, posterior, superior, inferior, and mediolateral) of 294 N and three moments (flexion, extension, and axial rotation) of 42 Nm. Finally, the average tensile strains of the ligaments when the flexion, extension, axial rotation, and flexion with axial rotation of 40 Nm were applied to the sacral base were compared to those in the previous study (Eichenseer et al., 2011). Six physical tests were selected based on their popularity, validity, and reliability (van der Wurff et al., 2000a, 2000b), and the boundary and loading conditions were provided as follows. The magnitudes of the applied forces and moments were decided by referring to experimental studies (Levin et al., 1998; Kokmeyer et al., 2002; Ozgocmen et al., 2008) though the amount of force in real clinical circumstances varies considerably. The detailed loading and boundary conditions as well as the x-, y-, and z-axis are depicted in Fig. 1. The contact pressure on the sacroiliac joint and the strain of each ligament according to each physical test were then investigated using Abaqus Standard v. 6.10 (Simulia, Providence, RI, USA). 1) Compression test The patient is in the side-lying position and the examiner’s hands are placed over the upper part of the iliac crest, pressing toward the floor. Thus, leftmost lateral region of the ilium was fixed, and a compressive (downward) force of 250 N along the righteleft direction was applied on the rightmost region of the ilium (Fig. 1(a)).
The patient lies in a prone position on a firm surface while the examiner places the base of his or her hand at the apex of the patient’s sacrum, and pressure is then applied to the apex of the sacrum. Thus, both of the most anterior regions of the ilia were fixed in the prone position and a compressive (downward) force of 250 N along the posterioreanterior direction was applied on the apex of the sacrum (Fig. 1(c)). 4) Thigh thrust test The patient lies supine and the hip is flexed to 90 (with bended knee) to stretch the posterior structures. The femur is used as a lever to push the ilium posteriorly by applying axial pressure along the length of the femur. One hand is placed beneath the sacrum to fix its position while the other hand is used to apply a downward force to the femur. Thus, the most posterior regions of sacrum were fixed in the supine position, and a compressive (downward) force of 250 N along the anterioreposterior direction was applied on the centre of the left ilium (Fig. 1(d)). 5) Patrick’s test The patient lies supine, and the examiner places the patient’s test leg so that the foot is on top of the opposite leg. The examiner then slowly lowers the knee of the test leg toward the examining table. Thus, the left anterior superior iliac spine was fixed, the most posterior region of the sacrum was fixed in the z-direction and with respect to y- and z-rotation in the supine position, and a clockwise moment of 60 Nm along the x-axis was applied on the most anterior region of the ilium (Fig. 1(e)). 6) Gaenslen’s test The patient lies supine on the edge of a table. The leg being tested is hyperextended at the hip so that it hangs over the table while the other leg is flexed at the hip and knee. The patient should hold the non-tested leg with both arms while the therapist stabilizes the pelvis and applies passive pressure to the tested leg to hold it in the hyperextended position. The therapist then applies more pressure so that the hip is further extended and adducted. Thus, the most posterior region of the sacrum was fixed, and clockwise and counter-clockwise moments along the y-axis were applied on the left and right ilia, respectively (Fig. 1(f)). 3. Results In the distribution of the maximum principal strain on the cortical bone of the pelvis in the hip joint, the maximum values were mainly located from the superior to the posterior acetabular
238
Y.H. Kim et al. / Manual Therapy 19 (2014) 235e241
4. Discussion
Fig. 2. Comparison of sacral displacements under eight loadings comparable to those in previous experimental and computational studies (Miller et al., 1987; Eichenseer et al., 2011).
