Lumbar extraforaminal ligaments act as a traction relief and prevent spinal nerve compression.

BACKGROUND: In a previous study, ligaments that connect the extraforaminal lumbar spinal nerves with the fibrous capsule of the facet joints and the dorsolateral side of the intervertebral disc were described. This anatomical configuration suggests a mechanical role in transferring extraforaminal spinal nerve traction. METHODS: One embalmed human lumbar spine was dissected from the twelfth thoracic vertebra to the first sacral vertebra to isolate the twelfth thoracic to the fourth lumbar spinal nerves. The spinal nerves from L1 to L4 were pulled at different angles with respect to the axis of the spine. Forces of 1-6N were applied. The displacements of reflective markers glued to the proximal and distal ends of the adjoining ligaments were recorded with a video system. FINDINGS: The spinal nerve proximal of the extraforaminal ligaments stays centred in the intervertebral foramen when pulling at an angle. At levels L1-L4 strain reduction by the extraforaminal ligaments was largest when pulling at a wider angle to the spinal axis in the sagittal plane. Proximal to the extraforaminal ligaments less displacement was seen compared to the displacement distal of the extraforaminal ligaments when pulling in longitudinal direction. A graded decrease in the displacement proximal to the extraforaminal ligaments was seen from the levels L1-L4. INTERPRETATION: Extraforaminal ligaments play an important role in the prevention of damage due to spinal nerve traction. The proximal attachments secure a spinal nerve position central in the intervertebral foramen and also reduce longitudinal tension.

Biomechanical analysis of reducing sacroiliac joint shear load by optimization of pelvic muscle and ligament forces.

Effective stabilization of the sacroiliac joints (SIJ) is essential, since spinal loading is transferred via the SIJ to the coxal bones, and further to the legs. We performed a biomechanical analysis of SIJ stability in terms of reduced SIJ shear force in standing posture using a validated static 3-D simulation model. This model contained 100 muscle elements, 8 ligaments, and 8 joints in trunk, pelvis, and upper legs. Initially, the model was set up to minimize the maximum muscle stress. In this situation, the trunk load was mainly balanced between the coxal bones by vertical SIJ shear force. An imposed reduction of the vertical SIJ shear by 20% resulted in 70% increase of SIJ compression force due to activation of hip flexors and counteracting hip extensors. Another 20% reduction of the vertical SIJ shear force resulted in further increase of SIJ compression force by 400%, due to activation of the transversely oriented M. transversus abdominis and pelvic floor muscles. The M. transversus abdominis crosses the SIJ and clamps the sacrum between the coxal bones. Moreover, the pelvic floor muscles oppose lateral movement of the coxal bones, which stabilizes the position of the sacrum between the coxal bones (the pelvic arc). Our results suggest that training of the M. transversus abdominis and the pelvic floor muscles could help to relieve SI-joint related pelvic pain.

The active straight leg raising test (ASLR) in pregnant women: differences in muscle activity and force between patients and healthy subjects.

Pregnancy-related low back and pelvic pain (PLBP) is a frequent complication of pregnancy. Although pathological mechanisms underlying PLBP are obscure, dysfunction of the sacroiliac joints (SI-joints) seems to play an important role. A cross-sectional study was performed on 24 pregnant women with and without PLBP. The objective was to determine muscle activation patterns of trunk and leg muscles during the active straight leg raising test (ASLR) and static hip flexion, and to determine maximal hip flexion force at 0 and 20 cm leg raise height. Moreover, the effort to raise the leg was scored. The measurements resulted in several significant differences between the patients and healthy controls; among others (a) patients scored subjectively more effort during ASLR, (b) at both 0 and 20 cm leg raise height patients had less hip flexion force, and (c) patients developed more muscle activity during ASLR. Since pregnant women with PLBP developed a higher muscle activity during ASLR with a significantly lower output at 0 and 20 cm than healthy pregnant women, it could be proposed that the ASLR demonstrates a disturbed load transfer across the SI-joints in this population.

