The iliolumbar ligament has been described as the most important ligament

      for restraining movement at the lumbosacral junction. In addition, it may

      play an important role in restraining movement in the sacroiliac joints.

      To help understand its presumed restraining effect, the anatomy of the

      ligament and its orientation with respect to the sacroiliac joints were

      studied in 17 cadavers. Specific dissection showed the existence of

      several distinct parts of the iliolumbar ligament, among which is a

      sacroiliac part. This sacroiliac part originates on the sacrum and blends

      with the interosseous sacroiliac ligaments. Together with the ventral part

      of the iliolumbar ligament it inserts on the medial part of the iliac

      crest, separate from the interosseous sacroiliac ligaments. Its existence

      is verified by magnetic resonance imaging and by cryosectioning of the

      pelvis in the coronal and transverse plane. Fibre direction, length,

      width, thickness and orientation of the sacroiliac part of the iliolumbar

      ligament are described. It is mainly oriented in the coronal plane,

      perpendicular to the sacroiliac joint. The existence of this sacroiliac

      part of the iliolumbar ligament supports the assumption that the

      iliolumbar ligament has a direct restraining effect on movement in the

      sacroiliac joints

Entius, C.A.

Kleinrensink, G.J. (Gert Jan)

Pool-Goudzwaard, A.L. (Annelies)

Snijders, C.J. (Chris)

Stoeckart, R. (Rob)