region, extending to the incisura ischiadica major and iliac crest as well as the rear acetabulum. The distribution and maximum strain values around 0.2% were in good agreement with those reported in a previous study (Zhang et al., 2010). The displacements under eight loading conditions were consistent with those in not only an experimental study (Miler et al., 1987) but also a computational study (Eichenseer et al., 2011) (Fig. 2). Ligament strains under four loading conditions were also in good agreement with those in a previous study (Eichenseer et al., 2011) (Fig. 3). The maximum contact pressures on the sacroiliac joint are summarized in Table 2. The compression, thigh thrust, Patrick’s, and Gaenslen’s tests showed high contact pressures more than 10 MPa, and the sacral apex pressure test had a low contact pressure about 3 MPa (Fig. 4). The maximum stresses were 10.2 MPa on the left joint in the compression test, 14.1 MPa on the left joint in the thigh thrust test, 23.6 MPa on the right joint in Patrick’s test, and 27.9 MPa on the right joint in the Gaenslen’s test while the sacral apex pressure test showed 3.1 MPa of maximum stress. The strains of seven ligaments for six physical tests are given in Fig. 5 and Table 2. The left ISL and right ISL had the highest strain values, which were 9.3% and 8.9% in the compression test. In the distraction test and the sacral apex pressure test, the ISL (left and right) was the most strained with strains of 4.4% in the distraction test and 6.6% in the sacral apex pressure test. In the thigh thrust test, the left SPSL, left ASL, and left ISL had the high strain values of 16.3%, 9.3%, and 7.1%, respectively. In Patrick’s test, the right ISL, left ISL, right SPSL, and left SPSL showed high strains of 14.9%, 13.9%, 8.8%, and 8.4%, respectively, while the right SPSL, left ISL, right ISL, right ASL, and left SPSL were highly strained at 22.2%, 15.0%, 11.8%, 9.7%, and 9.6%, respectively, in Gaenslen’s test.
Several physical examinations have been used to diagnose sacroiliac pain and to isolate the source of the pain, and their validities have been shown in clinical studies. However, more quantitative and objective information may be necessary to identify unstable or injured ligaments during these tests due to the lack of understanding of the quantitative relationship between the physical tests and the biomechanical parameters such as contact pressure distribution and ligament stress and strain that may be related to pains in the sacroiliac joint. This study provided quantitative information about the sacroiliac joint contact pressure and ligament strain during the common physical tests for sacroiliac joint pain using finite element analysis although the modelled tests may produce potentially pain provoking stress elsewhere, including intra-articular compressive forces. Previous studies (Levin et al., 1998; Cattley et al., 2002; Laslett et al., 2003; Robinson et al., 2007; Laslett, 2008; Magee, 2008) have reported stretched ligaments or ligament groups during various physical tests as listed in Table 2: the posterior ligaments and ISL were stretched in the compression test; the anterior ligaments and ISL were stretched in the distraction test; all ligaments were stretched in the sacral apex pressure test; the posterior ligaments were stretched in the thigh thrust test; the ASL was stretched in Patrick’s test; and the anterior ligaments were stretched in Gaenslen’s test. Our results were consistent with those from previous studies (Levin et al., 1998; Cattley et al., 2002; Laslett et al., 2003; Robinson et al., 2007; Laslett, 2008; Magee, 2008). In addition, the maximum hip contact pressure during different activities of daily living has been reported by Yoshida et al. (2006) to be about 3.3 MPa while walking, 3.8 MPa while walking down stairs, 5.7 MPa while walking up stairs, 9.0 MPa while standing up, and 9.4 MPa while sitting down. Hence, the contact pressures between 3.1 MPa and 27.9 MPa given in this study may be considered reasonable for the diagnosis of pain because they were similar to or several times larger than those observed during daily activities. There was some disagreement about which ligaments had maximum strain values, although the trend of ligament strains in this study agreed with those in previous studies (Table 2). The ASL and ISL had greater strain values in the compression test, while the posterior ligaments and ISL were expected to be more stretched. This discrepancy could be considered to have originated from the loading condition, in which the compressive force was applied on the rightmost region of the ilium. From a mechanical viewpoint, the posterior ligaments are more strained if the force is applied on a
Fig. 3. Comparison of ligament strains to those in a previous computational study (Eichenseer et al., 2011) for four different loading conditions.
