Is there a rational basis for post-surgical lifting restrictions? 1. Current understanding.

Lifting restrictions postoperatively are quite common, but there appears to be little scientific basis for them. Lifting restrictions are inhibitory in terms of return to work and may be a factor in chronicity. The mean functional spinal motion unit stiffness changes with in vitro or computer-simulated discectomies, facetectomies and laminectomies were reviewed from the literature. We modified the NIOSH lifting equation to include another multiplier related to stiffness change post surgery. The new recommended lifts were computed for different lifting conditions seen in industry. The reduction of rotational stiffness ranged from 21% to 41% for a discectomy, 1% to 59% for a facetectomy and 4% to 16% for a partial laminectomy. The recommended lifts based on our modified equation were adjusted accordingly. There is no rational basis for current lifting restrictions. The risk to the spine is a function of many other variables as well as weight (i.e., distance of weight from body). The adjusted NIOSH guidelines provide a reasonable way to estimate weight restrictions and accommodations such as lifting aids. Such restrictions should be as liberal as possible so as to facilitate, not prevent, return to work. Patients need more advice regarding lifting activities and clinicians should be more knowledgeable about the working conditions and constraints of a given workplace to effectively match the solution to the patient's condition.

Is there a rational basis for post-surgical lifting restrictions? 2. Possible scientific approach.

Lifting restrictions postoperatively are quite common but there appears to be little scientific basis for them. Lifting restricitions are inhibitory in terms of return to work and may be a factor in chronicity. The mean changes in functional spinal motion unit (FSU) stiffness with in vitro or computer-simulated discectomies, facetectomies and laminectomies were reviewed from the literature. We modified the NIOSH lifting equation to include another multiplier related to stiffness change post surgery. The new recommended lifts were computed for different lifting conditions seen in industry. The reduction of rotational stiffness ranged from 21% to 41% for a discectomy, 1% to 59% for a facetectomy and 4% to 16% for a partial laminectomy. The recommended lifts based on our modified equation were adjusted accordingly. There is no rational basis for current lifting resctrictions. The risk to the spine is a function of many other variables as well as weight (i.e., distance of weight from body). The adjusted NIOSH guidelines provide a reasonable way to estimate weight restrictions and accomodations such as lifting aids. Such resitrictions should be as liberal as possible so as to facilitate, not prevent, return to work. Patients need more advice regarding lifting activities and clinicians should be more knowledgeable about the working conditions and constraints of a given workplace to effectively match the solution to the patient's condition.

Cervical electromyographic activity during low-speed rear impact.

Whiplash motion of the neck is characterized by having an extension-flexion motion of the neck. It has been previously assumed that muscles do not play a role in the injury. Eight healthy males were seated in a car seat mounted on a sled. The sled was accelerated by a spring mechanism. Muscle electromyographic (EMG) activity was measured by wire electrodes in semi-spinalis capitis, splenius capitis, and levator scapulae. Surface EMG activity was measured over trapezius and sternocleidomastoideus. Wavelet analysis was used to establish the onset of muscle activity with respect to sled movement. Shorter reaction times were found to be as low as 13.2 ms from head acceleration and 65.6 ms from sled acceleration. Thus the muscles could influence the injury pattern. It is of interest that clinical symptoms are often attributed to muscle tendon injuries.

A review of studies on seated whole body vibration and low back pain.

The paper reviews the epidemiologic evidence linking low back pain (LBP) and exposure to whole body vibration (WBV). Particular emphasis is placed on studies where the exposure is quantified. Biomechanical studies show a resonance at 4-5 Hz. At the resonance the transmissibility exceeds 1.0, and is dependent on seat attenuation, posture and seat back inclination. Increased spinal loading is evidenced by increased muscle activity, muscle fatigue, and disc pressure, and by decreased stature. Physiologic changes also occur with WBV. The risk of LBP can be reduced by vibration damping, good ergonomic design, reducing exposure, and reducing other risks such as lifting.

Range of motion and motion patterns in patients with low back pain before and after rehabilitation.