PubMed

Pool-Goudzwaard, AL

Kleinrensink, Gert-jan

Snijders, Chris

Entius, CAC

Stoeckart, Rob

NARCIS 

The sacroiliac part of the iliolumbar ligament

EUR Research Repository

J. Anat. (2001) 199, pp. 457–463, with 8 figures Printed in the United Kingdom 457The sacroiliac part of the iliolumbar ligamentA. L. POOL-GOUDZWAARD1,3, G. J. KLEINRENSINK1, C. J. SNIJDERS2, C. ENTIUS1AND R. STOECKART1Departments of "Anatomy and #Biomedical Physics and Technology, Erasmus University Rotterdam, and $MedicalCenter Impact Zoetermeer, The Netherlands(Accepted 26 April 2000)The iliolumbar ligament has been described as the most important ligament for restraining movement at thelumbosacral junction. In addition, it may play an important role in restraining movement in the sacroiliacjoints. To help understand its presumed restraining effect, the anatomy of the ligament and its orientationwith respect to the sacroiliac joints were studied in 17 cadavers. Specific dissection showed the existence ofseveral distinct parts of the iliolumbar ligament, among which is a sacroiliac part. This sacroiliac partoriginates on the sacrum and blends with the interosseous sacroiliac ligaments. Together with the ventralpart of the iliolumbar ligament it inserts on the medial part of the iliac crest, separate from the interosseoussacroiliac ligaments. Its existence is verified by magnetic resonance imaging and by cryosectioning of thepelvis in the coronal and transverse plane. Fibre direction, length, width, thickness and orientation of thesacroiliac part of the iliolumbar ligament are described. It is mainly oriented in the coronal plane,perpendicular to the sacroiliac joint. The existence of this sacroiliac part of the iliolumbar ligament supportsthe assumption that the iliolumbar ligament has a direct restraining effect on movement in the sacroiliacjoints.Key words : Biomechanics ; sacroiliac joint ; low back pain.In the literature the iliolumbar ligament (IL) isdescribed as a biomechanically important ligamentfor the lumbopelvic region; it extends from thetransverse processes of the 4th and 5th lumbarverterbrae to the iliac crest (Leong et al. 1987; Chowet al. 1989; Yamamoto et al. 1989, 1990). Further-more Sims & Moorman (1996) mention the IL as animportant primary source of low back pain. This isplausible since immunohistochemically the presenceof a multitude of mechanoreceptors and nociceptorshas been shown in the lumbar posterior ligaments(Bogduk, 1983; Korkala et al. 1985; Yahia et al.1988; Rhalmi et al. 1993). It is postulated that theinnervation of the IL is similar to that of otherposterior lumbar ligaments (Sims & Moorman, 1996).Several biomechanical studies emphasise the import-ance of the IL, on the one hand, in restraining flexion,extension and lateral bending of L5 on SI (Leonget al. 1987; Yamamoto et al. 1989, 1990) and onCorrespondence to Dr Annelies Pool-Goudzwaard, Department of Anatomy, Erasmus University, Postbus 1738, 3000 DR Rotterdam, TheNetherlands. e-mail : m.p.c.impact!planet.nlthe other in maintaining torsional stability of thelumbosacral junction (Chow et al. 1989). This conceptsupports the study by Pun et al. (1987) showing thepresence of the IL in rhesus monkeys and its absencein quadrupeds with a more horizontal spine. Inaddition to this restraining function, Luk et al.(1986) suggested that in man the IL could play arole in locking the sacrum between the iliac bones.In other words the IL might also restrain movementin the SI joint. To analyse whether this holds trueand, if so, which movements of the sacrum andiliac bones can be restrained, first the topographicanatomy of the ligament and its orientation withrespect to the SI joint have to be clarified since theliterature is confusing.The IL has been described as consisting of 1(Maigne & Maigne, 1991), 2 (Moore, 1980; Luk et al.1986; Uhthoff, 1993; Hanson & Sonesson, 1994;Basadonna et al. 1996; Rucco et al. 1996), 3 (Williams& Warwick, 1980), 4 (O’Rahilly, 1986), or even 5separate bands (Bogduk & Twomey, 1987). Mostauthors have described the origin of the IL at thetransverse processes of L5 (O’Rahilly, 1986; Moore,1980; Williams & Warwick, 1980; Luk et al. 1986;Leong et al. 1987; Bogduk & Twomey, 1987; Chowet al. 1989; Yamamoto et al. 1989, 1990; Maigne &Maigne, 1991; Uhthoff, 1993; Hanson & Sonesson,1994; Basadonna et al. 1996; Rucco et al. 1996;Willard, 1997) and occasionally L4 (O’Rahilly, 1986;Moore 1980; Williams & Warwick, 1980; Bogduk &Twomey, 1987; Leong et al. 1987; Chow et al. 1989;Yamamoto et al. 1989, 