Gender Equality in Diastasis Rectus Abdominis in Chronic Back Pain: A Model of M. Transversus Abdominis Motor Control Impairment.

Introduction: Diastasis rectus abdominis (DRA) is defined as an increased distance between the left and right muscle of the m. rectus abdominis. Pregnancy-related factors are assumed to be dominant factors in the occurrence of DRA. However DRA is not only found in peri-partum women but also in men and nulliparous women with back or pelvic pain. This study provides an inventory of the incidence of DRA in subjects with chronic back and pelvic pain. If DRA is common in both men and women then other factors besides pregnancy, like impaired motor control, should be explored as cause for DRA. Material and Methods: This study was conducted with data from 849 back pain patients. Results from ultrasound assessment of the abdominal wall were combined with anamnestic data on age, gender, medical history and pregnancies (in women). Results: There was no difference in Inter Rectus Distance cranial of the umbilicus (IRD above umbilicus) between men and women. Almost half of all women and men (45% and 43%, respectively) exhibit an increased IRD above umbilicus. The incidence of an increased IRD above umbilicus is twice as high in women below 30 years, compared to men below 30 years old. This difference is not observed for men and women above 30 years old. Discussion: DRA occurs in women during pregnancy and increases with an increasing number of pregnancies. However, this condition does not affect significantly more women than men. Increased IRD above umbilicus already occurs in young men (mean age 30). Over 30 years of age, cranial of the umbilicus there is no difference in IRD between women and men. An alternative etiological mechanism is suggested.

Stabilization of the sacroiliac joint in vivo: verification of muscular contribution to force closure of the pelvis.

A model of sacroiliac joint (SIJ) function postulates that SIJ shear is prevented by friction, dynamically influenced by muscle force and ligament tension. Thus, SIJ stability can be accommodated to specific loading situations. The purpose of this study was to examine, in vivo, whether muscles contribute to force closure of the SIJ. SIJ stiffness was measured using a verified method combining color Doppler imaging with induced oscillation of the ilium relative to the sacrum in six healthy women. SIJ stiffness was measured both in a relaxed situation and during isometric voluntary contractions (electromyographically recorded). The biceps femoris, gluteus maximus, erector spinae, and contralateral latissimus dorsi were included in this study. Results were statistically analyzed. The study showed that SIJ stiffness significantly increased when the individual muscles were activated. This held especially true for activation of the erector spinae, the biceps femoris and the gluteus maximus muscles. During some tests significant co-contraction of other muscles occurred. The finding that SIJ stiffness increased even with slight muscle activity supports the notion that effectiveness of load transfer from spine to legs is improved when muscle forces actively compress the SIJ, preventing shear. When joints are manually tested, the influence of muscle activation patterns must be considered, since both inter- and intra-tester reliability of the test can be affected by muscle activity. In this respect, the relation between emotional states, muscle activity and joint stiffness deserves further exploration.

Isodynamic evaluation of trunk muscles and low-back pain among workers in a steel factory.

A cross-sectional study was conducted to explore the relationship between dynamic parameters of trunk muscle strength and the occurrence of low-back pain (LBP). Isodynamic strength measurements were performed among 31 male maintenance workers with spells of low-back pain in the past 12 months and 28 maintenance workers without a history of low-back pain. In general, workers with low-back pain showed a lower trunk muscle performance than the workers without low-back pain. Only the measures of torque during lateral movement differed significantly between both groups. Regression analysis revealed the importance of the nature of low-back pain for trunk muscle strength. Most parameters of trunk muscle strength were significantly decreased among workers with chronic low-back pain of a rather severe nature, showing reductions from 18% to 50%. None of the work-related risk factors for low-back pain contributed significantly to the prediction of trunk strength measures. The study suggests that isodynamic evaluation of trunk muscle strength may assist in determining objective measures for the severity of low-back pain rather than in evaluating a subject's capability of successfully coping with a specific work load.

Peripheral nerve tension due to joint motion. A comparison between embalmed and unembalmed human bodies.

Various joint positions of the upper extremity were used to study the tensile forces on the median nerve. To analyse the effect of embalmment, tensile forces were measured in situ in unembalmed and embalmed human bodies. A positive correlation was found between tensile force data from unembalmed and embalmed nerves. This finding justifies, for comparative studies, the use of embalmed human bodies, although the absolute tensile forces are higher. RELEVANCE: In daily activities or during certain operations positions of the upper extremity vary, hence creating tensile forces of different magnitude on peripheral nerves. Tensile forces are also applied in the diagnosis of nerve (root) lesions of the upper extremity. To analyse these tensile forces, in-situ experiments on unembalmed human bodies, though problematic, are supposed to be the most realistic approach. In this study it has been shown that in comparative studies on peripheral nerve tension, data obtained from embalmed human bodies can be used.

The posterior layer of the thoracolumbar fascia. Its function in load transfer from spine to legs.

