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.

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.

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.

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.

Provocation of epicondylalgia lateralis (tennis elbow) by power grip or pinching.

The etiology of epicondylalgia lateralis humeri (tennis elbow) is not fully understood. A biomechanical model is introduced for those types of epicondylalgia where damage at the origin of the wrist and finger extensor muscles is caused by overloading. It shows that grasping and pinching always cause a flexing moment at the wrist joint. To avoid flexion of the joint, there must be equilibrium of moments, which is attained by activity of the extensor muscles. Simultaneous measurements of force and electromyograms support the biomechanical model.

Lowered motor conduction velocity of the peroneal nerve after inversion trauma.

To analyze the effect of inversion trauma on peroneal nerve function, motor conduction velocity was measured in 22 patients. In the injured leg, 4-8 d post trauma motor nerve conduction velocity in the knee-caput fibulae segment of the superficial peroneal nerve was significantly smaller when compared with the contralateral leg and the control group. Five weeks post trauma these values were normal again. For three segments of the deep peroneal nerve, the motor conduction velocity was significantly reduced, 4-8 d post trauma, when compared with the control group. In the caput-ankle and knee-ankle segment, motor conduction velocity was still significantly lowered 5 wk post trauma. Lowered amplitudes of the Compound Motor Action Potentials of the extensor digitorum brevis muscle were found 4-8 d post trauma. No correlation was found between motor nerve conduction velocities and subjective clinical tests (anterior drawer sign and (manually performed) talar tilt test). The results of this study support the hypothesis that inversion trauma is frequently accompanied by lesions of the peroneal nerve. Motor conduction velocity measurements can be a valuable tool in assessing more objectively functional instability of the ankle joint induced by inversion trauma.

Design criteria for the reduction of shear forces in beds and seats.

Both with respect to the aspect of pressure sores and of comfort, the inclination of backrest and seat are, amongst other factors, important design criteria. In this study the combination of seat and backrest inclination which reduces shear forces on the seat in passive seating forms the centre of attention. A biomechanical model was developed to predict these combinations and a new measurement apparatus was used for verification of the model on 10 healthy subjects (age 24.4 S.D. 2.1 yr, height 1.77 S.D. 0.08 m, mass 66.3 S.D. 11 Kg). For chairs it was found that when little shear is accepted, a fixed inclination between seat and backrest can be chosen between 90 degrees and 95 degrees. For beds a parabolic relationship was found between seat and backrest inclination with a maximum seat inclination of 20 degrees at a backrest inclination of 50 degrees. When lying with the knees bent to a position with equal inclination of thighs and shanks, the model predicts a shear force on the seat that shoves the person into the bed for every combination of seat and backrest inclination.

Starting from standing; why step backwards?

At push-off, the mass centre of gravity of the body must be positioned in front of the foot to prevent a somersault. When starting a sprint from out the standing position the use of a step backwards is necessary for maximal acceleration. The aim of the present study was to quantify the positive contribution to push off from a backward step of the leg, which seems to be counterproductive. Ten subjects were instructed to sprint start in three different ways: (a) starting from the standing position just in front of the force platform on the subject's own initiative, (b) starting from the standing position on the force platform with no step backward allowed, and (c) starting out of the starting position with one leg in front of the force platform and the push-off leg on the force platform. A step backwards was observed in 95% of the starts from the standing position. The push-off force was highest in starting type (a), which had the shortest time to build up the push-off force. The results indicate a positive contribution to the force and power from a step backwards. We advocate developing a training program with special attention to the phenomenon step backwards.

A biomechanical model for the analysis of the cervical spine in static postures.

To gain a better understanding of the forces working on the cervical spine, a spatial biomechanical computer model was developed. The first part of our research was concerned with the development of a kinematic model to establish the axes of rotation and the mutual position of the head and vertebrae with regard to flexion, extension, lateroflexion and torsion. The next step was the introduction of lines of action of muscle forces and an external load, created by gravity and accelerations in different directions, working on the centre of gravity of the head and possibly a helmet. Although the results of our calculations should be interpreted cautiously in the present stage of our research, some conclusions can be drawn with respect to different head positions. During flexion muscle forces and joint reaction forces increase, except the force between the odontoid and the ligamentum transversum atlantis. This force shows a minimum during moderate flexion. The joint reaction forces on the levels C0-C1, C1-C2, and C7-T1 reach minimum values during extension, each in different stages of extension. Axial rotation less than 35 degrees does not need great muscle forces, axial rotation further than 35 degrees causes muscle forces and joint reaction forces to increase fast. While performing, lateral flexion muscle forces and joint reaction forces must increase rapidly to balance the head. We obtained some indications that the order of magnitude of the calculated forces is correct.