STUDY DESIGN: Data were collected from 27 patients who were participating in a rehabilitation program for chronic low back pain. The patients were tested on day 2 and day 11 of a 2-week rehabilitation program. OBJECTIVES: To determine specific characteristics of trunk motion associated with long-term dysfunction caused by low back pain of various origin, to determine if a neural network analysis system can be effective in distinguishing between patterns, and to determine if the rehabilitation has an effect on range and pattern of motion. SUMMARY OF BACKGROUND DATA: There is a lack of objective measures for evaluating the efficacy of rehabilitation programs. Numerous studies have established the difficulty of evaluating low back pain. Existing techniques, such as imaging methods, are in many cases either very rough and inaccurate or expensive and ineffective. A technique for evaluation of motion patterns in low back pain was developed based on analysis of dynamic motion features such as shape, velocity, and symmetry of movements. METHODS: Dynamic motion data were collected before and after rehabilitation from 27 patients with low back pain by using a triaxial goniometer. Range of motion and features of the movement, such as shape, velocity, and repetitiveness, were extracted for analysis. RESULTS: Motion features showed significant improvement after the rehabilitation program. CONCLUSIONS: A neural network based on kinematic data is an excellent model for classification of low back pain dysfunction. Such a system could markedly improve the management of low back pain for an individual patient.

Hyperextension and spine height changes.

STUDY DESIGN: The effect on spine height changes from different combinations of time and angle of static prone hyperextension, and one intervention of dynamic hyperextension was explored. OBJECTIVES: To explore whether controlled hyperextension would cause an height increase with greater duration than previously shown, and to find an optimal combination of hyperextension angle and duration of the intervention. SUMMARY OF BACKGROUND DATA: Hyperextension is a METHODS: Ten subjects were exposed to hyperextension in the prone position for different time periods and with different amounts of hyperextension. The effect was measured using the stadiometer for measurement of spine height changes. RESULTS: The study showed that time was the most important variable, and also that for a given time, there was an increased recovery with increased angle. CONCLUSIONS: The results indicate that hyperextension can be a beneficial maneuver to unload temporarily the spine after loading and to rehydrate the discs, providing enough time is given for the procedure. The optimal time and angle combination was 20 degrees for 20 minutes because this intervention resulted in the largest recovery that lasted for a relatively long period of time.

Muscular response to sudden load. A tool to evaluate fatigue and rehabilitation.

STUDY DESIGN: Subjects were exposed to fatiguing and restorative interventions to assess their response to sudden loads. OBJECTIVES: To investigate the erector spinae and rectus abdominis response characteristics to "sudden load" and the effect of fatigue and rehabilitation. SUMMARY OF BACKGROUND DATA: Unexpected loads which people often experience, can lead to high forces in the spine and may be a cause of low back injury. METHODS: Muscle responses to sudden load were mediated by fatigue, walking, expectation, method of load application, exposure to vibration, and cognitive-behavioral rehabilitation in patients with chronic low back pain. A novel technique, perfected in this work, called wavelet analysis, was used to analyze these data. RESULTS: Reaction time was affected by fatigue and expectation. Vibration exposure significantly increased the muscle response time. Walking was able to ameliorate that effect. Back muscles responded differently, depending on whether loads were applied to the back through the hands or through the trunk. Electromyographic reaction time and magnitude decreased in patients after a 2-week rehabilitation program. CONCLUSIONS: Sudden loads can exacerbate fatigue effects. Walking after driving reduces the risk to the back caused by handling unpredictable loads. Vibration exposure guidelines should be more conservative. Patients have longer response times than healthy subjects, but patients can improve their response to sudden loads via rehabilitation. Patients exhibit a flexion-extension oscillation at 5 Hz in response to a sudden load, suggesting that the 5-Hz, seated, natural frequency observed during whole-body vibration may result from neurophysiologic control limits.

Are occupational drivers at an increased risk for developing musculoskeletal disorders?