1990; Uhthoff, 1993; Willard,1997). In all studies the insertion of the IL isdescribed as being on the iliac crest and the ventral,upper part of the iliac tuberosity. In some textbooksattachments of the IL to the anterior layer of thethoracolumbar fascia are described (Moore, 1980;Williams & Warwick, 1980; O’Rahilly, 1986). Ac-cording to O’Rahilly (1986) and confirmed by Willard(1995), some fibres of the IL blend with the inter-transverse ligaments between L5-S1 and L4-L5 andblend with the interosseous SI ligaments. Frazer(1948) had earlier described fibres of the IL passingto the 1st sacral vertebra although detailed descrip-tions of length, width and thickness are lacking. Theaim of the present study is to confirm whether a partof the IL can be defined as a sacroiliac ligament. Ifso, its fibre direction, length, thickness, width andorientation are of interest.  In 10 female and 7 male cadavers (aged 72–86 y) skin,fat and muscles were removed by blunt dissectionkeeping all ligamentous structures intact. All attach-ments of the IL were analysed. After detaileddescription, the transverse processes of L5 werecarefully removed keeping fibres belonging to thesacroiliac part of the IL (SIPIL) intact. The attach-ments of these fibres were exposed and documented.By a calibrated scale, the length, thickness and widthFig. 1. The coordinate system at the base of the sacrum in thetransverse plane.Fig. 2. α, angle of the sacroiliac part of the iliolumbar ligament(SIPIL) in the transverse plane.Fig. 3. β, angle of the sacroiliac part of the iliolumbar ligament(SIPIL) in the coronal plane.of these fibres were measured. In the transverse plane,an imaginary coordinate system was placed at thebase of the sacrum (see Fig. 1). Two angles weremeasured: the angle α between the fibres of the SIPILand the X-axis in the transverse plane (Fig. 2) and theangle β between the fibres of the SIPIL and the Y-axisin the coronal plane (Fig. 3). Magnetic resonanceimaging (MRI) (Philips gyro scan T10-NT) was usedto verify the existence of a SIPIL in the coronal andtransverse plane. Cryosectioning was performed(2 mm) in the same plane as the MRI. An independentt test was used to test the differences between men andwomen in height, width, thickness and orientation ofthe SIPIL.In its entirety the IL is a fan shaped structure,consisting of various parts, highly variable in number458 A. L. Pool-Goudzwaard and othersFig. 4. Caudoventral view of the ligamentous structures in the lumbosacral region with the iliolumbar ligament consisting of the followingfibres and bands: (1) dorsal band; (2) ventral band; (3) sacroiliac part of the iliolumbar ligament (SIPIL); (4) lumbosacral band; (5) fusionof the dorsal band with the deepest layer of the thoracolumbar fascia or the fascia of quadratus lumborum; (6) attachment of the iliolumbarligament to the transverse process of L4; (7) fusion of the iliolumbar ligament with the intertransverse ligaments between L4-L5. SI,approximate site of the sacroiliac joint (interrupted line).Fig. 5. Cranial view of the ligamentous structures in the lumbosacral region with the iliolumbar ligament consisting of the following fibresand bands: (1) dorsal band; (2) ventral band; (3) sacroiliac part of the iliolumbar ligament (SIPIL); (4) lumbosacral band; (5) dorsal sacroiliacligaments ; (6) ventral sacroiliac ligaments. SI, approximate site of the sacroiliac joint (interrupted line) ; L5, 5th lumbar vertebra.Sacroiliac part of iliolumbar ligament 459Table. Dimensions and orientations (with standard devia-tions) of the SIPIL in women and menWomen (n¯ 10) Men (n¯ 7)Dimensions (mm)Length 31±0 (5±6) 30±5 (5±6)Width 12±7 (4±6) 14±5 (4±1)Thickness 1±6 (0±5) 1±5 (0±4)Orientation (degrees)Angle α 77±9 (4±9) 83±7 (3±6)Angle β 50±2 (6±8) 52±1 (7±2)and form. Although the several parts blend together,some ‘bands’ and parts can be distinguished. Thefollowing were seen in all specimens (n¯ 34).1. A dorsal band originating from the tip of thetransverse process of L5, inserting on the cranial partof the iliac tuberosity below the medial part of theorigin of the quadratus lumborum muscle and on themedial part of the iliac crest (Figs 4, 5).2. A direct attachment of the dorsal band to thedeep ventral layer of the thoracolumbar fascia or tothe fascia of quadratus lumborum (Fig. 4).3. A ventral band originating from the ventrocaudalFig. 