A newly designed ergonomic body support for surgeons.

BACKGROUND: One of the main ergonomic problems during surgical procedures is the surgeon's awkward body posture, often accompanied by repetitive movements of the upper extremities, increased muscle activity, and prolonged static head and back postures. In addition, surgeons perform surgery so concentrated that they tend to neglect their posture. These observations suggest the advantage of supporting the surgeon's body during surgical procedures. This study aimed to design a body support and to test its potential. METHODS: The optimum working condition for a surgeon is a compromise between the spine and arm positions and the level of effort and fatigue experienced performing a procedure. The design vision of the Medisign group has led to the development of an ergonomic body support for surgeons that is suitable for use during both open and minimally invasive procedures. The feasibility of the newly designed ergonomic body support was assessed during seven surgical procedures. Electromyography (EMG) was performed for back and leg muscles using the body support in an experimental setting. RESULTS: Six of seven participating surgeons indicated that the body support was comfortable, safe, and simple to use. The EMG results show that supporting the body is effective in reducing muscle activity. The average reduction using chest support was 44% for the erector spinae muscle, 20% for the semitendinosus muscle, and 74% for the gastrocnemius muscle. The average muscle reduction using semistanding support was 5% for the erector spinae, 12% for the semitendinosus muscle, and for 50% for the gastrocnemius muscle. CONCLUSION: The results of this study imply that supporting the body is an effective way to reduce muscle activity, which over the long term may reduce physical problems and discomfort. Additionally, the product supports the surgeon in his natural posture during both open and minimally invasive procedures and can easily be adapted to the current layout of the operating theater.

Hand and arm problems in flautists and a design for prevention.

Hand and arm problems are frequent in flautists. Severity is greatest in professional players, which can result in being unable to work. Based on a biomechanical analysis a support for the right hand was designed, which can be easily clipped on to the flute. Tests by professional flautists demonstrated that the right hand thumb support prevented rotation of the flute about its longitudinal axis. The latter reduces tension in forearm, wrist and fingers. This is the most important result of the study, which led to the introduction of the right hand thumb rest on the market.

Sensitivity for pressure difference on the ischial tuberosity.

Although research on sitting and sitting postures has been done for decades, the field of the subjective feeling of comfort or discomfort during sitting is still an unexplored field. On the basis of those studies some manufacturers claim enhanced subjective comfort because of pressure-relieving qualities of the seat cushions. The question is: does a relatively small pressure reduction enhance comfort? Before that question can be answered, the sensitivity for pressure differences applied to the skin must first be determined. The aim of this study was therefore, to determine the sensitivity of the ischial tuberosity for pressure difference in a healthy population. For this study five males and five females aged between 19 and 30 years with no exercise-induced muscle ache were selected. The (Deltaa) was determined for which stimulus (a + Deltaa) was judged as exceeding stimulus (a) in 50% of the trials. This value was called (Deltaa0.5) and was determined with an adapted simple up - down method with forced choice. Two different values for (a) were used: (a) = 13.3 kPa and (a) = 26.5 kPa and the pressure was applied with two different contact surface with diameters of 10 mm and 20 mm. For (a) = 26.5 kPa and d = 10 mm a Deltaa0.5 = 2.7 kPa was found. For (a) = 26.5 kPa and d = 20 mm a Deltaa0.5 = 3.5 kPa was found. For (a) = 13.3 kPa and d = 20 mm a Deltaa0.5 = 1.9 kPa was found.

Cyclic loading of sacroiliac screws in Tile C pelvic fractures.