STUDY DESIGN: This study analyzed the role of exposure to driving and other covariates in reports of back, neck, and shoulder pain and resultant disability. Cohorts in Sweden and the United States were compared. OBJECTIVES: To establish the effect of mechanical and psychosocial factors in reporting back, neck, and shoulder pain and work loss. SUMMARY OF BACKGROUND DATA: There are numerous reports of a positive relationship between back pain and driving. However, exposure data are minimal. The influence of job satisfaction has not been assessed. METHODS: The physical factors affecting reports of back, neck, and shoulder pain were investigated in a two-country cohort study of bus and truck drivers and sedentary workers. Vibration exposure was obtained by directly measuring the vibration imposed on the driver during a typical work day. Lifting exposure was attained by questionnaire. Cumulative exposure was computed based on work history. Musculoskeletal health information was based on a modified nordic questionnaire, and other questionnaires recorded the physical and psychosocial aspects of the work environment. RESULTS: Of the sample, 50% reported low back pain, with no difference between countries. The highest risk factors (odds ratios) for back and neck pain were long-term vibration exposure, heavy lifting, and frequent lifting. A combination of long-term vibration exposure and frequent lifting carried the highest risk of low back pain. Work loss from low back pain was influenced by perceived job stress. CONCLUSIONS: Vibration (resulting from driving) and lifting cause back, neck, and shoulder pain, whereas inability to work seems affected by stress at work.

European Spine Society--the AcroMed Prize for Spinal Research 1995. Unexpected load and asymmetric posture as etiologic factors in low back pain.

Unexpected loads, which often occur in the working environment, can lead to high forces in the spine and, thus, may be a cause of low back injury. This paper discusses the effect of "sudden load" on the erector spine reaction and amplitude. Muscle responses were mediated by several factors, including fatigue, posture, expectation and rehabilitation, in chronic low back pain patients. The subjects were fatigued by holding a 20% maximum voluntary contraction for 1 min. A functional restoration program was tested for its efficacy in reducing reaction time and EMG amplitude in chronic low back pain patients. Reaction time was longer and EMG amplitude lower in patients than in their matched controls. EMG reaction time and magnitude decreased in patients after a 2-week rehabilitation program, including specific training of coordination and posture control. The results of the modelling showed higher spinal compressive load and lower shear forces when the load was expected than when the load was unexpected. The effect of sudden loads can be exacerbated if a worker is not standing on a flat surface or is fatigued. Chronic low back pain patients have less ability to protect themselves from sudden loads, but they can be trained to improve their response by means of an appropriate rehabilitation program.

Does hyperextension have an unloading effect on the intervertebral disc?

A stadiometer (a device to measure the overall height of a subject) was used to determine the effect of hyperextension in rehydration of the intervertebral disc. Hyperextension for 20 minutes in a prone posture was compared with the prone posture alone for 20 minutes. The stadiometer measurement was made after the subject was exposed to 10 kg of loading applied to the shoulders for five minutes and after each of the recovery postures. It was found that hyperextension gave a significantly increased height recovery compared with the prone posture.

The effect of posture and seat suspension design on discomfort and back muscle fatigue during simulated truck driving.

Several studies have shown a relationship between low-back problems and exposure to seated whole-body vibration. The amount of vibration transmitted to the operator is influenced by the posture of the subject in the vehicle. The aim of this study was to determine whether a truck seat with a gas spring in its suspension is superior to the standard spring seat in slowing the onset of muscle fatigue and reducing the level of discomfort experienced during road vibrations while maintaining typical driving postures. The experiment used a 2 x 3 (2 seats x 3 postures) repeated measures design. It was conducted on six males free from low-back pain. Subject comfort was rated before and directly after exposure to typical vibrations. Muscle fatigue using centre frequency was determined during vibration exposure, and the magnitude and phase of acceleration transfer were calculated from the base plate to the seat pan and from the seat pan to the bite bar. None of comfort, fatigue rate or fatigue average were affected by seat type or seat suspension design in the short term, 10 min vibration exposure. Fatigue and comfort measures could continue to be used to detect postural defects, but the more sensitive measures of seat/driver interactions remain mechanical ones using motion-measuring techniques such as accelerometry and correcting for the heavily damped nature of the system. Until more sophisticated manikins are available the characteristics of vibration-attenuating seats should be confirmed using live humans.