Y.H. Kim et al. / Manual Therapy 19 (2014) 235e241
239
Table 2 Most highly strained ligaments and maximum contact pressures. Abbreviations are as follows: left (L), right (R), anterior sacroiliac ligament (ASL), interosseous sacroiliac ligament (ISL), long posterior sacroiliac ligament (LPSL), short posterior sacroiliac ligament (SPSL), sacrospinous ligament (SS), sacrotuberous ligament (ST), and iliolumbar ligament (IL). (*: Levin et al., 1998; Cattley et al., 2002; Laslett et al., 2003; Robinson et al., 2007; Magee, 2008). Strain (ε)
Compression (Right) Distraction Sacral apex pressure Thigh thrust (Left) Patrick (Right) Gaenslen
3% ε
Contents lists available at ScienceDirect
Manual Therapy journal homepage: www.elsevier.com/math
Original article
Quantitative investigation of ligament strains during physical tests for sacroiliac joint pain using finite element analysis Yoon Hyuk Kim a, *, Zhidong Yao a, Kyungsoo Kim b, Won Man Park a a b
Department of Mechanical Engineering, Kyung Hee University, Yongin 446-701, South Korea Department of Applied Mathematics, Kyung Hee University, Yongin 446-701, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 May 2013 Received in revised form 3 November 2013 Accepted 11 November 2013
It may be assumed that the stability is affected when some ligaments are injured or loosened, and this joint instability causes sacroiliac joint pain. Several physical examinations have been used to diagnose sacroiliac pain and to isolate the source of the pain. However, more quantitative and objective information may be necessary to identify unstable or injured ligaments during these tests due to the lack of understanding of the quantitative relationship between the physical tests and the biomechanical parameters that may be related to pains in the sacroiliac joint and the surrounding ligaments. In this study, a three-dimensional finite element model of the sacroiliac joint was developed and the biomechanical conditions for six typical physical tests such as the compression test, distraction test, sacral apex pressure test, thigh thrust test, Patrick’s test, and Gaenslen’s test were modelled. The sacroiliac joint contact pressure and ligament strain were investigated for each test. The values of contact pressure and the combination of most highly strained ligaments differed markedly among the tests. Therefore, these findings in combination with the physical tests would be helpful to identify the pain source and to understand the pain mechanism. Moreover, the technology provided in this study might be a useful tool to evaluate the physical tests, to improve the present test protocols, or to develop a new physical test protocol. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Sacroiliac joint pain Physical test Finite element analysis Biomechanics
1. Introduction The sacroiliac joint is a firm joint that lies at the junction of the spine and the pelvis and transfers the load of the upper body to the lower body. The stability of the sacroiliac joint is maintained mainly through the combination of its bony structure with very strong intrinsic and extrinsic ligaments. Thus, it may be assumed that the stability is affected when some ligaments are injured or loosened, and this joint instability causes sacroiliac joint pain, though the instability is resulted from a trauma incident by high energetic impact, and inflammation is one reason for the pain (Ozgocmen et al., 2008). In addition, it has been reported that sacroiliac joint pain was a source of low back pain with a prevalence that varied from 0.4% (Cyriax, 1978) to 35% (Schwarzer et al, 1995). The diagnosis of sacroiliac joint pain has usually been based on intra-articular anaesthetic blocks and physical examinations which may include physical tests, a medical history, and imaging. There are various physical tests, such as the compression test, distraction test,
* Corresponding author. Tel.: þ82 31 201 2028; fax: þ82 31 202 8106. E-mail address: [email protected] (Y.H. Kim). 1356-689X/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.math.2013.11.003
sacral apex pressure test, thigh thrust test, Patrick’s test, and Gaenslen’s test, that can help to isolate the source of pain during the physical examination, as the sacroiliac joint can be moved or compressed by physicians while the hips and legs are placed in certain positions. The validity and reliability of these physical tests for the diagnosis of sacroiliac joint pain have been shown in previous clinical studies (van der Wurff et al., 2000a, 2000b; Laslett et al., 2003; Robinson et al., 2007; Laslett, 2008; Ozgocmen et al., 2008; Arab et al., 2009). The physical tests may stress ligaments in the sacroiliac joint differently, and the ligaments stretched during each test were qualitatively reported (Levin et al., 1998; Cattley et al., 2002; Laslett et al., 2003; Robinson et al., 2007; Magee, 2008). However, there is no research that quantitatively demonstrates which ligaments are stressed by which tests. In addition, information regarding the relationship between the physical tests and the biomechanical parameters such as intra-articular contact pressure as well as ligament stress and strain that may be related to pains in the sacroiliac joint and the surrounding ligaments is insufficient. In this study, a three-dimensional (3D) finite element (FE) model of the sacroiliac joint was developed and the biomechanical conditions for six typical physical tests were modelled. The sacroiliac joint contact pressure and ligament strain were investigated for each test.