Mechanical effects of continuous passive motion on the lumbar spine in seating.

The aim of this study was to develop a model which describes the mechanical spinal response to small alternating pelvic stimulation induced by an active rotational movement of a normal chair. The rotary continuous passive motion (RCPM) of the seat about a vertical axis of only 0.6 degrees resulted in an increased in spinal length as opposed to the normal daily shrinkage, and back patients experienced pain relief. Passive and active exercies have been broadly applied for treating and healing spinal disorders. A rigid body package (ADAMS Android) was used to translate the stimulation of the ischial tubersoity in caudo-cranial handing-over visualisation. The parameters of the model were set so that the values of the global stiffness and geometry of the intervertebral discs could be changed. In vivo validation of the model was based on force and moment measurements using an internal AO fixator. The predicitons of the model concerning natural frequency (4.5Hz) in vertical direction and the axial torsion response on small pelvic torsion are comparable with experimental data.

A biomechanical model on muscle forces in the transfer of spinal load to the pelvis and legs.

Based on musculoskeletal anatomy of the lower back, abdominal wall, pelvis and upper legs, a biomechanical model has been developed on forces in the load transfer through the pelvis. The aim of this model is to obtain a tool for analyzing the relations between forces in muscles, ligaments and joints in the transfer of gravitational and external load from the upper body via the sacroiliac joints to the legs in normal situations and pathology. The study of the relation between muscle coordination patterns and forces in pelvic structures, in particular the sacroiliac joints, is relevant for a better understanding of the aetiology of low back pain and pelvic pain. The model comprises 94 muscle parts, 6 ligaments and 6 joints. It enables the calculation of forces in pelvic structures in various postures. The calculations are based on a linear/non-linear optimization scheme. To gain a better understanding of the function of individual muscles and ligaments, deviant properties of these structures can be preset. The model is validated by comparing calculations with EMG data from the literature. For agonistic muscles, good agreement is found between model calculations and EMG data. Antagonistic muscle activity is underestimated by the model. Imposed activity of modelled antagonistic muscles has a minor effect on the mutual proportions of agonistic muscle activities. Simulation of asymmetric muscle weakness shows higher activity of especially abdominal muscles.

Analysis of biomechanical and ergonomic aspects of the cervical spine in F-16 flight situations.

With the help of a biomechanical neck model, several normal postures of an F-16 pilot were analysed. Measurements of accelerations and head positions were obtained during four flights, including simulated air combat. With the help of a model, muscle forces and joint reaction forces in the neck were estimated. Although at the present stage of research results of calculations must be interpreted carefully, conclusions can be drawn with respect to sitting posture, head position and helmet devices. The backward inclined back rest of the F-16 chair decrease the lordosis of the cervical spine, resulting in reduced calculated forces in the lower cervical spine. In high load situations, calculated maximal forces are of the same order of magnitude as failure loads of vertebrae and estimations of maximum muscle forces. The calculated neck load is increased substantially by the helmet and helmet-mounted devices. This load can be reduced by lightening the helmet or shifting the centre of mass of the helmet backwards.

The effect of passive vertebral rotation on pressure in the nucleus pulposus.

To study the immediate effects of axial rotation on the intervertebral disc, six pig cadaver lumbar functional spinal units were exposed to rotations of up to 2 degrees, while disc height and intradiscal pressure were measured. The results showed that rotary movements are capable of causing an immediate increase in disc height and drop in nucleus pressure. However, the long-term effects were opposite in direction.

Biomechanics of the finger with anatomical restrictions--the significance for the exercising hand of the musician.

Exercise and teaching of musicians presupposes in the individual the constitutive ability to freely execute the finger movements required in the playing of the instrument. However, in the hand anatomical restrictions may exist that limit the mobility of the fingers and, thereby, the possibility to determine their movements voluntarily. In this article we investigate the kinematics of a monodigital system in which restrictions are present.