6. MRI in the coronal plane of the lumbosacral area of the same slice as in Fig. 7. Note the separation of the craniolateral part of theSIPIL (middle arrow) and the interosseous SI ligaments (lower arrow) by fat (asterisk). The upper arrow (see inset) indicates the ventral bandof the iliolumbar ligament. S, sacrum; I, ilium; SI, sacroiliac joint ; L5, 5th lumbar vertebra.part of the transverse process of L5 (Fig. 4) and in 3specimens also from the caudal aspect of the endplateof the vertebral body of L5. The insertion is at theventrocranial part of the iliac tuberosity on thesacropelvic surface.4. A lumbosacral band originating from theventrolateral aspect of the vertebral body of L5 andventromedial part of the transverse processes andinserting at the most ventrolateral part of the base ofthe sacrum, near the SI joint. These fibres blend withthe ventral SI ligaments (Fig. 4).5. A sacroiliac part (SIPIL), originating from thecranial surface of the ala of the sacrum directly caudalto the transverse process of L5 and inserting at theventromedial part of the iliac tuberosity, together withthe ventral band (Fig. 4). See Table for details onlength, thickness, width and orientation in womenand men, Figure 6 for MRI and Figures 7 and 8 forcryosectioned slices.6. Fibres of the SIPIL merging with the thinintertransverse ligament of L5-S1 (Fig. 4).7. Fibres of the SIPIL merging with the interosseousSI ligaments. The craniolateral part of the SIPIL isseparated from the interosseous ligaments by fattytissue (Fig. 6).460 A. L. Pool-Goudzwaard and othersFig. 7. Cryosectioned slice in the coronal plane of a part of the pelvis on the left side. I, ilium; S, sacrum; SI, sacroiliac joint; L5, 5th lumbarvertebra. The SIPIL is demarcated by the arrows.Fig. 8. Cryosectioned slice in the transverse plane of a part of thepelvis on the left side showing the SIPIL (between white arrows).In 10 specimens, the IL had an attachmentbilaterally to the ventrocaudal aspect of the transverseprocess of L4. In these specimens, fibres of theiliolumbar ligament blended with the intertransverseligaments between L4-L5 (Fig. 4).In all specimens the following muscles were at-tached to the IL.1. Muscle fibres of the erector spinae attached tothe dorsal aspect of the IL, although these fibrescould easily be removed by scraping.2. The most medial muscle fibres of the iliacusattached to the caudal part of the ventral band of theIL.3. The most medial muscle fibres of quadratuslumborum, mainly deriving from L4 and L5, attachedto the most lateral part of the dorsal band of the IL. In all specimens we found fibres originating from theala of the sacrum and inserting onto the medial aspectof the iliac crest. Since the site of insertion of thesefibres is just beneath that of the ventral band of the ILand since these fibres are separated from the in-terosseous SI ligaments by fat, we designate thesefibres as a distinct sacroiliac part of the IL, the SIPIL.The SIPIL can be considered as the ‘sacral head’ ofthe ventral band. The origin of this part is at the samesite on the sacrum as that of the interosseous SIligaments. Our findings on the SIPIL are an extensionSacroiliac part of iliolumbar ligament 461of the work of Frazer (1948), O’Rahilly (1986) andWillard (1995). Frazer (1948) described fibres of theIL passing to the transverse tubercle of the 1st sacralvertebra and the bone in front of this. O’Rahilly(1986) described the dorsal and ventral band ex-tending from the transverse process of L5 to thesacrum and ilium while Willard (1995) described apart of the IL blending inferiorly with the interosseousligaments of the SI joint. The attachment of a part ofthe IL to the sacrum suggests a role for the IL inrestraining movement in the SI joint. However, as yetno biomechanical studies are available to supportsuch an assumption.The SIPIL is mainly oriented in the coronal plane,perpendicular to the SI joint. The direct restrainingeffect of the SIPIL can thus be expected in the coronalplane, providing resistance to an outward movementof the cranial part of the ilium with respect to thesacrum. A restraining effect of the SIPIL on movementof the sacrum in the sagittal plane (nutation andcounternutation) can hardly be expected. Althoughthe SIPIL blends with the intertransverse ligamentof L5-S1, a direct influence of the SIPIL on themovement of L5-S1 is not likely either, since the fibreswhich blend with the intertransverse ligaments arethin and membranous. However, since a multitude ofmechanoreceptors and nociceptors are present in theIL, this connection could be of importance inmonitoring the motion of the lumbosacral junction.The dimensions and orientations of the SIPIL areabout the same in