236
Y.H. Kim et al. / Manual Therapy 19 (2014) 235e241
2. Materials and methods A 3D FE model of the sacroiliac joint was developed (Fig. 1). First, 3D CAD models of the fourth lumbar vertebra (L4), the fifth lumbar vertebra (L5), the sacrum, and the ilium were reconstructed from computed tomography (CT) images of a male subject (25 years old, 175 cm of height, and 66 kg of weight) using the 3D-DOCTOR (Able Software, MA, USA) and the RapidformÒ 2004Ô (INUS Technology, Inc., Seoul, Korea), where the cortical and cancellous regions of the bones were distinguished. Two intervertebral discs between L4 and L5 and between L5 and the sacrum were also modelled based on the CT images. The FE models of the bones and discs were developed from the CAD models using the FEMAP (MSC.Software Co., Santa Ana, CA, USA). The cartilages in the sacroiliac joint were developed with a uniform thickness, where the regions of the articular surfaces were chosen from CT images, and the thicknesses of the cartilages were obtained from the literature. The sacral and iliac cartilages had 2 mm and 1 mm of thicknesses, respectively. The
bone end-plate thicknesses of the sacral and iliac parts of the cartilage were 0.23 mm and 0.36 mm, respectively. The gap between two cartilages was assumed to be 0.3 mm (McLauchlan and Gardner, 2002). The material properties drawn from previous studies (Oonishi et al., 1983; Dalstra et al., 1995; Kim et al., 2010) were summarized in Table 1. Seven kinds of ligaments, the anterior sacroiliac ligament (ASL), interosseous sacroiliac ligament (ISL), long posterior sacroiliac ligament (LPSL), short posterior sacroiliac ligament (SPSL), sacrospinous ligament (SS), sacrotuberous ligament (ST), and iliolumbar ligament (IL), were modelled as 3D tension-only truss elements. The attachment regions were determined based on the literature (Gray, 2000). The ASL consisted of numerous thin bands connecting the anterior surface of the lateral part of the sacrum to the margin of the auricular surface of the ilium and to the preauricular sulcus. The ISL consisted of a series of short strong fibres connecting the tuberosities of the sacrum and ilium. The LPSL was attached by one extremity to the third transverse tubercle of the back of the sacrum,
Fig. 1. Loading and boundary conditions for six physical tests.
Y.H. Kim et al. / Manual Therapy 19 (2014) 235e241 Table 1 Material properties of the sacrum, ilium, lumbar spine, disc, and endplate.
Sacrum Ilium Lumbar spine
Disc
Cortical Cancellous Cortical Cancellous Cortical Cancellous Post Annulus ground substance Nucleus
Endplate
Young’s modulus (MPa)
Poisson’s ratio
17,000 100 17,000 100 12,000 100 3500 4.2
0.3 0.2 0.3 0.2 0.3 0.2 0.3 0.45
0.2 1000
0.4999 0.4
237
2) Distraction test The patient lies supine while the examiner applies pressure to the anterior superior iliac spines. Then, the examiner pushes down and out with the arms. In this study, the ideally simplified pressure in a dorsal direction was considered because it is difficult to define the dorsal and lateral direction dependent on the examiner. Thus, the most posterior regions of the ilia were fixed in the z-direction, the most posterior regions of sacrum were fixed in the supine position, and two compressive (downward) forces of 125 N along the anterioreposterior direction were simultaneously applied on both the left and right anterior superior iliac spines (Fig. 1(b)). 3) Sacral apex pressure test
and by the other to the posterior superior spine of the ilium. The SPSL passed from the first and second transverse tubercles on the back of the sacrum to the tuberosity of the ilium. The SS was a thin triangular ligament attached by its apex to the ischial spine, and medially, by its broad base, to the lateral margins of the sacrum and coccyx, in front of the sacrotuberous ligament with which its fibres are intermingled. The ST connected the sacrum (the lower transverse sacral tubercles, the inferior margins of the sacrum and the upper coccyx) to the tuberosity of the ischium. The IL was a strong ligament passing from the tip of the transverse process of the L5 to the posterior part of the inner lip of the iliac crest (the upper margin of the ilium). The material properties (Young’s modulus according to the strain level) of each ligament were obtained from the literature (Ivanov et al., 2009). To validate the developed models, three tests were performed. For the pelvis model, the distribution of maximum principal strain on the cortical bone of the pelvis in the hip joint was compared to that in a