The hand of the musician: the kinematics of the bidigital finger system with anatomical restrictions.

Tendons of the fingers are frequently interconnected by anatomic structures that limit the displacements of these tendons relative to each other. In this paper a bidigital finger system in which such interconnections between tendons are present is kinematically modelled. Using this model, an exhaustive description of the effects on finger movement of connections between the different tendons of the fingers is given. The study provides a context for the interpretation of typical difficulties of finger coordination in musicians, especially in pianists and string players.

Improved usability of a new handle design for laparoscopic dissection forceps.

BACKGROUND: Recent studies have shown that the shape of most instrument handles causes user discomfort and that none of the handles currently available on the market satisfies all ergonomic criteria. Therefore, we designed a handle with improved usability; i.e., it is easier to manipulate and its use entails less risk of injury for the operator. The aim of this study was to demonstrate that the intended improvements of the new design were successful. METHODS: Six handles representative of the types that are currently available were compared with the new version. Eight surgeons used the seven handles during a precision task and a rough task in a pelvi-trainer. A questionnaire and video analyses were used to assess the usability of the handles. RESULTS: Based on the responses to the questionnaire, we determined that there were significant differences between the new handle and the Aesculap handle (means of rotation and angle between handle and shaft). No significant differences were found between the new handle and the five other handles. The video analyses (documenting extreme vs neutral wrist excursions) showed significant differences between the new handle and the six other handles. CONCLUSION: Compared to the six existing handles, the new handle has significantly improved usability; in particular, its hinged design obviates the need to make extreme wrist excursions.

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.

Optimal mesh size for endoscopic inguinal hernia repair: a study in a porcine model.

BACKGROUND: Although the recurrence rate for endoscopic herniorraphy is low (0-3%), it can still be improved. In addition to using an expert technique that will minimize the risk of recurrence, it is essential that the mesh be large enough to cover the hernial defect adequately. To gain an impression of the optimal mesh size for such repairs, we performed an experimental study in a porcine model. METHODS: To mimic inguinal hernial defects, circular holes of different diameters were cut in the pigs' abdominal walls after the peritoneum was lifted from the transverse fascia. The abdominal walls were positioned in a hermetically sealed chamber in which air pressure was applied to replicate intraabdominal pressure. Measurements were obtained to relate the protrusion of the mesh to the following three variables: intraabdominal pressure, defect size, and mesh overlap over the defect after positioning of the mesh between the abdominal wall and the peritoneum. RESULTS: Mesh protrusion increased as defect size and intraabdominal pressure increased. Mesh protrusion decreased as overlap of the mesh over the defect increased. Protrusion was found to level off when the mesh overlapped the defect by 3 cm and adequate positioning of the mesh was maintained. CONCLUSION: Recurrences after endoscopic inguinal hernia repair due to inadequate mesh size and mesh protrusion can be reduced by using a mesh that overlaps the defect by > or = 3 cm.

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.

Measurement of tendon excursion velocity with colour Doppler imaging: a preliminary study on flexor pollicis longus muscle.

PURPOSE: To study the use of colour Doppler imaging (CDI) for the measurement of maximum and mean tendon velocity. Recent studies showed that CDI, normally used for blood flow examinations, can be used for the imaging of tendons at the hand and wrist region. Although other modalities are available for imaging of the muscle-skeletal system, in vivo measurements of the velocity of tendon excursion are not possible. METHODS: The flexor pollicis longus (FPL) tendon of 16 healthy volunteers was measured bilaterally at two levels (wrist and thenar). A splint from the fingers along the proximal lower arm was applied. The thumb was fixed to the splint from the the first phalanx to allow flexion of the interphalangeal (IP) joint only. Pulsed CDI was used for the measurements. The maximum and mean velocities of the FPL tendon were measured at spectrum display mode during continuous voluntary contractions. At least 10 sequential Doppler peaks (cm/s) were recorded at every trial. The measurements were repeated three times. Paired t-test and correlation coefficients were calculated between levels on the same side and the opposite side. RESULTS: No significant differences were found between two levels of the same hand and of the opposite hand. As expected, the data revealed variations in the inter-individual tendon velocities. CONCLUSIONS: The velocity of the excursion of the FPL tendon can be measured with CDI with good reproducibility. It is expected that velocity measurements can be used in the future for the assessment of other tendons affected by various disorders.