BACKGROUND: To investigate the stiffness and strength of completely unstable pelvic fractures fixated both anteriorly and posteriorly under cyclic loading conditions, the authors conducted a randomized, comparative, cadaveric study. METHODS: In 12 specimens, a Tile C1 pelvic fracture was created. The authors compared the intact situation to anterior plate fixation combined with one or two sacroiliac screws. In 2,000 measurements, each pelvis was loaded with a maximum of 400 N. The translation and rotation stiffness of the fixations were measured using a three-dimensional video system. Furthermore, the load to failure and the number of cycles before failure were determined. RESULTS: Both translation and rotation stiffness of the intact pelvis were superior to the fixated pelvis. No difference in stiffness was found between the techniques with one or two sacroiliac screws. However, a significantly higher load to failure and significantly more loading cycles before failure could be achieved using two sacroiliac screws compared with one screw. CONCLUSION: Although the combination of anterior plate fixation combined with two sacroiliac screws is not as stable as the intact pelvis, in this study, embalmed aged pelves could be loaded repeatedly with physiologic forces. Given the fact that the average trauma patient is younger and given the fact that the quality (or grip) of the fixation was a significant covariable for longer endurance of the fixation, this suggests that direct postoperative weight bearing could be possible if these results are confirmed in further research.

Relationship between everyday activities and spinal shrinkage.

BACKGROUND: Purpose of this study was to determine the spinal shrinkage in several activities of daily life and to assess a relationship with intradiscal pressure during these activities. Low back pain is thought to be related to spinal load. In a clinical evaluation of low back pain as provoked by everyday activities, we found a relationship between the amount of complaints during static activities and intradiscal pressure. However, because invasive intradiscal pressure measurements during dynamic activities like walking and cycling are complicated and hardly done before, an analogue relationship between low back complaints and dynamic activities is lacking. METHODS: Therefore spinal load was ascertained by stadiometric measurement of the decrease in standing height, so-called "spinal shrinkage", quantified by the exposure of a 1-h adopted posture or activity. Ten subjects performed five daily life activities: standing, sitting, walking, cycling and lying down. FINDINGS: By doing different activities during 1 h, immediate after getting up in the morning, following average values for shrinkage were measured: standing -7.4 mm (SD 0.5); sitting -5.0 mm (SD 0.6); walking -7.9 mm (SD 0.5); cycling -3.7 mm (SD 0.4) and lying down +0.4 mm (SD 0.5). INTERPRETATION: Overall, good correlation was found between spinal shrinkage and intradiscal pressure. The use of spinal shrinkage measurement seems a good alternative for intradiscal pressure measurement in static situations, but is still questionable in dynamic situations.

Extraforaminal ligament attachments of human lumbar nerves.

STUDY DESIGN: An anatomic study of the extraforaminal attachments of the lumbar spinal nerves was performed using human lumbar spinal columns. OBJECTIVES: To identify and describe the existence of ligamentous structures at each lumbar level that attach lumbar spinal nerves to structures at the level of the extraforaminal region. SUMMARY OF BACKGROUND DATA: During the last 120 years, several mechanisms to protect the spinal nerve against traction have been described. All these structures involved are located in the spinal canal, proximal to the intervertebral foramen. METHODS: Five embalmed human lumbar spines (T12-S1) were used. Bilaterally, the extraforaminal region was dissected to describe and measure anatomic structures and their relationships. Histology was performed with staining on the sites of attachment and along the ligament. RESULTS: The levels T12-L2 show bilaterally 2 ligaments, a superior extraforaminal ligament and an inferior extraforaminal ligament. The superior extraforaminal ligament emerges from the joint capsule of the facet joints and inserts in both, the intervertebral disc and the ventral crista of the intervertebral foramen, passing the spinal nerve laterally. In one specimen on level L2-L3, the superior extraforaminal ligament is not attached to the spinal nerve. The inferior extraforaminal ligament emerges from the intervertebral disc, passing the nerve medially and attaching the spinal nerve. At the levels L2-L5, the inferior extraforaminal ligaments are only attached to the intervertebral disc, not to the joint capsule. Histologically, the ligaments consisted of mainly collagenous structures. CONCLUSION: Ligamentous connections exist between lumbar extraforaminal spinal nerves and nearby structures.

Low back pain, the stiffness of the sacroiliac joint: a new method using ultrasound.

