Anatomy of the Iliolumbar Ligaments
The iliolumbar ligament is generally documented as being split into anterior and posterior bands extending from the L5 transverse process to the ilium (Rucco et al 1996).
However Kelihues et al (2001) found in only three out of thirty cadavers was the ligament made up of clearly identifiable bands. In a majority of cases, the ligament appeared as a spreading, connective tissue complex, which could be differentiated into two (9/30), three (14/30) or four (4/30) main bands.
The Iliolumbar ligaments blends with the posterior retinaculum sheat (Willard et al 2012) and the anterior sacroiliac ligaments (Vleeming et al 2012)
Back to the traditional description Rucco et al (1996) found the Iliolumbar ligament split into anterior and posterior components:
Anterior band: the anterior band of the iliolumbar ligament is broad and flat. It has two types (Rucco et al 1996):
Type 1 originates from the anterior aspect of the inferolateral portion of the L5 transverse process and fans out widely before inserting on the anterior portion of the iliac tuberosity.
Type 2 originates anteriorly, laterally, and posteriorly from inferolateral aspect of the L5 transverse process and fans out before inserting on the anterior portion of the iliac tuberosity
The anterior band inserts on the anterior part of the iliac tuberosity below the posterior band (Basadonna et al 1996).
Posterior band: the posterior band of the iliolumbar ligament is thinner than the anterior section. It originates from the apex of the L5 transverse process and inserts on the iliac crest above the anterior band (Basadonna et al 1996).
Rucco et al (1996) found in the coronal plane, the spatial disposition of the iliolumbar ligament varies greatly with the size of the L5 vertebra and its position in the pelvis:
When L5 is situated low in the pelvis, the bands of the iliolumbar ligament are longer and oblique.
When L5 is situated high in the pelvis, the bands of the iliolumbar ligament are shorter and horizontal.
More uncommon variations in the attachment of the iliolumbar ligament are mainly on its vertebral attachments. These include (Kelihues et al (2001):
- Lateral surface of the L5 vertebral body.
- Lateral surface of the L4 vertebral body and transverse process.
- Lateral surface of the L3 vertebral body and transverse process.
- Lateral surface of the S1 body.
Muscular and fascial attachments to the iliolumbar ligament
The muscular and fascial attachments to the iliolumbar ligament are:
- Quadratus lumborum: Barker et al (2007) found the quadratus lumborum divided into a superifical and deep layer. The superficial layer descends almost vertically from rib 12 with tendons attaching to the superolateral corner of each transverse process. The deep layer is oblique originating from the iliac crest and ascending superomedially to insert to the inferolateral corner of each transverse process. The most medial muscle fibres of quadratus lumborum, mainly deriving from L4 and L5, attached to the most lateral part of the dorsal band of the iliolumbar ligament (Pool-Goudzwaard et al 2000).
- Iliocostalis lumborum: this muscle consists of four fascicles that arise from the L1-L4 TP, ribs 4-12, and the middle layer of the thoracolumbar fascia adjacent to the respective transverse processes. Gilchrist et al (2003) found the iliocostalis lumborum lacks fascicle attachment to the L5 TP and is represented in the iliolumbar ligament posteriorly.
- Deepest layer of the thoracolumbar fascia or quadratus lumborum fascia fuses with the iliolumbar ligament (Pool-Goudzwaard et al 2000).
Biomechanics of the Iliolumbar ligament
Viehofer et al (2015) found fibrocartilaginous connective tissue between the Iliolumbar ligament and its bony attachment. This suggests the insertion sites of the ligament are subject to both tensile and compressive loading. This is probably because of the insertional angle changes between the ligament and bone during loading. This supports the suggestion that the iliolumbar ligament might play an important role in the stabilization of the lumbosacral junction.
Pool-Goudzwaard et (2003) concluded the iliolumbar ligaments restrict sacroiliac joint sagittal mobility (they didn't specify nutation or counternutation) and it's the anterior band of the iliolumbar ligament that mainly contributes to this restriction.
Sims and Moorman (1996) found the iliolumbar ligament the greatest resister of sacral flexion (nutation) although no reference was cited in their study. Snijders et al (2008) found contrary to this finding the iliolumbar ligament stretched in counternutation of the pelvis and flexion of the lumbar spine (and Miyasaka et al 2000).
Yamamoto et al (1990) found the iliolumbar ligament resists lumbar spine movement predominately in contralateral lateral bending, then flexion (& Miyasaka et al 2000, Snijders et al 2000), then extension and lastly axial rotation.
Innervation of the Iliolumbar ligament
Kiter et al (2010) showed the iliolumbar ligament to be richly innervated. As well as the biomechanical function suggested by authors such as Viehofer et al (2015) this also suggests the Iliolumbar ligament has an important proprioceptive coordination role in the lumbosacral region and can be a source of pain.
Palpation of the iliolumbar ligament
Maigne and Maigne (1991) claimed the iliolumbar ligament was inaccessible to palpation. They found the insertion of the iliolumbar ligament to the pelvis was shielded by the iliac crest. They believed the area tender to palpation was in fact the dorsal rami of the L1 or L2 nerve roots not the iliolumbar ligament attachment. These nerves cross the iliac crest 7 cm from the midline as they course through the fibroosseous tunnel.
However other authors such as Harmon and Alexiev (2011), Sipko et al (2010) and Rucco et al (1996) found painful palpation of the iliolumbar ligament at the iliac crest indicative of iliolumbar ligament pathology.
Iliolumbar ligament injury
Posterior bands of the iliolumbar ligament are more prone to injury due to their weaker structure (Basadonna et al 1996 and Rucco et al 1996).
Sims and Moorman (1996) identified the Iliolumbar ligament as the weakest component of the multifidus triangle which along with its angulated attachment they hypothesised lends it prone to injury.
Interestingly it is the insertional angle that changes during loading that Viehofer et al (2015) found subjected the ligament to both tensile and compressive loading.
Snijders (2004, 2008) found slouching to elongate and place excessive strain on the iliolumbar ligament.
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