previous study (Zhang et al., 2010) under the same loading and boundary conditions for the single-legged stance. For the sacrum model, the loadedisplacement relationship was compared to that in previous studies (Miller et al., 1987; Eichenseer et al., 2011), where the ilia were fixed and the displacements of a node lying in the mid-sagittal plane between the inferior S1 and superior S2 vertebral endplates were estimated under five translational forces (anterior, posterior, superior, inferior, and mediolateral) of 294 N and three moments (flexion, extension, and axial rotation) of 42 Nm. Finally, the average tensile strains of the ligaments when the flexion, extension, axial rotation, and flexion with axial rotation of 40 Nm were applied to the sacral base were compared to those in the previous study (Eichenseer et al., 2011). Six physical tests were selected based on their popularity, validity, and reliability (van der Wurff et al., 2000a, 2000b), and the boundary and loading conditions were provided as follows. The magnitudes of the applied forces and moments were decided by referring to experimental studies (Levin et al., 1998; Kokmeyer et al., 2002; Ozgocmen et al., 2008) though the amount of force in real clinical circumstances varies considerably. The detailed loading and boundary conditions as well as the x-, y-, and z-axis are depicted in Fig. 1. The contact pressure on the sacroiliac joint and the strain of each ligament according to each physical test were then investigated using Abaqus Standard v. 6.10 (Simulia, Providence, RI, USA). 1) Compression test The patient is in the side-lying position and the examiner’s hands are placed over the upper part of the iliac crest, pressing toward the floor. Thus, leftmost lateral region of the ilium was fixed, and a compressive (downward) force of 250 N along the righteleft direction was applied on the rightmost region of the ilium (Fig. 1(a)).
The patient lies in a prone position on a firm surface while the examiner places the base of his or her hand at the apex of the patient’s sacrum, and pressure is then applied to the apex of the sacrum. Thus, both of the most anterior regions of the ilia were fixed in the prone position and a compressive (downward) force of 250 N along the posterioreanterior direction was applied on the apex of the sacrum (Fig. 1(c)). 4) Thigh thrust test The patient lies supine and the hip is flexed to 90 (with bended knee) to stretch the posterior structures. The femur is used as a lever to push the ilium posteriorly by applying axial pressure along the length of the femur. One hand is placed beneath the sacrum to fix its position while the other hand is used to apply a downward force to the femur. Thus, the most posterior regions of sacrum were fixed in the supine position, and a compressive (downward) force of 250 N along the anterioreposterior direction was applied on the centre of the left ilium (Fig. 1(d)). 5) Patrick’s test The patient lies supine, and the examiner places the patient’s test leg so that the foot is on top of the opposite leg. The examiner then slowly lowers the knee of the test leg toward the examining table. Thus, the left anterior superior iliac spine was fixed, the most posterior region of the sacrum was fixed in the z-direction and with respect to y- and z-rotation in the supine position, and a clockwise moment of 60 Nm along the x-axis was applied on the most anterior region of the ilium (Fig. 1(e)). 6) Gaenslen’s test The patient lies supine on the edge of a table. The leg being tested is hyperextended at the hip so that it hangs over the table while the other leg is flexed at the hip and knee. The patient should hold the non-tested leg with both arms while the therapist stabilizes the pelvis and applies passive pressure to the tested leg to hold it in the hyperextended position. The therapist then applies more pressure so that the hip is further extended and adducted. Thus, the most posterior region of the sacrum was fixed, and clockwise and counter-clockwise moments along the y-axis were applied on the left and right ilia, respectively (Fig. 1(f)). 3. Results In the distribution of the maximum principal strain on the cortical bone of the pelvis in the hip joint, the maximum values were mainly located from the superior to the posterior acetabular
238
Y.H. Kim et al. / Manual Therapy 19 (2014) 235e241
4. Discussion
Fig. 2. Comparison of sacral displacements under eight loadings comparable to those in previous experimental and computational studies (Miller et al., 1987; Eichenseer et al., 2011).