Abnormal biomechanical properties of the sacroiliac joints are believed to be related to low back and pelvic pain. Presently, physiotherapists judge the condition of the sacroiliac joints by function and provocation tests, and palpation. No objective measuring device is available. Research is ongoing to identify the biomechanical properties of the sacroiliac joints from the dynamic behaviour of the pelvic bones. A new concept based on ultrasound (US) for the measurement of bone vibration is under investigation. The objective of this study was to validate this concept on a physical model and to assess the applicability in vivo. A model consisting of a piezo shaker covered by a layer of US transmission gel (representing bone and soft tissue) has been used. A packet of US detection signals is directed onto the shaker and correlation-based processing is used to estimate the difference in time-of-flight of their echoes. These variations of time are used to compute the displacement of the shaker at each pulse reflection. To assess the validity of our US technique, we compared the obtained measurements with the readings of the built-in strain gauge sensor. The experimental procedure has been tested on a volunteer where low-frequency excitation was provided through the ilium and vibration detected on the sacrum and ilia. The results demonstrated that the correlation-based approach is capable of reproducing the piezo shaker displacements with high accuracy (+/- 7%). Vibration amplitudes from 0.25 microm to 3 microm could be measured. The US technique was able to detect bone vibration in vivo. In conclusion, the principle based on US waves can be used to develop a new measurement tool, instrumental in studying the relation between the biomechanical properties of the sacroiliac joints and low back pain.

Biomechanical comparison of sacroiliac screw techniques for unstable pelvic ring fractures.

OBJECTIVE: To determine the stiffness and strength of various sacroiliac screw fixations to compare different sacroiliac screw techniques. DESIGN: Randomized comparative study on embalmed human pelvises. MATERIALS AND METHODS: In 12 specimens, we created a symphysiolysis and sacral fractures on both sides. Each of these 24 sacral fractures was fixed with 1 of the following methods: 1 sacroiliac screw in the vertebral body of S1, 2 screws convergingly in S1, or 1 screw in S1 and 1 in S2. On the left and right side of a pelvis, different techniques were used. The pubic symphysis was not stabilized. We measured the translation and rotation stiffness of the fixations and the load to failure using a 3-dimensional video system. RESULTS: The stiffness of the intact posterior pelvic ring was superior to any screw technique. Significant differences were found for the load to failure and rotation stiffness between the techniques with 2 screws and a single screw in S1. The techniques utilizing 2 screws showed no differences. CONCLUSIONS: Based on the results of this study, we can conclude that a second sacroiliac screw in completely unstable pelvic fractures increases rotation stiffness and improves the load to failure.

Lumbo-pelvic joint protection against antigravity forces: motor control and segmental stiffness assessed with magnetic resonance imaging.

The antigravity muscles of the lumbo-pelvic region, especially transversus abdominis (TrA), are important for the protection and support of the weightbearing joints. Measures of TrA function (the response to the postural cue of drawing in the abdominal wall) have been developed and quantified using magnetic resonance imaging (MRI). Cross-sections through the trunk allowed muscle contraction as well as the large fascial attachments of the TrA to be visualized. The cross sectional area (CSA) of the deep musculo-fascial system was measured at rest and in the contracted state, using static images as well as a cine sequence. In this developmental study, MRI measures were undertaken on a small sample of low back pain (LBP) and non LBP subjects. Results demonstrated that, in non LBP subjects, the draw in action produced a symmetrical deep musculo-fascial "corset" which encircles the abdomen. This study demonstrated a difference in this "corset" measure between subjects with and without LBP. These measures may also prove useful to quantify the effect of unloading in bedrest and microgravity exposure.

Sacroiliac screw fixation for tile B fractures.