men and women. Angle α tends tobe somewhat larger in men than in women, but thedifference is not statistically significantly (see Table).The minor differences may be due to the sexualdimorphism of the adult pelvis, since in women theiliac blades are relatively vertical and do not extend asfar upwards as in men (Williams & Warwick, 1980).This study shows the existence of 7 parts to the IL.Although highly variable in number and form, majorparts could be identified in all specimens. Thenumerous insertions and fibre directions suggest adiversity of biomechanical functions for the IL. Thisdiversity is not acknowledged by authors describing 1(Maigne & Maigne, 1991) or 2 separate bands of theIL (Moore, 1980; Luk et al. 1986; Hanson &Sonesson, 1994; Basadonna et al. 1996; Rucco et al.1996). Several biomechanical studies have shown theimportance of the IL in restraining motion at thelumbosacral joint and providing torsional stability ofthe lumbosacral junction (Leong et al. 1987; Chow etal. 1989; Yamamoto et al. 1989, 1990). However,these authors do not mention the connections of the ILto L4 or to the base of the sacrum. These connectionsimply a more diverse role of the IL than previouslydescribed but biomechanical studies are needed toconfirm the importance of the IL in stabilising the SIjoint and L4-L5.The authors thank J. M. A Mens and A. Vleeming fortheir advice.BASADONNA PT, GASPARINI D, RUCCO V (1996) Iliolumbarligament insertions. In vivo anatomic study. Spine 21, 2313–2316.BOGDUK N (1983) The innervation of the lumbar spine. Spine 8,264–267.BOGDUK N, TWOMEY LT (1987) Clinical Anatomy of theLumbar Spine. Melbourne: Churchill Livingstone.CHOW DHK, LUK KDK, LEONG JCY, WOO CW (1989)Torsional stability of the lumbosacral junctions. Significance ofthe iliolumbar ligament. Spine 14, 611–6151.FRAZER JE (1948) The Anatomy of the Human Skeleton. London:J&A Churchill.HANSON P, SONESSON B (1994) The anatomy of the iliolumbarligament. Archives of Physical Medical Rehabilitation 75,1242–1246.KORKALA O, GRONBALD M, LIESI P, KARAHARJU E(1985) Immunohistochemical demonstration of nociceptors inthe ligamentous structures of the lumbar spine. Spine 10, 156–157.LEONG JCY, LUK DK, CHOW DHK, WOO CW (1987) Thebiomechanical functions of the iliolumbar ligament in main-taining stability of the lumbosacral junction. Spine 12, 669–671.LUK KD, HO HC, LEONG JC (1986) The iliolumbar ligament. Astudy of its anatomy, development and clinical significance.Journal of Bone and Joint Surgery 68B, 197–200.MAIGNE JY, MAIGNE R (1991) Trigger point of the posterioriliac crest : painful iliolumbar ligament insertion or cutaneousdorsal ramus pain? An anatomic study. Archives of PhysicalMedicine and Rehabilitation 72, 734–737.MOORE KL (1980) Clinically Oriented Anatomy. BaltimoreLondon: Williams & Wilkins.O’RAHILLY R (1986) Anatomy. A Regional Study of HumanStructure. Philadelphia: WB Saunders.PUN WK, LUK KD, LEONG JC (1987) Influence of the erectposture on the development of the lumbosacral region—acomparative study on the lumbosacral junction of the monkey,dog, rabbit and rat. Surgery, Radiology and Anatomy 9, 69–73.RHALMI S, YAHIA LH, NEWMAN N, ISLER M (1993)Immunohistochemical study of nerves in lumbar spine ligaments.Spine 18, 264–267.RUCCO V, BASADONNA PT, GASPARINI D (1996) Anatomyof the iliolumbar ligament. A review of its anatomy and amagnetic resonance study. American Journal of Physical Medicineand Rehabilitation 75, 451–455.SIMS JA, MOORMAN SJ (1996) The role of the iliolumbarligament in low back pain. Medical Hypothesis 46, 511–515.UHTHOFF HK (1993) Prenatal development of the iliolumbarligament. Journal of Bone and Joint Surgery 75B, 93–95.WILLIAMS PL, WARWICK R (eds) (1980) Gray’s Anatomy, 36thedn, p. 447. Edinburgh: Churchill Livingstone.WILLARD FH (1997) The muscular, ligamentous and neuralstructure of the low back and its relation to back pain. In462 A. L. Pool-Goudzwaard and othersMovement, Stability & Low Back Pain, the Essential Role of thePelvis (ed. Vleeming A, Mooney V, Dorman T, Snijders CJ,Stoeckart R), pp. 3–37. Edinburgh: Churchill Livingstone.YAHIA LH, NEWMAN N, RIVARD CH (1988) Neurohistologyof lumbar spinal ligaments. Acta Orthopaedica Scandinavica 59,508–512.YAMAMOTO I, PANJABI MM, CRISCO T, OXLAND TR(1989) Three dimensional movements of the whole lumbar spineand lumbosacral joint. Spine 14, 1256–1260.YAMAMOTO I, PANJABI M, OXLAND TR, CRISCO JJ (1990)The role of the iliolumbar ligament in the lumbosacral junction.Spine 15, 1138–1141.Sacroiliac part of iliolumbar ligament 463