region, extending to the incisura ischiadica major and iliac crest as well as the rear acetabulum. The distribution and maximum strain values around 0.2% were in good agreement with those reported in a previous study (Zhang et al., 2010). The displacements under eight loading conditions were consistent with those in not only an experimental study (Miler et al., 1987) but also a computational study (Eichenseer et al., 2011) (Fig. 2). Ligament strains under four loading conditions were also in good agreement with those in a previous study (Eichenseer et al., 2011) (Fig. 3). The maximum contact pressures on the sacroiliac joint are summarized in Table 2. The compression, thigh thrust, Patrick’s, and Gaenslen’s tests showed high contact pressures more than 10 MPa, and the sacral apex pressure test had a low contact pressure about 3 MPa (Fig. 4). The maximum stresses were 10.2 MPa on the left joint in the compression test, 14.1 MPa on the left joint in the thigh thrust test, 23.6 MPa on the right joint in Patrick’s test, and 27.9 MPa on the right joint in the Gaenslen’s test while the sacral apex pressure test showed 3.1 MPa of maximum stress. The strains of seven ligaments for six physical tests are given in Fig. 5 and Table 2. The left ISL and right ISL had the highest strain values, which were 9.3% and 8.9% in the compression test. In the distraction test and the sacral apex pressure test, the ISL (left and right) was the most strained with strains of 4.4% in the distraction test and 6.6% in the sacral apex pressure test. In the thigh thrust test, the left SPSL, left ASL, and left ISL had the high strain values of 16.3%, 9.3%, and 7.1%, respectively. In Patrick’s test, the right ISL, left ISL, right SPSL, and left SPSL showed high strains of 14.9%, 13.9%, 8.8%, and 8.4%, respectively, while the right SPSL, left ISL, right ISL, right ASL, and left SPSL were highly strained at 22.2%, 15.0%, 11.8%, 9.7%, and 9.6%, respectively, in Gaenslen’s test.
Several physical examinations have been used to diagnose sacroiliac pain and to isolate the source of the pain, and their validities have been shown in clinical studies. However, more quantitative and objective information may be necessary to identify unstable or injured ligaments during these tests due to the lack of understanding of the quantitative relationship between the physical tests and the biomechanical parameters such as contact pressure distribution and ligament stress and strain that may be related to pains in the sacroiliac joint. This study provided quantitative information about the sacroiliac joint contact pressure and ligament strain during the common physical tests for sacroiliac joint pain using finite element analysis although the modelled tests may produce potentially pain provoking stress elsewhere, including intra-articular compressive forces. Previous studies (Levin et al., 1998; Cattley et al., 2002; Laslett et al., 2003; Robinson et al., 2007; Laslett, 2008; Magee, 2008) have reported stretched ligaments or ligament groups during various physical tests as listed in Table 2: the posterior ligaments and ISL were stretched in the compression test; the anterior ligaments and ISL were stretched in the distraction test; all ligaments were stretched in the sacral apex pressure test; the posterior ligaments were stretched in the thigh thrust test; the ASL was stretched in Patrick’s test; and the anterior ligaments were stretched in Gaenslen’s test. Our results were consistent with those from previous studies (Levin et al., 1998; Cattley et al., 2002; Laslett et al., 2003; Robinson et al., 2007; Laslett, 2008; Magee, 2008). In addition, the maximum hip contact pressure during different activities of daily living has been reported by Yoshida et al. (2006) to be about 3.3 MPa while walking, 3.8 MPa while walking down stairs, 5.7 MPa while walking up stairs, 9.0 MPa while standing up, and 9.4 MPa while sitting down. Hence, the contact pressures between 3.1 MPa and 27.9 MPa given in this study may be considered reasonable for the diagnosis of pain because they were similar to or several times larger than those observed during daily activities. There was some disagreement about which ligaments had maximum strain values, although the trend of ligament strains in this study agreed with those in previous studies (Table 2). The ASL and ISL had greater strain values in the compression test, while the posterior ligaments and ISL were expected to be more stretched. This discrepancy could be considered to have originated from the loading condition, in which the compressive force was applied on the rightmost region of the ilium. From a mechanical viewpoint, the posterior ligaments are more strained if the force is applied on a
Fig. 3. Comparison of ligament strains to those in a previous computational study (Eichenseer et al., 2011) for four different loading conditions.
Y.H. Kim et al. / Manual Therapy 19 (2014) 235e241
239
Table 2 Most highly strained ligaments and maximum contact pressures. Abbreviations are as follows: left (L), right (R), anterior sacroiliac ligament (ASL), interosseous sacroiliac ligament (ISL), long posterior sacroiliac ligament (LPSL), short posterior sacroiliac ligament (SPSL), sacrospinous ligament (SS), sacrotuberous ligament (ST), and iliolumbar ligament (IL). (*: Levin et al., 1998; Cattley et al., 2002; Laslett et al., 2003; Robinson et al., 2007; Magee, 2008). Strain (ε)
Compression (Right) Distraction Sacral apex pressure Thigh thrust (Left) Patrick (Right) Gaenslen
3% ε