BACKGROUND: The purpose of this comparative cadaveric study was to investigate whether the stability of partially unstable pelvic fractures can be improved by combining plate fixation of the symphysis with a posterior sacroiliac screw. METHODS: In six specimens, a Tile B1 (open-book) pelvic fracture was created. We compared the intact situation with isolated anterior plate fixation and plate with sacroiliac screw fixation. Using a three-dimensional video system, we measured the translation and rotation stiffness of the fixations and the load to failure. RESULTS: Neither absolute displacements at the os pubis or at the sacroiliac joint nor stiffness of the ilium with respect to the sacrum were significantly different for the techniques with or without sacroiliac screw or the intact situation. Load to failure was reached in only one of the six cases. In all other cases, the fixation of the pelvis to the frame failed before failure of the fixation itself. In these cases, a load of approximately 1,000 N or more could be applied. CONCLUSION: The addition of a sacroiliac screw in a Tile B1 fracture does not provide significant additional stability. Although cyclic loading was not tested, in these experiments forces could be applied that were similar to full body weight. Clinical experiments into direct postoperative weight bearing are recommended to examine the clinical situation.

Quantifying thumb rotation during circumduction utilizing a video technique.

Thumb rotation is an essential component of circumduction in order to achieve pulp to pulp contact. In order to evaluate opponensplasty, a device was developed to quantify thumb rotation utilizing a special jig to hold the hand and video analysis. Twenty-seven healthy volunteers (12 female and 15 male) were tested to obtain normative data. Thumb rotation was measured as the difference in angle between the thumb in abduction and extension and maximal circumduction. Rotation angles varied from 70 degrees to 110 degrees. No gender or right/left differences could be detected. We concluded that comparing rotation of the non-injured hand to the injured hand in evaluating opponensplasties can be used as an accurate measurement of thumb circumduction and opposition.

Improvement of foot pedals used during surgery based on new ergonomic guidelines.

BACKGROUND: This study aims to create new ergonomic guidelines for the design of foot pedals used during surgery. METHODS: Observations in the operating room, a questionnaire among 45 laparoscopic surgeons/residents, an ergonomic literature study, and clog measurements were used to assess the problems occurring during use and to compile new guidelines for foot pedals. Based on these guidelines a new foot pedal was designed and a prototype was manufactured. RESULTS: During the surgical procedure 91% of the subjects occasionally loses contact with the foot pedal, which 56% experience as very annoying. All subjects think that the current foot pedals obstruct their freedom of movement; 75% occasionally hit the wrong switch and 53% experience physical discomfort in their legs and/or feet. Therefore, 93% of the subjects would like to control the diathermy in a different way. The new prototype of a foot pedal was evaluated in a pilot test and proved to be ergonomically better than the currently used foot pedals. CONCLUSION: The new guidelines for foot pedals result in an ergonomic improvement in their design.

Revision of the design of a standard for the dimensions of school furniture.

In this study an anthropometric design process was followed. The aim was to improve the fit of school furniture sizes for European children. It was demonstrated statistically that the draft of a European standard does not cover the target population. No literature on design criteria for sizes exists, and in practice it is common to calculate the fit for only the mean values (P50). The calculations reported here used body dimensions of Dutch children, measured by the authors' Department, and used data from German and British national standards. A design process was followed that contains several steps, including: Target group, Anthropometric model and Percentage exclusion. The criteria developed in this study are (1) a fit on the basis of 1% exclusion (P1 or P99), and (2) a prescription based on popliteal height. Based on this new approach it was concluded that prescription of a set size should be based on popliteal height rather than body height. The drafted standard, Pren 1729, can be improved with this approach. A European standard for school furniture should include the exception that for Dutch children an extra large size is required.

Free shoulder space requirements in the design of high backrests.