English

Erasmus University Digital Repository

J. Anat. (2001) 199, pp. 457–463, with 8 figures Printed in the United Kingdom 457The sacroiliac part of the iliolumbar ligamentA. L. POOL-GOUDZWAARD1,3, G. J. KLEINRENSINK1, C. J. SNIJDERS2, C. ENTIUS1AND R. STOECKART1Departments of "Anatomy and #Biomedical Physics and Technology, Erasmus University Rotterdam, and $MedicalCenter Impact Zoetermeer, The Netherlands(Accepted 26 April 2000)abstractThe iliolumbar ligament has been described as the most important ligament for restraining movement at thelumbosacral junction. In addition, it may play an important role in restraining movement in the sacroiliacjoints. To help understand its presumed restraining effect, the anatomy of the ligament and its orientationwith respect to the sacroiliac joints were studied in 17 cadavers. Specific dissection showed the existence ofseveral distinct parts of the iliolumbar ligament, among which is a sacroiliac part. This sacroiliac partoriginates on the sacrum and blends with the interosseous sacroiliac ligaments. Together with the ventralpart of the iliolumbar ligament it inserts on the medial part of the iliac crest, separate from the interosseoussacroiliac ligaments. Its existence is verified by magnetic resonance imaging and by cryosectioning of thepelvis in the coronal and transverse plane. Fibre direction, length, width, thickness and orientation of thesacroiliac part of the iliolumbar ligament are described. It is mainly oriented in the coronal plane,perpendicular to the sacroiliac joint. The existence of this sacroiliac part of the iliolumbar ligament supportsthe assumption that the iliolumbar ligament has a direct restraining effect on movement in the sacroiliacjoints.Key words : Biomechanics ; sacroiliac joint ; low back pain.introductionIn the literature the iliolumbar ligament (IL) isdescribed as a biomechanically important ligamentfor the lumbopelvic region; it extends from thetransverse processes of the 4th and 5th lumbarverterbrae to the iliac crest (Leong et al. 1987; Chowet al. 1989; Yamamoto et al. 1989, 1990). Further-more Sims & Moorman (1996) mention the IL as animportant primary source of low back pain. This isplausible since immunohistochemically the presenceof a multitude of mechanoreceptors and nociceptorshas been shown in the lumbar posterior ligaments(Bogduk, 1983; Korkala et al. 1985; Yahia et al.1988; Rhalmi et al. 1993). It is postulated that theinnervation of the IL is similar to that of otherposterior lumbar ligaments (Sims & Moorman, 1996).Several biomechanical studies emphasise the import-ance of the IL, on the one hand, in restraining flexion,extension and lateral bending of L5 on SI (Leonget al. 1987; Yamamoto et al. 1989, 1990) and onCorrespondence to Dr Annelies Pool-Goudzwaard, Department of Anatomy, Erasmus University, Postbus 1738, 3000 DR Rotterdam, TheNetherlands. e-mail : m.p.c.impact!planet.nlthe other in maintaining torsional stability of thelumbosacral junction (Chow et al. 1989). This conceptsupports the study by Pun et al. (1987) showing thepresence of the IL in rhesus monkeys and its absencein quadrupeds with a more horizontal spine. Inaddition to this restraining function, Luk et al.(1986) suggested that in man the IL could play arole in locking the sacrum between the iliac bones.In other words the IL might also restrain movementin the SI joint. To analyse whether this holds trueand, if so, which movements of the sacrum andiliac bones can be restrained, first the topographicanatomy of the ligament and its orientation withrespect to the SI joint have to be clarified since theliterature is confusing.The IL has been described as consisting of 1(Maigne & Maigne, 1991), 2 (Moore, 1980; Luk et al.1986; Uhthoff, 1993; Hanson & Sonesson, 1994;Basadonna et al. 1996; Rucco et al. 1996), 3 (Williams& Warwick, 1980), 4 (O’Rahilly, 1986), or even 5separate bands (Bogduk & Twomey, 1987). Mostauthors have described the origin of the IL at thetransverse processes of L5 (O’Rahilly, 1986; Moore,1980; Williams & Warwick, 1980; Luk et al. 1986;Leong et al. 1987; Bogduk & Twomey, 1987; Chowet al. 1989; Yamamoto et al. 1989, 1990; Maigne &Maigne, 1991; Uhthoff, 1993; Hanson & Sonesson,1994; Basadonna et al. 1996; Rucco et al. 1996;Willard, 1997) and occasionally L4 (O’Rahilly, 1986;Moore 1980; Williams & Warwick, 1980; Bogduk &Twomey, 1987; Leong et al. 1987; Chow et al. 1989;Yamamoto et al. 1989, 1990; Uhthoff, 1993; Willard,1997). In all studies the insertion of the IL isdescribed as being on the iliac crest and the ventral,upper part of the iliac tuberosity. In some textbooksattachments of the IL to the anterior layer of thethoracolumbar fascia are described (Moore, 1980;Williams & Warwick, 1980; O’Rahilly, 1986). Ac-cording to O’Rahilly (1986) and confirmed by Willard(1995), some fibres of the IL blend with the inter-transverse ligaments between L5-S1 and L4-L5 andblend with the interosseous SI ligaments. Frazer(1948) had earlier described fibres of the IL passingto the 1st sacral vertebra although detailed descrip-tions of length, width and thickness are lacking. Theaim of the present study is to confirm whether a partof the IL can be defined as a sacroiliac ligament. Ifso, its fibre direction, length, thickness, width andorientation are of interest.materials and methodsIn 10 female and 7 male cadavers (aged 72–86 y) skin,fat and muscles were removed by blunt dissectionkeeping all ligamentous structures intact. All attach-ments of the IL were analysed. After detaileddescription, the transverse processes of L5 werecarefully removed keeping fibres belonging to thesacroiliac part of the IL (SIPIL) intact. The attach-ments of these fibres were exposed and documented.By a calibrated scale, the length, thickness and widthFig. 