STUDY DESIGN: The superficial and deep lamina of the posterior layer of the thoracolumbar fascia have been studied anatomically and biomechanically. In embalmed human specimens, the posterior layer has been loaded by simulating the action of various muscles. The effect has been studied using raster photography. OBJECTIVES: To study the role of the posterior layer of the thoracolumbar fascia in load transfer between spine, pelvis, legs, and arms. SUMMARY OF BACKGROUND DATA: It has been determined whether muscles such as the gluteus maximus, latissimus dorsi, erector muscle, and biceps femoris are functionally coupled via the thoracolumbar fascia. The caudal relations of the posterior layer of the thoracolumbar fascia have not been previously studied. METHODS: Dissection was directed to the bilaminar posterior layer of the thoracolumbar fascia of 10 human specimens. The superficial and deep lamina were studied using visual inspection and raster photography. Tension to the posterior layer of the fascia was simulated by traction to various muscles and measured by studying the displacement in the posterior layer. RESULTS: Traction to a variety of muscles caused displacement of the posterior layer. This implies that in vivo, the superficial lamina will be tensed by contraction of various muscles, such as the latissimus dorsi, gluteus maximus and erector muscle, and the deep lamina by contraction of the biceps femoris. Caudal to the level of L4 (in some specimens, L2-L3), tension in the posterior layer was transmitted to the contralateral side. CONCLUSIONS: Anatomic structures normally described as hip, pelvic, and leg muscles interact with so-called arm and spinal muscles via the thoracolumbar fascia. This allows for effective load transfer between spine, pelvis, legs, and arms--an integrated system. Specific electromyographic studies should reveal whether the gluteus maximus muscle and contralateral latissimus dorsi muscle are functionally coupled, especially during rotation of the trunk. In that case, the combined action of these muscles assists in rotating the trunk, while simultaneously stabilizing the lower lumbar spine and sacroiliac joints.

A comparison of working postures of parcel sorters using three different working methods.

The postures of the trunk of eight parcel sorters were measured continuously under three different working conditions, during whole shifts. The working methods used were two different sorting tables and a hydraulic lifting platform on which the carts were to be placed. The question posed by the PTT-Post occupational health service was whether the latter method proved to be the better one with respect to the load on the musculoskeletal system. This study will help them to make a well-considered decision on which working method to choose for the new distribution centre in Rotterdam. The method used for measuring the working postures and movements of the trunk is the Portable Posture Registration Set (PPRS). This method was developed at the department of Biomedical Physics and Technology of the Erasmus University Rotterdam. While using the lifting platform, the subjects stood 8-11% more erect compared to the work at the sorting tables, thereby reducing the load on the lumbar spine. For this reason the lifting platform is preferred, although sagittal flexion of the back was somewhat more. It is stressed that the way in which sorters use the lifting platform is very important.

A functional-anatomical approach to the spine-pelvis mechanism: interaction between the biceps femoris muscle and the sacrotuberous ligament.

Summary. Sacroiliac joint dysfunction is often overlooked as a possible cause of low back pain. This is due to the use of reductionistic anatomical models. From a kinematic point of view, topographic anatomical models are generally inadequate since they categorize pelvis, lower vertebral column and legs as distinct entities. This functional-anatomical study focuses on the question whether anatomical connections between the biceps femoris muscle and the sacrotuberous ligament are kinematically useful. Forces applied to the tendon of the biceps femoris muscle, simulating biceps femoris muscle force, were shown to influence sacrotuberous ligament tension. Since sacrotuberous ligament tension influences sacroiliac joint kinematics, hamstring training could influence the sacroiliac joint and thus low back kinematics. The clinical implications with respect to 'short' hamstrings, pelvic instability and walking are discussed.

Mobility in the sacroiliac joints in the elderly: a kinematic and radiological study.

Movement in eight sacroiliac joints was measured in preparations of embalmed elderly humans and compared with radiological findings. For the biomechanical part of the study the connections between sacrum and fifth lumbar vertebra were spared, as were the surrounding ligaments. The pelvis-spine preparation was fixed at the fifth lumbar vertebra. To induce movement, forces were directed at the acetabula. With digital displacement meters rotation was measured between the sacral and iliac part of the sacroiliac joint. In the sagittal plane both ventral rotation (as part of nutation) and dorsal rotation (as part of contranutation) could be demonstrated. Most sacroiliac joints were mobile, allowing a total rotation of up to 4°. Significant intraindividual differences in mobility occurred. One sacroiliac joint without mobility showed radiographically pronounced arthrosis. The impact of the findings on kinematic chain and clinical diagnosis is discussed. In the literature no data are available on the radiographic appearance of biomechanically studied sacroiliac joints. In the present study a biomechanical and radiological approach has been combined. The study emphasizes the clinical importance of intraindividual sacroiliac differences as well as the need for a thorough integration of pelvic and lumbar kinematics.

The effect on sitting posture of a desk with a 10 degree inclination for reading and writing.

A pilot study was carried out on 10 subjects to examine the effect that a desk with a 10 degree inclination had on their sitting posture while reading and writing. A continuous recording of the subjects head and trunk positions was made. Each subject was studied during two periods of 1.5 h on different days. The subject worked at a flat desk on the first day and at a desk with a 10 degree inclination on the second. On average, the position of the head in the sagittal plane was found to be 6 degrees more erect and the position of the trunk 7 degrees more erect when working at a desk with a 10 degree inclination than when working at a flat desk. The maximal decrease in load observed on the cervical spine was 35% and on the thoracic spine 95%. The angle between the head and the trunk did not change significantly when using an inclined desk. Differences in posture in the frontal plane were not observed in this study.