The objective of this study was to determine the influence of scapular support on the effects of lumbar support and to prove that a high and straight backrest is inappropriate. In literature the importance of a lumbar support is noted, although data about optimal dimensions is an under-researched topic and in earlier studies on force distribution and muscle activity the backrest had a fixed form. The lumbar support is needed to maintain the lumbar lordosis but no studies deal with the question of the precise dimensions of the backrest at shoulder level. With a specially designed apparatus, forces on shoulder and seat were measured separately, and the force on the pelvis calculated, while varying seat and backrest inclination within the range from 0 degrees to 17 degrees. Seat-to-backrest angle (at the level of lumbar support) was kept constant at 90 degrees. The distance between the tangent to the lumbar support and the parallel tangent to the scapular support was varied from 0, 2, 4, 6 and 8 cm. This distance is called the free shoulder space. Electromyography was measured at the erector spinae at the levels of the L1, T8 and T5 vertebrae. For all seat angles, a free shoulder space of d=0 cm resulted in the highest back muscle activity. In agreement with the biomechanical model, EMG activity reduced with an increase of seat tilt and increase of free shoulder space. With increasing free shoulder space, a larger part of the total backrest force was carried by the lumbar support. This study shows that a high and straight backrest overrules lumbar support. Offering free shoulder space of at least 6 cm reduces back muscle activity and allows for lumbar support.

Work load reduction through a new roll container traction device.

PURPOSE: For the distribution of dairy products, crates and roll containers are used. A roll container that is fully stacked with crates has a mass of 600 kg. The forces required to handle these roll containers, often aggravated by rough paving and inclined tailboards, are far in excess of ergonomic standards. This explains the high level of absenteeism among lorry drivers due to musculoskeletal complaints. The aim of this study was to reduce work load. METHOD: A new traction device for roll containers was developed, which couples easily and provides for easy manoeuvring. On a test circuit with obstacles, ten professional lorry drivers (aged 29-53 years) performed a user-test, both with and without the device. During the tests heart rate, blood pressure and time for completion of the track were measured. RESULTS: Heart rates were significantly lower with the traction device, the length of time needed to complete the track showed greater uniformity, and thanks to ease of use no prior lessons were necessary. CONCLUSION: The prototype was also tested by a lorry driver that was disabled by low back pain. With this device he was able to return to work.

Improvement of the laparoscopic needle holder based on new ergonomic guidelines.

BACKGROUND: The aim of this study is to create new ergonomic guidelines for the design of laparoscopic needle holders. METHODS: An ergonomic literature study, observations in the operating room, handle-shaft angle measurements, and anthropometric data were used to compile new ergonomic criteria, specified to the function of a laparoscopic needle holder. Based on these guidelines a new needle holder was designed. The prototype and three currently available needle holders were evaluated according to the new guidelines. In addition, a pelvi-trainer test was done to measure the extreme wrist excursions. RESULTS: The ergonomic evaluation of three commonly used handles and the new prototype indicate that the new handle is an ergonomic improvement in the field of laparoscopic needle holders: only the new handle satisfies all criteria. This is validated by the results of the pelvi-trainer test, which showed that the new prototype significantly (p <0.001) reduced the extreme wrist excursions. CONCLUSION: The new design guidelines for a laparoscopic needle holder result in an ergonomic improvement of the instrument.

Improvement of external fixator performance in type C pelvic ring injuries by plating of the pubic symphysis: an experimental study on 12 external fixators.

BACKGROUND: In an earlier study, we introduced a pelvic ring stability criterion for weightbearing stabilization. In a loading test, however, current external fixation systems alone did not meet this criterion. Internal fixation of the dorsal ring can significantly increase stability, but the condition of severely injured patients is often a contraindication for major surgery. The aim of this study is to optimize external pelvic ring fixation without dorsal ring stabilization to allow weightbearing in early mobilization of patients with unstable pelvic ring injuries. METHODS: The stiffness of external fixation systems alone and in combination with one or two anterior plates was measured by using a pelvic replica with a type C pelvic ring injury. Endpoints were 15 mm of dislocation or tolerance of 560 N. RESULTS: Addition of one plate at least doubles stiffness, whereas two-plate fixation results in at least a fourfold stiffer configuration. Frame configurations profit more than single-bar systems, and all but one system resist the weightbearing load after double-plating of the pubic symphysis. CONCLUSION: The choice of double-plate fixation of the anterior ring in addition to external fixation results in weightbearing capacity.