1. The coordinate system at the base of the sacrum in thetransverse plane.Fig. 2. a, angle of the sacroiliac part of the iliolumbar ligament(SIPIL) in the transverse plane.Fig. 3. b, angle of the sacroiliac part of the iliolumbar ligament(SIPIL) in the coronal plane.of these fibres were measured. In the transverse plane,an imaginary coordinate system was placed at thebase of the sacrum (see Fig. 1). Two angles weremeasured: the angle a between the fibres of the SIPILand the X-axis in the transverse plane (Fig. 2) and theangle b between the fibres of the SIPIL and the Y-axisin the coronal plane (Fig. 3). Magnetic resonanceimaging (MRI) (Philips gyro scan T10-NT) was usedto verify the existence of a SIPIL in the coronal andtransverse plane. Cryosectioning was performed(2 mm) in the same plane as the MRI. An independentt test was used to test the differences between men andwomen in height, width, thickness and orientation ofthe SIPIL.resultsIn its entirety the IL is a fan shaped structure,consisting of various parts, highly variable in number458 A. L. Pool-Goudzwaard and othersFig. 4. Caudoventral view of the ligamentous structures in the lumbosacral region with the iliolumbar ligament consisting of the followingfibres and bands: (1) dorsal band; (2) ventral band; (3) sacroiliac part of the iliolumbar ligament (SIPIL); (4) lumbosacral band; (5) fusionof the dorsal band with the deepest layer of the thoracolumbar fascia or the fascia of quadratus lumborum; (6) attachment of the iliolumbarligament to the transverse process of L4; (7) fusion of the iliolumbar ligament with the intertransverse ligaments between L4-L5. SI,approximate site of the sacroiliac joint (interrupted line).Fig. 5. Cranial view of the ligamentous structures in the lumbosacral region with the iliolumbar ligament consisting of the following fibresand bands: (1) dorsal band; (2) ventral band; (3) sacroiliac part of the iliolumbar ligament (SIPIL); (4) lumbosacral band; (5) dorsal sacroiliacligaments ; (6) ventral sacroiliac ligaments. SI, approximate site of the sacroiliac joint (interrupted line) ; L5, 5th lumbar vertebra.Sacroiliac part of iliolumbar ligament 459Table. Dimensions and orientations (with standard devia-tions) of the SIPIL in women and menWomen (nfl 10) Men (nfl 7)Dimensions (mm)Length 31–0 (5–6) 30–5 (5–6)Width 12–7 (4–6) 14–5 (4–1)Thickness 1–6 (0–5) 1–5 (0–4)Orientation (degrees)Angle a 77–9 (4–9) 83–7 (3–6)Angle b 50–2 (6–8) 52–1 (7–2)and form. Although the several parts blend together,some ‘bands’ and parts can be distinguished. Thefollowing were seen in all specimens (nfl 34).1. A dorsal band originating from the tip of thetransverse process of L5, inserting on the cranial partof the iliac tuberosity below the medial part of theorigin of the quadratus lumborum muscle and on themedial part of the iliac crest (Figs 4, 5).2. A direct attachment of the dorsal band to thedeep ventral layer of the thoracolumbar fascia or tothe fascia of quadratus lumborum (Fig. 4).3. A ventral band originating from the ventrocaudalFig. 6. MRI in the coronal plane of the lumbosacral area of the same slice as in Fig. 7. Note the separation of the craniolateral part of theSIPIL (middle arrow) and the interosseous SI ligaments (lower arrow) by fat (asterisk). The upper arrow (see inset) indicates the ventral bandof the iliolumbar ligament. S, sacrum; I, ilium; SI, sacroiliac joint ; L5, 5th lumbar vertebra.part of the transverse process of L5 (Fig. 4) and in 3specimens also from the caudal aspect of the endplateof the vertebral body of L5. The insertion is at theventrocranial part of the iliac tuberosity on thesacropelvic surface.4. A lumbosacral band originating from theventrolateral aspect of the vertebral body of L5 andventromedial part of the transverse processes andinserting at the most ventrolateral part of the base ofthe sacrum, near the SI joint. These fibres blend withthe ventral SI ligaments (Fig. 4).5. A sacroiliac part (SIPIL), originating from thecranial surface of the ala of the sacrum directly caudalto the transverse process of L5 and inserting at theventromedial part of the iliac tuberosity, together withthe ventral band (Fig. 4). See Table for details onlength, thickness, width and orientation in womenand men, Figure 6 for MRI and Figures 7 and 8 forcryosectioned slices.6. Fibres of the SIPIL merging with the thinintertransverse ligament of L5-S1 (Fig. 4).7. Fibres of the SIPIL merging with the interosseousSI ligaments. The craniolateral part of the SIPIL isseparated from the interosseous ligaments by fattytissue (Fig. 6).460 A. L. Pool-Goudzwaard and othersFig. 