The middle layer of lumbar fascia and attachments to lumbar transverse processes: implications for segmental control and fracture.

The anatomy of the middle layer of lumbar fascia (MLF) is of biomechanical interest and potential clinical relevance, yet it has been inconsistently described. Avulsion fractures of the lumbar transverse processes (LxTP's) are traditionally attributed to traction from psoas major or quadratus lumborum (QL), rather than transversus abdominis (TrA) acting via the MLF. This attachment is also absent from many biomechanical models of segmental control. The aims of this study were to document: (1) the morphology and attachments of the MLF and (2) the attachments of psoas and QL to the LxTP's. Eighteen embalmed cadavers were dissected, measuring the thickness, fibre angle and width of the MLF and documenting the attachments of MLF, psoas and QL. The MLF was thicker at the level of the LxTP's than between them (mean 0.62: 0.40 mm). Psoas attached to the anteromedial surface of each process and QL and TrA to its lateral border; QL at its upper and lower corners and TrA (via the MLF) to its tip. In three cadavers, tension applied to the MLF fractured a transverse process. The MLF has a substantial and thickened attachment to the tips of the LxTP's which supports the involvement of TrA in lumbar segmental control and/ or avulsion fracture of the LxTP's.

Postural activity of the abdominal muscles varies between regions of these muscles and between body positions.

The abdominal muscles have an important role in control and movement of the lumbar spine and pelvis. Given there is new evidence of morphological and functional differences between distinct anatomical regions of the abdominal muscles, this study investigated whether there are regional differences in postural activity of these muscles and whether recruitment varies between different body positions. Eleven subjects with no history of low back pain that affected function or for which they sought treatment participated in the study. Electromyographic (EMG) activity of the upper, middle and lower regions of transversus abdominis (TrA), the middle and lower regions of obliquus internus abdominis (OI) and the middle region of obliquus externus abdominis (OE) was recorded using intramuscular electrodes. All subjects performed rapid, unilateral shoulder flexion in standing and six subjects also moved their upper limb in sitting. There were regional differences in the postural responses of TrA with limb movement. Notably, the onset of EMG of the upper region was later than that of the lower and middle regions. There were no differences in the EMG onsets of lower and middle TrA or OI. The postural responses of the abdominal muscles were also found to differ between body positions, with recruitment delayed in sitting compared to standing. This study showed that there is regional differentiation in TrA activity with challenges to postural control and that body position influences the postural responses of the abdominal muscles. These results may reflect variation in the contribution of abdominal muscle regions to stability of the trunk.

Abdominal muscle recruitment during a range of voluntary exercises.

Various exercises are used to retrain the abdominal muscles in the management of low back pain and other musculoskeletal disorders. However, few studies have directly investigated the activity of all the abdominal muscles or the recruitment of regions of the abdominal muscles during these manoeuvres. This study examined the activity of different regions of transversus abdominis (TrA), obliquus internus (OI) and externus abdominis (OE), and rectus abdominis (RA), and movement of the lumbar spine, pelvis and abdomen during inward movement of the lower abdominal wall, abdominal bracing, pelvic tilting, and inward movement of the lower and upper abdominal wall. Inward movement of the lower abdominal wall in supine produced greater activity of TrA compared to OI, OE and RA. During posterior pelvic tilting, middle OI was most active and with abdominal bracing, OE was predominantly recruited. Regions of TrA were recruited differentially and an inverse relationship between lumbopelvic motion and TrA electromyography (EMG) was found. This study indicates that inward movement of the lower abdominal wall in supine produces the most independent activity of TrA relative to the other abdominal muscles, recruitment varies between regions of TrA, and observation of abdominal and lumbopelvic motion may assist in evaluation of exercise performance.

Regional morphology of the transversus abdominis and obliquus internus and externus abdominis muscles.

BACKGROUND: The mechanisms by which the abdominal muscles move and control the lumbosacral spine are not clearly understood. Descriptions of abdominal morphology are also conflicting and the regional anatomy of these muscles has not been comprehensively examined. The aim of this study was to investigate the morphology of regions of transversus abdominis and obliquus internus and externus abdominis. METHODS: Anterior and posterolateral abdominal walls were dissected bilaterally in 26 embalmed human cadavers. The orientation, thickness and length of the upper, middle and lower fascicles of transversus abdominis and obliquus internus abdominis, and the upper and middle fascicles of obliquus externus abdominis were measured. FINDINGS: Differences in fascicle orientation, thickness and length were documented between the abdominal muscles and between regions of each muscle. The fascicles of transversus abdominis were horizontal in the upper region, with increasing inferomedial orientation in the middle and lower regions. The upper and middle fascicles of obliquus internus abdominis were oriented superomedially and the lower fascicles inferomedially. The mean vertical dimension of transversus abdominis that attaches to the lumbar spine via the thoracolumbar fascia was 5.2 (SD 2.1) cm. Intramuscular septa were observed between regions of transversus abdominis, and obliquus internus abdominis could be separated into two distinct layers in the lower and middle regions. INTERPRETATION: This study provides quantitative data of morphological differences between regions of the abdominal muscles, which suggest variation in function between muscle regions. Precise understanding of abdominal muscle anatomy is required for incorporation of these muscles into biomechanical models. Furthermore, regional variation in their morphology may reflect differences in function.