7. Cryosectioned slice in the coronal plane of a part of the pelvis on the left side. I, ilium; S, sacrum; SI, sacroiliac joint; L5, 5th lumbarvertebra. The SIPIL is demarcated by the arrows.Fig. 8. Cryosectioned slice in the transverse plane of a part of thepelvis on the left side showing the SIPIL (between white arrows).In 10 specimens, the IL had an attachmentbilaterally to the ventrocaudal aspect of the transverseprocess of L4. In these specimens, fibres of theiliolumbar ligament blended with the intertransverseligaments between L4-L5 (Fig. 4).In all specimens the following muscles were at-tached to the IL.1. Muscle fibres of the erector spinae attached tothe dorsal aspect of the IL, although these fibrescould easily be removed by scraping.2. The most medial muscle fibres of the iliacusattached to the caudal part of the ventral band of theIL.3. The most medial muscle fibres of quadratuslumborum, mainly deriving from L4 and L5, attachedto the most lateral part of the dorsal band of the IL.discuss ionIn all specimens we found fibres originating from theala of the sacrum and inserting onto the medial aspectof the iliac crest. Since the site of insertion of thesefibres is just beneath that of the ventral band of the ILand since these fibres are separated from the in-terosseous SI ligaments by fat, we designate thesefibres as a distinct sacroiliac part of the IL, the SIPIL.The SIPIL can be considered as the ‘sacral head’ ofthe ventral band. The origin of this part is at the samesite on the sacrum as that of the interosseous SIligaments. Our findings on the SIPIL are an extensionSacroiliac part of iliolumbar ligament 461of the work of Frazer (1948), O’Rahilly (1986) andWillard (1995). Frazer (1948) described fibres of theIL passing to the transverse tubercle of the 1st sacralvertebra and the bone in front of this. O’Rahilly(1986) described the dorsal and ventral band ex-tending from the transverse process of L5 to thesacrum and ilium while Willard (1995) described apart of the IL blending inferiorly with the interosseousligaments of the SI joint. The attachment of a part ofthe IL to the sacrum suggests a role for the IL inrestraining movement in the SI joint. However, as yetno biomechanical studies are available to supportsuch an assumption.The SIPIL is mainly oriented in the coronal plane,perpendicular to the SI joint. The direct restrainingeffect of the SIPIL can thus be expected in the coronalplane, providing resistance to an outward movementof the cranial part of the ilium with respect to thesacrum. A restraining effect of the SIPIL on movementof the sacrum in the sagittal plane (nutation andcounternutation) can hardly be expected. Althoughthe SIPIL blends with the intertransverse ligamentof L5-S1, a direct influence of the SIPIL on themovement of L5-S1 is not likely either, since the fibreswhich blend with the intertransverse ligaments arethin and membranous. However, since a multitude ofmechanoreceptors and nociceptors are present in theIL, this connection could be of importance inmonitoring the motion of the lumbosacral junction.The dimensions and orientations of the SIPIL areabout the same in men and women. Angle a tends tobe somewhat larger in men than in women, but thedifference is not statistically significantly (see Table).The minor differences may be due to the sexualdimorphism of the adult pelvis, since in women theiliac blades are relatively vertical and do not extend asfar upwards as in men (Williams & Warwick, 1980).This study shows the existence of 7 parts to the IL.Although highly variable in number and form, majorparts could be identified in all specimens. Thenumerous insertions and fibre directions suggest adiversity of biomechanical functions for the IL. Thisdiversity is not acknowledged by authors describing 1(Maigne & Maigne, 1991) or 2 separate bands of theIL (Moore, 1980; Luk et al. 1986; Hanson &Sonesson, 1994; Basadonna et al. 1996; Rucco et al.1996). Several biomechanical studies have shown theimportance of the IL in restraining motion at thelumbosacral joint and providing torsional stability ofthe lumbosacral junction (Leong et al. 1987; Chow etal. 1989; Yamamoto et al. 1989, 1990). However,these authors do not mention the connections of the ILto L4 or to the base of the sacrum. These connectionsimply a more diverse role of the IL than previouslydescribed but biomechanical studies are needed toconfirm the importance of the IL in stabilising the SIjoint and L4-L5.acknowledgementsThe authors thank J. M. A Mens and A. Vleeming fortheir advice.referencesBASADONNA PT, GASPARINI D, RUCCO V (1996) Iliolumbarligament insertions. 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Spine 14, 1256–1260.YAMAMOTO I, PANJABI M, OXLAND TR, CRISCO JJ (1990)The role of the iliolumbar ligament in the lumbosacral junction.Spine 15, 1138–1141.Sacroiliac part of iliolumbar ligament 463

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The sacroiliac part of the iliolumbar ligament

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